Resource constrained project scheduling using simulation

Resource allocation is one of the most important issues of construction management. Two problems of resource allocation are of concern: resource levelling and resource scheduling. Traditionally, the resource scheduling problem is solved using either heuristic methods or optimization techniques. When heuristic methods are used, resource scheduling is treated as a subsequent problem for the CPM analysis. In this paper, the resource scheduling problem is handled using simulation, where logic dependence and resource availability limits are considered simultaneously during the time scheduling process. Simulation is applied to the resource scheduling problem at the project level. A simulation system called SIRBUS is used to schedule construction projects under resource constraints. Constant resource demand of activities is assumed, and the activity once started cannot be interrupted. Six example projects previously solved by different heuristic methods are re-solved using simulation. The results are compared with the latest heuristic models: current float technique and ranked positional weight method. In addition to the advantage that resource availability is considered during time scheduling as a starting point, which is an apparent feature of simulation, SIRBUS gives good results compared with existing heuristic methods.     

An integrated modeling mechanism for optimizing the simulation model of the construction operation

A planner may use the discrete-event simulation to analyze and design the construction operation process that optimizes the overall performance of a construction system. Normally, the basic elements used in construction operation process simulation system, such as CYCLONE (CYCLic Operation NEtworks), are “activity” and “queue.” Activity is used to model the task which consumes resources and takes time to perform. Queue acts as a storage location for resources entering an idle state. In the simulation system, queues have to be created according to the ways of assigning resources to activities. Conventionally, planner defines queues according to his/her judgment by determining which and what amount of resources should be allocated to which activity. Consequently, various modeling schemes have to be examined to obtain the best simulation model. However, such a process of creating queues and activities is time consuming and requires iterations. This paper introduces a Genetic Algorithms (GA)-based modeling mechanism to automate the process of selecting the optimal modeling scheme. Case study shows that this new modeling mechanism along with the implemented computer program not only can ease the process of developing the optimal resource combination but also improve the system performance of the simulation model.     

Augmented heuristic algorithm for multi-skilled resource scheduling

Conventional project scheduling is restricted to single-skilled resource assumption where each worker is assumed to have only one skill. This, in effect, contradicts real-world practice where workers may possess multiple skills and, on several occasions, are assigned to perform tasks for which they are not specialized. Past research has shown a simple process of heuristic approach for multi-skilled resource scheduling where a project is planned under the assumption that each resource can have more than one skill and resource substitution is allowed. Nevertheless, the approach has presented resource substitution step where an activity with higher priority can claim any resource regardless of its concurrent activities' resource requirements. Furthermore, the approach is subjected to all-or-nothing resource assignment concept where an activity cannot start and resources are not needed for that activity at all unless the required resources of that activity can be completely fulfilled. This research presents an alternative heuristic approach for multi-skilled resource scheduling in an attempt to improve the resource substitution approach. Augmented resource substitution rule and resource-driven task duration are presented to increase starting opportunity of activities on earlier time. Case studies are presented to illustrate the improved result of shorter project duration.     

Integrating building information models with construction process simulations for project scheduling support

Many construction practitioners and researchers have developed four-dimensional (4D) models by linking the three-dimensional (3D) components of a building information model (BIM) with the network activities of a project schedule. In such a 4D model, the BIM provides limited information, except for the 3D components. To enhance the benefits of using BIM in 4D applications, this study proposes an interface system that uses the BIMs ability with regard to quantity takeoffs of required materials (such as steel, forms, and concrete) to support site-level operations simulation, ultimately leading to the generation of a project schedule. Our proposed system includes mechanisms that collect, store, and transfer information among various software packages. Facilitated by the BIM's quantity takeoffs, the operations simulation is able to consider uncertain durations of work tasks, which allows it to consider the competing needs for resources among multiple work tasks, and to evaluate various resource allocation strategies in order to create a suitable construction plan. Finally, the resulting project schedule is also linked to the BIM 3D components, thus producing an improved BIM-based 4D model.     

Simulation-based methodology for project scheduling

This paper describes a discrete-event simulation that incorporates the critical path method (CPM) in generating comprehensive information for construction project scheduling or planning. An activity-based graphical model able to consider complexities in construction, for example, unbalanced logical dependencies, unbalanced resource involvements and repetitive activity operation is proposed. An activity scanning (AS)-based forward pass algorithm for early-time information and a backward search algorithm for late-time information are developed. The simulation results that include both resource utilization statistics and late-time information (i.e. latest start or finish time and total float (TF)) of every activity for each cycle of operation cannot be easily achieved through traditional simulation or CPM. Illustrations demonstrate the advantages of the activity-based graphical model and the impacts of resource allocation policies on the schedule. The proposed methodology aims at widening the application of construction simulation by providing float time information and enhanced modelling capability.     

Application of computer simulation to bridge deck construction: Case study

Bridge deck construction is performed in a cyclic manner and it involves different types of interacted resources. This paper presents a case study that discusses how computer simulation is used to aid bridges' contractors in planning of bridges' decks, taking into consideration the interaction amongst involved resources. As such, total duration of deck execution and the associated total costs, including direct and indirect costs, can be estimated. El-Warrak Bridge, which is a part of the Ring Road of Cairo, Egypt, is analyzed in a step-by-step procedure to demonstrate the capability of computer simulation in modeling construction of bridges' decks using cast-in-place on falsework and cantilever carriage construction methods. The presented methodology proves its practicality to contractors in estimating the time and costs of the repetitive process of bridge deck construction, considering complex interdependencies between construction resources and the uncertainties associated with construction activities.     

Resource scheduling and planning for tunneling with a new resource model of the Decision Aids for Tunneling (DAT)

Resource scheduling and planning are the strategies required to determine the sequence of activities and resource allocation during tunnel construction. Resource scheduling and planning have been implemented in a new resource model of the Decision Aids for Tunneling (DAT), which are a computer based tool used to simulate tunnel construction. Tunneling plans obtained with the new resource model of the DAT take into account the technical precedence of activities, the resource/space availability, the dynamic status of the process, and the work continuity. In particular, the new resource model of the DAT can provide the optimal tunneling plan, which produces the shortest construction time and the smallest construction cost, and satisfies the special characteristics of tunnel construction such as excavation methods, distance requirements between the headings, and preempting activities (e.g., blasting).The paper attempts to contribute to both theory and practice: Optimization of the construction process considering time, cost and resources is particularly complicated in tunneling where activities and resource availability have to be appropriately sequenced and interference has to be avoided. The paper addresses this fundamental problem with the development of different schematic tunneling plans that consider the relevant activities and optimizes them with regard to overall cost and time, also considering uncertainties. Equally important is to make the theoretical development practically useable. This is done through implementation of the resource optimization in the DAT and, very importantly, by demonstrating the practical use with an application to a real tunnel case.     

Mathematical model to optimally solve the lift planning problem in high-rise construction projects

The availability of resources such as workforce and materials at each level of a high-rise construction project just before the commencement of building tasks is a crucial issue that might have direct impacts on project progress. To avoid delays caused by lack of human resources and construction materials, a construction management team always tries to find a better way to facilitate supply chain process specifically for construction projects facing a significant number of simultaneous and repetitive tasks. The other challenge in a high-rise construction project is vertical transportation that requires special machinery e.g. cranes or lifts, and also, maximizing their utilities. In this paper, it is tried to automate vertical transportation planning process in high-rise construction projects by introducing a platform that handles the entire lifting process. This platform considers (i) tasks attributes (e.g. required resources, location and commencement time) from the project schedule, (ii) lifting system specifications (e.g. travel speed, weight, and volume capacity) and (iii) project geometrics (e.g. current height of the project). In details, the introduced platform provides an optimized daily delivery plan by developing a Mixed-Integer Programming (MIP) model that covers workforce and construction materials. In this paper, the proposed platform is also tested using field data obtained from a 34-story construction project in Mashhad, Iran. The model could find a solution with 0% optimality gap in approximately 1 h, which is an acceptable amount of computational cost for the problem. The results show how the introduced platform can assist the construction management team to efficiently handle the supply process within stories while avoiding delays caused by a lack of resources required for each task.     

A simulation approach for a periodic PCR buffer allocation strategy in organizational program management

In a dynamically changing environment, the manager of a maintenance and remodeling (M/R) program is confronted with an increasing complexity of coordinating and cooperating multi-resource constrained multiple projects. Uncertainty and interdependence are sources of the complexity, and cause an internal disruption of an activity and chain reactions of disturbance propagation that deteriorate the stability and manageability of the program. This paper evaluates previous endeavors to apply production control and management techniques to the construction industry, and investigates the possibility of applying other production concepts and theories to organizational program management. In particular, this paper proposes a buffer allocation strategy by which periodic buffers are allocated in the flows of program constraint resources (PCRs) to stabilize a master construction schedule instead of protecting individual activities. Comparative experiments by Monte Carlo simulations illustrate better performance of the proposed strategy in terms of program goals: productivity, flexibility, and long-term stability.     

A two-phase GA model for resource-constrained project scheduling

In construction scheduling, problems can arise when each activity could start at different time points and the resources needed by the activities are limited. Moreover, activities have required conditions to be met, such as precedence relationships, resource requirements, etc. To resolve these problems, a two-phase GA (genetic algorithm) model is proposed in this paper, in which both the effects of time-cost trade-off and resource scheduling are taken into account. A GA-based time-cost trade-off analysis is adopted to select the execution mode of each activity through the balance of time and cost, followed by utilization of a GA-based resource scheduling method to generate a feasible schedule which may satisfy all the project constraints. Finally, the model is demonstrated using an example project and a real project.     

A genetic-algorithm-based resource-constrained construction scheduling system

Resources for construction activities are limited in the real construction world. To avoid waste and shortage of resources on a construction jobsite, scheduling must include resource allocation. A new resourceconstrained construction scheduling system is proposed in this paper. A GA-based searching technique is adopted in the system. In this paper, new GA crossover and mutation operators, UX3 and UM3, are presented. These new operators overcome the drawback of traditional GA operators for sequencing problems. The system effectively can provide the optimal combination of construction duration, resource quantities and minimum project duration under the constraint of limited resources.     

A simulation optimisation tool for planning of low-income housing projects

Construction of low-income housing projects is a recurring process and is associated with uncertainties that arise from the unavailability of resources. This paper presents a case study that discusses how computer simulation and optimisation are used to aid government agencies and/or contractors in planning of such projects. It illustrates the optimisation of project objectives, taking into consideration the interaction amongst involved resources. As such, total duration and the associated total costs, including direct and indirect costs, can be estimated and optimised. One Youth Habitation project that is executed in 6th of October City in Egypt is analysed in a step-by-step procedure to demonstrate the capability of proposed computer simulation and optimisation prototype (named LIHouse{_}Sim) in the modelling construction of low-income housing projects using bearing block walls with hollow core technique. The presented tool proves its practicality to contractors in estimating the time and costs of the recurring process of low-income housing construction, considering complex interdependencies between construction resources and the uncertainties associated with construction activities. The LIHouse{_}Sim prototype is used to perform a wide analysis for the alternative of the effective optimisation criteria in the bearing block walls/hollow core technique and for the genetic algorithm optimisation approach elements.     

A simulation model to study the impact of early information on design duration and redesign

In the design process, it is common to utilize early information from precedent activities to shorten the project duration instead of having to wait for the confirmed parameter values to arrive after full analysis. However, the estimated preliminary parameter might be different from that obtained after the full analysis. Consequently, redesign may be needed in downstream activities to correct this discrepancy. Total amount of induced redesign may adversely impact loss of productivity and overall design completion. Furthermore, redesign requires additional resources which may exaggerate the project completion for a project with limited resources. This study presents a simulation model to describe the effect of utilizing early information on redesign and total design duration. The paper characterizes the reduction in project duration while accounting for the impact of redesign through sensitivity studies of the parameters of the simulation model. The sensitivity studies would provide valuable insight that project managers can take into account when utilizing early information in design.     

The use of a virtual building design and construction model for developing an effective project concept in 5D environment

The growing diversity of disciplines, participants, tasks, tools and events associated with project management at the design and construction stages, the increasing pressure of costing competition and tighter production deadlines, as well as continually increasing quality requirements and the need for technological enhancements, are the driving force of information modeling and numerical simulation in the construction industry. When choosing the most effective investment project in construction, a major problem associated with the actual demand for resources is underestimated. In order to solve this problem in the most effective way, the application programs, covering virtually every phase of the specific construction product development, e.g. planning, design, cost estimation, scheduling, fabrication, construction, maintenance and facility management were developed and supplemented with the calculation of the demand for resources, comparison of alternatives and determination of the duration of all the stages of the project life. Theoretical principles and practical innovative applications of building information modeling and construction process simulation technique, used to determine the most effective alternative of the project by applying the appropriate multiple criteria evaluation methods, are considered in the article.     

Queue performance measures in construction simulation models containing subjective uncertainty

In recent decades, discrete event simulation (DES) has been widely used for analyzing construction projects. Recently, fuzzy discrete event simulation (FDES), which is an integration of fuzzy set theory with DES, has been proposed for simulating construction projects. FDES provides a framework to consider subjective uncertainty (uncertainty due to vagueness, subjectivity, and linguistic expression of knowledge) in construction simulation models. Current FDES frameworks only calculate simulation time (e.g., project completion time) as the simulation output. However, queue performance measures (e.g., average queue length and waiting time)—though important simulation model outputs for decision making, finding bottlenecks, and optimizing construction resources—are not analyzed in current FDES methodologies. Using fuzzy logic to consider the subjective uncertainty of service time and the inter-arrival time of systems' queues may improve such simulation models by more realistically representing their results. This paper provides a novel methodology to consider subjective uncertainty in analyzing the fuzzy queues in construction FDES models. Incorporating fuzzy queuing theory with FDES methodology as proposed in this paper enhances the applicability of FDES in construction projects. The proposed methodology is validated through mathematically solved queueing examples, and its practical aspects are illustrated using an example of an asphalt paving operation.     

A regional planning system based on artificial intelligence concepts

In the paper we present a logic-based system that makes possible the comparison of the requirements of particular sectors (e.g. agriculture, industry, construction, mining, energy) and social requirements (e.g. living conditions, employment, education, culture) at the level of the territorial system. It is based on a hierarchical model of national, county and district level activities. Every level has its own goals and the problem is to find an acceptable solution for these goals. Its implementation depends upon a special extension of the logic-based programming language PROLOG, known as TSPROLOG. The basic function of a territorial system can be viewed as the reproduction of social resources on an increasing scale. The task (the basic activity) of the system is the production of the territorial conditions of living and of the way of life. During this process of production, the system takes up raw material, energy and information from its environment. The processes that take place in the system are determined by natural/human resources, social activities, markets of technical elements and technically utilized areas. The external and internal relations of the system are regulated by the market of transport activities.     

Development of methodology and virtual system for optimised simulation of road design data

Current virtual reality (VR) and augmented reality (AR) tools do not lend themselves well to the simulation of non-repetitive activities that could be involved in road construction and heavy civil engineering projects. Therefore it is argued in this paper that specialised functions are required to support the use of VR and AR tools to visually design and simulate such projects. The prime objective of this study is to develop visual design and simulation analysis functions to support optimum road design by extending the applicability of current virtual reality (VR) systems to the design phase of road construction projects. The VR simulation functions developed in this research enable visual inspection of road alignment and earthwork status, simulation of alternative routes, and selection of optimum design route. This study implements a methodology for configuring VR simulation functions and develops a VR system for optimising the road design data. The research results include an improved road design process as a result of the application of the VR functions developed.     

Study on construction material allocation policies: A simulation optimization method

Due to uncertainty in both demand and supply, material shortages are difficult to completely avoid. To reduce the effect on the schedule and cost performance of construction projects, managers should allocate limited material among activities effectively. Motivated by observations of construction practices, this paper investigates the integration of supply logistics and site logistics issues and develops a framework to model inventory replenishment and allocation decisions jointly. On the basis of the activity feature information (e.g., schedule, cost, and demand), we propose five allocation policies to support the integrated inventory management process: schedule-based, cost-based, demand-based, schedule-cost-based, and schedule-demand-based policies. Meanwhile, a genetic algorithm (GA)-based simulation optimization method is utilized to solve the integrated inventory model and find the optimal inventory level under a given allocation policy. Based on a large set of fictitious project networks with different path difference (PD), a computational analysis is conducted to make detailed interpolicy comparisons. It is shown that for a project network with a small (or large) PD value, the schedule-based (or schedule-cost-based) policy is the most appropriate choice.     

Near optimal solution for resource-constrained scheduling problems

This paper presents an efficient resource allocation algorithm, and examines its performance against a number of scheduling heuristic rules, aimed at minimizing project durations in a multiple resource-constrained environment. The algorithm has been coded in BASIC and can easily interface with available planning and scheduling software systems. Unlike other heuristic network-based algorithms, resources are allocated simultaneously to sets of activities, rather than to individual activities in a sequential manner. An experiment was conducted to study the performance of the proposed algorithm and compare its results with those generated by four different heuristic scheduling rules, including those found to have the most superior performance such as the widely used least total float rule. Thirty-one network examples adopted from the literature are analysed. The results indicate that the proposed algorithm is superior to the others. The proposed algorithm provides a reasonable trade-off between the best accuracy associated with optimization techniques and the ease of computational effort associated with the simple least total float model. As such, it maximizes the benefits of the two limiting approaches.     

Visual Construction Operation Simulation: The DISCO Approach

Abstract: Despite the great deal of attention given to project-level management tools (e.g., CPM, PERT, etc.) in recent years, the analysis of construction operations (processes) using computer simulation techniques has generated considerable attention commencing with the introduction of the CYCLONE methodology. Recently, the application of visual simulation (VS) techniques to assist in the planning and analysis of construction operations has directed further attention at the need to better understand the interaction of resources at the process level. Visual simulation takes advantage of advanced modern computer graphics techniques and facilitates the development and application of simulation experiments. Benefits of applying VS have been reported in several publications. Nevertheless, the effort required to design and construct an "appropriate" VS display for the system to be analyzed is usually time and data demanding. The magnitude of model definition is often increased due to certain characteristics of construction operations, such as their complexity and the distribution of work over large areas. An alternative approach, DISCO (Dynamic Interface Simulation for Construction Operations), which employs a schematic modeling format demonstrating the system dynamics on the computer screen during simulation run, is presented in this paper.