Structural analysis models for block pallets

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Virginia Polytechnic Institute and State University

A large percentage of the total annual lumber production in the U.S.A is consumed by the pallet industry. However, standardized design procedures for these products have only recently been developed. A four-year cooperative pallet research, development and application program was undertaken by the National Wooden Pallet and Container Association, Virginia Polytechnic Institute and State University, and the U.S Forest Service. This research is directed towards developing standardized design procedures for both stringer and block-type pallets. Phase I dealt exclusively with stringer-type pallets while Phase II expands the scope to include block-type pallets. The objective of this work was to develop methods to analyze the effects of loads, supports and geometry on the response of block-style pallets.

The developed analysis procedures are based on matrix structural analysis methods. A quarter symmetric 3-dimensional model is used to simulate pallets racked across the stringerboards (RAS) and a half symmetric 2-dimensional model is used for the racked across deckboards (RAD) and sling support modes. Both models are used in the stack condition. Deckboard/stringerboard joints are modeled as a single spring in the RAS model and the deck-block joint in both the RAS and RAD models are modeled as a framework of rigidly connected members and five springs (2 rotational and three axial). The procedure has the capability to handle both uniformly distributed and line loads in rack, stack, or sling support modes, and a wide variety of commonly used geometries.

The developed analysis methodology is presented in computerized form and will provide the user a means of communication with pallet manufacturers for defining expected performance.