Effects of elevated temperatures on ultimate moment capacity of bolted moment-connections between cold-formed steel members

Experimental investigations at ambient temperature into the behaviour of bolted moment-connections between cold-formed steel members have previously been described. Full-scale joint tests have demonstrated that the channel-sections being connected are susceptible to premature failure, the result of web buckling caused by the concentration of load transfer from the bolts. The results of non-linear elasto-plastic finite element analyses have been shown to have good agreement. No consideration, however, has been given to the behaviour of such connections at elevated temperatures. This paper describes non-linear elastoplastic finite element parametric studies into the effects of elevated temperatures on bolted moment-connections between cold-formed steel members; simple design rules are proposed that will enable designers to take into account the effects of elevated temperatures.postprin

Experimental and Numerical Investigation of Cold-formed Steel Sections with Web Openings under One-flange Loading Condition subjected to Web Crippling

Organised by Department of Civil Engineering, The University of Hong KongParallel Session F1D: Web Cripplingpublished_or_final_versio

Investigation of cold-formed steel top-hat sections under bending

In recent years, with the introduction of higher strength grades, cold-formed steel sections have become increasingly more slender. As a result, top-hat purlin sections have become an alternative to conventional zed purlins, particularly when smaller purlin spans (around 4 m) are required. Such top-hat sections are torsionally stiffer than zed purlins, and have greater resistance against lateral-torsional buckling. Furthermore, they do not require anti-sag rods. However, when determining their strength, they are susceptible to buckling. In this paper, a combination of full-scale laboratory tests and finite element analyses are used to investigate the bending strength of such top-hat sections. Both upward and downward loading conditions are considered. In this paper, twenty-seven full-scale experimental tests on top-hat sections are described. The moment capacities obtained experimentally are compared against those predicted by the Eurocodes and non-linear elasto-plastic finite element analyses

The ultimate strength and stiffness of modern roof systems with hat-shaped purlins

In this paper, the strength and stiffness of different roof structures has been investigated, in order to establish their ability to act as in-plane diaphragms for stressed skin design. In each test set-up, a roof panel of approximately 3m x 3m was constructed using top-hat purlins and standard sheeting profiles or composite panels. Different types of roofs, such as single and double skin, have been investigated, all using hat-shaped purlins. A total of 10 roof panels were examined by testing with and without shear connectors placed along the rafters. The experimental strength and stiffness of each panel was then compared against established theoretical methods and the effect of shear connectors was discussed. It was demonstrated that although it is possible to closely estimate the ultimate strength of the structure using standard calculation methods, it is often more difficult to accurately calculate its stiffness. As the panel stiffness is a function of many variables, testing is still the recommended method, in order to investigate the shear flexibility of modern roof panels

Stressed skin action of the roof systems with hat-shaped purlins

In this paper, the strength and stiffness of different roof structures has been investigated, in order to establish their ability to act as in-plane diaphragms for stressed skin design. A total of 10 roof panels were examined by testing with shear connectors placed along the rafters. In each test set-up, the roof was constructed using top-hat purlins and standard sheeting profiles or composite panels. Different types of roofs, such as single and double skin, have been investigated, all using top hat shaped purlins. The experimental strength and stiffness of each panel was then compared against established theoretical methods. It was demonstrated that although it is possible to closely estimate the ultimate strength of the structure using standard calculation methods, it is often more difficult to accurately calculate its stiffness. As the panel stiffness is a function of many variables, testing is still the recommended method, in order to investigate the flexibility of modern roof panels. © 2010 Taylor & Francis Group, London

Ultimate bearing shear strength of cold-formed steel members using bolted connections at elevated temperatures

The external columns of frames are usually protected against fire, the design requirement being, after failure of the joints or beams, that the columns must remain upright to prevent spread of fire to an adjacent building or compartment. To prevent collapse of the columns, the bolt-group must be designed to have sufficient shear strength to resist the tensile forces that result from the ensuing catenary action. Whilst experimental investigations at ambient temperature into the ultimate shear strength of cold-formed steel members using bolted connections have been described in the literature, no consideration has been given to the behaviour of such connections at elevated temperatures. This paper describes non-linear elasto-plastic finite element parametric studies into the effects of elevated temperatures on the shear strength bolted connections between cold-formed steel members. The numerical results illustrate how the shear strength of the bolt-holes is affected by elevated temperatures, from which design recommendations for the bearing shear strength of the bolt-hole at elevated temperatures are proposed.link_to_subscribed_fulltex

Effect of stressed skin action on the behaviour of cold-formed steel portal frames

This paper describes six full-scale laboratory tests conducted on cold-formed steel portal frames buildings in order to investigate the effects of joint flexibility and stressed-skin diaphragm action. The frames used for the laboratory tests were of span of 6 m, height of 3 m and pitch of 10°; the frame spacing was 3 m. The laboratory test setup represented buildings of length of 9 m, having two gable frames and two internal frames. Tests were conducted on frames having two joint sizes, both with and without roof cladding. It was shown that as a result of stressed-skin diaphragm action, under horizontal load the bending moment at the eaves was reduced by approximately a factor of three, relative to the bare frame. It was also shown that as a result of stressed-skin action, the deflection of the internal frame reduced by 90%, and that the stiffness was independent of joint flexibility. On the other hand, owing to redistribution of bending moment from the eaves to the apex, the effect of joint flexibility was shown not to be significant on the overall failure load of the frame