Mechanical Properties And Failure Mechanism Of Extended Endplate Joints For Square CFST Frames Under Fire

The studies on mechanical behavior of endplate joints to square steel tubular (SST) columns at constant high temperature, mechanical behavior of endplate joints to square concrete-filled steel tubular (SCFST) columns at constant high temperature, and temperature field and fire-resistance behavior of endplate joints to square concrete-filled steel tubular (SCFST) columns at high temperature were carried out by finite element numerical simulation. The main research work has been done as follow:1) The nonlinear finite element models of endplate joints to SST columns or SCFST columns at constant high temperature were made by ABAQUS software. Mechanical behavior and failure mechanism were studied. The effect of parameters such as the end plate width (bp), axial compression ratio (n), bolt diameter (db), the steel strength (fcy), the ratio of beam and column yield moments(km), the tube thickness (tc) etc, on the ultimate moment capacity and the initial stiffness of connections at the temperature of20℃,300℃,500℃,700℃,900℃were analyzed. The moment-rotation curves of connections, failure modes and influence coefficients of the ultimate moment capacity and the initial stiffness were obtained.2) The temperature field of endplate joints to SCFST columns at standard fire curve ISO-834curve were analyzed by finite element software ABAQUS. The change of temperature field under three or four side fire was also studied, including temperature and time curves, temperature distribution and development.3) Complex mechanic behavior of the coupling temperature field and load for endplate joints to square SCFST columns in the heating process was further analyzed. The material model of steel and core concrete at constant and heating temperatures were determined. The FEM of the endplate joints to square SCFST columns was made. The nonlinear FE analysis of the typed joints under fire and loads were estimated. The effect of load ratio, bolt pretightening force, fire protection thickness, material properties, geometry dimension of the main parameters on fire resistance of joints were studied.