Investigating the Effect of Random Variables on the Changes of IDA Curves in the Dual System of Steel Frames and Divergent Bracing

Incremental dynamic analysis is one of the most common analyses in evaluating the seismic performance of structures. Usually, in this method, the influence of uncertainties is ignored and only by considering different records, it attempts to evaluate the uncertainty of seismic load. In this research, an attempt was made to investigate the effect of random variables on these curves by using two methods Monte Carlo and Tornado diagram. A 10-story steel frame with a dual bending frame system with a divergent brace was selected and then the effect of uncertainties on its IDA curves was investigated. First, by using the Monte Carlo method, the sensitivity of the IDA curve of the Bam earthquake record with respect to six random variables including yield stress of steel, dead load, live load, span length, damping ratio and elastic modulus was investigated. Then, using the tornado diagram method, the sensitivity of these variables on the average IDA curves obtained from 18 records of different earthquakes was investigated. The results demonstrated that dead load and yield stress had the greatest impact on random variables. In addition, the degree of sensitivity of random variables increased with the increase of spectral acceleration. The comparison of the tornado diagram method with the Monte Carlo method illustrated that the tornado diagram method with a maximum error of 12.4% has a good accuracy in evaluating seismic sensitivity.