Dowel bearing strength and bolted connection behavior of oriented strand lumber

Peter John Cates

Oriented strand lumber (OSL) is a relatively new commercial wood composite product with limited research data available in the public domain. This project looked at two aspects of connection behavior in OSL. The first part of the study addressed the effects of strand geometry and level of strand orientation on dowel bearing strength of the composite material. The second part of the study involved evaluation of bolted connection performance in OSL. In particular, European yield model (EYM) equations and end distance requirements were evaluated for effectiveness in predicting connection performance. Dowel bearing strengths were determined for both the parallel to the strand orientation and the perpendicular to the strand orientation loading cases. Strand nominal lengths of 4, 8 and 12 inches and strand nominal widths of 0.50, 0.75 and 1.00 inches were used to determine the effect of strand geometry on dowel bearing strengths. The manufacturing process used to orient the strands consisted of vanes aligned in the direction of the length of the oscillating forming box. The mean strand angle was used to measure the degree of strand orientation consistency and was dependent on the vane spacing and strand length. A vane spacing of 3 inches was used with each strand length and an additional vane spacing of 1.5 inches was used with the smaller strand lengths of 4 and 8 inches. Specific gravity and mean strand angle were measured for each of the finished OSL panels. From the analysis of the data collected, it was determined that strand geometry alone did not affect dowel bearing strength. However, level of strand orientation (mean strand angle) was found to affect the dowel bearing strength of specimens loaded perpendicular to the strand orientation. Specific gravity was also found to influence the dowel bearing strength in both the loading scenarios. The European yield model (EYM) equations were analyzed using three different bolted connection configurations to determine if the EYM was an appropriate method in determining the yield load in connections made with OSL. End distance requirements currently specified in the National Design Specification (NDS) for solid sawn lumber were also investigated to determine if they are applicable for connections made with OSL. When using the EYM equations, actual test data for bolt bending yield strength and dowel bearing strength of the OSL were used in the calculations. Through the comparison of the EYM equations and tested OSL connections, it was determined that the EYM equations adequately model the yield behavior of bolted connections made with OSL. However, the 5 percent diameter offset method was found to be inadequate for determining connection yield load from test data. Based on the data from the connection tests with variable end distances, it was clear that in the Mode Im and Mode IIIs configured connection tests, the 5 percent diameter offset yield load was not affected by end distances as small as four times the fastener diameter (4D).

Dowel bearing strength and bolted connection behavior of oriented strand lumber

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