Parameter-based applicability analysis of Gerhards cumulative damage model in residual strength and life prediction of wood in bending

Many timber structures around the world were built hundreds of years ago, and they are still standing after a long period of service with environmental erosion and damages caused by human activities. This is due to a combination of excellent form of construction, careful maintenance and outstanding physical properties of wood. How to evaluate the safety margin of wood, understand its working performance and evaluate the residual life duration accurately are the common problems with all structural engineers. This paper proposes a set of simplified models based on the widely used Gerhards cumulative damage model to intuitively describe the relationship between the stress level and life duration of wood under different load conditions. The scope of application of these models with existing experimental data sets was then analyzed. Finally, a method to predict the residual strength and residual life duration of wood in bending is proposed based on the simplified model under constant load.