Finite element study on the flexural behaviour and edge-stiffening effect of cold-formed steel C-channel beams with elongated web holes

Abstract

Cold-formed steel (CFS) channel beams are commonly provided with web openings to allow building services to pass through the member. In practice, larger openings are often preferred because they provide more space for services. However, increasing the opening size may reduce the flexural resistance of the beam, especially when elongated web holes are used. This thesis investigates the flexural behaviour of CFS channel beams with elongated web holes under four-point bending. The main aim is to examine whether larger web openings can be introduced while maintaining an acceptable level of moment capacity. The effectiveness of edge stiffening around elongated web holes is also evaluated.

A nonlinear elasto-plastic finite element model was developed in Abaqus. The modelling approach was first validated against published experimental and numerical results for CFS channel beams with web holes. After validation, a parametric study including 282 finite element models was carried out. Two section sizes, C240 and C290, were considered. Their no-hole moment capacities were 13.591 kN·m and 20.058 kN·m, respectively. The main parameters included hole radius, elongated-hole aspect ratio, number of holes, clear spacing between adjacent holes, edge stiffening, and lip angle. Three hole radii of 70, 75, and 80 mm were examined. The elongated-hole aspect ratio was varied from 1.25 to 2.00. One-hole, two-hole, and three-hole arrangements were included, with clear spacings of 50 and 100 mm for the multi-hole models. For the edge-stiffened models, the stiffener depth and fillet radius were kept as 13 mm and 4 mm, respectively.

The results show that increasing the web opening area generally reduced the moment capacity of the unstiffened-hole beams. For the more severe practical cases, the strength retention ratio decreased to about 0.78–0.85. By contrast, edge stiffening was able to recover a considerable part of the lost strength. The maximum stiffening efficiency obtained in this study was approximately 26.6%. In several edge-stiffened three-hole models, the strength retention ratio remained above 0.85 even when the opening ratio exceeded 12%. The lip-angle study also showed that the flange-lip inclination can affect the flexural response. Among the investigated C290 EH1-HS80-ab15 models, the 60° lip-angle model gave the highest moment capacity. Overall, the results indicate that elongated web holes can be used more efficiently when suitable edge stiffening and geometric configurations are adopted.