A Benchmark System RRBDO Example Involving Progressive Collapse of Hyper-Static Truss

Henrique M. Kroetz¹; Rodolfo K. Tessari¹; André T. Beck¹

¹ University of São Paulo

doi:10.20906/CPS/CILAMCE2017-0082

Resumo

In conventional Reliability-Based Design Optimization (RBDO), a reliability constraint is specified for each possible failure mode of the structure. System RBDO is a more comprehensive formulation, because a single system failure probability constraint is specified; hence, the individual failure modes can compete with each other, leading to further reductions in the objective function. Unfortunately, not many examples of system RBDO are available in the literature. This paper presents a benchmark system RBDO example, which involves the progressive collapse of a hyper-static truss. Our solution corrects the problems encountered in two prior publications of the same academic example. Given the correct solution, this problem may become a reference benchmark for the solution of system RBDO problems. In the same line, limitations of a system RBDO formulation are discussed. It is shown that conventional system RBDO formulations always lead to isostatic optimal designs. In order for the solutions to include hyper-static structures, the benefits of having a primary failure of a hyper-static member as a warning, before final collapse, have to be quantified. In other words, failure consequences need to be differentiated. This can be accomplished via so-called risk-based optimization, discussed but not shown herein.

Palavras-chave: Structural Reliability; RBDO; reliability-based optimization; hyper-static truss