Experimental study on mechanical performance of shear connections in CLT-concrete composite floor

Abstract

The results of a series of an experimental study and theoretical analyses of the shear performance of self-tapping screw connections in composite concrete-topped cross laminated timber floor systems are presented. Twenty-four specimens were prepared and tested in direct shear under monotonic loading conditions. The test variables included screw configuration, geometry and thread type. Endoscopy was used to investigate the observed failure modes at the CLT-concrete interfaces. Screws loaded in shear-tension were withdrawn from the CLT panels, while those loaded in shear-compression yielded in the CLT panels due to flexure. Timber embedding failure, and concrete crushing failure were also observed around the shear-compression loaded screws. Analysis of variation (ANOVA) indicated that the screw configuration, inclination angle, and thread type were the primary factors affecting slip stiffness, while screw configuration, inclination angle, and penetration length into the CLT panel affected maximum capacity achieved. A connection shear bearing capacity prediction model based on Johansen theory was proposed and shown to result in modeling errors generally less than 15%.