Mechanical performance of full scale steel-timber epoxy joints after exposure to extreme environmental conditions

The use of adhesive joints with bonded-in steel rods or plates is of considerable interest nowadays for both new large timber structures design and timber strengthening. Bonded-in joints offer some advantages: high stiffness, high strength, ductile behaviour in some cases, easiness of factory production and possibility of in situ realization. Their use in Service Classess 1 and 2 is possible but not in Service Class 3, due to the extreme conditions. While the effect of the environmental conditions on the wood is well known, their effect on epoxy glue and on the mechanical properties of full scale timber joints requires ad hoc tests. In order to verify the effects of extreme environmental conditions, on the durability of the epoxy resin and on the mechanical behaviour of full scale ordinary joints, different epoxy specimens and timber joints were exposed to various conditions and ageing cycles: immersion in water (demineralized and swimming pool water), high and low temperature treatments cycles, treatments at different temperatures and R.H. Epoxy specimens showed transformation only in the case of immersion in swimming pool water. Full scale timber joints showed a shear strength variation only due to the moisture content variation between 12% and 24%. Joints submerged in water showed a strength reduction higher than the one expected for the reached moisture content, demonstrating that extreme conditions affect not only the timber strength, but also the performance of the full joints.