System reliability analysis of cold-formed steel structures for serviceability limit states

Resumo

The adoption of numerical analyses in structural design practice has ensured greater control over the actual behavior of structures. Design-by-analysis approaches deviate from traditional methods by directly considering the load-bearing capacity of the entire system rather than individual element checks. These approaches can even incorporate inherent nonlinearities into the analysis, such as second-order effects, material inelasticity, geometric imperfections, and semi-rigid connections. These advanced analysis models may produce results closer to the actual behavior of the structure in service, enabling the safe utilization of lighter structural systems. In this context, the evaluation of serviceability limit states becomes relevant, particularly for cold-formed steel structures, which are typically assembled using slender elements. This paper presents the application of a reliability-based procedure to assess the compliance of cold-formed steel frames with serviceability limit state criteria for excessive lateral displacement. Considering two groups of cold-formed steel structures based on their functions: single-story building frames and industrial storage rack frames, the lateral drift limits are extracted from the AISI S100, ASCE/SEI 7, ANSI MH 16.1, and Brazilian NBR 14762 and NBR 15524-2 standards, along with the target reliability indices for the corresponding limit state. The subsequent step involves evaluating system reliability, considering typical load cases for these structures (dead and wind loads for single-story frames and dead and product loads for racks) selected from the mentioned specifications, accounting for the uncertainties in loads and in the material and geometric parameters of the steel members. For this purpose, a MATLAB reliability framework is presented, coupling the First Order Reliability Method (FORM) to the MASTAN2 finite-element package, in order to apply the structural analysis results in each evaluation of the limit state functions. Conclusions regarding reliability indices and the potential adequacy of resistance factors are presented.