Optimization of tower crane and material supply locations in a high-rise building site by mixed-integer linear programming

Facility layout design and planning within construction sites are a common construction management problem and regarded as a complex combinatorial problem. To transport heavy materials, tower cranes are needed and should be well located to reduce operating costs and improve overall efficiency. Quadratic assignment problem (QAP), non-linear in nature, has been developed to simulate the material transportation procedure. Applying linear constraint sets, the quadratic problem can be linearized and the problem could be formulated into a mixed-integer-linear programming (MILP) problem solvable by a standard branch-and-bound technique for true optimal results. Numerical findings show that MILP results outperform those optimized by Genetic Algorithms with almost 7% on improving the objective function values in which facilities and locations can be modeled using integer variables. To demonstrate the design flexibility of using MILP formulation, the problem is also extended to non-homogeneous storages where different materials can be stored at a single supply point.