Uncertainty and bias in fragility estimates by intensifying artificial accelerations

Abstract

To comply with the objectives of Performance-Based Earthquake Engineering and gain a comprehensive understanding of a structure’s seismic response, the utilization of multiple ground motion records selected or scaled at various hazard levels is often necessary. Incremental Dynamic Analysis (IDA) and cloud analysis methods represent wide-range probabilistic approaches employed for this purpose. However, due to their computational complexity, researchers and engineers have sought alternative solutions. One such solution is the application of intensifying artificial accelerations (IAAs). By employing IAAs, the structural response can be recorded from linear elastic to nonlinear, and ultimately up to the collapse capacity, all within a single simulation.This paper presents a comprehensive summary of various generations of IAAs and their unique characteristics. To assess their performance on nonlinear single degree-of-freedom systems, the IAAs are compared against IDA results. As IAAs are typically generated to be independent of specific hazard levels, a series of generic (i.e., standardized) ground motion sets are used for IDA. Our objective is to quantitatively evaluate the bias in the mean response estimation by employing different generations of IAAs, developed based on various base response spectra and optimization objectives. Additionally, this paper provides a simplified estimation of fragility curves based on IAAs, and compares the resulting uncertainty with those generated through IDA. The findings aim to enhance the understanding of IAAs’ capabilities and limitations in capturing the seismic response characteristics of structures.