Finite Element Analysis And Design Of Cold-Formed Thin-Waled Steel Channels Subjected To Web Crippling And Combined Bending

A nonlinear finite element method (FEM) is implemented to study the ultimate behavior and the practical design of the cold-formed thin-walled steel channels subjected to web crippling, pure bending and combined bending and web crippling. The purpose of such an analysis is to validate the applicability of current specifications in a given parameter range using the results of FEM-based parametric studies. Nonlinear finite element models by incorporating geometric and material nonlinearities were developed using finite element program ANSYS. The FE models were then verified against the experimental results in terms of ultimate load-carrying capacity, web deformation and failure modes. It is demonstrated that the FEM results agree well with the test results. Hence, the verified FE model was used as a baseline for an extensive parametric study of different channel dimensions. Fifty- two groups of channels (104 specimens) were investigated respectively in the parametric study (both EOF and IOF loading conditions).The applicability of current specifications on cold-formed steel channels subjected to web crippling, pure bending and combined bending was discussed against the results of tests and parametric studies. It is found that the design strengths calculated from the North American Specification are generally unconservative for channel sections with unstiffened flanges having the web slenderness ranged from 7.8 to 108.5 subjected to web crippling under the End-One-Flange and Interior-One-Flange loading conditions. Therefore, the coefficients of the design formula in the North American Specification were updated in this thesis. It is demonstrated that the updated design formula met the demand of safety reliability index.The analytical results also demonstrate that the empirical-based web crippling design equation proposed by Young and Hancock through the lab tests is generally unconservative for the web slenderness greater than 45.0. Therefore, based on the results of web crippling tests and FEM-based parametric studies, a new empirical-based design equation were proposed for the web slenderness ranging from 7.8 to 108.5 in this thesis. The new proposed design equation can meet the demand of design reliability index (safety factor).It is noted that there is no design formula or closure for cold-formed thin-walled steel channels subjected to web crippling as well as combined bending and web crippling in either Chinese Code of Steel Structure Design or Cold-Formed Thin-Wall Steel Structure Design. After the comparison of the design formulas for bending members in both Chinese codes, it is found that the design formula in the Chinese code of Steel Structure Design is more close to the case of web crippling. Therefore, the ultimate web crippling strengths calculated from this Chinese design code were compared with those obtained from FEM-based parametric studies. It is demonstrated that the current code design formula for beams under patch load is generally unconservative to design the cold-formed steel channels subjected to web crippling. Finally, it is suggested that the designer can either consult the North American Specification or use the new proposed design formula when dealing with the design of cold-formed steel channels subjected to web crippling.As a result, it is demonstrated that the nonlinear finite element method is an effective and time efficient way to analyze the structural behavior of cold-formed thin-walled steel channels subjected to web crippling, pure bending and combined bending and web crippling. The verified finite element model can be used to substitute the expensive and repeated physical tests for an extensive parametric study.