Secondary Bending Stresses in High-Strength Hollow Section Joints

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The interest in high strength steel (HSS) shows an increasing trend mainly due to its high yield strength, low weight to strength ratio, decreasing costs of the base material and fabrication. The proposed 2020 version of the Eurocode 3 part 1-8, still under discussion at the time of writing of this thesis, covers steel with yield strength up to 700 MPa. This standard has recommended high material reduction parameter for joints with steel grades above S355 to S700. This is done to consider the low deformation observed for steel between 450 MPa and 460 MPa, to include the insufficient knowledge of the material properties of HSSs and the impact of these properties on the current standards. Secondary bending stresses are omitted for the static design strength of mild strength hollow section joints. But for high-strength joints rules regarding these stresses need to be re-analyzed, since the impact of HSS on hollow section joints may be different. Goal: In this study the main goal is to investigate the level of the secondary bending stresses in hollow section joints made of high-strength steel using numerical analyses. Furthermore, the magnitude of the material reduction factors recommended by the proposed 2020 version of the Eurocode 3 part 1-8 are evaluated. An attempt is made to validate the FEM against test data. The commercial finite element program ABAQUS® is used to build the FEM. Roughly good agreement between the test and the FEA is obtained. A parametric study is performed on an isolated gap K-joint. The joint geometries, boundary and loading conditions are taken from the literature. To study the impact of the material parameters on the secondary bending stresses in RHS joint, various parameters including material properties, gap size, brace width to chord width ratio and weld type are varied. These parameters influence the stiffness, strength, stress distribution and secondary bending stresses. A total of 32 gap K-joints is analyzed in this research. Also, an attempt is made to obtain the ultimate load resistance using the yield line theory. As results, valuable information about the joint behavior of high-strength hollow section joints is obtained. It is found that secondary bending stresses cannot be neglected when high-strength steels are used.