Long‑term behaviour of Norway spruce glulam loaded perpendicular to grain

Abstract

The mechanical behaviour of timber loaded in compression perpendicular to grain is essential for a rational design of many timber structures. Structural components frequently exposed to such loading include studs on bottom rails, stress-laminated timber decks, timber elements lying in between vertical load-bearing columns as well as traditional timber joints mating surfaces in compression. Compression perpendicular to grain has been a repeated topic for discussion both in the current European regulations for timber structures, as well as in the ongoing work with the next generation of Eurocode 5-timber structures. However, the long-term behaviour is quite complex, taking both time and moisture variation into consideration, and to improve the understanding and the ability to consider the long-term effects in practical design, a simplified one-dimensional model is given herein. The paper presents novel results from long-term compression orthogonal to grain tests performed with load and moisture control. The purpose of the testing was to evaluate the effect of transversal creep on the long-term behaviour of timber elements including the effect of the mechanosorptive deformation. The test results were in turn used to calibrate a one-dimensional model for the prediction of the long-term response of timber. The model takes into account the combined effects of loading and moisture variations. The effective material properties are defined by use of effective pith locations together with the orthotropic material parameters. Finally, a comparison between the model results and experimental observations is given, showing an overall good prediction of the response.