Experimental investigation and design of round ended elliptical steel tubular T-joints under axial compression

The round-ended elliptical steel hollow section (REHS) is a novel type of steel tube combining the features of circular and rectangular cross-sections. The circular part could provide excellent confinement, and the rectangular part offers connecting convenience. Hence, the REHS possesses a good prospect of application in truss structures. However, investigations on the behaviour of REHS tubular joints are scarce. Herein, this paper conducted testing of 13 REHS tubular T-joints under axial compression. The influence of various parameters, including the intersecting orientation, chord/brace diameter ratio, concrete infill, and angle between chord and brace, on the failure modes, strength, initial stiffness, and ductility of the axially-loaded REHS tubular T-joint were investigated. The strength feature index of the type of tubular joint was figured out by comparing its axial strength with those of circular hollow section (CHS) and rectangular hollow section (RHS) steel tubular joints. The loading mechanism of the joint node under brace compression was revealed. Finally, a design method for predicting the axial compression strength of the REHS tubular joints was proposed. The results indicated that the REHS tubular exhibited good axial compression behavior. The tubular joints whose brace was welded to the arc segment of the chord possessed superior strength advantage, and their strength was 1.07-1.66 times as compared to those of the CHS or RHS tubular joint. Filling concrete into the chord could highly improve the strength and initial stiffness of the axially-loaded REHS tubular joint, and the improvements were respectively 75.5%-103.4% and 11.9%-60.6%. The design method presented in this paper could assess the axial compression strength of the REHS tubular T- joint accurately via the test validation.