Evaluation of collapse strength ratio for structures subjected to near-fault pulse-like earthquake ground motions
摘要
This paper discusses the main results of a statistical study of the collapse strength ratio, Rc, for degrading single-degree-of-freedom systems under near-fault pulse-like earthquake ground motions. The parameter Rc 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, μmax. Results of this investigation highlight that the spectral shape of Rc is different to that showed for ordinary far-field earthquake ground motions, and earthquake ground motions recorded at soft soil sites. Particularly, Rc depends on the ratio of the period of vibration to the pulse period, T/Tp, as well as the displacement ductility capacity, μc, and the level of negative post-capping slope, defined by parameter αc, in the system’s backbone behavior. As a result of this study, an equation to predict Rc for the seismic evaluation of buildings under pulse-like earthquake ground motions is introduced in this paper, whose functional form depends on T/Tp, μc and αc, 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 Rc, measured by the logarithmic standard deviation.