Simulation Preemption of Construction Operations

Construction simulation models often need to interrupt activities in progress when events such as equipment breakdowns or differing soil conditions are encountered. The new functions and statements to support activity preemption directly in the STROBOSCOPE simulation system are described and illustrated by two examples.
The first example involves moving soil using two wheelbarrows and two laborers and investigates whether interrupting the loading of a wheelbarrow by the return of an empty wheelbarrow that starts loading immediately can improve long-term production. Variability in the loading and hauling times makes it difficult to predict when the preemption of loading would be beneficial, even when the operations are balanced.
The second model involves undersea land reclamation where two cranes unload barges loaded with construction fill material. When only one barge is available, then both cranes work together to unload the same barge. When a second barge arrives, it takes over one of the cranes and both barges continue to unload using one crane. When a barge departs and there are no other barges waiting, the barge still unloading can switch to using both cranes. Unloading a barge can switch between using one and two cranes multiple times, with the remaining unload time either cut in half or doubled each time. Modeling the multiple dynamic reallocations of cranes and the remaining time to unload illustrates how the new STROBOSCOPE preemption capabilities can be used to model preemption in general.