A constrained multi-objective multi-floor facility layout problem

To search for an optimal arrangement of facilities in multiple number of floors is known as the multi-floor facility layout problem (MFLP). Practical MFLPs encounter several objective functions and constraints which needs to be considered. Here, a constrained multi-objective MFLP (cmMFLP) is proposed for finding the optimum number of floors required for arranging the facilities such that the total material handling cost among them is minimized. In addition to the total material handling cost and the required number of floors, the inter-floor material handling cost and the elevator utilization are also minimized simultaneously. For calculating these objective functions the facilities are arranged from the left end of every floor without any clearance between two adjacent facilities. Investigating the proposed cmMFLP model with a permutation based Genetic Algorithm (pGA), the Pareto-optimal fronts in terms of the four objective functions are evaluated for a set of instances of sizes in the range [60, 80]. The pGA was found to be superior to other solution techniques developed for the facility layout problem in terms of its ability to handle large size problems in lesser computational time. For the set of instances taken for evaluating the cmMFLP, decreasing the number of floors decreases the inter-floor material handling cost but increases the total material handling cost due to increase in the horizontal material handling cost among the facilities. Again with higher non-uniform elevator utilization the total material handling cost increases.The cmMFLP solutions obtained for these instances can be used as benchmark in future research.