Abstract:

Objective: This study was carried out to explore the shear bearing capacity of an oblique screw connecting steel plate and CLT joint, to explore the failure mode and force mechanisms of steel plate and CLT joints connected by self-tapping screws, and to analyze the influences of angle on shear strength and stiffness. The development and application of new connectors would be expected to provide theoretical models and scientific bases. Method: Using Douglas fir as the study object and domestic full-threaded self-tapping screws as materials, the included angle between the main shaft of the self-tapping screw and the steel plate, those were 75°, 60° and 45°, respectively, was selected as the variable. The screw cap pulled in the tensile direction of the steel plate was shear force (T-S: tensile-shear), and the compression direction of the screw cap toward the steel plate was the compressive-shear force (C-S: compressive-shear). Referring to the American Standard (ASTM D1761-12) and loading at a constant speed of 1 mm ·min^-1, the stress of the node, the maximum load reached during the failure process, the deformation of the nail and the failure characteristics of the wood were observed and recorded. Result: For T-S and 90° shear force mode, the failure modes of nails were both that one side of the tapping screw was sheared. For C-S mode, the nail had three fracture modes under the 45° force mode, whereas the self-tapping screw on the one side produced two obvious plastic hinges and that on the other side was sheared at a distance of 8 mm from the nail cap under the 60° and 75° force modes. The bearing capacity under the T-S state increased gradually with the decreasing angle, and the opposite was observed under the C-S state; the stiffness under the T-S state increased gradually with the decrease of the angle. Conclusion: The bearing capacity of 45°, 60° and 75° joints under T-S state is 1.46, 1.35 and 1.22 times that of 90°, respectively, all higher than those of C-S state. The stiffness of 45°, 60° and 75° joints under T-S state is 3.58, 2.42 and 2.08 times that of 90°, respectively, and all higher than those of C-S state, of which the energy dissipation of 75° is the largest.

Key words: cross-laminated timber(CLT), self-tapping screw, steel plate-cross laminated timber joints, shear performance