Office building in Beijing (CCTV Building)

Office building in Beijing (CCTV Building)

Building use

Office building

Country/Region

All Regions

Overview

The CCTV new building is the headquarters building of China’s official media planned to be built after the 9.11 incident in the United States. Therefore, in addition to the need to ensure the safety of the main structure under the combination of vertical loads and earthquakes, the anti-terrorism and explosion-proof design of the structure, the resistance to progressive collapse, and fire prevention have become special concerns in structural design.

Basic information (construction date, number of stories, gross floor area, adopted design code, engineer(s), Contractor(s), etc.)

Construction date: 2012
Number of stories: 51
Gross floor area: 550,000m2
Adopted design code: GB 50009-2001; GB 50011-2001; GB 50010-2002; GBJ17-88; JGJ 138-2001; GB50007-2011; Eurocode 8
Engineer(s): East China Architectural Design and Research Institute Co., Ltd.(ECADI) and Arup Contractor(s): China State Construction Engineering Corporation(CSCEC)

Issue and/or innovation

The steel frame of the SRC column changes from single box to three boxes, and the basic modulus of the section size of the first box remains unchanged at 600mm. The thickness of the SRC concrete protective layer is 250mm, and the steel frame of the box body is a cavity. The main consideration is that it is difficult to pour and ram the map in the cavity, and the area is small. The maximum steel skeleton cross-section area of the SRC column is 0.62m2. The application of this type of SRC fills in some gaps in the specification. The steel ratio of the SRC composite column is 28% , which is much greater than the relevant regulations in the “Technical Regulations for Steel Concrete Composite Structures” (JGJ 138-2001). The comparison of finite element analysis and structural test results shows that the new SRC composite column not only has high compressive bearing capacity, but also has ductility comparable to steel columns, and 1~3 box-shaped steels in the composite column can be modularized according to the internal force of the column, which is convenient for the connection of outer cylinder support.

Reason for composite solution

The CCTV new building is the headquarters building of China’s official media planned to be built after the 9.11 incident in the United States. It is one of the infrastructures for the Beijing 2008 Olympic Games. Therefore, under this special background, in addition to the need to ensure the safety of the main structure under the combination of vertical loads and earthquakes, the anti-terrorism and explosion-proof design of the structure, the resistance to progressive collapse, and fire prevention have become special concerns in structural design. The main structure is a conjoined structure, the twin towers are inclined at 6 degrees, and the part above the 37th floor is connected by a 14-story L-shaped cantilever structure, and the structural system adopts a supporting cylinder structure. The outer column adopts steel column and steel concrete SRC column. The cross-sectional form and size of the outer cylindrical columns are mainly determined according to the distribution of the internal force of the structure, and at the same time, the cross-sectional area of the outer cylindrical columns should be reduced as much as possible to increase the effective use space of the building and the landscape view of the outer facade. Therefore, the steel columns are mainly arranged on the outside of the slanted cylinder to give full play to the characteristics of high tensile bearing capacity. Sectional steel composite columns are mainly distributed on the inner side of the inclined cylinder, which has the characteristics of high compressive bearing capacity. Because the architect strictly controls the size of the building section of the outer column, considering factors such as reducing the weight of the structure and building fire protection, 30% SRC with a high steel content is creatively applied to the new CCTV building for the first time.

Specific solution/technical details

The cross-section shape of the SRC column is complex, no concrete is poured in the cavity, and the surrounding of the steel frame is wrapped with constrained concrete. The calculation of the bearing capacity and the judgment of the ductility index of SRC columns with high steel content have become the difficulties in the design. Based on the integral algorithm of the cross-section fiber model and the assumption of a plane section, the designer compiled a general program for calculating the bearing capacity of SRC columns by using the powerful data processing capability of EXCEL and the convenient programming capability of VBA program according to the finite element principle. The ductility of SRC columns with high steel content can also be guaranteed by improving the structural measures of SRC columns, such as the arrangement of studs, the adjustment of steel section and the structure of stirrups. The ductility coefficient of the design axial compression ratio n=0.7 is greater than 3, which meets the ductility requirements during earthquake resistance. In addition, the on-site docking of two or more boxes of section steel is also a problem that needs to be solved. By staggering the height of two boxes of section steel for a certain distance, butt joints at different heights, the assembly welding seam of section steel within this section of height is welded on site.

Impact or effectiveness

This project adopts a new type of SRC column with high steel content, which combines steel and concrete to give full play to the advantages of each material. On the one hand, increasing the steel content improves the seismic performance of complex conjoined building structures in areas of high seismic intensity, and satisfies the transparent effect of building facades. On the other hand, due to the concrete protective layer, the fire performance of the SRC column is equivalent to that of the concrete structure, and at the same time it solves the corrosion protection problem often encountered in the steel structure. In addition, through reasonable construction, its seismic performance and ductility index are reliable. Compared with conventional SRC with steel content, the SRC column with high steel content can effectively reduce the cross-sectional area by more than 30%, effectively improving the efficiency of floor use. The modular arrangement of section steel is convenient for connection with the outer cylinder’s diagonal bracing. The stiffeners of the butterfly joints also serve as the side formwork of the SRC column, making concrete pouring and tamping more convenient. From the comprehensive calculation of the cost of the whole life cycle, the comprehensive economic benefits of SRC columns with high steel content are very significant.

References / Technical Papers Content

WANG Dasui, JANG Wenwei, BAO Lianjin, ZHANG Fulin, WANG Jian, SUN Zhanjin, TONG Jun, HUANG Yongqiang,LIU Zhibin. “Design and Study of New CCTV Building” J, Journal of Building Structures, 2008(03) 1-9. https://doi.org/10.14006/j.jzjgxb.2008.03.001
HU Jingli, CHEN Yiyi, ZAO Xianzhong, WANG Dasui, JANG Wenwei, BAO Lianjin. “Study on loading capacity of high steel ratio SRC columns under axial compression” J, Journal of Building Structures, 2008(03) 24-30. https://doi.org/10.14006/j.jzjgxb.2008.03.003
Wang Dasui, JiangWenwei, Bao Lianjin, Wang Jian, Liu Zhibin, Tong Jun, Huang Yongqiang, Sun Zhanjin. “Key Techniques for Structural Design of the New CCTV Tower of China Central Television” J, Journal of Building Structures, 2007(05). 1-7. https://doi.org/10.19701/j.jzjg.2007.05.001