Keywords: structural modelling, IBC, multi-storey building, response spectrum.

The seismic structural design of multi-storey buildings is often based on response spectrum analysis using design response spectra satisfying the provisions of building codes. Although the estimation of response spectra from various earthquake data has been a subject of research, little has been reported in the published literature to compare various different design response spectra in terms of the structural response of multi-story buildings. This paper presents data giving the sensitivity of structural response to the variations in the IBC-compliant [1] response spectra and at the same time demonstrates a technique for generating easy and error-free structural models of multi-storey buildings.

Generating sensitivity data for multi-story buildings is not easy. It involves repeated modelling of multi-storey buildings. Use of commercially available structural analysis software packages requires apriori visualization of the three- dimensional model for using joints and elements generation options. Due to the huge amount of data involved with three-dimensional structural models of multi-storey buildings the modelling process is laborious, time-consuming, and error-prone [2]. Easy and error-free modelling technique is required for generating such data with confidence. The paper describes a modelling approach for response spectrum analysis as an extension of the work presented in [2] using specialized pre-processor type software package called FEMBUS [3] and a companion software RESPECTRUM [4] in conjunction with SAP2000 [5]. SAP2000 was chosen mainly because of the minimized user's interaction in repeated analysis and its availability otherwise STAAD.Pro [6] and GTSTRUDL [7] could have been used equally well because FEMBUS generates ready-to-go data files for each of the three software packages.

Results are presented for two L-shaped buildings with assumed dimensions [8] and a real-world building with the actual dimensions and section properties. Each building is analysed for thirty different design response spectra. The design response spectra are obtained by varying the values of the short period and one-second period spectral accelerations. Each building was analysed for thirty different design response spectra. All of the thirty response spectra were IBC-compliant design response spectra generated using RESPECTRUM. The short period and 1-second period accelerations were used as the variable parameters in generating the response spectra.

The data are tabulated and presented graphically to show the sensitivity of the structural response to the variations in design response spectra. The data obtained clearly show same important unexpected trends for all cases. For short period acceleration of 0.1, the maximum shear forces drop instead of rising with increasing value of the one-second spectral acceleration. This is a purely academic observation because the shear forces and bending moments are insignificant for such small value of the short period spectral acceleration. For other values of SS it is observed that the bending moments and shear forces do not always increase with the increasing values of the input parameters but become constant after a rise. This is unexpected and indicates that in majority of cases, the structural response will be insensitive to the input IBC parameters. The presented data and the conclusions are helpful to the structural designers in estimating how the design of the structural elements of a building will be affected by changes to the input design response spectra. Also, the data will be helpful in improving the code provisions in the future

1

International Code Council, International Building Code 2000, International Code Council, Inc., Falls Church, Virginia, 2000.

2

Nahhas, T.M., Imam, M.H., Three-Dimensional Structural Modeling of Multi-Storey Buildings for Obtaining Moment Envelopes, Proc. The Eighth International Conf. Civil and Structural Engineering Computing, Edited by: B.H.V. Topping, Civil-Comp Press, Stirling, UK, 2001. doi:10.4203/ccp.73.16

3

Engineering Optimization Software, "FEMBUS", http://www.planopt.com, Georgia, USA, 2004.

4

Engineering Optimization Software, "RESPECTRUM", http://www.planopt.com, Georgia, USA, 2004.

5

Computer & Structures Inc., "SAP2000 software package", http://www.csiberkeley.com, California, USA, 2001.

6

Research Engineers, Inc., "STAAD-III/Pro software package", http://www.reiusa.com, California, USA, 2001.

7

Georgia Tech-CASE Centre, "GTSTRUDL software package", http://www.gtstrudl.gatech.edu, Georgia, USA, 2001.

8

S.H. Ju and M.C. Lin, "Comparison of building analysis assuming rigid or flexible diaphragms", Journal of Structural Engineering, 3, 25-31, 1999. doi:10.1061/(ASCE)0733-9445(1999)125:1(25)

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