Piotr Jaskowski

Multicriteria construction project scheduling method using evolutionary algorithm

The project owners demand that construction projects are to be accomplished on time and to budget. Regardless of the construction project procurement system, duration and cost are the key factors determining project’s economic efficiency and fulfillment of the owner’s needs and requirements. Beside quality, they are basic criteria taken into account in project planning, scheduling and contractors selection. The multicriteria optimization of schedules is a complex question being among NP-hard problems. There is a demand for methods of proved reliability that would facilitate solving practical cases within relatively short time and allow for numerous constraints typical for construction. Due to limitations of precise methods in solving complex practical issues and imperfection of heuristic methods, the metaheuristic approach (evolutionary algorithm) has been adopted to solve multiple-objective combinatorial optimization scheduling problems. The method has been applied to solve a practical case of bicriteria (time and cost minimization) scheduling optimization and contractor selection problem.

Using soft precedence relations for reduction of the construction project duration

Abstract Current network techniques used for project scheduling presume that there is only one logical sequence of activities. However, in reality, the precedence logic of activities is not necessarily unchangeable. There are two types of relations between activities: fixed (hard) and soft. Current scheduling methods do not differentiate between these two types of relations and require a planner to choose one particular logical sequence based on some assumptions. The paper presents a model that allows for “weakening” the links between activities, i.e. that permits concurrent execution of activities or reversing their order, but this may require additional resource-consuming works or expenditures. The model involves two subtypes of soft logic: REVERSED and CANCELED to represent the soft relations between activities. Its mathematical form is a mixed linear integer programming model of minimizing the project duration without exceeding the allowed budget. The paper presents an example of practical application...