ANALYSIS & DESIGN OF WEBS OF UN-STIFFENED COLD-FORMED CHANNELS SUBJECTED TO CONCENTRATED LOADS

Abstract

The formulation of the behavior of webs of un-stiffened cold-formed channels subjected to concentrated loads is rather complex due to many factors among which are: non uniform stress distribution under the applied load and adjacent portion of the web, stability of the web element, local web yielding in the immediate region of load application, bending produced by load eccentricity, geometric imperfection and variation in edge restraints. The current codes of practice identified four loading cases based on loading and edge configurations and adopted empirical design formula for each load case. The adopted design formulae were not only complex but did not reflect the governing mode of failure. On the other hand, the influence of possible web openings on web crippling strength was not addressed for all known loading conditions.

In this work, the finite element analysis ofun-stiffened cold-formed channels with un­ reinforced web subjected to concentrated loads was conducted by the general purpose finite element program, ANSYS. The analysis incorporated both material and geometric non-linearities to account for residual stresses and large deformations respectively. The finite element mesh configuration and material geometric imperfection were selected based on a sensitivity study for each loading case. The finite element analysis was verified by comparison to available experimental results. A comprehensive parametric analysis was established to investigate the effect of geometric parameters and circular web openings on web crippling capacity, mode of failure, and stress distribution. The effect of circular openings in the web was investigated considering all possible positions of openings outside and inside the bearing length. A set of design equations for un-reinforced webs subjected to concentrated loads were established by regression analysis of parametric analysis results. The assessment of the proposed design equations was established by comparison with AISI and Eurocode design rules and a set of independent finite element results that were not included in the regression analysis. The use of the proposed design equations provide a better reflection to the behavior obtained and consider a wider treatment of the effect of circular openings compared to current codes of practice.