Probing the probabilistic effects of imperfections on the load carrying capacity of flat double-layer space structures

Load carrying capacity of flat double-layer space structures majorly depend on the structure's imperfections. Imperfections in initial curvature, length, and residual stress of members are all innately random and can affect the load-bearing capacity of the members and consequently that of the structure. The double-layer space trusses are susceptible to progressive collapse due to sudden buckling of compression members. Progressive collapse is a chain of local failures leading to the collapse of either the entire or a part of the structure. In this paper, the effects of the probabilistic distribution of initial curvature and length imperfections on the bearing capacity of flat double layer grid space structures for different member’s length and support conditions have been studied. First, equal to the number of the members of the structure, two sets of random numbers have been generated using the Gamma and Gaussian distributions to account for the initial curvature and the length imperfections, respectively. Thereupon, the amount of the imperfection randomly varies from one member to another. Afterwards, based on the Push Down analysis, the ultimate load bearing capacity of the structure was determined through nonlinear analyzes performed through the OpenSees software and this procedure for certainty was repeated numerous times. Finally, based on the Monte Carlo simulation method, the structure’s reliability diagrams and tables were procured. The acquired results indicate that the behavior of flat double-layer space grids are sensitive to and can be affected by the random distribution of initial imperfections.