Resource Leveling in Construction Projects
A. Abstract: Management of the resources carries an indispensable importance for profitability and scheduling of construction projects. By their nature, construction projects require different sets of skills, equipment and materials during different stages of the process. Furthermore, the demand for amount of distinct assets fluctuates greatly depending to the project stage. Resource Leveling, also known as Resource Smoothing, shows interest in eliminating resource shortages and abundances by having a more optimized project schedule with regards to the utilization of the resources. The goals of the Resource Leveling are eliminating delays, failures and cost overruns, without interfering with the project’s scope, cost and time constraints. In Resource Leveling, the project duration, number of the resources and the completion date remains unchanged. It is assumed that the project has been provided sufficiently. Resource Leveling is closely tied to the project scheduling methods such as Critical Path Method (CPM) and Program Evaluation and Review Technique (PERT), which are predominantly used in construction industry. Usually, Resource Leveling is coupled with one them. Whereas, these scheduling techniques are interested in critical tasks and their connections to each other for completion of the project, they fail foreseeing any failures due to shortcomings. Resource Leveling takes advantage of float and moves tasks around in timetable with an eye on resources. Coming up with more efficient solutions for more balanced use is an area that has been attracting interest. For this purpose, various methods, algorithms and objective functions have been developed. The users have opportunity to select between them according to their project in order to achieve best results.
B. Introduction: Resource leveling assumes that there are sufficient resources, but the project duration is constant. The main idea behind resource leveling is moving non critical activities in the schedule for eliminating fluctuations, peaks and valleys in resource utilization. It is impossible to have a completely flat resource consumption, hence, it is important to identify most appropriate objective function in order to achieve a resource use as uniform as possible or have a non-uniform distribution which is in accordance with the project’s needs. Depending on the limitations, needs and processing power, an approach method can be implemented for generating results. They have their own advantages and disadvantages.
C. Critical Path Method & Program Evaluation and Review Technique: Resource leveling is often coupled with a scheduling method. Critical Path Method (CPM) and Program Evaluation and Review Technique (PERT) are the most common methods in construction industry. Knowledge on them is essential.
1. PERT: Program evaluation and review technique 2. CPM: Critical Path Method
D. Float: Construction projects consist of multiple linked, but distinct tasks. Some of them require completion of certain prior tasks. Such situation creates an unshrinkable path. On the other hand, some of the tasks can be completed independently from this chain. It is possible to move dates of these independent tasks in the time frame. This time availability is called float.
E. Objective Functions: There are multiple objective functions. They try to minimize different parameters; thus, they return different solutions. The most common criteria for construction sector are given below:
1. Minimization of the sum of the absolute deviations in daily resource usage [2] 2. Minimization of the sum of only the increases in daily resource usage from one day to the next [2] 3. Minimization of the sum of the absolute deviations between daily resource usage and the average resource usage [2] 4. Minimization of the maximum daily resource usage [2] 5. Minimization of the maximum deviation in daily resource usage [2] 6. Minimization of the maximum absolute deviation between daily resource usage and the average resource usage [2] 7. Minimization of the sum of the square of daily resource usage [2] 8. Minimization of the sum of the square of the deviations in daily resource usage [2] 9. Minimization of the sum of the square of the deviations between daily resource usage and the average resource usage [2]
F. Optimization Methods: Objective functions are optimized with three main methods, which are Mathematical Method, Heuristic Method and Metaheuristic Method. They will be simply explained. It’s also possible to combine them and have a hybrid approach.
1. Mathematical Method Even though, the model provides a definitive result, it consumes significantly more time and processing power. A larger space is investigated and distinct calculation methods, such as linear and nonlinear approaches, constraints are determined depending on the subject. 2. Heuristic Method The user proposes an algorithm. The method includes elimination of certain aspects; thus, it demands experience. As a result of narrowing the options, it is a useful method for results in limited timeframes; but it may miss the ideal result, it also requires validation. 3. Metaheuristic Method Optimization in the nature is reflected. The fact that everything in the nature is in the most efficient form for survival is the main reasoning behind the replication. Model takes inspiration from ants, mutation, chromosomes... The goal is generating a solution in a short time by mimicking effectiveness of the nature. Method may not generate the correct result.
G. Example: An example with Critical Path Method will be give given. No actual calculations will be shown. This part will only demonstrate the theoretical information, which can be found above, in an exemplary way with tasks and a schedule from an imaginary construction project.
H. References: 1. Damci, Atilla, et al. "Use of float consumption rate in resource leveling of construction projects." Frontiers of Engineering Management (2022): 1-13. 2. Damci, Atilla, and Gul Polat. "Impacts of different objective functions on resource leveling in construction projects: a case study." Journal of civil engineering and management 20.4 (2014): 537-547. 3. Damci, Atilla, et al. "Resource levelling with float consumption rate." Creative Construction Conference 2019. Budapest University of Technology and Economics, 2019. 4. Son, Jaeho, and Miroslaw J. Skibniewski. "Multiheuristic approach for resource leveling problem in construction engineering: Hybrid approach." Journal of construction engineering and management 125.1 (1999): 23-31.
