Reliability-Based Design of Truss Structures by Advanced Analysis (No. R936)

Abstract

A formwork for determining a system resistance factor in LRFD is presented. A truss composed of HSS members based on current design specifications is chosen for analysis. To reflect real structures, the truss system is analyzed by advanced second order analysis, which takes into account the variation in physical properties and directly models geometric and material nonlinear behavior. Measured data on the variation of physical properties reported in literature is located including member imperfections, residual stresses, member thickness, Young’s modulus and yield stress. Distributions of these values are obtained from data for recreation in the finite element models. Member imperfection profiles are generated and residual stress patterns through the thickness and around the cross-section are formulated. The variations of physical properties are represented in the finite element simulations using Latin Hypercube sampling of the random variables. Random loads are also modeled. A connection modeling technique is devised, and finite element models of the structure are created and compared to benchmark tests to assess their validity. A 2D model of a single truss and a 3D model of a system of trusses are created. Simulations are completed to obtain strength distributions of each system, followed by a reliability analysis to determine resistance factors for each system. The results of the system analysis and resulting reliability index and system resistance factors are compared to that of component based design. It is found that the system resistance factor for the specific system analyzed herein is lower than that of the resistance factor for individual components.