The shear resistance and flexibility of a steel roof diaphragm depend largely on shear resistance and slip flexibility of the single screw lap joint. In this paper, screw connections relevant to modern roof construction are investigated. The tests provided experimental values of shear/tearing resistance and joint flexibility of seam connections, cladding/purlin connections and purlin/rafter connections. The novel aspects of the experimental research include investigation of the behaviour of shear connections in 0.5mm thick sheeting and thick-to-thin connections in S550 high tensile steel. Overall, six series of tests were conducted and each test was repeated five times in order to demonstrate a scatter of test results. Test results were examined against existing semi-empirical formulas for predicting the shear resistance of screw joints. It was demonstrated that the design equation presented by Toma et al. (1993), without the additional condition included in Eurocode 3, offers the closest prediction in terms of joint shear resistance. In terms of joint flexibility, it was demonstrated that existing formulas developed for bolted connection (Zadanfarrokh and Bryan (1992) and Dubina and Zaharia (2006)) can be successfully used for screw connections. The flexibility reduction factor n_(pf)=0.4 was also proposed to take account of perfect fit screw connections.
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