Geometric Imperfections in Shell Finite Element Models of CFS Members - A Review of Current State of Practice

In cold-formed steel structures (CFS), the ultimate strength, stiffness, and post-buckling behavior are highly susceptible to geometric nonlinearity, in addition to material yielding or nonlinearity. It has long been standard practice in research to include initial geometric imperfections in shell finite element collapse simulations. The purpose of this paper is to provide a summary of efforts geared towards characterizing and modeling geometric imperfections in their full three-dimensional spatially varying forms. A close look at different geometric imperfection models proposed in the literature, reveals that, while seemingly different, almost all of these models express an imperfection profile by three components: imperfection shape, magnitude, and combination coefficient. Herein, the details required to setup high fidelity shell finite element nonlinear collapse analysis of CFS members to mimic the multitude of different imperfection models are presented. A careful comparison of the different strategies in seeding geometric imperfections shows a noticeable variability in the load carrying capacity and the stability behavior. The insights drawn from this work support our overall goals of developing an advanced analysis-based design framework for CFS members, through applying data driven stochastic modeling, and providing a platform for the validation of code-prescribed or practice-oriented geometric imperfection models.

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