TConstruction TechnologyUnit 1 Section 2

all Building

Subject Reading

� Text books- limited 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…

The nature of wind force acting on tall buildings.

The force increases exponentially with increases in building height

LateralLoads

Gravity Loads

Sway, Deflection and Oscillation

The demand for tall buildings

� Taipei 101

Currently the tallest Completed building in the world.

Height: 508mCost: £700millionSpace: 200,000m2

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,

KowloonHong 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

The BurjDubai

When complete, will become the Worlds Tallest Building at an unspecified height (believed to be in excess of 800 metres).

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 verti cal or gravity forces that tall buildings must resist means that the stru cture must react or fight against two different force components…..this in turn means that we can think of the structure as having two dimensi ons:-

� 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 r eact to each different force dimension; or, a single structural system can beorganised to resist both sets of forces simultaneou sly.

� The key goal is ‘Structural Efficiency’ and this is addressed in terms of weight.

Early Skyscrapers and the frame technologies used.

� 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 Home Insurance Building, ChicagoThe worlds first Skyscraper

The Reliance Building, Chicago

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’Connectionsbetween Beams and Columns in the frame.

These provide some resistance to the wind by shear force.

Shear bending pattern developed by the structure in response to lateral wind force.

WIND

The Shear or ‘Vierendeel’ frame approach where momen t connections between columns and beams are designed to resist the latera l force of the wind. The effectiveness of this approach depends on the rigid ity 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� Truss Resists moment forces� Frame Resists gravity forces

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 central ‘K’ braced truss in steelextends vertically from the foundationsand acts like a large cantilever toresist lateral loads

WIND

The development of the frame and core approach- Concrete

� Shear Wall or Core Braced Frames� Core or Walls Resist moment forces� Frame Resists gravity forces

A core braced frame as would be typical in Reinforced Concrete instead of steel.

WIND

The core resists the lateral force produced by wind and the perimeter columns support gravity loads

� 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.

Further increasing efficiencyCentral Core or Truss Structure

ExternalPerimeter Columns

Outrigger Trusses from core to external columns

Belt TrussesWrap around perimeter columns

View of outrigger and belt truss system without core and perimeter columns

Outriggers and Belt Trusses

Cross Section

Hat Truss andBelt Trusses

Outrigger Truss andBelt Trusses

Core

Perimeter Columns

Cross Section

Core

Wind

Core

Perimeter Columns forced into Tension

Perimeter Columns forced into Compression

The development of the ‘tube’approach

B

E E

A

C

D

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