Optimization of flexible lift processes on high-rise building construction sites

Timely delivery of materials and laborers to workface is critical to the smooth progression of a task on the construction site. This subject is of particular importance in high-rise building projects where the vertical transportation may turn into a bottleneck in the delivery process, if not precisely planned. In such contexts, lift cars represent a contested resource for movement of people and materials and any delayed lifting leads to disrupted tasks on the building floors. The available literature predominantly relies on predefined or rule-based scenarios in addressing the lifting problem which may result in suboptimal solutions to the operation of the lifts. Therefore, this research aims to develop a holistic mathematical model which identifies the optimum operational plan for the entire lift systems in high rise construction. The model has a mixed integer nature incorporating characteristics and constraints of lift cars, construction resources and activities, and site conditions. The optimality is targeted through minimum travel time both at the whole scale and for a single lift car. To improve generalizability, the model has been adapted to variant lift optimization problems under different construction scenarios. It is then integrated with the zoning problem in order to determine optimal zoning configuration for a given lift system. The model is tested on a hypothetical case replicating complexities and constraints of real-world situations. The results indicate that the model can efficiently find an optimal solution for the lift systems which imposes minimum vertical travel time to the project.