Static Experiment And Theoretical Research Of Endplate Semi-rigid Connection To Concrete Filled Steel Tubular (CFST) Columns With Blind Bolts

This paper describes the studies on mechanical behavior, mechanism and design methods of a new typed composite joint, namely that endplate connection to concrete filled steel tubular (CFST) columns with blind bolts. The specific aspects of work are:(1) Analytical models for the semi-rigid connections to square steel tube columns under monotonic loading were developed by finite element analysis (FEA) software ABAQUS. Through the analysis of parameters, the moment-rotation relationship, bending stiffness, the working mechanism, and etc were studied.(2) Four specimens of extend endplate connection to CFST columns with blind bolts were tested under combined constant axial load and monotonic loading. The column section type(circular and square) and the thickness of the endplate were selected as the main experimental parameters. The moment-rotation relationship, stiffness, ductility, failure mode and strains of key components were studied. It was showed that the proposed blind bolted connection, which is semi-rigid, has reasonable mechanical properties and deformation. The stiffness, strength, ductility and failure mode of bolted connections may be affected by the type of endplate, thickness of endplate and type of steel tube cross-section.(3) Analytical models for the semi-rigid connections to concrete filled square steel tubular columns under monotonic loading were developed by software ABAQUS. The nonlinear full-range analysis of a typical specimen were executed by using the analytical models. The moment-rotation relationship, deformation, stress and strain distribution under different failure modes such as the failure were studied comprehensively.(4) Parametric analysis on mechanical properties of the composite connections were performed by using the FEA modeling. The strength of steel, strength of concrete, steel ratio of the column section, axial load level in the column, slenderness ratio of column, linear stiffness ratio of steel beam to column, moment ratio of beam to column, thickness of endplate, width of endplate, and diameter of bolt, etc are considered as possible influencing parameters.(5) Based on the test results and FEM research studies, some reasonable structural measurement were proposed, such as setting level axillary on beam flange, stiffening ribs on column wall and endplate, and increasing the anchoring length of bolts. These reasonable measures can improve the stiffness and bearing capacity of the joints.