Conjoining MMAS to GA to Solve Construction Site Layout Planning Problem

An optimal construction site layout planning (CSLP) is vital for project management. It can reduce the transportation flows and thus the costs of a project. Genetic algorithm (GA) is the most used algorithm to solve site layout problems, but randomly generated initial population in GA will decrease solution quality. Max-min ant system (MMAS) can offer a better initial population than the randomly generated initial population at the beginning of GA. In this study, a modified GA (MMAS-GA) formed by conjoining MMAS to the step of initialization of GA is proposed to solve CSLP problems. In order to reveal the computational capability of MMAS-GA to solve CSLP problems, the results of MMAS-GA and traditional GA are compared by solving an equal-area CSLP problem. The results showed that the proposed MMAS-GA algorithm provided a better optimal solution under the objective function of minimizing the transportation flows between the site facilities. The proposed MMAS-GA algorithm could assist project managers and planners to design optimal construction site layout, and thus to reduce construction costs.     

Particle Swarm Optimization for Construction Site Unequal-Area Layout

Layout of temporary facilities on a construction site is essential to enhancing productivity and safety, and is a complex issue due to the unique nature of construction. This paper proposes a particle swarm optimization (PSO)-based methodology to solve the construction site unequal-area facility layout problem. A priority-based particle representation of the candidate solutions to the layout problem is proposed. The particle-represented solution in terms of priorities should be transformed to the specific layout plan with consideration of nonoverlap and geometric constraints. In addition, a modified solution space boundary handling approach is proposed for controlling particle updating with regard to the priority value range. Computational experiments are carried out to justify the efficiency of the proposed method and investigate its underlying performances. This study aims at providing an alternative and effective means for solving the construction site unequal-area layout problem by utilizing the PSO algorithm.     

New Mathematical Optimization Model for Construction Site Layout

Layout of temporary construction facilities (objects) is an important activity during the planning process of construction projects. The construction area layout is a complex problem whose solution requires the use of analytical models. Existing popular models employ genetic algorithms that have proven to be useful tools in generating near optimal site layouts. This paper presents an alternative approach based on mathematical optimization that offers several important features and generates a global optimal solution. The construction area consists of an unavailable area that includes existing facilities (sites) and available area in which the objects can be located. The available area is divided into regions that are formulated using binary variables. The locations of the objects are determined by optimizing an objective function subject to a variety of physical and functional constraints. The objective function minimizes the total weighted distance between the objects and the sites as well as among the objects (if desired). The distance can be expressed as Euclidean or Manhattan distance. Constraints that ensure objects do not overlap are developed. The new approach, which considers a continuous space in locating the objects simultaneously, offers such capabilities as accommodating object adjacency constraints, facility proximity constraints, object–region constraints, flexible orientation of objects, visibility constraints, and nonrectangular objects, regions, and construction areas. Application of the model is illustrated using two examples involving single and multiple objects. The proposed model is efficient and easy to apply, and as such should be of interest to construction engineers and practitioners.     

Optimal Construction Site Layout Considering Safety and Environmental Aspects

A good site layout is vital to ensure the safety of the working environment and effective and efficient operations. Site layout planning has significant impacts on productivity, costs, and duration of construction. Construction site layout planning involves identifying, sizing, and positioning temporary and permanent facilities within the boundary of the construction site. Site layout planning can be viewed as a complex optimization problem. Although construction site layout planning is a critical process, systematical analysis of this problem is always difficult because of the existence of a vast number of trades and interrelated planning constraints. The problem has been solved using two distinct approaches: Optimization techniques and heuristics methods. Mathematical optimization procedures have been developed to produce optimal solutions, but they are only applicable for small-size problems. Artificial intelligent techniques have been used practically to handle real-life problems. On the other hand, heuristic methods have been used to produce good but not optimal solutions for large problems. In this paper, an optimization model has been developed for solving the site layout planning problem considering safety and environmental issues and actual distance between facilities. Genetic algorithms are used as an optimization bed for the developed model. In order to validate the performance of the developed model, a real-life construction project was tested. The obtained results proved that satisfactory solutions were obtained.     

Genetic Algorithms for Construction Site Layout in Project Planning

Construction site layout is concerned with the existence, positioning, and timing of the temporary facilities that are used to carry out a construction project. Typically these problems are very complicated to formulate and difficult to solve. They are, however, very important to virtually any construction project, since the site layout can significantly affect the cost of the project. This paper describes the general site layout problem from both a theoretical and a practical point of view. It proposes genetic algorithms as a possible solution technique and includes a theoretical example of positioning temporary facilities. This is extended to a practical problem in which the cost of movement is modeled realistically using an augmented genetic algorithm. Some preliminary conclusions are drawn for the application of genetic algorithms to construction site layout problems.     

Dynamic Site Layout Planning Using Approximate Dynamic Programming

Dynamic site layout planning requires identifying and updating the positions of all temporary construction facilities such as offices, storage areas, and workshops over the entire project duration. Existing models do not guarantee global optimal solutions because they focus on optimizing the planning and layout of successive construction stages in a chronological order, without considering the future implications of layout decisions made in early stages. This paper presents the development of an approximate dynamic programming model that is capable of searching for and identifying global optimal dynamic site layout plans. The model applies the concepts of approximate dynamic programming to estimate the future effects of layout decisions in early stages on future decisions in later stages. The model is developed in three main phases: (1) formulating the decision variables, geometric constraints, and objective function of the dynamic site layout planning problem; (2) modeling the problem using approximate dynamic programming; and (3) implementing and evaluating the performance of the model. An evaluation example is analyzed to illustrate the use of the model and demonstrate its capabilities in generating global optimal solution for dynamic site layout planning of construction projects.     

Material Flow-Based Facility Layout Analysis of a Manufactured Housing Production Plant

The layout of an assembly line type production plant can be designed or evaluated based on multiple criteria including, qualitative and/or quantitative aspects according to Mehrotra et al. in 2005. This paper presents the process of quantitative modeling and evaluation of the facility layout alternatives of a manufactured housing plant based on the material flow aspect. Manufactured homes are built on an assembly line similar to other manufactured products. However, production process, facility layout, and material handling system of the manufactured housing industry in the United States are still primitive as compared to automobile or other technologically advanced manufacturing facilities. In many of the manufactured housing factories, the facility layouts are inefficient because the stations are arranged without any prior planning and evaluation. The facility layout technologies in industrial engineering are used to develop an efficient facility layout for a manufactured housing plant. A manufactured housing plant was used as a case study plant. A material-flow based quantitative model was developed and implemented in a facility layout evaluation software program, FACTORYFLOW by EDS in 2002. The software was used to analyze the impact of material-flow on the facility layout of the case study plant and to develop alternatives. These layout alternatives were evaluated based on the feasibility and the projected cost savings. The analysis results indicated that many alternatives will result in cost savings as compared to existing layout. Once the alternatives were generated and evaluated, the comprehensive process steps for evaluating the facility layout alternatives based on the material-flow were developed in the form of a process flow diagram.     

EvoSite: Evolution-Based Model for Site Layout Planning

Appropriate site layout of temporary facilities is crucial for enhancing the productivity and safety on construction sites. Site layout planning, however, is a complex problem, and researchers have attempted to solve it using a variety of optimization-based and heuristic-based techniques. In this paper, a genetic-algorithm-based model for site layout planning is presented. The advantages of the model stem from three main characteristics: (1) It applies to any user-defined site shape; (2) it accounts for the user preference in the relative closeness among the facilities; and (3) it incorporates a genetic algorithm procedure to search for the optimum layout in a manner that simulates natural evolution. Based on the proposed model, a comprehensive system for site layout planning (EvoSite) is developed. EvoSite uses an intuitive spreadsheet representation of the site and the facilities, and automates the evolution of layout solutions. Details of model development and implementation are described, and an example application is presented to demonstrate the capabilities of the EvoSite system. The advantages, limitations, and future extensions of EvoSite are then discussed.     

Trade-off between Safety and Cost in Planning Construction Site Layouts

Planning construction site layouts involves identifying the positions of temporary facilities on site, and accordingly it has a significant impact on the safety and efficiency of construction operations. Although available models are capable of minimizing the travel cost of resources on site, they do not consider safety as an important and separate objective in the optimization of site layouts. This paper presents the development of an expanded site layout planning model that is capable of maximizing construction safety and minimizing the travel cost of resources on site, simultaneously. The model incorporates newly developed concepts and performance criteria that enable the quantification of construction safety and travel cost of resources on site. The present model is developed in three main phases: (1) formulating decision variables and optimization objectives in this site layout planning problem; (2) identifying and satisfying all practical constraints in this optimization problem; and (3) implementing the model as a multiobjective genetic algorithm. An application example is analyzed to illustrate the use of the model and demonstrate its capabilities in optimizing construction site layouts and generating optimal trade-offs between safety and travel cost of resources on site.     

Materials Handling System Simulation in Precast Viaduct Construction: Modeling, Analysis, and Implementation

The interactive, complicated system environment of a construction site renders conventional site layout planning and scheduling techniques to be inadequate in coping with materials handling system design in construction. In this paper, we present a university-industry joint endeavor for improving the effectiveness of the materials handling system on a precast viaduct construction project in Hong Kong by implementing the simplified discrete-event simulation approach (SDESA) along with its computer platform resulting from recent research. How to apply the simulation methodology of SDESA is elaborated step by step. Particular emphasis is placed on procedures of establishing a simulation model, validation of the simulation model, design of simulation experiments, and analysis of simulation results. With process flowchart, site layout plan, and process animation produced in a view-centric simulation environment, it is straightforward to establish, validate, and communicate the operations simulation. The research team convinced the project director, as well as field managers, of the functionality and effectiveness of operations simulation. The knowledge derived from simulation added to experiences of site managers in materials handling system design. With the aid of simulation, even junior engineers would be capable and confident to draw up an actionable construction plan that would lead to enhancement of cost effectiveness and productivity in the field.     

Minimizing Construction-Related Security Risks during Airport Expansion Projects

Airport expansion projects often require the presence of construction personnel, material, and equipment near airport secure areas/facilities, leading to an increase in the level of risk to airport security. Construction planners and airport operators need to carefully study this challenge and implement active measures in order to minimize construction-related security breaches and comply with all relevant Federal Aviation Administration guidelines. This paper presents the development of an advanced multiobjective optimization model for planning airport construction site layouts that is capable of minimizing construction-related security breaches while simultaneously minimizing site layout costs. The model incorporates newly developed criteria and performance metrics that enable evaluating and maximizing the construction-related security level in operating airports. The model is developed using a multiobjective genetic algorithm, and an application example is analyzed to demonstrate the use of the model and its unique capability of generating a wide spectrum of optimal trade-offs between construction-related airport security and site layout costs.     

Utilization of Precast Concrete Elements in Building

Precast concrete components can be used in building construction within a comprehensive “closed” system, or as separate elements in conjunction with any building method. The feasibility of this second possibility was examined within the framework of a conventional building system and the following alternatives of elements utilization: prestressed modular floor slabs, exterior walls, and a combination of slabs and exterior walls. Each of these alternatives was compared to the conventional system without precast elements. The following criteria were used as a basis for the comparison: the labor requirement, the direct building cost (labor and materials), the construction time, and other considerations of more subjective nature. The findings of the study indicated that the utilization of precast elements might considerably reduce the labor requirement on site, and the project construction time. The direct building costs were almost unaffected by the alternative solutions.     

Key Performance Indicators for Strategic Healthcare Facilities Maintenance

The salient phases in a facility’s service life that are most decisive for the effectiveness of its facilities management (FM) are the preliminary design, construction, and maintenance. The effectiveness of facilities is vastly affected by decisions pertaining to the strategy of the organization that owns or uses the facilities. The goal of this study was to develop key performance indicators (KPIs) for strategic FM that will provide a conclusive approach towards the facility’s service life conditions. Parameters were developed by means of field surveys and statistical analyses, and were validated by means of case studies. The research resulted in a series of 11 KPIs for strategic healthcare FM, which can be classified into four categories: development, organization and management, performance, and maintenance efficiency parameters. The study proposes age and occupancy coefficients as essential parameters for the assessment of large healthcare facilities needs, as an effective measure for long term facility maintenance planning, and for measuring FM effectiveness. The paper stresses that strategic healthcare facilities management must integrate quantitative performance, manpower, and maintenance indicators.     

Genetic Algorithm for Solving Site Layout Problem with Unequal-Size and Constrained Facilities

This paper presents an investigation of the applicability of a genetic approach for solving the construction site layout problem. This problem involves coordinating the use of limited site space to accommodate temporary facilities so that transportation cost of materials is minimized. The layout problem considered in this paper is characterized by affinity weights used to model transportation costs between facilities and by geometric constraints that limit their relative positions on site. The proposed genetic algorithm generates an initial population of layouts through a sequence of mutation operations and evolves the layouts of this population through a sequence of genetic operations aiming at finding an optimal layout. The paper concludes with examples illustrating the strength and limitations of the proposed algorithm in the cases of (1) loosely versus tightly constrained layouts with equal levels of interaction between facilities; (2) loosely versus tightly packed layouts with variable levels of interactions between facilities; and (3) loosely versus tightly constrained layouts. In most problems considered where the total-objects-to-site-area ratio did not exceed 60%, the algorithm returned close to optimal solutions in a reasonable time.     

Production Scheduling for Precast Plants using a Flow Shop Sequencing Model

There are two alternatives for production organization in precast factories—namely, the comprehensive method and the specialized method. Production scheduling under the specialized alternative has been found to be a difficult optimization problem if heterogeneous elements are involved. A flow shop sequencing model that incorporates actual constraints encountered in practice is proposed for this difficult case of precast production scheduling. The model is solved using a genetic algorithm (GA). The traditional minimize makespan and the more practical minimize tardiness penalty objective functions are optimized separately, as well as simultaneously using a normalized weighted GA. Comparisons between the GA and classical heuristic rules show that the GA can obtain good schedules for the model, giving a family of solutions that are at least as good as those produced by the use of heuristic rules.     

Computer-Aided Site Layout Planning

This paper presents an interactive computer-aided site layout model to support site planning in a computer-aided design (CAD) environment and expands upon a model presented earlier by the writers. The developed model performs its task at two levels: Site representation, and site space analysis and allocation. The site representation is carried out using an open architecture supported by object-based concepts. The model offers three tiers of objects: (1) site objects, (2) construction objects, and (3) constraint objects. This structure facilitates the creation of new objects and reuse of domain knowledge, which allows for the gradual expansion and enrichment of the model’s knowledge base. At the space analysis and allocation level, the model introduces a geometric reasoning approach to analyze site space for finding an optimum or near-optimum location for facilities. This feature facilitates easy visualization of the site planning process and encourages user participation. The model is structured in three main modules: Database, Project Module, and Layout Control Module. The functionality of each module, along with their interconnectivity is described. The model is implemented using Visual Basic for Applications in AutoCAD environment and Microsoft Access. A numerical example of an actual site layout is presented to illustrate the functionality of the developed model.     

Concepts for Lunar Outpost Development

This paper summarizes the results of a qualitative investigation to identify concepts for design and construction of near‐term lunar facilities. Accomplishing such construction will require an adaptation or transfer of current terrestrial technology and methods. Discussions on modularization, geosynthetic materials, aluminum materials, static load analysis, and dynamic load analysis provide illustrative examples of how terrestrial technologies can be adapted to lunar applications. These discussions provide support for the development of a phased lunar construction strategy. The initial stage of construction is characterized by small self‐supporting accomodation and laboratory modules. The assembly facility stage is characterized by the construction of a large pressurized module‐assembly facility. The module production stage is characterized by the fitting together of terrestrial or low earth‐orbit subassemblies into completed modules within the module assembly facility. The completed modules are also tested and moved to their final location in this stage. The lunar materials stage is characterized by the construction of facilities with maximum use of lunar materials.     

Minimizing Construction-Related Hazards in Airport Expansion Projects

Airport expansion projects often require the presence and movement of construction labor and equipment near critical airport traffic areas. This close proximity between construction activities and airport operations needs to be carefully considered during the planning of construction site layouts in order to minimize and eliminate all potential construction-related hazards to aviation safety. This paper presents the development of a multiobjective optimization model for planning airport construction site layouts that is capable of minimizing construction-related hazards and minimizing site layout costs, simultaneously. The model incorporates newly developed optimization functions and metrics that enable: (1) maximizing the control of hazardous construction debris near airport traffic areas; (2) minimizing site layout costs including the travel cost of construction resources and the cost of debris control measures on airport sites; and (3) satisfying all operational safety constraints required by the federal aviation administration as well as other practical site layout constraints. The model is implemented using a multiobjective genetic algorithm and an application example is analyzed to demonstrate the use of the model and its capabilities in optimizing construction site layouts in airport expansion projects.     

Stay-in-Place Fiber Reinforced Polymer Forms for Precast Modular Bridge Pier System

This paper presents an innovative modular construction of bridge pier system with stay-in-place fiber reinforced polymer (FRP) forms filled with concrete. Two 1/6 scale precast modular frames were prepared of a prototype bridge pier system. Three different types of connections were considered: male-female, dowel reinforced with or without tube embedment, and posttensioned. The frames were load tested in negative and positive bending. Subsequently, the cap beams were cut from the frames and tested to failure in four-point bending. Posttensioned joints exhibited the most robust and ductile behavior and proved to be the preferred method of joining stay-in-place forms. Even with dowel bars, the male-female joints lacked the necessary structural integrity in the pier frames. Better surface preparation for FRP units and higher quality grouting may improve the response. Embedment of the columns into the footing provided additional stiffness for the connection. The study indicated that internal reinforcement is not necessary for the stay-in-place forms outside the connection zone. The experiments also showed the importance of maintaining appropriate tolerances and match casting for male-female and embedment connections. Overall, however, feasibility of the precast modular FRP system was demonstrated in this study.     

全国危险废物处置设施普查的分析和思考

对全国危险废物和医疗废物处置设施普查数据进行了全面分析,得出数量、布局、规模、工艺技术、运行等方面的总体情况,分别从加强清洁生产审核、开展危险废物产生源调查、完善危险废物鉴别体系、提高综合利用技术门槛、尽快淘汰落后医疗废物处理设施、严格控制《规划》项目建设规模、加大医疗废物非焚烧技术的宣传和应用、加快制定全过程管理的配套政策等方面,提出下一步加强管理和设施建设进程的工作建议。