Effects of Load Sharing in Wood Tongue-and-Groove Plank Decking under Concentrated Loads

Tongue-and-groove plank wood decking is a product that is commonly used in post and beam timber construction to transfer gravity loads on roofs and floors. Little research or development has been done on plank decking since the 1950s and 1960s. An experimental program was undertaken at the University of Ottawa’s structural laboratory to better understand the behavior of plank decking under concentrated loads. Destructive tests were conducted on plank decking systems to investigate their failure mode characteristics and to quantify their capacity. The failure mode of a decking system under a concentrated load was consistent with a combination of failure in the decking boards and the tongue-and-groove joints. Significant load sharing was observed for plank decking under concentrated loads and it was found that the assumption of basing the design capacity on that of one board was invalid. Placing sheathing on top of a decking system to create a diaphragm action had a very significant and positive effect on both the stiffness and ultimate capacity of the decking system, which currently is ignored in design. The increase in stiffness and capacity can be attributed to the sheathing aiding in distributing the concentrated load to the unloaded decking elements and preventing the failure of the tongue-and-groove joints.