Mechanical Testing of Mixed Oak In-Grade 8-Inch Thick Timbers and Mats

Ensuring the safety of engineered wood mats for temporary road applications requires evaluating their strength under varying design, ground conditions, and crane loads. This study aims to assess the design values for a single sample of mixed oak in-grade, 8-in. thick timbers and mats under various design and loading scenarios. Timbers, graded as select structural or number one, were drilled and assembled into three-bolted timber mats. The bending properties, including modulus of elasticity and modulus of rupture, were determined for both individual drilled and nondrilled timbers, as well as the assembled mats. Concentrated and distributed loads were applied exclusively to the three-bolted mats to assess their structural performance. Parametric and nonparametric strength values were determined at the fifth percentile, incorporating adjustments for uncertainty and a 10-year load duration. The significant results indicated that the parametric design value for the mat subjected to a line load across all mats was essentially equal to that for the mat with a concentrated load on the middle layer, with only a negligible increase of about 7%. The graded drilled timbers showed about a 36% increase in parametric design value compared to undrilled timbers; however, this difference is attributed to natural variability as there is no evidence that drilling holes and removing material makes timbers stronger. This finding supports timber mat design specifications and has important implications for material selection, load distribution, and safety margins for their use in construction, road maintenance, and infrastructure projects.