Evaluation of collapse strength ratio for structures subjected to near-fault pulse-like earthquake ground motions

Abstract

This paper discusses the main results of a statistical study of the collapse strength ratio, R_c, for degrading single-degree-of-freedom systems under near-fault pulse-like earthquake ground motions. The parameter R_c represents the normalized lateral strength required to avoid dynamic instability leading to collapse, which has been incorporated in the Nonlinear Static Procedure of the ASCE/SEI-23 standard for the seismic evaluation of existing buildings as the maximum strength ratio, μ_max. Results of this investigation highlight that the spectral shape of R_c is different to that showed for ordinary far-field earthquake ground motions, and earthquake ground motions recorded at soft soil sites. Particularly, R_c depends on the ratio of the period of vibration to the pulse period, T/T_p, as well as the displacement ductility capacity, μ_c, and the level of negative post-capping slope, defined by parameter α_c, in the system’s backbone behavior. As a result of this study, an equation to predict R_c for the seismic evaluation of buildings under pulse-like earthquake ground motions is introduced in this paper, whose functional form depends on T/T_p, μ_c and α_c, and it can be incorporated on future updates of the ASCE/SEI-23 standard. Additionally, this study introduces an equation to obtain an estimate of the dispersion of R_c, measured by the logarithmic standard deviation.