A contact free measurement method to determine internal stress states in glulam

Abstract

A method to determine the internal stress state across the grain of glued laminated wood (glulam), as well as the experimental equipment for measuring released deformation are described in this paper. The internal stress state is calculated from measured released deformations, which are measured by a contact free method based on a digital camera technique. Non-destructive measurement of the modulus of elasticity in the cross-grain direction is presented and the correlation between dynamic and static modulus of elasticity is shown. Results for a single specimen with induced moisture gradient show that the largest stress found in the tests was about 0.57 MPa, which is higher than the characteristic value of tensile strength perpendicular to the grain. This stress is based on released strain over the total length of the slices cut from the specimens. FEM-simulations evaluating the stress distribution within the specimen to account for end effects indicate that the maximum stress is about 30% higher.