CCTV Building, A Structural Design Overview

CCTV Headquarters, Beijing

A Structural Design OverviewBy Peter M. Bach (August, 2008)

Before we start…

Will it stand by itself?

Before we start…

It can! But the question is: How much effort does it take to make it

fall?

Before we start…

THIS?!

Topics

General Project DetailsArchitectureConstruction ChallengesDiagrid Framing SystemOther Structural FeaturesMiscellaneous TopicsThe Other BuildingsConclusion

General Project Details


Background The new HQ for China’s CCTV

Completion in time for Olympics

Will broadcast the Olympics to the World

Components:CCTV Building (Headquarters & Broadcasting)TVCC Wing (Cultural Center, Performing Arts)Media Park (Social Gathering Place)

First of 300 towers to be constructed in Beijing’s CBD


LocationIn Beijing’s CBD (Third Ring Road)East of Forbidden City


Admin – Site – History Project Manager: Dongmei YaoPartners in Charge: Ole Sheeren & Rem KoolhaasArchitects: Office for Metropolitan Architecture (OMA)Structural Engineers: Ove Arup & Partners

10-hectare site

Two L-Shaped Towers, tallest tower is 230m high

Total Estimated Construction Cost: €600million

Will employ 10,000 people


Admin – Site – History (cont.)

Comparing Building Heights in Asia

Comparing Building Heights in the World

“…The building is by any conventional definition a Skyscraper…”

(UK Telegraph)


Admin – Site – History (cont.) Towers Lean at 60o angles and “kink” at right angles at the top

Cantilever overhang starts after 36 floors and is 13 floors high.

The towers cantilever 75m outwards

History December 2002 - OMA wins design March 2003 – Project Start (after review) September 2004 – Groundbreaking Mid 2007 – Overhang Construction Underway Early 2008 – Finalizing Construction


Space Usage

Administration16.13%

Program Of-fices

13.98%

News Pro-duction15.05%Broadcasting

8.60%

Program Production

25.81%

Staff Facilities6.45%

Parking13.98%

CCTV Total Area Distribution

Administration

Program Offices

News Production

Broadcasting

Program Production

Staff Facilities

Parking


Space Usage (cont.)Yellow = CanteensDark Blue = StudiosGreen = Open StudiosOrange = Lobbies (Tower & Sky)Pale Green = BroadcastingLight Blue = Sports & RecreationRed = VIP Areas

- Lobbies on Ground & Top Floors

- Recreation mainly on bottom

- Elevators in both towers

- Separate Lobby & Elevator for

VIPs

- Two Ground Floor Lobbies

- Continuous Loop through

Towers

- Studios mainly on the lower

Floors


Nicknames & Descriptions

“Twisted Donut”

“The Pants”

“Two drunken, upside-down Ls”

“Each Tower is a banana, built with a deliberate slight curve…”

“Contorted Loop”

“Lopsided Colossus”

Architecture

Architecture

What do you think “logic” and “beauty” is defined as?

Architecture

The Skyscraper Concept

What do all the above buildings have in common?

Height! Human Capabilities

Architecture

The CCTV’s ConceptArchitect: Rem KoolhaasChina willing to try out new ideasEverything to do with TV Production is within the CCTV Building (“An inter-connected loop of inter-connected activities”)Iconographic Constellation instead of hopeless race for ultimate height“…As verticality soars, creativity crashes…”“…An Expression of Verticality…”Idea should create buildings that will actively engage the cityscape

Architecture

The Architect’s OpinionCommunity combined as opposed to separateConcentrate every program into a single system“It is important to encourage different kind of work of

engineering as it is with architecture”“Experimenting with Engineering liberates imagination

and makes other things possible”

The idea links a bit with communism as is still seen in China

“There is a natural affinity between the values of architecture and the values of socialism”

Hopes to spread this new building idea in Europe

Architecture

The Basic GeometryMobius Strip (continuous loop)Cantilever OverhangDiagonal Structural Grid SystemL-Shaped

Construction Challenges


What kinds of Challenges will this Project face?

A lot steel is used Weight Issues (instability)Beijing is an Earthquake Prone Area (need seismic stability)Every building encounters vertical and lateral loadsTemperature changes, material deformationSubsoil Conditions:

Shallow foundation not sufficientPore Water present in great amountsHigh Settlement Risk


What kinds of Challenges will this Project face?Needs to accommodate 10,000 people, heavy equipment High service loadsVulnerable to Natural or Man-Made DisastersHow to design & construct?

Performance-based Design Approach

Diagrid Framing System


What is it? Short for Diagonal Grid System

Triangulated structure with diagonal support beams

Similar to a typical moment frame

Triangles connected at Nodes and Rings intersect the nodes

Combines the benefits of a hollow tube with a truss

Loads follow diagonals, gravity and lateral loads can be transferred by the system to the ground

Swiss Re, London


What is it? (cont.)Can be constructed of either:

Steel (most common) Timber Reinforced Concrete

Steel is typical because of high tensile and compressive strengths

Essentially marrying columns, diagonals and bracings into one system

Not a new technology, used in early aviation and small-scale structures


Load Transfer

1.) Vertical Loads

2.) Lateral Loads


Load TransferLoad transfer happens primarily through diagrid

Internal Cores will transfer minimal amounts of gravity loads Floor Slabs do not have to transfer lateral loads Less internal columns required = more space Floor plates do not have to be of the same shape on each

floor

Continuous and Uninterrupted Load Transfer

Rings help to resist Buckling Loads transforming whole system into one big tube


Advantages of this SystemStructurally very strong

Less material required (~20% reduction in steel as opposed to typical moment frame method)

Aesthetically Pleasing – Blends in together with façade

Floor plan becomes open and free – more internal space

Most forms can be created with a triangulated form – architectural freedom

Self-reliant structure, simple in shape


Advantages of this System (cont.)Simple Construction Technique

Skyscraper Structural Failure minimized by diagrid construction

Better ability to redistribute loads than a moment frame (Failure of one portion does not mean complete structural failure)


Disadvantages of this SystemNot thoroughly explored for skyscraper construction yet

Inexperienced construction crews

A diagrid structure will definitely show in the aesthetics, very difficult to hide

Difficult to create a consistent window design

Heavy-handed if not executed properly

Material usage can be very excessive if loads are not high

Other Structural Features


Connections – Butterfly PlatesCritical Members in the Structural System

Must ensure a “strong joint-weak member” system

Must resist maximum probable load from braces with minimum yielding and stress concentration

Butterfly plates used to assist smooth load transfer

Finite Element Analysis of Connection


Connections – Butterfly Plates


Foundation – Piled Raft Total Settlement estimated as <100mm

Differential Settlement kept to 1:500

Piles are 1.2m diameter and 35m long

Piled Raft is 7m thick and has a footprint greater than the towers

Tension piles used away from towers to resist uplift pressures


Load Transfer Assistance - TrussesHidden from view for architectural purposes inside

Link up external columns with internal steel core via pin-joints

Trusses span the bottom two floors of the overhang, loads above are transferred to these trusses, which subsequently transfer loads to the diagrid system

Major trusses located at building base (podium) to support the above loads


Load Transfer Assistance - Trusses


Building Internal Cores

Three main cores accommodating elevators

Cores remain vertical despite Tower Slope (shifted against floor plates)

One core dedicated to “Grandness” (Administrative), the other to “Newness” (News & Technology)

Miscellaneous Topics


Construction Procedure


Seismic Stability Design ApproachCCTV Performance-based Design for Seismic Stability well outside National Building Codes

Analysis for different seismic events

Level 1: Frequent Earthquake No structural damage

Level 2: Intermediate Earthquake Repairable Structural Damage

Level 3: Rare Earthquake Severe Structural Damage permitted, must not collapse


Seismic Stability Design ApproachOther Research shows test results depicting Overhang vertical displacement with time during an Earthquake

Tests also show that some braces go into plastic buckling during the Earthquake Dissipate seismic energy (GOOD)

Maximum downward displacement = 700mm


Dealing with WindWind Tunnel Experiments had to be carried out to assess the severity of Wind Loads

Building strength against a 100-year Wind was assessed

Method: Dynamic Analysis using High-Frequency Pressure Integration Method

285 Pressure Taps installed on 1:500 Scale Model

North and West Winds Critical

Southwest Wind worst for Vertical Loads


Emergency ScenariosIn the event of a fire or a major disaster (natural or man-made) that causes major structural damage, what are the possible escape routes and how long will it take?


Emergency Scenarios (cont.)Numerous Escape Routes

Looped Structure an Advantage

Reduced Escape Time

Better Safety

The Other Buildings

The Other Buildings

The TVCC BuildingHotels, Theaters, Cultural Center for Performing Arts

The Other Buildings

Service Building & Media ParkService Building: Energy Center, Guards Dormitories, Major Broadcasting Vehicle Garages, Fire Control Center

Media Park: Social Gathering place, filming options

Construction Progress

Latest Pictures of the Building

Dated June 2008

Conclusion

Conclusion

Building is to become an icon of Beijing’s Cityscape once completed and will play an important role for the 2008 Olympics

Architecture looks at iconography rather than the race for height – engineering creativity is better than height

Many structural challenges to overcome in realizing the project Performance-based design needed

Diagrid System, Butterfly Plates, Piled Raft Foundations, Load Transfer Trusses all deemed good solutions

Seismic and Wind Stability ensured through rigorous analysis

Emergency Escape Routes are effective

Other buildings on-site serve unique functions

References[1] Carroll, C., Xiaonian, D., Gibbons, C., Lawson, R., Lee, A., Luong, A., Megowan, R., Pope, C., (2006), “China Central Television Headquarters – Structural Design”, Steel Structures 6

[2] CB Richard Ellis, (2007), “The CCTV Tower: Central Icon of Post-Urban Beijing?”, CBRE Research – Asia 2007 Issue 1

[3] “CCTV Address”, China Academic Journal Electronic Publishing House, http://www.ckni.net, Last Accessed 25th May 2008

[4] “CCTV by OMA”, A+U Architecture & Urbanism July 2005 Special Issue, Tokyo, Japan

[5] “China Central Television (CCTV) Headquarters”, Design Build Network, http://www.designbuild-network.com/projects/cctv/, Last Accessed 25th May 2008

[6] Koolhaas, R., (2004), “Beijing Manifesto”, Wired Issue 8 2004

[7] Lee, S., “Nonlinear Dynamic Earthquake Analysis of Skyscrapers”, CTBUH 8th World Congress, Dubai 3-5 March 2008

[8] McCain, I., “DiaGrid: Structural Efficiency & Increasing Popularity”, http:// daapspace4.daap.uc.edu/~larsongr/Larsonline/SkyCaseStu_files/Diagrid.pdf, Last accessed 25th May 2008

[9] “OMA – New Head Quarters – Central Chinese Television”, arcSpace.com, http://www.arcspace.com/architects/koolhaas/chinese_television/, Last Accessed 25th May 2008

[10] Telegraph.co.uk, “2008 Olympics: New Towers for a New Superpower”, UK Telegraph, http://www.telegraph.co.uk/arts/main.jhtml?xml=/arts/2007/12/29/babeijing129.xml, Last Accessed 25th May 2008

[11] Telegraph.co.uk, “China’s ambitious building passes key test”, UK Telegraph, http://www.telegraph.co.uk/news/uknews/1572347/China%27s-ambitious-building-passes-key-test.html, Last Accessed 25th May 2008

[12] Xie, J. , To, A., “Design-Oriented Wind Engineering Studies New China Central Television Headquarters”, Technotes Issue No. 26, RWDI Consulting Engineers & Scientists

http://www.designbuild-network.com/projects/cctv/

Questions