## 2 Unit Load Selection and Simplification  
In order to reach the goal of developing a general tool with which to study the load bridging effect in unit loads, limitations were defined. Without these limitations, any tool modeling unit loads would require extensive information and data collection, rendering the potential applications of the final model only to limited, expensive studies. This research project limited the support conditions studied to warehouse cracking across the pallet width. Previous research studies have identified this support condition as the one that most often limits the pallet load carrying capacity, given that it commonly presents the greatest pallet deformation [20; 21; 23]. The warehouse cracking condition where the pallet is racked across its width will be referred to as simply \"racking support.\" Additionally, it is assumed that under this condition, as shown in Figure 1, the displacement due to the bending of the supporting pallet and box movement is primarily along the _xy_-plane, with negligible displacement along the z-axis. This assumption is supported by the results in a study by [PERSON] et al. [23]. In this study, when varying the different load bridging factors, such as pallet design and package orientation, the rate of changes in pallet deflection generated were consistent for the center and the ends of the pallet, indicating that the effect of load bridging is not dependent on the location of the pallet deflection measurement. Based on the series of tests conducted by [PERSON] et al., the bending phenomena can be accurately described by a two-dimensional model. Therefore, a single row of boxes, shown shaded in Figure 1, was modeled to represent the unit load and the payload's interactions. The pallet geometry was simplified to be just one board, it being deep enough to support a single row of boxes. A similarly simplified unit load segment has been used for physical testing in previous studies [18; 19; 22]. All measurements of pallet bending were considered initial, ignoring the effects of long-term creep on the bending response. Corrugated boxes were modeled as nondeformable solid objects, subject to gravitational forces and frictional interactions. It is well-known that corrugated boxes are prone to buckling and other deformations while loading, especially the boxes located at the bottom of the stack in a unit load. While, undoubtedly, boxes with significant deformation would impact the results obtained in this study, the study is limited to unit loads carry new, undamaged packages. These packages have been properly designed to provide the required carrying capacity to support loading without significant deformation. Furthermore, the boxes used for the experimental validations contained rigid oriented strand board (OSB) containers closely fitted inside, preventing any buckling deformation from handling and loading during the experimental validation. Box contents were not considered in this model. This simplification is supported by previously conducted research that investigated the effects of box contents on pallet deflection [22]. Even though the strength of a corrugated box can be influenced by its contents, the shape or form of the contents does not affect overall pallet deflection as long as the boxes are not deformed. The pallet was represented in the model using a board as a pallet analog; thus, the effect of the pallet structure was not considered. Pallets can be designed in many different ways with many different materials, and some of these variations might have characteristics that affect the bending profiles. Other structural elements of pallets, such as the effect of stringers and deck boards, were also not considered. Only unit loads of boxes that provided full coverage of the pallet or pallet simulator deck were used. Under or overhanging packages on a pallet could possibly behave in a different manner. Pallet dimensions were based on the Grocery Manufacturers Association specification of 1219 mm \(\times\) 1016 mm.