Tensile behavior of bolted through-diaphragm connections to SHS columns

Steel hollow section (SHS) columns have been increasingly popular in structural systems due to high compressive capacity, excellent torsional strength, and symmetric bending stiffness. In moment-resisting frames, the structural performance of connections to SHS columns is important to ensure the ability to carry bending moment. Conventional connections utilize welds to connect the adjacent components to the columns. Brittle fracture often initiates at the welds and reduces the ductility of connections. In this research, bolted connections were proposed to connect the beam to the SHS column through through-diaphragm. Tensile tests were conducted on four specimens to evaluate the structural behavior of connections. Failure mode, load-displacement response, strength, stiffness, and ductility were analyzed. The test results showed that the specimens were failed by the necking down of the flange plate. All specimens had high load-carrying capacity and good ductility. Strain distributions at key locations were investigated to study the force flow path. The application of through-diaphragm was found to deliver the tensile load to larger area and thus reduced the stress concentration at the connecting zone. Moreover, large amount of stress was transferred directly through the diaphragm, and the required stress demand for the SHS column was decreased. Design method was then proposed to predict the yield and the ultimate strength of the bolted connections. Good agreement was found between the experimental results and the theoretical predictions.