HighRise Building Construction Profile

High-Rise Buildings

High-rise buildings in the course of history

M

Münchener Rück Munich Re Group

Technology of high-rise buildings

Risk potential

Insurance

Contents Page 1

Introduction

2

High-rise buildings in the course of history, technology and the environment 8

2.1 2.2 2.3 2.4 2.5 2.6

Historical development Architectural aspects and urban development today Financing models Infrastructural aspects Economic aspects Social and ecological aspects

12 14 17 21 21

3

Technology of high-rise construction

24

3.1 3.1.1 3.1.2 3.1.3

25 25 25

3.2.4.4 3.3 3.3.1 3.3.2 3.3.3 3.4

Planning Planners Regulations and directives Technical analyses and special questions Construction licensing procedure Other constraints Execution Foundations Supporting structure Load-bearing parts Special construction methods Facade Roof Interior finishing Service systems Installations Deliveries, vehicles Passenger transport, vertical development Waste disposal Occupancy Maintenance, administration Conversions Rehabilitation High-rise construction in the future

4

Risk potential

84

4.1 4.2 4.2.1

Design errors Fire Examples of losses during the construction phase Fire protection on construction sites Examples of losses during the occupancy phase Fire-protection regulations, loss prevention Regulations Structural fire protection Active loss-prevention measures

85 86

3.1.4 3.1.5 3.2 3.2.1 3.2.2 3.2.2.1 3.2.2.2 3.2.2.3 3.2.2.4 3.2.3 3.2.4 3.2.4.1 3.2.4.2 3.2.4.3

4.2.2 4.2.3 4.2.4 4.2.4.1 4.2.4.2 4.2.4.3

4

9

26 26 29 31 31 35 35 42 45 46 46 48 48 49 49 50 51 51 53 53 54

86 89 99 107 107 107 108

Page 4.2.4.4 4.2.4.5 4.2.4.6 4.3 4.4 4.5

110 111 111 111 115

4.5.1 4.5.2 4.6 4.7 4.7.1 4.7.2 4.7.3 4.7.4 4.8 4.8.1 4.8.2 4.8.3 4.8.4 4.9

Fire fighting Organizational measures Atriums Windstorm Earthquakes Foundations, settlement and subsidence Foundations Settlement and subsidence Water Special structural measures Conversions Rehabilitation Demolition Disposal Other risks Terrorism Impact Collapse Wear Loss of profit

5

Insurance

138

5.1 5.1.1

139

5.4.2 5.4.3 5.4.4 5.5

Property insurance Contractors’ and erection all risks insurance Advance loss of profit insurance Insurance of contractors’ plant and machinery Decennial liability insurance Insurance of buildings, fire insurance Loss of profit insurance Loss of rent Additional costs Contingency planning Prevention of access Third-party liability insurance Insurance of the designer’s risk Insurance of the construction risk Insurance of the operational risk Problem of maximum loss Construction phase Decennial liability insurance Operating phase Accumulation control Underwriting considerations Contractors’ and erection all risks insurance Contractors’ plant and machinery Decennial liability insurance Insurance of buildings, fire insurance Reinsurance

6

Summary and outlook

156

5.1.2 5.1.3 5.1.4 5.1.5 5.1.6 5.1.6.1 5.1.6.2 5.1.6.3 5.1.6.4 5.2 5.2.1 5.2.2 5.2.3 5.3 5.3.1 5.3.2 5.3.3 5.3.4 5.4 5.4.1

119 119 121 122 122 122 122 123 126 126 126 127 132 132 132

139 141 142 144 144 145 145 145 145 145 147 147 147 148 149 149 149 149 152 153 153 153 153 153 155

1 Introduction

1

Page 5

1 Introduction

High-rise buildings have always triggered major debates and aroused emotion. That is hardly surprising, considering that this type of building radiates more symbolic power than almost any other.

1

Introduction

From their beginning in the middle of the last century and right up to the present day, high-rise buildings have always been a dominant landmark in the townscape, visible from far and wide, like the towers of Antiquity and the Middle Ages. At the same time, this sky-scraping construction method has always been an ideal means of displaying power and influence in the community. In the light of this goal, reasonable economic considerations often recede into the background during the erection and subsequent use of these high-rise buildings. A prestige object for the builder, these edifices not only have an effect on their immediate neighbours, but also influence many areas of urban life in very different ways. These aspects will also be taken up in this publication. In the early years, the builders’ urge to rise to dizzying heights was limited by unsolved technical problems. In recent years, however, a real competition has developed among the builders of skyscrapers to be world champion at least for a few months before being outdone by a rival with an even higher building. Even seemingly Utopian projects now stand a good chance of becoming reality. This rapid development has only become possible because the technical conditions and methods used in constructing high-rise buildings have improved decisively and in some cases changed fundamentally in the last few years.

Up until the end of the last century, high-rise buildings were still made of solid brick masonry, which ultimately required foundation walls up to 1.8 m thick. When steel frames adapted from steel bridge construction were introduced, with their increased strength and lower weight, builders and architects were able to soar to greater heights. With this steel skeleton, the net weight of the structure was considerably lower than that of a solid masonry building; it thus not only cut the costs of construction, but also gave wings to the architects’ imagination. By the turn of the century, they were designing buildings that also looked light and delicate as even at that time the skeleton structure permitted a large proportion of windows on the outer facade. Since then, the construction of high-rise buildings has continued to change with the requirements imposed by air-conditioning and particularly office communications. The high-rise office buildings of the nineties have little in common with their predecessors. Instead of compact walls and ceilings, we now have a high-tech structure made up of largely prefabricated elements which are welded and bonded together on site. The building comprises a skeleton of steel or reinforced concrete which is rounded off by suspended ceilings and false floors creating the space required for installations. The originally

1 Introduction

Page 6

02 SAN GIMIGNANO

load-bearing outer wall has been replaced by a prefabricated facade. However, this complex method of construction promotes the spread of fire and fumes, and therefore, in conjunction with the considerable concentration of values involved, represents an extremely sensitive risk both during construction and throughout the service life of the building. The major fires which broke out in a number of high-rise office buildings shortly before their completion in the early nineties show how correct the appraisal of the fire risk in high-rise buildings is. The losses incurred through these fires are several times higher than the amounts of indemnity known to date. This is consequently one of the main reasons why highrise buildings constitute a new dimension of risk for the insurance industry, one which has made it necessary to draw up new concepts for underwriting, loss assessment and PML determination throughout every phase of construction and subsequent use. We therefore believe that this publication on high-rise buildings is an appropriate addition to our comprehensive series of special publications, particularly those on underground railways and bridges. We are fully aware of the fact that many of the aspects considered with regard to the construction, use and insurance of high-rise buildings naturally apply in the case of lower buildings too. Nevertheless, we do not wish to limit ourselves to aspects which only apply specifically to highrise buildings. After a brief historical overview, we will therefore consider in detail all the risks and problems

associated with high-rise buildings and the techniques that are applied in order to illuminate possible solutions from the point of view of both construction technology and insurance. Moreover, the more broadly based general information available will make it easier not only to assess the risk of high-rise building projects but also to arrive at a price for insuring such projects. The definition of a high-rise building differs from one country to the next. For our purposes, we will proceed on the basis of a minimum height of 30 m and will restrict ourselves to buildings used for residential or office purposes. Despite the various critical voices raised, the construction of high-rise buildings has by no means reached its zenith. The problem of high-rise buildings is one which we – as insurers and reinsurers – will also have to consider in the future. This special publication is also intended, last but not least, as a means of passing on to others our experience from the major losses that have occurred in the recent past.

03 MONADNOCK BUILDING

2 High-rise buildings in the course of history, technology and the environment

2 2.1 Historical development 2.2 Architectural aspects

2.3 Financing models 2.4 Infrastructural aspects

2.5 Economic aspects 2.6 Social and ecological aspects

Page 9


04 THE TOWER OF BABEL

According to the Bible, the Tower of Babel was to “reach unto heaven” (Genesis 11). But when the Lord saw what the people had done, He confused their language and scattered them abroad over the face of all the earth so that they left off building the city.

2 2.1

High-rise buildings in the course of history, technology and the environment Historical development

What could be a more appropriate point to begin our consideration of high-rise buildings than with the Tower of Babel and then to trace their historical development over the centuries. However, a distinction must be made between “high buildings” and “high-rise buildings”: “high buildings” have only a few floors and not uncommonly only one, albeit very high floor. They are crowned by a high roof and turrets (in the manner typical of medieval and Gothic cathedrals). “High-rise buildings”, on the other hand, have many, usually identical floors of normal height one above the other. Seen in this light, high-rise buildings have their origins in the towers of San Gimignano rather than in the Tower of Babel or ecclesiastical structures. The first high-rise office building according to this definition was built in Chicago in 1885: the Home Insurance Building. It still stands on the corner of La Salle and Adams Street, a witness of its times. It has twelve floors – there were originally ten, but two were subsequently added – and was built in roughly eighteen months. The architect W. L. B. Jenney used an uncommon new method for the construction of his building: the weight of the walls was borne by a framework of cast-iron columns and rolled I-sections which were bolted together via L-bars and the entire “skeleton” embedded in the masonry. The early Equitable Life Building in New York, which was completed in 1872, also contributed towards the development of high-rise buildings, for it was the first tall building to have an elevator. Although it only had six floors, the

edge of the roof was no less than 130 feet (roughly 38 m) above the road surface. Due to its elevator, the upper floors were in greater demand than the lower floors. Following completion of the “Equitable” building, it was the done thing to reside on one of the “top” floors. Burnham and Roof’s Monadnock building, which was completed in Chicago in 1891, must also be mentioned as one of the last witnesses of a whole generation of solid masonry high-rise buildings. Sixteen floors of robust brick masonry rise skywards in stern, clear lines: an astonishing sight to eyes accustomed to the frills and fancies of the late 19th century. Standing on an oblong base measuring 59 m ҂ 20 m, the building is reminiscent of a thin slice and not only recalls the industrial brick buildings of the late 19th century, but also anticipates the formal simplification of the later 1920s. The buildings rose higher and higher with the spread of pioneering construction methods – such as the steel skeleton or reliable deep foundation methods – as well as the invention and development of the elevator. The highly spectacular skylines of North American cities, particularly Chicago and New York, originated in the early years of the 20th century. Glancing over Manhattan’s stony profile, the silhouettes dotting the first 12 km of the 22-km-long island bear vociferous testimony to this dynamic development: – the World Trade Center, currently the tallest building in New York, 417 m high, – the legendary Empire State Building, built in 1931, 381 m,


Top left: 05 EQUITABLE LIFE BUILDING Bottom left: 06 HOME INSURANCE BUILDING Right: 07 NEW YORK PANORAMA


08 HONGKONGBANK HEADQUARTERS BUILDING, HONG KONG

– – – –

Page 12

09 MESSETURM, FRANKFURT AM MAIN

the United Nations building erected in 1953, 215 m, the Chrysler Building dated 1930, 320 m, the former Pan Am Building completed in 1963, 246 m, the Rockefeller Center (1931–1940), a complex of 19 buildings, – the Citicorp Center built in 1978, 279 m, and – the AT&T Building opened in 1984, a pioneering building by the post-modern architect Philip Johnson, with an overall height of 197 m. It is only recently that attention has also turned to interesting high-rise buildings outside North America: Norman Foster’s Hong Kong and Shanghai Bank, Ieoh Ming Pei’s Bank of China in Hong Kong and the twin tops of the Petronas Towers in Kuala Lumpur, currently the tallest building in the world at 452 m. High-rise buildings in Germany are a modern development and are concentrated particularly in Frankfurt am Main: today, Frankfurt is the only German city with a skyline dominated by skyscrapers. One of the tallest buildings in the city is the Messeturm built in 1991 with a height of 259 m, which is not much more than half the height of the Sears Tower in Chicago, currently the tallest office and business tower in North America with a total height of 443 m. It was the rapid growth in population that originally promoted the construction of high-rise buildings. New York once again provides a striking example: land became scarce well over a hundred years ago as more and more European immigrants streamed into the city. From roughly half a million in 1850, the city’s population grew to 1.4 million by 1899. More and more skyscrapers rose higher and higher on the solid ground in Manhattan, as buildings could only be erected with great difficulty on the boggy land to the right and left of the Hudson River and East River. In this way, New York demonstrated what was meant by “urban densification” despite the considerable doubts originally voiced by experts in conjunction with this development. The first area development code to come into force in New York was the so-called “zoning law” of 1916, accord-

ing to which the height of a building must not exceed twoand-a-half times the width of the road running alongside the building. The building mass was further limited by the requirement that the floor space index must not exceed twelve times the area of the site. Among other things, the zoning law stipulated that only the first twelve floors of a building were allowed to occupy the full area of the site and that all subsequent floors must then recede in zoned terraces – a requirement of major aesthetic significance, for this terraced form still dominates the silhouette of American skyscrapers today. All doubts as to the profitability of high-rise buildings were set aside with completion of the Empire State Building, the Chrysler Building and other skyscrapers in the 1930s, for they would never have been built if they could not have turned a profit. Although rentals proceeded slowly at first when the Empire State Building was completed in the heart of the recession in the 1930s and it was therefore known as the “Empty State Building” for many years, it subsequently generated satisfactory revenues once all the premises had been let. Cities in Europe and Asia grew horizontally and it was only when production and services acquired greater economic significance throughout the world and the price of land rose higher and higher in economic centres after the Second World War that they also began to grow vertically. Modern Hong Kong is a striking case in point: it encompasses an area of 1,037 km2 (Victoria, Kowloon and the New Territories), of which only one-quarter has been developed, but with maximum density and impressive efficiency. Almost all the new buildings, office towers and particularly residential towers in the New Territories have more than thirty floors.

2.2

Architectural aspects and urban development today

As the historical development of high-rise buildings has already shown, the construction of edifices reaching higher

10 PETRONAS TOWERS


and higher into the sky was – and to a certain extent still is – an expression of power and strength. This is equally true of both ecclesiastical and secular buildings: the power, strength and influence of entire families – i.e. their standing in society – is mirrored in the erection of ever taller buildings culminating in a battle to build. The towers of San Gimignano are one of the best preserved examples of this development. In many North African cities, too, this attitude has moulded the townscape for many centuries and will no doubt continue to do so in the future. The names of the builders and architects have only been known since the high Middle Ages around 1000 AD. They created new stylistic elements and added their “signature” to entire periods. Looking back, this makes it difficult for us today to decide whether these master craftsmen shaped the various stylistic developments or whether a number of master builders only became so well known because their work reflected the contemporary fashion trends most accurately. That still holds true today, the only difference being that tastes change very much more rapidly and “degenerate” into short-lived fashions. A building that reflects the spirit of the times when it is finished can appear “old” within only a few years. The brevity of the various stylistic trends is one of the reasons for the inhomogeneous appearance of modern towns and cities. Since architects must expect that later buildings will have their own, completely different formal identity, they do not see any reason why they should base their own designs on existing standards, particularly as this would merely cause them to be considered “unimaginative”. Three points become clear if we take a closer look at modern trends in high-rise construction: – The dictate of tastes mentioned above is expressive of the egotism prevalent in modern society with its desire for status symbols and designer brands. Unfortunately, the public not uncommonly bows to this dictate, as when town councillors set aside major urban development considerations and with seeming generosity set up public areas in the form of lobbies and plazas in high-rise buildings. – The sheer magnitude of the projects forces all planners to adopt a scale totally out of proportion to all natural dimensions and particularly to the people concerned when planning their buildings. In the past, urban development plans were easily drawn up on a scale of 1:100 or at most 1:200, a scale which could still be directly related to the size of a human being. With today’s highrise buildings, however, a scale of at least 1:1000 is required simply in order to depict the building on paper. This is illustrated by the example of the Sears Tower in Chicago: completed in 1974, the Tower measures 443 m in height. Drawn to a scale of 1:2000, a human being is represented by a minute dot measuring barely 0.9 mm. – In the past, it was the master builder and architect who defined the construction and consequently the appearance of a building; today, on the other hand, technical developments determine what can and cannot be done;

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the appropriate and basically essential symbiosis between engineering designer and artist has been abandoned. This critical discourse on the architectural, urban development and economic background is not basically to cast doubt on high-rise buildings as such, but it does illuminate some of the facets that are central to considering the risk potential inherent in high-rise buildings. This almost inevitably raises the question why high-rise buildings should have to be built in today’s dimensions. – One reason is indisputably the need for a “landmark”. In other words, to express economic and corporate power and domination in impressive visual terms. Nothing has changed in this respect since the very first high-rise buildings were erected. – The steadily rising price of land in prime locations and an increasingly scarce supply have made it essential to make optimum use of the air space. Prices in excess of DM 50,000 per square metre are not uncommon for land in conurbations and economic centres. Despite their height, however, high-rise buildings still occupy areas of truly gigantic proportions: the ratio of height-to-base width of the cubes in the 417-m-high World Trade Center, for example, is 6:1. – Connections to the infrastructure are improved by concentrating so many people in such a small area. The World Trade Center alone provides jobs for over 50,000 people – that is the equivalent of a medium-sized town. All institutions of public life are united under a single roof and the distances between them have been minimized. However, high-rise buildings do little to prevent land being sealed on a large scale. The suburbs of modern American cities are a prime example: as far as the eye can see, the landscape is covered with single-family homes, swimming pools and artificially designed gardens simply to provide sufficient private residential land for all the people working in a high-rise building occupying only a few thousand square metres. – Many of the techniques and materials which are also used for “normal” buildings today would never have been invented and would never have become established if high-rise construction had not presented a challenge in terms of technical feasibility. Rationalized, automated sequences are beneficial to high-rise buildings; at no time in the past were such huge buildings erected in such a short space of time. Short construction periods also mean shorter financing periods and consequently profits which partly compensate for the additional costs incurred in the construction and finishing of the building.

2.3

Financing models

The construction costs for high-rise buildings often run into hundreds of millions of dollars. The owner of the building will rarely be willing or able to bear these costs

11 HIGH DENSITY: HONG KONG SKYLINE

12 FLATIRON BUILDING, NEW YORK

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without outside assistance. On the other hand, however, debt service and exhausted credit lines will then constrict his operative freedom. Alternative financing models are therefore frequently sought; the best known models are briefly outlined below. LEASING Leasing of buildings, particularly high-rise buildings, can to a large extent be compared with rentals. This alternative is commonly chosen when a company finds itself in financial straits and needs cash. Selling the building – often a prestige object in a prime location – to a leasing company is of two-fold advantage to the company: firstly, it acquires the urgently needed capital, and secondly, it can continue to use the building in return for a monthly leasing fee which, however, amounts to no more than a fraction of the purchase price received. The composition of corporate assets is changed by such a transaction. This can be a disadvantage when new loans are needed, for the building is then no longer shown on the assets side as a property secured by entry in the land register. BOT BOT stands for “build, operate and transfer” (there are other variations but these will not be discussed in further detail here). In the case of this financing model, the owner of the land places his land at the disposal of a contractor who then erects a building on it, such as an office tower. The owner of the land can exert a certain influence on the planning and intended use, but does not share in the construction costs. The contractor must organize the project’s financing himself, be it with own funds or with the aid of loans (“build”). In return, the owner of the land waives all or some of the income from occupancy of the building for a certain period of time, usually 25 years. During this time, the builder must obtain rents that are calculated to cover his debt service and draw a profit from the invested capital (“operate”). The builder’s risk with regard to rents and debt interest is often considerable. At the end of the agreed occupancy period, both the land and the office tower become the property of the landowner (“transfer”).


The developer usually draws up what is known as a master plan for complete districts and then retains (usually prominent) architects to design the various components of the master plan independently of one another. The developer then seeks to find tenants or lessees for the building which at this stage only exists on paper. Construction work begins when tenants or lessees have been found. La Défense in the Paris Basin is a typical example of such a development. This suburb was created on the drawing board in the 1950s. A dilapidated district was demolished and completely redesigned. The traffic systems, such as Metro, urban railway, motorway and access roads were moved below ground level and covered by a concrete slab 1.2 km long. Mostly office towers were erected on this slab with open squares and green areas in between. The ensemble is rounded off by the Grande Arche de la Défense designed by the Danish architect Johann Otto von Spreckelsen and completed in 1989. The Grande Arche is a huge cube which is open on two sides with 37 office floors and a height of 110 m equal to its ground lengths. All the capital invested on the site came from private sources and was controlled by a public-law community of interests. In times of sluggish investment activity, however, it is not uncommon to find that only certain parts of the master plan are actually realized. Originally planned as a homogeneous townscape, the result is then nothing more than an unrelated fragment and areas that should have been filled with life appear to be deserted and uninhabited instead. In the mid-nineties London’s Docklands provided a dramatic example of such a development: the transformation of the West India Docks built between 1802 and 1806 resulted in what was for a while the highest mountain of debt in the world with the high-rise obelisk on Canary Wharf. After having consumed roughly US$ 3bn, the half-finished project was temporarily abandoned before finally being completed and let following a variety of financial transactions.

2.4 There are differences between these financing models: although the BOT model grants the landowner the right to ownership, he is for a long time excluded from occupancy of the property. With the leasing model, the high capital investment required is transferred to the lessor and the financing costs are replaced by monthly payments akin to rent by the lessee. DEVELOPER The developer is a new profession born out of the explosive rise in construction costs which has been intensified by increasingly large buildings and structures. This was triggered by urban renewal programmes and changes in tax regulations for large construction projects for which new financing models were developed in the USA in the sixties and seventies.

Infrastructural aspects

The different fates of La Défense and Canary Wharf are not (only) due to the extremely different planning periods of 30 years (La Défense) and 8 years (Canary Wharf), but above all to the manner in which the necessary infrastructure for the two projects was tackled. In the case of La Défense, the entire necessary infrastructure was completed before the construction work actually started: underground railway lines and roads, service systems were all planned and built beforehand. As a result, a fully functional and above all adequately dimensioned infrastructure was consequently available when the buildings were taken into service. This made La Défense attractive to investors and tenants alike; the new district soon pulsated with life as an economically sound basis for the entire project.

13 LA GRANDE ARCHE

14 CANARY WHARF

15 TRADITIONAL AND MODERN BUILDINGS IN PEACEFUL CO-EXISTENCE

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A jungle of political, economic and investment difficulties must be overcome for such prospective planning because the owner of the high-rise complex bears no direct responsibility for the large majority of these far-reaching infrastructural measures. The project’s progress is consequently controlled by the municipal authorities, as well as by supply and operating companies and not by the owner of the complex. The situation of Canary Wharf in London’s Docklands is exactly the opposite and proves that the La Défense type of planning is the economically more appropriate approach, despite the associated delay in starting construction work and the longer preliminary financing required. A second City of London was to be created in the heart of the Docklands within the shortest possible space of time, with thousands of square metres of tailor-made office space, hotels, shops and apartments for high-income tenants. A rail-bound fully automatic cabin railway known as the Docklands Light Railway was to ensure the necessary access. However, this transport system fell far short of meeting the requirements, as its capacity was far too low and it lacked the essential connection to the London Underground. The road connections for private traffic and public buses were similarly inadequate. This made the Docklands unattractive to both commercial and private tenants. An Underground link was finally built after extensive planning and at the enormous cost of roughly US$ 1.7bn; the road connections were likewise improved at the cost of almost US$ 1bn. Only then did the precarious economic situation of Canary Wharf improve. As these examples show, almost every high-rise construction project is doomed to at least economic failure if the infrastructure is not considered, planned and actually installed down to the very last detail.

2.5

Economic aspects

Hundreds of companies and thousands of people depend on the smooth operation of a high-rise building, from the one-man business of a newspaper vendor or shoeshiner and corporations with thousands of employees, such as banks, brokers or global players with a daily turnover in the order of several billions to radio, television and telecommunications companies which use the roofs and tops of high-rise buildings for the transmission and receiving installations. In addition, there are innumerable other businesses and workers with their families whose economic situation is directly or indirectly linked with the high-rise building. These range from transport companies and catering firms to tradesmen under long-term contract in the building. Nor should it be overlooked that even the municipal authorities and the service companies are also affected by the “failure” of a high-rise building and that its effects can be felt nationwide or even worldwide in the worst case. This scenario not only applies to such total failure as a


major fire or collapse of the building. Despite (or precisely because of) its size, a high-rise building is an incredibly sensitive and vulnerable system. Even a brief power failure can result in operational and economic chaos. The same applies to outside disturbances in the form of strikes by public transport corporations or a malfunction in the underground or urban railway system.

2.6

Social and ecological aspects

Criticism today focuses particularly on the social and ecological effects of high-rise buildings. The most commonly voiced reservations with regard to high-rise apartment blocks concern the social aspect. It is claimed – and there are probably a number of studies to prove – that cohabitation in high-rise buildings does not work as smoothly as in homogeneous, historically grown districts with numerous small, manageable dwellings. The anonymity suffered by the people in these “residential factories” is criticized in particular – above all on account of the total isolation from other residents in order to avoid the stress of permanent contact. Organic, homogeneous population structures with their positive effects on social conduct are rarely found and the charge that high-rise apartment blocks are hostile to families and children is consequently not entirely unfounded. Two diametrically opposed ghetto situations can easily arise in high-rise apartment blocks: since the costs for construction and maintenance of these buildings are disproportionately high, correspondingly high rents must be charged, with the result that these blocks are more or less reserved for the well-off, while the socially weaker classes are excluded. Conversely, however, high-rise apartment blocks can rapidly cease to be attractive if compromises are made with regard to the building quality, maintenance or infrastructure on account of the high investment costs entailed. A building in disrepair will soon drive away the “good” tenants and become a slum. The ghetto situation is intensified when high-rise apartment blocks are built in newly developed fringe areas – far away from cultural and social centres – on account of the high cost of land in inner city areas. It is not without good cause that these areas are commonly referred to as “dormitory towns”. Studies have also proved beyond all doubt that criminal activity is promoted by huge apartment blocks and particularly high-rise buildings. According to these studies, this phenomenon is attributable to the anonymity of the residents, as well as to the “pro-crime” environment with elevators, poorly lit corridors devoid of human beings, refuse collection rooms and bicycle garages, laundries and above all underground parking lots. It is a proven fact that considerably more murders, burglaries, muggings, rapes and other crimes are committed in such buildings than in residential areas with smaller rented or private homes. Not only high-rise apartment blocks have a usually negative effect on people’s social environment: office towers are equally disadvantageous. The vertical structure of the


buildings simultaneously underlines the vertical hierarchy: the location of the office space becomes an indicator of a company’s “importance” and, if the company occupies several or all the floors in a high-rise building, it may also be indicative of the employee’s standing in the company. The company’s top executives reside on the uppermost floors with the best views; the floors below provide a shield and every employee can positively see the distance between himself and “them up there“. It is therefore not wrong to question whether high-rise office towers are really appropriate to modern organizational structures with their emphasis on team work and interdisciplinary cooperation. Excessive energy consumption is a major shortcoming of high-rise buildings and one which could possibly lead to their demise one day. High-rise buildings are the farthest removed from the ideal form as regards energy efficiency – namely the sphere, or the cube in the case of houses. That applies to both heating and cooling: some skyscraper facades have to be cooled by day and heated by night in order to avoid undue stresses and the resultant damage. The World Trade Center, for example, consumes some 680,000 kWh/day electricity for air-conditioning during periods of strong solar irradiation; the Messeturm in Frankfurt burns up energy worth DM 40 per square metre of useful floor space for heating and cooling every month. A well insulated low-energy house, by comparison, uses energy worth less than DM 1 per square metre. The “energy balance” of high-rise buildings is also poor in other respects such as the water supply, which usually only operates with the aid of booster pumps, as well as in terms of the disposal systems and operation of the elevators, etc. From the point of construction economy in general, highrise buildings will probably always be the poorest conceivable solution, from the particularly energy-intensive and therefore expensive construction as such to the disproportionately high demolition costs. Moreover, high-rise buildings are made almost exclusively of materials which a construction biologist would take great pains to avoid, namely concrete, steel, light metal, plastics and a wide variety of chemicals. Although subjectively unaware of the fact, the residents are frequently exposed to constant stresses in the form of pollutant emissions and electrosmog. High-rise buildings are sometimes described as microcosms; that is no doubt meant in a positive sense, but the reality is different. The people in a high-rise building are totally cut off from the world around them, from wind and weather, from temperature, from smells, sounds and moods. They live in an artificial world. At the same time, however, the high-rise buildings also have a negative effect on the world around them, for they not uncommonly generate air turbulence and downdrafts in their immediate vicinity; they can be a source of unpleasant reflections and some adjacent areas remain permanently in the shade. Illuminated facades and large glass fronts are a death trap for many birds. The people outside the high-rise buildings also often have the feeling that they are being observed or threatened by

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the possibility of falling objects. That fear is surely not entirely unfounded, for there have been cases in which parts of buildings, such as glass panes, have been torn out of their anchorage by strong winds and injured or even killed people on the street below. Our love-hate relationship with high-rise buildings is finally also revealed in such recent box-office hits from Hollywood as “Deep Impact”, “Godzilla” or “Independence Day”. It seems that their directors simply cannot avoid the temptation of reducing one of New York’s most beautiful buildings – the Chrysler Building – to a smouldering heap of rubble with the help of floods, monsters or meteorites. As a result, these skyscrapers more or less become the real stars of the film on account of their magic attraction and immediate recognizability.

16 CHRYSLER BUILDING, NEW YORK

3 Technology of high-rise construction

3 3.1 Planning

3.2 Execution

3.3 Occupancy

3.4 High-rise construction in the future

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Skyscrapers are gigantic projects demanding incredible logistics, management and strong nerves among all concerned in their planning and construction. As long ago as 1928, the American Colonel William A. Starrett wrote that no peacetime activity bore greater resemblance to a military strategy than the construction of a skyscraper.

3

Technology of high-rise construction

3.1 Planning 3.1.1 Planners The complexity of the trades to be coordinated has become several times greater since then. Take, for example, the new block built for Südwest-Landesbank in Stuttgart: many disciplines and different experts were involved solely in the project planning: – Architects – Planning engineers for the supporting structures (engineering design and structural analyses) – Construction and site management (resident engineer) – Planning of the technical building services (particularly heating, ventilation, sanitation, cooling and airconditioning) – Interior designers – Construction physics and construction biology – Planning and site management for data networks – Planning of the lighting and materials handling – Planning of the electrical and electronic systems – Planning of the facades – Surveying engineers – Geotechnology, hydrogeology and environmental protection – Design of outdoor facilities and vegetation – Surveying of the actual situation in surrounding buildings If we were to include all the contractors and specialists involved in the project as well, the list would probably be ten times longer. And if we then consider that bankers, construction authorities, legal advisers and even advertising agencies or brokers must also be coordinated in the

course of the entire planning and construction of a skyscraper project, it soon becomes clear that highly professional management is essential for such a project. Project management companies have come to play an increasingly important role in recent years as they take over the entire organization, structurization and coordination of construction projects. They act as professional representatives for the client and embody the frequently voiced desire for the entire project to be coordinated by a single partner. 3.1.2 Regulations and directives The various laws, regulations, directives and standards in force must be taken into account when planning and erecting a building. The planning engineers are also obliged to observe what are known in Germany, for instance, as the “generally accepted technical rules for construction“; in other words, generally applicable technical and trade rules must be taken into account and observed in addition to the standards and regulations. Although each country has its own regulations and directives governing the construction of high-rise buildings, they are all basically similar in content with a few differences depending on the local circumstances. It is standard practice in some countries to base the bidding and planning phase for projects on foreign standards (particularly on the American ANSI Codes and UL Standards, British Standards or the German DIN standards) or to include various elements of these foreign standards in the national system of standards. As a rule, these regulations are primarily designed to ensure personal safety and then to protect the building against damage and defects. In addition to the requirements imposed by public authorities, there are also re-


quirements imposed by insurance companies with the aim of ensuring greater protection for property. These requirements can be classified in four groups: FIRE PROTECTION AND OPERATIONAL SECURITY

Many of the construction regulations concern fire protection. There can be many thousands of people in a highrise building at any one time. If a fire breaks out, they must all be able to leave the building in the shortest possible space of time and without risk of injury. This is why regulations concerning the number and execution of escape routes and fire escapes, fire compartments and the choice of materials must be observed (see Section 4.2.5). Operational security encompasses regulations governing the safety of elevators and escalators, the execution of stairs, railings and parapets or the installation of emergency lighting. Some regulations also include CO2 alarm systems for underground parking lots; indeed, there are even regulations governing the non-slip nature of floor coverings in traffic areas, sanitary rooms and kitchens. STABILITY AND CONSTRUCTION PHYSICS

The regulations governing the stability of a building are usually met by the requisite structural analyses. In addition to demonstrating the internal structural strength of the construction and safe transfer of loads to the subsoil, the stability calculations must also include possible deformation due to thermal expansion, wind loads and live loads or dead weight, for example. This is closely related with demonstrating the safety of the construction, for instance by taking steps to limit the (unavoidable) cracks in concrete elements. PROTECTION AGAINST NATURAL HAZARDS

The regulations and directives governing protection against natural hazards are usually closely associated with the demonstration of stability. Windstorms and earthquakes are the most serious natural hazards for high-rise buildings. As a rule, the assumed loads and design rules for the “load cases” of earthquake and windstorm will be specified by the regulations in order to ensure that the building will withstand windstorms or earthquakes up to certain load limits. At the same time, this will serve to rule out the risk of bodily injury due to falling parts of the building, especially parts of the facade. SOCIAL ASPECTS AND PROTECTION OF THE SURROUNDINGS

The regulations governing social aspects and protection of the area surrounding high-rise buildings are designed above all to prevent any indirect risk or threat to people. Such regulations may concern planning aspects, such as the minimum distance between a high-rise building and neighbouring buildings, or they may take the form of rules defining the maximum permissible influence that a building can have on the microcosm surrounding it. Depending on the location of the high-rise building, corresponding statutory instruments may also govern the effects on air traffic safety or the building’s influence of radio communications.

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This exceedingly concise outline of applicable regulations illuminates only some of the rules to be observed when building a skyscraper. If all the regulations governing highrise construction were to be stacked one on top of the other in printed form, they would themselves be as high as a multi-storey building. 3.1.3 Technical analyses and special questions Planning a high-rise building would be inconceivable today without the help of experts and technical consultants. Extensive soil analyses are required to determine the strength of the subsoil before deciding on the location for a high-rise building. In the majority of cases, cores are drilled into the load-bearing subsoil to obtain soil samples. The drilling profile of the geological strata making up the subsoil and laboratory analyses of the soil samples provide the basic data for the soil report which is in turn used as the basis for planning the supporting structures and choosing a suitable foundation structure with due regard for the loads exerted by the high-rise building. The forces acting on the high-rise structure in the event of an earthquake must be taken into account when erecting high-rise buildings in areas prone to seismic activity. The same applies to wind loads and particularly to the dynamic effects of windstorm or earthquake loads. The additional vibration loads can result in overall loads of the same order of magnitude as the load exerted by the dead weight of the structure. The situation is particularly critical if the vibrations reach the resonant frequency of the building: in such a case, the vibrations can intensify until the entire building collapses. The collapse of the Tacoma Bridge in Washington State, USA, was probably the most spectacular case of destruction due to resonant vibration in a man-made structure. In many cases, these effects cannot be determined by ordinary computation. Even computer simulation cannot always help. Sometimes a decisive element may be lacking to obtain a mathematical approximation; in other cases, the computer may be too slow or the storage capacity inadequate. This frequently makes it necessary to carry out model experiments in a scientific laboratory. Models of the highrise buildings are exposed to artificial earthquakes on a vibratory table or subjected to a simulated hurricane in the wind tunnel. A detailed knowledge of mathematics and physics is necessary to ensure that the same physical properties and serviceable results are obtained despite the reduction in scale. For this reason, these studies can only be carried out by highly specialized test institutes. 3.1.4 Construction licensing procedure The construction licensing procedure is normally specified in the construction laws of the country concerned. As a rule, the principal will file an application with all the requisite documents (description, plans, analyses, etc.) to the relevant construction supervisory authority. The involvement of specialists is obligatory in the case of larger and more complicated projects, such as those involving high-

17 DETAILS FROM PLANNING DOCUMENTS Next page: 18 EXTRACT FROM A TECHNICAL REPORT


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rise buildings. Such specialists include experts from the municipal fire brigade, water authorities, trade supervisory offices, environment protection agencies or similar offices in other specific fields. These specialists review the applications for a construction licence and specify any additional requirements to be met. The licence is then sent to the principal together with the requirements specified by the specialists; responsibility for complying with these requirements rests with the principal or owner of the building. 3.1.5 Other constraints

19 OPENING IN AN APARTMENT COMPLEX ALLOWING NEGATIVE VIBES TO PASS THROUGH

Even in our high-tech era, the planning and construction of a high-rise building are not dictated only by naked factual constraints. Tradition, religion and even the belief in spirits and demons still play a not insignificant part in many countries. Take, for example, the Hong Kong and Shanghai Bank building in Hong Kong: during the planning phase, a geomancer or expert on “fung shui” (i.e. “wind and water“) repositioned the escalators and moved executive offices and conference rooms to the other side of the building on the basis of astrological investigations and measurements in order to guarantee an optimum sense of well-being for clients and employees. However, it must be said that such intervention is limited by technical and structural requirements. In western countries, too, the owners are guided by similar considerations when the 13th floor is omitted from the planning or the technical installations are deliberately located on this floor in order to avoid the unlucky number 13.

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3.2 Execution 3.2.1 Foundations Although the foundations are out of sight once the building is completed, they are of immense importance for ensuring that the dead weight and live loads of the building are safely transmitted to the native subsoil. These loads are not inconsiderable. The dead weight of a high-rise building can amount to several hundred thousand tonnes. This value may be exceeded several times over by the live loads which are taken as the basis for designing the building and include the loads from equipment and furnishings, people or moving objects, as well as wind or earthquake loads. Moreover, these loads often exert different pressures on the subsoil, thus resulting in uneven settlement of the building. In order to avoid such developments where possible, these buildings must be erected on subsoil of high load-bearing capacity, such as solid rock. Yet even if a strong native subsoil is found near the surface, shallow foundations will frequently be disregarded in favour a system that transfers the load to deeper layers on account of the high bending moments to be absorbed from horizontal forces. This can be done in several ways. One is to produce round or rectangular caissons which are lowered to the required depth and bear the foundation structure. Pile foundations are probably the most widely used method, however. The piles can either be prefabricated and then inserted in the native soil or they can be produced on site in the form of concrete drilling piles. Which method is chosen will ultimately depend on both the structural concept and the soil

20 LARGE-BORE PILE FOUNDATION PROCESS Bottom: VARIOUS STAGES IN THE DIAPHRAGM WALL PROCESS 21 Following page: DIAPHRAGM WALL ROTARY CUTTER


conditions prevailing on site. Drilling piles in a whole variety of forms can be used when working with large pile diameters and very long piles. Modern equipment can easily ram piles measuring up to 2 m in diameter to depths of well over 50 m. The piles are then combined into appropriate pile groups in accordance with the loads to be transmitted by the building. Although the load-bearing capacity can be roughly calculated on the basis of soil characteristics, the maximum permissible pile load is determined by applying test loads to the finished piles with the aid of hydraulic presses and comparing the resultant settlement with the permissible settlement. Diaphragm walls are another means of producing deep foundations. These walls are produced directly in the ground and are between 60 and 100 cm thick. They are produced in sections with the aid of special equipment and a stabilizing bentonite slurry. The result is a continuous wall in the ground. This method is used in particular when subsoil of high load-bearing capacity is only found at considerable depth. Diaphragm walls and piles are also used to safeguard the foundation pit required for construction of the underground part of the building. The effort entailed can be considerable, particularly if the neighbouring buildings are very close. Rotating drills are mostly used today to minimize vibrations when installing the retaining wall. Foundation pits can easily be produced to depths of 30 m or more using this method.


22 RETAINING WALL TO PROTECT NEIGHBOURING BUILDINGS

23 VIEW OF A BUILDING PIT WITH COMPLETED RETAINING WALL

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3.2.2 Supporting structure 3.2.2.1 Load-bearing parts The steel skeleton permitted hitherto inconceivable flexibility in construction and layout planning. It also permitted series construction up to great heights, since the vertical dead weight was considerably lower than when using solid masonry and did not make it necessary to grade the sectional steel profiles in these areas. The tradition of steel skeleton structures predates the first high-rise building to have been erected by this method, namely the Home Insurance Building in Chicago (1885): mills and granaries, as well as engineering structures (bridges, silos) had already been built in England with an iron framework towards the end of the 18th century. The first frame structures used for the steel skeleton were flexurally rigid frames corresponding in height to one floor. New York’s Empire State Building, which was completed in 1932, is one example which clearly shows the advantage of this new method, namely the short time required for the construction work. Moreover, the complete separation of outside wall and supporting structure permitted absolute freedom of design for the facade. Instead of requiring around 300 kg of steel per square metre of base area as in the past, modern supporting structures only require roughly 125 kg of steel on average. As the buildings became taller and taller, however, the main problem was no longer the vertical loads but such horizontal loads as wind and earthquake forces, as well as their transmission. This led to the development of what was known as the core method. The individual floors with their secondary supporting structure, namely the columns, are suspended from a central core as the primary supporting element, normally in the form of a reinforced concrete or steel structure with reinforcing shear walls. The columns merely transmit vertical loads, while the core transmits both vertical and horizontal loads. Its primary function is to reinforce the building in horizontal direction. The cores and their surrounding walls normally accommodate vertical service installations, such as elevators, stairs, primary service shafts for electric power and HLS (heating, lighting, sanitation). A similar supporting effect is obtained with the aid of horizontal reinforcing elements in the form of shear walls, which may be considered as an “open core“. However, such supporting structures are rarely found in taller buildings. Since the middle of the 20th century, a number of improvements in the supporting structures for skyscrapers have been introduced by the architects Skidmore, Owings & Merrill (SOM) in Chicago. One such development by SOM is the “outrigger truss”: a rigid superstructure known as the outrigger is mounted at the top of a reinforcing core with movably connected floors and columns. The outrigger connects the columns to the core. They are suspended from the outrigger and are therefore under tension, thus eliminating the risk of buckling that is associated with pressure elements. A supporting system in the form of


such an outrigger truss yields further advantages over a simple core construction when it comes to transmission of the horizontal loads. The bending stress applied to the core area in the lower floors is considerably reduced when using an outrigger truss. The outrigger itself usually accommodates such technical floors as the heating and ventilation systems. The Fort Wisconsin Center built in Milwaukee in 1962 is one example of an outrigger truss structure. The production of such suspended structures gave rise to a number of innovations, such as the lift-slab process for concrete structures. The load-bearing cores are first of all erected with the outrigger on top; the individual floors are then concreted on the ground, one above the other (separated by a release spray). Finally, they are raised to their installation position by means of hydraulic jacks and then connected to the core (see Section 3.2.2.2). Supporting steel structures in the form of tubes are often used for extremely tall buildings. In this case, the supporting structure is located in the outer facade, which is consequently designed in the form of a load-bearing facade with small openings. The result is an enclosed, intrinsically rigid tube without any unnecessary space-filling columns inside. The World Trade Center in New York is an example of such a structure. The outer walls are studded with vertical steel columns roughly one metre apart. A generously dimensioned development area was obtained on the ground floor by “collecting” the descending columns. America’s tallest skyscraper, the Sears Tower in Chicago (443 m high), is a further development of the conventional tube: it is a “bundled” tube. The layout of the building is subdivided into a number of tubes to relieve the columns in the corners of the building when subjected to horizontal loads; this results in more uniform distribution of the load over the facade columns. In this case, however, the interior can no longer be designed with the same flexibility as when using a single tube. The “truss tubes” perfected by Fazlar Khan (SOM) in the John Hancock Center in Chicago are another further development of the basic tube. These tubes are additionally reinforced by diagonal struts in the facade plane and are a structural feature that has almost become a hallmark of SOM buildings. It was only in the mid-1970s that concrete began to be more widely used in constructing skyscrapers. Until then, the length of time required for concrete construction and the associated financing problems were the main reasons for the predominant use of steel structures in the construction of high-rise buildings. New developments in shuttering, however, resulted in dramatically shorter construction times. The octagonal concrete core of the Messeturm in Frankfurt, for example, was erected with the aid of a slipform which was hydraulically raised one metre every day. The latest developments in supporting structures for highrise buildings include composite structures of steel and concrete, for instance in the form of steel sections embedded in concrete.

24 EXAMPLES OF HIGH-RISE BUILDINGS WITH STEEL SKELETONS

25 DEFORMATION AND BENDING MOMENTUM DUE TO WIND WITH THE CORE CONSTRUCTION METHOD 26 Background: COMMERZBANK BUILDING

A

B

C

D

E

F

G

27 DEFORMATION AND BENDING MOMENTUM DUE TO WIND WITH THE OUTRIGGER TRUSS METHOD Below: 28 EXAMPLES OF CORE CONSTRUCTION METHODS (A-E) AND BUNDLED TUBES (F-G)


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B Wind

29 VARYING LOAD DISTRIBUTION WITH TUBES AND BUNDLED TUBES

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Top: 30 EXAMPLE OF THE ARRANGEMENT OF BUNDLED TUBES Right: 31 STEEL SKELETON



3.2.2.2 Special construction methods BMW HEADQUARTERS, MUNICH

The headquarters of BMW A.G. differs from conventional buildings to create an impressive corporate symbol in the form of a 100-m-high four-cylinder structure. The requirements for appropriate office organization yielded a basic outline in the shape of a clover leaf. Stairways, elevators and sanitary areas are accommodated in the central core. In this way, all the offices can be reached by the shortest possible route. Trendsetting methods were also used for the construction work. A reinforced concrete version was chosen as the most economical solution. According to the design concept, the entire building with 18 office floors and a technical floor was to be suspended from a girder cross at the top of the roughly 100-m-high core via four central king posts. This is a modification of the outrigger truss (Section 3.2.2.1). The entire load of the building is transmitted to the foundations via the core as the central element; it also absorbs all wind forces. A mighty girder cross with a projection of 16 m is mounted at the top of the core. The four king posts are secured to this central girder cross, each king post comprising 105 threaded steel bars with a load-bearing capacity equal to a suspended weight of 4,600 Mp. Small outer columns are additionally located between the floors. These outer columns are designed as compression columns above the technical floor (12th floor) and as king posts below. Time and costs were the decisive reasons for choosing this innovative construction method. All 19 floors were successively produced at the foot of the shell and core; the first floors were even produced complete with facade and

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glazing during construction of the supporting cross. The finished floors were then connected to the supporting cross via the king posts and raised one floor at a time every week with the aid of hoisting gear so that another floor could be produced in the space vacated at the foot of the core and then connected to the floor above (lift-slab method). Completion of the facade, glazing, installation and interior finishing proceeded on the suspended floors, unimpeded by the structural works and lifting operations. In addition to reducing the construction time required, this method also eliminated the need for expensive tooling and assembly work. LA GRANDE ARCHE, PARIS

This building, which has already been mentioned in Section 2, takes the form of a giant cube open on two sides with edge lengths of 110 m. It was completed at the end of 1989 on the 200th anniversary of the French Revolution and took 5 years to build (see photo on page 18). The building has a weight of more than 300,000 Mp and is mounted on neoprene bearings, the loads being transmitted 30 m into the subsoil via twelve concrete pillars. The cube’s main support is in the form of four prestressed upright reinforced concrete frames 21 m apart. They are complemented by horizontal members measuring roughly 70 m at ground and roof level. Each of these members is 9 m high, the equivalent of a 3-storey building. Since the two vertical sides of the cube would be without roof-level transverse bracing during construction, the required stability for that phase of the work was produced by means of horizontal steel truss reinforcements. A total of 37 office floors are accommodated in the two 18-m-wide wings of the cube (each with an area of 42,000 m2).

Top: VIEW FROM THE HEADQUARTERS BUILDING Bottom: 32 HEADQUARTERS OF BMW A.G. IN MUNICH

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3.2.2.3 Facade The skeleton construction which has increasingly been used since the turn of the century has inevitably given rise to new possibilities for the facade. The size, shape and number of windows were no longer limited by structural requirements following the introduction of curtain facades, since the loads were now primarily transmitted by posts and columns. PLANNING

Most facade designs today are still based on empirical know-how and are not tested until the design has been established in detail. The tests are carried out on true-toscale models of individual facade elements in order to test adequate resistance to air and water, load-bearing capacity and the possibility of excessive deformation or glass breakage when subjected to corresponding loads, e.g. with the aid of firmly anchored aircraft engines. DESIGN

Today’s modern facades are characterized by external wall elements equal to one floor in height and inserted between the respective structural floors. Non-supporting metal facades suspended in front of the building have increasingly become established for economic reasons, particularly in high-rise construction. The scope for design is enlarged by coloured or mirrored window panels and linings of natural stone, ceramic tiles or brick. Almost any desired appearance can be produced. TECHNICAL PROPERTIES

Modern facades must meet complex requirements as regards construction technology, engineering design and construction physics. Thanks to its lightness and almost unlimited possibilities for profile design, aluminium has largely become the material of choice for the outer framework. The panes are made of high-grade glass filled with noble gases or with a surface coating that reflects infrared light. On the inside, modern facades are highly impermeable to water and water vapour in order to prevent damage due to moisture. Despite the large areas of glass, protection against the sun is more important than heat loss today due to good thermal insulation of modern facades. Even where soundproofing and fire protection are concerned, glass and

33 FACADE ASSEMBLY


metal facades are at least the equal of conventional constructions. Modern facades also require a sophisticated ventilation and cooling system. The air-conditioned or twin facade is a case in point. Here an additional facade of laminated glass is arranged in front of the conventional facade, thus creating a space through which air can circulate. More complex ventilation concepts for routing air into and out of the building may be realized by including additional vertical and horizontal bulkheads. Individually controlled ventilation flaps are capable of providing a more natural and far less complex exchange of air. PRODUCTION AND ASSEMBLY

Due to the extensive know-how required with regard to material properties and construction physics and on account of the great manufacturing depth, modern facades are only produced by specialized companies based on the architect’s design and in accordance with functional, as well as structural aspects before subsequently being assembled. The degree of prefabrication in modern facades is considerable. The frames, glazing, parapet lining, sunshades and anti-glare finish, as well as thermal insulation and sealing are all assembled into single-storey facade elements in the manufacturer’s plant. In many cases, such technical equipment parts as radiators, air outlets and the ducting for electrical and electronic equipment are also already integrated at this stage. In the meantime, fixing elements can be mounted on the shell of the high-rise building. These elements can usually be displaced in three planes to compensate the dimensional tolerances occurring in the shell. The facade elements as such are fitted without the help of scaffolding, thus greatly reducing the time required for this work. The frame profiles are assembled with labyrinthine indentations to compensate the deformation arising in the building as a result of wind and live loads, as well as temperature differences. Permanently elastic rubber profiles ensure that the facade remains impermeable to air and water.


3.2.2.4 Roof There are no fixed rules governing the roofs of high-rise buildings. The roof design depends only on the architect’s draft and on the purposes and functions to be fulfilled by the roof. Most roofs are flat. The electromechanical drive system for the elevators is usually installed on the roof; in some cases, there is also a rail around the perimeter of the building to accommodate the equipment required for cleaning the facade, as well as the pertinent connections and facilities. A heliport or parking space can also be set up on the flat roof of large high-rise buildings. It is sometimes even used in Japan for golfing practice. Air-intake towers for air-conditioning systems, on the other hand, have become less common on modern highrise buildings. Due to the great height of buildings, airconditioning and heating systems are now decentralized and spread over several individual floors. Moreover, every installation and every superstructure on the roof means another opening in the intact roof skin and this can give rise to leakage problems, particularly on flat roofs. It is therefore advantageous to transfer such systems to lower floors. Overhead glazing is another type of roof commonly found in high-rise buildings. Such roofs keep out the elements while at the same time creating spacious assembly areas, usually in the centre of the building. Atriums and convention halls are two pertinent examples. High-rise buildings with a sloping roof are usually rounded off by an antenna system with appropriate lightning protection. 3.2.3 Interior finishing Walls, ceilings and floors in high-rise buildings are no different to those in other buildings. The choice of materials and structures depends on the intended use of the building rather than on its form (high-rise, low-level or cubic). Since particular importance is attached to flexible use of high-rise buildings, the partition walls, floor structures and (usually suspended) ceilings will be of corresponding design. When considering the interior finishing, a distinction must basically be made between load-bearing or supporting elements which are required for structural reasons and those which merely partition off the rooms and installations. Load-bearing elements are almost exclusively made of concrete or steel today, as well as of combinations of these materials.

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Due to the relatively small area available per floor, fireresistant elements (fire walls) are usually only to be found in the core areas incorporating the elevators, stairwells, service and installation shafts, sanitary and ancillary rooms. A vertical breakdown into fire compartments is mostly obtained with the aid of fire-resistant floor constructions (for further details see Section 4.2.4). The installations for air-conditioning, ventilation, lighting and fire alarms are usually located between the load-bearing ceiling and a suspended false ceiling into which the lamps are normally integrated. Small-scale electrical installations are contained in trunking in the screed flooring; elevated false floors are installed if numerous connections are required, such as in computer centres. Cables can then be routed as desired in the space below the floor; the equipment is connected to sockets in so-called floor tanks. False floors are to be found almost everywhere in modern office towers, since cables can be rerouted without difficulty, as is increasingly required on account of the rapid pace of change in office and communications technology. Moreover, the space below the floor can also be used for ventilation and air-conditioning installations, particularly in computer centres. Particular attention must be paid to the question of fire protection in such false floor constructions. Connection of the flexible partition walls to both the suspended ceiling and the elevated false floor can pose problems. From the point of view of soundproofing and thermal insulation, it would be better to install the partition walls between the load-bearing floors. However, since the suspended ceilings and false floors normally extend over the entire area and are not confined to any single room on account of the technical installations, the partition walls must also be fitted between the suspended ceiling and false floor. This consequently makes it necessary to use soundproofing and thermally insulating floor coverings, as well as ceiling materials. Facade elements into which technical components have already been incorporated by the manufacturer (see Section 3.2.3) are conveniently linked to the remaining network by means of screw-in and plug-in connections. However, it is becoming increasingly rare for such technical service connections to be installed in the external walls, as they do not permit as flexible use of the room as floor tanks.

34 CEILING INSTALLATION 35 DOUBLE FLOORING


3.2.4 Service systems

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3.2.4.1 Installations

– It must be possible to shut off individual plant segments when the corresponding parts of the building are not in use.

ENERGY AND WATER SUPPLY

SUPPLY OF HEAT AND COOLING

Unlike the case with normal multi-storey buildings, the technical service components in high-rise buildings must meet special requirements – if only on account of the height – since the required supply of energy, water and air and the effluent volume are incomparably larger. The twin towers of the World Trade Center in New York, for instance, with around 50,000 employees and 80,000 visitors every day, requires more than 25,000 kWh of electricity every hour. These utilities must also be transported to the very last floor in sufficient quantities, under adequate pressure and at sometimes totally different temperatures. The planning effort required on the part of the service engineers responsible for the supply and disposal services in high-rise buildings is therefore very much greater than in the case of smaller and medium-sized projects. The costs for electrical and electronic systems in the recently completed Petronas Towers in Kuala Lumpur, currently the tallest building in the world, amount to more than US$ 90 per square metre – and that does not include any other services. The pressure load on the individual components is reduced through subdivision into several pressure stages with technical service centres in the basement or on the ground floor, on intermediate floors and on the roof.

Unlike the case with the majority of normal multi-storey buildings in which the installed heating capacity is several times the required cooling capacity, the ratio is normally reversed completely in most high-rise buildings, due above all to the larger ratio of window area to total exterior area. The energy required for this purpose, such as heating, steam, refrigeration and electricity, must be supplied with due regard to cost-efficiency and the minimum possible environmental impact due to emissions. A number of alternative solutions are drawn up during the planning phase and compared in order to determine the most costefficient source of energy on the basis of the investment costs and expected annual costs for operation and maintenance of the equipment. The essential difference between high-rise buildings and other buildings in terms of designing the components (particularly fittings, pumps, gaskets) lies in the higher pressure stage. A water column in a 300-m-tall building, for instance, exerts a stagnation pressure of 30 bar. The fittings on the lower floors must therefore be dimensioned for the maximum stagnation pressure (possibly with the aid of pressure reducers). This makes for a major difference in costs.

VENTILATION AND AIR-CONDITIONING

SANITATION

The systems should be designed in such a way as to ensure flexible division of the areas (large rooms, individual rooms) so that their use can subsequently be changed without extensive conversions. A variety of ventilation and air-conditioning systems can be installed, depending on the purpose for which the building is used. The high-rise headquarters of the Deutsche Bank in Frankfurt am Main, for instance, is supplied by a two-channel high-pressure system in which the air is injected from above and discharged through corresponding exhaust air windows. A second, independent two-channel high-pressure system additionally blows air into the rooms from the false floors. The concept used in the Messeturm in Frankfurt am Main is completely different: in this case the required air is supplied via what is known as a one-channel continuous-flow system in combination with a “fan-coil four-conductor system” in the outer facade. In principle, all air-conditioning and ventilation systems must meet the same basic requirements:

Pressure stages are also required for the sanitation, thus permitting the use of smaller pumps. Sanitary dispensing points must additionally be isolated from the building as such for soundproofing reasons. The internal heat loads (e.g. hot exhaust air, exhaust heat from refrigeration systems) accumulated in high-rise buildings are commonly used to heat water with the aid of heat pumps or heat recovery systems. Studies undertaken in the USA have shown that the height does not have any effect on the flow rate and rate of fall, since faecal matter and effluent do not simply drop to the ground under the force of gravity, but more or less wind their way downwards along the pipe walls.

– The air in the room must be continuously renewed (a three to sixfold exchange of air is normally required per hour). – The outside air flow must be guaranteed with a minimum fresh air flow of 30 to 60 m3/h per person. – The risk of drafts must be minimized and any nuisance due to the transmission of sound eliminated.

CONTROL SYSTEMS

Today’s complex, ultra-modern control systems are primarily based on intelligent digital controllers. This technology permits a direct link between DDC (direct digital control) substations and the centralized instrumentation and control which also takes over energy management functions, such as: – optimization of the overnight and weekend temperature reduction, – linking the heating of service water with re-cooling of the refrigeration system, – operation of the external blinds.

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3.2.4.2 Deliveries, vehicles Although most high-rise buildings are centrally located and within a convenient distance to public transport systems, a sufficient number of parking spaces must still be provided for employees, suppliers and visitors. The number of parking spaces required is usually stipulated in the construction regulations in relation to the number of jobs or useful office space; similar ratios also apply to other business premises, shops, restaurants and meeting halls. The ratio may be more than 5:1 – i.e. one parking space for more than five jobs – if the building is well supplied by public transport, such as direct connection to the underground railway. Even in such cases, however, several hundred or a few thousand parking spaces may still be required for large high-rise buildings. The recently completed Petronas Towers in Malaysia, for instance, is set to accommodate around 70,000 workers. In extreme cases, if adequate public transport is not available, it may be necessary to provide one parking space for every job. For financial reasons, the size of a high-rise building is often also dictated by the number of parking spaces required. Depending on the nature, location and execution of the garages and on the building’s structural system (nature of the subsoil), the manufacturing costs for one parking space can easily amount to around DM 50,000. This means that the cost of building 2,000 parking spaces can reach as much as DM 100m with complex engineering and location on several levels, including the required ramps and traffic areas. Traffic links must be created not only for the parking spaces, but also for delivery traffic to the building, as well as for refuse-collection vehicles. High-rise buildings are commonly said to represent a “town under one roof“. That, however, also means that the traffic to, around and from the building is equal to that of a small town, the only difference being that the entire traffic is concentrated on a handful of access roads and adjacent traffic areas which must be able to handle this volume of traffic at peak periods. 3.2.4.3 Passenger transport, vertical development In addition to escalators and automatic walkways, which usually only serve to connect a few floors conveniently and without delays, passengers and goods are normally carried up and down by elevators in high-rise buildings. The comparison made above between a high-rise building and a small town also applies with regard to the number of people inside the building: in the course of a few hours every morning, tens of thousands of people stream into a megabuilding to start work and leave again within a very short space of time at the end of the day. They are supplemented by visitors, guests and customers, with the result that the elevators often have to transport well over 100,000 people every day.


It is therefore not unfair to assert that the American inventor of our modern “safety elevator”, Elisha Graves Otis, was also one of the pioneers who paved the way in 1852 for high-rise construction. Asked what they feared most in a high-rise building, the respondents claimed that their greatest horror scenario was not a fire, but a malfunction in the elevator system. Such catastrophes may be exceedingly rare, but they cannot be excluded entirely. A fully occupied elevator plummeted when a B25 bomber crashed into the Empire State Building in 1945 (see Section 4.8.2). In the beginning, when the high-rise buildings had no more than about 20 floors, every elevator led from the entrance level (not necessarily the ground floor) to every other floor in the building. The simple control technology was offset by a number of disadvantages: numerous elevators and elevator shafts were needed. The numerous stops and, above all, the low speed (with frequent braking and restarting) meant that it took a long time for the elevator to reach its destination. It was soon found that elevators – like every mass transit system – needed a sophisticated operating concept. The two operating systems commonly used today – namely group and changeover operation – only became possible with the development of powerful drive systems and controllers, as well as highly effective braking systems with multiple braking for safety reasons. In group operation, for which a separate shaft is (still) required for each elevator, the elevators or groups of elevators only serve certain floors: one group of elevators serves the first ten floors, for example, while a second group serves floors 10 to 20 from the entrance level, the next group then serves floors 20 to 30, etc. The groups must overlap on at least one floor so that people can transfer from the 17th to the 23rd floor, for example, although they must change elevators in the process. The advantage of this system is that the number of elevator shafts decreases towards the top of the building, thus counteracting the lower floor space frequently found on the top floors. In changeover operation, large and very fast express elevators serve a small number of central floors which are often also highlighted architecturally. In New York’s Empire State Building, these elevators take no more than a minute to travel from the ground floor to the 80th floor. “Local elevators” serve the floors between the “changeover floors“. Here too, the elevators may serve groups of floors in exceptionally large high-rise buildings. If the equipment rooms are located alongside the elevator shaft, a number of local elevators can be operated one above the other in the same shaft; in this way, the number of shafts can be reduced while maintaining the transport capacity. Up to three elevators are contained one above the other in each of 36 open shafts in New York’s World Trade Center. The volume of traffic is analysed by microprocessors, thus avoiding long delays. The floor area has been increased by 25% as a result of these sophisticated systems.


At least one goods elevator with high load-bearing capacity and therefore lower speed is usually required to transport goods and to serve the building. Depending on the size of the high-rise building, there must also be a sufficient number of elevator cabins large enough to accommodate stretchers. Elevators should never be used to evacuate people following a catastrophe. It is therefore a statutory requirement in most countries that a warning be affixed to all elevators prohibiting use of the elevator in the event of a fire. Elevators are often directed automatically to the ground floor following a fire alarm and remain there with their doors open. So-called firemen’s lifts are additionally installed in high-rise buildings for use in the event of a fire (see Section 4.2.4). Apart from the statics, there is no other structural part or equipment in a building subject to so many regulations and technical controls as the elevator – and with good reason, too. Constant care and regular maintenance combined with stringent inspections by an independent test institution, such as the Technical Inspection Agencies (TÜV) in Germany, are an absolute must for the safe operation of high-rise buildings.

36 ELEVATOR IN THE WORLD TRADE CENTER, NEW YORK

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3.2.4.4 Waste disposal In the days when waste was collected without preliminary sorting on site, waste chutes were frequently installed in residential and administrative buildings, as well as in highrise buildings with up to 20 floors. Such waste chutes are not advisable in taller buildings – due to the associated greater height of fall – for paper or plastic bags tear open as they fall and considerable noise is generated by the waste as it falls and collides with the walls and bottom of the chute. The fire hazard is also enormous. Standard practice today is to collect the waste separately on each floor: paper, recyclable secondary materials, compostable organic waste and residual household waste which is collected in large containers and then transferred via the goods elevator (or service elevator) to a central collecting point (in the basement) alongside the delivery area or to the underground parking deck. The waste is compressed to a fraction of its original volume in special containers at the central collecting point. Mobile waste collecting bins are ready and waiting in the goods elevators in the World Trade Center in New York, for instance. In addition, there are five filling hoppers which can comminute all manner of objects, including desks.

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Too little attention is frequently paid to the problem of waste disposal when planning a building. The following rough estimate illustrates just how much waste can accumulate in a high-rise building: if each of the 5,000 assumed employees in a high-rise building “produces” only 2 kg of waste per day, that makes a total of no less then 10 tonnes to be disposed of every day. In addition, there is the waste from shops, kitchens and restaurants, as well as special waste from service facilities and filling stations for motor vehicles. A sophisticated logistical system is consequently needed simply to dispose of the waste.


When the high-rise building is completed, it is taken into service and occupied by the owner or tenants. Costs are continuously incurred during this time for maintenance and care of the building; these costs can have a significant effect on the financial result of the building’s operator. He must decide whether to employ his own staff to deal with the problems (e.g. cleaning, maintenance, security, administration) or whether to assign intrinsic functions to exter-

nal service-providers (“outsourcing“). Both alternatives require an efficient building management capable of taking over the following responsibilities, particularly in the case of high-rise buildings: a) Technical building management – Energy supply – Disposal – Equipment operation – System communication b) Commercial building management – Cost accounting – Property accounting – Rentals – Contract management c) Infrastructural building management – Cleaning services – Caretaker services – Security services – Secretarial and postal services A new market segment known as “facility management” has developed in recent years and caters to the needs of users in larger properties in particular. It differs from classic building management in that it is not limited solely to the occupancy phase, but is already in action during the planning phase and therefore covers the entire life cycle of the building right up to its demolition.

37 ELEVATOR DEMONSTRATION BY OTIS

38 MAINTENANCE

3.3 Occupancy 3.3.1 Maintenance, administration


Top: 39 RENOVATION OF A HIGH-RISE BUILDING Bottom: 40 PILE-DRIVING MACHINERY FOR WORKING IN BASEMENT FLOORS

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Cost-efficient optimization of all processes during the occupancy phase of a high-rise building requires an efficient and powerful computer system including CAD (computer-aided design) applications. The latter is particularly important for internal planning changes, conversions, rehabilitation and changes in occupancy, as well as for permitting documentation of important information (e.g. layout drawings, general drawings of the building, security information, furniture inventories, telephone connections). New requirements are often imposed on the performance of technical equipment in a high-rise building in the course of its occupancy phase. Different times of day and seasons, as well as changing tenants require rapid adaptation of the heat, cooling, electric power and lighting. In office buildings, manufacturing premises and high-rise buildings, this adjustment is handled by freely programmable DDC systems which record all the data of the connected technical equipment, such as fans, burners, pumps, valves and external blinds, analyse these data and then optimize the corresponding process sequence. Unnecessary energy consumption is avoided, consumers are switched off when their offices are not in use and switched on again shortly before occupancy recommences. The recorded data are forwarded to either the centralized instrumentation and control in the building or via the public telephone network to an external control centre. Expensive call-outs on site can be reduced through remote programming by the maintenance company if faults arise or limit values change. If more complex maintenance work is required, the technician on duty can immediately see which spare parts are required to remedy the fault. 3.3.2 Conversions In the planning a high-rise building, care is normally taken to ensure that the building can subsequently be used in a relatively flexible manner. Internal conversions due to changes of use following a change of tenant or the changing needs of the present user should not be a problem. In this way, the operator of the building can also respond more effectively to changes in the property market. To ensure such flexibility, the service systems are centrally located in the building. The partition walls separating the individual rooms are non-supporting and can be relocated to permit subsequent changes in room size. As a rule, the building’s supporting structure is totally isolated from the system of partition walls inside the building. Where possible, reinforcing walls are located outside the useful floor area, such as in the core area. The columns are consequently the only remaining load-bearing elements causing a “nuisance” in the useful area. A column spacing of 6 to 7 m is widely used as a standard grid, meeting both architectural and structural requirements. If the conversion nevertheless affects the load-bearing structure of the high-rise building, it is essential to draw up a structural analysis for all building states during the conversion work in order to avoid damage. If other parts of the building remain in use during the conversion work,


special precautions must be taken and the work efficiently coordinated to ensure that the conversion proceeds without a hitch. The only possibility for expansion in densely populated cities is normally upwards – i.e. by adding floors – if additional space is required at a later date. In such cases, particular care must be taken to ensure that the additional loads can be absorbed by both the existing building and the existing foundation structure. It may even prove necessary to extend the foundations in such a case. This can be achieved by a technically complex method using additional piles which must be produced with the aid of special drilling equipment in the underground parking levels on account of the low working height. Demolishing old skyscrapers in inner city areas is an exceedingly complicated business. Such buildings are normally demolished by blasting after months of preparation and a great deal of expert knowledge so that the explosive charges are positioned at precisely the right points to ensure that the building collapses like a stack of cards without a single piece of rubble leaving the site. 3.3.3 Rehabilitation There are many reasons why a high-rise building should have to be rehabilitated. The criteria to be met here are basically the same as for conversions, i.e. the safety of the building and its residents or users must be assured completely and at all times during the rehabilitation work. Particularly high safety standards must be maintained in conjunction with asbestos abatement – i.e. when removing the asbestos installed as insulation or for fire-protection purposes and replacing it with physiologically safer materials. Asbestos fibres are considered to be highly carcinogenic and are released in particular during demolition work. The technical equipment in the building, such as heating, sanitation or elevators, must also be rehabilitated after a certain period of time. In many cases, however, such renewal or modernization work is undertaken without shutting down the entire building. It is often sufficient to shut down only part of the building, and sometimes the work can even be carried out without interrupting operation of the building at all.


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3.4 High-rise construction in the future

In view of the anticipated population explosion and the concentration of dwellers in the conurbations, the need for high-rise buildings will continue to grow, especially with building land becoming increasingly scarce and property prices soaring as a consequence. The Australian Embassy in Tokyo sold 500 m2 of its garden in return for DM 1.25m – per square metre! Such astronomical prices can be more easily understood if we consider that there are currently 5,400 people per square kilometre in Tokyo and that the population in this conurbation is forecast to increase from 18.5 million at present to almost 30 million in the coming decades. In some regions, it will only be possible to settle new residents or businesses if they can be accommodated in high-rise buildings.

It is already certain that today’s (1999) world record for the tallest building – the twin Petronas Towers in Kuala Lumpur (452 m) – will not be held for long. A new recordbreaking edifice, the Chongqing Tower, is already under construction in Shanghai. Specific plans have already been drawn up for an 800-m-high building in Tokyo (Millennium Tower), and totally inconceivable, gigantic projects involving heights of several kilometres are also under discussion. One of the most unusual is the Japanese project TRY 2004, a pyramid rising 2004 m into the sky. It is to be made up of 204 octahedral elements which can be mutually sealed off from one another if a fire breaks out. In this way, living space is to be created for one million people over an area of 8 km2. Economic considerations could impose limits on these gigantic plans, for the costs for construction and operation of a high-rise building increase exponentially with its

height. It does not take a prophet to forecast that the future of high-rise buildings – these “architectural dinosaurs”, as one critic recently wrote – is highly uncertain in their traditional form. The disproportionately large manufacturing effort, the high operating costs due above all to the excessive consumption of energy, and reservations as regards health and safety will result in a new kind of highrise building totally different from today’s. Since technological progress is advancing steadily, however, and the attitudes of both owners and architects will also be of decisive importance, one would almost require the skills of a clairvoyant to predict with any accuracy the specific changes which are impending. Nevertheless, we shall at least venture a rough prediction of possible future developments.

41 PETRONAS TOWER


MESSETURM 259 m

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LANDMARK TOWER 296 m

CENTRAL PLAZA 310 m

EMPIRE STATE BUILDING 381 m

JIN MAO BUILDING 381 m

42 TREND TOWARDS EVER-TALLER MODERN HIGH-RISE BUILDINGS

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ASIA PLAZA 431 m


SEARS TOWER 443 m

PETRONAS TOWERS 452 m

CHONGQING TOWER 457 m (under construction)

MILLENNIUM TOWER 800 m (planned)

800m (2624 feet)

43 THE MILLENNIUM TOWER – a vision for the 3rd millennium

452 2 (1482 feet)

2m

44 PETRONAS TOWERS, KUALA LUMPUR, MALAYSIA

45 SEARS TOWER, CHICAGO

443m (1453 feet)

46 EMPIRE STATE BUILDING, NEW YORK

381m (1250 feet)

47 MESSETURM IN FRANKFURT AM MAIN

259m

(850 feet)


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ENERGY SAVINGS

POWER GENERATION

Consistent use of the savings potential already available today will indisputably be the most important “source” of energy in the future. Numerous studies have proved that energy savings of up to 80% can be realized in both the private and the commercial sector without any loss of comfort or convenience. “Intelligent energy consumption” is a term that is increasingly being used in this context. As a result, the foundations for a building’s future consumption of energy are already set in the planning stage: the topographical surroundings are of importance here, as is consideration of the prevailing wind strengths and directions, and any shadows cast. An energy-efficient building will be positioned with its “broadside” away from the sun in warmer climates, while every effort will be made to ensure that as much of the facade as possible faces the sun in colder climates. Windows facing the sun should be as large as possible, those facing way from the sun as small as possible (the keyword is: passive solar architecture). A rotary building is another conceivable possibility and could be turned towards or away from the sun as required. Particular attention must be paid to thermal insulation of the facade. Northern European construction standards are a positive example here, as they specify a thickness of several decimetres for the insulating layers. Transparent thermal insulation will probably become established in future, as it not only reduces the heat loss, but can also attract additional heat by allowing the radiated heat to reach the facade without obstruction. Thermopane glazing with a k-value of less than 1 already represents the state of the art today, as does solar glazing with almost 100% reflection of the radiated heat. Considerable savings can also be achieved inside the building, for instance by using a combined heat and power generating unit instead of conventional heat and power generation, or by using variable-speed forced-circulation pumps in the sanitation, heating and air-conditioning sectors, or by using energy-efficient fluorescent tubes which require up to 80% less electricity than conventional filament lamps, or by controlling the lights via movement detectors and naturally by ensuring the energy efficiency of every single appliance used in flats or offices, from well insulated fridges to personal computers with low power consumption. Reusing the off-heat from air and water will be a matter of greater importance in the future. Ideally, our future energy requirements should all be met by regenerative sources.

High-rise buildings are positively ideal for generating power: the huge facades are usually exposed to the sun from dawn to dusk and the prevailing winds on the roof are considerably stronger and more persistent than those on the ground. And these are also the main sources of energy to be used in the future: wind-operated plants to generate electricity on the roof or particularly exposed edges of the facade, collectors to heat air or water and photovoltaic systems to generate electricity on the facades and possibly also for producing hydrogen at a later stage. Generation of heat via the deep-pile foundations associated with virtually every high-rise building is a less obvious possibility. When the building is complete, water can be circulated through heat exchanger tubes integrated into the pile reinforcements. Due to the feed and return flow of the water, the different energy potential between footing and building can be exploited and the subsoil used as a seasonal or temporary store of energy. One of the first projects of this type has already been realized in the rebuilding of the Commerzbank headquarters in Frankfurt am Main. CONSTRUCTION BIOLOGY

The more we know and learn about the harmful effects of modern materials and installations on health, the less probable it becomes that future generations will voluntarily accept this hazard. Research and industry must therefore find acceptable alternatives, such as emission-free materials, installations, insulating and isolating materials, adhesives and coatings, as well as avoiding the use of chemicals which give off toxic gases in the event of a fire.

48 ADDITIONAL HEAT RECOVERY VIA PILING FOUNDATIONS IN THE COMMERZBANK HIGH-RISE BUILDING


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CONSTRUCTION PRACTICE

The construction of high-rise buildings will be dominated by four factors in future, namely: time savings, personnel savings and financial savings, in addition to the energy savings already mentioned above. As examples in Japan show, it is already possible to erect buildings with the help of assembly robots. The required elements are designed and drawn with the aid of computers (CAD = computer-aided design). The computer automatically retrieves all the required (dimensional and design) data from the saved architectural and engineering drafts, as well as from detailed libraries. The parts are then manufactured by fully automatic machines on the basis of these production data (CAM = computer-aided manufacture) and transported to the site “just in time“. Assembly robots pick out the right part in the right sequence, transport it to the assembly point and install the finished element in the right place.

Thanks to the efficiency of the computers and robots, buildings erected in this way bear little resemblance to the conventional edifices erected with prefabricated parts: the precision and arithmetic accuracy of these machines permits a hitherto inconceivable variety of forms and even the most complex structural analyses are mastered with the help of computers. If the engineers who developed and built these robot-controlled “construction machines” are to be believed, then this method can not only considerably cut the time required for construction work, but can also reduce the construction costs by up to 40% and reduce the workforce required for conventional construction projects by up to one-third (roughly onehalf of these would then find work in the component manufacturing plants). Above all, the dangerous and physically strenuous work would be eliminated. In this way, something that was considered Utopian only a few years ago has already begun to become an everyday reality: huge edifices and even complete towns are erected by robots as if guided by a ghostly hand. In spite of this, however – or perhaps for precisely this reason – highly qualified experts will be needed to develop, operate and control the necessary computer programs, techniques and technologies.

49 FULLY AUTOMATED BUILDING SITE

50 JIN MAO BUILDING

51 SHANGHAI PUDONG

52 NEW YORK 53 CHINA, GUANGZHOU

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54 NEW YORK

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55 NEW YORK: VIEW FROM THE WORLD TRADE CENTER

56 NEW YORK

4 Risk potential

4 4.1 Design errors 4.2 Fire

4.3 Windstorm 4.5 Foundations, settlement 4.7 Special structural measures 4.9 Loss of profit 4.4 Earthquakes 4.6 Water 4.8 Other risks

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4 Risk potential

The following sections consider all of the hazards constituting the greatest risk potential during the construction and occupancy of a high-rise building. The commentaries will be illustrated by examples of losses and rounded off by proposals which need to be implemented to minimize such risk potential and prevent losses.

4

Risk potential

4.1 Design errors Fortunately, no-one really knows just how many rumoured design errors by architects are actually true. They are said to have forgotten not only the toilets, but even complete stairwells in multi-storey buildings. And today’s construction practice makes such design errors more probable than ever: since the supporting structure, shell and core, and interior finishing are totally isolated from one another not only during the design phase, but also during the subsequent construction phase, errors may possibly not be discovered until the work has reached a fairly advanced stage. This leads to time-consuming and costly changes and corrections, usually at the expense of the professional indemnity insurance prescribed for architects in many countries. The most commonly occurring design errors can be subdivided into two groups: failure to observe building and planning codes on the one hand, and errors in the choice of materials and wrong or inadequate construction details on the other. FAILURE TO OBSERVE BUILDING AND PLANNING CODES

It may be assumed that, in the majority of countries, when a building exceeds a certain size – and this will certainly apply to high-rise buildings – corresponding plans must be submitted to the construction licensing and supervisory authorities for inspection. The inspection and approval procedure not only encompasses aspects under the building code, such as compliance with specified distances and the specified height and size of a building or its type of use, but also the safety of the people inside the building.

Such aspects include compliance with fire protection requirements in the building, the position and number of escape routes and the number, location and execution of stairwells and traffic areas. Even such seemingly less important aspects as compliance with accident prevention regulations are reviewed, for instance as regards the height of railings or the distance between bars in railings and grids. In many cases, however, the design is changed at short notice during the construction phase, with the result that the plans submitted for inspection no longer reflect the actual situation. If errors are made by the designer at this stage in violation of building and planning codes, they will only be discovered (if at all) during final inspection of the building by the construction supervisory authority as specified in many countries. Such changes frequently cannot be undone, and this forces both sides to accept compromises possibly at the expense of the building’s safety. Despite the numerous statutory instruments and court rulings in test cases, the complex legal relationship between principal and architect makes it necessary for the courts to decide who is to bear the costs incurred as a result of such errors. In most cases, both the architect’s legal protection insurer and his professional indemnity insurer will be involved. If the errors are not discovered and the building is taken into service, however, this may not only increase the probability of a loss occurring, but also pose an acute risk to life and limb for its users. Particularly grave defects only become evident when the loss actually occurs, for instance when a fire occurs. Fire insurers, personal accident,

4 Risk potential

Page 86

health and life insurers, occupational disability insurers and once again the liability insurers may all be called upon to bear the costs once the courts have settled the question of blame. If a guilty party can be identified, that party can face considerable penalties for any shortcomings ascertained. It is irrelevant in this context whether this party was actually aware of these shortcomings or merely must have been aware of them. For this reason, all insurers – and particularly fire insurers – are well advised to ascertain whether all of the safety requirements have been met before they conclude a policy for buildings entailing high risk potential.

can be sure of having underwritten a completely new risk. As already mentioned in Sections 3.2.3 and 3.2.4, the construction of modern office towers has little in common with the construction methods employed in the past. Instead of solid ceilings and walls, we now have a skeleton structure – usually made of steel – with endless kilometres of wiring for telecommunications, switching, control and air-conditioning running vertically and horizontally through the entire structure. During both the construction and the operating phases, this combination consequently poses an enormous risk for the spread of fire and smoke, as well as for the harmful effects of heat, fumes and water.

MATERIALS AND CONSTRUCTION DETAILS

BROADGATE

Not only the legal relationship between principal and architect is exceedingly complex; just as complicated is that between architect and (sub)contractors and particularly among the (sub)contractors themselves. Although the architect or specialist engineer specifies which materials are to be used or installed, the (sub)contractor must check whether these materials are indeed suitable for such use. Modern and unconventional construction practices frequently make it difficult or even impossible for (sub)contractors to determine whether the specified materials or the execution intended by the designer are indeed suitable and correct. Unsuitable materials and connections in sanitary installations, for instance, can rapidly result in water damage due to burst pipes. Unsuitable insulating materials can give off toxic gases or acids in the event of a fire; incorrectly dimensioned fixtures for suspended ceilings or facade elements can cause bodily injury or property damage if they fall down. In extremely simplified terms, it could be said that most of the damage incurred in or on a building is ultimately attributable to design errors.

This new 12-storey office tower is one of fourteen buildings erected over the railway tracks of a station in the City of London. Due to the extremely confined conditions, the containers accommodating the construction workers were installed on the first floor of the shell. During the evening of 22nd June 1990, an electrical appliance or short-circuit caused a smouldering fire in one of these containers. Undiscovered for several hours, this smouldering fire charred the interior furnishings until it reached the polystyrene foam inside the steel walls of the container. This resulted in major generation of smoke until the container literally burst apart around midnight and caused a major fire. The fire was only discovered by a security patrol roughly 30 minutes later after a smoke detector was tripped. When the fire brigade arrived another seven minutes later, the temperature around the container was apparently already in excess of 1,100 °C. Twenty fire-fighting teams with over 100 firemen fought for almost five hours to bring this difficult fire under control. The extreme heat ultimately caused the steel skeleton and a number of ceilings to fail. A large area in the middle part of the roughly 40-m-high building subsequently dropped by between 0.6 and 1.2 m. The fire also destroyed material which was stored on the first and second floors. This led to even more intense smoke emission, which in turn caused extensive damage to the aluminium facade and valuable interior fittings. The considerable property damage worth around £36m was the highest fire loss to have been incurred in a highrise building in the United Kingdom up to that time and was due to the absence of an early-warning system, the widespread propagation of fumes due to the chimney effect of the atrium and the presence of numerous openings in walls and ceilings. Moreover, neither the fire-alarm system nor the risers and sprinkler system had been activated in this stage of the building’s construction.

4.2 Fire Fire is one of the greatest risks for every building and particularly for high-rise buildings. Due to the spectacular photographs and film sequences shown in the media, major fires have always made – and will continue to make – headline news not only during the construction phase, but above all during the occupancy phase. They are a major headache to all insurers and reinsurers due in particular to the exorbitant rise in repair and restoration costs, as well as the loss of human life. A few examples of major fires during the construction and occupancy phases are provided below.

LONDON UNDERWRITING CENTRE

4.2.1 Examples of losses during the construction phase GENERAL

It is not always easy for an insurer to determine which risks may be associated with technical improvements, new techniques, new materials or combinations of different materials. It is only when the loss occurs that the insurer

A fire broke out during the interior finishing work in this over 55-m-high office tower in London’s banking and insurance centre in August 1991. The cost of repairing the damage consumed £110m or around 75% of the insured value of the building and was far higher than the cost of repairing the damage following the Broadgate fire in the previous year. First estimates indicated that the loss would

57 FIRE IN THE BROADGATE BUILDING, LONDON: sunken roof support beams Following page: 58 FIRE-PROTECTION INFORMATION

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be no more than a fraction of the final cost, and to the man on the street the building appeared to have survived largely unscathed, at least from the outside, and merely had to be cleaned. The fire broke out on the ground floor at the beginning of the morning shift, near the atrium where it was extensively nourished by the considerable material and packaging scrap which had been stored there. Although the fire brigade arrived within minutes despite the early morning rush-hour and narrow streets, it proved extremely difficult to bring the fire under control. Thanks to the atrium, the flames had already reached the roof and were reaching out towards the unsealed floors leading off to the sides. The atrium itself was difficult to reach since it was completely encased in scaffolding for installation of 16 large escalators. The stairwells were almost impassable on account of the immense heat and smoke. It was only when the roof above the atrium broke and the smoke was dispelled that the firemen were able to make progress in bringing the fire under control. The considerable increases in the cost of repairing the building during the ensuing months were due almost exclusively to the extreme spread of harmful fumes. These fumes (including chloride-laden fumes from burning PVC cable installations) had spread through openings in walls and ceilings, as well as the false floors, to all floors above and below ground and had settled on most of the installations and facade elements. Further damage was caused by contaminated fire-fighting water in the false floors and basement floors. The supporting structure, on the other hand, suffered very little damage. In addition to requiring extensive decontamination, such fires also raise questions with regard to warranties. Suppliers may have guaranteed the serviceability and appearance of their parts and installations over a period of several years, but no-one can judge how the frequently complex switchgear, for example, will respond over the years to the extreme heat and corrosive fumes produced by the fire. In addition, the commonly used PVC sheathing also produces highly corrosive substances. MERIDIEN PRESIDENT TOWER

This 36-storey hotel and shopping centre in Bangkok was almost complete and about to be inaugurated when a fire broke out following an explosion during installation of parts of the air-conditioning. The fire very rapidly spread through the air-conditioning shafts and soon reached the 10th floor, as well as lower floors. When the fire broke out, more than 150 construction workers were adding the finishing touches to the inside of the building. Since the workers on the upper floors were unable to make their way downwards, roughly 40 fled onto the roof while others used ropes to lower themselves onto a veranda on the 5th floor so that they could escape from the flames. Despite the intense smoke, seven helicopters succeeded in rescuing the men on the roof, as well as another 50 from lower floors with the aid of ladders and straps. One of the helicopters was even forced to make an emergency landing after its tail rotor touched the building in the dense

4 Risk potential

smoke. Three men died in the fire or as a result of jumping out of a window. Altogether, 40 fire brigades with over 2,000 firemen fought for roughly six hours to bring the fire under control. Their work was impeded from the very beginning by the narrow access roads. The water pressure from their nozzles only reached up to the 10th floor. Subsequent investigations revealed that although all the fire-prevention requirements, such as smoke detectors, fire walls, firemen’s lifts and sprinkler systems, had been met, these systems had not been activated during the construction phase. It is assumed that the fire was most probably caused by a bucket of thinners igniting on contact with sparks from welding work being done on parts of the air-conditioning system. Despite the extensive damage, the hotel – which is located on the 17th to 36th floors of the building – was opened without undue delay. In the department store, around 3,000 m2 out of more than 130,000 m2 was seriously damaged by the fire, but the supporting structures remained unscathed. Completion of the store is expected to be delayed by several months. The total loss is estimated to be in the region of DM 25m. 4.2.2 Fire protection on construction sites Numerous similar major fires in the recent past have clearly shown that too little attention is still being paid to fire prevention on construction sites for buildings in general and for high-rise buildings in particular. This has led to devastating fires and immense costs for the insurance industry. These fires are more likely to be caused by human negligence than by technical defects, for example workers carelessly throwing away glowing cigarette ends and the improper use of cooking appliances in the workers’ quarters, which are frequently located in the shell of the building. Moreover, as the fires in the Broadgate Building (1990) and the London Underwriting Centre (1991) clearly showed, an atrium in the building can have extremely negative effects in the event of a fire, as its considerable area positively invites misuse as a place for storing large quantities of material, particularly during the construction work. These materials are easily combustible on account of their packaging, which is usually not removed beforehand and therefore constitutes an increased fire risk. In addition, the chimney effect (i.e. vertical draft) due to the atrium helps the fire to spread rapidly to the roof and other floors leading off from the atrium. The situation is further aggravated by the fact that, even if the risk potential is acknowledged, safety features are the first to be sacrificed under the rising pressure of time and costs. The growing use of combustible materials, the higher fire load and its distribution over all floors are therefore the main reasons for catastrophic major fires. This trend has become unacceptable in the United Kingdom. In an unrivalled campaign, fire brigades, insurance companies and the construction industry have drawn up a “Joint Code of Practice” for fire protection on construction sites. Compliance with the regulations and requirements

59 ESCALATOR DESTROYED BY FIRE

60 FIRE IN THE MERIDIEN PRESIDENT TOWER, BANGKOK

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61 MERIDIEN PRESIDENT TOWER, INCREASED RISK OF FIRE DURING THE FINAL FIT-OUT PHASE

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62 DIFFICULT FIRE-FIGHTING CONDITIONS IN THE MERIDIEN PRESIDENT TOWER

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contained in this Code has now become an indispensable element in the terms of insurance for the construction of major high-rise projects. This Code specifies in detail how fire protection is to be effectively organized and implemented in all the various areas and phases of construction. Adequate protection against fires can only be guaranteed by clear instructions and standards which are implemented from the very beginning of the construction work and which are regularly monitored and supported with corresponding investments in time, money and material. Particularly in the case of high-rise construction, preventive fire protection must be included from the planning phase onwards so that the various construction phases can be taken into account accordingly. One of the essential conditions for effective fire protection is the appointment of a safety officer responsible for risk management on site. A whole team of safety officers may be appointed for a high-rise construction site; in such cases, they are often responsible for personal and occupational safety, as well as for fire protection. In addition to drawing up, implementing and verifying the fire-protection concept, it is important to train the site personnel in fire-fighting techniques and to familiarize the fire brigade with the site. Since the situation on site is subject to constant change in line with the progress made during the various construction phases, the site drawings must be regularly updated with regard to access roads for the fire brigade, fire compartments, water supply lines and fire loads in particularly high concentrations. Such risks as combustible liquids, gas depots, cable ducts and temporary openings in walls and ceilings must be highlighted in the same way as the available fire-fighting equipment. Above all, particular attention must be paid to preventive fire protection. The primary objective must be to reduce the fire load. Waste materials must be removed regularly and combustible waste collected from the individual floors every day. The value of material stored for construction and assembly work should be limited, the material spread over several storage units and protected by special measures, such as fire walls or sufficient distance, in order to reduce what is frequently a very high fire load. Specific control of all work constituting a fire hazard is another essential precaution. A special approval procedure is being introduced to ensure safer practices with grinding, cutting or welding work, for example, as well as work with soldering lamps, application of hot asphalt or other work with radiant heat. At least one person trained in fire-fighting techniques and equipped with a fire extinguisher must always be present during such work. Even when the work is complete, however, the area must be inspected again to ensure that a fire cannot break out subsequently (e.g. as a result of glowing welding slag). The site should be fenced off and access controlled in order to minimize the risk of fires due to third parties.

63 COMBUSTIBLE WASTE INCREASES RISK OF FIRE

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4.2.3 Examples of losses during the occupancy phase GARLEY BUILDING IN HONG KONG

“Elevator to hell”, “Trapped in a burning skyscraper”, “Towering inferno” – these are just a few of the headlines in world press reports on one of the most devastating fires in Hong Kong in almost 40 years. During welding work in an elevator shaft in the 16-storey Garley Building in Hong Kong’s Kowloon district on 21st November 1996, a fire broke out which killed 39 people and seriously injured around 80 others. More than 90 people were rescued, some of them in daring scenes in which a helicopter pilot risked his own life. Maintenance and repair work was in progress in the office and business tower when highly flammable material caught fire during welding work in the basement. The fire made its way up through the elevator shafts and spread like lightning through the top three floors of the building. The immense heat and smoke made these floors a death trap for the people working there: the windows could not be opened to let the heat and smoke out, and escape routes were filled with smoke or impassable on account of the fire. As a result, 22 charred bodies were subsequently found in a single office on the 15th floor. The fire brigade was called shortly after the fire broke out and arrived on the scene shortly afterwards, so that many of the people in the building were fortunately saved. Although hundreds of firemen were at the scene of the fire, it took over 20 hours to bring the fire under control. What were the reasons for the fire being able to spread so rapidly, for the magnitude of the loss and the numerous fatalities? The primary cause lay in the totally inadequate fire-protection installations in the 21-year-old Garley Building. There was neither an automatic fire alarm nor a sprinkler system. From the speed at which the fire spread through the elevator shaft to the upper office floors, it may be assumed that the structural fire protection was also inadequate. It is claimed that plywood had been used as provisional elevator doors. The Hong Kong Fire Prevention Act stipulates that all highrise buildings licensed after 1973 must be equipped with a sprinkler system, among other things, but this did not apply to the Garley Building. In view of the large number of older buildings in a similar condition to that of the Garley Building, the headline in one Hong Kong newspaper – “700 office buildings could become death traps” – is not so far-fetched. FIRST INTERSTATE BANK BUILDING IN LOS ANGELES, USA

Once the tallest building in California, the 261-m-high, 62-storey office tower fell prey to what is considered to have been one of the most destructive skyscraper fires in the USA in recent years when, for reasons unknown, a fire broke out on the 12th floor on the evening of 4th May 1988. From the fire-fighting point of view, it represented one of the biggest challenges for the Los Angeles City Fire Department. With 383 firemen, almost one-half of the entire shift on duty in the city was called out to fight this fire. The fire was brought under control after 31/2 hours. The 12th to 16th floors were gutted. The floors above suffered

64 LIMITED EVACUATION ROUTES THROUGH SMOKE-FILLED STAIRWAYS

65 HONG KONG, FIRE IN THE GARLEY BUILDING

66 TOWERING INFERNO 67 DIFFICULT FIRE-FIGHTING CONDITIONS

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considerable damage due to smoke and those below were extensively damaged by fire-fighting water. One maintenance technician died when he took the elevator to the floor in which the fire had broken out because an open fire door had evidently jammed between the burning office area and the lobby in front of the elevator. Around 50 people were injured, including several firemen. The loss totalled more than US$ 50m, plus losses amounting to tens of millions for business interruption. The building had been completed in 1973 before the sprinkler regulation for high-rise buildings in Los Angeles came into force. This regulation stipulates that sprinklers must be installed throughout the building. At the time of the fire, work was under way to install a sprinkler system in the rest of the building to ensure better fire protection for the roughly 4,000 employees and tenants in the building and to supplement the sprinkler system which was originally only installed on the lower level of the underground car park. Work on the new sprinkler system was already 90% completed at the time of the fire, even in the floors affected by it, but the system had not yet been taken into service. Parts of the riser had also been drained and fire pumps switched off in the building. The fire brigade was alerted by a neighbour, as there was a delay before the alarm warned security personnel despite the fact that the automatic fire-detection system was functioning correctly; this delay was due to human error and incorrect regulations. As a result, the security personnel disregarded a fire alarm triggered manually by the installation workers in response to minor smoke emissions, as well as other alarms by smoke detectors on the 12th floor. By the time the fire brigade arrived, most of the 12th floor was already in flames. Since use of the elevators was prohibited by regulations, the firemen had to carry their heavy equipment up the stairs to the scene of the fire. As a result, roughly half an hour passed before they were actually able to start fighting the fire with water from the risers in the four stairwells. Fighting the fire proved to be a difficult matter. Once again, the excessively low water pressure had to be boosted with the aid of fire pumps and additional water supplied via the risers. Since the fire doors leading to the stairs had been opened, smoke and fumes soon spread upwards. In the meantime, the fire had spread to floors above the 12th floor with flames up to 10 m high leaping from broken windows on the outer facade. Fire and smoke also penetrated through incompletely sealed cable openings and air-conditioning ducts, as well as through the 31 elevator shafts. In addition to the intense heat and smoke in the stairwells, the firemen’s work was further impeded by failure of the power supply and of the emergency lighting in the stairwells. The vital radio link was similarly impeded by the shielding effect of the building’s steel skeleton and the large number of firemen on the scene. Helicopters were called in to drop firemen onto the roof of the building to allow them to head down towards the seat of the fire via the stairwells. However, this attempt had to

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be abandoned on account of the major smoke in the stairwells with their chimney effect. Broken glass panes on the facade posed another problem as they fell down onto firemen and fire engines feeding water into the fire connections at the foot of the building. Cut hoses had to be replaced more than once. The glass panes also came down in large units, as they were bonded together by the reflecting plastic coating; even the coating was burning in some cases. As a precautionary measure, the newly installed sprinkler groups on floors 17 to 19 above the burning floors were also activated so that they would have provided effective assistance had the fire spread above the 16th floor, but this proved unnecessary. The defects and negative factors will be discussed in more detail in the next section. The positive factors in this difficult fight against a fire are summarized here: – Concentrated and well organized deployment of firemen. – Resistant supporting steel framework thanks to the fireresistant spray-coating. – Sophisticated emergency plans by the bank made it possible to continue bank operation without a hitch in an emergency centre on the morning following the fire and throughout the months of cleaning and repair work in the building. – As a result of this fire, a regulation was issued specifying that sprinkler systems had to be retrofitted in all 450 high-rise buildings without such sprinkler protection in Los Angeles within a transition period of three years. ONE MERIDIAN PLAZA IN PHILADELPHIA, USA

On the evening of 23rd February 1991, a fire broke out on the 21st floor of this office tower with 38 floors above ground and three underground floors. Three firemen were killed in action and 24 others injured. There were only a few people in the building when an automatic fire-detection system on the 21st floor triggered an alarm on the central control panel on the ground floor at 20.23 hours. The fire brigade was called by neighbours before an alarm could be sent from there to the fire brigade. The first firemen arrived on the scene after seven minutes and took the elevator up to the 10th floor. From there, they took the stairs up to the burning floor. Since the power supply, including the emergency power supply, failed in the entire building shortly afterwards, the firemen had to carry all their equipment up the stairs, thus considerably delaying the commencement of their fire-fighting efforts. Licensed in 1969 and completed in 1972, the building was only equipped with sprinklers in a few areas of the underground floors. In 1988, the building’s owner decided successively to install sprinklers throughout the whole building. Only a few floors from the 29th upwards had been equipped with sprinklers when the fire broke out. Originally dry risers had been converted into wet risers to supply the sprinklers during the installation work. Two sprinkler pumps were similarly installed, as were pressurereducing valves on the connections for the wall hydrants installed on all floors. Following the fire, it was found that

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these valves had been wrongly set so that the water pressure from the wall hydrants was too low. This also explains why the firemen’s efforts proved unsuccessful – the fire on the 21st floor had turned into a conflagration in the meantime. Due to the excessively low water pressure, both the volume of fire-fighting water and the range were inadequate. After four hours, the sprinkler installer succeeded in adjusting the pressure-reducing valves with the aid of special tools so that the required water supply could be guaranteed. In the meantime, the fire had spread to three other floors and the stairwells were filled with smoke. The fire spread particularly along the outer facade. Three firemen died as they tried to clear the smoke in one of the stairwells by smashing windows. After roughly 11 hours fighting the fire, the firemen had to retreat from the burning floors because the ceilings threatened to collapse. It was therefore decided to fight the fire via the sprinkler system already installed on the 29th floor. The required water pressure was to be obtained by feeding water into the risers. Ten sprinkler heads were activated by the heat of the fire and it was finally brought under control around 15.00 hours on 24th February. Altogether 19 hours were needed to put the fire out completely. It is assumed that the fire was caused by spontaneous ignition of oil-soaked rags. In addition to total destruction of the entire furnishings on the floors affected by the fire, the building’s structure and outer facade also suffered considerable damage. The owner of the building demanded over US$ 250m indemnification from the insurers for the repair costs and other losses. In his view, the steel structure of the upper floors from the 19th floor upwards had been so severely damaged by the heat that the only alternative was to demolish and subsequently rebuild the tower. An expert appointed by the courts, however, agreed with the insurers that the building could be repaired without demolishing it. After protracted negotiations, the claim was settled six years after the fire. The building had neither been repaired nor was it partly occupied at that time. Barely a year later it was demolished, probably on account of the significant deterioration in its condition and on account of its contamination with asbestos and PCB (polychlorinated biphenyls). The robust roof and facade construction considerably impeded the demolition work. The building’s location in the city centre and adjacent buildings, as well as underground rapid-transit railways under the building, prohibited the use of explosives. The demolition costs were estimated at US$ 25m over a period of two years.

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CONCLUSIONS

These fire catastrophes have once again shown that the threat posed by fires in high-rise buildings still exists. Although in some cases exceedingly more stringent regulations and fire-protection requirements were introduced for high-rise buildings in many countries throughout the world in the 1960s and 70s after a series of devastating fires in various countries with in some cases numerous fatalities (Brazil, Colombia, Venezuela, Korea and others), there are still a large number of older high-rise buildings which do not come under the more stringent regulations or at least not fully – as the fire in Hong Kong proves – since separate statutory rules and regulations are required to retrofit structural changes and fire-protection equipment in existing buildings. The following list of negative features can be drawn up on the basis of these fires during the occupancy phase, more or less representative of numerous similar occurrences in high-rise buildings: – absence of fire compartments on large open-floor areas; – vertical spread of fire and smoke through stairwells and air-conditioning ducts not sealed by fire dampers (chimney effect); – lack of sealing on cable ducts in stairwell walls; – inadequate evacuation of people due to smoke-filled stairwells; – impeded access to the actual seat of the fire; – absence of a suitably protected firemen’s lift with separate power supply in high-rise buildings with more than 30 floors; – threat of ceilings collapsing on account of inadequate resistance to fire; – failure of the emergency power supply since it was not isolated from the shaft of the main power supply; – no continuous, automatic fire-detection system to give early warning of a fire, to signal a fire and to permit rapid location of the fire; – inadequate instruction and training of security personnel regarding the action to be taken in the event of an alarm and fire; – lack of standardized procedures between the alarm regulations and the guidelines published by the fire brigade; – inadequate supply of fire-fighting water due to excessively low pressure in the risers, often on account of a partly closed shutoff valve or incorrectly set pressurereducing valves; – external attempts to boost the water pressure thwarted by inappropriate marking of the fire connections; – no automatic fire-fighting systems, such as sprinklers; – failure of the sprinkler systems installed to function properly.

68 SPECIAL COATING ON THE STEEL SKELETON GUARANTEEING ADEQUATE FIRE RESISTANCE

69 FIRE-DETECTION SYSTEM IN THE MESSETURM IN FRANKFURT

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4.2.4 Fire-protection regulations, loss prevention The facts and shortcomings outlined in the preceding section have significantly increased the magnitude of the fire losses described. For this reason, efforts are being made to limit the fire risk with the aid of corresponding fire-protection regulations and loss-prevention measures. A high-rise building does not constitute any extra risk with regard to occurrence of the fire, but it certainly does with regard to the spread of fire, smoke and fumes. This is due to the vertical nature of the building, which greatly promotes the spread of fire in the main propagation direction, namely from the bottom upwards. Compared with buildings below the limit for a high-rise building – regardless of definition – a high-rise building will always have significant disadvantages when it comes to rescuing people and fighting fires. People cannot be rescued from outside the building if they are trapped on floors out of range of the fire ladders; they can only be located and rescued via the stairwells. The same applies to fighting the fire, since outside intervention is impossible. The firemen must concentrate on tackling the fire from inside the building and must make their way to the scene of the fire with their equipment through stairwells filled with smoke and heat. 4.2.4.1 Regulations Due to these difficulties, the standards and regulations in force in the majority of countries include special provisions for high-rise buildings, with corresponding requirements to be met in respect of fire prevention and protection. In this way, they take account of the higher risk potential. In Germany, for instance, these requirements are laid out in the 1978 “directives”. Besides, compliance with all the provisions of the Construction Codes in force in each federal state is compulsory.

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The German directives specify a fire-resistance period of 90 minutes for the supporting structure in high-rise buildings and 120 minutes for buildings with a height of more than 60 m. In both cases, only non-combustible materials may be used for the supporting elements. Since high-rise buildings are largely constructed with steel skeletons, unprotected steel cannot be used on account of its inadequate resistance to fire. Composite structures of concrete and steel or fire-resistant coatings or fire-proof panelling must be used instead. So that the building itself cannot contribute towards the spread of fire, non-combustible materials are largely stipulated for the structural parts and elements. Combustible, normally or barely flammable materials are only permitted if structural measures ensure that they cannot contribute towards a fire. FIRE COMPARTMENTS

As already mentioned, fire can also spread via the outer facade if windows have been shattered by the heat. It has been found in such cases that the flashover distance of at least 1 m between two floors as required by the directives is frequently too short. The alternative possibility of parts projecting from the facade is similarly not always effective, and it is therefore perfectly appropriate to use fireresistant glazing. In the cases described above, it was sometimes found that the fire had spread over the entire floor and also over several floors inside the building. Fire compartments with vertical and horizontal structural seals must be created to prevent fire spreading in this way: – The ceilings must be fire resistant and made of noncombustible materials. – Partition walls must be made of non-combustible materials and must also be fire resistant for certain uses. – Doorways should at least be sealed with tightly closing, fire-retardant doors; any other openings required in the walls must be sealed in an equivalent manner. – Partition walls in corridors should reach right up to the structural ceiling.

4.2.4.2 Structural fire protection STAIRWELLS

Most of these directives relate to the requirements for structural fire protection, including the rescue routes. The examples described in the preceding section clearly show, both in a positive and negative sense, how important it is to meet these requirements. FIRE-RESISTANT MATERIALS

To ensure the stability of a high-rise building in the event of a fire, the supporting structure and ceilings must be resistant to fire. The characteristic “fire resistant” must be defined in the applicable standards. However, this means that the requirements to be met by fire-resistant parts can easily differ from one country to the next, depending on the standards applied. The same holds true for the inspection procedures specified for verification.

Stairwells are areas of particular importance, since they must usually permit safe evacuation of the building in the event of a fire. Their number depends on the area, height and shape of the building. Several stairwells are normally required. Stairwells must have fire-resistant walls of non-combustible materials. Internal stairwells may only be reached via lobbies sealed by smoke-tight self-closing and at least fireretardant doors. Smoke vents must be installed at the top of all stairwells; internal stairwells must be equipped with a mechanical, automatically activated ventilation system connected to an emergency power supply. If a fire breaks out, excess pressure must be generated in the stairwells to prevent the ingress of smoke.

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VENTILATION AND AIR-CONDITIONING SYSTEMS

Ventilation and air-conditioning systems must be installed in such a way that fire or smoke cannot be transmitted to stairwells and other floors or fire compartments. The cases outlined above clearly show how difficult it is to meet this requirement. Stairwells, lobbies, safety locks and elevator lobbies must be equipped with ventilation systems which are isolated from other systems. As a rule, several floors are normally combined into one area for the ventilation and air-conditioning systems. To prevent fire and smoke being transmitted via the ventilation ducts, fire dampers must be installed in the fresh air and exhaust air ducts on each floor; these fire dampers must be activated automatically by smoke detectors as well as manually. More stringent requirements must be imposed on the stairwells in taller buildings (safety stairwells). In particular, the safety locks outside the stairwells must be equipped with mechanical ventilation systems.

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4.2.4.3 Active loss-prevention measures STANDBY POWER SUPPLY

Standby or emergency power supplies must be installed in high-rise buildings from a specified height onwards. These power supplies operate independently of the public grid; following a power failure in the public grid, they automatically switch on to supply electric power to all safety equipment: – fire-detection and gas-alert systems; – fire pumps and their control systems; – firemen’s lifts and passenger elevators; – ventilation systems, as well as smoke and heat vents; – fire-resistant sealings of openings; – emergency lighting for rescue routes; – electroacoustic alarm systems and/or paging systems. The equipment providing the standby power supply must be isolated from the general power supply and protected by fire-resistant materials.

SHAFTS AND ELEVATORS

FIRE DETECTORS

To prevent fire and smoke spreading vertically inside a building, the continuous installation shafts for ventilation, electric power, telecommunications, sanitation and document conveyors must be of the same fire-resistant design as the stairwells. Cable ducts should be sealed with fireresistant elements on every floor. Openings must be sealed with fire-resistant doors or flaps. Automatically activated smoke and heat vents must be installed here too. Waste-disposal chutes must be protected in the same way. Elevator shafts must also be enclosed by fire-resistant walls; access to the elevators must be restricted to the corridors or enclosed lobbies. Elevators should be connected to the standby power supply so that they can automatically be lowered to the ground floor following a power failure or fire alarm. Firemen’s lifts must be installed so that the firemen can arrive at the scene of a fire without delay; this is already specified by public authorities in certain standards and directives. The time lost in fighting a fire due to the absence of such firemen’s lifts has already been shown by the cases described above. According to the German directives governing high-rise construction, a firemen’s lift is required for all buildings over 30 m high. Additional firemen’s lifts may be specified for buildings over 100 m high. Every firemen’s lift must be located in a separate fireresistant elevator shaft. The associated equipment rooms must likewise be of fire-resistant design and sealed by fireresistant elements. In many cases, these lifts are additionally equipped with rescue materials and radio equipment. Lobbies with fire-resistant walls and at least fire-retardant doors must be provided at the stopping points for the firemen’s lifts. A mechanical ventilation system must also be provided. The required electrical switchgear and supply lines must be physically separated from other systems and lines. It is also important to ensure that the firemen’s lifts are connected to the standby power supply specified for the building or that they can be operated via permanently charged batteries.

The importance of rapid and reliable detection and reporting of fires has already been highlighted in the preceding section. In larger high-rise buildings, it is therefore essential to install an area-wide automatic fire-detection system which triggers a fire alert on the building’s central control panel. This central control panel should preferably be located on the ground floor or in a permanently manned security centre. Automatic or manual signalling of an alarm to the local fire brigade – preferably via a direct line – depends on the conditions prevailing on site. The security and maintenance personnel must have clear and precise rules of conduct; they must also be fully familiar with these rules so that human error can largely be excluded. Automatic fire-detection systems should be installed in addition to the existing sprinkler systems, since the latter’s fire-detection sensors are only tripped much later – by the heat of a fire – and trigger an alarm when the sprinkler nozzles open. The type of smoke or heat detector to be used must be determined according to suitability in each individual instance. Manual detectors – e.g. push-button fire detectors – must be installed in addition to automatic detectors so that fires can also be signalled by the people present. These detectors should preferably be located in a prominent position in the corridors and rescue routes, as well as in the lobbies to stairwells. The installation of automatic fire or smoke detectors is problematical due to the presence of ventilation and airconditioning systems in high-rise buildings and the associated air streams. Appropriate specialist companies are consequently considering the use of highly sensitive smoke detectors (HSSD) and very early smoke detection apparatus (VESDA). With such apparatus, detection of the smoke at a very early stage in the fire could be used to activate the fire dampers and then to switch off the airconditioning.

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4.2.4.4 Fire fighting FIRE EXTINGUISHERS

Hand-operated fire extinguishers must be installed at clearly marked and generally accessible points in high-rise buildings in order to fight incipient fires. These extinguishers are intended for use by the building’s residents. However, teams should be present on every floor made up of the people who work and live there; they must then be instructed on what to do if a fire breaks out and also be familiarized with the use of these hand-operated fire extinguishers. FIRE-FIGHTING WATER

The cases outlined above have shown how important it is to have an effective supply of fire-fighting water when combatting a fire in a high-rise building. So that the firemen can start to fight the fire as soon as they arrive on the scene, wet risers must be installed in every stairwell or in their vicinity and a wall hydrant with hose line connected to these risers on every floor. The hoses must be sufficiently long to direct fire-fighting water to every point on that floor. An adequately dimensioned water line and adequate water pressure must be ensured when planning and designing the building. In very high buildings, booster systems must be installed in the wet risers to increase the water pressure. Whether the water for fire fighting can be taken from the public mains or from separate water reservoirs or tanks must be decided in each individual instance in accordance with local conditions and regulations. For greater safety, it may be useful to install not only wet risers, but also dry risers into which the fire brigade can feed water at the required pressure from the ground floor. SPRINKLERS

An automatic sprinkler system is the most effective protective measure for fighting and controlling a fire in a highrise building. Care must be taken to ensure that the complete building is protected by such sprinklers. In the cases outlined above, there were either no sprinklers at all or no activated sprinklers on the burning floors. In the case of “One Meridian Plaza”, the fire was subsequently brought under control with the aid of the sprinkler system and an additional supply of fire-fighting water. Based on past experience, the installation of sprinkler systems is in many countries prescribed by law for highrise buildings from a certain height onwards – as from 60 m in Germany, for example. In some cases, the statutory regulations even stipulate that sprinklers have to be installed retroactively in high-rise buildings erected before the regulations came into force. Automatic sprinkler systems throughout the building are important since they must fight a fire as early as possible and must either extinguish the fire directly or keep it under control until the fire brigade arrives to finish off the job. However, a sprinkler system will normally be unable

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to control a fire in full flame, for instance if it leaps from a floor with no sprinklers to one with sprinklers. Sprinkler systems are simply not dimensioned to cope with such developments. Sprinkler systems must meet the following requirements: – they must rapidly control a fire in the fire compartment in which it breaks out; – they must limit the emission and spread of flames, hot fumes and smoke; – they must trigger an alarm in the building, preferably also indicating to the central control panel where the seat of the fire is located; – the alert must be forwarded to the fire brigade or other auxiliary forces. The ability of the system to indicate to the central control panel where the seat of the fire is located presupposes that a separate sprinkler system with an alarm valve is assigned to each floor and to each fire compartment. As already mentioned in connection with fire-detection systems, the installation of an automatic fire-detection system in addition to the sprinkler system is advisable so that fires can be discovered and signalled more quickly. Sprinkler systems must be installed in accordance with the applicable directives or standards, the best known of which include NFPA, CEA, FOC and VdS. All the components used for installation must comply with the relevant standards. The various directives and standards permit a variety of solutions with regard to the water supply: – water supply from the public mains – possibly via an intermediate tank on the ground – via booster pumps on the ground to supply several groups of floors with different pressure levels – intermediate tanks on various upper floors, under either normal pressure or excess pressure, to supply the sprinkler groups above or below – deep tanks and pressurized tanks on the roof, as well as intermediate tanks in the middle of the building, to supply the sprinklers below with static or high pressure Tanks on upper floors can be replenished via low-capacity pumps. Depending on the type of supply selected, it may be necessary to install pressure-reducing valves on the individual floors. For a sprinkler system to operate smoothly, it must not only be correctly installed and set, but also be regularly inspected and serviced by specialist personnel. OTHER FIRE-FIGHTING EQUIPMENT

Other automatic fire-fighting equipment may be appropriate for certain systems in a high-rise building, such as transformers, electrical switchgear and control rooms, computer centres and telephone switchboards. Depending on the systems concerned, CO2 or – if still permitted by law – halon fire extinguishers are two possibilities worth mentioning here, as well as extinguishing systems based on inert gases.

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4.2.4.5 Organizational measures As already mentioned, emergency and alarm plans must be drawn up in consultation with the relevant authorities and auxiliary forces, especially the local fire brigade. So that all fire-protection facilities are fully functional when required, they must be regularly inspected and serviced. The test and maintenance intervals applicable to the different facilities and systems must be scrupulously observed. It is also important to ensure that the maintenance and security personnel know what procedures to adopt in the event of an alarm or fire, reinforced by recurrent staff fire and safety training at regular intervals. The catastrophic consequences due to taking the wrong action have already been outlined in Section 4.2.4. 4.2.4.6 Atriums The situation described in Section 4.2.2 with regard to atriums also poses an additional risk for people during the building’s occupancy as a hotel or department store, for example. Atriums in particular have a magnetic effect and a concentration of visitors and customers is consequently to be found in these areas. A number of special requirements must be met in order to ensure personal protection. The required rescue routes must not be directly linked to the atrium. Instead, they must lead away from the atrium, towards the outside walls of the building. This consequently means that the stairwells should be located along the outside walls to keep them clear of smoke and to permit more effective illumination in the event of a power failure. Flashover from one floor to the next must be prevented in the atrium area. This can be achieved, for example, by installing fire-resistant glazing. The supporting elements must also be at least fire-retardant to prevent the top of the atrium crashing down onto the inner area. Care must also be taken to ensure that smoke is adequately discharged in the event of a fire. This is particularly difficult on account of the large volume and resultant dilution and mixing of the smoke. Frequently, discharging the smoke via a smoke and heat vent will suffice; in critical cases, however, an additional mechanical means of discharging the smoke must also be installed. 4.3 Windstorm Each of the two twin towers of New York’s World Trade Center, which will be discussed in more detail in the following sections, has a base area of roughly 4,200 m2. That is roughly equal to a square base measuring 65 m ҂ 65 m. The towers are 417 m and 415 m high, respectively. Using the highly simplified wind load permitted by German standards, this yields a total static load of roughly 4,500 tonnes per tower from dynamic pressure and wind suction. These values do not, however, include the conditions prevailing locally which must be taken into account when designing a high-rise building. The building’s surround-

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ings, for example, have an immensely important effect on the active wind and flow conditions. The location of the building – on open ground or surrounded by other highrise buildings – has a massive influence on the wind profile. The effect of wind separating off the edges of neighbouring buildings, reduced wind velocities due to obstacles at ground level and effects similar to friction or deflection of the wind loads due to neighbouring buildings cannot be taken into account in the standard loads. Local wind effects have repeatedly been observed in the canyons formed by skyscrapers in large cities. One such effect is known as the “spinning effect”, a tornado-like effect near ground level which affects pedestrians. In bygone days, the strong upwinds encountered on the Flatiron Building in New York used to cause not a few ladies considerable problems as they strolled past. It is also known as the Marilyn Monroe effect in construction aerodynamics. The shape of the building is another factor influencing the wind forces actually at work. When wind meets an obstacle, it normally generates compressive forces on the windward side of the building and suction forces on the leeward side. In addition, air streaming around the building produces suction forces on the sides parallel to the wind direction. The shape of the corners and edges of the building is particularly important. Separation effects can cause suction and compressive forces several times greater than the original dynamic pressure. The magnitude of these edge and corner forces depends primarily on the geometry of the building round which the air flows. Basically, it may be said that the more sharp-edged and irregular the building is, the more irregularly the wind forces will be distributed. Suction forces cause major problems around the roof in particular. If the roof structure has not been adequately anchored, parts of the roof may be lifted off and catapulted away unhindered. In addition to the roof, such elements as light-metal facades, antennas, promotional signs and water tanks are some of the parts most seriously threatened by wind on high-rise buildings. The risk of parts being blown away and flying around is greatest during the construction phase. Such parts can cause considerable property damage to their surroundings, and harbour potential for bodily injury which cannot be neglected. During the autumn gales in 1972, for example, several hundred glass elements worked themselves loose from the outer facade of the John Hancock Tower in Boston and crashed down onto the pavement. An area of 50,000 m2 had be reglazed. Facades and roofs are also exposed to driving rain and hail. “Updraughts”, which cause the rain to move upwards instead of down as a result of different inner and outer pressures, can cause moisture to penetrate inside the building. No fewer than 5,000 panes had to be replaced for this reason on the UN Secretariat Building in New York in 1952. A purely structural consideration of the wind will not suffice in the case of larger building structures. Wind is a phenomenon which varies strongly in strength and direction and can produce dynamic effects in combination with vortices separating off from the buildings around which

71 DYNAMIC-PRESSURE APPROACHES: effects from friction impact wind speed

Wind load W (kN/m) Height h (m)

Horizontal load H = W x H Bending moment M = W x h2 2

72 TYPHOON TRACKS FOR JAPAN AND CALIFORNIA

Wind

Core to stiffen the building

Foundation

Ground-bearing pressure from vertical load

Ground-bearing pressure from wind

Total (Ground-bearing pressure from vertical load and wind)

73 REPRESENTATION OF WIND IMPACT ON A BUILDING’S GROUND-BEARING PRESSURE

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the air flows. Particularly in the case of slim buildings capable of vibration, such as towers, smokestacks and skyscrapers, this can lead to stresses which must not be neglected. These vibrations are particularly critical when the wind excites the building to vibrate at its resonant frequency, thus producing the resonant effects already mentioned in Section 3.1.3. In response to these fluctuations in the wind, the building begins to vibrate and can continue to do so until the vibrations reach an amplitude threatening the building with collapse. There are also other, less spectacular problems to be solved by the planners. Depending on their frequency and amplitude, vibrations will be perceived by the building’s users. These vibrations can become unpleasant or even intolerable when they reach a certain limit which, however, is normally still far away from threatening the stability of the building. In the 1970s, for instance, this resulted in one of the greatest “building losses” anywhere in the world: due to wind vibration, almost all the tenants moved out of a high-rise building as if in panic, resulting in a loss of roughly US$ 75m in lost rent. Such dynamic effects can be counteracted by changing the rigidity of the building or by installing active or passive damper systems. Passive dampers include baffle plates, for example, to reduce vortex formation. Active systems can be made up of water tanks, movable weights or rotating unbalanced flywheels. Shortly after completion of the John Hancock Tower in Boston in the early seventies, it was found that gales caused enormous vibrations in the tip of the tower. A damping system comprising a 600-tonne counterweight which can be moved around as required in accordance with the wind direction had to be installed on the 58th floor. It was discovered that the building could have toppled over at any time. To everyone’s surprise, however, it would have fallen onto its narrow side, rather like a book falling onto its spine. Damping systems are always based on a similar principle. A large mass is moved by hydraulic computer-controlled equipment or pendulum constructions in the direction opposite to the actual direction of vibration by the building. The vibration energy of the wind is absorbed in this way. The amplitudes and horizontal acceleration forces are reduced considerably, thus also largely eliminating the effect of dynamic forces. It can be extremely complicated to take wind loads into account in calculations, and it is therefore almost standard practice today to test the response of a high-rise building in the wind tunnel first. As already mentioned in Section 3.1.3, even computer simulations cannot always provide a satisfactory answer to the problem. Over the years, this has given rise to a separate engineering discipline – model analysis – to solve the structural and dynamic problems of a building on the basis of miniaturized models. The widespread belief that it is sufficient to divide all the parameters of the original by the same factor in order to obtain an adequate model is unfortunately not correct. Complex mathematical problems are frequently encountered when drawing up models and it has taken a long time for model-making to become a precise science.

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The main problem for the planning engineers are not the horizontal loads but the much more complicated question of transmitting the bending moment due to these loads. In the case of a uniformly applied area load, for example, the horizontal load acting inside the building will represent a linear function over the height of the building, while the bending moment increases quadratically in proportion to the building height. This means that the bending moment increases much more strongly than the horizontal load with every additional metre in height. More and more sophisticated solutions must be found for these loads to be controlled by the supporting structure of a skyscraper. Supporting structures of the type developed in particular by the architects Skidmore, Owings & Merrill (SOM), such as the “tube” (e.g. World Trade Center, New York), the “bundled tube” (e.g. Sears Tower, Chicago) or the “truss tube” (e.g. John Hancock Center, Chicago), have been produced as a result of the problem that conventional supporting structures are no longer in a position to transmit the wind loads safely (see Section 3.2.2.1). In the subsoil, the bending moments caused by wind must be absorbed by soil pressures which can lead to considerable pressure on the leeward side of the foundations. So far, we have only considered “normal windstorm loads“. If we consider, however, that many of the metropolitan centres with skylines dotted with skyscrapers are located in areas exposed to severe windstorms – Hong Kong and Tokyo, for instance, are located in the track of typhoons and even New York can suffer a hurricane, while Chicago is exposed to tornadoes – then it becomes clear that the planning engineers must also consider this problem. The high wind speeds associated with typhoons, hurricanes and tornadoes are not the only problem: a tornado, for instance, can cause a sudden pressure drop of up to 10% of the atmospheric pressure within only a few seconds, with the result that the outer skin of “airtight” buildings literally bursts – and that applies particularly to the windows. Compared with the simplified wind load assumed in accordance with German standards, this would lead to an actual assumed wind load of around 10,000 to 13,000 tonnes for New York’s World Trade Center if we were to take into account all the effects mentioned in this section. PRECAUTIONS DURING CONSTRUCTION

The loss potential during construction is an aspect which cannot be neglected. Although the stability of the building during the various construction phases is documented by corresponding structural analyses, such equipment items as facade elements or temporary structures are usually not taken into account, or only inadequately. Additional precautions must therefore be taken during the construction work, particularly if the contractor is given sufficient advance warning of an impending windstorm. A loss of more than DM 5m was incurred during construction of a 90-storey high-rise building in the Far East. Subcontractors had temporarily stored such electrical installation material as control cabinets and relays on the upper floors of the building shell, but delivery bottlenecks led to

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a delay in assembly of the facade elements on these floors. A considerable proportion of the electrical material stored on these floors was soaked by Typhoon Herb as it passed over in 1996 and consequently exposed to the risk of corrosion. Since the damage was foreseeable and precautionary measures were not taken, the insurer was only obliged to indemnify part of the loss under the policy.

4.4 Earthquakes The Richter scale is a logarithmic scale for determining the energy dissipated in an earthquake. This means that an earthquake measuring 7 on the Richter scale dissipates 32 times the energy of a size-6 quake, while one measuring 8 dissipates roughly 1,000 times as much energy. The energy dissipated by these earthquakes is expressed in horizontal and vertical acceleration forces acting on the skyscrapers. The immense forces transmitted from underground must be absorbed by the supporting structures of the buildings. These dynamic loads are replaced by structural equivalent loads in horizontal and vertical direction when a structural analysis of the building is performed. The highest acceleration forces measured to date in an earthquake were recorded during the Northridge earthquake in Los Angeles (17th January 1994) and amounted to 2.3 times the acceleration due to gravity “g” (g = 9.81 m/s2) in horizontal direction and 1.7 times the acceleration due to gravity in vertical direction. In simplified terms, this means that the planning engineers would additionally have to apply roughly 2.3 times the dead weight in horizontal direction and roughly 1.7 times the dead weight in vertical direction to the building when dimensioning the supporting structure so that these earthquake forces can safely be absorbed. Such values are fortunately exceptional. Moreover, they only act on the supporting structure very briefly and are subject to rapid changes of direction. The values assumed in the majority of standards correspond to between 5% and 10% of the acceleration due to gravity. Assumed loads of up to 0.4 g are required in extreme cases and US standards already include more recent earthquake zones in which even higher values must be assumed in certain frequency ranges. In spite of this, however, experts still doubt the adequacy of these assumed loads under certain conditions. HOW DO SEISMIC LOADS ACT ON A BUILDING?

The horizontal and vertical acceleration of the subsoil due to an earthquake causes the building to vibrate. In simplified form, these loads can be represented by horizontal and vertical equivalent loads acting on the mass centre of gravity of the building. The magnitude of these equivalent loads depends directly on the mass of the building. This leads to the conclusion that as the height of the building increases, the mass centre of gravity normally wanders upwards and the flexural effect on the building is intensified by the longer lever arm. The potential earthquake damage suffered by high-rise

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buildings varies. The damage depends more on the rate of motion and magnitude of the displacement than on the acceleration. The most important and most serious effects are outlined below, together with the possible protective measures. SUBSOIL

Natural rock is the best subsoil from the point of view of its earthquake properties. Sandy soils saturated with water and artificially backfilled land are considered to be particularly critical. The widely-feared liquefaction effects (plasticization of the soil) can occur if an earthquake coincides with high groundwater levels. The building may subsequently remain at a slant or both the building and the surrounding terrain may subside. The importance of the subsoil was revealed in particular by the earthquake in Mexico in 1985. The epicentre of the earthquake was located near the Pacific coast, at Lázaro Cárdenas. The intensity of the earthquake decreased rapidly as the distance from the epicentre increased, but then rose strongly (up to 3 points on the modified Mercalli scale) in Mexico City, some 350 km from the epicentre. The main reason for this increase lay in the fact that Mexico City is built on the soft sediment of a dried-up lake, a subsoil that massively reinforces the effect of the incoming seismic waves through resonant vibration. FOUNDATIONS

Deep foundations generally display better seismic resistance than shallow foundations. Floating foundations can prove advantageous on soft ground, since they may be better able to attenuate resonance action. The risk of subsidence is considerably greater with floating foundations than with deep foundations. “Base isolation” is an anti-seismic construction technique that uses the principle of attenuation to reduce vibrations. The building is isolated from the solid subsoil by damping elements arranged on a foundation ring or foundation plate. Another version was employed for the Court of Appeals in San Francisco: the building was retroactively more or less mounted on ball bearings which are intended to gently damp down the impact of a future earthquake. The requirements to be met by all the various anti-seismic bearings are set out, for example, in the Uniform Building Code (Division III, 1991). When using these methods, it is important to ensure that the damping system is correctly attuned to the applied frequency spectrum and to the resonant frequency of the building. Resonance action can be avoided in this way. As in the case of wind loads, earthquakes can also give rise to resonant vibration. These are described in more detail in Section 4.3. The resonant frequency and consequently also the resonance effects can be influenced with the aid of damping systems. In addition to the isolation systems for foundations mentioned above, vibrations can also be damped by using heavy moving counterweights. “Soft” skeleton structures have a period of fundamental natural oscillations equal to roughly one-tenth of the number of floors in seconds. The period of a 15-storey building consequently equals roughly 1.5 seconds. Higher edifices

74 IMPACT OF EARTHQUAKE LOADS ON THE CENTRE OF GRAVITY

HIGH-RISE BUILDING Static equivalent system

V = ay x g

H = aH x g Mass centre of gravity

Horizontal (aH) + Vertical (aV)

H = horizontal equivalent load which acts on the mass centre of gravity

acceleration V = vertical equivalent load which acts on the mass centre of gravity h = building’s own weight

75 50 T AND/OR 90 T HEAVY DAMPERS TO BE INSTALLED IN TWO JAPANESE HIGH-RISE BUILDINGS TO REDUCE RESONANCE VIBRATIONS CAUSED BY EARTHQUAKES

76 EFFECTIVE ARRANGEMENT OF DAMPERS IN HIGH-RISE BUILDINGS

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require a certain time before they oscillate at maximum amplitude. This excitation period lies between 20 and 30 seconds. Enduring earthquakes, such as that in Mexico City in 1985 (around 3 minutes), consequently represent a particularly high risk. A so-called whiplash effect was observed in the high-rise buildings in Mexico City, for example, as the buildings abruptly moved back from their maximum deflection. Extremely high acceleration forces and consequently high horizontal forces were involved here and resulted in damage to the upper floors, including such superstructures as tanks and antennas. HEIGHT OF THE BUILDING

Tall buildings are more susceptible to damage from strong remote earthquakes than from weak earthquakes close at hand. They normally have a lower resonant frequency and a lower attenuation than low buildings. Short-wave oscillation components in earthquakes are rapidly damped, while the long-wave components (frequency f < 1 Hz) can still make themselves felt at a distance of several hundred kilometres, particularly in the form of surface waves.

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The system of active variable stiffness (AVS) is one such system. With this system, the rigidity of the building is specifically varied by securing the bonds to the members of the frame structure by means of a variable connection which is essentially made up of hydraulic cylinders controlled via valves. An operating power of 20 W is sufficient for this purpose. The incoming seismic vibrations are detected by sensors which transmit the information to a central computer. The computer determines the required rigidity and opens the valves at the individual points to increase the building’s flexibility in these areas. This ensures that the vibrations are optimally damped and overstressing is avoided. SYMMETRY

Symmetric layouts, rigidity and mass distribution lead to a considerably better seismic response than asymmetric layouts, rigidity and mass distribution. This is because asymmetric buildings are subjected to stronger torsion (twisting) around the vertical axis by horizontal seismic loads.

SUPPORTING STRUCTURE

SHAPE OF THE BUILDING

A distinction can generally be made between rigid and elastic supporting systems. Rigid systems, such as solid wall and ceiling elements, are difficult to deform and transmit the seismic loads through their rigidity. Due to the stiffness and lack of ductility in the supporting structure, however, shear cracks can develop in the building. The problem is that more and more energy must be absorbed through the high rigidity and that more and more material is required for this purpose. Elastic supporting structures, such as reinforced concrete or steel frames, are highly deformable and absorb the applied seismic energy in this way. The nodes connecting the horizontal and vertical elements of the supporting structure are highly stressed, however, and peak loads occur both here and on the reinforcing elements (bonds) which must be taken into account when producing these connections. However, integrated non-supporting partition walls may suffer excessive stresses and break out on account of the major deformation of the frame structure. Skyscrapers with steel frames were hitherto considered to be particularly resistant to earthquakes, but the Northridge earthquake in January 1994 brought new insights. In an unexpectedly large part of the flexurally rigid steel frame structures, cracks were found in the welds in the corners of the frames. Comprehensive studies were undertaken to determine the causes and lay down rehabilitation measures. This strong earthquake also showed that steel supporting structures do not immediately come crashing down when overstressed and that plastic supporting reserves are activated first. The ductility and load-bearing capacity of reinforced concrete frames, however, can be improved by increasing the percentage of reinforcement. When overstressed, the concrete will usually fail at the risk of a total collapse. A number of systems based on the principle of flexibility and energy absorption are currently being developed to protect buildings against seismic activity.

When parts of different height are permanently connected to one another as, for example, is often found in high-rise buildings with atriums, then the various structures in the building can be subjected to considerable torsional stresses by the seismic loads. Buildings of different heights can also be subjected to a whole series of effects in an earthquake, such as the jackscrew effect observed in Mexico City in 1985: higher buildings were literally jammed in between lower buildings, thus extensively damaging the floors at the clamping point. In some cases, the buildings simply buckled over at the edge of the lower adjacent buildings. Resonance effects can also cause buildings to oscillate so strongly that they hammer against one another. Another effect observed in high-rise buildings is the soft-storey effect: due to lobbies, atriums or glazed shopping passages, some floors – usually near the ground floor – are distinctly “softer” than those above them. These “soft” floors then collapse in an earthquake. A further source of loss potential relates to the standards applied. Many countries do not have their own earthquake standards and simply adopt the corresponding regulations from others, such as the Uniform Building Codes from the USA. This means, however, that common local seismic effects are not covered. Moreover, application of the standards is not mandatory in many countries and their supervision not sufficiently stringent. One of the main problems that is repeatedly found in conjunction with earthquake damage lies in the quality of the work. Poor-quality materials, poor training from the engineers to the workers, corruption and the pressure of time must be mentioned in this context. “Only fools, liars and charlatans predict earthquakes”, according to C. F. Richter, the man who gave his name to the Richter scale. New and potentially promising methods are being developed in the meantime, but the question remains whether these methods can ever be properly applied in practice.

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Such predictions are naturally of subsidiary importance where physical losses are concerned, such as a catastrophic loss estimated at up to US$ 3bn in the metropolitan district of Tokyo. Where personal protection is concerned – and up to 600,000 fatalities are assumed for the aforementioned scenario – such precise earthquake forecasts would be of inestimable value.

4.5 Foundations, settlement and subsidence 4.5.1 Foundations Particular attention must be paid to additional foundation measures (see Section 3.2.1) when erecting a high-rise building and above all if it is to be built on poor or damaged subsoil. Foundation structures up to 100 m deep and known as “barrettes”, each comprising four diaphragm wall elements, were required to transmit the loads safely into natural foundation soil under the Petronas Towers in Kuala Lumpur, Malaysia, which we have already mentioned above. Load tests should really be performed on such foundation structures before starting the high-rise construction work, but they are economically unacceptable

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and technically almost impossible on account of the high vertical loads to be applied. Instead, the load-bearing capacity of the deep foundation is determined in addition to routine investigation of the drilling explorations (assessment of the soil strata encountered). The integrity of the respective pile and diaphragm walls can be continuously monitored with the aid of such special methods as ultrasound; special pipelines are integrated into the foundation structures to permit a certain degree of rework if defects arise, for instance by means of subsequent injection. Although such complex foundation work can only be undertaken by highly specialized and experienced civil engineering contractors, mishaps occur all the time. When producing the trenches for the diaphragm walls, for instance, or when drilling holes, particularly at great depth, opened fissures or existing but undetected channels result in loss of the bentonite supporting slurry, thus jeopardizing the stability of the trench or hole or even causing it to collapse. The long cages of reinforcing steel can become wedged against the wall of the deep trench or drill hole, making it impossible to lower them to the required depth. It is not uncommon for the freshly positioned reinforcing cage to be pulled upwards a short distance when the casing string

77 EARTHQUAKE IN KOBE, JAPAN

78 CORRODED SUPPLY LINES 79 TENSION CRACK IN A CROSSLINKED POLYETHYLENE PIPE

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is raised after completing the pile. This can impair the intended load-bearing capacity or even make it necessary to abandon the pile in question. The required load-bearing capacity may likewise not be achieved if deviations from the vertical axis exceeding the theoretically permissible limit occur as a result of encountering obstacles or due to carelessness while drilling (sinking). This is not uncommon, particularly in the case of long piles. Simple repairs or reworking are rarely possible in such cases. Extensive supplementary measures, such as replacement piles, pile bents or injections, will usually be required on account of the simultaneous disturbance produced in the subsoil. These supplementary measures may prove considerably more expensive than the original foundation. In many cases, this will also give rise to the question whether a mere defect is involved or whether it is a physical loss with corresponding consequences for indemnification under the policy. In the latter case, the indemnification for such supplementary costs should be suitably limited by correspondingly worded clauses, limits or other restrictions when concluding the policy before construction starts. 4.5.2 Settlement and subsidence Settlement and subsidence are another risk. It must be pointed out, however, that a certain degree of settlement will be unavoidable in all these projects. The equilibrium of forces originally present in the ground is disturbed by excavation of the soil for the underground floors and by application of the structural loads. Depending on the type of building, the soil conditions and the foundation selected, settlement will occur immediately or at a later date. Depending on the method selected (diaphragm wall, bore diaphragms), the retaining wall can also cause the ground to settle and result in damage to third-party property. For this reason, it is advisable to record prior damage on neighbouring buildings as evidence before starting the work. The planning engineer is responsible for ensuring that such settlement is determined correctly and for ordering appropriate structural precautions so that the settlement remains within tolerable limits. This can be achieved by a corresponding arrangement of joints in the building and

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other structural measures, such as the use of hydraulic jacks. Problems only arise, however, if defective work, undetected disturbances, subsequent changes in the subsoil or an incorrect appraisal of the load-bearing capacity lead to abrupt and extensive subsidence which may threaten the stability of the entire building. Such subsidence can occur during the construction phase, when the building has already reached a certain height and consequently also a certain weight. It may also occur after several years and may not only cause the building to collapse, thus resulting in a total loss, but can also result in devastating casualties. The spectacular collapse of a high-rise building will in many cases be due to a combination of causes, such as a combination of design errors, inadequate workmanship and problematical soil conditions. Attention must be devoted to the horizontal forces in particular when designing the foundations for high-rise buildings on sloping ground. In one case, reject railway tracks were used as the foundation element for a high-rise building instead of the usual steel or reinforced concrete piles. Although the tracks were welded together to give them the requisite loadbearing capacity, they still did not conform to the applicable regulations. When heavy rainfall subsequently caused a landslide on a nearby slope, these piles were neither structurally nor theoretically in a position to absorb the additional active horizontal earth pressure. The piles buckled and some sheared off, with the result that the high-rise apartment block literally tipped over and then collapsed. It is very difficult to repair a high-rise building when its stability has been jeopardized by such severe subsidence. The defective foundations can be reinforced with the aid of injections, supplementary piles or root piles if necessary on account of the limited height available on the underground floors. However, such measures are almost impossible in a completed high-rise building, due to its immense overall weight, and the only alternative is usually to demolish the building. Even when high-rise buildings are still under construction, i.e. in a phase where repairs would still be possible on account of the lower dead weight, demolition of the shell will usually prove to be the more economical, time-saving and generally better alternative for the principal.

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4.6 Water GENERAL

Like other buildings, high-rise buildings can also suffer damage due to water. As a rule, this damage will be due to soaking, soiling, discoloration, corrosion, shrinkage or expansion and mould. DEVELOPMENT OF LOSSES

The damage is due to the interplay between the nature of the media concerned (e.g. drinking water, heating water, effluent), the quality of the installation materials, design and execution of the plants and the prevailing operating conditions. In the case of high-rise buildings, the risk is further aggravated by the fact that leaking water rapidly finds its way to floors below the actual leakage point, with the result that several floors may be affected, depending on the duration of the leak and the amount of water involved. The considerably larger size of the installations in comparison to “normal” buildings is another risk factor: booster systems and pumps, pressure reducers, etc., are all needed in order to distribute or discharge the drinking water, heating water and effluent horizontally and vertically, thus increasing the number of possible leaks.

4.7 Special structural measures Considerations on the conversion, rehabilitation and finally demolition of high-rise buildings have been subsumed under this heading. 4.7.1 Conversions Conversions are constantly being made to any high-rise building with thousands of square metres of useful floor space. Redecoration and modernization are the commonest conversions, in addition to those necessitated by changes in operational procedures and use of the building. More stringent or additional requirements in respect of fire protection, installations or computer systems can also make conversions necessary. On the one hand, conversions and changes of use are facilitated by the separation of shell (= supporting structure), installations and interior finishing commonly applied in the construction of modern high-rise buildings; at the same time, however, it is precisely this separation that imposes limits on what is economically acceptable. Even if technically feasible, conversions involving changes to the existing structural system, i.e. to the supporting structures, will usually be rendered impossible on account of the costs involved. For this reason, conversions will almost always only affect the interior finishing and the installations. The range of possible conversions extends from simply relocating interior wall elements or fitting complete new false ceilings or laying new floor coverings to “gutting” the building completely. In such a case, all or part of the

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building is restored to the condition of a shell and then refinished with corresponding installations and interior finishing in line with its new use. However, if these conversions result in considerably higher loads for the building, these loads will have to be discharged via extended foundations in extreme cases. Particular attention will have to be paid to settlement in this context. The problem can be minimized by providing additional piles, for example. From a technical point of view, however, this will prove fairly difficult as the working height of the drills is usually limited by the height of the various levels in the underground car parking. The fact that conversions are often undertaken while operation continues without interruption in those parts of the building and on those floors not affected by the work not only makes the work more difficult, but also increases the risk for the insurer. The nuisance due to noise and unpleasant odours or temporary failure of the sanitary installations, heating or ventilation are relatively harmless phenomena. The dust inevitably generated by such conversions, on the other hand, can have serious consequences if high standards of purity and hygiene must be met by those areas still in operation, such as computer systems or doctors’ offices. As in the case of “normal” building work, the use of such flammable substances as adhesive and bituminous materials or naked lights, for instance for soldering and welding, will be unavoidable when carrying out conversions. Extremely stringent requirements must therefore be imposed on the fire-protection measures due to the incomparably greater risk potential. In particular cases, the fire brigade will have to be ready on site to take immediate action if an emergency arises. Another problem associated with conversions is that the normally strict controls with regard to access and authorization are often suspended for the conversions: workers, suppliers and the vehicles transporting materials and equipment need “open doors”. This naturally also increases the risk of unauthorized persons exploiting the situation and simply marching into the building. Conclusion: all conversions, no matter how slight, must be thoroughly planned in advance and organized in detail with due consideration given to all eventualities. 4.7.2 Rehabilitation Rehabilitation is an extreme form of conversion. The two commonest reasons making rehabilitation measures necessary are – physiologically harmful materials, such as materials containing asbestos or materials with excessive formaldehyde concentrations, or – potentially dangerous structures. All the aspects already mentioned in the previous section also apply here in particular. In addition, there is the problem of disposing of the physiologically harmful materials. Correct disposal of contaminated materials and substances not only poses a technical challenge, but is also one of the most difficult jobs for third-party liability insur-

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ers on account of the possible environmental impact and health hazard. In the majority of cases, it will be impossible to continue normal operation of the building while the rehabilitation work is in progress. For this reason, such rehabilitation will usually also be associated with conversion and a completely new interior finish. An alternative method was employed when Winterton House in London was rehabilitated in the 1960s. All false ceilings and facade linings were removed first. The new brick facade was then built up on its own foundations around the steel supporting structure. The facade was secured to the supporting structure by means of steel brackets for reinforcement. An active construction was required to compensate the differences in thermal expansion of the facade and supporting structure. In this case, the roof structure links the inner skeleton with the outer wall via hydraulic presses. These presses are in continuous duty and maintain a constant compressive strain on the upper edge of the masonry. The building’s outer and inner columns were reanchored in the roof structure, thus reducing the load in the columns. Ceilings in line with today’s state of the art were then installed. 4.7.3 Demolition Demolition remains the method of last resort when even changes in use, conversion and rehabilitation can no longer meet the more stringent requirements imposed on a building. It is no longer standard practice today and in many countries even illegal simply to demolish a building – often with the help of unskilled labourers. Experienced specialists are needed not only in order to meet environmental regulations requiring that all materials and parts accumulated in the course of the demolition work be carefully sorted, but also to judge how the complex supporting structures will react during the demolition. Within only a few years, the demolition of a building has ceased to be a low-tech job and become a highly specialized technical task. Specialists often take over when the building has finally been gutted, i.e. when all interior finishings and installations have been removed and duly disposed of (recycling) and when there are no further physiologically harmful materials in the remaining supporting structure. Either the building is then dismantled carefully and with as little noise and dust as possible, the reinforced concrete literally being “nibbled away” by special machines, or – if the circumstances permit – explosives experts apply their precisely primed charges to the predetermined points after analysing the drawings and inspecting the remaining building. As spectacular explosions of high-rise buildings have proved, experienced experts can make a building collapse in such a way that the surrounding structures remain undamaged. Less carefully planned explosions, on the other hand, have caused serious damage to the surrounding areas.

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80 BLASTING OF A HIGH-RISE OFFICE BUILDING

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In addition to taking into account the existing supporting structure, it is also important to investigate the effect of conversions, rehabilitation and demolition work on the existing supporting structure, neighbouring buildings and the site environment. The most appropriate methods are then selected on the basis of such influencing factors as – vibrations, – noise, – dust, – site traffic, – contamination. The work is preceded by detailed analyses of the existing structures. 4.7.4 Disposal As already mentioned in the preceding section, particular attention must be paid to disposal of the materials accumulated in conjunction with conversions, rehabilitation measures and demolition jobs. Specific reuse of the materials will be unavoidable as contaminated materials must be dumped on special landfills in some regions and landfill space for construction rubble becomes scarcer and increasingly more expensive. The materials must be analysed before starting the work and classified according to their contamination, suitability for disposal and reusability. The primary objective is to reduce the volume of contaminated rubble so that it can be decontaminated (if possible), for instance by washing the soil. If this is not possible, the material must be dumped on special landfills. The degree to which the materials can ultimately be sorted depends on the local regulations and on the landfill capabilities and costs. Separating and sorting the contaminated materials often entails a great deal of work. Such reusable materials as concrete, steel and PVC are sorted, delivered to recycling plants and reprocessed. In the case of concrete or masonry, this can also be done on site using mobile plants. The resultant materials (crushed stone, etc.) can then be used in the construction of a new high-rise building, thus also reducing the volume of traffic on site.

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4.8 Other risks For the sake of completeness, mention must also be made of a few other risks which, although closely associated with high-rise buildings, either occur very rarely, such as terrorism, are unavoidable, such as wear, or are often underestimated, such as the consequential costs due to physical damage. 4.8.1 Terrorism High-rise buildings with their characteristic silhouette in a city’s skyline not only represent a magnet for tenants, customers and guests, but unfortunately also become a popular, sometimes inadvertent, target for terrorist attacks, as the 1998 bombing attacks in Nairobi and Dar es Salaam show. A skyscraper’s famous name is enough to assure the terrorists of the desired media attention following an attack. In many cases, however, the dominant presence of a highrise building will suffice to obstruct the devastating shock waves of an explosion somewhere else. OFFICE TOWER OF COMMERCIAL UNION INSURANCE IN LONDON

Precisely that was the fate of the office tower of Commercial Union in London when a bomb exploded on the evening of Friday, 10th April 1992, in the immediate vicinity of this newly renovated tower with its completely new facade. The physical damage sustained by the building amounted to more than £40m, plus the loss of rental income during the tower’s restoration. Although there is no effective protection against such indirect effects of terrorist attacks, the crisis management set up by CU for such events passed its first test with flying colours and saved the company from potentially ruinous loss of business. After corresponding reports in the national press and thanks to availability of the complete data in Croydon, the company was able to resume its business at 9 a.m. on the following Monday. The problem of such business interruptions will be discussed in the next section. WORLD TRADE CENTER IN NEW YORK

The consequences of a car-bomb explosion in the underground car park of New York’s famous World Trade Center on 26th February 1993 were even more devastating. Six people were killed in the explosion and more than 1,000 were injured; the explosion caused immense physical damage estimated at around US$ 500m. The bomb fortunately exploded around lunchtime when many of the offices were empty. Around 50,000 people normally work in the skyscraper and over 80,000 visitors are additionally recorded every day. Contrary to the recommendations of experts, there were no special precautions against such terrorist attacks on the World Trade Center with its 417-m and 415-m-tall twin towers and the 22-storey Vista Hotel between them. The emergency power generators and central water supply were located on the uppermost of the six underground floors immediately above the parking decks and therefore

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highly vulnerable, as this underground car park was open to all users. Three underground railway lines also have their own stations on two of these parking decks. When the bomb concealed in a delivery van detonated, it blasted a hole in the concrete floors of the decks above and below and left a crater roughly 30 m deep. Numerous fires broke out on the three levels affected. Caustic smoke rapidly spread through service and elevator shafts in the two towers and in the hotel. FEDERAL BUILDING IN OKLAHOMA

The world was even more deeply shocked by the explosion of a car bomb outside the Alfred P. Murrah Federal Building in Oklahoma City, USA, on the morning of 19th April 1995. The nine-storey office building accommodated not only several federal authorities, but also a daycare centre for young children. The blast killed 168 people and injured 475. The bomb with almost two tonnes of explosive had been concealed in a small closed pick-up truck parked near the main entrance to the building. The building was positively “lifted” by the shock wave from the detonation and the supporting structure so severely damaged that almost one-half of every floor collapsed and the glass facade was sheared off. The people inside the building were buried under the rubble. Several nearby buildings also suffered considerable damage and numerous cars caught fire. Windows shattered even at a distance of several kilometres. Altogether 43 fire brigades and auxiliary organizations, many of them from other federal states, took part in the rescue operation which commenced immediately. Many people were recovered alive from the rubble. The complete loss was estimated at more than US$ 300m, but the damaged building itself was not insured. It had to be completely demolished on account of the major damage suffered. What insights and conclusions can be drawn from these occurrences? There is naturally no such thing as complete protection against the inventiveness and fanatical destructive urge of terrorist attackers. Nevertheless, appropriate security and fire-protection measures should make it more difficult for them to achieve their objectives. One such measure would be total control of all incoming and outgoing people and vehicles. Thanks to the attentiveness of the security personnel, for example, it was possible to defuse the bomb placed by a terrorist organization in a delivery van outside the new office tower on London’s Canary Wharf. If such an attack cannot be prevented, however, it is extremely important that the emergency plans and fire-fighting measures already discussed in the preceding sections be applied and function smoothly. 4.8.2 Impact The risk of an “impact or crash of a manned flying object or parts thereof or its cargo” which is normally included in the insurance cover for buildings, is considered a necessary but rarely claimed insurance element. The number of losses of this type reported to date is admittedly small, although the media frequently feature such “near misses”. When an accident of this type does occur, however, it is al-

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most always a genuine catastrophe, possibly with numerous fatalities and enormous losses. Two of the most spectacular cases in which an aircraft collided with a high-rise building occurred in New York and near Amsterdam. EMPIRE STATE BUILDING, NEW YORK CITY

A light fog lay over the city on the morning of Saturday, 28th July 1945. Visibility was no more than 2 miles, the cloud ceiling had dropped to roughly 500 m. Shortly before 10 a.m. a B25 bomber of the US Air Force with a crew of three approached Newark airport, New Jersey, just a few miles from the centre of Manhattan. The 12-ton aircraft was scheduled to land at Newark a few minutes later. At a cruising speed of roughly 320 km/h, the bomber crossed the East River and Manhattan above 42nd Street. Witnesses saw the aircraft heading directly towards a high-rise building on Park Avenue at a height of roughly 2,000 ft. Pedestrians and shoppers saw how the aircraft just managed to evade this building at roughly the level of the 22nd floor and then avoided colliding with another skyscraper on Fifth Avenue. Most of the witnesses subsequently said that it seemed as if the pilot was having technical problems. Whether that was indeed the case is still unknown today. What is known is that, for whatever reason, the aircraft could not be pulled up in good time and drilled its way into the 78th and 79th floors of the Empire State Building at precisely 9.52 a.m. Fire broke out immediately in the building. The bomber’s wings broke off first. The fuselage ripped a 6-m hole into the facade and penetrated more than 25 m into the building. One engine continued right through the 79th floor and emerged through the outer wall on the southern side of the building, from where it dropped onto the roof of a 12-storey building which also caught fire. The 800 gallons of kerosene in the tanks exploded and totally destroyed the western half of the two floors concerned. The other engine made its way through an elevator shaft and ultimately came to rest in a stairwell, blocking this escape route. The suspensions on several elevators were destroyed and two cabins crashed 300 m to the bottom basement floor. By a miracle, two people in the lifts survived the crash with serious injuries, while 14 people were killed in the offices directly affected by the explosion on the 79th floor. The 78th floor was fortunately only used as a store and there were no further fatalities there. All in all, the catastrophe could have been even worse. Hundreds of people would probably have been killed in the offices and on the surrounding streets on a normal working day. The physical loss totalled around US$ 1m – an immense sum in those days and the equivalent of 4% of the contract price – and it took over a year to repair the building.

81 INTERIOR OF A HIGH-RISE BUILDING FOLLOWING A BOMB ATTACK

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82 Left: WOODEN PANELS ON A GLASS FACADE DESTROYED BY A CAR-BOMB ATTACK Top: INTERIOR VIEW OF ONE FLOOR

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BIJLMERMEER NEAR AMSTERDAM

A Boeing 747-200 F operated by the Israeli airline El Al with a crew of four and 320 tonnes of freight on board was on its way from New York to Tel Aviv via Amsterdam on 4th October 1992. Ten minutes after taking off from Schipol Airport, the fully laden aircraft had evidently not gained sufficient height and crashed into the two high-rise buildings “Groenevenen” and “Kruitberg” in a modern satellite town near Amsterdam. Both buildings caught fire within seconds of the crash as a result of the full tanks. According to official figures, 43 people were killed in addition to the crew; 233 flats were destroyed. Insiders assume, however, that many more people were actually killed, since these flats were inhabited by numerous immigrants and asylum seekers, and not all residents may have been officially registered. Not long before the accident, experts at Schipol airport had considered the risk of an aircraft crashing into this residential area to be “negligible” – a disastrously false assessment, as it turned out. Despite adequate lighting, inclusion in flight maps and designation of air corridors with sufficient distance, highrise buildings will always constitute a certain impact risk if only on account of their height. 4.8.3 Collapse The collapse of a building could be considered the “worst case” for everyone involved in its planning and realization. The financial consequences for its owner and the exposure risk for the people inside the building and in its vicinity when it collapses are devastating. The possible causes are often complex and difficult to ascertain retrospectively, but risk potential can be identified and corresponding precautions taken. The following risks are a potential source of errors during the planning and construction phases: – Flawed analysis of the subsoil – Flawed structural analyses – Lack of coordination between the parties involved in the planning and realization (changes which are not taken into account, etc.) – Defective work (stripping times, wrong quality of materials, etc.) – Incorrect use of the building during the construction phase (e.g. concentrated storage of materials on floors not structurally dimensioned for this purpose) During the occupancy phase, a building may collapse for the following reasons: – Structural changes which have not been taken into account in the structural analysis of the building (e.g. by adding floors or removing supporting structures) – Poor maintenance Evacuation of the people in the building depends very strongly on the manner in which it collapses. No precautions can be taken against a sudden failure of the supporting structure. Cracks in the tension zone of the concrete or plastic deformation of the steel structure could be detected if the building is properly serviced. It would then have to be closed due to the risk of collapsing.

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The leaning tower of Pisa, on the other hand, shows just how long it can take for an impending collapse actually to take place. Due to poor soil conditions, the tower has leaned over further and further over the centuries, but it has still not collapsed. 4.8.4 Wear A high-rise building is exposed to time-dependent influences during its occupancy period. Ageing processes on such building parts as windows, joints and seals are influenced in particular by temperature, wind, UV radiation, moisture, dust and gaseous emissions. They play an important part in conjunction with plastics and rubber materials and differ from the corrosion processes primarily affecting metallic materials. In the majority of cases, corrosion of metallic materials on facades and roofs does not constitute any form of wear – assuming that mistakes have not been made in the planning, execution and choice of materials – but is instead a desired process covering the metals with a protective layer. Inside the building itself there are numerous installations, machines and units, such as pumps, fans, compressors, elevators and garage doors, the moving parts of which are subject to wear in accordance with their operating conditions. Maintenance schedules (for maintenance, inspection and repair) must be drawn up and observed in order to minimize the probability of losses occurring due to component wear. Unfortunately, such intentions do not always function as smoothly as with motor vehicles. 4.9 Loss of profit The risk potential and examples of losses discussed in the preceding sections have focused above all on the physical damage to the building as such, while the considerable consequential losses following such an occurrence have only been mentioned in passing. This problem will now be discussed in more detail here. CONSTRUCTION PHASE

As already mentioned, the realization of high-rise construction projects requires considerable financial resources and investments, for which interest and repayment instalments are often already due during the planning phase or at the latest when the land is purchased. The owner’s primary aim will be to ensure that the high-rise building is completed as quickly as possible, not only on account of the considerable borrowed capital and higher resultant interest burden, but also in order to make a profit. Every major loss during the construction phase will consequently thwart his efforts to achieve this aim and can even jeopardize his financial survival. Particularly in the case of high-rise buildings, the investor will also seek to conclude a large number of contracts with future tenants or lessees during the construction phase. Such contracts usually not only govern the tenancy as such, but also the approval for often expensive interior finishings tailored specifically to the tenant’s requirements.

83 AIRCRAFT DEBRIS AFTER A PLANE PLOUGHED INTO THE EMPIRE STATE BUILDING

84 AIRCRAFT CRASH ONTO A BLOCK OF FLATS IN AMSTERDAM

85 BOMB ATTACK ON A FEDERAL GOVERNMENT BUILDING IN OKLAHOMA, USA

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Delayed completion of the building can therefore also have negative effects on the contracts already concluded, as well as on the dates agreed between the tenant on the one hand and tradesmen, suppliers or service-providers on the other. Innumerable other consequential costs are also possible, the least of which will be media advertisements publicizing the forthcoming opening of new premises. Since these are consequential losses, the best precaution is to avoid the physical losses leading to such delays in completion of the construction work. These statements thus merely serve to underline the measures already outlined in the preceding sections with regard to loss prevention. The possibility of covering some of these consequential losses through corresponding insurance products will be discussed later. OPERATING PHASE

The main financing aspects concerning the construction phase also apply equally to the operating phase. Regardless of whether own or borrowed capital has been invested, the investor will expect a guaranteed return on his investment. Even as the property is being let, the owner will therefore seek to attract solvent tenants guaranteeing a profit in line with his cost calculations within the framework of a long-term lease. This is particularly true if the owner has during the construction phase already provided advance financing for complex interior finishing meeting the tenant’s wishes. The owner of a high-rise building will therefore wish to know what impact a maximum foreseeable physical loss due to the aforementioned risk potential could have on his calculated revenues and expenditures: – How long will it take for the property (offices and business premises) to be restored and when can they be relet? – Can the property be relet immediately and generate the calculated revenues or must rents be expected to decline due to the growing supply in the neighbourhood of the property? – What is the term of the individually concluded leases? – What revenues are guaranteed by these leases over their entire term? Under what conditions could a tenant rescind the contract completely or insist on a pro rata reduction in rent due, for example, to a physical loss of the aforementioned type? – What is the maximum term to be foreseen by the owner of a high-rise building, i.e. from occurrence of the physical loss until the calculated rent revenues are obtained again; and what losses will he in all probability have to include in his calculations during this period?

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Investors and owners are not the only people, however, whose fate largely depends on the profitability of a highrise building and who must precisely identify, appraise and control their associated risks before considering a well-conceived insurance. The following risk potential and other aspects must also be weighed up by the tenants renting offices and business space in what is no doubt an attractively located high-rise building from a strategic business point of view: – If the tenants have obtained very favourable long-term leases in the past which, however, can be terminated prematurely on account of material physical damage to the building or to the rented furnishings, these tenants must expect to pay considerably more when renting comparable business premises if rents have risen substantially in the meantime. – Quite apart from the additional rent to be paid for temporary or definitive removal to alternative premises, the tenants concerned will possibly also have to reckon with considerable additional costs for all the special measures required in order (preferably within the scope of contingency plans) to avoid or at least minimize any negative effects on the company’s operating and earnings situation. In spite of this, however, it will probably be impossible to prevent all loss of gross profit between occurrence of the physical loss and restoration of normal operating conditions. The economic environment of the high-rise construction project must also be taken into account – depending on the order of magnitude in each instance. It was mentioned in Section 3.4.2.4 that high-rise buildings could be compared to a “town under one roof”. The World Trade Center (WTC) in New York (see Section 4.8.1) is an example of this economic aspect underlining the loss-of-profit risk. The WTC is made up of seven buildings accommodating some 1,200 businesses on an area of 7 hectares. The two office towers are 415 and 417 m high, respectively, and are linked by a 22-storey hotel complex. With 110 floors, they provide roughly one million m2 of useful floor space for various offices, such as investment companies, brokers, raw commodity markets, customs authorities and television companies. A 100-m television mast with various antennas is mounted atop one of the towers. The second tower additionally accommodates a switchboard for New York’s telephone system with, among other things, the telecommunications for air traffic control at New York’s three largest airports. Underneath the extensive open-air plaza are the largest covered shopping promenade in Manhattan, six department stores and shops, 2,000 parking spaces, two vehicle tunnels and the stations for three underground railway lines carrying the roughly 50,000 people working in the two towers and the roughly 80,000 visitors recorded every day. Numerous businesses, organizations and a complex infrastructure are consequently dependent on the smooth functioning of the two towers.

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The magnitude of the direct losses caused by the car bomb on 23rd February 1993 has already been described in detail. Both office towers were closed by official order until further notice. Due to the surplus of offices available in New York City in 1993, the towers’ owner – the Port Authority Risk Management – was naturally anxious to do everything possible as quickly as possible in order not to lose tenants. Perfect contingency plans meant that 220 floors were cleaned up within only 21 days and the towers reopened for use as offices on 19th and 26th March, respectively. During this one-month break, the tenants in the towers had to find alternative premises at considerable expense and had to finance the temporary furnishings. This was not always an easy matter in view of the special technical equipment required in various cases. One Japanese institute quoted lost revenues in the order of US$ 12m per day, while another cited a figure of US$ 20m daily. The absence of the people working in the office towers inevitably also led to loss of profit for the other businesses and organizations in the area and surrounding districts, particularly the transport corporations and the toll bridges and tunnels over and under the Hudson River, which separates New York from New Jersey. In this way, an economic loss of roughly US$ 1bn was incurred in a onemonth period. Particularly when assessing the loss of profit risk, it is important always to remember that “if anything can go wrong, it will – at the worst conceivable moment – and everything always takes longer than expected“.

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5 5.1 Property insurance 5.2 Third-party liability insurance

5.3 Problem of maximum loss 5.4 Underwriting considerations

5.5 Reinsurance

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Compared with normal building construction, there are a number of additional risks associated with the construction and subsequent occupancy of highrise buildings which can only be appraised by an experienced insurer. The project documents provide an initial overview of these risks.

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The project documents usually only provide information on the finished building and how it is integrated into the townscape. Since different methods are often employed for the construction work, the respective risk potential during the construction phase must also be weighed up and valued by the insurer. Almost every blueprint of a high-rise building also includes a series of tailor-made elements, such as facades or special foundations, with divergent risks which consequently can be considered a kind of prototype, at least in part. The effects of such semi-prototypes for contractors’ all risks insurance must be investigated separately. At the end of the planning phase, if not before, the principal must decide how the risks during the construction work are to be spread between himself and the contractors. This must already be specified in the tenders. Such early and precise demarcation of risk between the principal and the contractors is of great importance, not only for determination of the premium, but also for subsequent loss events.

5.1 Property insurance A distinction must first be made between construction of a high-rise building (construction or erection) and the subsequent occupancy phase. The first phase will be covered

by contractors’ all risks insurance, possibly including cover for construction and erection equipment. The second phase, however, requires a series of policies covering such risks as fire, complete or partial collapse (decennial liability) and various additional perils (natural hazards, water damage, glass breakage, etc.). 5.1.1 Contractors’ and erection all risks insurance Construction work on a high-rise building is normally covered by contractors’ all risks (CAR) insurance. If coverage in accordance with an erection all risks (EAR) policy is required in certain cases for the interior finishing, including installations for air-conditioning, electric and telecommunications systems, this can be included in the CAR policy through corresponding extensions of cover without making it necessary to issue two separate policies. A separate EAR policy is only meaningful if a strict distinction is to be made between the structural works and the interior finishing on account of different insurance interests (principal/tenant). Since, however, it is impossible both physically and chronologically to separate the structural works from the interior finishing, care must be taken in this specific case to ensure that the scope of cover is precisely defined in relation to the concurrent CAR policy. GENERAL

Unless explicitly stated otherwise, the following comments apply equally to the cover granted under a CAR and

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an EAR policy. Both policies cover the construction or erection work specified in the Schedule against unforeseen and sudden physical losses of every kind.

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exact documentation of the final sum insured declines after conclusion of the construction work. PERIOD OF COVER

It concerns all-risks coverage, i.e. every cause of loss is covered unless explicitly excluded. This naturally means that the insurer must take account, in particular, of the risks from ground and soil and the exposure due to natural hazards, especially windstorm and flooding. The terms of insurance must be clear. In very rare cases, it may be necessary to introduce a limit of indemnity for losses due to natural hazards, such as earthquakes. This may be necessitated by inadequate capacities or uncertainties when estimating the possible maximum loss.

Insurance cover is provided until the policy expires or until the construction work is finally accepted by the principal or until the building is taken into service or used, if this occurs before expiry of the policy. However, there are exceptions, particularly in this context and especially if completed floors are let earlier in order to earn income from rentals or sales proceeds as soon as possible. In such cases, a clear distinction must be made between the cover defined for the CAR policy and that of the subsequent insurance for the building. In spite of all efforts to boost efficiency, construction work usually continues over several years, with the result that during risk assessment the construction schedule should be consulted in order to include seasonal hazards, such as monsoon rains or autumn gales. Extensive preparatory work (routing of supply lines, erection of the retaining walls, excavation and water management) is necessary before work on the high-rise building actually starts. Insurance cover is also required for this preparatory work, since losses can arise even in this phase of construction. A so-called maintenance agreement is often concluded between the principal and the contractor for the period after completion of the construction work. Under these agreements, the contractor is obliged to remedy any defects occurring in the building during the term of the maintenance agreement (usually 12 months). Two types of insurance cover can be granted for property losses in this period: – Insurance of physical losses following maintenance work (Clause 003: Maintenance visits), or – In addition to the aforementioned cover, insurance of physical losses occurring during the maintenance period but caused by an event originating in the construction phase (Clause 004: Extended maintenance).

SUM INSURED

LOSS ADJUSTMENT

Particular expertise is required of the insurer when determining the sum insured. As a rule, the approximate contract value at the beginning of the insurance term can serve as a provisional sum insured and is used as the basis for calculation of the premium. However, the contract value must be regularly reviewed by the insured to take account of inflationary price rises or higher sums due to supplementary contracts during the construction period, and this sum insured must then be adjusted correspondingly in the policy. The sum insured can also be increased by a safety margin in order to avoid the danger of underinsurance. If this margin exceeds the actual sum insured upon completion of the construction work, the insured is granted a corresponding premium refund. In all cases, however, the total sum insured is equal to the maximum indemnification for all claims payments. On the other hand, it is not advisable to wait until the end of the construction phase before adjusting the sum insured, as experience has shown that the policyholder’s interest in

In cases of physical damage to the insured contract works, the insurer will indemnify the necessary costs incurred for restoring or replacing the damaged contract works. The repair costs will sometimes be higher than the original expenditure up to occurrence of the loss. However, if the cost types are the same as those included in the sum insured, they will be indemnified in full. This is not the case with costs which are first incurred during repairs (e.g. removing damaged parts in order to carry out repairs). The policies recommended by Munich Re include such costs only if this has been specifically agreed and a first-loss sum provided for this purpose. This procedure should be applied above all to cleanup costs (removal of debris) and loss-locating costs. In both cases, the duty to indemnify depends on whether or not expenditure was incurred in conjunction with an indemnifiable loss. We believe that this procedure allows insurers to assess their liabilities more accurately. And it is also in the interests of the policyholder, who can then decide on

POLICYHOLDER

The interests of all parties involved in the construction work are normally insured by the principal. The group of insured persons or companies is therefore very large; both the principal and the general contractor are policyholders in a CAR/EAR policy, although all subcontractors are also covered. These are often specialists, particularly in highrise construction. This explains why the general contractor is not the only party of interest to the insurer, for the special jobs undertaken by subcontractors can frequently represent a greater risk. Here, too, the general contractor is liable as contractor to the principal. It is therefore essential to obtain full information on the work of these specialized companies as well, in order to appraise the physical and moral hazard. If – in deviation of the norm – only the contractor takes out CAR/EAR insurance to safeguard his own interests, then the contractual agreements reached between principal and contractor must be reviewed in order to assess the risk to be borne by the insurer. The risk for losses due to force majeure will normally pass partly or entirely to the principal. This reduces the risk to the contractor’s insurer. FORM OF COVER

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the amount of cover required in view of the potentially very high “additional loss costs”. The same also applies to indemnification of additional planning costs which may be incurred due to repairs if the original planning costs were not included in the stipulated sum insured or if new plans are required on account of the circumstances surrounding the loss. Only those costs will be indemnified which are necessarily incurred in order to restore the building to the same technical condition as immediately before occurrence of the loss. However, if the original condition is improved or changed as a result of the repair, this also means that any costs associated with such improvement or change will not be indemnifiable. The same applies if other, more complex methods are used for the repairs; they, too, are only indemnifiable to the extent that they were included in the original sum insured. The agreed deductible must in all cases be taken into consideration in the calculated amount of indemnity. RISK ASSESSMENT

Assessment of the physical hazard by insurers should be based on the same considerations as those underlying the choice of a certain construction method. In addition, however, they must also consider, for example, whether a certain method or material was perhaps only selected in order to save time or money. The insurers must then determine whether, in the light of known risk factors, a higher risk of physical damage was knowingly accepted by the principal or contractor as a result of this choice. Assessment of the moral hazard always begins with the planning process. The manner in which the planning has been organized must be reviewed; for instance, to determine whether principals assign the planning and supervision of the construction work to their own office or whether they retain various engineering offices for this purpose. The question whether planning and execution were done under time pressure and whether the schedule allowed for adequate time buffers can also be of decisive importance. Last but not least, the contractors’ experience on similar high-rise construction projects, and particularly the quality of the contractors’ construction or erection personnel, can also be of great importance when assessing the moral hazard. EXTENDED COVERS

The CAR policy can be suitably extended with the aid of various other standard clauses, including those applicable to EAR insurance, in order to provide sufficiently comprehensive cover for the erection work concerned. The following most commonly used clauses provide extended cover for political risks (Clause 001), cross liability (002), extended maintenance (004), overtime (006), airfreight (007), fire-fighting facilities (112) and designer’s risk (115).

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5.1.2 Advance loss of profit insurance The large proportion of borrowed capital required to finance high-rise construction projects has made principals increasingly aware that conventional property policies will only cover a limited part of the overall loss, but not the loss of operating profit or standing charges due to delayed commissioning or occupancy following a loss. Even such additional agreements as contractual penalties or liquidated damages provide only inadequate relief here. For this reason, the existing CAR (EAR) policy can be extended by means of an ALOP cover. The purpose of this extension of cover is to insure the principal’s financial losses due to delayed commissioning or occupancy following an indemnifiable CAR loss during the construction phase. FORM OF COVER

ALOP risks are written in line with Section III in the Schedule to the standard policy for property cover. If the property policy provides for a very large scope of cover, this may have to be reduced to take account of the ALOP cover. This applies particularly to the exclusion of losses following delayed completion of the construction work as a result of earthquakes. Stand-alone ALOP covers without property insurance should as a rule be declined because, when it comes to adjusting property losses, the necessary information is lacking and there is no way to influence the adjustment process. POLICYHOLDER

Since ALOP covers exclusively protect interests of the principal, the latter should be the sole beneficiary. In order to ensure that they are able to exert their full influence in the event of a loss, however, both the principal and the contractor should be named as policyholders in the basic policy cover. Contractors on the other hand cannot obtain ALOP cover to insure their consequential losses – above and beyond the property losses covered by Section I of the CAR policy – such as penalties, interest due on withheld warranty sums and other “soft costs”. Banks should also be excluded as policyholders, since their interests should be regulated in the financing agreements concluded with the principal, independent of the terms and conditions of insurance. A special situation only arises in conjunction with the increasingly widespread “build-operate-transfer” (BOT) projects where principal and contractor act together and therefore are joint usufructuaries of the building following its completion. In such a case, they are both named policyholders under the ALOP cover, but with due regard to the possibility of a higher moral hazard.

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SUM INSURED

The sum insured is normally equal to the gross annual profit, i.e. projected fixed costs and operating profit for the high-rise building. This gross profit is determined by deducting the variable costs from the sales or profit. Insurance is not required for these variable costs (e.g. cost of electricity, water, personnel), since they are not yet incurred when the delay occurs. However, the principal’s possible losses are not limited solely to the lost profit from letting or leasing the high-rise building. The following can therefore also be insured: – “Ongoing rent costs” if the policyholder must pay rent for continued occupancy of other business premises when completion of the new high-rise building is delayed, since he or his tenants cannot move into the new premises on schedule. – “Ongoing interest charges” incurred by the principal if he cannot sell the building at the planned time and must repay the loans taken out to finance construction of the building or if the interest due cannot be paid at the planned time out of income from rental or leasing. – “Additional costs” if the loss of profit can be avoided or reduced in this way, for instance by purchasing outside electricity, renting flats, office or computer capacities. Loss-minimization expenditure will also be indemnified up to the value of the indemnifiable loss of profit which has been avoided in this way. If the agreed period of indemnity exceeds one year, the projected sum insured for the entire indemnity period must also be specified in addition to the one-year sum insured. PERIOD OF INDEMNITY

The maximum period of indemnity to be specified in the policy should be sufficient to allow damaged or destroyed parts of the building to be repaired or replaced. Due to the difficulties often encountered in removing rubble and in obtaining new licences, this can easily result in indemnity periods considerably longer than the originally planned construction period. EXCESS

Time excess is always preferable to monetary excess with this form of cover and should be equal to at least four weeks per twelve months of construction time. In view of the long time required for the construction of high-rise buildings, this results in a highly desirable time excess of several months.

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The policy recommended by Munich Re for this cover provides for a one-off application of the time excess, since numerous cases of physical damage during the construction period will ultimately delay commissioning of the high-rise building, thus resulting in only one ALOP loss during the agreed indemnity period. CLAIMS HANDLING

The handling of claims, i.e. determination of the indemnifiable period of delay in completing the building and the resultant loss of profit is normally complex and time-consuming. For this reason, progress should be verified at regular intervals during the construction phase, so that loss-related delays can be distinguished from those unrelated to losses and so that their impact on the original completion date can be traced. So-called one-off costs cannot be insured, i.e. sums which are due for payment or which are lost in full on a fixed date, such as tax benefits, seasonal business, lost orders and licences. 5.1.3 Insurance of contractors’ plant and machinery Construction plant and machinery can be insured under the CAR policy, through Clause 202 in the EAR policy or in a completely separate contractors’ plant and machinery insurance. The scope of cover is the same in all three cases. Basically, this concerns machinery insurance for contractors and is limited to external causes of loss. In other words, the insurance does not cover losses due to internal mechanical or electrical problems. In high-rise construction, such machinery and plant is required above all for the retaining walls, foundation structures and excavation. Cranes are used for construction of the high-rise building as such. However, care should be taken to ensure that all the plant and machinery is insured and not just such highly exposed plant as cranes and scaffolding. The sum insured should correspond to the replacement value of the insured machinery and plant, since this is the only value that can be objectively determined; in the case of partial losses – which make up the bulk of all losses – the repair costs can then be indemnified newfor-old without deduction. It is only with the much less common total losses that the amount of indemnity is limited to the current value. Experience has shown that numerous individual losses must be expected in particular when insuring contractors’ plant and machinery. Appropriate deductibles can therefore reduce not only the claims burden, but also claimshandling costs, while at the same time creating an incentive for the policyholder to prevent losses and ensure the orderly organization of construction work.

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5.1.4 Decennial liability insurance This special form of cover for buildings originated in France. In accordance with the Napoleonic Code, all buildings are insured against total or partial collapse for a period of ten years (hence the term “decennial”) following their completion, provided that the loss is attributable to a defect or fault in the performance of one of the parties involved in construction during the construction phase. This form of long-term cover has only become established in a few markets and is normally limited to buildings, including high-rise buildings. The scope of cover varies. The commonest extended cover includes leaks in underground levels, facades and the roof, which can prove problematical due to the frequently unknown long-term performance of seals and the highly complex, cost-intensive repairs. A distinction is made between countries, such as France, in which this cover is obligatory and markets which only offer this form of cover in isolated cases. Technical inspection of the construction work by an independent inspection agency or engineering office is normally essential before decennial liability cover can be granted. The availability of such cover is dependent on this agency or office having submitted a satisfactory final report stating that it has no reservations as regards the stability of the high-rise building. The principal is the insured party and also beneficiary in the event of a loss. However, the insurer can also seek recourse from contractors, subcontractors and suppliers if they can be held liable for the loss. Due to the long period of liability, insurers must make adequate provisions with regard to administration and when carrying forward reserves. 5.1.5 Insurance of buildings, fire insurance For property insurers, insurance of high-rise buildings is nothing unusual in terms of designing the policy. As in the case of “normal” buildings, the policy is designed along the lines of industrial or commercial insurance for buildings and sometimes also of insurance for residential buildings. A distinction is merely made between two essential forms of cover: NAMED-PERILS COVER

The model of named-perils cover is derived from the basic perils of fire, lightning strikes, explosions and crashes by manned flying objects or parts thereof or of their cargo. This form of cover allows the insurer a very good overview of the perils to be covered and ensures the transparency necessary for fixing prices.

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This basic cover is normally extended accordingly with additional inclusions in line with individual requirements, such as – natural hazards: earthquakes, floods, windstorm, landslides, hail, volcanic activity, snow pressure, avalanches; – political risks: strikes, riots and civil commotion, sabotage, possibly terrorism; – other perils: impact of vehicles, water damage, sprinkler leaks, glass breakage, malicious damage, graffiti. ALL-RISKS POLICIES

Policyholders in a number of markets are increasingly demanding all-risks policies for high-rise buildings as well. This form of cover includes all of the risks under one policy which are not explicitly excluded. Although these policies offer the policyholder extensive insurance cover, they must be examined with particular care by the underwriter. Calculation of the premiums is no longer transparent in these cases, since the extensive scope of cover may tend to “veil” the insured perils. A distinction must also be made from one country to the next with regard to the scope of liability. Such political risks as terrorism and sabotage, for instance, may be included in an all-risks policy without additional premium in some countries, but excluded from the standard cover in others on account of local claims experience. Inclusions from non-property classes, such as third-party liability and machinery breakdown insurance, are also increasingly to be found in all-risks covers. The owner of a high-rise building and its users or tenants are frequently separate and distinct legal entities with different policyholders, i.e. the owner for the building as such and the tenant for its contents and furnishings. For the insurer, this may result in exposure to accumulation, which must be taken into account accordingly. Depending on the purpose for which the building is used by its tenants, e.g. offices, computer centre, flats, hotels, possibly also commercial businesses (multi-occupancy building), the loss exposure can be quite substantial. In conclusion, from the insurer’s point of view high-rise buildings are exposed to the same risks as other residential and/or office buildings as far as the scope of cover is concerned; for this reason, they are not different from other risk groups with regard to insurability. Only the special characteristics of certain risk situations have a limited influence on pricing (see PML, loss prevention). The possibility of accumulation must be taken into account, however, when the building and its contents are insured separately. The policyholder’s primary interest is to obtain the most extensive insurance cover possible in return for a premium commensurate with the risk.

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5.1.6 Loss of profit insurance

5.1.6.2 Additional costs

Standard covers or customized insurance (on request) are offered for the loss of profit risks mentioned in Section 4.9.

On the other hand, it is also perfectly possible that if a business is favourably and strategically located in the high-rise building, the tenants may have decided on a long-term investment by concluding a lease over several years in order to protect their interests. The following circumstances may have to be taken into account: – The rental value of the premises at the time of the loss, and probably throughout the remaining term of the lease, is appreciably higher than the rent actually paid, with the result that the tenant must expect to pay more in order to rent comparable premises elsewhere. – Advance payments of the rent which have not yet been amortized and which, under the terms of the lease, need not be refunded in the event of a loss. – Improvements in the value of permanent fixtures and fittings which have been financed by the tenant, but which have not yet been amortized and which, according to statutory regulations, he cannot remove when vacating the premises following a loss. – Under the terms of the lease, the tenant is obliged to continue payment of all or part of the rent although the premises cannot be used on account of the loss. American insurers offer “leasehold interest coverage” to cover such eventualities. European insurers offering loss of profit insurance will indemnify the additional costs incurred to minimize the impending insured loss.

5.1.6.1 Loss of rent The high-rise building owner’s interest in steady income from rent is normally protected through loss-of-rent insurance. In accordance with the applicable General Terms and Conditions of Insurance (ABM 89), insurers in Germany will indemnify the insured loss of rent for the building specified in the insurance contract, as well as for other parts of the property which have been destroyed or damaged by specified perils. Where rented property has been destroyed or damaged, tenants are entitled by law or under the lease to refuse payment of part or all of the rent. The value insured is normally equal to the value of one year’s rent and the sum of ongoing ancillary costs for a period of one year. The loss of rent will be indemnified, at most, until the premises are reusable, regardless of official restrictions on restoration. If the tenancy ends on account of the damage and if the premises cannot be relet when restored even if due care and diligence have been exercised, then the loss of rent will be indemnified after this time until the premises have been relet, but at most for three months. Unless otherwise agreed, loss of rent is indemnified for a maximum of twelve months as from occurrence of the insured event. On Anglo-Saxon markets loss of rent can generally be covered as a supplementary item under insurance of buildings. However, coverage ends when the rooms are finally restored, i.e. reusable, regardless of any further loss of rent until a new tenant can be found. In such cases, the owners of high-rise buildings of the type described here are advised to take out loss of profit insurance corresponding precisely with the terms of the lease. This applies in particular to the period of indemnity until the entire establishment has been economically rehabilitated; agreements with terms of up to ten years are therefore entirely possible. Another advantage of loss of profit insurance is that it covers all additional costs, insofar as they actually reduce the threatened loss of rent. Such costs include, for example, additional expenditure for short-term emergency repairs, overtime for contractors’ employees and other trades, as well as special advertising measures taken to find new tenants.

5.1.6.3 Contingency planning The more exposed a skyscraper’s position as a regional attraction and the more special the fixtures and fittings in the rented premises, the greater the business-interruption risk, for it will probably be very difficult and exceedingly expensive to relocate business operations to suitable alternative premises. The survival of a company may often depend on detailed and regular reviews to assess the feasibility of such contingency plans which would be triggered by a potentially catastrophic loss. Although loss of profit insurance can indemnify financial expenditure for a calculated period of time, it cannot compensate for the loss of contact with key customers, a situation which could easily be averted by adequate contingency planning. The results of such perfect planning were demonstrated following the bomb attacks on the Commercial Union building in London on 10th April 1992 and the World Trade Center in New York in February 1993. 5.1.6.4 Prevention of access Loss of profit insurance (business interruption, additional costs, etc.) can be extended to cover other risks, including the risk of a company being dependent on external operations, institutions and special circumstances. Physical damage on the underground levels (garages) or approach roads to a high-rise building due to fire, explosion, earthquake or flooding can lead to at least temporary closure of the entire building complex. Although the

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offices, shops, etc., have not suffered any property loss as such, they can expect profits to be affected in different ways – unless they have appropriate insurance (prevention-of-access insurance). American standard policies permit claims for damages for up to two weeks in such cases.

5.2 Third-party liability insurance As can be seen from what has been said so far, third-party liability risks are also to be expected during the construction of high-rise buildings. A distinction must be made between liability risks during planning and construction and those during occupancy of the high-rise building. The product liability risk of the manufacturers of the individual construction elements will not be discussed further here. The high technical requirements to which engineers and contractors are subject in the construction of a high-rise building naturally also pose a special challenge for the liability insurer in terms of recording, assessing and underwriting such risks. 5.2.1 Insurance of the designer’s risk A planning engineer or office can obtain professional indemnity insurance to cover the liability risks associated with planning and site management. In the case of larger projects, a customized property policy is advisable with correspondingly higher limits of indemnity which should also be available separately, instead of an annual policy for twelve consecutive months. SCOPE OF COVER

The scope of cover under professional indemnity insurance for civil engineers basically corresponds to the generally applicable professional indemnity insurance for architects and construction engineers. Insurance cover is provided for all statutory claims for damages from errors and omissions by the insured in the discharge of his precisely defined responsibilities. The geological conditions on site play an important part on account of the considerable load concentrations. If soil analyses are performed by the designing engineer himself or if he is contractually responsible for selecting, employing and possibly supervising a geologist, then he may be liable for the consequences of inadequate soil analyses as well as for incorrect soil analyses during the planning phase. The most important scope of cover relates to the so-called object loss, i.e. loss or damage to the high-rise building as such, insofar as such loss or damage is attributable to an error for which the planner is responsible. However, object

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losses should only be included if the designer and site manager have no interests in the widest possible sense in the delivery, erection and execution of the work. Such independence is only feasible with freelance engineering offices which have no financial or personnel links to the contracting companies and suppliers. Only then is it possible to distinguish between a claim for damages based on fault on the one hand and a claim for performance and warranty, which is not covered by the liability policy, on the other. This condition is not met, for example, by engineering offices which act as general contractor. In such cases, the liability policy should be limited to the second essential scope of cover, namely third-party losses (bodily injury and physical losses). The term of the object policy generally covers the planning and construction phase up to final acceptance of the construction work with a period of secondary liability of between two and five years as agreed. RISK ASSESSMENT

Every high-rise building could be considered a prototype on account of such different parameters as location, height, intended use, choice of materials and natural hazards. Particularly high standards are therefore imposed with regard to the skill and experience of the planning engineer. Technical know-how is also required of the liability insurer so that these difficult planning risks can be assessed and rated. The following criteria in particular must be taken into account when assessing the risk: – Qualifications and experience of the policyholder – Number of partners and number of engineers involved in the project – Total fees – Contract price – Responsibilities and liabilities accepted – Construction method applied (Does it reflect the latest scientific and technical findings? Have any comparable projects already been completed?) – Particular geological conditions, groundwater conditions and natural hazards to be taken into account in the planning (earthquakes, wind, possibly floods) – Surrounding area (e.g. closely built-up city centres, public roads: damage due to falling parts) – Planning period – Particular circumstances aggravating the risk (e.g. use of new materials, facade elements) – Effect of construction work on the neighbourhood (shadows, poor television reception, noise) 5.2.2 Insurance of the construction risk The specific liability risk of the contractor responsible for construction of a high-rise building lies firstly in the risk of injury to his own employees (employers’ liability). This particular risk of bodily injury is due to the fact that the workers often have to work at dizzying heights and if a fire breaks out in the high-rise building, the number of casualties and fatalities is likely to be very high.

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Secondly, the risks depend on the location of the high-rise building, as it will normally be located in a city centre, with dense traffic and narrow streets. Falling parts or crashing scaffolding and cranes can cause physical damage to nearby main traffic arteries (urban motorway, tramways, railway lines) or to adjacent buildings, as well as bodily injury to road/rail users and local residents. Interruptions to traffic can lead to consequential financial losses. This highlights the particular risk of a major loss during the construction phase of a high-rise building. Moreover, the extensive foundation work and construction of the underground levels make it necessary to excavate deep pits, which often reach below the groundwater table. Depending on the type of retaining wall used, it may also be necessary to lower the groundwater table. The risk of subsidence, ground motion and even shear failures resulting from such work must be assessed with particular care due to the risk of major losses. SCOPE OF COVER

The normal limits of indemnity are usually insufficient for such major projects or particularly exposed risks. Two alternatives can be chosen in such cases: either the limit of indemnity in the annual policy is increased for the particular object in return for a correspondingly higher premium or separate liability insurance is concluded, tailored to the individual project in question. For the insured, the latter alternative has the advantage that this limit of indemnity is available exclusively for this one project, thus eliminating the risk of limits in the annual policy being exhausted by losses on other projects. However, there is also another possible variation: high-rise construction involves not only the general contractor, but also numerous other contractors (main and ancillary construction trades). In order to obtain uniform and adequate insurance cover for all contractors, large or small, it is standard practice for all companies to agree on a single policy with a uniform limit of indemnity. The policyholder is frequently the principal who takes out the policy on behalf of the contractors (third-party account); the latter are then deemed to be insured persons. From the insurance point of view, they are treated as if they each had their own policy. However, it is also standard practice to agree that the individual companies must take out their own liability insurance with certain minimum limits and that this liability insurance takes precedence over the joint project policy. The project policy thus takes the form of a surplus cover. The principal’s risk can also be included from the outset. Cover is occasionally also extended to include the risk of independent planners (property loss and third-party liability), albeit usually with considerably lower indemnity limits and, analogous to the procedure outlined above for the contracting companies, only subsidiary to higherranking basic covers.

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What are the problems associated with an insurance solution employing a common project policy for all contractors involved in the construction work? Since the principal is the policyholder and some of the principal’s claims against contractors/designers are also included in the insurance, this means that there is – at least formally – a certain degree of cover for first-party losses. In practice, however, the problem is mitigated by the surplus function in that claims for damages are first examined and, where justified, also settled by the insurers of the mutually independent basic covers. Indemnity under the project policy would only kick in thereafter. CAR or EAR policies include the possibility of insuring the third-party liability risk of all contractors involved in the construction work under Section II. In both policies, however, the indemnity limits of the third-party liability insurance section are subject to certain limitations. An additional third-party liability policy known as the contractors’ excess liability (CEL) policy can be concluded if higher indemnity limits are desired, as may be assumed for highrise construction, for instance on account of the particularly exposed nature of the risk. RISK ASSESSMENT

When assessing the risk, it is important to appraise the potential degree of bodily injury losses within the framework of employers’ liability and particularly the possible third-party losses to the direct surrounding area as a result of falling parts, tools or even partial collapse of the high-rise building. Damage to adjacent buildings as a result of lowering the groundwater table or damage due to ground motion as a result of piledriving, underpinning and driving underpasses can often prove more expensive. The following aspects must be taken into account in particular: – Contract price – Number of site employees and total payroll – Responsibilities and liability accepted – Construction methods and schedule – Location, surrounding area, neighbourhood – Particular geological conditions – Lowering of the groundwater table, blasting, underpinning, driving underpasses – Contractor’s experience – Construction period, maintenance period, period of secondary liability 5.2.3 Insurance of the operational risk When the construction work is complete and the high-rise building has finally been taken into service, it is taken over by the operator or principal, who is consequently responsible for all losses suffered by third parties through the operation of the high-rise building. This operational risk would be covered by the usual insurance for homeowners and property owners: it protects the owner in his capacity as owner and lessor of the high-rise building.

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The main risk lies inside the building, particularly if it is open to the public. The most commonly occurring losses will be personal accidents on improperly serviced stairs or elevators and bodily injury due to falling objects. However, the owner is only liable for causes within his sphere of responsibility. These include regular servicing and maintenance of elevators, safety and control facilities, as well as compliance with statutory regulations or official requirements (e.g. fire protection). For this reason, the relevant maintenance, safety and fire-protection schedules, as well as fire procedures should be inspected by the insurer when underwriting a third-party liability policy for the owner and lessor of a high-rise building. The premium is normally calculated on the basis of the gross annual rent value, i.e. the total income from rent.

5.3 Problem of maximum loss Due to the high concentration of values, the probable maximum loss (PML) must be estimated separately for each of the risk phases, also in the case of a high-rise building. 5.3.1 Construction phase As is usual for all major projects, the PML estimate should be based on a separate assessment of the risk. In the case of high-rise buildings, fire will normally be considered a peril relevant to the risk and therefore form the basis for the PML estimate. The measures required for active and passive fire protection should not lead to any reduction in the PML, since some of these measures only become fully effective when the building is finished. This explains why fixed percentages are not specified here; at best, a deduction for the often extensive and expensive foundation measures can be justified when assessing the parts at risk, since these foundation measures are not exposed to fire. Depending on local conditions, exposure to windstorm, earthquakes and natural hazards may also be of relevance for the PML estimate during the construction phase. 5.3.2 Decennial liability insurance The same considerations basically also apply to decennial liability insurance, except that here fire is replaced by the fairly rare risk of collapse. With major projects, it may also be advisable in view of the limited capacity available worldwide to introduce a limit of indemnity in order to facilitate placement of the risk.

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5.3.3 Operating phase From an underwriting point of view, the fire PML is the most important element during operation of a high-rise building. The PML for a given risk refers to the probable maximum loss which must be expected if the event occurs, with due regard to the conditions surrounding the risk and based on conservative estimates. When estimating the PML of “normal” risks, we base our assessments on complexes, but this is not possible in the case of high-rise buildings, as they usually comprise only one complex. What is important, however, is that we – unlike many other companies – do not take account of the existing fire-protection facilities and precautions in our PML estimate. The following are disregarded in particular: – Manual and automatic fire detection systems – Fire-extinguishing equipment, such as wall hydrants, sprinkler systems, CO2 or inert-gas fire-extinguishing equipment – Efficiency of the fire brigade These points are not considered to be factors which reduce the PML because they occasionally fail when the insured event occurs. Structural fire-protection measures, such as fire-resistant construction practice, fire-resistant sealing and fire compartments (see Section 4.2.4.2), on the other hand, can be considered as PML-reducing factors. Experience has shown that the total loss of a high-rise building is highly improbable, so that an assumed PML of 100% should remain the exception. Although fires resulting in total demolition of the high-rise building are known to have occurred (see Section 4.2.3), this was essentially due to other reasons and not primarily to the impossibility of repair. Moreover, the total sum insured was not paid as indemnification in these cases. On the other hand, we do not believe that it is right to specify flat-rate percentages of the sum insured as the PML for high-rise buildings, nor to define a certain number of floors as determining the PML, as is sometimes done. We believe that an individual approach is required which takes into account the following criteria: – Form of the building – Construction practice – Internal layout – Facade design High-rise buildings are frequently erected on a podium with one or more levels. When estimating the PML, it is important to establish whether a fire breaking out in the podium can spread to the rest of building or whether this is prevented by protected fire-resistant separations. Three forms of building must be taken into account here: – small dot-like layout/towering building, – flat slice-like building (length of the building equals at least three times its width), – large sprawling layout (base area in square metres equals at least 50 times the height of the building in metres).

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The probability that entire floors will be gutted by fire is highest in the case of the first group of buildings. With the second group, subdivision into fire compartments is more likely, if only on account of statutory requirements with regard to the length of rescue routes. If the partition walls have been correctly designed and dimensioned, a lower percentage loss may therefore be assumed per floor. An even larger number of fire compartments is to be expected with the third group of buildings, and this should reduce the loss per floor still further. Going purely by the form of the building, the percentage PML must be highest in the first and lowest in the third group. Regardless of the form of the building, the combustibility of the materials used and the fire-resistance period of the parts must also be considered. The characteristics of the supporting structure and of floors as well as the fire-resistant elements protecting the openings to stairwells and elevator or service shafts are important in this respect. The facade design is a very important factor for vertical propagation of the fire and consequently for the PML. A fire must be expected to spread from one floor to the next if the window glazing is not fire-resistant and if the flashover distance between the windows on consecutive floors is too short. The risk of fire spreading is even more serious if the building includes an atrium, since the resultant chimney effect also has to be considered. When estimating the PML, it is useful to consider the building’s supporting structure and its finishings separately. The finishing work must be taken to include all nonbearing inner and outer walls including panelling, all building service installations and elevators, all doors, windows, floor coverings and ceilings. In the past, it was common to do a 50:50 split on supporting structure and finishings, but this ratio has now changed to 30:70 on account of the more complex building services and more extensive wiring in modern buildings. Experience has shown that considerably less than 50% of the supporting structure of a high-rise building will be damaged by fire, depending on its type, particularly as regards its fire resistance. In the case of the finishings, on the other hand, the loss must be expected to be in the region of 40–100% due, among other things, to damage caused by smoke and fire-fighting water. The highest percentage losses are suffered by the supporting structure and finishings in the first group of buildings and the lowest by those of the third group. What has been said above must be considered one possible approach for estimating the PML and not as an algorithm, since numerous different criteria must be taken into account separately in each case. In addition, such covered items as cleanup and demolition costs, increased costs of working due to conditions imposed by the authorities and price rises during the restoration period, must be added to the PML. These are normally first-loss risk items which should be included 100%.

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So far, we have only considered the building as such. Its contents are normally insured separately, the policyholders usually being the building’s users or tenants. If the building is insured together with its contents, the PML for the contents must be taken as a cumulative figure when estimating the PML. Contents require similar consideration to interior finishings. Once again, special attention must be paid to “multi-occupancy buildings” (see Section 5.1.5). How appropriate is it to specify a terrorism PML for highrise buildings? In our point of view, there is little point in specifying such a PML, as we would not like to consider terrorism a “probable” event. Moreover, it is impossible to give any precise estimate of a loss due to terrorism and the PML would always have to be set at 100%. A bomb attack is the most effective terrorist attack. It is perfectly conceivable that trained experts, such as specialists in the use of explosives, could be used for the “most effective” result. After surveying the building, such specialists can easily position their bomb or bombs in such a way that it will cause the entire building to collapse. What is more likely, however, is that a car bomb containing a large charge of explosives will be detonated in an underground car park or in the immediate vicinity of the high-rise building. The extent of the destruction is consequently a matter of chance and therefore hard to estimate. It is necessary to adopt a country-specific approach to this issue, also taking account of the building’s location and occupancy. An office block in an industrial complex will undoubtedly be a less likely target for terrorists than a city-centre office tower. There have been sufficient examples of such cases in the recent past. If cover for terrorism cannot be excluded for reasons of market policy in a country with high exposure to terrorism, then it is perfectly appropriate to assess the PML at 100% of the sum insured. Earthquake exposure must also be taken into account for the PML during the operational phase. The major earthquakes experienced in recent years caused such extensive damage to high-rise buildings as to make repair impossible (Mexico City, Kobe). Older buildings and particularly buildings with “soft storeys” (see Section 4.4) were worst affected. When estimating the earthquake PML in regions exposed to this risk, it is therefore important to establish whether modern anti-seismic construction codes exist and whether they were also applied to the high-rise building under consideration. If these construction codes are known to have been violated or if there are any doubts in respect of compliance, then a PML of 100% should also be assumed for earthquakes. The same applies to windstorm, volcanic activity and other natural hazards in regions exposed to these particular risks. 5.3.4 Accumulation control This problem must be considered above all in conjunction with the perils windstorm, earthquake and fire primarily in respect of buildings covered by CAR, EAR or fire policies.

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This naturally only applies to areas or cities with a corresponding concentration of values in the property insurers’ portfolios. Munich Re has already stated its views on this subject in a number of publications; it has also drawn attention to the need for accumulation control and issued corresponding explanations. As far as the natural hazards windstorm, earthquake and flooding are concerned, the values currently at risk in the respective exposure zones or specific catastrophe scenarios are determined using computer-aided data analyses. The respective loss accumulation zones and corresponding loss potential are then determined for these catastrophes. We will gladly answer any queries from our clients on such issues.

5.4 Underwriting considerations Different construction methods, different finishings and the exposure to external influences demand careful analysis of the resultant risks. For this reason, only approximate rates can be specified for insuring the construction and operational phases of high-rise buildings, despite the availability of statistical analyses extending over many years. 5.4.1 Contractors’ and erection all risks insurance When determining the premium rate, different degrees of exposure during construction of the high-rise building (foundations, structural works, finishing) must be taken into account in the same way as the proportion of temporary auxiliary structures (e.g. retaining walls) and their exposure during use. The following documentation should normally be available: – General drawing and layout plan of the site with an overview of the immediate surroundings – Technical details concerning the construction method, progress made and materials used – Breakdown of the contract price according to the most important parts (foundations, structural works at underground levels/floors above ground, finishing) – Schedule of construction work, particularly in conjunction with regularly recurring natural phenomena (e.g. monsoon) – Expert report on soil conditions – Description of the foundation method, retaining wall, possible lowering of the groundwater table – Layouts, longitudinal and transverse sections of the building in different planes, details of the most important structural parts (e.g. facade connections). The premium rates required for underwriting are determined on the basis of an assessment of these documents and of the structural analyses. Premium rates are not

5 Insurance

specified here on account of the considerable scope for variation and additional, highly commercial influences prevailing in the various markets. Where the deductible is concerned, difficult soil conditions and the exposure to windstorm due to structural reasons or progress in construction must also be taken into account in addition to the long time frequently required for the construction work. If necessary, it must be possible to calculate the risk by including suitable special terms, limits of indemnity or exclusions. This applies particularly to high-rise buildings over 500 m, as their exposure to windstorm has not yet been sufficiently investigated, and when using inadequately tested materials and construction methods. 5.4.2 Contractors’ plant and machinery When determining the premium rate, the number and period in use of the highly exposed cranes must be taken into account in addition to the scope of cover. Elevators for transporting materials to great heights are less exposed to loss, since they are firmly connected to the shell on the outside or are located inside the high-rise building. 5.4.3 Decennial liability insurance The level of premium rates for this cover is also largely dependent on the specific market, the market situation and scope of cover. For this reason, the premium rate can range between 5‰ and 15‰ for the ten-year period. In addition to the premium, the principal must also bear the costs of technical inspections; these costs vary in line with the size and complexity of the project. The waiver of a deductible is prescribed by law in some markets; as a rule, however, the long term of this cover should be taken into account when determining the amount of excess. 5.4.4 Insurance of buildings, fire insurance As with all risks, the terms, quality of the risk and price are components which must be taken into account when underwriting high-rise buildings. Where the terms are concerned and particularly in conjunction with the scope of cover, the statements made in Section 5.1.5 apply, with “named perils” and “all risks” as the two main forms of cover. All the criteria listed in Section 4.2.4 must be considered in order to determine the quality of the risk. Under no circumstances should the underwriter assume that all statutory measures have been taken or that the quality of the risk is satisfactory simply because of compliance with the regulations. As the cases outlined in Section 4.2.3 have shown, the standard of protection applying when the highrise building was erected may well be far below the standards required today. It therefore follows that the construction practice and standard of protection must be considered individually. Particular attention must be paid to

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structural fire protection, as well as sprinkler protection commensurate with the risk. Although quantitative statements cannot be made, the probability and frequency of a loss occurring and the amount of loss to be expected will be lower if the quality of the risk is “good” than in the case of inadequately protected buildings. Higher shares can therefore be written in the case of “good” risks. In the case of extended basic cover, the risks due to supplementary perils, e.g. earthquake, windstorm, hail, flooding, water damage and glass breakage, must naturally also be taken into account in the underwriting. The same also applies to all-risks covers, special attention being devoted to the exclusions (see Section 5.1.5). General statements cannot be made here with regard to the price, i.e. premium rate. Claims experience and local exposure play a vital role in pricing, as do commercial considerations. Above all, the premium calculation also has to take into account supplementary perils such as natural hazards and political risks on the basis of individual loss exposure. The quality of the risk is naturally also reflected in the price; in other words, appropriate protective measures or generally “good” quality of the risk will result in a correspondingly lower premium rate.

5.5 Reinsurance In the majority of cases, there should be no particular problems in reinsuring individual high-rise buildings, provided that the necessary conditions have been met for the individual classes (contractors’ all risks, erection all risks, insurance of the building, fire insurance, decennial liability insurance, third-party liability insurance). On account of the different forms of cover, the main thing is to ensure that the policies in question are allocated to the appropriate classes, e.g. engineering insurance, third-party liability insurance and fire insurance (as described in detail in the preceding sections) and that the risk is properly assessed in line with the respective policy. Special need for reinsurance may arise, however, in the case of individual major high-rise-building risks and extensive accumulation risks resulting from the concentration of numerous high-rise buildings within a small area. This is indeed the case with skyscrapers of record-breaking heights and sums insured due to the high fire PML or the risk of earthquakes or windstorm in areas particularly prone to such hazards. The need to insure these risks will normally exceed the capacity of the local insurance market. The same also applies with regard to decennial cover for such risks. However, even reinsurers with the soundest financial backing cannot accept unlimited liability. In some cases, it will therefore be necessary to introduce a limit of liability which makes the risk more manageable and easier to calculate; this will also ensure that the available underwriting capacity can be fully utilized. The type of limits to be speci-

89 EXTERIOR HOIST

5 Insurance

fied in the classes concerned should be decided in accordance with individual requirements. In addition, limits of liability also facilitate matters for insurers and reinsurers; liability accumulations can be determined and updated more easily and precisely. This is particularly important in countries or regions which are constantly exposed to natural hazards, such as Japan or California, where comprehensive insurance cover is provided for a large number of high-rise buildings in an area of intense seismic activity and where there is consequently a substantial accumulation risk. Even in these extreme cases, however, the demand for adequate insurance cover is and was satisfied by insurers and reinsurers working together as partners. This is particularly true of insurance markets marked by high investment and growth. The benchmark has been raised in terms of what insurers require and expect of reinsurers, especially with regard to know-how, professional competence, market experience, innovativeness and ultimately also adequate capacity combined with long-term financial strength. Munich Re is optimally positioned to meet these challenges. The lead it has built up globally over the decades in terms of experience and information is based on extensive databases. With the help of modern computer-based tools, the latest data can be rapidly made available to the insurers. Comprehensive geo-scientific and underwriting analyses of these data by experts at Munich Re’s head office and in the engineering offices around the world ensure that natural hazards and loss potential can be reliably assessed. Experienced underwriters are available to our clients at more than 45 business units and subsidiaries in our international organization, all of which are linked online to the head office. This enables us to advise prospective clients on assessing risk, defining the terms of insurance, and determining and providing the required reinsurance capacity. During the period of cover, our specialists can actively participate in inspections, loss prevention or settlement of complex losses. Extensive know-how and the courage to take innovative steps make it possible for our specialists to provide our clients with professional support in developing new concepts for cover or new insurance products. We will gladly answer any queries by our clients, provide further information or outline possible solutions in connection with reinsurance and our range of services.

6 Summary and outlook

6

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6 Summary and outlook

The historical and technical development of high-rise buildings as seen from the point of view of insurers and reinsurers has been outlined in the individual sections of this publication. Needless to say, development does not stand still, and therefore by the time this publication appears in print some of the technical details described here may already have been superseded by research, progress and the pressure of costs.

Most of the statements made here, however, will continue to apply to future high-rise buildings. Despite certain reservations and all economic bottlenecks, the quest to reach for the sky and erect higher and higher buildings goes on, particularly in Asia. For this reason, we as insurers and reinsurers will continue to devote our attention to these projects in the new millennium. We are also confident that, thanks to our worldwide know-how and long-standing experience, we will be able to offer our clients solutions in line with the specific risks involved.

1

Die Bezeichnung höchstes Bauwerk der Welt beansprucht zur Zeit der Fernsehturm von Toronto, der neben dem Ontariosee 553 m in den Himmel ragt. Das zweitgrößte Bauwerk ist der Fernsehturm von Moskau mit 537 m.

2

Eine Geschoßflächenzahl von 12 bedeutet, daß die Gesamtfläche aller Geschosse über Straßenniveau maximal das Zwölffache der Grundstücksfläche betragen darf. . Bentonit ist ein spezielles Tonmineral, das das Mehrfache seines Gewichts an Wasser absorbieren kann und dabei auf das 8–15fache seines Volumens anschwillt. Es bildet an den Wänden des Schlitzes eine Schicht, wodurch dieser gegen Materialeinbruch stabilisiert wird, ohne den Aushubvorgang zu beeinträchtigen.

3

4

Weitere Details sind in unserer Brandschutztafel nachzulesen.

5

Advance loss of profit.

Picture credits

Page

Picture No.

Page 158

Title

Picture credits

Cover

01

Manhattan, New York

Image Bank, A. Becker, Anzenberger, Loccisano

6

02

San Gimignano

Picture Press, Riedmüller

7

03

Monadnock Building

Library of Congress

9

04

The Tower of Babel

AKG, Berlin

10

05

Equitable Life Building

Museum City of New York

10

06

Home Insurance Building

Philipp Holzmann, Frankfurt a. M.

10/11

07

New York panorama

Image Bank, A. Becker

12

08

HongkongBank Headquarters Building, Hong Kong

HongkongBank

12

09

Messeturm, Frankfurt am Main

Werkfoto HOCHTIEF, Essen

13

10

Petronas Towers, Kuala Lumpur

Munich Re

15

11

Hong Kong skyline

Pacific Century, Hong Kong

16

12

Flatiron Building, New York

Photonica, B. Hubert

18

13

La Grande Arche, Paris

Munich Re

19

14

Canary Wharf, London

Munich Re

20

15

Traditional and modern buildings in peaceful co-existence

Laif, Arthur Selbach

23

16

Chrysler Building, New York

Image Bank, B. Frommer

27

17

Details from planning documents

Munich Re

28

18

Extract from a technical report

Munich Re

29

19

Opening in an apartment complex

Munich Re, J. Eber

30

20

Large-bore pile foundation process

Bilfinger & Berger

Various stages in the diaphragm wall process

Bauer Spezialtiefbau, Schrobenhausen

30 32/33

21

Diaphragm wall rotary cutter


34

22

Retaining wall to protect neighbouring buildings

Munich Re

34

23

View of a building pit with completed retaining wall


36/37

24

Examples of high-rise buildings with steel skeletons

Munich Re, A. Kleiner

38

25

Deformation and bending momentum due to wind with the core construction method

Munich Re

38

26

Background: Commerzbank Building

Minimax

39

27

Deformation and bending momentum due to wind with the outrigger truss method

Munich Re

39

28

Examples of core construction methods and bundled tubes

Munich Re

40

29

Varying load distribution with tubes and bundled tubes

Munich Re

41

30

Example of the arrangement of bundled tubes

Munich Re

41

31

Steel skeleton

Büro X

43

32

View from the headquarters building/Headquarters of BMW A. G. in Munich

Pressestelle BMW A. G., Munich

44

33

Facade assembly

Munich Re

47

34

Ceiling installation

Top: Munich Re

47

35

Double flooring

Bottom: Fa. Mero, Würzburg

50

36

Elevator in the World Trade Center, New York

Visum, Michael Wolf

51

37

Elevator demonstration by Otis

Left: Otis

51

38

Maintenance

Right: Laif, REA/P. Bressard

52

39

Renovation of a high-rise building

Top: Werkfoto BASF

52

40

Pile-driving machinery for working in basement floors

Bottom: Bauer Spezialtiefbau

55

41

Petronas Tower

Munich Re

56/57

42

Trend towards ever-taller modern high-rise buildings

Büro X

58/59

43

The Millennium Tower – a vision for the 3rd millennium

Forster and Partners, London

60/61

44

Petronas Towers, Kuala Lumpur, Malaysia

Munich Re

62/63

45

Sears Tower, Chicago

Anzenberger, G. Sioen

64/65

46

Empire State Building, New York

Visum, J. Röttger

66/67

47

Messeturm in Frankfurt am Main

Laif, C. Emmler, P. Langrock

69

48

Additional heat recovery via piling foundations in the Commerzbank high-rise building

Minimax

71

49

Fully automated building site

Obayashi Corporation, Japan

72/73

50

Jin Mao Building

Shanghai Educational Publishing House

74/75

51

Shanghai Pudong

Airphoto International Ltd./Pacific Century Publishers Ltd.

76/77

52

New York

Visum, M. Wolf

76/77

53

China, Guangzhou

action press, SABA-Laif, REA/Sinopix

78/79

54

New York

Image Bank, A. Becker

80/81

55

New York: view from the World Trade Center

Visum, M. Wolf

82/83

56

New York

Munich Re, J. Eber

87

57

Fire in the Broadgate Building, London: sunken roof support beams

Munich Re

88

58

Fire-protection information

Munich Re

90/91

59

Escalator destroyed by fire

Munich Re

92/93

60

Fire in the Meridien President Tower, Bangkok

Munich Re

94/95

61

Meridien President Tower, increased risk of fire during the final fit-out phase

Munich Re

96/97

62

Difficult fire-fighting conditions in the Meridien President Tower

Bangkok Post

98

63

Combustible waste increases risk of fire

Munich Re

100

64

Limited evacuation routes through smoke-filled stairways

Bangkok Post

101

65

Hong Kong, fire in the Garley Building

South China Morning Post

102

66

Towering inferno

Munich Re

Page 159

Picture credits

Wooden panels on a glass facade destroyed by a car-bomb attack/Interior view of one floor 103

67

Difficult fire-fighting conditions

106

68

Special coating on the steel skeleton guaranteeing adequate fire resistance

Munich Re Top: HongkongBank, Minimax, Eissing-Kister

106

69

Fire-detection system in the Messeturm in Frankfurt

Bottom: HOCHTIEF/Landis & Gyr

109

70

Atrium in a bank building

HongkongBank

112

71

Dynamic-pressure approaches: effects from friction impact wind speed

Top: Munich Re, A. Kleiner

112

72

Typhoon tracks for Japan and California

Bottom: Munich Re

113

73

Representation of wind impact on a building’s ground-bearing pressure

Munich Re, A. Kleiner

116

74

Impact of earthquake loads on the centre of gravity

Top: Munich Re, A. Kleiner

116

75

50 t and/or 90 t heavy dampers

Bottom: Mitsubishi Heavy Industries Ltd.

117

76

Effective arrangement of dampers in high-rise buildings

Mitsubishi Heavy Industries Ltd.

119

77

Earthquake in Kobe, Japan

Munich Re

120

78

Corroded supply lines

Munich Re, W. Schromm

120

79

Tension crack in a crosslinked polyethylene pipe

Munich Re, W. Schromm

124/125

80

Blasting of a high-rise office building

Iduna Versicherung

128/129

81

Interior of a high-rise building following a bomb attack

Munich Re, J. Eber

130/131

82

Wooden panels on a glass facade destroyed by a car-bomb attack/Interior view of one floor

Commercial Union, G. Evans

133

83

Aircraft debris after a plane ploughed into the Empire State Building

Associated Press

134

84

Aircraft crash onto a block of flats in Amsterdam

action press, F. Bründel

135

85

Bomb attack on a federal government building in Oklahoma, USA

action press, SABA

143

86

Heavy plant in use during foundation work


146

87

Dangerous workplace

Laif, REA/Sinopix

150/151

88

World Trade Center, New York

Laif, P. Gebhard

154

89

Exterior hoist

Munich Re

References Title

Author

Architektur des 20. Jahrhunderts

Gossel/Leuthäuser

Architektur und Städtebau des 20. Jahrhunderts

Lampugnani

Das Hochhaus in Gegenwart und Geschichte

Goldberger (1984)

DIN 1055, Part 4

Publisher

DVA Stuttgart Issue 8/86, 5/89

Elevators and Escalators

Strakosch

Erdbebenprognose

Geo 3/96

Facility Management 1/95

John Wiley & Sons, New York Bertelsmann Verlag

Fassadengestaltung

Dr. Gartner

Fire Letter No. 24

Munich Re

Hongkong, Architekturmuseum Frankfurt a. M.

Exhibition catalogue (1993–94)

La Grande Arche

Tˆete Défense (1990)

Marvels of Engineering

National Geographic

Prestelverlag

Massivbau Vertiefungsvorlesungen

J. Schlaich

Universität Stuttgart

Messeturm Frankfurt a. M.

Kolodziejczyk

Technik am Bau (Periodical)

Messeturm Frankfurt a. M.

J. Murphy

Schriften zur Architektur der Gegenwart

MR Handbook “Water Damage Insurance”

Munich Re

Preliminary Report on the Northridge Earthquake

WSSI

Schadenspiegel 1/84

Munich Re

Schadenspiegel 1/95

Munich Re

Schadenspiegel, Special issue 1994

Munich Re

Skyscrapers

Starrett

Charles Scribner's Sons, New York

Special publication “Earthquakes of the Caribbean Plate” Munich Re (1976) Special publication “Earthquake Mexico ’85”

Munich Re (1985)

Special publication “Windstorm”

Munich Re (1990)

The Empire State Building

Theodore James, Jr.

Harper & Row, New York

The Skyscraper Book

Giblin

T. Y. Crowell, New York

Tuned Active Dampers

Mitsubishi Heavy Industries

Wie man Wolken kratzt

P. v. Seidlein

Wolkenkratzer – Ästhetik und Konstruktion

J. Schmidt

A publication of the Munich Reinsurance Company © 2000 Münchener Rückversicherungs-Gesellschaft Address for letters: D-80791 München Germany http://www.munichre.com E-mail: [email protected] Design: Büro X, Hamburg Order number 2840-V-e The paper used for this brochure was produced without chlorine bleaching.

Dumont Verlag

HighRise Building Construction Profile

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