A Study on the Effective Lateral Drift Control of Super-tall Buildings in Korea

Transcription

1 Technical Article Steel Structures 6 (2006) A Study on the Effective Lateral Drift Control of Super-tall Buildings in Korea Young-Hak Kim 1, * and Sung-Woo Shin 2 1 Senior Researcher, Research & Development Institute, Lotte Engineering & Construction Co., Ltd., Korea 2 Professor, Department of Architectural Engineering, Hanyang University and Chairman, KSTBF (Korea Super-Tall Building Forum), Korea Abstract High-rise residential buildings, especially multi-use residential and commercial buildings, have been prospering in Korea since the late 1990s. Although six of the 200 tallest buildings in the world are in Seoul, no building over 100 stories tall has yet been constructed. The characteristics of Korean high-rise buildings are as follows: they are located in Seoul City, Sungnam City, Kyung-gi province, and Busan City; they are m tall; and they are multi-use residential and commercial buildings. The purpose of this study is to determine special features of super-tall buildings in Korea through the value of their displacement contribution factor, calculated using the principle of virtual work. Ultimately, the most effective methods for controlling lateral drift are controlled analysis of real structural models using computer programs. Effects of lateral loadresisting systems are evaluated and compared in this study. Consequently, the most effective members for controlling lateral drift are presented in this study through an analysis using computer programs on a real structural model. Keywords: Super-tall building, lateral drift control, principle of virtual work, displacement contribution factor 1. Introduction 1.1. Social background Six Korea high-rise buildings are ranked among the world s tallest buildings. In the last decade, Korean construction companies have built high-rise buildings such as the KLCC and Telecom builiding, overseas buildings, and so many domestic high-rise buildings m high (Fig. 1). As a result, Korea now has more than 70 over-100-mhigh buildings mostly in Seoul City and Busan City. In addition, over-100-story building projects have been announced one after another, and so many tall buildings are still under construction (Fig. 2) Research objective and background A survey carried out during the 1 st KSTBF International Symposium (2002) showed that the necessity of super-tall buildings is acknowledged by 70.6% of.experts and the public in Korea. Current circumstances such as demand for ESSD (Environmentally Sound and Sustainable Development) and the search for a solution to population explosion are leading to expectations that tall buildings will be continually *Corresponding author Tel: , Fax: novice00@lottenc.com Figure 1. Chart of height of buildings in Korea. constructed. Hence, technologies for constructing supertall buildings in Korea have shifted from those in the initial phase to more advanced technologies. Tall buildings are uniquely characterized by the prime necessity for lateral loads to be considered in their design. Two types of loads normally associated with lateral loads are wind and earthquake loads. This study first analyzes emerging issues with respect to Korean super-tall buildings (STBs), then selects existing or proposed structural systems of tall buildings, analyzes these structural systems using a computer program, calculates the displacement contribution factor

2 238 Young-Hak Kim and Sung-Woo Shin Lotte world II (555 m) Lotte world II (510 m) IBC130 Project (570 m) Songdo tower (510 m) Figure 2. Korea super-tall building projects being planned. of the structural components such as the beam, column, shearwall, and outrigger using the principle of virtual work, and evaluates the results. Therefore, this study aims to present data for effective structural control of lateral drift Research method In this study, after analyzing a structural model similar to a real structural model using a computer program (MIDAS Genw ) and values calculated as one member force of each structural component under the ultimate loading condition and the member force of each structural component under the unit load (P = 1), the displacement of each structural component is calculated, and then the value is divided by the volume of each component. Finally, the impact on the relative size and locations of various structural elements is evaluated. 2. Emerging Status of Structural Systems of STBs in Korea Korean super-tall buildings are mainly located in Seoul City, Kyung-gi province, Sung-nam City, and Busan City; are m tall; and are mostly multi-use residential and commercial buildings. In selecting the structural systems, economic considerations demand that the economics of the structural system be considered the most important factor in Korea. The possible structural systems for the defined high-rise buildings are: a reinforced concrete shearwall + a moment-resisting frame (MRF), a reinforced concrete shearwall + an outrigger system, a tubular system, a multi-tubular system, and a mega-structure system. Among these, the structural system composed of a shearwall with high-strength concrete in its core, a moment-resisting system, and an outrigger is the more popular structural system in Korea (Table 2). The quest for more efficient structural systems has led Figure 3. Super-tall buildings in Seoul. to a new generation of hybrid mixed steel and concrete building structures. The displacement contribution factor of each component is calculated by applying it to the lateral resisting system of Korean super-tall buildings that consist of a reinforced concrete corewall, a moment resisting frame, and an outrigger and beltwall system. The purpose of this study is to find the most essential element in controlling lateral drift and to suggest the most effective method of lateral drift control. 3. Importance of the Core Position in the Building Plan The higher the building is, the more important it is to solve the vertical flow. For an effective structural system, it is important to determine the shape of the building plan and to determine the position of the core in the plan.

3 A Study on the Effective Lateral Drift Control of Super-tall Buildings in Korea 239 Rank Name Table 1. List of Korea s Super-tall Buildings No. of stories Height (m) Type of plan Structural system 1 Tower Place Y RC Core + RC Belt (16, 55 F) + SRC 2 Hyperion (Mok dong) A 동 X RC Core + MRF + Outrigger Truss (9, 32, 50 F) 3 KLI 63 building Rectangular MRF + Interior Brace 4 Tower Place I Box RC Core + Steel Outrigger with Belt Truss + SRC 5 Trade Tower Box RC Core + MRF 6 Star Tower Rectangular RC Core + MRF + Outrigger/Belt Truss/Cap Truss 7 Tower Palace Box+Box RC Core + Steel Outrigger With Belt Truss + SRC 8 Techno Mark (Kang Byun) ASEM Tower Tube + Brace + Moment Frame 10 Lotte World (Busan) Table 2. Lateral force resisting system in Korea Table 3. Types of plans of Korean super-tall buildings Rectangular Boxed Triangular Box + Box Y T X Free Figure 4. Analytical models Classification of STBs in Korea according to plan type Table 3 presents the types of plans of Korean super-tall buildings, which are generally classified into 8 groups Study on the efficiency of building plans according to the building s core position To design super-tall buildings effectively and economically, the position of the core in the plan should be carefully determined. This study demonstrates a simple example using a 60-story building structural analysis model that has the same size plan under the same loading condition. Figure 5. Diagram of test results. The design variable is the position of the core in the plan; the central reinforced concrete corewall, the eccentric

4 240 Young-Hak Kim and Sung-Woo Shin Table 4. Analytical model (Real structural model in Korea) Group A B C Name Lateral force resisting system Shearwall MRF Outrigger Belt Truss Number(s) Outrigger position H-239-A O O O O 4 9, 30, 50, 69 F C-175-A O O O O 1 19 F S-145-AA O O O O 1 15 F D-133-A O O O O 2 23, 43 F H-106-A O O O O 1 10 F H-156-C O O Ü Ü - - D-129-AA O O Ü Ü - - HW-109-Y O O Ü Ü - - S-81-B O O Ü Ü - - S-79-B O O Ü Ü - - S-56-B O O Ü Ü - - H A A: Type of plan 239: Overall height H: Construction company Table 5. Lateral force resisting system with outrigger Lateral force resisting system with outrigger Table 6. Lateral force resisting system without an outrigger Lateral force resisting system without an outrigger H-156-C D-129-AA HW-109-Y H-239-A C-175-A S-145-AA Table 7. General structural buildings Approximately 20-story structural buildings D-133-A H-106-A S-81-B S-79-B S-56-B

5 A Study on the Effective Lateral Drift Control of Super-tall Buildings in Korea 241 Table 8. H-239-A diagrams Displacement contribution factor of H-239-A Table 9. C-175-A diagrams Displacement contribution factor of C-175-A Outrigger Outrigger & Belt Truss Truss reinforced concrete corewall, and the exterior reinforced concrete corewall (Fig. 4). The results show that the most effective case is the application of the central core, the second eccentric core, and the third exterior core. If the application of the exterior corewall will be used, however, a reinforced concrete brace should be used. This is very unreasonable, though. Figure 5 graphically shows the difference according to the application of concrete compressive strength.

6 242 Young-Hak Kim and Sung-Woo Shin Table 10. S-145-AA diagrams Displacement contribution factor of S-145-AA Table 11. D-133-A diagrams Displacement Contribution Factor of D-133-A & Outrigger & Outrigger 4. Analysis of the Displacement Contribution Factor Once the structural layout of a tall building is defined, the main effort is to size the structural elements to satisfy the lateral serviceability performance criteria. Generally, under wind or seismic loading conditions, the lateral top deflection is limited to H/500 and the interstory drift is limited to h, where H is the overall height of the building above the pile cap level and h is the story height in Korea. Using the principle of virtual work, explicit serviceability stiffness constraints can be expressed in terms of the cross-sectional properties of the structural elements Analytical method of determining the displacement contribution factor Principle of virtual work The exterior virtual work ( ext ) done by a unit load (P = 1) in a linearly elastic structure is the verified work done by a unit load while accruing virtual deformation, as shown in Eq. (1). W ext =1 (1) Deformation occurs by unit load (P = 1). The interior virtual work is shown in Eq. (2). l NN MM f l W e VV l l TT ext = dx dx (2) 0 EA dx + 0 EI 0 GA dx 0 GI The deformation is presented in Eq. (3) based on the virtual work. l NN MM f l e VV l l TT = dx dx (3) 0 EA dx + 0 EI 0 GA dx 0 GI Using the unit loading method, the maximum lateral drift of the building is calculated. Adding this to the unit load (P = 1) at the top position of the building in the same

7 A Study on the Effective Lateral Drift Control of Super-tall Buildings in Korea 243 Table 12. H-106-A diagrams Displacement contribution factor of H-106-A Table 13. H-156-C diagrams Displacement contribution factor of H-156-C direction, the sum of the values of the components is the lateral drift of the building Analysis of the displacement contribution factor in a real structural model Analytical structural model Table 4 presents 11 analytical models. The structural systems are classified into three groups. One group consists of five models with outrigger systems, another group consists of three models without outrigger systems, and the third group consists of three 20-story or so models. The variables are the structural height and the outrigger system Analysis of the displacement contribution factor of structural components Displacement contribution factor of H-239-A The outriggers are located at the 9th, 30th, 50th and 69th floors. Thus, stiffness is more significant on these floors than on other floors. The displacement contribution factor of the truss and the beam is distributed uniformly. In the upper floors, the outrigger affects the column more than the wall, so that the what? of the column is larger than that of the upper floors. The outrigger on the upper floors contributes more than the outrigger on the lower floors Displacement contribution factor of C-175-A The rigidity of the upper and lower floors and the outrigger is larger than that of the other floors. The displacement contribution factors reach their maximum value on the 19 th floor Displacement contribution factor of S-145-AA The residential and commercial building, S-145-AA, has a marked stiffness at its podium. The displacement contribution factor of the beams is influenced by the outrigger on the middle floor. That of the columns and walls on the lower floors is relatively large. The outrigger on the 15 th floor has maximum value Displacement Contribution Factor of D-133-A The stiffness of the lower floors is large. The rigidity of the wall on the 41 st floor is larger than of the beam on the 23 rd floor.

8 244 Young-Hak Kim and Sung-Woo Shin Table 14. D-129-AA diagrams Displacement contribution factor of D-129-AA Table 15. HW-109-Y diagrams Displacement contribution factor of HW-109-Y Displacement contribution factor of H-106-A The stiffness of the lower and upper floors is large. The rigidity of the beam on the 10 th floor is larger than on the other floors. Transfer Girder Displacement contribution factor of H-156-C The structural system consists of a flat slab and a reinforced concrete shearwall that affect the displacement contribution factor of the beams. The value is especially large at the beams on the middle floor Displacement contribution factor of D-129-AA The structural system is similar to that of H-156-C. Also, the results were similar to those shown in Table 13. The value is especially large at the beams on the middle floor Displacement contribution factor of HW-109-Y This structural model has a transfer layer on the 2 nd floor.

9 A Study on the Effective Lateral Drift Control of Super-tall Buildings in Korea 245 Table 16. S-81-B diagrams Displacement contribution factor of S-81-B wall is popular in Korea. b. In the case of the usage of an exterior corewall in the plan, a concrete brace should be used in the reinforced concrete building. c. The structural system consisting of a reinforced concrete corewall, a moment-resisting frame, and an ooutrigger is common in Korea. d. To determine the structural system of a super-tall building, a Korean construction company reviewed the structural system at the point of economic efficiency. e. It is important to determine the position of the core in the plan close to the center to promote the efficiency of the structural system. f. The value of the displacement contribution factor is as follows: - In the structural system with an outrigger: > > - In the structural system without an outrigger: > > g. The curve of the displacement contribution factor is similar to the curve of the stiffness ratio of the building. h. In using a structural member such as an outrigger, the stiffness of which is higher than of others, the displacement contribution factor also has a higher factor. Moreover, in using an outrigger system, the position of the outrigger must be considered carefully. i. The stiffness curve of the structural models, the lateral drift curve, and the displacement contribution factor curve have a similar behavior. j. Generally, stiffness is inversely proportional to stiffness; but the concentration of the stress makes the drift is larger. Acknowledgments The displacement contribution factor of the beam is distributed equally on all floors Displacement contribution factor of S-81/79/ 56-B These buildings were selected to evaluate the behavior of super-tall buildings in Korea. The displacement contribution factor of the beams is distributed equally on all the floors. 5. Conclusions In this paper, the lateral resisting system was analyzed and the most effective method of lateral drift control was suggested. The results of the study are as follows. a. To control the lateral drift effectively, the structural system consisting of a reinforced concrete corewall, a moment-resisting system, outriggers, and a belt The authors would like to thank MIDAS IT and STRESS (advanced STructure RESearch Station) at Hanyang University for their technical support. References A. An-Sun et al. (1998), Stiffness Design Method of Twodimensional Frames under a Lateral Load, AIK, 18(1). A. Jaafari (1998), Cost and Performance Analysis of Tall Structures, Journal of Structural Engineering, 114(11), 2594 and Alex Coull and W. H. Otto Lau (1989), Analysis of Multioutrigger-braced Structures, Journal of Structural Engineering, 115(7), 1811 and Bungale S. Taranath (1988), Structural Analysis and Design of Tall Buildings, McGraw-Hill. Council on Tall Buildings and Urban Habitat (1993), Mimimum Design Loads for Buildings and Other Structures, ASCE. David Spires and J. S. Arona (1990), Optimal Design of Tall RC-framed Tube Buildings, Journal of Structural

10 246 Young-Hak Kim and Sung-Woo Shin Engineering, 116(4), 877 and 897. Eun-Jong, Yu, et al. (1996), Design of an Effective Tubular System through the Minimization of the Shear Leg Phenomenon, AIK, 12(5) 181 and 187. Hassan S. Saffarini and Musa M. Qudaimat (1992), In-plane Floor Deformation in RC Structural Engineering, Journal of Structural Engineering, 118(11), 3089 and Ji-Young, Kim, et al. (1997), Structural Behavior and Efficiency According to the Distribution and Number of Outriggers, AIK, 13(4), 351 and 359. Sung-Woo, Shin (1991), Applications and Problems of High-rise Buildings Using High-strength Concrete, AIK, 35(1), 46 and 49.