We consider the problem of scheduling multiple projects subject to joint resource constraints.All approaches proposed in the literature so far are based on the assumption that resources can be transferred from one project to the other without any expense in time or cost. In many realworld settings this assumption is not realistic. For example, cranes have to be transported to another location and reinstalled there. In order to consider this additional aspect, we generalise the multi-project scheduling problem by additionally including transfer times which represent transportation, installation, adjustment, (re-) learning and other setup activities necessary when a resource is removed from one project and reassigned to another (or from one job to another within the same project).In this paper, we define the modified multi-project scheduling problem with transfer times (called RCMPSPTT), formulate it as an integer linear programme, propose heuristic solution procedures and present results of comprehensive computational experiments.

Most approaches to multi-project scheduling are based on the assumption that resources can be transferred between projects without any expense in time and cost. As this assumption often is not realistic, we generalise the multi-project scheduling problem (RCMPSP) by additionally including transfer times and cost. To integrate this aspect, in a first step, we develop a framework for considering resource transfers in single and multi-project environments. It includes managerial approaches to handle resource transfers, a classification of resource transfer types and new roles that resources can take in these transfers. Afterwards, we define the multi-project scheduling problem with transfer times (RCMPSPTT) and formulate it in a basic and an extended version as integer linear programmes. Eventually, it is supplemented for the first time by cost considerations and introduced as resource constrained multi-project scheduling problem with transfer times and cost (RCMPSPTTC). Computational experiments compare the presented managerial approaches and prove the necessity of explicitly considering transfer times in project scheduling. Moreover, the experiments evaluate the presented MIP models and show that specialised solution procedures are vital.