DYNAMIC PLANNING FOR SITE LAYOUT

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1 Congrès annuel de la Société canadienne de génie civil Annual Conference of the Canadian Society for Civil Engineering Montréal, Québec, Canada 5-8 juin 2002 / June 5-8, 2002 DYNAMIC PLANNING FOR SITE LAYOUT Farnaz Sadeghpour, Osama Moselhi, Sabah Alkass Department of Building, Civil, and Environmental Engineering, Concordia University, Canada ABSTRACT: This paper, presents a framework for a site layout system designed to accommodate the dynamic nature of construction sites. In the proposed system, construction facilities are considered as objects, and the knowledge associated with each is encapsulated. In that, it allows the user to add, delete, and reconfigure a physical object in relation to others within the project being planned. This open architecture assists in benefiting from experts knowledge. The computer model is developed in CAD environment and makes use of object-based design concepts. The main features of this model and the inter-connectivity among its basic components will be described in the paper. 1. INTRODUCTION Efficient site layout planning is essential for optimum material handling, which generally results in higher productivity, and helps in minimizing accidents on job-sites. Since the early 1960 s the topic has received considerable attention, starting in industrial engineering and continued to construction (Lee and Moore 1967, Hamiani 1987, Cheng 1992, Tommelein and Zouein 1993, Zouein 1996, Hegazy and Elbeltagi 2000). With some exceptions (Tommelein and Zouein 1993, Zouein 1996), site planning has often been treated as a static problem. The underlying assumption in all static models is that the layout of the construction site does not change once it is designed, which makes such models incompatible with the dynamic nature of construction sites. In addition, existing site layout tools are rigid in defining the site layout problem and its associate constraints. The constraints considered in locating facilities are often limited to minimizing travel distance (e.g. Lee and Moore 1967, Li and Love 1998, Hegazy and Elbeltagi 1999 and 2000) and as such, important safety constraints and security requirements are overlooked. Existing site layout tools suffer from being limited to conditions and configurations that apply only to a specific problem. In reality, construction practice varies depending on site and project conditions; i.e. construction facilities, equipment, and material change from one project to another. As well, site planners consider various rules and constraints in locating objects on site according to their knowledge and experience or project conditions. 2. FACTORS AFFECTING SITE LAYOUT In this study, three entity classes affecting site layout modeling are identified to be objects, site properties, and constraints. Clearly, the components and different entities of the system affect its capacity and versatility to generate practical layouts. The factors considered here are based on a thorough literature review and information gathered from visits of three construction sites in the city of Montreal. The three entities of the proposed model and their respective attributes and methods support the functional 1

2 requirements envisaged for site layout. These factors affect the way site planners approach the site layout problem. Objects refer to equipment, material, temporary support facilities, buildings, lay down areas, working areas, and generally anything that exists on site and occupies space. As a result, objects address a range of items that are diverse in nature. Site properties are existing items on site that affect the final layout of that site. Examples of these are trees and existing buildings on site. There may also be areas on the site that are not available -or site planner recognizes them as unavailable- for locating facilities (e.g. unsafe areas, hazardous spots, small pond). In spite of their impact on site layout, site properties have often been overlooked in previous research works covering site layout, except in few (e.g. Lundberg and Beliveau 1989). Constraints are rules defined to fulfill layout objectives. In other words, the formulation of the site layout problem is to locate a set of facilities on a site while satisfying a set of constraints. The structure of the proposed model is based on the three identified factors mentioned above, which will be discussed in next section. 3. PROPOSED MODEL The proposed model is essentially a space planning model that accounts for a set of productivity, safety, and security constraints, as well as rules extracted from common industry practice. The structure of the model is modular and consists of four main parts: user interface, database, project module and layout control module (Figure 1). The user interface is used for acquiring problem-specific knowledge. The database integrates three libraries: object library, site property library and constraint library. The project module sets the entities for initiating a project and the layout control module performs spatial analysis and locates objects on site. User User Interface System Output Database Site Property Library Object Library Constraint Library Project Module Object Module Site Module Constraint Module Spatial Analysis Module Locating Module Layout Control Module Figure 1- System Architecture 3.1 User Interface The knowledge and experience used for site planning is multi-facetted and, to same degree, is difficult to extract. This represents a communication problem that has its roots in knowledge acquisition and representation (Cheng and O Connor1993). The user interface of the proposed model behaves in two different levels. In the first level, it provides the domain knowledge expert with tools to enrich the system s knowledge and databases. It leads the planners to apply their individual problem solving skills and directly contribute to the knowledge base of the system. This eliminates the traditional need of a knowledge engineer for acquiring and structuring the knowledge, and hence decreases the risk of losing knowledge or having it misinterpreted. 2

3 On the second level, the system provides a decision support to assist members of project teams in generating site layouts utilizing the system s current status of knowledge. Once the system is set up by the expert at first level and upon entering the rules and data, it will be saved into the database and can be reused later by a non-expert as long as the design needs has not changed. At this level, the system provides the ready-to-use data in its database and the user has to select the preferred entities or use the default settings as is. 3.2 Database A relational database is used in the proposed system. As such the data is presented in a table format, where each individual cell in the table stores data for a particular variable. The database of the proposed model is formed of three libraries; namely site property, constraint, and object libraries. Upon the creation of an entity in the graphical screen, the system prompts the user for the non-geometric userdefined features of that entity. This information will then be merged with the geometric data of each entity to form a record in its respective library. There will be a two-way dynamic link between the record and its corresponding physical object in the graphical screen. This facilitates retrieving of the information linked to a physical entity, or conversely finding the physical entity by its record. 3.3 Project Module At the start of a new project, the user has to define the construction requirements from each entity group: site properties, objects, and constraints. The creation of each entity will be carried out by one of the object, site, or constraint modules depending on the type of entity. The construction site and its properties are the first to be defined in order to initiate a new project. Next, the required objects for the project are defined in the object module, followed by the constraints. Finally the defined constraints are assigned to defined objects to become part of their attributes. This completes the process of setting up a new project (Figure 2). Control Module Project Module Define Site Properties Define Objects Define Constraints Assign Constraints to Objects Determine Optimum Location Locate Objects on Site Site Property Library Object Library Constraint Library Figure 2- Schematic Site Layout Process in the Proposed Model 3

4 For defining entities, the user is given two options. The first is to select the entities from their respective libraries. This is done through browsing the existing entities in each library. Once an entity is selected from the library, the entity along with the knowledge and data associated with it are retrieved into the new project. The user also has the possibility of editing this information. However, if the required entity is not part of the libraries, the user has the option of creating a new entity. Each time a new entity is defined, it is added to the corresponding library. In this way there is no need to define the same entity each time there is a request for it. This supports the expansion and enrichment of the libraries, but more importantly it customizes the system according to design needs and preferences of the user party. 3.4 Layout Control Module Once the entities for a new project are defined the system starts locating objects on site. The layout control module is comprised of the spatial analysis and locating modules (Fig.1). The spatial analysis module is responsible for finding all possible locations for an object. This process is path-dependent, i.e. it depends on the order in which facilities are selected to enter the layout. The areas that satisfy specified constraints for the entity being considered are geometrically identified and drawn on separate layers. When locating an object on site, all the constraints that need to be satisfied, along with their assigned weights, are retrieved. This is made possible through to the structure of the database and its dynamic link to the graphical screen and the physical objects being considered. Based on these constraints and their corresponding weights, the whole site will be analyzed to find the optimum location for each object. The optimum location is the area with the highest overall satisfaction weight. The locating module is responsible for laying each object on the identified location. This module verifies if the area selected has enough space to accommodate the object. Once the final location of the object is identified, the object is positioned on site. A graphical instance of the object is imprinted on the site drawing and the area it occupies is deducted from the area available to other objects. This feature ensures the committed area is no longer available for locating other facilities. 4. IMPLEMENTATION In the proposed model, an effort is made to buildup comprehensive default libraries for each of the identified site layout entities (i.e. site properties, objects and constraints). This is done through site visits, interviews with domain experts and examination of the Construction Safety Code (ASP Construction 2001). However, in view of the dynamic nature of construction industry and emerging new methods and products, it is impossible to identify all items (e.g. facility, material, equipment, rules, etc.) that might be used on a construction project. A feasible construction site layout system should be flexible enough to accommodate the diversity of construction practice. To comply with this diversity, an open architecture for the layout system is adopted. If a required entity is not part of the default libraries, the system will provide the user with tools to create it. As a result, the information modeling approach for this research is chosen to be object-based. Object-based approach strongly promotes the formalism of data typing and information encapsulation. The basic modeling elements (i.e. physical objects, site properties, and constraints) are implemented as objects with their attributes encapsulated in them. These encapsulated attributes include the geometric information of the entities, coupled with non-geometrical ones, as well as the knowledge associated with each entity. These attributes are associated with graphical entities via the attribute handling mechanism described earlier. The system is being developed using VBA (Visual Basic for Applications) in AutoCAD environment, and utilizes Microsoft Access. VBA provides a seamless link between the user interface, AutoCAD, and the Access database as main components of the proposed model. Since AutoCAD is a commonly used CAD tool for preparing project drawings, it will facilitate the reusability of previously generated drawings. The drawing capabilities of AutoCAD make it possible to generate various shapes with the desired precision when designing the objects and site properties. Using AutoCAD also facilitates data entry for each object. The geometric information of each entity is recorded in the built-in AutoCAD databases. This information can be coupled with other information assigned to each particular object in an external database. MS 4

5 Access is considered to serve as external database. A dynamic link from each component to its respective database is established so that the data can be accessed and edited from within AutoCAD. 5. SUMMARY AND CONCLUDING REMARKS In this paper a model for site layout planning was introduced and its configuration was described. The basic components of the system and the inter-connectivity among them were described. The system has a number of interesting features. Its open-architecture makes the system flexible and easily adaptable to various projects. This feature makes this model capable of receiving and processing user-defined rules and constraints. The interactive graphical capabilities of the proposed model facilitate the site planning process and make it more comprehensible to planners. Finally, its easy-to-use and efficient interface eases data entry process. 6. ACKNOWLEDGMENT The authors would like to acknowledge Mr. John Marcovecchio and Mr. Rami Bebawi of Magil Construction, and Mr. Richard Pigatto of Drago Inc. for their interest in this research and for sharing their valuable time and experience. 7. REFERENCES ASP Construction (2001) Safety Code for the Construction Industry (S-2.1, r.6), Association Paritaire pour la Sante:: et la Se::curite:: du Travail du Secteur de la Construction, Anjou, QC, Canada. Cheng, M.Y. (1992) Automated Site Layout of Temporary Construction Facilities Using Geographic Information System (GIS), Ph.D. Dissertation, University of Texas, Austin, TX, USA. Cheng, M.Y., O Connor, J.T. (1993) Site Layout of Construction Temporary Facilities Using Enhanced- Geographic Information System (GIS), Proc. of 10 th Inter. Symp. on Automation and Robotics in Construction, Houston, TX, USA, Hamiani, A. (1987) CONSITE: A Knowledge-Based Expert System Framework for Construction Site Layout, Ph.D. Thesis Dissertation, University of Texas, Austin, TX, USA. Hegazy, T.M., and Elbeltagi, E. (2000) Simplified Spreadsheet Solutions: A Model for Site Layout Planning, Journal of Cost Engrg., 42(1): Lee, R.C., and Moore, J.M. (1967) CORELAP: Computerized Relationship Layout Planning, Journal of Industrial Engrg., 8(3): Lundberg, E.J., and Beliveau, Y.J. (1989) Automated Lay-Down Yard Control, Journal of Construction Engrg. and Management, ASCE, 115(4): Li, H., and Love, P.E.D. (1998) Site-level Facilities Layout Using Genetic Algorithms, Journal of Computing in Civil Engrg., ASCE, 12(4): Tommelein, I.D., Zouein, P.P. (1993) Interactive Dynamic Layout Planning, Journal of Construction Engrg. and Management, ASCE, 119(2): Zouein, P.P. (1996) MoveSchedule: A Planning Tool for Scheduling Space use on Construction Sites, Ph.D. thesis dissertation, University of Michigan, Anna Arbor, MI, USA. 5