structural resistance variability in directional simulation in load space

directional simulation, among techniques for reliability analysis of engineering structures, is well known. in this context, directional simulation in load space, because of the considerable advantages of lower dimension of working space, is of considerable interest. as is expected due to structural resistance variability, the location of the relevant limit state(s) is no longer constant and must be taken as a random variable. the accuracy of the results obtained using this type of simulation therefore depends on how well this variability and consequently the location of limit state(s) (which are mostly assumed to be time-independent random variables) are accounted for in the analysis. to take this variability into account, the use of only the first two moments in each directional samples was proposed earlier [7]. the present paper intends first to verify how this assumption may affect the accuracy of the results (i.e. estimation of the probability of failure) second, to investigate the alternative solution(s) in order to enhance the quality of the method of working in load space. some worked examples show that in some circumstances where probabilistic properties of the resistance parameters depart considerably from a normal distribution, considerable differences may result for estimates of structural reliability.