Reinforcement of Timber Structures Versus Climate Impact

Abstract

Wood is a hygroscopic material. The moisture content of wood changes due to ambient climate variations. The moisture content changes first on the surface and a moisture gradient develops over the cross section and results in moisture induced stresses (MIS). MIS occur in addition to normal stresses for the load-bearing resistance and can affect mechanical reinforcements. The paper shows results from experimental test series on the load, moisture, and deformation investigation of structural glulam members reinforced with internal mechanical fasteners. Stepwise climate scenarios were applied and considered climates experienced by the structural timber member before or after reinforcement. For the estimation of the swelling and shrinkage behaviour, effective hygro-expansion coefficients have been determined. The coefficients are significantly lower than previously assumed in the standards. This enables engineers to estimate more realistic wood deformations and the impact on reinforcements which is not neglectable and reduces damage in a wide range of applications. The research results promote the use of wood by ensuring quality, performance, and aesthetics in timber constructions.