Climate impact on reinforcements in wooden members: effective hygro-expansion coefficients

Wood is a hygroscopic material. The moisture content changes due to ambient climate variations e.g. according to erection and service time. The moisture content adapts first on the surface, and moisture gradient develop 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 reinforcements. To achieve a reliable evaluation of the safety level of reinforced timber structures, the present 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 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