Joe Keller's Research
Predicting the Rotational Stiffness of Pallet Joints Made Using Lag Screws and Carriage Bolts
Joseph Keller came to Virginia Tech from Charlottesville, VA where he lived with his family and three sisters. He was a competitive swimmer and has run half-marathons. Joe came to the SBIO department in 2017 for a Packaging Systems and Design degree. In the spring of 2021, as he was almost done, he was convinced to pursue a graduate degree after speaking with Dr. Laszlo Horvath about the Masters research topics that were currently available to him. Joe told us that “after talking with Dr. Horvath and the other graduate students, I decided to join the program and not looked back since!”
When asked to simplify it, Joe explained the subject that he chose for his graduate research this way: “I am investigating the stiffness of a wooden pallet when using lag screws and carriage bolts to hold them together. Most pallets have nails holding them together but some companies need stiffer pallets or stronger fasteners like lag screws and carriage bolts. I am testing the exact values companies should expect from these fasteners.”
The load that a pallet can carry is determined by the construction and durability of the given pallet. One of the biggest factors that influences pallets’ load capacity is the fastener type used during construction. While the strength values of different fastener types are well documented, the stiffness values that result from their use in the joints of wooden pallets have not been studied to the same level. There was a Seminole study performed in 1989 that predicted the rotational stiffness of a pallet joint constructed using nails. Utilizing the predictive model developed from that earlier study, the goal of this research was to calculate the rotational stiffness of pallet joints when other types of fasteners were used for construction.
The objective of this research was to replicate the same testing conditions using different fastener types, as seen in heavy-duty pallets, in order to predict the rotational stiffness of the joints that are held together by these alternative fasteners. The fasteners investigated were lag screws and carriage bolts, which are commonly seen in heavy pallets. To accomplish this, the head embedment stiffness, shank withdrawal stiffness, and rotational stiffness were all tested to give the constants necessary to calculate the stiffness of the simulated pallet joint. It was found that the stiffness of the joints was mainly influenced by the crushing of the wood where the block meets the top deckboard. The head embedment stiffness was significantly greater than calculated for the nails in the original study because this research used washers in the test setup. Washers are commonly seen in pallets that use lag screws and carriage bolts, which has proven to greatly increase withdrawal strength.
The results of this study will be included in the Pallet Design System (PDS) software in order to allow customers to more-accurately design pallets using the investigated fastener types. PDS will now be able to give them an accurate estimate of the stiffness values that can be expected from their pallet designs.
Joe Keller's research is funded by The Pallet Foundation and the National Wood Pallet and Container Association.
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