Modelling of Laminated Veneer Lumber (LVL) beams with holes using cohesive elements

Openings are usually required in timber beams to allow services like plumbing, sewage pipes, and electrical wiring to run through. These openings can cause significant stresses perpendicular to the grain direction, which may create cracks in the timber due to the low tensile strength perpendicular to grain. Initiation and propagation of cracks markedly decrease the load-carrying capacity of a beam with a hole with respect to a beam without a hole. The use of plywood or screw reinforcement can recover the full capacity of the beam. Crack initiation and propagation in timber is a challenging issue that requires a good numerical model for an accurate prediction. Analysis methods such as linear elastic fracture mechanics (LEFM) have previously been used to predict the failure load of beams with holes with initial and iteratively extended crack length. In this paper, cohesive elements with traction-separation behavior are used for the modeling of the fracture layer in laminated veneer lumber (LVL) beams with holes. In this case, the crack can propagate in the timber as the applied load increases. The model was calibrated on experimental tests carried out at the University of Canterbury, New Zealand, on LVL beams with holes, with and without plywood and screw reinforcement. The model shows great potential for predicting the load-carrying capacity of the timber beams with holes. Cohesive elements can be effectively used to investigate timber members with notches where crack propagation can govern the failure of the member.