Experimental and analytical investigation of the behavior of diaphragm-through joints of concrete-filled tubular columns

Static tensile loading experiments and nonlinear finite element analysis were carried out to study the mechanical properties and failure modes of diaphragm-through joints of concrete-filled square steel tubular columns. Comparison between experimental data and finite element analysis revealed that the FE predictions of failure modes, load-displacement curves and bearing capacity agree with the test results. It was found that the tensile load from the steel beam flange is mainly shared by the square steel tube and the diaphragm. The plastic zone of the tube appears around the intersections of the tube and the diaphragm whereas the diaphragm plastic zone appears along the cross-section lines enclosed by the steel square tube. Calculation models of yield lines on square steel tube and diaphragm are established based on distribution pattern of plastic zone, and an analytical method for the design of such joints is proposed as well. The experimentally obtained bearing capacities of the tested specimens are in good agreement with the analytically computed capacities.