An Investigation of Efficiency and Accuracy of Energy-Based Capacity Spectrum in Estimating the Seismic Demands of Buildings

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An Investigation of Efficiency and Accuracy of Energy-Based Capacity Spectrum in Estimating the Seismic Demands of Buildings

Original Article, C40
Vakili H, Shakeri K, Seyyedi Viand S.M, Azadi Hir M.
Journal. Civil Eng. Urban. 3(5):251-259. 2013

ABSTRACT:In the conventional methods of pushover analysis, the capacity spectrum is obtained with linking roof displacement to base shear, while this relationship only is meaningful in pushover analysis with load pattern that is proportional to the first mode. In the higher modes, changes of the roof displacement is not proportional to the changes of other stories displacement, and even in some cases roof displacement is decreased with increasing base shear and reverses. Therefore, using the roof displacement for establishing the capacity spectrum in the higher modes is faced with ambiguities. Using the energy method for establishing the capacity spectrum of structure is one of the proposed methods to eliminate these ambiguities. In this method, not only the amount of the roof displacement, but also the amount and the sign of other stories displacements participate in the establishment of capacity spectrum of structure. In this research, the accuracy and efficiency of energy-based capacity spectrum has been studied on two steel moment-frame buildings under different earthquakes for using in different pushover analysis with various load patterns. The results show that using the energy method for establishing the capacity spectrum not only eliminate the existent ambiguities and problems in establishment of capacity spectrum, but also the responses of the different nonlinear static analysis by using the energy-based capacity spectrum instead of the conventional capacity spectrum (based on roof displacement) have better accuracy and efficiency.
Keywords: Seismic Demands, Modal Pushover Analysis, Higher Modes, Capacity Spectrum, Energy Method

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