2014 Issue 3

TheStructuralEngineer

March 2014

Volume 92 | Issue 3

The flagship publication of the Institution of Structural Engineers

ENGINEERING THE FUTURE AKT II’s design for Europe’s largest biomedical research institute

STRUCTURAL GLASS 1976 MONTREAL OLYMPICS INSOLVENCY – A ROUGH GUIDE E-PILE SCHEDULE FOR EUROCODE DESIGN PRESTRESSED COMPOSITE TRUSS BRIDGES

TSE27_01 COVER.indd 1

27/02/2014 09:04

Design more effectively than ever before.

FIXPERIENCE, the new generation of software from fischer.

The new modular structure includes engineering design software and special application modules: C - FIX: The new user friendly fischer anchor design.

WOOD - FIX: For fast calculation of your application using fischer Power-Fast and Construction screws.

REBAR - FIX: To design post-installed reinforcement connections in concrete constructions.

MORTAR - FIX: To determine the volume of injection resin for bonded anchors.

Whether you are a craftsman, a design or structural engineer, FIXPERIENCE, the fischer software suite, gives you safe and reliable support in designing and fulfilling your projects. Download your free software at www.fischer.co.uk/fixperience

p02_TSE.03.14.indd 2

26/02/2014 11:03

›

www.thestructuralengineer.org

Contents

PAGE 10 The Francis Crick Institute

TheStructuralEngineer March 2014

PAGE 20 Prestressed composite truss bridge design

3

PAGE 38 Structural glass

TheStructuralEngineer Volume 92 | Issue 3

Upfront

Professional guidance

Opinion

5

Editorial Institution news: Young Structural Engineering Professional Award 2014 Report of the Institution’s EGM

30 Project management failure: The 1976 Montreal Olympics

56 Verulam

6

Project focus

34 Managing Health & Safety Risks No. 25: Personal safety on site

At the back 60 Products & Services

Technical

10 The Francis Crick Institute, London 20 Prestressed composite truss bridge design

59 Book review: Steel Bridges

32 Contracting party insolvency - a rough guide

38 Technical Guidance Note: Introduction to structural glass

62 Services Directory 63 TheStructuralEngineerJobs

45 Composite and Steel Construction compendium Part 3: The concrete flange of a composite beam 48 Concrete Bridge Design and Construction series No. 3: Prestressing for concrete bridges 53 FPS E-Pile Schedule for Eurocode design

The Structural Engineer www.thestructuralengineer.org PRESIDENT Nick Russell BSc (Hons), CEng, FIStructE, FICE, MCMI CHIEF EXECUTIVE Martin Powell

EDITORIAL MANAGING EDITOR Lee Baldwin t: +44 (0) 20 7201 9120 e: [email protected] DEPUTY EDITOR Ian Farmer t: +44 (0) 20 7201 9121 e: [email protected]

TSE27_03 Contents.indd 3

ADVERTISING

EDITORIAL ADVISORY GROUP

DISPLAY SALES Patrick Lynn t: +44 (0) 20 7880 7614 e: [email protected]

Research: Ian Burgess, MIStructE Project focus: Allan Mann, FIStructE Features: Don McQuillan, FIStructE Technical: Chris O’Regan, MIStructE Opinion: Angus Palmer, MIStructE Professional guidance: Simon Pitchers, MIStructE

RECRUITMENT SALES Paul Wade t: +44 (0) 20 7880 6212 e: [email protected]

DESIGN SENIOR DESIGNER Craig Bowyer CREATIVE DIRECTOR Mark Parry

Price Institution: £345 (12 issues incl. e-archive and p&p) Individual: £120 (12 issues incl. p&p) Individual - student: £40 (12 issues incl. p&p) Single copies: £35 (incl. p&p) Printed by Warners Midlands plc The Maltings, Manor Lane Bourne, Lincolnshire PE10 9PH United Kingdom

© The Institution of Structural Engineers. All non-member authors are required to sign the Institution’s ‘Licence to publish’ form. Authors who are members of the Institution meet our requirements under the Institution’s Regulation 10.2 and therefore do not need to sign the ‘Licence to publish’ form. Copyright for the layout and design of articles resides with the Institution while the copyright of the material remains with the author(s). All material published in The Structural Engineer carries the copyright of the Institution, but the intellectual rights of the authors are acknowledged. The Institution of Structural Engineers 11 Upper Belgrave Street London SW1X 8BH United Kingdom t: +44 (0) 20 7235 4535 f: +44 (0) 20 7235 4294 e: [email protected] The Institution of Structural Engineers Incorporated by Royal Charter Charity Registered in England and Wales number 233392 and in Scotland number SC038263

27/02/2014 11:07


26/02/2014 11:03

›



Upfront Editorial

5

Upfront Last call for research (in The Structural Engineer) Lee Baldwin Managing Editor

Last month we announced an exciting collaboration between the Institution and world leading academic publisher, Elsevier, to publish a new research journal from early 2015. Structures aims to bring academics and industry practitioners closer together, as a worldclass forum for cutting-edge research that has direct applicability to (and can be discussed/debated by) practicing engineers. Institution members will be able to access all of the content published in Structures for free. We’re already working with Elsevier on a number of background activities in preparation for launch; indeed we expect the Structures webpage and electronic manuscript submission platform to be live and operational shortly. We’ve also finalised the journal’s Editorial Board which, led by Imperial College London’s, Prof. Leroy Gardner, contains some of the most influential names in global structural engineering research today. This information will be available via the Structures website very soon. While the other sections of The Structural Engineer (Technical, Project focus, Professional guidance etc) will continue as usual, the practicalities of launching an Institution research journal mean that this magazine will cease its publication of research material from January 2015. Taking into account the time it takes for research submissions to be reviewed, revised, re-reviewed, edited and published, it’s necessary to impose a deadline of 31 March 2014 for the submission of research material to The Structural Engineer. If you have prepared a research article for consideration, please submit before the deadline, or alternatively, delay your submission for a The Structural Engineer provides structural engineers and related professionals worldwide with technical information on practice, design, development, education, training and research associated with the profession of structural engineering, and offers a forum for discussion on these matters promotes the learned society role of the Institution by publishing peer-reviewed content which advances the science and art of structural engineering provides members and non-members worldwide with Institution and industry related news provides a medium for relevant advertising

TSE27_05 Editorial.indd 5

short while until the Structures platform is live. We’ll do our best to minimise the gap between the deadline and the launch of the new platform, but there may be a few weeks in-between. We’ll keep you updated with developments via this page and other Institution news channels. The first of two Project focus articles in this issue discusses the design challenges that a team from AKT II were faced with, in the delivery of the structural/civil engineering aspects of the largest biomedical research facility in Europe. The construction of London’s Francis Crick Institute is detailed on page 10. Meanwhile, in ‘Prestressed composite truss bridge design’ on page 20, authors describe a form of design, citing several recent projects, that despite being rarely seen outside of France and Japan, can provide significant cost savings for medium/long span concrete bridge projects. Our technical series’ from the SCI and CBDG continue on pages 45 and 48 respectively, while a short article from the UK Federation of Piling Specialists (FPS) can be found on page 53. Coinciding with the publication of the Institution’s new technical guide Structural use of glass in buildings: second edition, this month’s Technical Guidance Note ‘Introduction to structural glass’ can be found on page 38. The series on structural failure will be taking a break after this issue – hopefully to return next year. In this month’s article, Sean Brady explores the catalogue of problems surrounding the 1976 Montreal Olympics project on page 30. After a two issue hiatus, Verulam makes a welcome return on page 56.

The Institution has over 27,000 members in over 100 countries around the world is the only qualifying body in the world concerned solely with the theory and practice of structural engineering through its Chartered members is an internationally recognised source of expertise and information concerning all issues that involve structural engineering and public safety within the built environment supports and protects the profession of structural engineering by upholding professional standards and to act as an international voice on behalf of structural engineers

The Structural Engineer (ISSN 1466-5123) is published 12 times a year by IStructE Ltd, a wholly owned subsidiary of The Institution of Structural Engineers. It is available both in print and online.

Contributions published in The Structural Engineer are published on the understanding that the author/s is/are solely responsible for the statements made, for the opinions expressed and/or for the accuracy of the contents. Publication does not imply that any statement or opinion expressed by the author/s reflects the views of the Institution of Structural Engineers’ Board; Council; committees; members or employees. No liability is accepted by such persons or by the Institution for any loss or damage, whether caused through reliance on any statement, opinion or omission (textual or otherwise) in The Structural Engineer, or otherwise.

27/02/2014 09:06

› www.thestructuralengineer.org

6


Upfront Institution news

Judges wanted for Young Structural Engineering Professional Award 2014 The Institution is seeking judges for its Young Structural Engineering Professional Award 2014, which opened for entries on 21 February. The Institution is looking to broaden its judging panel with experienced professionals working in industry, to identify outstanding achievement among its young members. As a judge, you will play a key role in the decision making process. Responsibilities will include completing a preliminary score sheet, attending the judging day in May 2014, and providing an analysis of shortlisted projects. Joining the judging panel provides an excellent networking opportunity at the Awards Luncheon, a chance to meet some of the brightest young talent in the industry, and an opportunity to get more involved with the Institution and its work. Travel expenses will be paid for attending the judging day. To be considered for this voluntary role, please email: [email protected] with the following information:

exciting new talent at work in the structural engineering profession and is open to any member aged 30 years or under. In addition to the cash prize, the winner will receive two tickets to this year’s worldrenowned Structural Awards event. The runner up will receive a prize of £500. Winning the award is a unique opportunity to be marked out as “one to watch” among the Institution’s global membership, and an internationally recognised mark of outstanding achievement in structural engineering. The award winner will become an ambassador for the Institution and the

• A CV (including date of birth) • A 1 000 word report on ONE engineering project with which you have had significant involvement, describing the project and including supporting images • A video recorded presentation (max. five minutes) on the selected project and your role in it • A 250 word opinion piece on what structural engineering means to the world • A 300 word endorsement from your employer

• Full name • Current occupation • A short statement (no more than 100 words) outlining your relevant industry experience and why you would like to become a judge The deadline for applications is Monday 24 March.

About the Young Structural Engineering Professional Award This prestigious annual award, re-launched this year, includes a £1 500 cash prize. The Institution presents the award to recognise

profession, showcasing the crucial role engineers play in shaping the built environment - and providing identifiable role models for young people interested in engineering careers. Institution Chief Executive, Martin Powell, said: “The Young Structural Engineering Professional 2014 Award is an important opportunity for the Institution to recognise and reward our younger members. I would encourage any ambitious young engineer to enter the competition. Winning is a great way to stand out from the crowd, gain recognition from your peers, and access networking opportunities with the world’s leading industry figures.” To enter, candidates must prepare and submit:

Last year’s joint winners: Kai Qu and Harriet Eldred

The judging day will take place in May 2014. For more information on the Young Structural Engineering Professional 2014 Award, visit: bit.ly/YSEP2014

Report of the Institution’s EGM An Extraordinary General Meeting of the Institution of Structural Engineers was held at 11 Upper Belgrave Street, London SW1X 8BH, on Friday 17 January 2013 with Mr N Russell, BSc(Hons), CEng, FIStructE, FICE, MCMI (President) in the chair. A quorum of more than 10 voting members was present. Mr D M Powell (Chief Executive) read the notice convening the meeting. It being agreed that the minutes of the 104th Annual General Meeting, held on 25 July 2013, (published in The Structural Engineer, September 2013) be taken as read, it was duly proposed and seconded that they be confirmed. The resolution was passed and

TSE27_06 News v2.indd 6

the minutes were signed by the Chairman. The Chairman then introduced the Special Resolution, of which due notice had been given. He stated that a commentary had accompanied the notice. It was proposed by Mr N C Train (Past President) and seconded by Mr Y K Cheng (Past President): THAT, subject to the approval of Her Majesty’s Most Honourable Privy Council, Bye-law 8 of the Institution be altered and amended as set out in Schedule 1 hereto, subject to such changes, if any, as the Privy Council may require and the Board of the Institution accept.

During discussion of the resolution a poll was demanded by Mr R T Walker (M). His demand was not supported by at least 19 other Voting Members present, as required by Regulation 5.8 for a poll to take place. Upon being put to the meeting the Special Resolution was adopted on a show of hands by Voting Members present. There being no further demand for a poll the Chairman declared the Special Resolution to be carried. The business for which the meeting had been convened having been concluded, the Chairman then declared the Extraordinary Meeting closed.

27/02/2014 09:06

IDEAS

US

FOR A SM A RT A PPROACH TO TH E B U I LT EN V I RON M ENT

YOUNG STRUCTURAL ENGINEERING PROFESSIONAL AWARD

20 14

C L E A R N OW ?

WS P: TH E B R A I N S TO PICK

The Award The Institution of Structural Engineers’ Young Structural Engineering Professional Award recognises outstanding new talent at work in the structural engineering profession and is open to any member, worldwide, under the age of 30.

For a smart approach to careers www.wspgroup.co.uk/careers #brainstopick

Winner: – £1,500 cash prize – Two tickets to the industry’s most prestigious awards ceremony, The Structural Awards in November 2014 Runner-up: – £500 cash prize

How to enter: All entries should be submitted via the online form by Friday 11 April 2014. 4OlNDOUTMOREABOUTTHEAWARDANDENTRY process please visit bit.ly/YSEP2014 or contact the Events Team: [email protected]

P07_TSE.03.14.indd 24

©Photo credit: Serpentine Pavillion by Adam Bowie, Flickr

The prizes will be presented at the People and Papers awards ceremony in June 2014. Winners will also be invited to act as ambassadors of the profession on behalf of the Institution, participating in Institution activities and providing media comment where appropriate.

26/02/2014 11:08

The Institution of Structural Engineers is pleased to announce the launch of Structural use of glass in buildings: second edition which is now available to purchase from the Institution’s bookshop. .SHZZOHZPUYLSH[P]LS`YLJLU[[PTLZ\UKLYNVULZPNUPÄJHU[PUJYLHZL in its use within our built environment, especially as a structural material. This Guide updates and revises The Institution of Structural Engineers’ well renowned and respected text Structural use of glass in buildings. This Guide is not intended to be a code of practice, but rather a principal source of information and reference for those interested in the structural use of glass. It also provides general guidance sourced from all over the world that is based on existing good practice as a starting point from which designers can carry out further studies and research according to circumstances.

Institution member price: £45 Non-member price: £70

It is intended that this Guide be used by experienced structural engineers and construction industry professionals. It assumes varying degrees of prior knowledge of the structural use of glass, in VYKLY[VWYV]PKLHUPUZPNO[PU[VKLZPNUTL[OVKVSVN`ZWLJPÄJH[PVU materials and techniques in the design and construction of glass structures. 3PRL[OLÄYZ[LKP[PVU^VYRLKL_HTWSLZHYLNP]LU[OYV\NOV\[[OL .\PKLMVY[OLZPTWSLKLZPNUVMNSHZZLSLTLU[ZZ\JOHZÅVVYWSH[LZ beams and columns. Connection design is also considered, as JVUULJ[PVUZWSH`HZPNUPÄJHU[YVSLPU[OLKLZPNUVMNSHZZLSLTLU[Z Unique to this edition is the inclusion of advice on the modelling of glass structures within structural analysis computer applications [VYLÅLJ[[OLJVU[LTWVYHY`^VYRPUNWYHJ[PJLZ^P[O[OLPUJYLHZLK reliance of such tools. This Guide also addresses some of the V[OLYPZZ\LZ[OH[TH`PUÅ\LUJLZ[Y\J[\YHSILOH]PV\YVYWSHJL constraints on what can be achieved, such as extreme loading JVUKP[PVUZHUKÄYLWYV[LJ[PVU

Visit shop.istructe.org or email [email protected] for more information.


26/02/2014 11:11



9

Project focus Peer-reviewed papers focusing on the structural engineering challenges faced during the design and building stages of a construction project.

10 The Francis Crick Institute, London Since winning the structural engineering commission in 2008, AKT II have been responsible for all construction information on the primary structure. As the structural aspects of the project near completion, the team report on the challenges involved in designing the largest biomedical research institute in Europe.

20 Prestressed composite truss bridge design Authors describe a form of bridge construction that, despite being rarely seen outside of France and Japan, can provide significant cost savings for medium to long span concrete bridge projects.

TSE27_09 Project focus opener.indd 9

27/02/2014 09:07

›

10

Project focus The Francis Crick Institute


S

The Francis Crick Institute, London

Figure 1 Aerial view of site

R. Partridge MEng, CEng, MIStructE Director, AKT II Ltd, London R. Baptista Licenciatura MSc (Hons), DIC Technical Director, AKT II Ltd, London C. Neugart Dipl.-Ing. (FH) Associate, AKT II Ltd, London

S

Figure 2 Architectural render

approach completion, AKT II highlight the structural challenges involved with such a prestigious development and discuss how a continual focus on construction methodology throughout the design process can lead to efficiencies in such a testing economic climate.

Architecture and form

Introduction Currently under construction opposite St Pancras International railway station, The Francis Crick Institute will create a world leading centre for biomedical research and innovation; the largest of its kind in Europe. Formerly known as the UK’s Centre for Medical Research and Innovation (UKCMRI) the project is now named after the scientist that, together with James Watson, discovered the structure of DNA in 1953. The development is a unique partnership between six of the UK’s most successful scientific and academic organisations

TSE27_10-19 PROJECT FOCUS 1 CRICK v3.indd 10

namely: Cancer Research UK; the Medical Research Council; the Welcome Trust; University College London; Imperial College London and King’s College London. Expected to be complete in 2015, The Francis Crick Institute will provide approximately 80 000 m2 of net floor area for 1250 scientists (Figures 1 and 2). AKT II has been working on the project since winning the structural and civil engineering commission in 2008 and is responsible for the delivery of all construction information on the primary structure. As the structural packages

The architectural concept led by HOK with PLP breaks down the massing of the development into interconnecting components enveloped by a form derived and articulated by the surrounding context. This is realised by splitting the development into four blocks above ground which are linked by a series of floors and bridges providing an opportunity for scientists from different fields to integrate (Figures 3 and 4). The laboratory areas which are planned over the first four floors above ground, are designed to be adaptable - allowing change with new emerging scientific opportunities. This requirement had to be respected in the architectural and structural design. From the fifth floor, springs a vaulted steel roof enveloping the blocks and providing architectural continuity with the ground by forming four full height façades between the blocks. Within the roof volume the remaining floors provide plant space. This change in function is articulated by the delineation from terracotta and curtain walling cladding of the laboratory floors below, to the louvred curving steel roof above. It was this

27/02/2014 09:08


11

Substructure

Figure 3 Architectural concept

The development boasts an impressive basement volume which extends over the entire footprint of the building covering a plan area of approximately 150m × 70m, with a depth of 16m to the west and 9m to the east. This step in basement level was a strategic volumetric decision driven by AKT II early in the project, to limit the basement depth to the elevation bounded by St Pancras International. Internally, two levels of laboratory space served by two interstitial floors make up four levels to the west, while the eastern section provides uninterrupted volume for plant. Figure 5 illustrates the long section of the building. Constraints and adjacencies The site was underlain and was surrounded by all manner of obstructions and third party assets (Figure 6). These included 120 year old cast-iron gas mains to the north, brick arch sewers to the north and west, The British Library’s buried pumping station to the south and the buried structure of the Kings Cross Thameslink Station to the east, which also provides support to the new roof of St Pancras International. The site itself was home to the Somers Town Railway Goods Depot constructed in the 1880s and was underlain by a dense grid of masonry footings on mass concrete - to a depth of 8m in some areas.

Figure 4 Structural concept

S

Figure 5 Indicative long section

integration of form and cladding types which provided a distinctive link to the features of St Pancras International which was key to the successful planning application. A third of the building is located below ground to reduce the visible massing and therefore, the link between below ground and above ground construction was critical to the success of the programme.

BIM

S

Figure 6 Site constraints


The scale and complexity of the development, together with the sheer number of interfaces between disciplines, drove the need for the team to work within a central building information model (BIM) led by HOK, which has been utilised since stage C and up to and including procurement and construction, with an aspiration for asset tagging at FF&E handover. This process was complicated by a demanding build programme which ran ahead of the conclusion of detailed design, and as such AKT II’s work streams had to follow suit, with 2D construction drawing, 3D coordination modelling and 3D parametric design for the curved roof all running in parallel.

Basement construction methodology Given that the basement makes up almost a third of the development, the construction methodology was key to the overall construction programming, sequencing and cost. With multiple level basements, 'top down' construction has clear programme advantages but comes with a cost premium. Potentially, the method also carries a greater risk profile due to the confined nature of the build and elements of 'blind' construction. The choice of construction methodology was also linked to the foundation and retaining wall solutions and thus a holistic approach was required, integrating the technical design parameters of all the structural elements with the overall project objectives. AKT II therefore carried out a thorough assessment of all available options ranging from full 'top-down' techniques utilising plunge piling, to traditional 'bottom-up' methodologies with temporary propping and raft solutions. Between these two extremes were many hybrid permutations where the benefits of different options are balanced. All our options were evaluated in collaboration with the wider design team, balancing cost and programme with logistic and engineering efficiencies to converge on an optimum solution for the development.

27/02/2014 09:08

›

12



W

S

Figure 7 Open dig construction to second lower basement (LB2)

Figure 9 Top down construction

S

Figure 8 Basement construction (facing south)

The chosen method utilised top-down techniques from the second basement level (LB2), therefore balancing the programme advantages of simultaneous construction activities in the west basement with the benefit of 'blue-sky' build to the east (Figures 7-9). This decision was further reinforced by the dense array of heavy obstructions thought to be located in the top 8m of excavation. Another major driver for this solution was a strategic decision to provide a cantilevering retaining wall, resulting in open dig to LB2 uninterrupted by any temporary propping – although the east basement did require temporary diagonal propping as the requirement of the plant room below pushed the basement dig below its original 8m limit. Retaining walls As discussed, a pre-requisite for the chosen construction sequence was a solution which could limit lateral deflections and associated ground movements in the temporary condition as a free cantilever of 8m. As such, a 1.0m thick diaphragm wall was adopted. The benefit in stiffness coupled with advantages in watertight construction favoured this solution over the more traditional piled-wall alternatives. The reinforced concrete diaphragm wall was constructed using panels with lengths of 2.8m - 7.0m which were installed under a bentonite support fluid to a maximum depth of 28m. To ensure a robust interlock


between the panels, a bespoke precast stop-end equipped with central water bars was developed and located at every joint (Figure 10). Given that the integrity of the wall is paramount, a dense array of sonic logging tubes were also installed, providing an accurate method of locating any inclusions prior to excavation. Ground movements and gas mains The choice of construction sequence (i.e. the retaining wall solution) was predicated on achieving movement profiles which would not adversely affect the surrounding third party assets. Very early in the design process AKT II collaborated with Geotechnical Consulting Group (GCG) to undertake extensive ground modelling. A full 3D non-linear finite element analysis was generated, modelling the complete basement including all adjacent structures and services. The model was also built incrementally, such that predicted movements could be assessed over time, during the different phases of the construction sequencing. Early assessments of movements were important not only to validate the proposed solutions, but also to commence the approval process with statutory authorities and third parties. This was particularly critical for the two 120 year old low pressure gas mains running parallel to the northern boundary of the site. These mains have an external diameter of approx. 950mm and the

N

Figure 10 Diaphragm wall precast stop-end

nearest is located approx. 1m from the back of the diaphragm wall and with a cover below pavement level of only 350mm. Early results of the analysis suggested that although the nearest gas main may experience horizontal movements of up to 45mm, the rate of change of gradient of the pipe was relatively smooth over the majority of the basement due to the stiffness of the diaphragm wall system. As such, the largest rotations were found to occur at the extremities of the site where abrupt changes in stiffness occur. Monitoring of the mains continued throughout the project and as as a result, a number of joints have been

27/02/2014 09:08


13

encapsulated to the two extremities of the basement dig to mitigate the risk of the lead joints opening up in areas of high rotation (Figure 11). Piles and plunge columns Following the chosen construction methodology, single large diameter bored piles were used and installed from LB2, thus pulling the basement slabs off the critical path. A total of 260 bearing piles were required, extending into the Thanet Sand layer some 40m below ground. The piles generally range from 900 - 1900mm diameter with 2400mm diameters located below transfer structures supporting loads of up to 26MN. To enable top down construction from LB2 level, plunge columns were utilised in the form of fabricated steel box sections 'plunged' into the piles via bespoke temporary steel guide frames. The plunge columns were designed to a maximum size of 600mm × 600mm with a varying plate thicknesses of 30 - 55mm to suit the various temporary load cases, accounting for limited construction of the upper frame prior to

"The development is a unique partnership between six of the UK’s most successful scientific and academic organisations" installation of the basement propping slabs (Figure 12). In the permanent condition concrete encasement provides composite action to the plunges, and transfer to the in situ columns above is ensured via steel head plates and welded shear studs. Load transfer into the piles is achieved through friction only, leading to a maximum embedment depth of 5m into the piles. Parts of the LB4 basement laboratory will be occupied by equipment which will

require the surrounding structure to be of a low relative magnetic permeability. As such, there are areas where the use of epoxy coated stainless steel reinforcement is necessary. These requirements also affect four of the plunge columns and so precast concrete plunges with stainless steel reinforcement were designed and procured in lieu of stainless steel plated columns (Figure 13). These precast columns were 775mm × 775mm in size and matched the final dimension of the concrete encased columns. They weighed approximately 15t each. The ends were slightly chamfered and a centrally located tube cast-in to allow any trapped air to escape. This solution not only solved the electromagnetic interference issue but also now exists as a precedent for precast plunges, a process that AKT II and Laing O’Rourke will be progressing as an alternative to the traditional steel fabricated sections in the future. Hanging floors A key driver for the design of the interstitial floors at LB1 and LB3 was to limit slab depth, maximising head room

N

Figure 11 Gas main encapsulation

W

Figure 12 Steel plunge columns

E

Figure 13 Precast plunge column


27/02/2014 09:08

›

14



in the laboratories below, as well as providing a continuous uninterrupted flat soffit for application of the air seal. The construction also had to support dense plant and servicing equipment and be able to provide flexibility in terms of the nonrepetitive and non-standard nature of the required service penetrations. The final decision was to adopt a precast concrete solution of lattice planks and in situ topping with an overall structural thickness of 175mm. This shallow depth was made possible by hanging the slabs from the floors above with steel rods at half-grid centres (Figure 14). The pre-fabrication of this system led to efficiencies in the quality control of the dense array of service penetrations as well as benefits in programme, cost and logistics. However, this advantage is only realised if the builders' work drawings (which define the manufacture) are fully coordinated. As such, the management of this process between design team, manufacturer and sub-contractors became critical. The requirement for a flat and continuous concrete soffit meant that panel joints had to be fully grouted and that the cast-in steel hanger connections could not be exposed at the underside of the slab, leading to a construction where bearing steel plates were recessed into the top of the precast panels and connected to the steel rods (Figure 15).


Superstructure The four blocks above ground are formed by reinforced concrete frames up to seven levels on the northern bar and nine on the southern (Figure 16). Internal circulation between the different blocks is ensured by either central floor plates of composite slabs on steel beams and trusses, spanning up to

N

Figure 14 Hanging interstitial floors

S

Figure 15 Hanger detail

20m, or steel bridges with spans up to 24m. The cladding of each block includes curtain walling to the main elevations, with terracotta panels applied to the back of cores and risers. Due to the internal volumetric planning there is a need for various transfer systems to bridge load over spaces which need to be column free, such as the loading bay, lecture theatre and areas of upper plant floors – these are materialised by either large reinforced concrete beams, steel fabricated

27/02/2014 09:09


15

beams or deep trusses (Figure 17). The chosen structural grid was the result of an intense space planning exercise balanced with structural efficiency and cost, and as such a defined laboratory module of 3.1m yielded a grid of 6.2m × 9m. Reinforced concrete flat slab construction supported on square reinforced concrete columns, provides the structural frame; realising the inherent benefits of flat slab in terms of flexibility, adaptability, construction and services integration - not to mention the mass required to provide adequate damping to the vibration affects. Stability Given the plan dimensions of the building (approx. 150m × 70m), movement joints are incorporated at the junctions between the four blocks carried through the roof, such that each block can move independently, minimising the effects of thermal expansion and shrinkage movements. This jointing strategy means each of the four blocks has its own stability system, formed by pairs of cores or dedicated shear walls. All stability concrete elements continue through the basement and are further assisted by the perimeter retaining walls. The stability of the roof steelwork that springs from the last concrete slab is provided by a combination of dedicated braced bays and frame action. Precast construction Laing O’Rourke has extensive experience of the precast industry and so, when appointed as main contractor in 2011, they collaborated with AKT II to construct various elements of the primary structure, using precast techniques. In terms of horizontal elements, this was limited to the hanging interstitial floors in the sub-structure but included all superstructure floors above ground level. For vertical components all the cores were changed to precast construction and there


N

Figure 16 Superstructure construction

N

Figure 17 Transfer trusses

was also a desire to change the columns to precast. The main advantage of precast construction is off-site fabrication that allows a reduction of site operations and materials such as temporary formwork and fixing of reinforcement, leading ultimately to a faster and more efficient construction process. Furthermore, the quality control measures of a factory environment provide efficiency in the fabrication and construction processes, especially with respect to the quality of finish. Nevertheless, detailing at joint locations is a significant challenge, particularly when buildings are not designed with precast construction in mind from the outset.

S

Figure 18 Precast lattice construction

Precast lattice slabs were chosen as the floor construction for both the interstitial slabs and superstructure slabs and consist of precast reinforced concrete biscuits, which are used as a temporary formwork, and form the final soffit of the slabs. These biscuits are nominally 75mm but this was reduced to 65mm in the interstitial floors to maintain structural efficiency over the shallow depth. In order to provide the required stiffness in the temporary condition, lattice reinforcement girders are cast into the precast panels which also aid the transfer of horizontal shear between the biscuit and topping, assuring full composite action is developed (Figure 18). The joints between precast floor

27/02/2014 09:09

›

16


N

Figure 19 Twin wall construction

panels form slightly weaker points within the slab due to the fact that the bottom reinforcement layer sits above the precast biscuits at these splice locations. This affects the local stiffness and subsequently the vibration performance of the slab. There is also an impact, from a punching shear point of view, if the preference is to fix the punching shear reinforcement on site such that it is located above the biscuit i.e. at a reduced depth. The proposal for the core walls was to use a twin-wall technique consisting of two 75mm thick precast panels connected by lattices of reinforcement. The hollow middle section is then filled with in situ concrete to provide the integral structural element. The required reinforcement necessary for axial forces and bending moments is cast into the precast panels, therefore minimising the amount of 'loose bar' needed to be fixed in the in situ middle section (Figure 19). Given the construction sequence and programme, the intention was always to construct the cores per floor, i.e. even for the in situ option, these would not be slipped or jump-formed ahead of the concrete frame. This meant that the introduction of the twin wall system, clearly suited to a floor by floor approach since the panels require propping to the slab below, did not impact on the timings of the construction.



Various precast elements are also exposed as part of the final architectural language of the Institute and thus the factory control of these components was critical. An example of this is the exposed edges of the floor slabs where coffer units are used as part of the internal finishes hierarchy (Figure 20). Although these precast techniques had been proven in a number of previous projects, this method of construction had never been used in a facility with such a stringent vibration criteria, unlike in situ concrete construction, a more traditional and therefore 'tried and tested' method. Thus a rigorous research and analytical study was carried out to accurately predict the behaviour of the precast system. Vibration A critical part of the briefing process related to structural-borne vibration. Very early in the design process AKT II presented the client with a range of options; from global flexibility within the structural frame to local isolation at equipment level. This evaluation resulted in a solution utilising deeper slab thicknesses than if driven by strength or deflection alone, but provided the client with full flexibility throughout the entire facility, with every floor designed to a vibration threshold limit of 50mm/s (VCA) – approximately 16 times stricter than the typical limit for

commercial spaces. For the more sensitive equipment such as MRIs and NMRs, which need to operate in considerably less responsive environments (up to VCF), local isolation was clearly efficient and as such this equipment is located on local mass concrete inertia bases on the stiffer basement floors. This result was evidenced through a rigorous modelling exercise using a combination of analysis software and in-house interface coding to prove this vibration limit could be maintained over all floors. Extensive modelling using different support conditions, damping effects and ranges of applied modes was carried out with alternative mesh densities and material properties to balance the theoretical results with an expected reality. The precast construction alternative also had to undergo the same rigour, especially given that the technique has not yet been proven in a facility with such stringent vibration limits. Firstly, an exercise was carried out with Laing O’Rourke to try and balance pallet efficiency with structural

27/02/2014 09:09


17

S

Figure 20 Exposed precast coffer units

Figure 21 Lattice plank layout


optimisation. Key from a structural point of view was the minimisation of joints across the floor plate and the locating of necessary joints away from areas of maximum sagging moments. The conclusion of this study was to adopt a panel configuration for a typical bay, where the precast panels have been split into column strips, spanning between columns in the short direction, and middle strips, which in turn span between the column strips (Figure 21). Thus, joints between panels are not located in the middle half of bays, i.e. away from zones of maximum sagging moment. Following the agreed layout, one key assumption to the modelling and analysis process was how to address the joints. When the precast slab experiences sagging moment, the concern was that the pattern of cracking to the soffit, which would typically spread across the whole area, is forced to occur at the panel joints, resulting in larger cracks than in the in situ case. Initially therefore, the depth of slab at joint locations was modelled as the actual depth minus the depth of the precast panel. The width

27/02/2014 09:09

› Project Focus The Francis Crick Institute


18

S

Figure 22 Vibration analysis a) In situ concrete slab

b) Precast concrete slab

Figure 23 Roof steelwork section

c) Precast concrete slab with precast vertical elements

Figure 24 Roof analysis model

d) Voided precast concrete slab layout

of the joint however, was more problematic and hence was the subject of a series of sensitivity studies. There were concerns that the relative size of the joint compared to the slab bays would lead to inaccuracies in the finite element meshing. Various joint widths and mesh patterns were tested and results


were similar with no significant anomalies – the response factors slightly increased as the joint width increased, as expected. However, deviations were deemed minor and a decision was taken to proceed with a joint width of 300mm to achieve the best compromise between modelling accuracy and analysis time. In terms of supports and connections, and in order to assess the effects of precast vertical elements, connections were modelled using a range of fixity ratios. The resulting affects of some of these iterations for one of the block floors can be seen in Figure 22. The results of this exercise suggested that while the precast behaved in a similar way to the in situ, there was generally a slight decrease in the structural response of the precast, and so further detailed analysis was carried out to try and reverse the trend. The

results of this final analysis predicted that it was possible to improve the response of the precast by tailoring the precast detailing and interfaces to align with the behavior of the frame. Such adaptations included: reducing the precast biscuit to 65mm to maximise lever arms; further optimisation of panel layout; fully grouting all joints; limiting chamfers to precast corners and maximising the concrete strength. Steel roof The envelope of the building, which encompasses the roof and the four façades, is formed by two vaulted volumes that enfold the four blocks below. This distinctive strategy relates to the form of the adjacent Barlow Shed at St. Pancras International, with the delicate engineering of the roof contrasting with the robust masonry of the

27/02/2014 09:09


19

façades with spans ranging from 3m - 15m. The largest cantilever occurs along the south-east edge producing the need for a denser and heavier two-directional structural system, in order to limit deflection and vibration effects caused by wind uplift and aerodynamic instabilities (Figure 24). The cladding to the roof is generally aluminium louvres with glass louvres above the north and south façades, and photovoltaic panels on the lower south elevations. The façades can be split into two types. The east and west façades are straight vertical walls that support the roof cantilevering edges at the respective ends, with their structure formed by continuous steel columns, propped at slab levels by horizontal trusses that span the full width of the atrium i.e. 8m on the west and 24m on the east (Figures 25 and 26). The north and south façades follow the curvature of the envelope all the way to ground floor and are also propped at floor levels by horizontal elliptical sections spanning between cores and risers. All the façade steelwork will be fully exposed as part of the architectural language, hence careful detailing of all connections is critical to the architectural intent – these include thermal break details where there is potential for areas of cold bridging.

W

Figure 25 East façade architectural render

base of the building. The resulting geometry is derived from a torus which marries the desire to curve the roof about both elevations with the spatial requirements of the plant below. The rationalisation of this surface to an optimised structural frame followed an intense iterative and parametric modelling exercise between AKT II and PLP that utilised Bentley’s Generative Components as the preferred base platform. Fundamental to this process was defining the structural zone and offset from the theoretical surface, followed by rationalisation of the hoop curvatures from B-splines to arcs within specified deviation tolerances. As the cycles converge towards a true structural frame model, an intelligent structural model was created which formed the interface between our analysis software and the structural


component of the BIM model, leading ultimately to the production of construction information. The roof structure consists of steelwork frames springing from the first plant floor on the north and south elevation which curves over each block to form enclosures to the plant floors (Figure 23). The leaning nature of the members set out in the north-south direction contrasts with straight members in the east-west direction and hence (and in order to maintain verticality of the steel columns) there is an offset between columns and lines of structure which adds complexity to the roof framing. Another issue is the cleaning and maintenance strategy, which requires a continuous east-west recess for the mobile unit, resulting in larger supporting steelwork due to the travelling loads. All roof edges cantilever over the different

N

Figure 26 East façade analysis model

27/02/2014 09:09

›

20


Project focus Composite truss bridges

Prestressed composite truss bridge design N. Terada BEng, MEng, PE Jp (Central Nippon Expressway, Japan) K. Terada Fellow of JSCE, PE Jp (Kazumi Terada Technical Adviser Office, Japan) D. Saito BEng, MEng, PhD, DIC (Mott MacDonald, UK)

Introduction Prestressed composite truss bridges are a novel form of bridge construction, that can provide substantial savings for the construction of medium to long span concrete bridges (spans longer than 50m). They typically consist of steel diagonal truss members, and top and bottom concrete slabs with prestressing cables (Figure 1). The bridge can be seen as a type of prestressed concrete box girder bridge, though steel truss members replace the webs. The integration of the steel into the concrete construction means that the total weight of the bridge can be significantly reduced without compromising the stiffness of the structure.

This innovative structural system was developed for the design of the Albois Bridge (Pont d’Albois) in France, in 1985. After the construction of the Albois Bridge, this technology was disseminated and was well received in Japan. Since then a number of composite truss bridges have been constructed in Japan with further technical improvements. For example, the prestressed truss bridge system was combined with the extradosed system in the Fudo-Ohashi bridge1,2 as part of the Yamba Dam project (Figure 2). Despite the track record of the composite truss system and potential economic savings, the composite truss bridge has scarcely been adopted outside France and Japan.

•

Figure 1 Prestressed composite truss construction

•

Figure 2 Fudo-Ohashi Bridge, Japan (Image courtesy of Kouji Oosawa)

This paper describes the composite truss system, citing Japanese projects in which the authors were involved.

Development of composite truss construction Structural system and application The prestressed composite truss bridge comprises steel diagonal members, top and bottom slabs, and prestressing cables. The diagonal member is normally designed as a closed steel section (typically either tubular or square hollow section) to effectively resist axial compression. The compressive diagonal member can be designed as a composite structural component by encasing concrete in the section. The bottom slab can also be replaced by steel members to achieve a further reduction in the self-weight e.g. the Nagata Bridge (Figure 3). In the structural system with the steel bottom flange, prestressing cables can be seen as a cable truss system, which allow applied forces in the main system to be reduced3. The external cables,


21

•

Figure 3 Steel members of Nagata Bridge, Japan

•

Figure 4 Slab and diagonal member connection, Arbois Bridge, France³

especially for long span bridges, typically introduce the prestress force because cranked external cables enable a reduction in forces in the steel diagonal members. Internal cables also are placed within the top and bottom slabs. Since there are no concrete webs, the top and bottom slabs are the only places where the internal cables can be installed, which ensure the tensile stress of the top and bottom slabs remains at an acceptable level. This prestressed composite truss system has the following advantages over a conventional prestressed concrete box girder bridge:

• The total weight of the bridge is 10-20% lower than the equivalent sized box girder bridge • No reinforcement cages and formwork are required for the web construction • The open appearance of the structure can enhance the aesthetic quality of the bridge

Furthermore, the lightness of the bridge allows the span to be longer than a conventional prestressed concrete box girder bridge. The composite truss is particularly advantageous where a long span bridge construction is required and steel construction cannot be adopted. This situation often occurs in mountainous regions, where access for heavy trailers carrying long steel girders and construction cranes is not possible. It should be noted that the reduced weight is also beneficial for balanced cantilever construction. Furthermore, the relative lightness is advantageous in minimising the size of the substructure, especially in a seismic region where the inertia force induced by seismic force governs the foundation design. Panel point The panel point of the truss needs to be capable of transferring axial forces between the diagonal members and the chord members. Since the axial forces need to be transferred between the steel

and concrete, the design of the panel point is a challenging aspect of the design of the composite truss. It should also be noted that steel and concrete components are constructed to different tolerance levels. Steel components are typically produced with a precision to within 1mm, whereas concrete elements are constructed to within 1cm. The design of the component needs to allow for this construction tolerance. The panel point is one of the most important components in the bridge and therefore has attracted widespread attention from design engineers and researchers3. In the Arbois Bridge, the diagonal members were designed to be continuous; therefore the vertical components of the axial forces in the diagonal members are transmitted through the steel member at the panel point. The slab and diagonal members are connected by rebars fixed on to a gusset plate, which is welded onto the diagonal members (Figure 4). It is evident that the rebars are acting as shear connectors to

›

22



•

Figure 5 Boulonnais Viaducts, France

•

Figure 7 Boulonnais Viaducts: precast segment

•

Figure 6 Panel point of Boulonnais Viaducts3

transfer the horizontal component of the axial force in the diagonal members at the panel point. Since the shear force that can be transferred through the rebars is limited, the design resulted in the large gusset plate size, hence the large size of the panel point system. In the Boulonnais Viaducts (Figure 5), the diagonal members were not designed to be continuous; each steel member is directly fixed to the concrete slab through the rebars welded on the end plate of the diagonal member (Figure 6). This bridge was constructed from precast segments (Figure 7) and the location of the panel point for the bottom chord coincides with the interface between two precast segments. The shear force between the two adjoining precast segments is transferred through concrete shear keys provided on the two matching surfaces of the segments at the panel point of the truss. Various types of panel point have also been developed and constructed in Japan3.

Design examples of pressed composite truss bridges in Japan Sarutagawa and Tomoegawa Bridges The Sarutagawa (Figures 8-10) and Tomoegawa (Figure 11) Bridges form part of Shin Tomei Expressway, which was opened to the public in 2011 as an alternative motorway between Kanagawa and Nagoya, located in Shizuoka, Japan. These were

Table 1: Comparison of Boulonnais Viaducts and Sarutagawa and Tomoegawa Bridges Component

Boulonnais Viaducts

Sarutagawa and Tomoegawa Bridges

Construction

Precast concrete segment blocks cantilevering construction with shoring

Cast in situ concrete, cantilevering construction with movable platform

Structural system

Multi-span continuous bridge with bearings

Rigid connection between girder and piers

Panel point

Concrete shear key

Cast steel interlocking system*

*Proposed system at the preliminary design stage


23

S

Figure 8 Sarutagawa Bridge, Japan

N

Figure 9 Sarutagawa Bridge: elevation

N

Figure 12 Cantilever construction using movable platform

N

Figure 10 Sarutagawa Bridge: cross section

N

Figure 11 Tomoegawa Bridge: elevation

TSE27_20-28 BRIDGES v4.indd 23

the first composite truss bridges to be designed for construction in Japan. These bridges were initially designed by Kazumi Terada at the same time as the Boulonnais Viaducts were being designed. It is interesting to note that the main spans of both of the Japanese bridges and the French bridge are approx. 110m long, albeit there are fundamental differences between the Japanese and French designs (Table 1). Short line match cast precast segment construction was adopted for the Boulonnais Viaducts, whereas concrete was cast in situ for the Sarutagawa and Tomoegawa bridges. With the Japanese bridges being located in the mountains, it was not possible to prepare sufficiently large stockyards for the precast segments close to the site, resulting in the bridges being designed as in situ concrete structures. The bridges were constructed with the cantilevering method using a moveable platform suspended by a gantry (Figure 12). A 5m length of the block can be constructed by the gantry system in one cycle and as such, the unit length of the Warren truss was also designed to be 5m for constructability. The Boulonnais Viaducts were designed

27/02/2014 09:12

›

24



Interlocking connection

Figure 13a Proposed cast steel panel point system

as multi-span continuous bridges, whereas the Sarutagawa and Tomoegawa Bridges were designed as frame structures with rigid moment connections between the girders and piers (apart from those shown in Figs 9 and 11 to be elastic bearings). Since the pier heights of the Japanese bridges are considerable (up to 70m), these piers, rigidly connected to the superstructure, can allow longitudinal movements of the bridges caused by concrete shrinkage and temperature change, without causing a significant increase in stress to the superstructure. Owing to the frame action, the longitudinal seismic forces can be resisted by both the superstructure and substructure. This structural system therefore results in smaller bending moments at the bottom of the bridge pier, compared with those for the standard bridge pier which supports the superstructure through bearings. It is evident that this system also allowed the size of the substructure to be minimised. It should also be noted that seismic rubber bearings for this scale of bridge are expensive, typically accounting for 5% of the total superstructure costs in Japan. Hence, it is reasonable to suggest that the proposed system was very cost-efficient under the given design constraints. As previously mentioned, the panel point of the Boulonnais Viaducts was designed as a concrete shear key system, which increased the total weight of the structure. In the preliminary design of the Sarutagawa and Tomoegawa Bridges, Terada and partners proposed a cast-steel interlocking connection for the panel point (Figure 13a). The shear force is transferred though the cast-steel system (Figure 13b). Since the cast-steel has a greater structural strength


Figure 13b Flow of axial forces and location of strain gauge for testing

N

Figure 14b Interlocking connection (in position)

N

Figure 14a Interlocking connection (male)

than the concrete, the structure of the panel point is more compact. Cast-steel was prefered to steel, as the structure can be formed in a complex shape without welding. Omitting any welded parts is beneficial to the structure as it maintains a high fatigue resistance. A gap, which allows for adjustment in positioning of the diagonal members, was provided at the interface between the male and female connections (Figure 14 a and b). Static and fatigue loading tests were performed on the prototype of the proposed panel point4. The results of static testing are reproduced in Figure 15, plotting external force applied to the prototype against strain measured at the strain gauge (the location of which is shown in Figure 13b). The graph suggested that the concrete and the cast steel structure acted as a composite section, with a

"Despite the track record, the composite truss bridge has scarcely been adopted outside France and Japan" slight increase in strain when the load was applied up to 1 500kN. Beyond this level, softening in the structural response was observed, which implies that the composite effect had been diminished and the cast steel interlocking system largely resisted

27/02/2014 09:13


25

the external force. Even when the force reached its maximum level, the strain of the cast steel was just above 500 x 10–6, which was well below the yield of the cast steel. In fatigue testing, 200M load cycles were applied to the proposed panel point at 1.0Hz, such that the axial force in the diagonal members ranged between 1 126kN and 557.1kN, which corresponds to the fluctuation of the force in the diagonal member caused by live loads. Residual strain near the interlocking connection was periodically monitored during the course of testing at the same location as the static load testing. Figure 16 plots the residual strain against the number of load cycles. As can be seen, there is no increase in the residual strain in the structure, suggesting that there was no deterioration in the cast steel due to the cyclic loading. These two test results confirmed that the system has sufficient structural strength and fatigue resistance. Despite success in testing, the proposed system was not adopted for actual construction, since estimated fabrication costs of the panel point turned out to be prohibitive. However, this panel point design was value engineered by Oriental Construction and Nippon Steel in the Shitsumi Ohashi Bridge project, which is explained in detail later. For the Sarutagawa and Tomoegawa Bridges, the following two types of panel point system were designed for construction by a joint venture of Obayashi, Showa Concrete and Haltec. Sleeved panel point connection Two perforated short sleeves, tied together through steel plates, encapsulate the adjoining two ends of the diagonal members (Figure 17). The external surface of the diagonal members and both the internal and external surfaces of the sleeve are deformed in order to ensure suitable bond strength between the steel and concrete members. Perforations in the sleeves also enhance the composite effect (Figure 18). An annulus is provided between the diagonal member and sleeve, which allows a greater level of adjustability for the installation of diagonal members. Despite this advantage in construction, the connection can only provide a limited capacity because the shear force at the panel point needs to be transferred though the concrete. This system was adopted in the mid-span sections of the bridges, where a greater level of adjustability is required during construction.


E

Figure 15 Static loading test results

E

Figure 16 Fatigue loading test results

S

Figure 17 Visualisation of sleeved panel point connection

E

Figure 18 Perforated sleeves encapsulating diagonal members

27/02/2014 09:13

›

26



W

Figure 19 Gusset plate connection

S

Figure 20 Visualisation of gusset plate connection Figure 21 Shitsumi Ohashi Bridge

"The composite truss is particularly advantageous where a long span bridge construction is required" Gusset plate connection The diagonal members are connected though gusset plates using tension control bolts (Figures 19 and 20). This system can sustain a greater level of shear force because the force at the panel point is transferred through the steel components. Despite the advantage in strength, this connection only provides a limited amount of flexibility in placing the diagonal members. This system was adopted near the supports, where the axial forces in the diagonal member are high.

Shitsumi Ohashi Bridge The Shitsumi Ohashi Bridge is located near the Shitsumi Dam across the River Kandogawa, in Shimane, Japan (Figure 21). The bridge consists of two sections: prestressed composite truss and concrete box girder. The length of the maximum span of the bridge is 75m. Although this bridge was designed after the Sarutagawa and Tomoegawa bridges, it was completed


before either of them, due to the scale of its construction, making it the second composite truss construction in Japan. Since the bridge is situated in an area of outstanding natural beauty, visited by many tourists, the aesthetic quality of the bridge was considered important. As such, the client organised a design advisory committee comprising university professors and the local governor. The advisory committee supported the prestressed

composite truss bridge design proposal because the transparent appearance of the bridge would have positive aesthetic effects. The height of the bridge varies along its length, with the intent of avoiding a monotonous appearance. This design was also conceived in order to minimise the size of abutment A1 (Figure 22), and therefore reduce the amount of ground excavation required, which contributed to

27/02/2014 09:13


27

Figure 22 Shitsumi Ohashi Bridge: elevation

W

Figure 23 Proposed panel point system with 'ring shear key'

Figure 24 Proposed panel point system adopted for testing


the sustainability of the project. As mentioned previously, the final design of the panel point for this bridge was based on the system proposed for the Sarutagawa and Tomoegwa Bridges and developed by the contractors, Oriental Construction and Nippon Steel. The cast steel male/female interlocking connection was replaced by a steel tubular pipe or 'ring shear key', welded onto the end plate of one of the diagonal members at the panel point (Figure 23). The use of steel reduced the cost of the system. Static and fatigue load testing were once again performed on the proposed panel point. Figure 24 shows the structure of the panel point system adopted for a series of tests. In static load testing, the external force was applied in a static manner in

27/02/2014 09:13

›

28


Figure 25 Static load testing

order to investigate the structural behaviour and capacity of the proposed system. Figure 25 shows the static load test results, plotting the axial force against the strain measured on the ring shear key. As can be seen, stiff response was observed initially with a slight increase in the strain until the axial force reached 1 770kN, suggesting that the concrete and the cast steel structure acted as a composite section. Less stiff behaviour was observed beyond this point, suggesting that cracking in the concrete had occurred and the concrete at the panel point was no longer transferring the load. The force increased linearly with strain until 3 380kN when first yield of the ring shear key was observed. When the maximum loading of 4 025kN was applied, the panel point still maintained stability, which implies that the ultimate capacity of the panel point was even higher than the maximum load applied. In fatigue testing, 200M load cycles were applied to the proposed panel system, with the axial force ranging between 1 126kN and 552kN. Figure 26 shows the results of fatigue testing, showing the maximum and minimum principal strains when the maximum force is applied against the number of load cycles. It is evident that the values of the principal strains are almost constant. The testing confirmed that a crack on the surface of the concrete, which would appear under high loading, did not lead to a reduction in the stiffness of the global system, meaning that the proposed system would not cause a brittle failure. This is because the ultimate strength of the proposed system is not dependent on the strength of concrete. Since the failure of a panel point would lead to the collapse of the truss, the sound structural behaviour of the panel point is important5.


Project Focus Composite truss bridges

Figure 26 Fatigue load testing

Conclusion

Acknowledgments

The prestressed concrete truss bridge system has been outlined. The technology can provide remarkable cost-saving and construction benefits compared to prestressed concrete box girder bridge construction. The paper has also shown (through several examples) that the panel point is a critical structural element in the design of the composite truss bridge. This is the structural component that differentiates the composite truss bridge from the conventional prestressed box girder system. The authors believe that the technology will continue to provide competitive design solutions for bridge design engineers.

The authors would like to thank Norifumi Wada of Central Nippon Expressway, and Narimichi Oba of Obayashi Corporation for giving us dedicated support and providing up-to-date information on the Sarutagawa and Tomoegawa Bridges. We are grateful to Dr Akio Shoji, a company executive of Oriental Shiraishi Corporation and Tadayuki Noro of Nippon Steel & Sumikin Engineering, who provided valuable information on the Shitsumi Ohashi Bridge. Finally, we would like to thank Brian Stewart, a technical director at Mott MacDonald Special Services Division, for his constructive criticism as well as his help with the English language.

References E1

Hara K. et. al. (2010) ‘Design of second Yamba Dam Bridge and confirmatory experiment’, Bridge and Foundation Engg, 44 (11), pp. 5-11 (in Japanese)

E2

Hara K. et. al (2010) ‘Construction of second Yamba Dam Bridge’, Bridge and Foundation Engg, 44 (12), (in Japanese)

E3

Furuichi K. et. al. (2006) ‘The proposal of a design method of the joint structure for the steel/concrete truss bridge’, Journal of Japan Society of Civil Engineers F, 49 (2), pp. 349-366 (in Japanese)

E4

Honma T. et. al. (1998) ‘Experimental testing on connection systems for composite truss bridges’, Proc. 8th Symp. Development for Prestressed Concrete, pp. 53-64 (in Japanese)

E5

Eguchi S. et. al. (2000) ‘Static and fatigue testing on a joint system for the steel diagonal members of concrete composite truss bridges’, Proc. Jpn Conc. Inst., 22 (3), pp. 1015-1020 (in Japanese)

27/02/2014 11:08



29

Professional guidance Articles that provide information and advice on everyday matters affecting the practicing structural engineer.

30 Project management failure: The 1976 Montreal Olympics 32 Contracting party insolvency - a rough guide 34 Managing Health & Safety Risks No.25: Personal safety on site

TSE27_29 Prof guid opener.indd 29

27/02/2014 09:14

›

30


Professional guidance 1976 Montreal Olympics

Project management failure: The Based on a recently published case study in ASCE’s Journal of Performance of Constructed Facilities1, Sean Brady highlights the systemic management failings that resulted in huge financial cost and significant reputational damage to a high profile project. In 1970, Montreal was awarded the 1976 Olympics, beating bids from Moscow and Los Angeles. World politics had been in Montreal’s favour – there were concerns that giving the games to Moscow or Los Angeles would inflame Cold War tensions, a view subsequently confirmed by the US boycott of the Moscow Games in 1980 and the Russian boycott of Los Angeles in 1984. At the outset, Montreal Mayor, Jean Drapeau, stated that the games would cost no more than $124M and declared they would be the first self-financing games in Olympic history. It was planned that the selffinancing would largely be achieved through the sale of commemorative gold coins and reuse of the Olympic facilities, with Mayor Drapeau suggesting that the ‘real problem’ would be in determining how to spend the Games’ surplus. But over the next six years the dream of a self-financing Olympics would evaporate, with the original cost estimate being revised to $310M in November 1972, before finally blowing out to a staggering $1 500M upon completion. The project stands as a potent example of poor planning, poor project management, fraudulent practice and corruption, and serves as a warning of the dangers of architectural and financial freerein combined with political ambition and immovable deadlines.

Mayor Drapeau and Roger Taillibert At the centre of the debacle were Mayor Drapeau and architect Roger Taillibert. By 1972, after two wasted years where little

TSE27_30-31 PRO_GUID 1 (2 page) v3.indd 30

planning occurred, Mayor Drapeau scrapped the original plans and selected architect Roger Taillibert, without competition, to deliver the games. Mayor Drapeau had become ‘enamoured’ with Taillibert’s Parc des Princes, a 48 000 seater football stadium, which had been recently completed. But neither Mayor Drapeau nor Taillibert had a good track record in financial management. Taillibert’s Parc des Princes had cost $25M, up $16M from its original budget of $9M, and Mayor Drapeau’s 1967 Expo had cost $430M instead of the estimated $160M. A further consideration was that the price tag of $124M for the Montreal Olympics appeared very optimistic – the 1972 Munich Games had cost the equivalent of $600M. In addition to financial considerations, the Olympic complex would include complicated structures: the main stadium and velodrome would be constructed from precast, posttensioned concrete, which presented significant construction challenges. Additionally, the Canadian winter would require consideration, as well as the fact that the design would be completed in France, with the drawings being presented in SI units, which would require conversion to the English system. So now, in 1972, with just four years until the games, a mayor and architect (selected without competition), with a history of cost overruns and delays, equipped with an optimistic budget and a non-negotiable deadline, set out to prepare for a world class event with Mayor Drapeau declaring that “The Montreal Olympics can no more have a deficit than a man can have a baby”1.

Velodrome The contract for the velodrome construction was won by Charles Duranceau at a bid value of $12M. This bid was based on semi-complete plans, and it was the first and last part of the project to be awarded by competitive bidding – the remaining structures would, due to time constraints prohibiting a tender process, simply be awarded to contractors. The design called for three arches supported by abutments, with the structure in plan representing a cycling helmet. The three arches were 171m long and 27m high, composed of precast concrete sections. Due to the arch’s low profile, significant thrust forces had to be resisted at each of the

velodrome’s four abutments. This presented the first technical challenge. At one abutment, the rocky subsoil could not support the thrusts from the roof; a fact that went undiscovered in the original geological testing. In order to address this issue, tendons had to be driven and extensive grouting work was undertaken, blowing the foundation budget of $497 576 to a cost of more than $7M; more than half that budgeted for the entire structure. Delays and cost overruns continued, many caused through waiting for Taillibert to actually finish the plans. Labour issues began to plague the site. Indeed, the velodrome was due to be finished in 1974, in time for Montreal to host the World Cycling Championships, but this deadline passed, forcing the championships to be held at a temporary facility, hurriedly built at the Universite de Montreal football stadium. In order to expedite matters, new subcontractors were hired, cost-plus contract arrangements became the norm, overtime was granted, and after spending $34M the velodrome was still not complete - labour problems alone, such as strikes and overtime, added an estimated $12M to the cost. In what would become part of a recurring theme, Taillibert did not consider value adding engineering. He insisted that architecture was, first and foremost, an art form. When complete the structure would cost $70M, more than five times the original budget. By way of comparison, while the 7 000 seat velodrome cost $70M, the 60 000 seat domed stadium in Seattle, Washington, cost $60M. From a technical point of view, Anton Tedesko, an expert in thin concrete structures, argued that the height of the roof should have been significantly increased to reduce thrust forces, and he said that the structure does ‘damage to the cause of concrete’, arguing that it should have been constructed in steel1 (Figure 1). But, if the velodrome represented a project management failure, the construction of the Olympic Stadium would become a project management nightmare.

Olympic Stadium The Olympic Stadium had an elliptical, as opposed to circular, configuration and it became known as ‘The Big O’ (although it would come to be known as ‘The Big Owe’

27/02/2014 09:15


31

1976 Montreal Olympics in 1972, the final cost of the stadium was $836M. Each seat cost $13 000; more than five times the cost per seat of the New Orleans Superdome.

© BETTMANN/CORBIS

Project failure

as construction progressed). As with the velodrome, the contract was awarded, this time without public tender, to Duranceau. Amazingly, this occurred after it became apparent that he was running into difficulties with the velodrome. The structure was comprised of precast concrete ribs that cantilevered out over the stadium, with the ribs being post-tensioned together - a very inefficient structure compared to a dome with a compression ring at the centre. Due to the roof’s gentle slope, and because it was elliptical in plan, no two sets of ribs were the same. (It is estimated that if they had been, a saving of $20-$30M could have been achieved). Horrendous erection problems would ensue, with rib misalignment being common, which resulted in significant issues because post-tensioning cables had to be threaded through these ribs, requiring perfect alignment. To make matters worse, empty post-tensioning ducts filled with water, froze, and required clearing. The design failed to consider constructability: it left no room for internal scaffolding, resulting in extensive crane use to hold the ribs in place. At one point 80 cranes were in use and it was estimated that doubling the number of cranes would only have increased productivity by 25% because of crane congestion.

TSE27_30-31 PRO_GUID 1 (2 page) v3.indd 31

N

Figure 1 The site for the 1976 Olympics is still a clutter of cranes, rods and boards as workmen press ahead to finish construction. The roof of the velodrome (left) is the only structure to have been completed

With mounting time pressure and fear of embarrassment at missing the opening of the Games, a licence for free spending, corruption and union strong-arming flourished. Cost-plus contracts provided little incentive to reduce costs, and more and more manpower was thrown at the project, with diminishing returns. Poor weather would also hamper construction - at one stage, $400 000 per day was being spent on heating. Costs continued to balloon, until finally, in November 1975, the Province of Quebec stepped in and took the project away from the City of Montreal - with the Province now footing the bill for completion. Drapeau and Taillibert were off the site, and in early 1976 the Province gave an ultimatum to contractors that if work did not speed up, the project would be shut down and the Games moved elsewhere. In perhaps one of the best illustrations of how the system was being abused, this ultimatum resulted in a productivity increase of 500%. But the damage had been done. From the original estimate of $40M in 1970 and the Stadium’s revised estimate of $130.8M

No one reason contributed to the failure. Mayor Drapeau appointed himself project manager and gave free rein to his architect. Time pressure played a key role, preventing a tender process. Taillibert was perpetually late with plans, generating a situation that could easily be taken advantage of, and his designs were complex and paid little attention to constructability. These issues would run through many aspects of the project. In addition to the stadium and velodrome, there were significant issues with the Olympic village and the construction of a viaduct; the viaduct required formwork that was 15 times the cost of conventional formwork, and the contractor only accepted the work on a cost-plus basis and on the condition that he would not be responsible for the completed structure. In the end, a commission of enquiry would blame Drapeau, Taillibert, and the Olympic Organising Committee for the failure, as well as the labour unions, contractors and suppliers that took advantage of the situation. In the aftermath, to retire the debt generated by the Games, the City of Montreal set up a special Olympic Tax on real estate, the Olympic Lottery was extended beyond the games, to 1979, and a special tobacco tax was imposed in 1976. Finally in 2006, a full 30 years following the ‘first self-financing Olympic Games’, the debt was finally paid. Perhaps a key insight into what went so very wrong is best summarised by Taillibert himself: “That’s all Canadians and the American’s talk about – money, money, money” he said, “It doesn’t interest me at all”. Sean Brady is the managing director of Brady Heywood (www.bradyheywood.com. au), based in Brisbane, Australia. The firm provides forensic and investigative structural engineering services and specialises in determining the cause of engineering failure and non-performance. REFERENCES: 1) Patel A., Bosela P. and Delatte N. (2013) ‘1976 Montreal Olympics: Case Study of Project Management Failure’, J. Perform. Constr. Facil., 27 (3), 362–369

27/02/2014 09:15

›

32


Professional guidance Insolvency

Contracting party insolvency - a rough guide • Define insolvency as a termination event Despite grounds for optimism in the UK economy, Peter Westlake advocates a mindful approach during contract preparation, to mitigate potential issues. Whilst the green shoots of economic recovery may appear to have finally arrived, the threat of insolvency remains and may even increase. According to Max Firth, Managing Director at Experian Business Information Services: “as businesses start to think about growth and companies start to restock and rehire, the insolvency rate could well go up as cash flow becomes an issue”. This is a short guide to some of the common insolvency issues that arise in the construction industry.

in their contract • Consider setting up a project bank account. In the event that an employer becomes insolvent, it is likely (although not tested by the courts) that the funds in a properly drafted project bank account will not be swallowed up with the employer’s other assets, but can instead be used to pay the contractor and its supply chain. There is a cost and administrative burden in setting up and maintaining the account which may be uneconomical on a smaller project • Obtain a parent company guarantee. In the event of an insolvency, this can oblige a contractor’s parent guarantor to indemnify the employer for loss and damage, or an employer’s parent guarantor to pay any outstanding amounts due to the contractor. Of course, a parent company guarantee only provides protection in the event that the company providing it is itself solvent

I am an employer and my contractor is insolvent. What do I need to do? First, check whether or not the liquidator will adopt the building contract and complete the works. This will avoid the cost of engaging a new contractor and disrupting the progress of the works. If this is not possible, then consider the following: Immediately • Are all relevant insurances in place? Commonly the contractor is responsible for these. Check with the insurance broker that all premiums are fully paid up • Check whether, under the building contract, the contractor has retained title to the plant, equipment and materials/goods on site, and practically confirm whether or not such items are secure and cannot be removed • Are all copyright licences, drawings and documents fully paid up and provided? You will want to pass these onto any new contractor

Employers could also consider:

How can I spot if a counterparty is headed towards insolvency? Whilst not necessarily determinative, typical signs of insolvency can include:

• employers: repeatedly delaying payments to the contractor; making regular omissions from the project; suspending the project without explanation • contractors: employees not attending site; plant, equipment and materials being removed from site; a general slow down in the progress of work (or work being undertaken out of sequence); non payment of subcontractors’ applications for payment; seeking to change payment mechanisms (e.g. requesting advance payments)

How can I protect myself against the risks of counterparty insolvency? The best protection against insolvency is likely to come in the form of your contract or methods of working which have been agreed before the project begins. For example, parties can:

TSE27_32-33 insolvency v2.indd 32

• Seeking a performance bond • Inserting step-rights in all collateral warranties (saving the time and cost of formally novating each contract) • Including a clause in the building contract allowing it the ability to enter the site to secure and use the plant, equipment and materials and/or • Including a clause in the building contract allowing it to recover the cost of engaging a new contractor to complete the works from the original contractor Contractors could consider the use of an escrow account1. During the course of a contract, if you suspect that a counterparty is at risk of insolvency, it is important to consider whether you have a crystallised dispute. If so, you may want to consider commencing adjudication before insolvency, since you will require a court’s permission to do so, post insolvency. Some steps that employers and contractors can take are as follows:

"The threat of insolvency remains and may even increase" Continuing the works • Is the contractor’s insolvency an event of termination under the building contract? Do you need consent from any third parties in order to terminate the building contract? • Is all the security documentation (e.g. a parent company guarantee or performance bonds) in place and completed? Check the terms of these documents to see how and when the guarantor’s obligations are discharged • Are any payments outstanding to the contractor? Does your building contract provide for set off or abatement?

27/02/2014 09:16


33

• Will the consultants and sub-contractors continue to carry out the works and services? Do your collateral warranties have step-in rights? If so, when are you are obliged to exercise them and what is the process for stepping-in? • Public bodies - will you need to retender the works and/or services to comply with the EU Public Contracts Regulations 20062 ? • Any new contractor may seek to negotiate the building contract. Consider which clauses you are willing to take a view on, ahead of negotiations, in order to keep legal costs to a minimum

I am a contractor and the employer is insolvent. What do I need to do? Immediately • Are all your plant, materials and equipment on site secure? Have you retained title to these goods under the building contract? (In the case of materials incorporated into the building, you will only be able to claim as an unsecured creditor as opposed to owner

of the goods). Are you able to enter the site to recover them? • Are you able to take advantage of any ‘pay when paid’ clauses? The Construction Act 3 generally prevents the use of such clauses, save in the event that the third party who is making the payment is insolvent. You will need to check that the party in question is insolvent for the purposes of the Construction Act (Sections 113 (2) to (5)) Continuing the works • Will any third party (e.g. a funder or tenant) be stepping-in to the building contract? • Are any payments outstanding? You may want to submit a proof of debt form in the event a third party does not step-in to the building contract The content of this legal update is reproduced with the kind permission of Browne Jacobson and is provided for the purposes of general interest and information. It contains only brief summaries of aspects of the subject matter and does

not provide comprehensive statements of the law. It does not constitute legal advice and does not provide a substitute for it. Peter f-k Westlake is a Partner in Construction & Engineering: [email protected] Browne Jacobson is a national law firm offering a unique collection of specialisms across the commercial, construction, corporate, property, public, health and insurance sectors. REFERENCES: 1) Browne Jacobson LLP (2014) ‘What is the issue with late payments?’ The Structural Engineer, 92 (2), pp. 16-17 2) UK Government (2006) The Public Contracts Regulations 2006 [Online] Available at: www. legislation.gov.uk/uksi/2006/5/contents/made/ (Accessed: February 2014) 3) UK Government (1996) Housing Grants, Construction and Regeneration Act 1996 [Online] Available at: www.legislation.gov.uk/ ukpga/1996/53/contents (Accessed: February 2014)

IABSE Annual Lecture

Cool Designs: Engineering at the Ends of the Earth The design of facilities in polar regions presents unique challenges in terms of extreme climate, logistics and sustainable remote living. These challenges and how they have been overcome through thoughtful, innovative design are discussed with particular reference to the recently completed Halley VI Antarctic Research Station, winner of the Sustainability Award at The Structural Awards 2013.

Peter Ayres BEng CEng MIStructE MICE Peter, Senior Structural Engineering Director with AECOM, has over 25 years’ experience leading multidisciplinary design teams on innovative projects around the world and has the rare distinction of having worked on every continent on Earth. He led the AECOM team which won the design competition and delivered the Halley VI Antarctic Station, THEWORLDSlRSTFULLYRELOCATABLEPERMANENTLYMANNED!NTARCTICBASE-ORE recently, he has led engineering teams on major international sports programmes including stadia for the Rio 2016 Olympic Games, Russia 2018 and Qatar 2022.

Annual Institution Events

Conferences & Seminars

Date Time Price Venue

Special Interest Series

| | | |

Thursday 15 May 18:00 for 18:30 start Free RIBA 66 Portland Place London W1B 1AD

Technical Lecture Series

A series of lectures organised in partnership by the Institution and other leading organisations.

British Group

TSE27_32-33 insolvency v2.indd 33

Space is limited, and registration is required in advance. To book your place, please visit the events section of the Institution website, www.istructe.org and register before Wednesday 30 April. If you have any questions please contact the Events Team at [email protected]. Price and venue for the post-lecture dinner is tbc. You can request further details about this during registration.

27/02/2014 09:16

›

34


Research Health and safety

Managing Health & Safety Risks No. 25: Personal safety on site At certain times, engineers will be required to visit construction sites. All sites, whether large or small, are potentially hazardous1. Junior engineers need to become acquainted with not only the general hazards they might encounter, but also the corresponding means of assuring personal health and safety.

Security Many sites now have controlled access i.e. boundaries are made secure and access onto site is restricted. Nevertheless, members of the public aren’t always completely protected. With city centre developments for example (particularly high rise), there are risks of dropping construction materials onto pavements. To limit this risk, it’s customary to sheet cover scaffolding and to provide physical coverings such as crash decks over the pavement. There is also a need to control the risk to normal highway users of site traffic entering and leaving. Even for simple activities carried out on pavements, fencing is commonplace to prevent members of the public falling down excavations or to guard against slips and trips. Warning notices are generally provided. Site security is also required to minimise theft. Unfortunately, all manner of items are stolen including valuable plant. Metal theft is currently a serious problem and includes the theft of manhole covers, which leaves behind the legacy of an opening for somebody to fall down. Theft of copper electric cables is also an issue; presenting a danger to those who attempt to steal, as well as financial loss and general inconvenience to others.

Site entry and egress For all sites, it’s necessary for the contractor to know exactly who is on the site at any given time. Visitors must make themselves known to those in charge and obtain permission before proceeding. On larger sites, control will be quite a formal process, recording both access and egress since if there is a incident, such as a fire, it’s very important for the authorities to be able to account for everyone.

TSE27_34-35 H&S v2.indd 34

Site induction

Delivery of materials/storage

During the process of admittance control, there will be opportunities to advise visitors of any particular hazards that might apply. On larger sites, there will be a formal induction procedure whereby visitors will be informed of hazards and other requirements such as: compulsory PPE2; alarms; means of evacuation; assembly points; welfare and first aid facilities. The main contractor will most likely have staff dedicated to operating the appropriate procedures and will be providing all essential facilities. At the site boundary there will very commonly be warning notices advising of the safety policy and particular hazards such as water or deep excavations and perhaps any special requirements of entry. If an induction or information on site hazards is not provided by the contractor, site visitors should ask for such information before proceeding or, better still, be accompanied. Risks come from lack of familiarity or because site conditions have changed. The greatest dangers apply when personnel first start on a site or if they only visit occasionally or alone.

Materials delivered to site are often heavy and unwieldy. Problems have been encountered during delivery and unloading when materials have shifted suddenly, where stacked materials have toppled or been supported inadequately. Paletted items such as sheeting, stacks of powder materials and waste bins can all be extremely heavy and can overload scaffolds or other temporary floor systems. Lifting items (and dropping them) presents risks8. Articles featured on the CROSS website reveal numerous cases of cranes toppling due to poor practice9. There are also regulations pertaining to the storage of hazardous materials, substances and items such as gas bottles.

Hazards On all construction sites there are common hazards as well as hazards particular to that site. There are likely to be trip hazards, potential openings in the ground and vehicle movements (potentially clashing with people, stacked materials or newly formed construction). There may be projecting reinforcement, nails and other sharp objects. For the workers, there will be generic hazards associated with construction, and with concreting3-4 and steelwork5. In other cases e.g. where construction is over water, a particular hazard might be falling in or contracting disease. In those circumstances, the contractor might provide additional protection, special PPE or perhaps a rescue boat. There might be a requirement for asbestos removal6 or other hazardous substances and materials may be present7. Any site with excavation, from trenches to deep basements, is potentially hazardous. Most sites will require both temporary and permanent electrical power supplies. A key management process to limit risk is simply clearing up. Any site visitor will commonly observe waste materials and spillages, all acting as: trip hazards; potential skin irritants; fire hazards and hygiene hazards.

Machinery and processes Sites require the extensive use of machinery, in activities ranging from simple nailing to heavy cutting, welding, laying of bitumen and other ‘hot’ processes. Nailing (either by hand or mechanically) can cause eye or hand injuries; cutting can cause horrific injuries to limbs or eyes. Hot processes can cause eye damage or burns or even set sites on fire. Any generation of dust is hazardous to health and may act as a catalyst for explosion. This can arise during cutting or demolition. Contractors can control general dust through the deployment of water spray, while local dust problems can be combatted through ventilation and appropriate PPE. To control these risks it is common for the main contractor to institute a ‘Permit to Work’ system. This offers special control over certain processes. Welding for example, might only be permitted if appropriate sub-screening is brought into place and if appropriate fire precautions have been instigated.

Access Access within the site to all levels of working is commonly by ladders or scaffolding10. Scaffolding is a skilled trade which clearly presents hazards if not correctly carried out. Working at height11 is a generic risk responsible for a large number of injuries. It is not considered safe to work anywhere near a free edge without appropriate PPE retention. On some sites, dedicated rope access is the best and safest means for carrying out certain tasks such as inspection and painting. Visitors are unlikely to use such means themselves as special training is required. Visitors might gain access via

27/02/2014 09:18


35

mobile elevating work platforms (MEWPs) or via slung gantries - in which case they should always be accompanied by an appropriately trained operator and should be conversant with essential safety demands, such as wearing a safety harness. A key risk is fear of height or fear of being in certain areas. No matter how intrinsically safe a location might be, if visitors are nervous they should not venture into such situations.

Temporary works Many construction activities require temporary works12; these can be anything from simple trestles and props to major centring and supports for the temporary holding up of bridges prior to completion. Historically, failure of temporary works has been a recurring theme in accidents and engineering catastrophes. The causes are partly human e.g. not giving sufficient attention to something that only appears temporary, and sometimes technical in the sense that predicting the applicable loads and stability conditions can be confusing. Temporary works need to be afforded at least the same level of engineering scrutiny that is applied to permanent works. When this is done properly, there will be

THE INDUSTRY’S MOST PRESTIGIOUS AWARDS CEREMONY IS NOW OPEN FOR ENTRIES

#StructuralAW14

TSE27_34-35 H&S v2.indd 35

appropriate calculations and drawings to the same standard as the permanent works. There will often be a document known as a Method Statement which describes: the background to what is required; how it will be constructed; the equipment required and any necessary checks and controls that should take place as the project progresses. REFERENCES: 1) The Institution of Structural Engineers (2012) ‘Managing Health & Safety Risks No. 8: Common construction hazards’, The Structural Engineer, 90 (9), pp. 25 2) The Institution of Structural Engineers (2013) ‘Managing Health & Safety Risks No. 12: Personal Protective Equipment (PPE)’, The Structural Engineer, 91 (1), pp. 18 3) The Institution of Structural Engineers (2013) ‘Managing Health & Safety Risks No. 20: Working with concrete: associated risks (1)’, The Structural Engineer, 91 (9), pp. 25 4) The Institution of Structural Engineers (2013) ‘Managing Health & Safety Risks No. 21: Working with concrete: associated risks (2)’, The Structural Engineer, 91 (10), pp. 40 5) The Institution of Structural Engineers (2013) ‘Managing Health & Safety Risks No. 18:

Hazards in structural steelwork – fabrication and erection’, The Structural Engineer, 91 (7), pp. 32 6) The Institution of Structural Engineers (2014) ‘Managing Health & Safety Risks No. 23: Dangers of asbestos’, The Structural Engineer, 92 (1), pp. 27 7) The Institution of Structural Engineers (2012) ‘Managing Health & Safety Risks No. 9: Hazardous materials’, The Structural Engineer, 90 (10), pp. 23 8) The Institution of Structural Engineers (2013) ‘Managing Health & Safety Risks No. 15: Using cranes, The Structural Engineer, 91 (4), pp. 30 9) Structural-Safety (2014) Structural-Safety: incorporating SCOSS and CROSS Available at: www.Structural-Safety.org (Accessed: February 2014) 10) The Institution of Structural Engineers (2013) ‘Managing Health & Safety Risks No. 16: Standard tied independent scaffolds’, The Structural Engineer, 91 (5), pp. 12 11) The Institution of Structural Engineers (2013) ‘Managing Health & Safety Risks No. 17: Working at height’, The Structural Engineer, 91 (6), pp. 18 12) The Institution of Structural Engineers (2013) ‘Managing Health & Safety Risks No. 19: Temporary works design and management’, The Structural Engineer, 91 (8), pp. 36

The Structural Awards showcase the work of the world’s most talented structural designers and projects at the forefront of the industry. Being shortlisted, commended or winning an award is a highly recognised accolade across the construction industry. With a range of diverse categories to choose from accommodating a diverse range of structures, now is the time to submit your project for consideration.

Deadline for entries is Friday 18 April 2014.

27/02/2014 09:18

ASD metal services klöckner & co multi metal distribution

ASD Westok design software... Helping you every step of the way

ENTRUSTED TO DESIGN AND DELIVER METAL SOLUTIONS ASD Westok Cellbeam V.9 | Now with Revit® BIM integration. Visit www.asdwestok.co.uk to download our free cellular beam, plate beam, USFB and vibration software.

Call us today on: 0113 205 5270 | e: [email protected] | w: www.asdwestok.co.uk


26/02/2014 11:18



37

Technical Technical Guidance Notes (with junior engineers in mind) written by the Institution’s inhouse technical team and independently peer-reviewed, in addition to submitted articles that are technical in nature; focusing on methods of analysis, material properties and aspects of design of structures.

38 Technical Guidance Note: Introduction to structural glass 45 Composite and Steel Construction compendium Part 3: The concrete flange of a composite beam 48 Concrete Bridge Design and Construction series No. 3: Prestressing for concrete bridges 53 FPS E-Pile Schedule for Eurocode design

TSE27_37 Technical opener.indd 37

27/02/2014 09:18

› Note 35 Level 1

38

Technical Technical Guidance Note


Introduction to structural glass Introduction

As with all materials, the design of structural glass elements requires a good understanding of how the material behaves when placed under load. Glass is a very strong material, but also extremely brittle. This key attribute causes it to fail suddenly as it cannot yield, unlike more traditional materials such as steel and timber. This fact presents unique challenges to structural engineers when designing structural elements to be made from glass. This technical guidance note is an introduction to glass as a structural material. It aims to describe glass in terms of its properties, how it reacts when subjected to various forces and the methods currently being explored and adopted by structural engineers when designing structural glass elements. Much of the guidance written here reflects what is provided in the recently published Institution guide: Structural use of glass in buildings: second edition.

ICON LEGEND

W

Glass as a structural material

W Applied practice

W Further reading

W Web resources

Glass as a structural material Glass has been in use for more than 5 500 years, with the earliest examples being from Egypt in the form of coloured jewellery and small vessels to store liquids. Glass manufacture was further developed by the Romans (Figure 1) who were the first to use it as a glazing material. It was very rare to have glazing in households during the Roman era, being considered highly prestigious. The manufacture of glass changed little during the Iron Age and it wasn’t until the 19th century that technology developed to the point where large glass panes could be created. This led to its wholesale adoption as a cladding material in the 1970s, but its use as a structural material is even more recent. This is one of the reasons why a Eurocode has yet to be created for the design of structural glass elements. It was in the 1990s that the first steps towards a European wide code of practice began with the release of prEN 14174, which eventually became prEN 16612. This is a draft methodology for determining the bending strength of glass using limit state theory, and forms the basis of this technical guidance note.

Glass behaviour Glass does not yield like timber and steel as it is a brittle material. Its failure is difficult to

TSE27_38-42 TGN 4.5p v3.indd 38

N

Figure 1 Roman glass vessels

predict once it begins to fracture. This behaviour has been borne out from destructive tests carried out on 6mm thick sheets of annealed glass using the test method described in EN 1288-2 Glass in building. Determination of the bending strength of glass. Coaxial double ring test on flat specimens with large test surface areas. The results shown in Figure 2 show how unpredictable the failure of glass is.

With glass’s inability to yield, stress concentrations around connections are of great concern as they can become the primary cause of failure. To further illustrate this point Figure 3 shows the stress/strain curve of steel and glass. This indicates how steel extends beyond its plastic limit, yet still manages to maintain its structural integrity, whereas glass will instantly fail as soon as it exceeds its elastic limit.

27/02/2014 09:50


39

Number of results

Results of 740 tests on 6mm annealed glass using EN 1288-2 test method, samples were from nine European factories

Breakage stress N/mm2

N

Figure 2 Test results of failed annealed glass panes, 6mm thick

Figure 3 Stress/strain curves for steel and float glass

after the manufacturing process. In order of characteristic strength (low to high) the forms of glass are:

• wired glass • patterned glass • annealed (or basic annealed) glass • heat-strengthened (or semi-tempered) glass • thermally-toughened (also referred to as heat-toughened, fully-toughened and fullytempered) glass • chemically-toughened (also referred to as chemically-tempered) glass • laminated glass

N

Figure 4 Large deflection theory vs. simple deflection theory

Another behavioural aspect of glass elements is that they typically deflect more than their own thickness. This requires the adoption of large deflection theory when designing structural glass elements, which is an unfamiliar approach to most. Historically, stresses in glass have erroneously been expressed as if small deflection theory were valid using ad hoc methods, leading to the correct thickness. This gave rise to the use of unrealistic allowable stresses and typically led to the oversizing of glass elements by making them thicker than they needed to be. Quoted design stresses for use with small deflection theory will be larger than realistic design stresses used with large deflection theory. This is described diagrammatically in Figure 4.

Glass types There is actually only one core type of soda-lime glass; basic annealed. It is from this glass that all other forms are derived, as they are essentially panes of basic annealed glass that are treated during or

TSE27_38-42 TGN 4.5p v3.indd 39

What follows is a very brief description of each. For a more detailed explanation refer to Chapter 2 of Structural use of glass in buildings: second edition. Wired glass Wired glass has a welded mesh that has been laid into the glass while in its semimolten state. It is sometimes thought of as stronger than basic annealed glass because the wires are thought to act as a form of reinforcement. In fact, the opposite is true as the wires act as crack inducers that weaken the glass. However, they do provide greater post-breakage strength as the wires reduce the risk of glass panes falling from their supports. Patterned glass Patterned glass is manufactured by passing float glass between two rollers (which is why it was formerly known as ‘rolled glass’), one of which forms an impression or pattern in the glass. It is very difficult to ascertain the base thickness (and therefore the strength) of patterned glass. This is due to the varying thickness of patterned glass panes as well as sandblasting and other causes of flaws that tend to be found in the material. Due to this uncertainty the draft methodology text prEN 16612 advises a factor of 0.75 be applied to stress limits for this type of glass.

If, however, the minimum thickness at any section is known and the quality of the glass itself is of a reasonable standard, then it can be used as a base against which the full stress capacity can be applied. Basic annealed glass Commonly made using the Float Process, and hence sometimes referred to as ‘float glass’; it is made from silica sand, soda ash, limestone and salt cake. These are blended together into a cullet, which includes recycled broken glass, and heated in a furnace to 1 500ºC until it becomes molten glass. This is then fed onto a tin bath and controlled heating allows the glass to flow into a uniform thickness. The molten glass is then slowly cooled within an annealing lehr/oven. The speed at which the glass passes through the lehr defines its thickness. Basic annealed glass has no intentional locked in stresses and breaks into large shards when it fails. Heat-strengthened glass Also known as ‘partially toughened’ or ‘semi-tempered’, this type begins life as basic annealed glass which is then heated to approximately 620ºC. It is then quenched by jets of cooled air. This has the effect of cooling and solidifying the surface, before the interior has a chance to cool. As the interior cools it tries to shrink and goes into tension. This is opposed by an equal compression in the quenched surfaces. The maximum thickness of heat-strengthened glass is around 10-12mm due to the way in which it is manufactured. Its mode of failure is similar to that of basic annealed glass, i.e. large shards. Thermally-toughened glass Thermally-toughened glass is sometimes called ‘fully tempered’, although it must be borne in mind that the strength range is different depending on the term adopted. Its creation follows a similar process to that of heat-strengthened glass, but with more pronounced and effective locked-in stresses.

27/02/2014 09:50

› Note 35 Level 1

40



S

Figure 5 Broken thermally-toughened glass

N

Figure 7 Section through laminated glass indicating bending stress within plies for short-term and long-term conditions

In Europe, the surface compressive stress ranges of thermally toughened glass are usually between 80 and 150N/mm2. When thermally-toughened glass fails it breaks into small fragments, commonly referred to as ‘dice’ (Figure 5).

The interlayer can be from 0.38 - 6mm thick and usually comes in multiples of 0.38mm for PVB. Though two layers of glass is the most common arrangement, more than 25 layers have been successfully bonded in an assembly over 100mm thick.

Chemically-toughened glass A different pattern of stresses can be achieved by chemical toughening, in which the composition of the surface of the glass is altered. This is achieved by dipping the panes into electrolysis baths in which the sodium ions on the surface of the glass are exchanged for potassium ions, which are 30% bigger (Figure 6).

Laminates can incorporate many thicknesses and combinations of glass types to give a range of products with the required selection of mechanical and optical properties. Other materials such as polycarbonates can be included. Basic annealed, heat-strengthened and toughened glass can all be laminated.

The structural behaviour of laminated glass depends on the type(s) of glass used and the properties of the interlayer. Generally for the PVB and resin interlayer materials, short-term out-of-plane loads can be resisted by both leaves acting compositely. Due to creep in the interlayer long-term out-of-plane loads are generally considered to act non-compositely, with the loads being shared by each leaf in proportion to their relative stiffnesses (Figure 7). This, however, is not the case with laminated glass that has an ionoplast interlayer. Such panels exhibit some composite action even during long-term loading conditions, although their strength is diminished somewhat. This is due to the stiffness of the ionoplast interlayer decreasing over time.

Material properties The material properties for all types of glass are as follows:

• Density = 2 500kg/m • Young’s modulus = 70 000N/mm • Poisson’s ratio = 0.22 3

The two key advantages of this process over thermal toughening are that there is minimal deformation during the toughening process and thinner sheets of glass can be toughened. The disadvantage is a much thinner surface compressive layer, which is likely to be less resistant to surface damage than the thicker layer produced by thermal toughening. It is also significantly more expensive than thermal toughening.

"There is actually only one core type of soda-lime glass"

TSE27_38-42 TGN 4.5p v3.indd 40

The characteristic strength of glass increases if it is pre-stressed. The values provided in Table 1 are based on a single pane of glass. The coefficient of thermal expansion of glass depends on its chemical composition. In basic annealed glass additives such as alkalines can vary the coefficient from 8-9 # 10-6K-1. Borosilicate glass has a coefficient of 3-5 # 10-6K-1 and purer silicone dioxide glass (i.e. fused silica or quartz glass) has lower values around 5 # 10-7K-1; this makes it useful in the construction of cooking surfaces such as ceramic hobs.

Laminated glass Laminating is a process in which two or more pieces of glass are bonded by means of a viscoelastic interlayer, to give redundancy post breakage. The six materials that are used for the interlayer are:

• polyvinyl butyral (PVB) • thermoplastic polyurethane (TPU) • ethyl vinyl acetate (EVA) • polyester (PET) • resins (such as acrylic) • ionoplast

2

Design criteria

N

Figure 6 Section through toughened glass showing comparison between stresses in thermal and chemical processes

Draft methodology for determining the design strength of glass (prEN 16612) is based on applying material factors on the glass itself, and coefficients that address the

27/02/2014 09:50


41 Table 1: Characteristic strength of common types of glass Glass type

Characteristic strength (N/mm2)

Basic annealed/wired

45

Heat-strengthened

70

Toughened

120

load duration and the way in which the glass has been manufactured. The fundamental tenet of the draft methodology is that the applied bending stress (EULS;d) must not exceed the design bending strength (Rd).

Table 2: Partial factors for variable actions (cq) on structural glass elements Type of element

Partial factor for variable actions (cq)

Primary structure

1.5

Secondary structure

1.3

Infill panel

1.2

Low risk infill panel* *An infill panel whose failure would not cause injury

1.1

The calculation of the design strength is based on the design characteristic strength for basic annealed glass (fg;d) and is determined using the following equation:

Table 3: Values for kmod Duration

Example

kmod

5 seconds

Single gust

1.00

30 seconds

Domestic balustrade load

0.89

5 minutes

Workplace/public balustrade load

0.77

10 minutes

Multiple gust (storm)

0.74

30 minutes

Maintenance access

0.69

5 hours

Pedestrian access

0.60

1 week

Snow load short-term

0.48

1 month

Snow load medium-term

0.44

3 months

Snow load long-term

0.41

50 years

Permanent (e.g. self-weight and altitude pressure)

0.29

fg;d =

Type of glass

As produced

Sandblasted

Float

1.0

0.6

Drawn sheet

1.0

0.6

Enamelled float or drawn sheet

1.0

0.6

Patterned

0.75

0.45

Enamelled patterned

0.75

0.45

Polish wired

0.75

0.45

Patterned wired

0.6

0.36

Table 5: Values for kv

1.0

Vertical toughening

0.6

Load duration has a significant impact on structural glass elements due to the microscopic flaws on its surface. As loads are applied to glass elements these flaws can grow and cause cracking to the point of overall failure of the glass. In recognition of this, coefficient kmod has been developed within prEN 16612 that is always applied when determining the design strength of glass. Table 3 is a list of values for kmod with increasing typical load duration periods. The coefficient ksp concerns what posttreatment the glass pane’s surface may have received prior to installation. The values for this coefficient are listed in Table 4. When considering pre-stressed glass (i.e. heat-strengthened and toughened) an additional expression is installed into the equation for determining the design strength of basic annealed glass:

Strengthening factor kv

Horizontal toughening

Table 6: Values for fb;k Base type

fg;d =

Values of fb;k of pre-stressed glass (N/mm2) Thermally-toughened

Heat-strengthened

Chemically-toughened

Sheet float

120

70

150

Patterned

90

55

100

Enamelled float

75

45

-

Enamelled patterned

75

45

-

TSE27_38-42 TGN 4.5p v3.indd 41

k mod k sp fg;k c M;A

where: fg;k is the characteristic strength of basic annealed glass (45N/mm2) kmod is the factor for load duration (Table 3) ksp is the factor for glass surface profile (Table 4) cM;A is the material partial factor for basic annealed glass (1.6)

Table 4: Values for ksp

Manufacturing process

With the guidance being based on limit state theory, partial factors must be applied to actions. For permanent actions the partial factor (cg) is 1.35. Partial factors for variable actions (cq) are based on EN 1990-1 and are summarised in Table 2:

k mod k sp fg;k k v (fb;k - fg;k) c M;A + c M;v

where: kv is the factor derived from the method of strengthening of the glass (Table 5) fb;k is the characteristic bending strength of pre-stressed glass (Table 6) cM;v is the material partial factor for surface pre-stressed glass (1.2)

27/02/2014 09:52

› Note 35 Level 1

42


Eurocode 0.

Applied practice British Standards Institution (2013) 13/30281354 DC: BS EN 16612: Glass in building. Determination of the load resistance of glass panes by calculation and testing (draft for public comment) London: BSI British Standards Institution (2000) BS EN 1288-2:2000 Glass in building. Determination of the bending strength of glass. Coaxial double ring test on flat specimens with large test surface areas London: BSI British Standards Institution (2002) BS EN 1990:2002 Basis of Structural Design London: BSI


Glossary and further reading Cullet – crushed glass that is ready to be melted as part of the manufacturing process of float glass. Enamel – A glassy material which is melted into the surface of the base glass at high temperatures to form a ceramic coating. Float glass – Glass which has been manufactured by floating the molten glass on a bed of molten tin until it sets, producing a product with surfaces which are flat and parallel. Interlayer – The material used to bind plies of glass together in laminated glass.

Pre-stressed glass – method of re-heating basic annealed glass that introduces a surface compressed stress, thus making it stronger in bending.

Further Reading The Institution of Structural Engineers (2014) Structural use of glass in buildings: second edition London: The Institution of Structural Engineers Eurocode 0.

Web resources The Institution of Structural Engineers library: www.istructe.org/resources-centre/library

Errata In Technical Guidance Note No. 9 (Level 2) ‘Designing a reinforced concrete retaining wall’ (The Structural Engineer, January 2014) the worked example contained errors which impact on the calculation of the bearing stress under the wall base:

• In Figure 3, the location point about which the wall rotates should have been positioned at the level of the base slab and not at the bottom of the heel beam (see revised version below)

Assumed excavation

Corrected pivot point at toe

Incorrect pivot point as used in original Figure 3

• The surcharge should have been included in the bearing stress calculation, which equates to an additional 30kN/m of unfactored load being applied to the section of the base below the surcharge

• The corrected pivot point results in a revised calculated design bearing stress under the base of the wall of 226.06 kN/m2 (maximum) and 51.19 kN/m2 (minimum). Therefore, there is no resulting tension between the soil and the base of the wall

TSE27_38-42 TGN 4.5p v3.indd 42

27/02/2014 09:50

Our Tedds trial will change your world. Automate your daily structural calculations, analyse 2D frames and transform the way you work.

Free software trial Download your Tedds trial at

You can:

You will:

Use a broad library of calculations

Save time & increase profit

Write your own calculations

Reduce calculation errors

Work within Microsoft Word

Improve consistency

Analyse frames

Reduce overheads

Produce transparent output

Enhance QA processes

cscworld.com/TryTedds

Thousands of engineers worldwide choose CSC because we deliver robust and reliable software, alongside expert technical support and training.

0844 686 9300 Lo call Evolutionary software. Revolutionary service.

www.cscworld.com

Delivering:

#cscworldglobal


26/02/2014 11:19

The Institution of Structural Engineers is pleased to announce the launch of Building for a sustainable future: An engineer’s guide which is now available to purchase from the Institution’s bookshop. Sustainability has evolved in recent years to become the focus of national and international attention. This Guide is an evolution of the Institution’s thought-leading Building for a sustainable future: Construction without depletion, published in 1999, and delivers guidance to support and encourage structural engineers to engage with and deliver increasingly sustainable projects.

Institution member price: £45 Non-member price: £70

This Guide refers in the main to the building sector, though it is appreciated that structural engineers also work on many other types of project. However, many of the structural components in such projects have similar sustainability issues to the components of buildings, so much of the content of this Guide is still pertinent and will be useful for projects other than buildings. (S[OV\NOP[PZLU]PYVUTLU[HSZ\Z[HPUHIPSP[`[OH[ÄYZ[JVTLZ[VTPUK for most people, this Guide also includes references to socioeconomic sustainability issues, which are essential in order to achieve a balanced ‘triple bottom line’ approach. This Guide highlights possible actions for structural engineers in dedicated sections entitled ‘What can structural engineers do?’ at the end of each chapter. It is intended that these will help engineers to implement the changes needed to achieve sustainable design, and also provide a summary of those issues V]LYÔPJO[OLZ[Y\J[\YHSLUNPULLYOHZPUÅ\LUJL)PISPVNYHWOPLZ are provided at the end of each chapter for those wishing to seek additional information, as well as references for detailed guidance on the topics covered in this Guide.

Visit shop.istructe.org or email [email protected] for more information.


26/02/2014 11:22

›


Part 3

Technical Composite/Steel compendium


45

Composite and Steel Construction compendium Part 3: The concrete flange of a composite beam This article is part of a series that will gradually build to form a Composite (steel-concrete) and Steel Construction compendium. Written by leading experts from the SCI, the articles aim to provide a real insight into composite and steel construction, to help practicing engineers get the most from these materials.

Introduction So far in this series we have looked in general at the development of composite products and design codes, and several detailed issues concerning shear connection. In this article we will look at the concrete slab, considering the beam effective flange, and how disruption to the concrete can be accommodated. Further information can be found on www.steelconstruction.info. The exploitation of a concrete flange is what makes a composite beam more structurally efficient than the bare steel section on which it is based. For normal downstand beams compression is transferred from the upper steel flange into the concrete slab, via discrete shear connectors running along the line of the beam. The in-plane stiffness of the concrete slab enables the localised compressive forces to disperse into the concrete over a certain breadth, which, as discussed in the following section, is represented by an ‘effective breadth’ (or width) in design codes. Figure 1 shows a recent beam test with an effective breadth of concrete supported at its edges on secondary beams, supported by cantilevers off the beam being tested (to represent unpropped construction). Because a part of the slab acts structurally in conjunction with the steelwork, any disruption to the concrete may have a detrimental

W

Figure 1 Long span unpropped composite beam prior to testing (University of Bradford, October 2013)

TSE27_45-47 CSCC 3 v3.indd 45

effect. This is true not only for the slab but also for the composite beams. Two forms of disruption are discussed in this article; holes passing through the depth of the slab, and pipes cast into the body of the slab.

The effective flange breadth Considering the easily understood example of a genuinely simply supported beam (with no slab continuity at either end), there is no compression in the slab at the supports. As the first row of shear connectors is ‘passed’ moving towards the centreline of the beam, some force is introduced. At mid-span the compressive force is at maximum, and a function of the number of connectors present. The force distributes away from the beam centreline into the slab as it increases in magnitude. Codified guidance The limits of the concrete put into compression by the shear connectors are not defined by straight lines. However, to make life much easier for the designer, design codes adopt this simplification when defining the effective breadth. Both representative and codified limits are shown in Figure 2. For the majority of the span EN1994-1-11 adopts the same value as BS 5950-3.12, so the effective flange has a breadth up to span/4 (when double connectors are present the designer is allowed to add the few centimetres that separate them – b0 in Fig. 2). If an adjacent beam is not sufficiently far away, as an alternative criterion the flange is assumed to stop at the halfway point between beams, as no overlap of flanges is permitted. In the end quarter spans, the Eurocode recognises a reduction in the effective flange breadth (clause 5.4.1.2(6)), although when elastic global analysis is used it notes that a constant breadth may be assumed for simplicity. Why is an effective flange breadth specified? The first answer to this question is obvious, namely that a designer needs to know what cross-section(s) to consider when carrying out stiffness and strength checks for the composite beam. The second answer is more subtle, and was considered in Part 23 of this series. To keep the slip at the steel-concrete interface to a manageable level (one below which the connection will not be broken, in an ‘unzipping’) the shear connection must have a certain stiffness. Minimum degree of shear connection rules ensure there will be enough studs to satisfy a certain resistance requirement (defined as a function of the effective flange breadth), in order to indirectly ensure there are enough to satisfy the stiffness requirement. This is often misunderstood, resulting in designers thinking it is acceptable, even conservative, to specify a narrower effective flange. It is not acceptable.

27/02/2014 09:24

› Part 3

46


Technical Composite/Steel compendium Actual effective width of beam Idealised effective width used for design

L/4

L/8 b0 3L/32

Slab span

Figure 2 Boundaries of an effective flange (design to Eurocode 4)

B

W

Figure 3 Reinforced ‘beam strips’ around slab opening

B Opening

A

A

Extra bars in slab (over the deck) Extra bars in troughs

Fabric reinforcement

Fabric reinforcement

Extra bars over deck

Extra bars in troughs

Section A - A

SCI is currently leading a large pan-European research project to investigate various issues concerning shear connection. It is hoped that alternative rules for the minimum degree of connection will be one of the outcomes. They will complement the Eurocode rules by providing less onerous limits for a comprehensive range of specific cases, such as unpropped beams and beams with large web openings.

Disrupting the flange Holes through the slab Often, the place where a structural engineer would like to have material contributing to the stiffness and strength of a floor, is also the place where a services engineer wants to remove it to place a duct. Our considerations of effective flange breadth in the previous section identify why, if holes must be cut in the slab adjacent to a beam, it is preferable that they are nearer to the beam supports than its mid-span. Where an opening is present, that part of the


Section B - B

slab should be ignored when defining the cross-section of the composite beam at that location. For a composite slab (as an element spanning between beams), the way to treat small, medium and large openings is different:

• Openings with a side length up to 300mm can simply be formed by boxing out the concrete during construction. The area of decking is then cut away • Openings up to 700mm will normally require extra reinforcement to be placed in the slab, forming ‘beam strips’ to distribute the load around the opening (Figure 3) • Larger openings will require trimming steelwork to provide additional (permanent) support to the composite slab Cutting holes in a slab after the concrete has been cast should be avoided.

27/02/2014 09:24


47

W

Figure 4 Heating pipes within composite slab

E

Figure 5 Reinforcing bars passing between hollowcore units

Pipes in the slab A relatively recent development has been the desire to cast heating pipes into composite slabs (Figure 4). The pipes are usually about 20mm diameter and laid in a single plane between the decking and fabric, on supports. The practical thickness of a floor incorporating these pipes will be at least 150mm. SCI is unaware of any testing that has been carried out to demonstrate the performance of composite beams and slabs with heating pipes present within the concrete, and accepts that in the absence of better justification the following recommendations may be conservative. The pipes may affect three aspects of structural behaviour:

The strength of any in situ concrete topping, and the amount of transverse reinforcement provided (bars running between opposing units across the beam axis, Figure 5) strongly influence the effective breadth of the slab that may be considered in the composite beam design. While the rules from Eurocode 4 may still apply, the effective breadth of the slab should not normally be taken as greater than the total width of the concrete infill plus the width of the gap between the ends of the hollow-core units. This dimension will typically be less than 1.5m, but the full depth of concrete is assumed (justified by tests) to be mobilised within this width. The design of composite beams using precast concrete units will be considered, in detail, in Part 4 of this series.

• The cross sectional area of concrete that can act in compression (for either the composite beam or composite slab)

• Shear connection between the steel and concrete (either the resistance of the shear connectors or concrete-to-decking mechanical interlock in the case of a slab) • The longitudinal shear resistance of the slab adjacent to a beam The area of any pipes in the compression zone should be deducted from the cross sectional area of concrete contributing to the beam or slab resistance, although clearly if it is running in the spanning direction the impact of an individual pipe will be negligible. Contrary to this, to ensure conservatism when checking that the minimum degree of shear connection rules are satisfied, the presence of the pipes should be ignored when determining the force associated with 100% connection.

References and further reading 1) British Standards Institution (2005) BS EN 1994-1-1:2004 Eurocode 4. Design of composite steel and concrete structures – General rules and rules for buildings London: BSI 2) British Standards Institution (1990) BS 5950-3.1:1990+A1:2010 Structural use of steelwork in building. Design in composite construction. Code of practice for design of simple and continuous composite beams London: BSI

For a slab, the presence of pipes should not affect the mechanical interlock between the concrete and decking, provided that the concrete can be properly compacted beneath the pipes. Grouping of pipes should therefore be avoided (they should have a spacing of at least minimum aggregate size plus 5mm, and not less than 25mm). For a beam, SCI has previously recommended that the contribution of a shear stud should be neglected if a pipe, running transversely, is placed less than 1.75 times the stud height away from the stud. Strictly speaking, this requirement would only apply to solid slabs with the pipes laid on the steel flange. When the pipes are laid on top of decking, a limit of 1.0 times the stud height will be adequate.

3) The Steel Construction Institute (2014) ‘Composite and Steel Construction compendium, Part 2: Shear connection in composite beams’, The Structural Engineer, 92 (2), pp. 25-27

It is important that the pipes do not affect any potential shear failure plane in the zones either side of a beam. Pipes running parallel to the beam will certainly have an effect, and the area of concrete should be reduced accordingly when checking the longitudinal shear resistance.

Johnson R. P. (2011) Designers’ Guide to Eurocode 4: Design of Composite Steel and Concrete Structures (2nd ed.) London: ICE Publishing

The use of hollow-core units Having considered how the presence of voids due to heating pipes may affect the behaviour of composite beams and slabs, it is worth mentioning the use of hollow-core units (where clearly the voids are bigger and more frequent). Although an effective concrete flange can still be formed, because the slab construction is no longer monolithic, the effective breadth will be smaller than for slabs using in situ concrete.


Further reading Steel Construction Institute (2011) Composite design of steel framed buildings (P359), Ascot, Berkshire: SCI MCRMA/Steel Construction Institute (2009) Composite Slabs and Beams using Steel Decking. Best Practice for Design and Construction (Revised Edition) (P300) Ascot, Berkshire: SCI

Steel Construction Institute (2008) Curtailment of transverse bar reinforcement in composite beams with steel decking (AD 325) Ascot, Berkshire: SCI

Web resources The Steel Construction Institute: www.steelconstruction.info

27/02/2014 09:25

› Number 3

48


Technical CBDC series

Concrete Bridge Design and Construction series

This series is authored by the Concrete Bridge Development Group (CBDG) The group aims to promote excellence in the design, construction and management of concrete bridges. With a membership that includes owners, designers, academics, contractors and suppliers, it provides a focus for the use of best practice, innovation, training initiatives and research and development. Further information on the CBDG can be found at: www.cbdg.org.uk

No. 3: Prestressing for concrete bridges Introduction This article from the Concrete Bridge Development Group’s technical committee examines the prestressing for a concrete bridge. In concrete bridges, for deck spans more than 20-30m, prestressing should generally be used. As described in last month’s article1, prestressing enhances the capacity of a member that is weak in tension, but strong in compression. It effectively creates a new material that is strong in tension. Prestressing allows a bridge to be more economical, with lighter and more slender members, which improves the appearance. The sections are generally compressed under permanent effects, which give greater durability due to the reduced incidence of cracking. The sections also behave elastically with greater stiffness, allowing deflections to be more easily controlled. A prestressed bridge has much less steel to be handled, which reduces congestion, leading to easier and quicker concrete placing.

Prestressing basics Prestressing is an active system that opposes externally applied loads and actions with a set of internal forces. The designer has to fully understand this range of actions, and the difference between loads and imposed deformations. Only a brief introduction to prestressing can be given in this article and designers should consult other texts for more detail (see References and further reading section). For the design of the concrete deck section, the top slabs are governed by traffic loads and transverse bending effects, the webs by shear and torsion at the supports (but by minimum requirements for concreting at midspan), and the bottom slabs/heels by the layout of the prestressing cables and by any compressions at the supports (or the minimum thickness for concreting at midspan). Self-weight

TSE27_48-52 CBDC-3 v3.indd 48

N

Figure 1 Concrete box section sizing

dominates many bridge designs and the areas of concrete should therefore always be kept to a minimum. It is particularly important to minimise the web concrete in a bridge, as these areas are also inefficient for the prestressing. For most bridge widths up to around 20m, it would generally be best to have only two webs, though with precast beam solutions, the number of webs is greater, as will be seen in future articles. However, for efficiency, the number of webs should still be minimised by spacing the beams as far apart as possible. For the design of box girders, which will generally be used for all spans over 30-40m, single cells are much preferred as they are far easier to cast than multi-cell boxes. Boxes are very efficient in distributing eccentric traffic loads, though some care is needed with the analysis of torsional/distortional warping. In order to achieve the sufficiently high covers that are needed for durability, the minimum slab thickness is about 225-250mm, though 200mm is often seen in less aggressive environments. Making proper allowances for how the concrete flows during the casting process (and how longitudinal shear is controlled) will often

27/02/2014 09:25


49

compressing too many webs, or creating webs that are too thick. A simple way to calculate the inertia I is to note that I = Aηytyb. A is easy to calculate, η is usually about 60% and the product ytyb is insensitive to exactness. These section properties are vital components in calculating the required prestress force for the whole span.

N

Figure 2 Prestressed section properties

The prestress force (P at eccentricity e from the neutral axis) at each section carrying a moment M is then determined using P = M/ lever arm, where lever arm = (a + e), which would be (at + eb) for Msag and (ab + et) for Mhog. Alternatively, if the moment range were critical, then P is defined by Mrange/(at +ab). Cables zones can thus be calculated for the whole span. This use of kern heights is the same as examining the extreme fibre stresses under the critical set of moments M using inequalities such as:

P/A +/- Pe/Z +/- M/Z > zero These equations are all based on the assumption that the section remains fully compressed under all moments i.e. that the minimum concrete compression fc is zero. The equations can easily be adjusted to suit either a higher positive value of fc (to allow for residual effects of warping or temperature difference), or a lower negative value of fc (to accommodate some allowable tension).

M should be taken as the critical combination of either the maximum

N

Figure 3 Secondary prestress moments on a 3-span bridge

determine the thicknesses of the section in the regions where the webs meet the slabs. These transition zones between webs and slabs are also the areas where prestressing cables can be located. All these basic section parameters, which are often governed by the practicalities of the construction rather than any detailed analysis, can therefore be sized quickly by an experienced bridge engineer (Figure 1). The section properties can be calculated using any relevant software, but the designer must concentrate on the kern height and efficiency of the section. The kern height is the area within which a prestressing force can be applied without causing the section to go in to tension. The top kern height at is Zb/A and the bottom kern height ab is Zt/A (Figure 2 defines all these parameters). The efficiency of the section η is defined as (at + ab)/h – it defines how effective a section is in carrying the prestress. It is 33% for a rectangle (i.e. the well-known middle third rule) and 55-65% for typical I-beams or box girders. It needs to be as high as possible to avoid wasting prestress by


values (under full traffic load combinations), or the minimum values (under permanent or construction loads, or from any reversed traffic loads taken from the relevant influence lines). Due allowance should then be made for the prestressing forces, which will drop over time from higher values at the time of jacking, to lower values after the effects of creep, shrinkage and relaxation have occurred. A tabular list of the stress history at every section should always be shown at the end of the design process, partly as a check and partly as a clear means of seeing all the stresses in the section at all stages. Magnel diagrams exist to allow the prestressing to be designed for both the minimum and maximum compressions in the section. However, though they are useful in understanding the overall parameters, these diagrams are generally too cumbersome for the design process and any issues with maximum compression will not be solved by adjusting the prestress force, but by increasing the concrete area or strength. For all indeterminate structures (continuous bridges, for example), the prestressing primary moments Pe also produce secondary, or parasitic, moments Mp. These moments are needed to ensure the compatibility of rotations at each support position – they are generally very significant sagging moments that vary linearly between supports (Figure 3). Their values must be iterated with the required values of Pe at each section, as Mp is dependent on the Pe profile of the whole structure. The calculation can be carried out using numerical integration of Pe with the flexibility method, or equivalent prestressing loads with the stiffness method. Designers should appreciate the effects of this moment, as Mp can be used to real benefit in the design, by allowing the engineer to transfer moments between support and midspan sections. When bridges are built in stages, creep of both the self-weight moments and Mp occurs, though it tends to work in opposite directions, negating the need for too much precision in the calculation of the creep factor.

27/02/2014 09:25

› Number 3

50



S

Figure 4 Pre-tensioning bed (Banagher Precast Concrete)

Pre-tensioned bridges With pre-tensioning, the prestressing steel is stressed first and the concrete member is then cast around this steel (Figure 4). It has the advantage that as the prestressing is embedded in the concrete, there is no need for any grouting. The prestressing consists of individual strands, each made up from seven spirally-wound steel wires. The most common strand is a low relaxation superstrand, having a 15.7mm diameter, an area of 150mm2 and an ultimate strength fpk of 1 860MN/m2. As the strands are generally straight, the system usually only allows straight beams to be produced. Standard precast, pre-tensioned concrete beams have been used for years in many countries. Various shapes and depths are produced, suitable for a range of spans from 5-40m (Figure 5). They are generally cast off-site in precast factories and transported to site. Typical beams weigh 5-60t and are generally erected by crane. Smaller beams are placed adjacent to each other and the space between the beams filled with concrete to form a solid slab, with typical spans varying from 5-25m. Larger beams are spaced 1-2m apart, permanent formwork is placed between the beams and an in situ deck slab is cast over the top. Typical spans in this case vary from 15-35m, though up to 40m is possible. Various arrangements of bespoke pre-tensioning also exist, allowing much larger I, T or

Solid Box Beam

MY Beam

T Beam

TY Beam

U-beams to be cast. These beams are then spaced 2-4m apart, with beam weights of 40-200t, and spans of up to 60m can be used. For very long viaducts, whole span precast units (with spans of 35-50m) can be cast and pre-tensioned in purpose-made factories on site. Such units might weigh up to 1 000t and be erected using special transporters and gantries. The prestress and self-weight loads are carried on the precast beam while all other loads (finishes and traffic loads) are carried on the composite section i.e. including the top slab. The top surface of the beam is suitably prepared and has projecting reinforcement so that the slab and beams act together. The prestress is applied to the ends of the member by bond action between the strand and the concrete, resulting in a length over which the force is transmitted (of 500-1 000mm). Elastic deformation, creep and shrinkage losses (all of which are high due to the early transfer of the prestressing onto young concrete) combine with steel relaxation losses to give longterm stresses in the prestressing of 1 000-1 100MN/m2, or 55-60% fpk. De-bonding of some of the strands is often used at the ends of the beams, so as not to either overstress the bottom fibre or put tension into the top fibre. Standard precast beams, produced in a factory, can therefore be of high-quality, with a proven record of durability. These precast beams can be quickly erected on site and are therefore particularly useful when bridging over live roads, railways and waterways, where interruptions to the traffic must be minimised. See CBDG CPS 42 and CBDG TG 133 for further details. Hybrid schemes also exist where an initial phase of pre-tensioning is then augmented with post-tensioning at a later phase.

Post-tensioned bridges

M Beam

TY Beam

Y Beam

Figure 5 Standard precast beams


SY Beam

U Beam

W Beam

With post-tensioning, the concrete member is cast first and the prestressing is applied afterwards. The range of possible bridge types and construction methods is wide, and most concrete bridges over 30-40m spans (and up to 300m spans) will use post-tensioning. Bridges can be formed in to any shape and the most intricate alignments can be accommodated. The same superstrands are used, but they are bundled together to form cables. Typical cables may be formed from 12-37 strands, and be designated as 12/15mm or

27/02/2014 09:25


51

S

Figure 6 Post-tensioning jack stressing a cable (Clackmannanshire Bridge, UK)

N

Figure 7 Anchorage blisters inside box (East Moors Viaduct, UK)

N

Figure 8 Internal cable ducts at pier (STAR LRTS Viaducts, Malaysia)

37/15mm. Each cable sits inside its own duct which, after threading and stressing, is then usually filled with a high-performance cementitious grout. The specification and application of these grouts needs to be very well controlled in order to achieve a completely filled duct4. The prestress is applied to the ends of each cable via a steel anchorage, which is cast in to the concrete. Each strand is then clamped by a set of wedges that locks the strand in to the anchorage. The prestress force is applied to the anchorage with hydraulic jacks, which typically apply loads of 2-8MN, i.e. 200-800t (Figure 6). Elastic deformation, creep and shrinkage losses (all of which are lower with post-tensioning due to the later transfer of the prestressing onto more mature concrete) combine with duct/cable friction and wedge lock-off losses, and with steel relaxation losses to give similar long-term stresses in the prestressing steel, i.e. 1 000-1 100MN/m2, or 55-60% fpk. The prestress can be finely tuned to suit the required forces at every section. As such, it is common for post-tensioned bridges to have many sets of cables, each starting and stopping in a variety of locations to suit both the construction method and applied loads. Each anchorage is housed within a lump of concrete that transmits the huge forces into the main body of the member – these lumps might be at diaphragms, abutments, pockets or a variety of blisters (Figure 7). The design of these highlystressed locations will be covered in a future article in this series. As post-tensioned cables follow the bending moments within the member, they also move up and down the section. This inclination of the cables provides a shear force, which acts against the applied shear forces, in


N

Figure 9 External cable profiles inside box (A13 Viaduct, UK)

turn providing a significant shear relief which reduces the amount of reinforcement needed in the webs. There are two types of cable configuration – internal cables that are grouted inside ducts, which are within the concrete and bonded to it, and external cables that are also grouted inside ducts, but which are outside the concrete and not bonded to it. Each type provides a three-layer protection system to the cables using grout (or wax), the duct and the concrete. Internal cables are more compact with smaller cables, anchorages and blisters – often using 12/15mm or 19/15mm cables. They can more closely follow the pattern of moments in the member and thus have a better eccentricity and ULS performance than external cables. In the UK, ducts are required to be made from a continuous, corrugated plastic, whereas elsewhere, away from road salts in particular, ducts are often formed from corrugated, galvanised steel. Cables are located in the top slab regions within hogging zones (Figure 8), and in the bottom slab regions within sagging zones, with cables moving up and down the webs in between these regions. These bonded sections tend to be designed as fully compressed under all frequent traffic loads. This is the requirement in both BS 54005,6 and Eurocode 27. As a result, these internally prestressed sections are generally governed by SLS, and ULS will not be critical. External cables are generally larger with fewer anchorages. As they sit outside the concrete, they tend to follow more simple profiles and need deviator blocks at all changes of direction (Figure 9). The

27/02/2014 09:25

› Number 3

52



cables are housed within continuous HDPE ducts, which are 6-10mm thick in order to resist the grouting pressures. These large external cables - often using 27/15mm or 37/15mm cables - need large anchorages and deviator blocks, which can contain considerable volumes of concrete and reinforcement. Sitting outside the concrete, external cables have a lower eccentricity than internal cables and, being unbonded, their ULS performance is not as good as internal cables. However, they do allow thinner webs and many construction methods (such as span by span precast segmental or whole span precast) work very well using external cables, where it is quicker to install a smaller set of larger cables. They also allow the use of partial prestressing (covered in the following section). External cables were first introduced to enable the ducts/cables to be easily inspected, maintained and replaced. However, with the improved grouting technologies introduced by TR 72 in 2010, and indeed its forerunner in 1996, the need for such inspection is significantly reduced. Subject to local regulations, designers should therefore choose between external and internal systems, or a mixture of the two, on the basis of what is best for the design and construction method.

though, bridges with spans over 20-30m will need a significant level of prestressing in order to make them satisfactory in all regards.

Conclusions Of all the materials available to a bridge engineer, prestressing is the most challenging as it is an active, not passive, system. One cannot simply add more prestressing steel in order to be conservative, as the addition of prestress is just as likely to be detrimental to the section as is its removal. The designer must therefore calculate all the effects along all sections of the member, and then design the prestress to counter them at all locations. This process needs a determined effort from skilful designers, and throughout, they must consider the critical construction issues, as these affect all subsequent decisions.

References and further reading 1) Concrete Bridge Development Group (2014) ‘Concrete Bridge Design and Construction series No.2: Concrete bridge layouts’ The Structural Engineer, 92 (2), pp.28-32

Partially prestressed bridges As noted previously, partial prestressing is possible when external cables are used. As the cables are protected within the envelope of the concrete, the concrete section can be allowed to crack, as this cracking would have no detrimental effect on the cables. The designer thus has the option to consider a full range of prestressing, from full compression to none (i.e. just reinforced concrete). Further discussion on this topic can be found in the 2012 Milne Medal paper8, where it is concluded that a high level of prestressing is likely to provide a better set of results. High levels of prestressing provide the benefits described in this article’s introduction, whereas low levels of prestressing are not really suitable for spans over about 30m, primarily due to the much higher deflections and ongoing levels of creep (Figure 10). This ability to consider much lower levels of prestressing has arisen because of Eurocode 2, which allows more partial prestressing than BS 5400. In BS 5400, which was augmented by BD 589, the section had to remain fully compressed for all permanent loads and then crack widths were checked under frequent traffic loads. Other codes around the world require the section to be fully compressed for frequent traffic loads and then crack widths to be checked under rare traffic loads. However, Eurocode 2 now requires there to be no decompression check at all, with crack widths being checked under permanent loads only. Consequently the design is generally governed at ULS. Theoretically, Eurocode 2 is saying that external partial prestressing is simply a form of reinforced concrete. Practically

W

Figure 10 Permanent deflections vs. level of prestress

2) Concrete Bridge Development Group (2013) Current Practice Sheet No. 4: Prestressed Concrete Bridge Beams, Camberley, UK: CBDG 3) Concrete Bridge Development Group (2010) Technical Guide No. 13: Integral Concrete Bridges to Eurocode 2, Camberley, UK: CBDG and The Concrete Society 4) The Concrete Society (2010) Technical Report 72: Durable Post-tensioned Concrete Structures, Camberley, UK: The Concrete Society 5) British Standards Institution (1990) BS 5400: Steel, Concrete and Composite Bridges, Part 4 – Code of Practice for Design of Concrete Bridges, London: BSI 6) The Highways Agency (1992) BD 24: The Design of Concrete Highway Bridges and Structures – Use of BS5400: Part 4: 1990, London: The Highways Agency 7) British Standards Institution (2005) BS EN 1992-2: Eurocode 2 - Design of concrete structures – Part 2: Concrete bridges – Design and detailing rules, London: BSI 8) Bourne S. (2013) ‘Prestressing: recovery of the lost art’, The Structural Engineer, 91 (2), pp. 12-22 9) The Highways Agency (1994) BD 58: The Design of Concrete Highway Bridges and Structures with External and Unbonded Prestressing, London: The Highways Agency Further reading Menn C. (1990) Prestressed Concrete Bridges, Berlin: Birkhauser Benaim R. (2008) The Design of Prestressed Concrete Bridges, Concepts and Principles, Abingdon, UK: Taylor & Francis Hewson N. (2012) Prestressed Concrete Bridges, Design and Construction, London: Thomas Telford Concrete Bridge Development Group (2014) Technical Guide No. 14: Best construction methods for concrete bridge decks, Camberley, UK: CBDG (publication in 2014)


27/02/2014 09:26

›


Technical E-Pile Schedule


FPS E-Pile Schedule for Eurocode design D. Selemetas BEng, MSc, PhD (Cantab), CEng, MICE Design Manager, Cementation Skanska, UK A. Bell BEng, MSc, CEng, MICE, FGS Chief Engineer, Cementation Skanska, UK Synopsis

The introduction of Eurocodes has altered the format of pile loading information and the procedures with which the structural and geotechnical design resistances for piles are determined. The E-Pile Schedule has been developed by the UK Federation of Piling Specialists (FPS) to accommodate the latest Eurocode requirements for loading on foundations. This article highlights the considerable benefits of adopting a standard pile schedule for Eurocode design.

Notation

Gk Characteristic value of permanent action Qk Characteristic value of leading variable

Tk Characteristic value of net tensile action (if present)

Gk,m Characteristic value of permanent component of applied moment

Qk,m Characteristic value of variable component of applied moment DA1 Comb1 (ULS-STR) Ed, max Design Approach 1 (Ultimate Limit State - structural case) Design value of effects of actions (maximum value) DA1 Comb1 (ULS-STR) Ed, min Design Approach 1 (Ultimate Limit State - structural case) Design value of effects of actions (minimum value) DA1 Comb2 (ULS-GEO) Ed, max Design Approach 2 (Ultimate Limit State geotechnical case) Design value of effects of actions (maximum value) DA1 Comb2 (ULS-GEO) Ed, min Design Approach 1 (Ultimate Limit State geotechnical case) Design value of effects of actions (minimum value)

action

Introduction

Qk,wind Characteristic value of accompanying

Historically, the design of piles in the UK followed the British Standard philosophy where an overall Factor of Safety (FoS) was used against a safe working load (SWL), i.e. an un-factored working load. This was a simple and robust method, with only one input parameter (the safe working

wind action Qk,i Characteristic value of accompanying variable action i (if present) Qk,j Characteristic value of accompanying variable action j (if present) Ad Design value of accidental action (if present)

TSE27_53-54 FPS v2.indd 53

53

load) and the designer was only faced with the choice of FoS depending on the testing regime. With the introduction of Eurocodes, the complexity of pile loading information has increased due to the requirement to apply different partial factors to individual components of actions to demonstrate verification against ultimate limit states (ULS). With the extra inherent complexity of Eurocode design, the need for standardising the format of pile loading has never been greater.

Background to Eurocode 7 pile design In the UK, Eurocode 7 (EC7) pile design is typically carried out by the method of calculation in accordance with Design Approach 1 (DA1) of BS EN 1997-1:2004 (Eurocode 7)1, as prescribed in the UK National Annex of BS EN 1997-12. In this approach, reliability is ensured by applying partial factors to verify the adequacy of the design against two ULS combinations. Combination 1 is the structural ULS case (STR-ULS) and Combination 2 is the geotechnical ULS case (GEO-ULS). Combination 1 applies partial factors to actions (permanent actions Gk and variable actions Qk) with pile resistances kept unfactored, while Combination 2 applies partial factors to pile resistances and partial factors of smaller magnitude to variable actions. It is important to recognise that the designer is required to examine both Ultimate Limit States (GEO-ULS and STR-ULS) and that different limit states govern different aspects of the design. Indeed, the GEO-ULS will typically control the required pile toe, and toe of reinforcement (due to the factors applied on pile resistances and soil strength), while STR-ULS will govern the amount of reinforcement required (due to the higher partial factors applied on the actions). With this background in mind, it is easy to appreciate why the pile designer requires all individual actions (un-factored) and even if the scheme designer provides the STR-ULS factored actions, it is important that they also provide the individual actions (Gk and Qk) so that the pile designer can calculate separately the GEO-ULS factored actions, which would govern the length of the piles. In the simple case, where the total pile load consists of a permanent action and a variable action, the factored actions (Ed, max) for the two ultimate limit states are calculated as follows: (STR-ULS)

Ed,max = 1.35 x Gk + 1.50 x Qk

(GEO-ULS)

Ed, max = 1.00 x Gk + 1.30 x Qk (2)

(1)

In other cases, where the total pile load consists of a number of leading and

27/02/2014 09:27

›

54


accompanying variable actions, the designer is required to consider all possible combinations of variable actions for both STR-ULS and GEO-ULS as prescribed in clause 6.4.3.2 of BS EN 1990:20023: E d, max = (3)

/ c G, j G k,j " + " c Q,1 Q k,1 " + " / c Q,1 } 0,i Q k,i

j$1

Technical E-Pile Schedule

Table 1: Limitations of various formats of Eurocode pile loading Format of pile loading

Limitation

Pile loading given in the form of Safe Working Load (SWL)

The pile designer does not know the proportion of permanent and variable actions. The load breakdown is required as there are different partial factors applicable to Gk and Qk

Pile designer to assume Gk and Qk. For the same SWL, the EC7 design will give different pile lengths depending on the proportion of Gk and Qk

Pile loading given in the form of maximum STR-ULS loads and GEO-ULS loads

The pile designer does not know the un-factored actions which will allow verification of the serviceability limit state (SLS) and the calculation of minimum ULS loads

Pile settlement/serviceability cannot be verified in the absence of un-factored working loads. Pile reinforcement design may be incorrect in the absence of minimum axial ULS loads

Pile loading given in the form of maximum STR-ULS loads only

The pile designer does not have the information required to calculate the GEO-ULS which controls pile lengths

The pile designer may assume that STR-ULS = GEO-ULS (conservative for geotechnical calculations) but this will not provide a cost-effective piling scheme

i$1

Need for a standard pile schedule Although there is an ever increasing expectation that the design of piles in the UK should comply with EC7, it is surprising to see that there is no agreed format for issuing pile loading information. The lack of consistency and clarity introduces a component of unnecessary confusion in pile design and may result in different interpretations of the required pile loading for EC7 design. Table 1 lists three examples of different formats of pile loading that have been encountered by the authors over the last few years and highlights the associated design implications when executing the design to EC7.

Table 2: Extract of E-Pile Schedule showing pile reference and pile geometry data Pile geometry

Reference Pile

Loading

ref

ref

Drawing ref

Pile

Pile

Cut-off

Piling

Pile

Design

Design

Vertical

type

cap

level

platform

diameter

Easting

Northing

/raking

ref

(mOD)

level

(mm)

(m)

(m)

angle

E-Pile Schedule format The FPS E-Pile Schedule comprises five sections; pile reference, pile geometry, EC7 vertical actions, EC7 horizontal actions and pile design. Tables 2 and 3 give examples of the input required in the first three sections. The input required for the horizontal actions is similar to the input for the vertical actions. The pile design section is the output generated by the pile designer (for simplicity these two sections are omitted from this article). In Section 3 of the E-Pile Schedule (Table 3), the scheme designer can provide all individual components of pile loading (e.g. Gk, Qk, Qk,wind, etc.), as well as the serviceability limit state (SLS) working load (previously known as the safe working load). The E-Pile Schedule also provides input for the factored actions (Ed, max and Ed, min) for both ULS and GEO limit states and where the Ed,max has been provided for only one of the limit states, it is important that the scheme designer explains the combination factors used to derive the ULS loads.

Benefits The FPS E-Pile Schedule has been created to provide a consistent and transparent approach to the design of piles to EC7 and will give the pile designer access to all the information required. By agreeing on the format of pile loading information, the industry will create a level platform for pile design and will minimise any confusion that may exist due to incomplete information, which in turn will eliminate delays and/or extra cost due to re-design at a later stage. The E-Pile Schedule is free to download from the FPS website at: www.fps.org.uk/fps/guidance/technical/ pileschedule/pileschedule.php.

TSE27_53-54 FPS v2.indd 54

Design implications

(mOD)

1

Rev P1

XX-CSL-001

CFA

A

4.00

5.00

(°)

450

XXX.XXX

YYY.YYY

0

Table 3: Extract of E-Pile Schedule showing pile reference and pile geometry data EC7 vertical actions Gk

Qk, l

Qk, wind

Qk, I

Qk, j

Tk

Ad

Gk,m

Qk,m

SLS

DA1

DA1

DA1

DA1

(kN)

(kN)

(kN)

(kN)

(kN)

(kN)

(kN)

(kNm)

(kNm)

(kN)

Comb1

Comb1

Comb2

Comb2

(ULS

(ULS

(ULS

(ULS

STR)

STR)

GEO)

GEO)

Ed, max

Ed, min

Ed, max

Ed, min

(kN)

(kN)

(kN)

(kN)

1410

600

1120

600

600

400

–

–

–

–

–

–

–

1000

Conclusions This article presents an E-Pile Schedule that has been developed by FPS to accommodate the latest Eurocode requirements for loading on foundations and provide a common framework for pile design and analysis in the UK. The article explains why a consistent format of pile loading to EC7 is essential, highlighting the considerable benefits of adopting a standard pile schedule for Eurocode design.

E2

British Standards Institution (2007) NA to BS EN 1997-1: 2004, UK National Annex for Eurocode 7. Geotechnical Design. General rules, London: BSI

E3

British Standards Institution (2005) UK National Annex to Eurocode 0, BS EN 1990: 2002+A1: 2005, Basis of structural design, London: BSI

References

Bibliography

E1

British Standards Institution (2004) NA to BS EN 1990: 2002+A1:2005, UK National Annex for Eurocode. Basis of structural design, London: BSI

British Standards Institution (2004) BS EN 1997-1: 2004, Eurocode 7. Geotechnical Design. General rules, London: BSI

27/02/2014 09:27



55

Opinion Letters or longer articles written from a personal perspective on topics of current interest, that offer a particular opinion and often encourage further discussion and/or debate.

56 Verulam 59 Steel Bridges: Conceptual and Structural Design of Steel and Steel-Concrete Composite Bridges (Book review)

TSE27_55 Opinion opener.indd 55

27/02/2014 09:27

›

56


Opinion Letters

Verulam

Send letters to… All contributions to Verulam should be submitted via email to: [email protected] Contributions may be edited on the grounds of style and/or length by the Institution's editorial department.

Topics of importance openly discussed

CDM guidance Andrew Minson of The Concrete Centre writes expressing disappointment regarding the apparent omission from the professional guidance article ‘Managing Health & Safety Risks No. 21’ to any reference to the substantial guidance available from the concrete industry on this subject.

The October 2013 article ‘Managing Health & Safety Risks No. 21: Working with Concrete: associate risks (2)’ in The Structural Engineer made no reference to the guidance that is available on the safe design, installation and construction of concrete structures. There is a wide range of resources available to assist your members including:

our book was peer reviewed by SCOSS. Once again, this guidance helps members fulfill their CDM obligations and can be purchased from www.concretecentre.com/ publications

I started out in construction in 1960 and worked in this field until 2013 when I was retired due to my age. The following systems were in place throughout the 1990s when I was working in Singapore:

Also please be aware of the training available:

• Any bridge design had to have its

• The specialist concrete frame contractor group, CONSTRUCT, has collaborated with CITB in producing a new suite of H&S training videos for concrete frame construction to add to its various H&S initiatives: www.CONSTRUCT.org Health and safety is the highest priority for the concrete industry, and as detailed in our recent industry performance report (also downloadable) the members of BRMCA, British Precast and The Concrete Centre are committed to reducing lost time incidents during production by 50% from 2009-2014 with the aim of zero harm.

• Code of Practice for Safe Installation of Precast Flooring and Associated Components, updated in May 2013 and endorsed by the Health & Safety Executive. It is freely downloadable from www.precastfloors.info. The Precast Flooring Federation (PFF) members have demonstrated their commitment to this new Code of Practice through signing up to mandatory installation audits. Specifying the PFF Code of Practice can help structural engineers fulfil their CDM obligations. Codes of Practice for structural precast and architectural cladding are also obtainable, and are currently being updated. These codes demonstrate that the precast industry take the safe use of their products seriously, over and above ensuring safe manufacturing processes

My thanks to Andrew for sending us this information.

• Design of Safe Concrete Structures,

I have just read about the problem regarding scaffolding + formwork collapsing in Singapore in S. H. Mak’s letter in a recent issue of The Structural Engineer, and would like to offer him some advice.

published by and available from The Concrete Centre. The author is John Carpenter, who also authored CDM Guidance for Designers, and ensured that

TSE27_56-58 verulam v2.indd 56

Scaffolding guidance S. H. Mak from Singapore previously wrote to Verulam (December 2013) commenting on recent scaffolding (falsework) failures and requesting advice. Verulam has had several offers, starting with Vic Warden (also with Singaporean experience).

foundations checked for failure (i.e. drainage) and a guide of how to concrete, without producing deflection when concreting, was followed

• All building support systems and formwork should be checked by a qualified engineer. I spent five years in Singapore and in all this time there weren’t any collapses, as all the systems were checked by myself and all calculations were checked by an independent engineer before any concrete pouring was carried out and it was signed for by the engineer in charge. Independent checking must certainly help, but practice across countries varies as the following letters explain. It seems much information is available.

Robert C. Hairsine writes in highlighting currently available advice.

I refer to the contribution by S. H. Mak in the December 2013 issue, in which he regrets that guide books on scaffolds and formwork design are not readily available. Whilst there are fewer publications on such temporary works than for other topics in structural engineering and therefore scope for new books and papers, I would say that there is some readily available guidance. BS 5975:2008 (as amended 2011) Code of practice for temporary works procedures and the permissable stress design of

27/02/2014 09:28


57

falsework gives very extensive guidance on temporary works in general and has a section on the use of scaffolding. It is so extensive that it verges on being a textbook. I understand that a new version is in preparation including structural design in ‘limit state’ partial safety factor format. With regard to scaffolds for access rather than falsework, the current code of practice is BS EN 12811 Temporary works equipment. Within this, Part 1:2003 Scaffolds-performance requirements and general design is most relevant. However, this deals only with principles and not practical applications. In the UK, the trade body the National Access and Scaffolding Confederation (NASC) www.nasc.org.uk has many publications available in their safety and technical guidance series and its publication TG20 deals with the practical design of tube and fitting scaffolds for access. A new version, TG20:13, was published last month in four parts: 1. NASC TG20 Operational Guide. A colour illustrated 223 page manual for executives in scaffolding and the construction industry generally. 2. NASC TG20 Design guide. A 204 page guide for structural designers of scaffolding. 3. NASC TG20 eGuide. Software for the selection and specification of standard designs of common access scaffolds. 4. NASC TG20 UserGuide – A 26 page colour illustrated summary for site operatives. TG20:13 has been researched and produced by a small team of my colleagues at CADS with practical advice and support from the TG20:13 working party and contributions by members of the NASC technical committee and Council. Thanks to Robert for bringing these sources to our attention.

Conrad De Souza, HM Specialist Inspector – Structural Integrity Lead on Scaffolding UKCS for the HSE, writes in offering further guidance on scaffolding technology.

I work in the oil and gas industry and there is sufficient guidance being followed by the industry on the UKCS. The British Standards Institution has also published information via codes and guidance on scaffolding. Plus the Health


and Safety Executive (HSE) has published information on its website for onshore scaffolding. Additionally there are competent companies such as Stork Technical Services looking at innovations offshore that are equally applicable onshore. Offshore, we are seeing the use of composite scaffolding that has benefits in reducing injuries and floating when dropped, so is easily recoverable. Accidents offshore are mainly when loads are cross-hauled and I refer to Standards I consulted when investigating scaffolding incidents. In the UK, compliance is required with parts of these Standards:

• Health and Safety at Work etc. Act 1974 • Lifting Operations and Lifting Equipment Regulations 1998 • Management of Health and Safety at Work Regulations 1999 • Provision and Use of Work Equipment Regulations 1998 Evidently there is great deal of technology associated with scaffolding, falsework and its installation, which must be bewildering for more junior and nonspecialist engineers. Articles 16 and 19 of The Structural Engineer’s Health & Safety series (May 2013 and August 2013 respectively) included an overview for junior engineers. Readers can also find upto-date thinking at www.twforum.org.uk/

Finally, David Quinion reminds us of how serious this topic can be.

In the 1970s there was considerable concern about construction failures and the absence of pertinent guidance documents. The Advisory Committee on Falsework, the Bragg Committee, emphasised the need for a Code of Practice for Falsework. I was selected to prepare the draft for a BSI Committee. Information was gathered widely from practices in Britain and abroad. These resulted in a new Code of Practice for Falsework BS 5975 in 1982. With others involved, many lectures were given at home and abroad. The Concrete Society also produced Formwork: A guide to good practice. BSI also extended its Standards on Scaffolding. There was thus good general availability of practical advice some 30 years ago. I am not familiar with the present situation regarding that availability. The restrictions on lessons learnt from construction failures should be considered by The Standing Committee on Structural Safety (SCOSS).

Despite the efforts of 30 years ago, failures in temporary works still occur. This is an example of the need for engineers to keep on learning and to be aware of dangers and not ignore past lessons. CROSS attempts to disseminate examples of contemporary failures and spread the message and is always interested in receiving new incident reports.

Design failures Continuing on the theme of failures, Brian Pyle refers to Sean Brady’s articles in the December 2013 and January 2014 issues.

For design failure cases, I learned decades ago that the courts expect the expert to be a practicing design engineer. Unless familiar with the particular facet of the design failure, the expertise of the expert engineer was under question. What better example do we have than the majority of MPs who have no background in business! Finding a solution to rectify a failure was, in my experience, seldom carried out by an appointed expert. On one such occasion the expert discovered that he had an embarrassing conflict of interest. 40 years ago I accepted an expert instruction for a ram damping system failure. The rams were connected to 10t hanging concrete weights in a power station chimney. Considerable damage was caused when the ram system disintegrated and the chunks of concrete crashed about inside. An eminent mathematician had produced an analysis for amplitude of relative movement of half a metre. The damper designer decided to allow a 40% tolerance, so designed the damper 0.7m long (all this in inches of course). How can we overcome such error in transfer of information when it is not realised by the many persons involved that the total movement is twice the amplitude? The dispute was settled with no more expert input. Later it made me consider why I had accepted the instruction. I had never designed a tall reinforced concrete chimney. From then on I realised I should not accept any instruction which was not in my design field. I had in fact taken the instruction as a forensic engineer although the term was not yet in common use. A specialist forensic engineer is likely to accept any instruction. If there is a lack of specific design knowledge then the learning process starts on receiving instruction.

27/02/2014 09:28

›

58


How can this be correct? More importantly why should the court accept this ‘expert evidence’? I am convinced that all experts should be actively involved in similar work as the subject of the dispute. With a construction failure it is not a consultant who is necessarily the appropriate expert and I would suggest that the solicitor’s best way forward is to instruct a contractor’s engineer who regularly does similar work. A forensic engineer, without current practical design experience, can more easily be forced into opinions based upon the ‘wise after the event’ approach. From my experience of the ‘other sides’ experts, the best were engineers working currently in the field of the dispute. I recollect that few disputes went to court when both (or all) the experts were experienced in design work similar to the subject of the dispute. My summary of what works for the expert investigation is: 1. Obtain all factual evidence from site. Extensive photography is essential. To have too many is easily solved by using only the images which prove to be relevant. 2. An initial opinion on the reason for the failure can be formed in the majority of cases. Is it a design failure or is it a construction failure? As sometimes happens is it a combination of doubtful design and defective construction? 3. Advise those instructing on how the investigation should proceed. This may involve a further expert e.g. a metallurgist, geotechnical engineer etc. If it involves a construction defect suggest a construction engineer. 4. With all evidence in place along with the appropriate experts, the analysis to determine the cause can proceed. If the failure is probably due to defective design then it is the practicing engineer, in that design field, who must be the best expert to prepare and present the evidence. In my opinion Mr Brady is decrying the ability of the design engineer to think laterally. Is that not how and why we were trained? An Expert’s duty is to explain to his side (or the court) what has gone wrong in terms that can be understood, and an Expert should certainly assess themselves to see whether they feel competent enough for the task. Ideally, experts from opposite sides should seek a consensus


Opinion Letters

as it is not their role to be an advocate. However, where total consensus cannot be achieved, the Expert who has the better experience is the one most likely to be believed. If an Expert feels he cannot speak authoritatively on a topic, he has a duty to warn relevant parties. A point Mr Pyle’s letter brings out in terms of failures, is how easy it is to make a gross mistake. An Expert should always tread carefully in advising failure cause. Failures rarely come about from a single error.

Vested interests? Alan F. Granby writes in…

I was interested to read Brian Edmondson’s comment regarding Brian Clancy’s quote (The Structural Engineer, December 2013). I would refer Mr Clancy to paragraph 6.3 of the Institution’s publication Subsidence of Low Rise Buildings and where he was the Chairman of the Task Group responsible for the publication. I have had experience recently where, in one case, the insured was offered a £3 800 cash settlement and after our involvement the offer increased to £11 500. Another case was where the Insurers offered just under £2 000 and since then they have funded initial repairs costing in the order of £5 000, with the eventual costs possibly being five times that amount. Like Mr Edmondson I’m also offended, because the inference is that a Chartered Engineer does not have the expertise to establish the cause of any cracking or movement in a building, or worse still will give a dishonest opinion on the cause of the damage. We are much better qualified than a claims handler on the telephone or a loss adjuster who may have a vested interest in limiting the value of a claim or initially repudiating it.

Fortunately, Verulam also has a letter from Mr Clancy himself in which he responds to recent letters of criticism of unguarded quotes.

My attention has been drawn to the short note by Brian Edmondson (Verulam – December 2013). He says that he is offended by my opinion and quotes it. I have consulted the book in question and it does contain the quote made by him, but Mr Edmondson is very selective.

His quote is only six lines of some 70 that summarise my views; what about the next four lines? I also reviewed (at the author’s request) the whole of Chapter 5. Not all of my many suggestions were accepted by the author, but most were. If one reads the section on Loss Adjusters immediately before my contribution, the totality of my ‘quote’ and the rest of the whole chapter, then I think the total picture is clear, fair and good advice overall; it extensively recommends the use of structural engineers and the advice given by the Institution. Yes, with hindsight, and for sensitive souls, perhaps I should have picked up the point Mr Edmondson makes and put ‘may’ before ‘have’! Mea culpa! I apologise. Could the inimitable Mr Clancy be anything other that supportive of the structural engineer’s role?

Verulam’s role Readers are reminded that Verulam is a mysterious being whose mood changes. Bill Harvey writes in, responding to a letter from David Wadsworth (December 2013) on the subject of Verulam, calling for more scathing comments.

I was disturbed by the letter criticising Verulam for commenting on letters. A look back over the years would be a very interesting exercise. I believe that the first Verulam was Bill Henderson, sometime bridge engineer for Scotland and known for his work on arch bridges. I am not sure how many more there were before Stefan Tietz tenancy but since then the atmosphere has changed more than a little. In the old days, Verulam would have been described as acerbic. Comments were sharp and not infrequently critical. These days, on the whole, they are gentle and therefore, to a large extent valueless. And yet they attract criticism, very strange. I suspect that the sharp tone was evidently backed up by deep engineering understanding whereas the softer tone, by its nature cannot make such understanding so evident. Bring back the old style. Well, Verulam is getting older and more cantankerous. Who knows how he/she will respond!

27/02/2014 09:28

›


Opinion Book review


59

Review Winner of the Institution’s Guthrie Brown Award for a bridge-related paper published in The Structural Engineer in 2012, Matthew Myerscough comments on a book by two steel bridge experts.

Steel Bridges: Conceptual and Structural Design of Steel and SteelConcrete Composite Bridges

Authors: : Jean-Paul Lebet and Manfred A. Hirt Publisher: EPFL Press Price: $149.95 ISBN: 978-1-466-57296-6

This work is the product of two professors at the Swiss Federal Institute of Technology at Lausanne (EPFL). Based on over two decades of courses taught at the university, the principal focus of this text is highway bridge engineering, both in steel and composite construction. Beam type structures are covered almost exclusively, comprising plate girders, box girders and trusses, although a chapter towards the end of the book examines arch bridges. The subject matter has been divided into five principal sections, with the introduction containing a brief history of steel bridge construction which is beautifully illustrated with numerous large colour photographs. The core of the book is contained within the next two sections; conceptual design, and analysis and design. The former deals with structural forms, construction details, fabrication and erection of steel structures, and includes a chapter dedicated to reinforced concrete slabs for composite bridges. Understandably, this section is not mathematically heavy, and the wealth of practical guidance provided (for example the detailing of slab edge drip features) demonstrates the strong links EPFL

TSE27_59 book reviews v2.indd 59

has established with industry partners. Individual chapters have been divided with sub-headings, italic phrases and plenty of diagrams and illustrations (usually at least one on every page), so there are no dense blocks of text. Using Eurocode terminology, the analysis and design section explores actions on bridges and the limit state philosophy, before detailing calculation methods for determining bending moments, forces and torsions. Subsequent chapters contain all the principal calculation checks required for plate and box girders, followed by the analysis and design of composite beams, cross and plan bracing and consideration of

overall bridge stability. Numerical examples are included within these chapters, and although mathematical complexities are present (for example the simplified method for calculating pre-stress losses in a composite bridge), they are not overbearing. Final sections touch upon the specifics of railway and pedestrian bridges by highlighting key differences compared with highway structures, such as the increased importance of dynamics in footbridge design and fatigue in railway structures. The last chapter exercises the analysis and design concepts detailed earlier, through a worked numerical example of a multi-span plate girder composite highway deck. It is not hard to see why the original French edition won the Roberval Award 2010 for best book for higher education in the French language. While the content is accessible to students, the book would certainly be of great value to the professional engineer too. Clearly the authors have significant expertise in this field and their interest in bridges is apparent, which increases readability. This text would make a worthy addition to the bookcase of any aspiring or practising bridge designer.

"IT IS NOT HARD TO SEE WHY THE ORIGINAL FRENCH EDITION WON THE ROBERVAL AWARD 2010"

Mathew Myerscough Matthew Myerscough is a Bridge Engineer at Cass Hayward. He studied Civil Engineering at University College, Durham, and is currently enrolled on the University of Surrey’s MSc in Bridge Engineering.

27/02/2014 09:29

›

PRODUCTS & SERVICES

Telephone: 020 7880 7633 Email: [email protected]

60


Hidden steel frame award ‘winner’ Cold roll-formed steel specialist Metsec was the ‘hidden’ winner at the FPDC’s Annual Plasterer’s Awards 2014 following its involvement in the design of all three framing projects shortlisted in the ‘Steel Framed Systems Contract’ category. Framing Technology Ltd won the Steel Framed Systems award, demonstrating engineering excellence with its work on a ‘Homes for Islington’ scheme in London. The challenging scheme required a tailored design solution as floor plans differed, with cantilevers on the walls and floors not lining up from floor to floor. Working with Metsec’s engineers, Framing Technology projected a solution that used a load-bearing site fixed steel framing system that was smoothly incorporated with hot rolled steelwork. Metsec’s other contributions were for 167 residential units in Acton, London, realised by Stanmore for Countryside Properties, and the supply of steel framing and design assistance to the Emerald Square residential scheme in Roehampton, which was delivered by Ferns Drylining for St James Homes. For further details visit www.metsec.com or follow @MetsecPlc on Twitter

New brochure aids window replacement and external wall insulation projects Helifix has produced a new ‘Structural Preparations’ brochure to help those undertaking window replacement or external wall insulation, to avoid potentially expensive and time consuming structural problems. The brochure focuses on the structural preparatory works frequently required when undertaking improvement projects of this type and provides a guide to costeffective, well-proven systems. Problems with failed or missing lintels, which in severe cases may include the collapse of masonry, can cause major contract delays during window replacement, which can lead to increased costs and serious inconvenience. The Helifix Helibeam bar and grout system reinstates failed lintels and creates new lintels using the existing brickwork, with all repairs being fully concealed and undertaken externally. When external walls are to be cladded with new insulation panels it may first be necessary to install additional wall ties to ensure that the building can bear the weight of the cladding. Helifix remedial wall ties are quick and easy to install and provide reliable connections in all materials from soft blocks to concrete. Copies are available on request. Call 020 8735 5200, email: info@helifix.co.uk or visit www.helifix.co.uk

P&SMAR14.indd Sec1:60

New shoring system unveiled Layher Ltd is introducing a new frame-based shoring system to the UK designed to provide quick, efficient and safe assembly with maximum versatility. The Layher Allround® TG60 shoring system has been developed as a complement to the company’s proven Allround® range of scaffolding systems. The new system is designed to provide 60kN loading capacity per leg or standard and the shoring frames are available in three size options on two faces of each tower. The remaining two sides can be constructed from existing Allround® stocks. The erection procedure complies with NASC Safety Guidance SG4:10 so that the scaffolder is always behind a protective guard rail, standing on a relocatable platform that ascends with the erection procedure. The lightweight components facilitate ease of handling, and the reduction in the number of standard parts required means less time is taken in setting up, which owes much to the ‘Rosette’ connection system used by the Allround® system. For more information call 01462 475100, email: [email protected] or visit our website: www.layher.co.uk

26/02/2014 11:24

›

PRODUCTS & SERVICES




61

Setting the standard on cutting systems safety ESAB Welding & Cutting Products has effectively implemented the new European EN ISO standard 17916 for the safety of thermal cutting machines. ESAB spearheaded the initiative to establish the new EN ISO standard, which provides enhanced worker safety, and is the first and only cutting systems manufacturer to currently stand in full compliance. From now on all the cutting systems manufactured at ESAB’s Karben, Germany facility will meet the new EN ISO safety requirements, scheduled to go into effect throughout the industry in late 2014. The new standard mandates that OEMs conduct their own evaluation and testing for the safety of their thermal cutting machines. The standard defines the potential risks to cutting systems operators and the measures to counter them. In addition to compliance with the new EN ISO directive and all applicable industry standards, ESAB provides a variety of innovative and continually improved safety options to ensure optimum worker protection during machine operation. Visit www.esab.co.uk for further information or call 0800 389 3152

Design of Liquid Retaining Concrete Structures This third edition of a successful text provides guidance for the subject of retaining structures following the new suite of Eurocodes. The book provides a clear path through the design process and the introduced modifications, such as: changes to surface zones, the critical steel ratio, the maximum crack spacing (flexural and imposed strain) and edge restraint are highlighted and discussed in detail. In keeping with the Eurocodes this new edition provides more theoretical background with reference to current and previous research, helping the reader to achieve a greater understanding and a wider application of the basic design. For further information email: info@whittlespublishing. com, visit www.whittlespublishing.com or call +44(0)1593 731333

WANT TO ADVERTISE YOUR PRODUCTS & SERVICES? Contact Adam Dickinson on 020 7880 7633 or email your press release to [email protected]

TheStructuralEngineer

Low energy ties solutions launched at show Stainless steel masonry support and restraint fixings manufacturer, Ancon, is teaming-up with brick manufacturer, Ibstock, to present its range of sustainable and low energy construction solutions at Ecobuild at ExCel London this month. A new version of the company’s ultra-low thermal conductivity TeploTie featuring a stainless steel L-shaped upstand for connecting to steel, concrete or timber frames is due to be launched. The new tie will be displayed alongside the original TeploTie and other stainless steel wire ties from the company’s range of thermally efficient cavity wall ties. The company will also be displaying its range of thermally insulated connectors for minimising heat loss at balcony/building junctions. Solutions are available for concrete-to-concrete, steel-to-concrete and steel-to-steel applications. Other products on display include thermal breaks for masonry support systems, stainless steel bed joint reinforcement and windposts and technical experts will be on hand to discuss CE-compliant fixing systems. Further information visit www.ancon.co.uk

The flagship publication of The Institution of Structural Engineers

P&SMAR14.indd Sec1:61

26/02/2014 11:24

›

SERVICES DIRECTORY


62

TheStructuralEngineer March 2014 STRUCTURAL DESIGN & CAD DRAWING

ANALYSIS & DESIGN

TONY DOYLE ASSOCIATES LTD COMPUTER AIDED DESIGN & DRAWING

Au t o CAD D r a u g h t i n g S e r v i c e s We are a UK based team of professional technicians and engineers providing an efÀcient, on-demand service for our clients - Structural Design & Detailing - RC Detailing Specialists - Bespoke Drawings for all Applications -

Tel: 01275 390482 www.tonydoyleassociates.co.uk STRUCTURAL DESIGN

Don't use a sledgehammer to crack a nut. Our software is easy to use, easy on the pocket and produces easy to read output ...

SuperBeam

BS449/BS5268

ProSteel

BS5950

Beam and column design using the codes you know and understand.

EuroBeam

EC3/EC5

Eurocodes made simple? Perhaps not simple, but hopefully less scary! For free demo versions visit our websites www.superbeam.co.uk www.eurobeam.co.uk

Greentram Software Pty Ltd SITE INVESTIGATION

Paul Benham Partnership has survived the recession Àt and well, with a few changes, and is now looking for new business for 2014 and beyond. Established 1980. Extensive experience. Proven reliability. In years gone by our turnover was split 50/50 between General Arrangement drawings and RC Detailing.These days we almost exclusively specialise in RC Detailing with AutoCAD/CADS RC. [email protected]

Paul Benham Partnership Ltd Civil & Structural Engineering Draughting Service

DirectoryMarch14.indd 62

www.paulbenhams.co.uk 01273 730956 South Coast and London OfÀces

HERTS AND ESSEX SITE INVESTIGATIONS + Contaminated Land Investigation + Soil Surveys + Field & Laboratory Testing + Subsidence Investigations The Old Post Of¿ce, Wellpond Green Standon, Ware Herts SG11 1NJ Tel: 01920 822233 Fax: 01920 822200

26/02/2014 11:23

›

TheStructuralEngineerJobs

Telephone 020 7880 6212

Email [email protected]

Register to receive latest jobs by email - visit www.thestructuralengineer.org/jobs.


Sterling Services Architectural Precast Specialists Design/Project Manager Are you an intuitive and charismatic engineer? Sterling Services design, manufacture and install bespoke architectural pre-cast products and we are looking to expand our capability. We are looking for someone to lead our design office and assist in the front end management of our projects, attending design workshops (London), advising our clients and directing our designers. Specific training and experience relating to our products will be gained during employment. The ideal candidate will have:• A good understanding of engineering principles, RC design, and concrete technology • A ‘can do’ approach to design • Knowledge of ACAD, MS Project and intranet based PM • Confident, enthusiastic and commercially aware

Further opportunities are available within the business. We also have opportunities for pre-cast designers and engineers. To find out more or to apply, please contact Chris Bell on 01784 490060, [email protected] www.sterlingservicesltd.com

www.garenne.gg Sterling Services are part of the Garenne Group

Jobs WE CAN HELP YOU FIND GRADUATE/SENIOR STRUCTURAL ENGINEER Based just a short distance from Cheltenham, Gloucestershire, Rowntree Partnership is a well established Consultant Civil and Structural Engineering company with a large, varied and retained client base. Our projects naturally therefore follow a similar path of interesting and varied complexity including commercial, industrial, retail, public building contracts and domestic developments across the South West and Midlands. Applicants should be degree qualified in Civil and/or Structural Engineering and ideally chartered or working towards chartered status with minimum of 2 years experience within a structural consultancy environment. The candidate must have excellent inter-personal skills, with good leadership capable of communicating information and instruction effectively to other members of the project team, and be self-motivated and enthusiastic. Competent use of design software such as CSC Tedds, Fastrak and Building Designer would be of significant advantage whilst the ability to design in all of the major building materials, steel, concrete, timber and masonry would be essential. This role is to work as part of a building structures team, taking a design and supervisory role in project work, focused on production, delivery, client liaison and site inspections /meetings etc. This position provides excellent prospects for continued career advancement, a friendly working environment, and Rowntree Partnership will offer a competitive salary to the right applicant who can demonstrate the above qualities. Please send your CV with a covering letter outlining your key attributes which you feel make you ideally suited to this opportunity by email to Practice Partner David Williams: [email protected]

RecruitmentMar14.indd 63

your perfect role Jobs by Email Be the first to receive your perfect job straight to your inbox. To sign up simply; Enter your name and email address Choose the sector, salary and location you would like to work in Create up to 5 different tailor-made alerts

www.thestructuralengineer.org/jobs

26/02/2014 15:04

›


Telephone 020 7880 6212



-/#

Á,@ ! ú A 8 8 02031595387 8 8 02031595387 * #ú

" ú * ú

Ð73A333JÐ78A333( (

Ð57A333JÐ5:A333(

This international award winning engineering firm is seeking hands-on senior structural design engineers for their offices in London. You will be experienced in delivery of high value projects, for high profile clients within the residential, commercial and mixed use development sectors. Experience in steel structure and reinforced concrete design would be beneficial. This is an urgent requirement, and an excellent package is on offer.

Our client is looking to expand their Edinburgh office. They are an architecturally led practice, having worked with many of the best known Architects in Scotland. Currently they are seeking a Graduate Structural Engineer with 1-2 years post Graduate experience with an interest in structural design and architecture. This position will allow you to benefit from working on a broad spectrum of building projects ranging in value from a few hundred pounds to more than £20million.

=========================================== ** Ð74A333JÐ77A333( Our client is a small consultancy, based on the outskirts of Bristol. They are seeking a senior structural engineer to join the team, someone who has potential to take on a Director role within the next few years. You will be Chartered, or near Chartered, and have hands-on design experience in all building structures materials. You will take a lead role in projects, and be given full autonomy. A team leader, who can motivate and encourage the best out of their team. Interesting and varied project base.

===========================================

- #ú #ú Ð93A333JÐ98A333( This international consultancy requires a structural engineer who is looking to progress their career to Associate Director level. Your technical expertise will be required on a number of projects covering residential, commercial, industrial and various educational and leisure sectors. As well as technically leading the projects you will also play a major part in running the office. This will require good man-management, training and mentoring skills. It is a fantastic opportunity for you to lead all aspects of the structural division from the projects you take on through to the development of your team.

" ú * Ð59A333JÐ63A333( Our client is a well established national firm of consultants, who are currently seeking a Graduate Structural Engineer. You will have a fair degree of post Graduate experience, with good all round building design ability in a consultancy environment. Capable of working in a team on a variety of projects and with good communication skills. This is an excellent opportunity for an up and coming engineer to join a thriving consultancy.

!ú M =À¿Àø À ::

À¿À ¿øøøÀ=À Á ³À¿Àø À ::l02031595387

STRUCTURAL ENGINEER Davies Maguire + Whitby is a leading design focused Structural Engineering practice based in central London. Our projects range across all sectors with values up to £120m, including bespoke private homes, landmark Listed buildings and major new build developments. Recently shortlisted in the SME Consultant of the Year category in the 2014 NCE/ACE Consultant of the Year Awards. We pride ourselves on delivering exceptional engineering solutions through a personal and proactive approach. As part of our strategic growth we are looking for Graduates, Senior structural engineers and an Associate, with good technical and communication skills along with an enthusiastic nature. We offer engineers an opportunity to build on their current experience within a friendly environment where everybody, including the directors, are very much handson. We offer a competitive salary, annual bonus and a range of company benefits. Please send your CV by email to Jane Powell at [email protected] Davies Maguire + Whitby is an equal opportunities employer.

Global-MSI is seeking a commercially orientated Structural Engineer with a minimum of 3 years steelwork design experience, gained with a steelwork fabricator or consultant engineering practice. Global-MSI is a specialist design and build contractor specialising in the design, manufacture and installation of petrol filling station forecourt structures through our operation centres in the UK, Ireland and Poland. We are a highly competent professional organisation comprising an in-house team of structural engineers, draftsmen, project managers, site engineers and skilled tradesmen operating in modern manufacturing facilities. The position is based in Doncaster, South Yorkshire and offers a competitive salary, appropriate to qualification and experience, and other benefits. A working knowledge of current British Standards & Eurocodes, Building Regulations, construction details, and basic foundation design is required. An understanding of sustainable construction would be an advantage. Knowledge of relevant CAD software with steelwork Design Standards is essential. An appreciation of Lean Manufacture techniques and principles would be beneficial but not a pre-requisite. Interested candidates should email a current CV with covering letter to the Managing Director [email protected]

global-msi.com


26/02/2014 15:04


-/# Á,@ ! ú A 8 8 02031595387 8 8 02031595387 - a- - a- ú ú Ð85A333JÐ88A333(

** * * $ $ Ð6;A333JÐ75A333(

A rare opportunity has arisen to join a world leading engineering consultancy, at Associate / Associate Director level. You will be a Chartered Engineer with experience in managing large projects, from concept to completion. You will have excellent client liaison skills, and the ability to build our client’s presence within the local market. A focused and enthusiastic approach, with attention to detail and team leading skills is a must.

Our client is an award winning multi discipline international consultancy, who work on high profile projects throughout the UK. Their success has resulted in continued growth to the North East of England, and they have an urgent requirement for a senior structural engineer in their Newcastle office. You will be experienced in managing all types of buildings structures projects, from concept to completion. A knowledge of civiling engineering would be useful, but is not vital. Natural team leader with good hands-on design ability is required. Contact us for more details.

=========================================== ( * ' Ð7;A333( This international firm of engineers, who have won many awards for their innovative project designs, is seeking a principal engineer to join the structures team in their Manchester office. You will head up the design team, supporting the Associate, supervising team members and ensuring projects are delivered on time and within budget. You will be degree qualified, and Chartered, with a CV that demonstrates experience in a similar role. This is an excellent opportunity to join a blue chip company.

=========================================== * -ú Ð66A333JÐ6;A333( Our client is a national company with an enviable reputation for creating high quality residential and commercial developments, and an impressive portfolio of projects throughout the United Kingdom and its offshore islands. They are seeking a self-motivated and ambitious Engineer to work on a broad range of building structures. You will have at least 5 years’ post Graduate experience, with good client liaison skills. This is a superb opportunity that would suit an engineer looking to progress their career.

Á ::: ø¿? Q. Qú-ú Q$ ú* Q; ; ú

=========================================== ** ú Ð75A333JÐ78A333( Our client is a global engineering firm, with an enviable reputation. Their Cambridge office is currently seeking a Chartered, or near Chartered, senior structural design engineer to join their buildings team. Your client base will be public and private sector, and you will work on a broad range of projects including commercial, healthcare and educational. Experience in running your own projects is a must, including ensuring projects are completed on time and within budget. This is an excellent opportunity to join a company who offer unlimited career progression.

** Ð6;A333JÐ76A333( An ambitious and self-motivated Chartered or near Chartered Structural Engineer is required by our client to work on a broad range of building structures projects. You will need to have a strong technical design background, excellent project and team leading ability, as well as good client liaison skills. This is a superb career opportunity that would suit a senior engineer looking to progress their career within a highly regarded consultancy.

===================================== - Ð85A333JÐ88A333( Our client is an international consultancy with a strong client base both within the UK and abroad. They are looking for an Associate Director within their Structures team in Birmingham, who can adopt combined hands on and managerial role, and who will be able to rise to Director status. The practice is able to offer an excellent variety of work that will encompass new build work in the private and public sector, as well as a stream of challenging projects. You should have good design, project management and leadership skills.

!ú M :À¿Àø À ::

=========================================== * * æ #ú Ð75A333JÐ78A333( Our client is an international consultancy who recognises the value of their staff and rewards hard work. Their success has ensured an increasing workload, and to assist they are seeking structural surveyors to work on projects in their Birmingham and Central London offices. You will, ideally, be a Chartered structural/civil engineer with extensive surveying experience of domestic and commercial, as well as historic and industrial buildings. The ability to attend site inspections, undertake investigations and identify defects, and suggest solutions is vital and you will therefore require a good understanding of the structure and fabric of buildings. There is the possibility of travel to other offices. Enthusiastic team player required.

' øøÀ(ÁÀ ± ÀA ô

ú

===========================================

À¿À ¿øøøÀ=À Á ³À¿Àø À ::l02031595387


26/02/2014 15:04

›


Telephone 020 7880 6212



This is my story “Sharing knowledge and expertise as we deliver inspirational structural engineering design projects across the world.”

“Working closely with clients, architects and developers on a wide variety of building structures, we lead all kinds of projects from nuclear power stations to airports and railway stations.”

Ed, Associate Director | London

Associate Directors Potential salary package up to £70k Epsom/London If you’ve a real passion for building design, we can offer you the opportunity to lead a brilliant team and deliver multidisciplinary projects across a variety of sectors. Able to inspire all around you and build excellent client relationships, you must have an impressive track record of driving structural engineering design projects from concept to construction. Large-scale projects. Flexible working. Some of the biggest challenges of our time. Your story starts here. There’s more to us than meets the eye, so discover more and apply at www.atkinsglobal.com/careers/structuralengineering Or contact [email protected] / 0207 121 2675. For a preview of what we do visit www.atkinsglobal.co.uk/theatkinsfilm

We are a busy practice with a varied and interesting portfolio of commissions, working with a number of interesting Clients in all forms of development. We are now seeing an upturn in our project workload after some years of stagnation and we need staff in the following grades to assist with our current portfolio and to assist with the future development of the Practice.

SENIOR ENGINEER You will be a proactive engineer, either chartered, or nearly chartered and experienced with most structural materials, with a proven ability to design and manage projects from feasibility stage to completion. You should be keen to advance your career as this position offers the possibility of Associateship within the Practice.

ENGINEERS Ideally you will be a graduate engineer with relevant experience or be able to demonstrate equivalent experience in the field of structural engineering. You should be keen to advance your career and to progress to Chartered status (if applicable). Both of the above positions offer competitive salary and holiday packages in a friendly and progressive atmosphere. Please send CV initially to Ms. Denise Merton at R J Witt Associates, 7 Aberdeen Road, Croydon, CR0 1EQ or email [email protected]

www.rjwitt.co.uk

R J WITT ASSOCIATES CONSULTING CIVIL AND STRUCTURAL ENGINEERS We are a small award winning consultancy based in Coventry who specialise in historic buildings and conservation as well as new build structures. We are looking to expand our current team due to increased workload and opportunities and seek the following:

Senior Structural Engineer Chartered engineer who has experience in the design of all construction materials and has past experience of acting as project engineer on schemes up to £5m. We are looking for the candidate to also have an interest in historic structures although past experience in this field is not essential.

Structural Design/Detailer Engineer who is working towards chartered status or already chartered and has experience in the design and detailing of all structural materials. The candidate will have an opportunity to further their knowledge on a variety of projects and will be expected to organise their own projects from concept through to supervision on site, as well as working within a team on the larger projects.

Senior Detailer Experienced detailer/technician who is proficient in the use of AutoCAD and familiar with steelwork, reinforced concrete and traditional construction who can also oversee the current small draughting team.

Salaries are negotiable and applicants CV’s can be sent via post to 13 Allesley Old Road, Coventry, CV5 8BU or via email to [email protected]

www.fwhaywood.co.uk


Tel: 024 76 678921

26/02/2014 15:04


2 Structural Design Engineers SW London Ref: 12341/3-4 Up to £34,000 + Benefits

knowledge based recruitment in structural engineering consultancy

EAST LONDON HOUSE

Unique leading global Architects/ Engineers has a requirement for 2 Structural Design Engineers to join the business as it expands its teams post-recession. Candidates will need to be a Graduate member of IStructE, have a MEng/MSc in Civil, Structural or Architectural Engineering and must have good design skills in high-profile new-build construction.

ASTLEY CASTLE

STRAND EAST TOWER

4 Structural Design Engineers Central London Ref: 585/8-11 Up to £47,000 + Benefits No 1 premier global consultancy has a HEYNE TILLETT STEEL requirement for 4 Structural Design Engineers to join different teams in its London studio as it continues to win new commissions. 2 Associate Candidates will need to be near or Structural Engineers recently Chartered with IStructE and/ or ICE (2012-2015) and must have Central London Ref: 87/131-132 worked previously in another Up to £44,000 + Benefits design-focused, high-profile Unique rapidly-expanding design-focused consultancy environment. consultancy with the largest structures team in London has a requirement for 2 new CHETHAM’S SCHOOL OF MUSIC Associate Structural Engineers to join the expanding business post-recession. Both candidates will need to be Chartered with IStructE and/or ICE and will be considered if looking for a stepup from their current Senior Engineer grade.

PRICE & MYERS

Chartered Senior Structural Engineer Central London Ref: 93/73 Up to £46,000 + Benefits eHRW & WOOD BETON SPA PEMBROKE COLLEGE FOOTBRIDGE W

Leading medium-sized niche consultancy has a requirement for a Chartered Senior Structural Engineer to join the business as workload continues to build. Candidates will need to be Chartered with IStructE and/or ICE and will be experienced in the design and project-running of typical London refurbishment and new-build developments under £50million.

SOUTHEND PIER HEAD

Structural Revit Technician Central London Ref: 585/7 Up to £55,000 + Benefits

PRICE & MYERS

No 1 global consultancy has a requirement for a Structural Revit Technician to join one of its London studio teams working on a large complex project with a top Architect. 2 Senior Structural Candidates will need to have extensive Engineers “building structures” draughting and coordination experience and will need London Ref: 201/59-60 to have several years Autodesk Up to £46,000 + Benefits Revit Structure working 100 strong design-focused niche knowledge. consultancy has a requirement for 2 Senior Structural Engineers to join both its Central BISHOP EDWARD KING CHAPEL London & South West London offices. Candidates will need to be near or recently W Chartered with IStructE and/or ICE, hold a MEng/MSc and must have gained good design and project-running skills in another design-focused London consultancy. PRICE & MYERS

2 Structural Design/ Project Engineers Central London Ref: 7002/46-47 Up to £42,500 + Benefits One of London’s best young niche consultancies has a requirement for 2 Structural Design/Project Engineers to join different teams as it continues its expansion. Candidates will need to be a Graduate member of IStructE (prefer) and/or ICE and must have a MEng/MSc combined with excellent design and/or projectrunning skills gained in London consultancy.

PRICE & MYERS EMIRATES AIR LINE W

STRUCTURAL AWARDS

WINNERS 2013

For the third year running we were a proud sponsor of The Structural Awards by IStructE and this year we sponsored the “Award for Arts or Entertainment Structures”. Well done to all the winners and see featured iconic projects by some of this year’s successful nominees and clients of Walker Dendle Technical Recruitment.

Walker Dendle Technical Recruitment would like to congratulate Price & Myers x2 & Expedition/Buro Happold/URS on winning their categories at the Structural EXPEDITION, BURO HAPPOLD, URS Awards 2013 for their projects featured with a W. For the 7th year running we again had a table for the night with guests from AECOM, Conisbee, Eckersley O’Callaghan, Elliott Wood, Engenuiti, Heyne Tillet Steel, Lyon’s O’Neill, Price & Myers and Webb Yates. IMAGES SHOW RECENT PROJECTS

UNDERTAKEN BY SOME OF OUR CORE CLIENTS


PRICE & MYERS

T 020 8408 9971 E [email protected]

uualkerdendle.co.uk

26/02/2014 15:04

Push the boundaries... Analysis

Concrete

Steel

Composite

Timber

Masonry

Retaining Walls

Drafting

Lite Suite

The UK’s leading range of integrated structural analysis, design, drafting and detailing software. Its power, versatility, user friendliness and excellent technical support make it the designer’s first choice. Visit us at:

www.masterseries.com Building Design Suite

Live Webinars Our Free MasterSeries Webinars showcase the modules in the MasterSeries and also offer free training to MasterSeries users.

MasterSeries 2014 Launch 25 Mar 2014 | 1pm - 2pm

The MasterSeries Building Design Suite brings together the

Connection Design to EuroCode 3 29 Apr 2014 | 1pm - 2pm

core MasterSeries analysis, design and drafting components to provide the ultimate building design solution. Its extreme versatility allows you to design almost any structure in one multi-material modelling environment. Visit our website

Design of Portal Frames to EuroCode 3 27 May 2014 | 1pm - 2pm

to see why it has become the software of choice for thousands of Structural Engineering professionals.

Civil and Structural Computer Services Ltd 1 Circular Road, Newtownabbey Co. Antrim BT37 0RA United Kingdom [email protected]


Contact us on:

+44 (0)28 9036 5950

26/02/2014 11:23

2014 Issue 3

Recommend Documents