Experimental and numerical study on the withdrawal behaviour of lag screws on wood side-grain

Abstract

In wood connections using lag screws as mechanical fasteners, the tension force transfer mechanisms occur through the interaction between the screw threads and the wood surface. It is necessary to understand the screw withdrawal behaviour in order to make a simple but representative interaction model instead of modeling the geometry of the screw threads. This study aims to evaluate experimentally and numerically the withdrawal failure modes, stiffnesses, and capacities of lag screws on wood side-grain. The experiment is conducted on the withdrawal of lag screws with different diameters and penetration lengths in Meranti wood cubes. The numerical analysis is carried out using ABAQUS finite element program and compared with the experimental results. Both experimental test and numerical analysis results show that the failure of all specimens occurred in the wood around the hole, not due to the slip between the lag screw and the wood's surface, which validates the proposed interaction model between the screw and the wood’s surfaces. The wood's effective material stiffness and strength in numerical models are obtained by matching the load-displacement curves with the experiment results. The effective Fy value range is between 18.5 MPa - 24 MPa, while the effective E value range is between 115 MPa - 680 MPa.