Moisture-induced stresses in large glulam beams. Case study:Vihantasalmi Bridge

The structural performance of timber elements may depend on the environmental conditions and in particular on the cyclic variations of the moisture content. Moisture gradients in the sections of the structural elements can produce additional stresses, the so-called moisture-induced stresses (MIS), which can cause the formation of cracks and delamination in wooden components. In order to achieve a reliable evaluation of the safety level of timber structures, the present paper proposes a numerical methodology to evaluate the MIS in glulam beams of timber bridges under Northern European climates and mechanical loads. A hygro-thermal multi-Fickian model for prediction of moisture content, relative humidity and temperature in wood is sequentially coupled with an orthotropic-viscoelastic-mechanosorptive model for calculation of wood stresses. Both models were developed by some of the authors in Abaqus FEM code in previous works and their coupling is used here to analyse the hygro-thermo-mechanical response of a glulam beam of Vihantasalmi Bridge in Finland under bending loads. Both perpendicular and parallel to grain MIS in a beam section sheltered from rain are evaluated during a 10-year analysis and conclusions on the crack risk related to these stresses are given.