Behavior of Cold-Formed Steel Built-Up Sections with Intermediate Stiffeners under Bending. I: Tests and Numerical Validation

Abstract

An experimental investigation of simply supported built-up section beams with different sectional configurations has been conducted under both four-point bending and three-point bending. Intermediate stiffeners were employed to the webs of built-up sections to improve the buckling strength that is susceptible to local buckling and/or distortional buckling. In this study, the built-up sections were assembled by self-tapping screws from two channels with web stiffeners, which were brake-pressed from high-strength, zinc-coated grades G500 and G550 structural steel sheets with nominal 0.2% proof stresses of 500 and 550 MPa, respectively. The screws were located either at the flanges or webs, and the built-up sections include both open sections and closed sections. The moment capacities and observed failure modes of the beam tests are presented, and no failure was found in the screws. The local and distortional buckling behavior of the built-up section beam specimens were found to be different from the single profiles. Finite-element (FE) models were developed, and numerical analysis that includes material nonlinearity, geometric nonlinearity, and contact nonlinearity was performed. The FE and the experimental results were found in good agreement in terms of ultimate moments and failure modes. The verified FE models are used to perform parametric studies in the companion paper. The structural behavior and design rule for built-up section beams with intermediate stiffeners is then explored and presented.