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ProcediaProcedia Engineering 00 (2011) 000–000 Engineering 31 (2012) 474 – 480
Procedia Engineering www.elsevier.com/locate/procedia
International Conference on Advances in Computational Modeling and Simulation
Study on High-rise Structure with Oblique Columns by ETABS, SAP2000, MIDAS/GEN and SATWE Kai Hua,b*, Yimeng Yang a, Suifeng Mua, Ge Qua a
China Shipbuilding NRDI Engineering Co., Ltd，N0. 303 Wuning Road, Shanghai 200063，China b Tongji University，N0.1239 Siping Road, Shanghai 200092，China
Abstract Facing a large number of new-type complex structural system and progressively consummate earthquake-resistant theories, the conventional software can no longer meet the needs of calculation and analysis. Meanwhile, some international finite element programs, such as ETABS, SAP2000, MIDAS/gen and SATWE, were updating themselves but remained respective limitations. In this paper, response spectrum, time history and linking slab in-plan stresses analysis were executed combined with a practical project by these programs, which were also compared following the analysis results.
© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Kunming University of Science and Technology Keywords: out-of-codes high-rise building , response spectrum analysis, time history analysis,in-plane stress analysis;
1. Introduction The level of high-rise buildings is an important indicator of a country or city’s economic and technological strength. With the continued development and progress of economy, technology and material in recent years, pretty a few countries are conceived to design and built more and higher buildings. Due to the large population and small per capita area, the needs of ultra high-rise buildings become much more urgent. By the various architectural features and style, more and more complex high-rise buildings are appearing.
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1877-7058 © 2011 Published by Elsevier Ltd. doi:10.1016/j.proeng.2012.01.1054
KaietHu al. / Procedia Engineering 31 (2012) 474 – 480 Hu Kai al./etProcedia Engineering 00 (2011) 000–000
Meanwhile, China has two largest seismic belt in the world, circum-Pacific seismic belt and EuropeAsia seismic zone. China, a developing country with densely populated and low seismic capacity building, in which the earthquake can be simply summarized as high frequency, wide distribution, high intensity and shallow focal depth, was described as the world's most earthquake disaster area. And the earthquake has just occurred in Wenchuan is so that we still remember now. Therefore, the seismic performance analysis and research of building structures look more indispensable. However, facing a large number of new, complex structure system and increasingly sophisticated seismic performance requirements, many conventional design and analysis software cannot ever meet all the needs. Meanwhile, a number of international design and analysis software, such as ETABS, SAP2000, MIDAS/Gen and SATWE are constantly improving themselves, but remained respective limitations. In this paper, response spectrum, time history and linking slab in-plan stresses analysis was executed combined with a practical project, by the programs mentioned above, which were also compared following the analysis results. 2. Project Overview and Calculation Models The project is located in the Shanghai. The main structure is a 29-storey building, including 3 floors underground and 26 floors above ground. In-situ reinforced concrete frame-core tube structure system was used in this 115.4-metre-high building, with a 12-metre-high steel frame on the top, and the architectural rendering is shown in Figure 1. According to the local codes [1], its seismic precautionary intensity is 7, design earthquake group is Group I, basic acceleration of ground motion is 0.10g, site classification is Class IV.
Fig. 1. Architectural Rendering
Fig. 2. Structural analytic models (a) ETABS; (b) SAP2000; (c) MIDAS
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Based on the local design guide [2], this building is identified as an out-of-code high-rise building, and its structural irregularity can be proposed as follows: (1) Unilateral oblique columns structure: Quite a lot of unilateral oblique columns exist from 1st to 19th floor, on which the detailed regulations are still unavailable. (2) Floor partial discontinuous: There is big opening on each floor from 2nd to 16th, and the opening size along x-axis is greater than the half of the typical floor width. (3) Torsional irregularity: The maximum displacement ratio and story drift ratio under Y-direction frequent earthquake effect exceeded the limit value (1.2). Therefore, ETABS, SAP2000, MIDAS/Gen and SATWE were used respectively to model, calculate and analyze this building. The structural analytic models are shown in Figure 2. 3. Response Spectrum Analysis under Frequent Earthquake Effect The first 60 modes were taken and combined by CQC method to calculate the structural seismic response through elastic response spectrum method. While the effective mass participation factor is larger than 90%, the reliability of the analysis results was improved. The main structural indicators calculated by various program are listed in Table 1, the overturning moment ratio of columns is shown in Figure 3, and the inter-story displacement angle is shown in Figure 4. Table 1. Main structural indicators Main structural indicators Period(s)
Overturning moment (ratio) of columns (kN-m)
ETABS
SAP2000
SATWE
T1
2.6535
(0.83+0.17+0.00)
2.6384 (0.79+0.21+0.00)
2.7237 (0.85+0.15+0.00)
T2
2.2572
(0.20+0.77+0.03)
2.3039 (0.26+0.74+0.00)
2.2533 (0.15+0.83+0.02)
T3
2.0052
(0.01+0.16+0.83)
2.053 (0.05+0.95+0.00)
1.7964 (0.01+0.02+0.97)
T4
0.88728 (0.68+0.32+0.00)
1.974 (0.00+0.01+0.99)
0.9188 (0.69+0.30+0.01)
T3/T1
0.76
0.78
0.66
T3/T2
0.89
0.89
0.8
X
946900 (32.10%)
1545632 (52.86%)
1347282 (57.91%)
Y
592700 (24.80%)
1324125 (54.77%)
1353829 (51.80%)
Fig. 3. Overturning moment ratio of columns (a) X Direction; (b) Y Direction
KaietHu al. / Procedia Engineering 31 (2012) 474 – 480 Hu Kai al./etProcedia Engineering 00 (2011) 000–000
Fig. 4. Inter-story displacement angle (a) X Direction; (b) Y Direction
According to Table 1, all the results calculated by different programs are basically similar. Meanwhile, the periodic pattern of SAP2000 is slightly different with those of the other two programs. That’s because that the T3 mode of SAP2000 is a local mode with very low participation, which needs to be paid attention to tell out in future analysis by mode shape and mass participation factor. Also, Table 1 and Figure 3 show that there’s a big difference of columns’ overturning moment ratio between ETABS and SAP2000, which is due to the missing statistic of oblique columns by ETABS. And the Inter-story displacement angles under X and Y direction frequent earthquakes both meet the code limited value as shown in Figure 4. 4. Elastic Time History Analysis under Frequent Earthquake Effect In view of the irregularity of the structure, ETABS and MIDAS were used for the supplement calculation to exam the structural performance under frequent earthquake by elastic time history analysis method. Considering seismic parameters, such as peak acceleration, spectral properties and duration time, three artificial waves: SHW1 (artificial wave by response spectrum), SHW3 (fitting by natural wave El Centrol) and SHW4 (fitting by natural wave Taft) were selected to be input along the X and Y direction respectively. The peak seismic acceleration is 35gal, using mode superposition method to calculate the structural time history response, with the first 60 vibration modes involved, and the modal damping ratio is taken as 0.05 while the construction material were taken into account. Through analysis, the maximum storey shear and inter-story displacement angle under X and Y direction earthquake are shown in Figure 5 and 6 respectively.
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Fig. 5. Maximum storey shear (a) X Direction, MIDAS; (b) X Direction, ETABS; (c) Y Direction, MIDAS; (d) Y Direction, ETABS
Fig. 6. Maximum inter-story displacement angle (a) X Direction, MIDAS; (b) X Direction, ETABS; (c) Y Direction, MIDAS; (d) Y Direction, ETABS
It can be seen from the figure 5 that the results all meet the requirements of the code [3]: The bottom shear calculated by each time history wave should be no less than 65% of the response spectrum result; and the average of time history results should be no less than 80% of the response spectrum result. Meanwhile, the maximum inter-story displacement angle under X and Y direction frequent earthquakes also meet the code limited value as shown in Figure 6. 5. Slab Elastic Stress Analysis by Partition Rigid Diaphragm Model Slab, important lateral force resistant component, plays a vital role to transmit, distribute and balance the force and deformation during earthquake, but has not been paid enough attention by engineer. Conventional designs methods are usually based on “rigid diaphragm assumption”, which assumes infinite rigid in-plane without any rigid out-plane. This assumption is suitable to most regular structure with acceptable error, and effectively reduces calculating freedom degree to improve the computational efficiency. However, in some complex structures, such as local large opening in floors, irregular plane or elevation, inclined column and weak connection, the in-plane stiffness of slab will be greatly reduced due to complex force conditions and discontinuity of floor. In these cases, besides the out-plane internal forces
KaietHu al. / Procedia Engineering 31 (2012) 474 – 480 Hu Kai al./etProcedia Engineering 00 (2011) 000–000
due to vertical loads, the in-plane internal forces, which are usually caused by the transfer and coordination of shear deformation, should also not be ignored. Therefore, in order to accurately take the real floor force conditions into account, the “elastic membrane” model is used as a rule. This model, considering true in-plane stiffness and neglecting the outplane, could accurately estimate the reduction of in-plane stiffness, not weaken the reinforcement reservation of beams around, and also remain the real effects of inclined columns or other components. Whereas, setting the “elastic membrane” model for the whole building will greatly increase the computational complexity, especially in the analysis of complex structures. Thus, to those local irregular floors, the “partition rigid diaphragm” model is introduced, which assumed the regular part of floors still follow the “rigid diaphragm assumption”, the weak connection parts between them are set as the “elastic membrane” model, and each “rigid diaphragm” has its own centroid and stiffness center respectively [4]. With accurate estimation of the slab in-plane stiffness, this model can also simulate the opposed phase motion between rigid diaphragms, with a remarkably quickened computational speed. As noted above, the floors of most stories in this structure are partial discontinuous with big openings, while a large lateral load affects on the building just under static load case due to the existence of quite a lot unilateral inclined columns. So, with the partition rigid diaphragm assumptions to the north and south partitions of floors, a slab elastic stress analysis were executed by ETABS and MIDAS/Gen program respectively. Because of the effect of inclined columns, the static loads on the structure cannot be ignored, and the stress nephograms of the slabs on 2nd floor by ETABS and MIDAS/Gen are respectively shown in Figure 7 and 8.
Fig. 7. Stress nephograms of the slabs on 2nd floor by ETABS (a) S11 (Direct stress-X); (b) S22 (Direct stress-Y); (c) S12 (Shearing stress)
Fig. 8. Stress nephograms of the slabs on 2nd floor by MIDAS/Gen (a) S11 (Direct stress-X); (b) S22 (Direct stress-Y); (c) S12 (Shearing stress)
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It can be easily seen from the figures that the stress distributions calculated by these two programs are roughly equal. Meanwhile, due to the inclined columns, partial slabs need to transmit and balance the force and deformation between inclined and right columns, and then bear a larger in-plane load under gravity. This shows that, for complex structures, it is necessary to take the slabs stress analysis at weaken positions. By comprehensive comparison of these two programs, ETABS has some advanced functions in preprocessing, such as automatically line constraint and area units division; while MIDAS/Gen has superior post-processing functions which could combine direct and shearing stresses and calculate the principal tensile stress of slabs. 6. Conclusion In this paper, the response spectrum, time history and linking slab in-plan stresses analysis were executed combined with a practical project with inclined columns by several programs such as ETABS, SAP2000, MIDAS/gen and SATWE, and the main conclusions of study are as follows: (1) All the results of response spectrum analysis calculated by different programs are basically similar, while ETABS may miss the statistic of oblique columns, which need to be paid attention to in future designs. (2) The results of time history analysis by SAP2000 and ETABS are roughly similar. However, SAP2000 does not have the concept of “storey”, which made the post-processing much more complicated. Therefore, to the regular structure, ETABS is recommended; and to those gymnasium or space truss structures, SAP2000 has its irreplaceable advantages. (3) As for the slab stress analysis, ETABS and MIDAS/Gen have their respective advantages: ETABS’s good at preprocessing with automatically line constraint and area division; and MIDAS/Gen does well in the post-processing such as the stresses combinations. (4) Slab, as the important lateral force resistant component, should not be ignored in design works. Especially to those complex structures, the slabs stress analysis at weaken positions is really essential. References [1] Ministry of Construction of People’s Republic of China. The earthquake intensity, basic accelerations of ground motion and design earthquake group of main cities in China. In: Code for Seismic Design of Buildings GB50011-2010, Beijing: China Architecture & Building Press; 2010, p. 172–193 [2] Xilin Lu. Idenfication and seismic conceptual design of out-of-code high-rise building. In: Guide to Seismic Design of Out-ofcode High-rise Buildings, Shanghai: Tongji University Press; 2009, p. 5–23 [3] Ministry of Construction of People’s Republic of China. Structural calculation and analysis. In: Technical Specification for Concrete Structure of Tall Building, Beijing: China Architecture & Building Press; 2010, p. 38–48 [4] Fu Changsheng, Liu Chunming, Li Yongshuang, Ying Jun. Structural seismic design and analysis of linking RC slab in tallbuilding. In: J Building Sturcture, 2008;38:106-110.
