Hardwood and softwood timber - natural stone composite connections

Abstract

This paper describes fabrication and testing to ultimate of timber-stone composite (TSC) connections using unreinforced limestone slabs fastened to hardwood or softwood stubs by screws at 45° or 90° to the interface, bonded-in meshes or interface bonding. The stone’s tensile strength prevented crack-formation during drilling or grooving of holes to accommodate the screws and meshes. Connections failed by splitting of the stone along the connectors (meshes, 90° screws in hardwood), pullout of 45° screws from softwood (S45), shear-flexure yield fracture of 90° screws in softwood (S90), longitudinal shear failure of softwood adjacent to interface adhesive, and tensile yield fracture of 45° screws in hardwood (H45). In descending order the glued, H45 and mesh connections were the strongest while the glued, meshed and 45° screw connections exhibited the highest slip stiffnesses, with the S90/S45 connections showing the most ductility. Likely influences of randomness in the stone’s tensile strength and in observed bond variabilities from fabrication of the mesh connections are discussed. The TSC connections performed well against timber-concrete composite connections. Stiffness predictions incorporating screw axial and lateral contributions are excellent for H45 and S90, but need improvement for S45 and H90. Strength predictions work well for all screw connections. These TSC connections can significantly reduce consumption of the natural materials stone and timber in low-carbon composite floor systems.