Load-duration behavior of wood-plastic composites

The load-duration, or creep-rupture, behavior of wood and wood composite products has been studied extensively by numerous researchers, and simplified design procedures to account for creep effects are in place. However, the load-duration behavior of composite products made out of the combination of wood and plastic is not well understood or documented. Currently, wood-plastic composite (WPC) products are available on the commercial market, yet no standardized design procedures to account for creep or load-duration effects exist. Given the lack of understanding of the load-duration behavior of wood-plastic composites, a research effort was initiated to investigate the load-duration behavior of various wood-plastic composite formulations and to compare the observed behavior to that of solid sawn lumber. It was found that the wood-plastic composite formulations tested exhibited a more pronounced load-duration response than that of solid wood; however, the behavior trend was similar to that of solid wood and was successfully modeled using an exponential damage rate model originally developed for solid wood. Existing procedures for developing load-duration design adjustment factors for wood were used to develop load-duration design adjustment factors specifically for the WPC formulations tested.