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The fundamental principle of critical chain project management is to use the critical chain instead of a traditional critical path, to insert a project buffer at the end of the project and to insert feeding buffers wherever non-critical chains join the critical chain to protect a timely project completion. Due to the complexity of project, inserting feeding buffers may cause a conflict, such as precedence conflict or resource conflict, which can be solved by rescheduling. However, after rescheduling some new problems may arise: non-critical chain may start earlier than critical chain (non-critical chain overflow), or a gap may occur between activities on the critical chain (critical chain break-down). This paper is aiming to solve these new problems by a two-stage approach combined with feeding buffer for rescheduling. In the first stage, a first-stage rescheduling based on priority rules together with a backward-recursive procedure is proposed for rescheduling to solve resource and precedence conflicts, resulting in a critical chain break-down or a non-critical chain overflow. In the second stage, a second-stage rescheduling based on a heuristic algorithm is proposed to eliminate new problems and generate a better rescheduling scheme. Finally, we do simulations on the 110 Patterson instances set to verify the feasibility, effectiveness and applicability of our two-stage approach for rescheduling. Simulation results show that, it is an effective approach to generate reliable rescheduling schemes in most projects with excellent performances, i.e. the average project length, timely project completion probability and etc.

The critical chain scheduling and buffer management (CC/BM) methodology has proven to be a favorable approach to schedule resource-constrained projects and to offer a valuable control tool for monitoring projects under uncertainty. The previous studies on CC/BM seem to have neglected the cost performance, which might render its wider applications to the modern economic activities that are mostly performed in a project way. This paper presents an improved CC/BM framework that allows additional resource allocation/reallocation to bring forward activity starting times based on cost and schedule stability criteria. In the planning phase, the decision is made concerning the regular resource availability period in order to minimize the expected resource costs. In the execution phase, a scheduled order repair method for rescheduling along with two reactive resource allocation procedures as the corrective action whenever delays are beyond a certain buffer threshold are presented and examined in order to exhibit a comprehensive project schedule/cost control system that is adaptive to the CC/BM management logic. Finally, our computational experiment demonstrates the benefits of the proposed reactive methods under different cost or availability parameters.

The Critical Chain Scheduling and Buffer Management (CC/BM) methodology, proposed by Goldratt (Critical chain, 1997), introduced the concepts of feeding buffers, project buffers and resource buffers as well as the roadrunner mentality. This last concept, in which activities are started as soon as possible, was introduced in order to speed up projects by taking advantage of predecessors finishing early. Later on, the railway scheduling concept of never starting activities earlier than planned was introduced as a way to increase the stability of the project, typically at the cost of an increase in the expected project makespan. In this paper, we will indicate a realistic situation in which railway scheduling improves both the stability and the expected project makespan over roadrunner scheduling.

In previous research (Tian and Demeulemeester 2010), we have shown that in realistic situations railway scheduling improves both the stability and the expected project length over roadrunner scheduling. In this paper, we introduce the concept of resource flow networks in this analysis and determine what the impact of combining roadrunner or railway scheduling with priority lists or resource flow networks is on the average project length, the standard deviation of the project length, the timely project completion probability and the stability cost. Extensive computational results will be presented on both small and larger projects and a statistical analysis will be conducted by using SAS PROC GLM, indicating that in smaller projects the optimal combination strongly depends on the performance indicator of interest, while in larger projects a combination of roadrunner scheduling with a resource flow network seems optimal.