In this paper, we present complexity results for storage loading problems where the storage area is organized in fixed stacks with a limited common height. Such problems appear in several practical applications, e.g., in the context of container terminals, container ships or warehouses. Incoming items arriving at a storage area have to be assigned to stacks so that certain constraints are respected (e.g., not every item may be stacked on top of every other item). We study structural properties of the general model and special cases where at most two or three items can be stored in each stack. Besides providing polynomial time algorithms for some of these problems, we establish the boundary to NP-hardness. 
Complexity results for storage loading problems with stacking constraints