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Browsing by Author "Osborn, Lawrence E."

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    Evaluation of the joint performance estimates within the PDS durability procedure
    Osborn, Lawrence E. (Virginia Polytechnic Institute and State University, 1985)
    The model used to estimate pallet life in the durability section of PDS is a composite of several computed "factors" which are intended to reflect the impact of design characteristics on pallet durability. The objective of this study was to evaluate the reliability of the estimates of joint performance and the resulting estimates of pallet life relative to the estimated joint performance. A series of delayed fastener axial withdrawal tests were performed on a wide range of pallet fasteners to evaluate the estimates of joint separation resistance that are used in the computation of the F ( 1) factor, the factor for joint separation resistance perpendicular to the pallet deck. This data, in addition to data obtained from previous studies, suggested that the model underestimated the delayed withdrawal performance of threaded nails. An improved relationship was derived for helically threaded, twisted square wire and annularly threaded nails which had the additional advantage of being sensitive to lumber moisture content both at the time of joint assembly and at the time of joint testing. Both the original and the improved relationships were found to grossly overpredict the withdrawal performance of plain shank nails and staples. A series of pallet corner drop tests were performed to evaluate the reliability of the estimates of joint torsional shear resistance that used in the computation of the F(2) factor, the factor for joint separation resistance parallel to the pallet deck. The pallets tested varied by lumber species, number of fastener couples, and fastener stiffness as measured by the MIBANT bend angle. The observed affect of changes in fastener stiffness on pallet diagonal rigidity was found to be accurately reflected in the computed F(2) values. The observed affect of changes in the number of fastener couples on pallet diagonal rigidity was overpredicted in the computed F(2) values. The observed affect of changes in the lumber specific gravity on pallet diagonal rigidity appeared to be overpredicted in the computed F(2) values but this might be due to the fact that the measured pallet distortions were adjusted to account for differences in pallet weights. Pallet weight is specific gravity dependent and adjusting pallet distortion by weight may have reduced the observed affect of specific gravity. It was not possible to statistically confirm a relationship between the estimates of pallet durability relative to pallet diagonal rigidity and observed pallet life. However, such a relationship appears likely. Also, the estimates of pallet durability were found to be conservative.