Static Behaviour of High‐Strength Steel CHS T‐Joints under In‐Plane Moment Loading

Abstract

In steel moment frames or vierendeel trusses comprised of hollow section members, T‐shaped joints are formed that are subjected to brace in‐plane bending moment (IPB). For mild steel, a large number of studies have been conducted on the behavior of tubular T‐joints subjected to IPB. However, the studies for high‐strength steel T‐joints are quite limited and mostly focused on axially loaded cases. In this paper, recent testing program conducted by the authors for high‐strength steel circular hollow section (CHS) T‐joints under IPB was presented. Supplemental numerical parametric study was conducted using the test‐validated nonlinear finite element (FE) analyses. In the FE analyses, various geometric shapes were considered such that the effect of key geometric factors and important failure modes could be identified. Based on the experimental and numerical results, a more rational deformation limit criterion under IPB loading was first proposed which can be applied to both mild and high‐strength steel joints. The chord plastification strength of high‐strength steel joints was evaluated using existing formulae and the required material factor for 700 MPa steel was suggested.

Experimental investigation of cold formed high strength steel tubular joints subjected to moment loading

“…From the moment-rotation diagram, the ultimate resistance ( M ip,1,u ) was determined based on the rotation angle limit proposed by Kim and Lee (2021) for IPB-loaded CHS joints (see equation (6) below). This ultimate limit allows less joint rotation angle for high strength steel joints; it accounts for their lower ductility and reduced rotation capacity through the strain hardening ratio f u0 / f y0 .…”

“…While the moment-rotation curve of S700_S500_1/2v or R-X-I-700 represents a typical chord face plastification, the curve of S700_S700_1/2v more belongs to chord sidewall failure or a combined behavior between chord face plastification and chord sidewall failure. It is worth noting that Kim and Lee (2021) suggested an equation for the borderline width ratio ( β bo ; equation (11)), beyond which the chord sidewall failure begins to involve in the joint behavior. The calculated borderline width ratio corresponds to β bo = 0.70 for S700_S500_1/2v and S700_S700_1/2v, thus well demarcating the chord face plastification behavior of S700_S500_1/2v ( β = 0.67 < β bo ) and the sidewall failure-involved behavior of S700_S700_1/2v ( β = 0.81 > β bo ).…”

“…For R-X-I-700, β bo is significantly higher than β = 0.50 ( β bo = 0.85), this again well corroborates the highly ductile behavior observed. Although equation (11) was originally proposed for RHS X-joints subjected to brace axial compression (Kim & Lee, 2021), the same equation for the borderline width ratio may be extended to RHS T/X joints loaded by IPB.…”

“…HSA650 is a thermo-mechanically rolled high strength steel recently developed in Korea. Although HSA650 has a nominal yield stress slightly lower than 700 MPa, the actual mechanical properties of HSA650 are comparable to typical grade 700 steels such as the European S700 MC (Kim & Lee, 2021). ATOS80 is another Korean high strength steel belonging to grade 700.…”

“…Kim and Lee (2021); Kim et al (2022) proposed a deformation limit criterion for IPB-loaded CHS joints which is applicable to both mild and high strength steels. The proposed criterion, which was validated both experimentally and numerically, allows less joint rotation angle for high strength steel joints accounting for their lower ductility and reduced rotation capacity.…”