Mechanical Behavior of Treated Timber Boardwalk Decks under Cyclic Moisture Changes

Timber boardwalk decks are widely installed in parks and scenic areas to provide pedestrians an elevated footpath as well as harmony with the surrounding natural scene. In order to extend the lifespan of boardwalks in the outdoor environment, industrially treated pine timber, such as Pinus sylvestris, is often adopted. However, accidents of pedestrians injured by damaged boardwalk decks have been constantly reported. Therefore, the mechanical behavior of two different types of treated timber was examined in this study under repeated wetting and drying. An increasing number of radial cracks appeared with increasing length and width as more cycles were performed. A loss of more than 40% of the screw withdrawal capacity was observed in both end grain and face grain for the two types of timber after twelve accelerated wet-dry cycles, which coincides with the observation of damaged timber boardwalks in the field investigation. At the same time, it was found that both the compressive and the flexural strength was not sensitive to the wet-dry cycles especially at large cycle numbers.