W.M. Gho

Ultimate capacity of high-strength rectangular concrete-filled steel hollow section stub columns

Abstract The ultimate capacity of high-strength rectangular concrete-filled steel hollow section (CFSHS) stub columns is experimentally investigated. In the experimental programme, 22 rectangular CFSHS specimens with cross-sectional aspect ratios of 1.0, 1.5 and 2.0 were tested to failure under axial concentric loading. All the specimens were fabricated from high-strength materials. The average yield stress of the steel hollow sections was 550 MPa (N/mm 2 ) while the average compressive strengths of concrete were 70.8 and 82.1 MPa (N/mm 2 ). In the study, the ultimate loads obtained from the experiment were compared with the values calculated from design codes, namely EC4, AISC and ACI. The comparison of results shows that EC4 closely predicts with a difference of 6% while AISC and ACI underestimated the critical loads by 16 and 14%, respectively. It is noted that the strength of specimens decreases with the increase of cross-sectional aspect ratios.

Ultimate capacity of completely overlapped tubular joints: I. An experimental investigation

Abstract This paper presents the experimental finding of a full-scale completely overlapped joint tested to failure under lap brace axial compression. The failure mode of the joint was due to the through brace face plastification. An ovalising effect of the through brace cross-section and bending on the gap region were noted. The onset of non-linear behaviour occurred at 72% of the ultimate load. The capacity of the joint was found to be 7.3% higher than that of the simple gap K-joint, which was determined from the ultimate strength formula. The deformation limit of the joint was 3.82 times the lap brace yield deformation. In the numerical study, the 8-node thick shell element was used to model the joint. No weld element was modelled, but the material with strain hardening property was necessary in the model. The comparison of the load–displacement curve with the experimental results showed a reasonably good agreement, with 5% less for both the ultimate load and the corresponding lap brace axial displacement. As the finite element method was verified to be reliable and accurate, a detailed parametric study was performed to intensively investigate the ultimate load behaviour of the completely overlapped joint as described in the companion paper on behavioural study.

Ultimate capacity of completely overlapped tubular joints. II: Behavioural study

Abstract This paper presents numerical results on the ultimate strength behaviour in terms of load–displacement characteristics and failure mechanisms of completely overlapped tubular joints. The effect of the gap length on the behaviour of the joints is also investigated. In the study, the end of the lap brace was axially loaded. Criteria were set up to determine the minimum failure load. It was found that a joint subjected to compression load gave the lowest ultimate capacity. The geometric parameters of the chord were shown to have an insignificant impact on the joint behaviour. The joint strength increased as the gap reduced. A sharp increase in the joint strength at small gap was noted for a relatively high βTL(=dL/dT=0.768). The Y-joint capacity was reached at a sufficiently large gap. τTL(=tL/tT) had a crucial influence on the joint failure behaviour. A relatively mild βTL(=dL/dT=0.616) and τTL(=tL/tT=0.560) resulted in lap brace failure prior to joint collapse. The failure mechanisms changed from “chord” (through brace) bending, followed by localised plastification of the through brace face to yielding of the lap brace when the gap was reduced from a large gap to a small gap of 51 mm.