“…The chord preload ( N 0 ) was included in the chord stress, but the chord axial stress resulting from the lateral brace loading ( N ) was negligibly small and thus excluded. Although some chord cross-sections fall within Class 3, the chord stress level ( n 0 ) for all joints was determined on the basis of full plastic capacities, i.e., f y0 A 0 and f y0 W pl,0 , following the observation made by Kim et al (2019); the chord stress effect in high strength steel CHS X-joints with Class 3 or 4 cross-sections was shown to be comparable to that in geometrically identical mild steel joints with Class 2 cross-sections.Figure 11.Chord stress level ( n 0 ) in IPB-loaded joints. (a) X-joint.…”
In recent years, simple design methods for high strength steel tubular joints have been proposed by several design standards. According to these standards, the design resistance of high strength steel joints is obtained from the same design equations used for mild steel joints, but the resistance should be reduced properly by applying the material factor and/or the design yield stress. The material factor is a direct reduction factor to design resistance which generally corresponds to 0.9 for 460-grade and 0.8 for 700-grade steels, while the design yield stress (or fu/ fy limit) is a measure to account for the low fu/ fy ratios of high strength steels. In this study, a recent experimental program on moment-loaded high strength steel tubular joints is reported, which covered both circular (CHS) and rectangular (RHS) hollow section joints and both in-plane bending (IPB) and out-of-plane bending (OPB) moments. Based on the test results and additional test data collected from available database, the design equations, material factor, and design yield stress recommended by the revised draft of EN 1993-1-8 (prEN 1993-1-8) are evaluated for moment-loaded tubular joints made of grade 700 steels. It is shown that the prEN 1993-1-8 equations, combined with the material factor and design yield stress, generally provide conservative moment resistances for 700-grade tubular X and T-joints. However, based on the experimental implication that nonuniform stress distribution may cause an early fracture in CHS joints, it is suggested that the effective width, which is usually considered only for RHS joints, be considered also for CHS joints subjected to OPB.
“…The chord preload ( N 0 ) was included in the chord stress, but the chord axial stress resulting from the lateral brace loading ( N ) was negligibly small and thus excluded. Although some chord cross-sections fall within Class 3, the chord stress level ( n 0 ) for all joints was determined on the basis of full plastic capacities, i.e., f y0 A 0 and f y0 W pl,0 , following the observation made by Kim et al (2019); the chord stress effect in high strength steel CHS X-joints with Class 3 or 4 cross-sections was shown to be comparable to that in geometrically identical mild steel joints with Class 2 cross-sections.Figure 11.Chord stress level ( n 0 ) in IPB-loaded joints. (a) X-joint.…”
In recent years, simple design methods for high strength steel tubular joints have been proposed by several design standards. According to these standards, the design resistance of high strength steel joints is obtained from the same design equations used for mild steel joints, but the resistance should be reduced properly by applying the material factor and/or the design yield stress. The material factor is a direct reduction factor to design resistance which generally corresponds to 0.9 for 460-grade and 0.8 for 700-grade steels, while the design yield stress (or fu/ fy limit) is a measure to account for the low fu/ fy ratios of high strength steels. In this study, a recent experimental program on moment-loaded high strength steel tubular joints is reported, which covered both circular (CHS) and rectangular (RHS) hollow section joints and both in-plane bending (IPB) and out-of-plane bending (OPB) moments. Based on the test results and additional test data collected from available database, the design equations, material factor, and design yield stress recommended by the revised draft of EN 1993-1-8 (prEN 1993-1-8) are evaluated for moment-loaded tubular joints made of grade 700 steels. It is shown that the prEN 1993-1-8 equations, combined with the material factor and design yield stress, generally provide conservative moment resistances for 700-grade tubular X and T-joints. However, based on the experimental implication that nonuniform stress distribution may cause an early fracture in CHS joints, it is suggested that the effective width, which is usually considered only for RHS joints, be considered also for CHS joints subjected to OPB.
“…This limitation hinders the use of many HSS hollow sections with a practical diameter (or width, in the case of rectangular hollow sections) to thickness ratios. Kim et al [17] found that the current EN 1993-1-8 compactness requirement could be waived for many HSS CHS joints. The compactness issue is beyond the scope of this study.…”
In this study, an experimental program on welded hollow section joints fabricated from high‐strength steel is presented. The experimental program tested a total of six T or Y cold‐formed circular hollow section (CHS) joints under brace axial compression. One mild steel with a nominal yield stress of 355 MPa and two high‐strength steels with nominal yield stresses of 460 and 650 MPa were included. The test results and existing test database were used to evaluate the relevant design provisions for high‐strength steel joints. The material factor – used in the current standards to reduce the design resistance of high‐strength steel tubular joints – was found to be adequate for CHS T/Y‐joints with steel grades up to 700 MPa. The chord stress effect resulting from a particular test setup needs to be considered when evaluating the experimental joint strength. The experimental load‐indentation relationships were analysed to appraise the behaviour of high‐strength steel CHS T/Y‐joints from the perspectives of ductility and serviceability. The ductility of high‐strength steel T/Y‐joints is slightly lower than that of mild steel joints. T/Y‐joints show relatively lower ductility and serviceability performance compared to CHS X‐joint counterparts that comprise identical members. Local strain distributions in tested T/Y‐joints of different steel grades were analysed to identify the location and intensity of strain concentration. The possibility of fracture failure near the weld seam of the cold‐formed chord member is discussed.
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