Ultimate shear bearing strength and flange contribution analysis of hybrid I-sections subjected to combined shear and bending

This paper presents the experimental and numerical investigations on ultimate shear bearing strength and structural behavior of hybrid steel I-sections. A total of eight I-sections were tested under four-point load condition, including six hybrid I-sections and two homogeneous I-sections. The hybrid I-sections were fabricated by different grades of steel, including steel grades Q355, Q460 and Q690. The geometric dimensions of the sections were varied to achieve different web height-to-thickness ratios and flange width-to-thickness ratios. Initial geometric imperfections of the hybrid I-sections were measured using 3D scanning, and the residual stresses of the I-section due to welding were also measured by adopting the strip method. The hybrid I-sections mainly failed by shear yielding failure in the web. A nonlinear finite element (FE) model was developed, and the accuracy of the model was validated by comparing the FE results with test results in terms of ultimate strength, failure mode and load-deformation curves. After successful validation, a comprehensive parametric study was conducted. The test and FE strengths were compared with the shear bearing strengths predicted by using the current design codes (including AISC and the Davies’ method). It was found that the current predictions are conservative, mainly due to the ignorance of the representation of flange-related strength, especially the flange frame-action contribution. Modified design equations were proposed by correcting the flange frame-action term. The proposed strength predictions were also compared with the test and FE results. It is shown that the proposed equation improves the mean prediction accuracy of the ultimate shear bearing strength than the existing design methods.