Experimental study on shear performance of steel-timber screw connectors with grout pockets

Abstract

The steel-timber composite floor is an environmentally friendly structural form. The shear connectors between the timber and H-steel are the key to designing the steel-timber composite floors, and the strength and ductility of the connection are directly affected by the failure modes of the connectors. A new connection that anchors the screw tips in the grout pockets is presented in this paper. In this connection, the glulam around the screw tip is removed, and the grout is added after the screws have been tightened in the glulam to form a hybrid anchorage of the grout and glulam to the screw. Nine groups of double-shear tests were conducted to investigate the influences of with or without grout pockets, the size of grout pockets, and the row number of connectors on the performance of steel-timber composite connections. Firstly, compared with the common specimens connected by screws, the screw tips were restrained more firmly in specimens with grout pockets. The peak load Fmax, initial stiffness ks,0.4 and ductility D of the specimens with grout pockets were increased by a maximum of 25.2, 55.9 and 33.6%, respectively. Secondly, with the increase in the radius and depth of the grout pockets, the secondary stiffness ks,0.7 and the peak shear capacity Fmax of the specimens increased accordingly. Thirdly, after the screw tips were anchored in the grout pockets, the screws stably exhibited the failure mode of double plastic hinges (model III), achieving active control of the failure modes of the screws. There is a critical ratio of grout anchor length to the total length of the screw (L0/L) such that the tip plastic hinge is close to the grout pocket. In the end, the shear capacity equation for failure mode of double plastic hinges (model III) in Eurocode 5 can be used to calculate the peak capacity of this new connection, and the calculation results have a large safety margin.