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.     

General-Purpose Systems for Effective Construction Simulation

This paper examines the characteristics of discrete-event simulation systems in terms of their application breadth (general or special purpose), modeling paradigm (process interaction versus activity scanning), and flexibility (programmable or not). Several construction simulation systems are examined with primary emphasis on CYCLONE and STROBOSCOPE as representatives of the wide range of tools that are currently available. CYCLONE is a well-established, widely used, and simple system that is easy to learn and effective for modeling many simple construction operations. STROBOSCOPE is a programmable and extensible simulation system designed for modeling complex construction operations in detail and for the development of special-purpose simulation tools. The characteristics of these systems, as well as other recent developments, illustrate that an effective general-purpose simulation tool for construction is in essence one based on extended forms of activity cycle diagrams and the activity scanning modeling paradigm. As explained through several examples, these representations are indeed the most convenient and intuitive for construction simulation systems. Furthermore, the programmability of such a system is the principal factor that determines its power, flexibility, and ease of learning and use.     

Modeling Time-Constraints in Construction Operations through Simulation

Construction operations often face time constraints that influence the execution of activities, which are not addressed enough when modeling through general discrete-event simulation. This paper describes a simulation-based methodology to handle the time constraints including the cyclical break, preemption, and overtime use. In consideration of the variable number of breaks or variable break duration for different activities, an algorithm to determine the execution of the time-constrained activities is proposed, in which the concepts of time cycle and time window are introduced. The proposed algorithm is incorporated with an activity scanning simulation strategy to develop a construction simulation for modeling the time-constrained construction operations. Some examples are presented to illustrate and validate the algorithm, and highlight the effectiveness of the developed construction simulation. The study provides an alternative to improve construction simulation in modeling of the time-constrained construction operations and is expected to assist researchers or practitioners at analyzing or planning construction operations.     

Simulation Approach to Evaluating Cost Efficiency of Selective Demolition Practices: Case of Hong Kong’s Kai Tak Airport Demolition

This research resorted to the use of construction operations simulation modeling to investigate the cost efficiency of waste-handling practices on the Kai Tak Airport demolition project in Hong Kong. By modeling the site operation of sieving and stockpiling broken concrete, the well-established construction simulation methodology of CYCLONE was contrasted with the newly developed simplified discrete event simulation approach (SDESA). Further, the SDESA model was readily extended to include (1) raw demolition waste collecting and sorting; (2) broken concrete sieving and stockpiling; (3) steel bar recycling; and (4) debris disposal at the landfill. The production rate derived from simulation was indicative of a close match between the simulation model and the actual site system. The resulting simulation model provided a basis for evaluating the cost efficiency of actual site operations and alternative resource provision scenarios being postulated. Through computer simulation, the actual site operation was found smooth and efficient with utilization rates for resources of different types ranging from 79 to 99%. In addition, the cost–time reduction ratios were calculated for four alternatives of resource provisions in comparison with the original base case. The research findings suggested that provided the project budget had satisfied the higher cash flow requirement, doubling the resource provision on site would potentially cut the project duration by half and not increase the total direct cost.     

RISim: Resource-Interacted Simulation Modeling in Construction

Discrete-event simulation is an effective approach to analyze construction operations. However, it is usually time-consuming and knowledge demanding to develop a practical simulation model, and thus not cost-effective due to the uniqueness and relatively short life of construction projects. The capability of discrete-event simulation modeling has not been popularly recognized by site managers until recently. A clear and explicit solution is to simplify and speed up the model development cycle, so as to enable users without much knowledge of simulation technology to easily generate a model in a relatively short period of time. In this paper, a resource-interacted simulation (RISim) modeling approach is presented, which adopts a resource oriented methodology to promote an intuitive feel to simulation modeling. In RISim, an operation is modeled in two abstraction levels—namely, the resource level and process level. An operation is viewed as a collection of resources and their interactions. Complex resources and simple resources are used to respectively represent resources with or without their own processes. The operation logic is mainly represented with internal complex resource flows, which are integrated by simple resource flows between complex resources. Resource flows can be easily conceived by site managers, enabling them to build up the logic naturally and simply. A resource library is used to implement resource reusability. Finally, an example in concrete delivery operation illustrates the methodology of resource-interacted simulation modeling and its potential for “plug-in and simulate.”     

Activity-Based Construction (ABC) Modeling and Simulation Method

This research presents the activity-based construction (ABC) modeling and simulation method. ABC modeling (ABC-Mod) uses one single element (e.g., activity) for modeling general construction processes instead of multiple elements as required by current simulation systems. ABC simulation (ABC-Sim) executes the ABC model by manipulating activities in three stages: (1) Select activity; (2) advance simulation; and (3) release simulation entities. ABC-Mod and ABC-Sim constitute a unique simulation method, generally addressed as ABC. In summary, ABC is a general-purpose modeling and simulation method with an emphasis on construction application. Compared with existing simulation systems, it has all of the major features required for modeling and simulating the dynamic and random behaviors of a construction process. It requires no more knowledge to use than the critical path method does. Therefore, ABC is a simulation method for construction engineers and it has a potentially wide range of application in the industry.     

Methodology for Conducting Discrete-Event Simulation Studies in Construction Engineering and Management

This paper suggests the methodology to follow when conducting discrete-event simulation (DES) studies in construction engineering and management research. Emphasis is made on the steps that, due to the uniqueness of the construction environment, are particularly important yet are not discussed extensively in the general DES literature. Guidelines are provided to determine what aspects of a DES study demand a rigorous application of the theory depending on the purpose of the study. The paper concludes with the importance of properly understanding the probabilistic concepts upon which DES relies and on coupling this understanding with engineering judgment as a key for successful use of DES in construction research.     

HKCONSIM: A Practical Simulation Solution to Planning Concrete Plant Operations in Hong Kong

Newly developed approaches for construction simulation have been used to model the one-plant-multisite ready mixed concrete (RMC) production system, validated by real-life operations data in Hong Kong. HKCONSIM—a computer system for simulation modeling and analysis of Hong Kong’s RMC production operations was developed in-house. The system is suitable for the resource provision planning and the production planning of a RMC plant, so as to meet given demands at a number of sites for concrete over a working day. The emphasis of the simulation modeling is on the interactions of multiple sites with the plant, and the objective is to improve the supply service levels and the utilization of plant resources. One significant improvement achieved via the research is that to simulate the RMC production operations with HKCONSIM does not require familiarity by the user with any software-specific terminology and modeling schematics, in contrast with existing simulation methods; the process of constructing a simulation model is reduced to specifying the attributes for each pour and site and providing the plant and truckmixer resources available on self-explanatory on-screen forms. Therefore, by experimenting on a HKCONSIM produced model the user, being a practitioner in the concreting industry, can readily study complicated relationships between the pattern of demand for concrete, the resources available to the system, and the service levels achieved together with the utilization levels achieved for the resources involved. Conclusions are given on the research and recommendations for future work made.     

Generic Process Mapping and Simulation Methodology for Integrating Site Layout and Operations Planning in Construction

The present research is intended to address dynamic construction-process simulation methods, with a focus on how to effectively model resource transit among various activity locations in the site system. Following a review of basic simulation paradigms and recent research developments, we propose a new process mapping and simulation methodology for modeling construction operations. The simulation algorithm is presented and the process mapping procedure is illustrated step by step using an earth-moving example featuring technology and resource constraints. It is straightforward to convert the resultant process mapping model describing workflows and resource flows over site locations into a simulation model. A STROBOSCOPE model is formed for the same problem definition to contrast and cross-validate our methodology with the established activity cycle diagram-based modeling approach. One additional case of modeling the concreting site operations by the hoist and barrow method is also given to demonstrate the application of the proposed methodology in practical settings.     

Research in Modeling and Simulation for Improving Construction Engineering Operations

Construction simulation, a fast-growing field, is the science of developing and experimenting with computer-based representations of construction systems to understand their underlying behavior. This paper provides a history of construction simulation theory, explores the CYCLONE modeling methodology and its major subsequent developments, examines the development of the Simphony.NET and COSYE modeling environments and their functionality as more generic simulation platforms, and reviews effective strategies for applying simulation in construction. A construction simulation case study is presented that illustrates one successful approach for adopting simulation technology in the industry and outlines the benefits to industry of integrating these technologies. The paper provides an overview of long-term simulation initiatives leading to the next generation of computer modeling systems for construction, where simulation plays an integral role in a futuristic vision of automated project planning and control.     

Dynamic Three-Dimensional Visualization of Fluid Construction Materials

The presented work extends the state-of-the-art of visualizing discrete-event construction simulations in three dimensions (3D). Efficient methods are presented along with a tool, ParticleWorks, that can be used to animate simulated construction processes that involve unstructured, fluid construction materials as resources or byproducts. Common construction processes that involve such fluid materials include placing concrete, dumping dirt, shotcreting, sandblasting, dewatering, water distribution, and inserting slurry. The writers capitalize on a classical computer graphics concept called particle systems to design simple, simulation model-authorable, parametric-text methods that can describe arbitrary volumes of dynamic fluid construction materials in animated 3D virtual construction worlds. These methods can be used to instrument discrete-event simulation models (or other external authoring interfaces) to automatically generate dynamic visualizations of any modeled construction operations that commonly handle and process fluid construction materials.     

Integrated Simulation System for Construction Operation and Project Scheduling

Simulation modeling is important in predicting the productivity of construction operations and the performance of project schedules. It would be desirable if operation and project models are vertically integrated in practice. However, existing discrete event simulation systems do not allow integrating operation and project models. This paper introduces an integrated simulation system named “Construction Operation and Project Scheduling” (COPS). COPS analyzes the productivity of construction operations as well as the performance of a project schedule individually and jointly. It creates operation models, maintains these models in its operation model library, conducts sensitivity analysis with different resource combinations, finds the optimal resource combination that satisfies the user’s requirements relative to hourly production and hourly cost of the operation, feeds this information into a project schedule, and executes stochastic simulation-based scheduling. A case study is presented to demonstrate this integrated simulation system.     

Runtime User Interaction in Concurrent Simulation-Animations of Construction Operations

Current state-of-the-art tools allow for the accurate modeling of complex construction operations using discrete-event simulation and their realistic postprocessed three-dimensional animation. Due to the postprocessed nature of these animations it is not possible to interact with them so as to affect the remaining course of actions. The next logical step in the evolution of simulation modeling and visualization in construction is for simulations and animations to run concurrently and in a manner that allows interaction with the animation to affect the course events in the simulation. This effectively enables the creation of virtual environments with logic based on discrete-event simulation. This paper presents the user interaction architecture that accomplishes this. In particular, the paper presents: (a) the conceptualization developed to design the components for user interaction and (b) the design of the components with a focus on (i) empowering model developers to enable user interaction in their models and (ii) extensibility to enable the development of more advanced user interaction techniques.     

Mathematical modeling of pharmacy systems

Mathematical modeling and its potential applications in pharmacy are discussed. A model is a simplified representation of the real world. As an experimental approach, modeling minimizes expense, risk, and disruption, but its validity can be hard to ascertain. Mathematical models describe numerically the relationships among elements of a system and are a powerful tool in making decisions affecting that system. There are two types of mathematical models: analytical models, which directly describe the relationships between system inputs and outputs using mathematical equations (such as pharmacokinetic models), and simulation models, which involve the replication, usually with a computer, of events as they occur in the real world. Analytical models are easier to develop but are not appropriate for describing highly complex systems. In continuous-time simulation, the system is represented as an uninterrupted flow of material; in discrete-event simulation, it is assumed that events occur only at distinct times. Various simulation programs are commercially available. The stages of a mathematical modeling study are (1) formulate the problem, (2) determine the model's structure, (3) collect and analyze initial data, (4) develop the model further, (5) validate the model, (6) experiment using the model, and (7) use the results. There have been many applications of modeling in health care, but relatively few have involved the study of pharmacy systems. Mathematical modeling offers pharmacists a low-risk, low-cost tool for aiding decisions about pharmacy systems by predicting alternative futures.     

Describing a Beta Probability Distribution Function for Construction Simulation

A typical proposed application for a construction simulation model is to assess the productivity of a future operation. This type of application inherently presents the modeler with a situation where there is only a limited amount of data available for choosing an underlying probability distribution function (PDF). This paper presents a formulation for developing a Beta PDF for use in construction simulation modeling. The hypothesis of this paper is that there is a ratio that relates the 75th percentile to the mode of the activity duration. The research demonstrates that using such ratios, along with the minimum, mode, and maximum activity durations, results in estimates of a beta PDF that accurately describes the underlying duration distribution of construction activities. In the methodology proposed here the minimum and maximum activity durations are predicted using deterministic methods based on the physical characteristics of the job and equipment employed. The beta-shaped parameters a and b are estimated using a procedure for fitting beta distributions to activity times when sample data are not available.     

Role of Simulation in Construction Engineering and Management

Construction simulation is the science of developing and experimenting with computer-based representations of construction systems to understand their underlying behavior. This branch of operations research applications in construction management has experienced significant academic growth over the past two decades. In this paper, the author summarizes his views on this topic as per his Peurifoy address, given in October 2008. The paper provides an overview of advancements in construction simulation theory as reported in literature. It then summarizes the key factors that contribute to successful deployment of simulation in the construction industry, and the key attributes of problems that make them more amenable for simulation modeling as opposed to other tools. The paper then provides an overview of long-term simulation initiatives leading to the next generation of computer modeling systems for construction, where simulation plays an integral role in a futuristic vision of automated project planning and control.     

Building Integrated Architecture/Engineering/Construction Systems Using Smart Objects: Methodology and Implementation

Integrated project systems hold the promise for improving the quality while reducing the time and cost of architecture/engineering/construction (AEC) projects. A fundamental requirement of such systems is to support the modeling and management of the design and construction information and to allow the exchange of such information among different project disciplines in an effective and efficient manner. This paper presents a methodology to implement integrated project systems through the use of a model-based approach that involves developing integrated “smart AEC objects.” Smart AEC objects are an evolutionary step that builds upon past research and experience in AEC product modeling, geometric modeling, intelligent CAD systems, and knowledge-based design methods. Smart objects are 3D parametric entities that combine the capability to represent various aspects of project information required to support multidisciplinary views of the objects, and the capability to encapsulate “intelligence” by representing behavioral aspects, design constraints, and life-cycle data management features into the objects. An example implementation of smart objects to support integrated design of falsework systems is presented. The paper also discusses the requirements for extending existing standard data models, specifically the Industry Foundation Classes (IFC), to support the modeling of smart AEC objects.     

Activity Object-Oriented Simulation Strategy for Modeling Construction Operations

The application of an object-oriented (OO) approach including the OO modeling concept and the OO programming mechanisms to develop an activity object-oriented (AOO) simulation strategy for modeling construction operations is introduced. After discussing simulation strategies generally used for construction simulation and analyzing the problems related to the simulation strategies, the AOO simulation strategy that guides modeling or controls simulation experiments for construction simulation is introduced. The AOO simulation strategy considers activities to be objects and is able to overcome some pitfalls that result from other general simulation strategies. In addition, the AOO graphical modeling interface associated with the AOO simulation strategy is described. Finally, comparisons of the graphical model or the simulation results of the AOO simulation system with other simulation tools are illustrated.     

Application Framework for Mapping and Simulation of Waste Handling Processes in Construction

This research is focused on modeling waste-handling processes in construction, with particular emphasis on how to map out and simulate on-site waste sorting processes. The research proposes an application framework for (1) guiding the development of process mapping models and simulation models; and (2) further assessing the cost effectiveness of on-site waste sorting efforts under practical site constraints (such as labor resource availability, time control on refuse chute usage, and limited working area space in a building site). The connection has been established between the mapping and simulation techniques in the context of modeling waste handling processes in construction sites, such that the process flowchart resulting from the mapping technique can serve as convenient model input to facilitate the creation of a “dynamic” operations simulation model. A case study of the on-site waste sorting method with one refuse chute for waste classification is presented to demonstrate the complete application framework spanning (1) process mapping; (2) mapping-to-simulation model conversion; and (3) method optimization based on valid simulations.     

Potential Computational Benefits of Geometric, Kinematic, and Behavioral Downsampling of Microscopic Traffic Network Simulation

This paper introduces the concept of microscopic simulation system scalability for the purpose of reducing the computational requirements of microsimulation modeling of large-scale traffic networks. This exploratory stage of research investigates scalability of both lane-changing and car-following behavior. The main objective of the proposed methodology is to create a reduced-scale network (microcosm) that retains most of the significant characteristics of the full-scale network (prototype). To achieve this objective a systematic downsampling procedure has been applied to a case study of a one-lane homogeneous freeway corridor in order to create a geometrically, kinematically, and behaviorally equivalent microcosm environment. This paper examines the scalability of lane-changing behavior, assuming a shifted negative exponential headway distribution, and investigates the scalability of car-following behavior under various operating conditions and downsampling ratios. The paper focuses on the tradeoff between performance and scalability of microscopic simulation systems. For each of the 48 cases considered, optimal behavioral parameters were determined based on two optimization methods: (1) Microscopic based on minimization of trajectory errors in both environments and (2) macroscopic derived from minimization of density errors in both environments throughout the simulation period. The results show that both optimization solutions were consistent in determining the optimal behavioral parameters.