Multi-objective reliability-based seismic performance design optimization of SMRFs considering various sources of uncertainty

Abstract

The purpose of this paper is to present an approach for multi-objective reliability-based seismic design optimization of Steel Moment Resisting Frames (SMRFs), considering weight and drift uniformity ratio (DUR) as objective functions plus deterministic and probabilistic criteria as constraints, while taking into account the effects of aleatory and epistemic uncertainties. To this end, structural reliability and performance-based seismic design criteria were used to preserve desired levels of structural safety during its life-time. The aleatory uncertainties were applied using estimated incremental dynamic analysis fractile curves, and epistemic uncertainties were applied by realization of stochastic variables. The mean annual frequency was used as a limit-state parameter to check reliability criteria. The novel technique of “shifting displacement-control node” was used to fix drawbacks of previous studies in SMRFs optimization, for non-convergence of solving finite element (FE) equations of different failure mechanisms, especially in the inelastic region and high drifts of pushover curve, as well as reaching the gravitational instability point for more reliable assessment of non-linear structural behavior. The proposed method, applied to 3 cases, ultimately led to the design of cost-effective structures with a desirable seismic performance. In some generated structures, the snap-back phenomenon occurred for inter-story as well as the overall drift of structures. Identification of this phenomenon in SMRFs has received less attention due to the difficulty of solving related FE problems. The effects of considering uncertainties and DUR in high drifts were studied, whereby unexpected results were achieved, such as occurrence and effects of the snap-back phenomenon, relation between DUR and reliability constraints, differences of structures satisfying deterministic and reliability criteria, the importance of selection of control node in pushover analysis, etc. The tools and algorithms developed through this research could help implement performance-based engineering in the design process of SMRFs, in a cost-effective, consistent, and repetitive manner. These algorithms help designers provide project stakeholders with decision-making tools suitable for risk-based structural engineering design for seismic hazard and methods to compare as well as evaluate alternative designs. These algorithms and methods also allow designers to easily compare and contrast structural designs concerning the expected performance.