Mechanical investigations on axially-compressive behaviour of RRS tubular T-joints: Testing, modelling and design methods

Round-ended rectangular steel (RRS) tubes combine the structural efficiency provided by circular hollow sections (CHS) with an aesthetically elegant profile, presenting significant potential for truss applications. Nonetheless, comprehensive studies on the structural performance of RRS tubular joints persist in being notably scarce, which currently limits their broader implementation in structural engineering practice. Aiming to fill the pressing research void, this investigation builds a finite element framework for RRS tubular T-joints under axial compression, capturing the geometry of the chord-to-brace junction and contact nonlinearity. After validating against 7 experimental tests, a parametric study of 146 FE models was conducted to elucidate the effects of key design variables, including intersection orientations, brace-to-chord diameter ratio, brace-to-chord thickness ratio, section aspect ratio, brace angle, and steel yield strength on the mechanical behavior of such axially-compressed joints. Further FE simulations explored typical failure modes, load-displacement curves, distribution of stress within the joint core region, and characteristics of strength. Combining the component method with analytical results, theoretical formulas were proposed to predict the axially-compressed capacity of RRS tubular T-joints, achieving a mean predicted-to-test/FE ratio of 0.96 (COV = 0.005). The results demonstrated that RRS tubular T-joints showed advantages in axial compressive capacity relative to conventional tubular T-joints when the brace was welded to the arc segment of the chord (type-A and -C joints). The proposed design formulas accurately predict the axial compressive capacity of RRS tubular T-joints, as confirmed by experimental and numerical validations.