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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 86
Edited by: B.H.V. Topping
Paper 213

Variability and Limitations of Seismic Analysis and Modelling Techniques

O.A. Mohamed

Department of Civil, Environmental, and Biomedical Engineering, University of Hartford, West Hartford CT, United States of America

Full Bibliographic Reference for this paper
O.A. Mohamed, "Variability and Limitations of Seismic Analysis and Modelling Techniques", in B.H.V. Topping, (Editor), "Proceedings of the Eleventh International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 213, 2007. doi:10.4203/ccp.86.213
Keywords: dynamic, static, analysis, steel, nonlinearity, earthquakes, scaling.

Building codes and design standards permit the use of a variety of analysis methods and structural engineers use a number of accepted modelling techniques for seismic analysis and design of structures. Some of these methods include the Equivalent Lateral Force (ELF) method, the Nonlinear Static (NS) method, and Nonlinear Response History (NRH) method. The simpler methods such as ELF are permitted subject to certain restriction while the rigorous methods such the NRH are permitted for most structures. An important limitation of the ELF method, even when permitted, is that it does not provide a mechanism to track plastic hinge locations and failure mechanisms. The computationally expensive NRH Analysis is sensitive to the suite of ground motions used in the analysis.

This paper discusses the three of the seismic analysis methods permitted by the seismic design guide FEMA 450, also known as the NEHRP recommended provisions for seismic regulations for new buildings and other structures [1], published by the United States Federal Emergency Management Agency (FEMA). FEMA 450 was prepared on behalf of FEMA by the Building Seismic Safety Council (BSSC). This design guide is updated approximately every three years and assigned a different publication number. Analysis and design based on the ELF method was discussed by Mohamed and Khamwan [2]. The key analysis and design requirements in the former edition of the NEHRP provisions were discussed by Mohamed [3].

A case study steel building is used to demonstrate the implementation of the three analysis methods and the restrictions and requirements on each method. Key points discussed include pushover curves produced by the NS method and the selection and scaling of ground motions required for the NRH method. The base shear forces calculated using the three methods is analyzed and their differences are discussed. The variability of the analyses produced by these methods and the limitations of their applicability are presented.

"NEHRP recommended provisions for seismic regulations for new buildings and other structures (FEMA 450)", Prepared by, The Building Seismic Safety Council National Institute of Building Sciences, Washington DC, 2004.
O.A. Mohamed and P. Khamwan, "Design of reinforced concrete buildings according to the new NEHRP provisions", Proceedings of the 6th International Conference on Earthquake Resistant Engineering Structures, Bologna, Italy, 2007. doi:10.2495/ERES070031
O.A. Mohamed, "Remarks regarding FEMA 368 seismic analysis guidelines", Proceedings of the 5th International Conference on Earthquake Resistant Structures, WIT Press, pg. 765-774, 2005.

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