Exploratory study on fatigue behaviour of laterally loaded, nailed timber joints, based on a dissipated energy criterion

Abstract

Abstract Exploration of damage accumulation and reliable prediction of the fatigue lives of laterally loaded, nailed timber joints, are important to proper engineering design of wood structural systems subjected to earthquakes, cyclones/hurricanes or other loads causing fluctuating force flows in such joints. Failure of nailed timber joints typically involves the combination of yielding at plastic hinges in nail and/or the crushing of wood under nails. Force-based criteria can predict the static strength of such joints but cannot reliably predict fatigue behaviour because that depends on loading history and the dissipation of energy within plastic nail hinges and/or crushed wood. In this study, the failure modes, damage accumulation and fatigue life of nailed timber joints subjected to reversed cyclic loads under load-control condition were studied. The results showed that there are two failure modes of nailed timber joints, i.e., ductile failure of nails when the applied load level was higher than 85% of the static maximum load to failure (Pmax) and brittle failure when the applied load level was <85% of Pmax. The damage accumulation involved three phases, i.e., damage initiation, damage propagation and failure. Fatigue life of nailed joints under reversed cyclic loads was modelled by an energy criterion that separated dissipated energy into non-damaging and damaging components demarcated by the fatigue limit. This approach replicated the behaviour of nailed joints tested at 20 load levels of fully reversed repetitive cyclic loading.