Duration-dependent seismic collapse capacity prediction for steel moment-resisting frames

This paper presents a prediction model for the seismic collapse capacity of multi-storey steel moment-resisting frames with due account of duration effects. The main objective is to provide a simplified and accurate analytical approach for the prediction of the duration-consistent collapse capacity. For this purpose, incremental dynamic analyses are carried out on 96 steel frames designed to Eurocode 8 for various combinations of ground conditions and drift limits. A set of 67 earthquake records with varying 5–75% significant duration is matched by scaling to a target Eurocode 8 response spectrum and employed in the analyses, to avoid spectral shape bias in the results. The influence of duration on the collapse capacity is quantified with due consideration of other ground motion properties and structural characteristics. It is shown that a decrease in the fundamental period or in the P−Δ effect results in more pronounced duration effects. Correlation analyses are also carried out between the logarithmic collapse capacity and the strong motion duration, as well as other ground motion and structural parameters. Based on the results, the most important parameters are identified, and a regression model is developed for predicting the collapse capacity as a function of the fundamental period, second-order level, plasticity resistance ratio, first-mode participation factor, and the 5–75% significant duration. Comparative assessments with other models from the literature highlight the importance of including the strong motion duration as a collapse predictor, since duration-independent models may result in unrealistic predictions. Finally, possible approaches for incorporating the strong motion duration in practical code-based collapse assessment procedures are outlined and discussed.