General Substitute Frame Model (GSF) for efficient estimation of seismic demands of steel and RC moment frames

Abstract

This paper proposes an approach to simplify 2D moment-resisting frames (with equal or non-equal bay lengths) to an equivalent single-bay framed MDOF model. This model, named the General Substitute Frame (GSF), is a promising development of the recently introduced Substitute Frame (SF) model by the authors that was restricted to equal-bay moment frames. The proposed GSF model which resolves the limitation of the SF model is applicable for both the steel and RC moment frames from low-rise to high-rise buildings. In order to evaluate the accuracy of the GSF model rigorously, a combination of 24 full-frame 2D moment frames including 4-, 12-, and 20-story buildings was designed and the results of nonlinear dynamic analyses were compared with their corresponding GSF models in terms of engineering demand parameters. In addition, modal and pushover analyses were also performed. Earthquake ground motions employed in this study include mild far-fault, moderate far-fault, and severe near-fault records selected by the Conditional Spectrum method. To accurately perform the required analyses, OpenSEES software was used, and 3600 runs of nonlinear time history analysis have been carried out. Based on the results of the analyses, it was demonstrated that the GSF model could predict the seismic response of moment frames well enough into both the linear and nonlinear ranges with high accuracy and can be a reliably practical substitution for moment-resisting frames. Moreover, the GSF model can be easily extracted from the primary full-frame based on the proposed equations.