An experimental investigation of fire behaviour of screw shear connections between oriented strand board and cold-formed steel sections

This paper presents the results of an experimental study on the fire behaviour of the shear connection of OSB-CFS composite beams using screw shear connectors. The tests include 2 ambient temperature push-out tests and 6 standard fire resistance tests on shear connections. The key variables of the shear connection tests include OSB thickness (20 mm and 40 mm), number of gypsum plasterboard fire protection layers (1 and 2), and load ratio (0.35 and 0.70). The final observed failure mode was shearing of the screw. However, with localised charring around the screws in specimens with lower load ratios and associated high screw temperatures, the screw shear connector was able to cut through the charred timber and bear on the remaining un-charred timber. This suggests that it would be necessary to consider both local charring and remote properties of the timber when calculating the bearing resistance. The experimental results were also able to validate the authors’ recently proposed modification to the calculation method in Eurocode 5 for screw shear connectors in timber components.