Effects of structural uncertainties on seismic performance of steel moment resisting frames

• Effect of modelling uncertainties on seismic performance of steel MRF is considered.
• Uncertainties substantially change the results of seismic performance evaluations.
• Seismic fragilities at different performance levels are considerably affected by ductility level of frame.
• No correlation observed between properties of accelerogram and dispersion in collapse capacities of structural realizations.

Prediction of structural response to seismic loads is a complex problem with many parameters involved that some of them can behave highly uncertain. Nonetheless, it is needed to have a clear understanding of how these uncertainties affect seismic structural performance. In this matter, it is convenient to separate uncertainties into two categories: aleatory (due to variability of strong ground motions) and epistemic (related to numerical model of structure).This paper aims to investigate effects of structural uncertainties on seismic performance of steel moment resisting frames, through extended IDA of two sample 5-story frames. In this regard, damping, mass, yield strength and ultimate strength of structural steel have been considered as probabilistic variables. Latin Hypercube Sampling (LHS) has been used to create random realizations of structures.With the aid of reliability methods, different sources of uncertainty and their ranges of influence on seismic performance have been disaggregated. Two steel moment frames, despite having the same geometry, have been designed with different levels of ductility. This can give an idea about how the ductility of structure affects different aspects of probabilistic performance evaluations.Considering the results, it can be seen that uncertainties in selected parameters have important effects on seismic performance. In other words, capacity and demand estimations based only on deterministic procedures may ignore some substantial points. Including these uncertainties in performance calculations can considerably change, at some levels, the probability of achieving desired performance. Also, a clear superiority in performance capacities can be seen for special moment frame.