Case Study: CCTV Building - Headquarters & Cultural Center
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ctbuh.org/papers Title: Case Study: CCTV Building - Headquarters & Cultural Center Authors: Chris Carroll, Arup Craig Gibbons, Arup Goman Wai-Ming Ho, Arup Michael Kwok, Arup Paul Cross, Arup Xiaonian Duan, Arup Alexis Lee, Arup Ronald Li, Arup Andrew Luong, Arup Rory McGowan, Arup Chas Pope, Arup Subjects: Architectural/Design Building Case Study Structural Engineering Keywords: Construction Design Process Form Foundation Performance Based Design Structure Publication Date: 2008 Original Publication: CTBUH Journal, 2008 Issue III Paper Type: 1. Book chapter/Part chapter 2. Journal paper 3. Conference proceeding 4. Unpublished conference paper 5. Magazine article 6. Unpublished © Council on Tall Buildings and Urban Habitat / Chris Carroll; Craig Gibbons; Goman Wai-Ming Ho; Michael Kwok; Paul Cross; Xiaonian Duan; Alexis Lee; Ronald Li; Andrew Luong; Rory McGowan; Chas Pope Case Study: CCTV Building - Headquarters & Cultural Center Authors Chris Carroll, Paul Cross, Xiaonian Duan, Craig Gibbons, Goman Ho, Michael Kwok, Richard Lawson, Alexis Lee, Ronald Li, Andrew Luong, Rory McGowan, Chas Pope Arup Arup is a global firm of designers, engineers, planners and business consultants providing a diverse range of professional services to clients around the world. The firm has over 10 000 staff working in more than 90 offices in 37 countries. Arup has three main global business areas – buildings, infrastructure and consulting – although their multi-disciplinary approach means that any given project may involve people from any or all of the sectors or regions in which they operate. Arup has extensive experience in the field of tall buildings, having provided core multidisciplinary Figure 1. Architect’s impression of the building design services for such notable projects as 30 St. Mary Axe in London, the International Commerce Center (ICC) in Hong Kong, and the I.Q. Tower in Doha, Qatar. The new headquarters of China Central Television contains the entire television-making process within a single building. The 234m tall tower redefines the form of the skyscraper, with the primary system comprised of a continuous structural tube of columns, beams and braces Arup around the entire skin of the building. In order to gain structural approval an Expert Panel 13 Fitzroy Street London process was necessary, for which a performance-based analysis was carried out to justify the W1T 4BQ design. This made extensive use of finite element analysis and advanced non-linear elasto- t: (+44) 020 7636 1531 plastic time history to evaluate the structural behaviour and ensure the building safety under www.arup.com different levels of seismic event. The leaning form and varied programme, including the need to accommodate large studio spaces, posed additional challenges for the gravity structure, and resulted in the introduction of a large number of transfer trusses throughout the tower. Erecting and connecting the two massive towers presented the structural engineers and contractors with further design and construction challenges. Introduction Architectural Concept This article describes the structural design and China Central Television (CCTV), the country’s construction of the CCTV Building in Beijing, state broadcaster, plans to expand from 18 including development of the structural con- to 200 channels and compete globally in the cept, performance-based seismic design and coming years. To accommodate this expan- Expert Panel Review process. sion, they organized an international design competition early in 2002 to design a new “Prior to connection, the two Towers would headquarters building. This was won by OMA (Office of Metropolitan Architecture) and Arup, move independently of each other due to which subsequently allied with the East China Design Institute (ECADI) to act as the essential environmental conditions, in particular wind and local design institute (LDI) for both architecture thermal expansion and contraction. As soon as and engineering. The unusual brief, in television terms, was that they were joined, therefore, the elements at the all the functions for production, management, and administration would be contained on the link would have to be able to resist the stresses chosen site in the new Beijing Central Business caused by these movements. ” District (CBD), but not necessarily in one build- 14 | CCTV Building CTBUH Journal | 2008 Issue III Figure 2. Uniform bracing pattern Figure 3. Unfolded’ view of final bracing pattern ing. In their architectural response, however, Development of the structural form two-storey module (see Figure 2). This was OMA decided that by doing just this, it should From the outset, it was determined that the chosen to coincide with the location of several be possible to break down the ‘ghettoes’ that only way to deliver the desired architectural double-height studios within the Towers. A tend to form in a complex and compartmen- form of the CCTV building was to engage the stiff floor plate diaphragm is therefore only talized process like making TV programmes, entire façade structure, creating in essence an guaranteed on alternate storeys, hence lateral and create a building whose layout in three external continuous tube system. This would loads from intermediate levels are transferred dimensions would force all those involved to give the structure the largest available dimen- back to the principal diaphragm levels via the mix and produce a better end-product more sions to resist the huge bending forces gener- internal core and the columns. efficiently. ated by the cranked, leaning form – as well as loads from wind and extreme earthquakes. However, results of the preliminary analysis The winning design for the 473,000m², showed that the forces in the braces varied 234m tall, CCTV building (see Figure 1) thus The ‘tube’ is formed by fully bracing all sides of considerably around the structure, with combines administration and offices, news the façade. The planes of bracing are continu- particular concentrations near the roof of the and broadcasting, programme production ous through the building volume in order to Overhang and at the connection to the Base. and services – the entire TV-making process reinforce and stiffen the corners. The system This led to an optimization process in which – in a single loop of interconnected activities is ideally suited to deal with the nature and the brace pattern was modified by adding or around the four elements of the building: the intensity of permanent and temporary loading removing diagonals (i.e. ‘doubling’ or ‘halving’ nine-storey ‘Base’, the two leaning Towers that on the building, and is a versatile, efficient the pattern), depending on the strength and slope at 6° in each direction, and the nine to structure which can bridge in bending and stiffness requirements of the design, based on 13-storey ‘Overhang’, suspended 36 storeys in torsion between the Towers, provide enough a Level 1 earthquake analysis. This also enabled the air. strength and stiffness in the Towers to deliver a degree of standardization of the brace ele- loads to the ground, and stiffen up the Base ment section sizes (see Figure 3). to reinforce the lower Tower levels and deliver The public facilities are in a second building, loads to the foundations in the most favour- the Television Cultural Centre (TVCC), and both able possible distribution, given the geometry. This was an extremely iterative process due are serviced from a third Service Building that to the high indeterminacy of the structure, houses major plant as well as security. The with each changing of the pattern altering the whole development will provide 599,000m² The tube was originally envisaged as a regular dynamic behaviour of the structure and hence gross floor area and covers 187,000m², includ- pattern of perimeter steel or steel-reinforced the seismic forces that are attracted by each ing a landscaped media park with external concrete (SRC) columns, perimeter beams, element. It was carried out in close features. and diagonal steel braces set out on a typically CTBUH Journal | 2008 Issue III CCTV Building | 15 collaboration with the architect, since the pat- design engineers who are relieved of any legal Seismic Fortifi- Level 1 Level 2 Level 3 tern of visually expressed diagonals was a key responsibilities by virtue of compliance. The cation Level aesthetic aspect of the cladding system. Chinese code for seismic design of buildings Description Minor Moderate Severe (GB50011 – 2001), sets out its own scope of Peak ground 0.07g 0.20g 0.40g applicability, limiting the height of various acceleration The braced tube structure gives the leaning systems and the degree of plan and vertical Towers ample stiffness during construction, Average Return 1 in 50 1 in 475 1 in 2475 irregularities. Design of buildings exceeding Period years years years allowing them to be built safely within tight the code must go through a project-specific tolerances before they are connected and Probability of 63% in 50 10% in 50 2% in 50 seismic design expert panel review (EPR) and exceedance years years years propped off each other. The tube system also approval process as set out by the Ministry of suits the construction of the Overhang, allow- Fortification No Repair- No col- Construction. Criteria damage able lapse ing its two halves to cantilever temporarily (remain damage from the Towers. elastic) Although the 234m height of the CCTV build- Table1. Seismic performance objectives ing is within the code’s height limit of 260m The continuous tube has a high degree of for steel tubular structural systems (framed- inherent robustness and redundancy, and of- tube, tube-in-tube, truss-tube, etc) in Beijing, Elastic superstructure design fers the potential for adopting alternative load its geometry is noncompliant. The Seismic A full set of linear elastic verification analyses paths in the unlikely event that key elements Administration Office of the Beijing Municipal were performed, covering all loading com- are removed. Government appointed an expert panel of 12 binations including Level 1 seismic loading, eminent Chinese engineers and academics to for which modal response spectrum analy- closely examine the structural design, focusing ses were used.