Multiple limit state functions- based reliability analysis of steel frames equipped with FVD

In this paper, the reliability of steel frames equipped with fluid viscous damper (FVD) is discussed using multiple limit state functions defined based on the drift ratio and acceleration of the structure. Monte-Carlo Simulation (MCS) method has been used for reliability analysis and determining the failure probability. For numerical analysis, three steel frames of 4-, 8- and 12 -storey equipped with linear and non-linear FVDs designed based on direct-displacement method have been considered which FVDs distributed using shear-based and uniform distribution methods. By applying uncertainties in the structural and FVD parameters, for each frame the necessary number of random frames have been generated by using the Latin-Hypercube Sampling (LHS) method. The generated random frames subjected to 20 earthquake records and the time history dynamic analysis has been performed. By performing reliability analysis, the structural failure probability for single and multiple limit state functions has been determined with threshold values for maximum drift ratio and acceleration corresponding to different performance levels. The results of evaluations show that for the acceleration limit values almost corresponds to the moderate failure level in seismic codes, such as the limit value of 0.6g in Hazus-MH requirements, the increase in the probability of structure failure with multiple limit state functions compared to the drift ratio limit state function was less than 10%, while for a lower limit value of acceleration such as 0.3g, this increase is up to 87%. It was also observed that despite the fact that linear and non-linear dampers with different distributions have met the design criteria, they performed differently in reliability analysis. According to the results, it is suggested to consider the effect of acceleration-based limit state function in evaluating the reliability of acceleration-sensitive structures that have lower acceleration limit values.