Study On Shear-slip Constitutive Relationship Between Self-tapping Screw Connection Of Cold-formed Thin-walled Section Steel After Rust And Its Application

Cold-formed thin-walled steel structures are widely used for their lightweight,high-strength,green environmental protection,high degree of prefabrication,short construction period,long service life and good seismic performance.Self-tapping screws are commonly used for connections,and their reliability directly affects the bearing capacity and stability of the structure.Currently,most scholars at home and abroad focus on studying the shear bearing capacity,while neglecting the constitutive relationship in the case of rust.Therefore,this study aims to investigate the shear bearing capacity of self-tapping screw connections in cold-formed thin-walled steel after rust by conducting experiments and finite element simulations.A shear-slip constitutive model of cold-formed self-tapping screw connections in the form of a three-fold line is proposed and applied to flattened columns to explore its influence on the axial compression performance.540 self-tapping screw connections were subjected to 6 salt spray rust tests of different ages to simulate their rust in the natural environment.According to the results analysis,the self-tapping screw connection of cold-formed thin-walled steel after rust has three typical failure modes when sheared,namely screw shear failure,hole wall pressure failure and screw pull-out failure.Moreover,the shear stiffness,shear bearing capacity and other mechanical properties of the same type of specimen gradually decrease with the deepening of the degree of rust.Based on experimental and numerical analysis,the calculation method of shear stiffness and bearing capacity of self-tapping screw connections after rust is established,the parameter relationship between the characteristic values is established,and the constitutive model in the form of shear-slip trifold line connected by self-tapping screws of cold-formed thin-walled steel after rust is fitted.Using the finite element analysis software ABAQUS,the shear-slip constitutive relationship of the shear slip connection of cold-formed steel self-tapping screws was applied to the analysis of cold-formed thin-walled steel split columns.By comparing the test results with the numerical analysis results,it is found that the failure morphology and load-displacement curve of the two specimens are highly consistent,which ensures the correctness of the finite element model.The corroded connection shear slip constitutive relationship is considered to be applied to the study of the flattened column,and the influence of rust on the cold-formed thin-walled steel flattened column is explored.It is concluded that the ultimate bearing capacity of cold-formed thin-walled steel split column after rust shows a downward trend with the increase of rust age.