ALTERNATIVE APPROACHES TO SOLVE THE MULTI-FLOOR FACILITY LAYOUT PROBLEM

Alternative approaches to solve the multi-floor facility layout proble m are compared in this paper. In particular, because the multi-floor f acility layout problem is NP-complete, the effectiveness of heuristica lly solving it via a single-stage approach (where each department, unl ess it is fixed or constrained by the user, is allowed to occupy any f loor during the execution of the heuristic) versus a two-stage approac h (where in the first stage each department is permanently assigned to one of the floors and in the second stage the layout is determined fo r each floor) is evaluated. Generally speaking, given no limits on run times, one would expect the single-stage approach to outperform the a bove two-stage approach because the former allows departments to chang e floors during the execution of the algorithm. However, if the run ti mes are required to be reasonable and comparable, it is no longer clea r that the single-stage approach will lead to superior solutions becau se it has to explore a larger solution space. The performance of the t wo-stage approach, on the other hand, depends on the quality of the fl oor assignments obtained in stage one. Instrumental to the quality of these assignments is a newly developed simplified formulation with a l inear objective to optimize the inter-floor handling cost in stage one . The resulting two-stage approach is then evaluated with respect to a single-stage approach using various test problems. The evaluation inc ludes a variation of the above two-stage approach where the floor assi gnments obtained in stage one are not permanent; that is, departments are allowed to change floors in the second stage. The evaluation indic ates that the proposed two-stage approach compares quite well to both of the other approaches. The results obtained by the two-stage approac h are shown from a data set that is based on a real-world manufacturin g facility.