Experimental behavior of Laminated Veneer Lumber (LVL) joists with holes and different methods of reinforcement

Abstract

Holes in timber beams used as part of a floor system within a building are often required to allow services (such as electrical and plumbing) to pass through the beams. Cutting holes can initiate cracks that can propagate when beams are loaded, mostly because of low tension strength perpendicular to grain of timber. Crack propagation changes the failure mechanism of beams, and fracture can occur at considerably lower than predicted loads. Reinforcing of timber beams to stop or prevent crack formation or propagation can be accomplished using different methods including glued in screws, fully threaded screws, plywood, and steel plates. The effectiveness of each method depends on many factors such as bonding with the timber, the area covered (for plates or gussets), proximity to the crack surface (for crack control), and mechanisms of stress distribution and transfer.This paper presents the results of an experimental program conducted at the University of Canterbury, New Zealand on Laminated Veneer Lumber (LVL) beams with holes and reinforcement methods around holes. Experiments showed that opening have considerable effect on the strength reductions of LVL beams that is recoverable through reinforcing around the hole. Different sizes and shapes of openings were tested. The effectiveness of several methods of reinforcement was investigated. Experiments showed that plywood worked most effectively for reinforcing LVL beams. Screws and glued in rods were effective for limited the hole diameters.