T
all Building
Construction Technology Unit 1 Section 2
Subject Reading Text book Text bookss- lim limite ited d value value…. …... Internet Sites:
www.ctbuh.org (Council for tall buildings and urban habitat)
Definitions
When is a building a tall building? European definition: A building can be considered tall or ‘high rise’ when it exceeds 30 storey’s in height… Engineering definition: Buildings can be classified as ‘tall buildings’ when the structure of the building must resist significant lateral forces in addition to resisting significant gravity forces.
Lateral forces developed by the wind and gravity forces developed by weight… Lateral Loads Sway, Deflection and Oscillation
The nature of wind force acting on tall buildings. The force increases exponentially with increases in building height
Gravity Loads
The demand for tall buildings
Taipei 101
Currently the tallest Completed building in the world. Height: 508m Cost: £700million Space: 200,000m 2
Tall buildings presently under construction or in the process of development The World Financial Centre Shanghai
Tall buildings presently under construction or in the process of development
The International Conference Centre, Kowloon Hong Kong.
Tall buildings presently under construction or in the process of development
The ‘Trump’ Hotel Dubai
Tall buildings presently under construction or in the process of development
The Burj Al Alam Dubai
Tall buildings presently under construction or in the process of development
Al Burj Dubai
When complete, will become the Worlds Tallest Building at an unspecified height (believed to be in excess of 800 metres).
The Burj Dubai
BURJ DUBAI Information as of 5th Feb 2008 Floor level
=
159
Height
=
604.9m
Estimated construction cost =
£410
Cost of apartments =
£556,000£4,450,000
Freedom Tower
New York
Tall buildings presently under construction or in the process of development The ‘Shard of Glass’
London, UK
Why?......
Engineering Technology: Making Buildings Tall
The horizontal or lateral wind forces and the vertical or gravity forces that tall buildings must resist means that the structure must react or fight against two different force components…..this in turn means that we can think of the structure as having two dimensions:
A gravity structure; and, A ‘moment’ structure.
The structure for a skyscraper can be organised so that it has two separate but connected structural systems, one to react to each different force dimension; or, a single structural system can be organised to resist both sets of forces simultaneously.
The key goal is ‘Structural Efficiency’ and this is addressed in terms of weight.
Early Skyscrapers and the frame technologies used.
The Home Insurance Building, Chicago The worlds first Skyscraper
The Reliance Building, Chicago
Steel Frame organised to resist gravity loads….
A relatively straightforward system of columns, primary and secondary beams as is now familiar to all of you…
This type of frame is efficient at resisting the gravity loads, but what about the moment forces caused by wind?
Moments have to be resisted primarily by the connections between the beams and columns…..additional strength was offered by masonry encasement to columns and beams.
The culmination of straightforward steel frame structures
In early skyscrapers, the masonry encasement offered additional stiffening to the frame to assist it in carrying the moment forces produced by wind. Although present the effects of masonry encasement were ignored in the design of the Chrysler Building and the Empire State Building and the steel frames were designed to resist 100% of the gravity forces and 100% of the moment forces, but this produced a problem…..
Weight…., making the structural connections strong enough to cope with the moment forces encountered at height increases the overall weight of the building and this in turn increases the magnitude of the gravity loads that have to be resisted.
This leads to inefficiency in the structure….inefficiency = unnecessary cost. The Chrysler Building, New York
The Empire State Building, New York.
The ‘vierendeel’ or ‘shear’ frame. ‘ Moment’ Connections between Beams and Columns in the frame.
WIND
These provide some resistance to the wind by shear force.
Shear bending pattern developed by the structure in response to lateral wind force.
The Shear or ‘Vierendeel’ frame approach where moment connections between columns and beams are designed to resist the lateral force of the wind. The effectiveness of this approach depends on the rigidity of the connection and on the continuity of beam elements.
The Seagram Building, Mies van der Rohe, New York.
The development of the frame and core approach- Steel
Shear Truss Frames
WIND
Truss Resists moment forces Frame Resists gravity forces
The central ‘K’ braced truss in steel extends vertically from the foundations and acts like a large cantilever to resist lateral loads
Perimeter columns participate in bending but are primarily transferring gravity loads to foundations. Members in the truss forced into tension by wind force. Members in the truss forced into compression by the wind force
The development of the frame and core approach- Concrete
Shear Wall or Core Braced Frames
WIND
Core or Walls Resist moment forces Frame Resists gravity forces
By providing a truss or core to resist the moment forces, these solutions remove the requirement for connections between columns and beams to resist moment forces. This means that connections can be designed primarily around gravity forces and this in turn removes weight from the structure. Removing weight improves efficiency and this in turn reduces cost. These factors allow greater heights to be reached for the same cost or for the same weight of structure.
A core braced frame as would be typical in Reinforced Concrete instead of steel.
The core resists the lateral force produced by wind and the perimeter columns support gravity loads
Further increasing efficiency Central Core or Truss Structure Outrigger Trusses from core to external columns External Perimeter Columns
Belt Trusses Wrap around perimeter columns
View of outrigger and belt truss system without core and perimeter columns
Outriggers and Belt Trusses
Hat Truss and Belt Trusses Perimeter Columns
Core
Cross Section
Outrigger Truss and Belt Trusses
Wind
Perimeter Columns forced into Tension Core Core
Cross Section
Perimeter Columns forced into Compression
The development of the ‘tube’ approach
B
A D C
E
E
Tube in Tube and Bundled Tube approaches ‘Tube in Tube’ Systems
‘Bundled Tube’ Systems
Examples of ‘Tube’, Framed (Braced) ‘Tube’, ‘Tube in Tube’ and Bundled ‘Tube’ systems
Examples of ‘Tube’, Framed (Braced) ‘Tube’, ‘Tube in Tube’ and Bundled ‘Tube’ systems
