Development of flexural design values for pallet shook

Abstract

Rational design of wood pallets requires estimates of average flexural properties of pallet lumber of many species and visual grades. The objective of this study was to develop procedures for estimating these design values for use in a first-order second-moment design format.

Preliminary studies were performed to assess the effects of increased loading rates on in-grade flexural data, size effects between deckboard and stringer properties, and the effectiveness of the ASTM strength ratio concept as applied to pallet shook. An increased load rate (ten times the ASTM rate) resulted in an 8.0% increase in average MOR and a 4.7% increase in average MOE. No definite conclusions could be reached concerning the relative strength of deckboards vs. stringers. Several factors, other than a statistical size effect, may influence their relative strength. Estimated strength ratios (ESR) generally underpredicted the experimentally determined actual strength ratios (ASR). As knot size increased, the ESR increasingly underpredicted the ASR.

Two approaches were used to values. The best is full-size commercial material. However, derive pallet shook design in-grade testing of only yellow-poplar and eastern oak species have currently been evaluated in this manner. For all other species, a modified procedure based largely on the methods of ASTM D 2555 and D 245 was recommended. This procedure yields conservative estimates of strength for grades allowing large knots.