Introduction Site space is a resource that is as important as money, time, material, labour and equipment. Like any resource, the amount of site space demanded by the various activities changes with the schedule of the work. Therefore, during the project the site layout may need to be efciently re-organized at various intervals to satisfy the upcoming schedule requirements and to maintain site safety and productivity. Thus, efcient planning is needed to facilitate the re-organization of the site as the schedule evolves. Since the early 1970s, several researchers have applied various heuristics or mathematical optimiza- tion techniques to solve the static site layout planning problem in construction (e.g. Warszawski and Peer, 1973; Popescu, 1981; Rodriguez-Ramos, 1982; Rad and James, 1983; Tommelein, 1989). In late 1990s, non-traditional techniques based on articial intelli- gence (AI) were applied to solve the problem (e.g. Yeh, 1995; Dweiri and Meier, 1996; Li and Love, 1998; Elbeltagi and Hegazy, 2000). These models generated static layouts that span the entire project duration. Models that deal with dynamic layout planning in construction are limited. Cheng (1992) developed a system called ArcSite, a knowledge-based system inte- grated with a geographic information system (GIS) to locate the temporary facilities on construction sites. In this model, facilities are placed one-by-one on the site and, accordingly, the resulting layout solution is sensi- tive to the facility order. Also, the one-by-one place- ment of facilities may not yield the optimal site layout Construction Management and Economics (2001) 19, 689–697 Schedule-dependent evolution of site layout planning EMAD ELBELTAGI 1 , TAREK HEGAZY 2* , ABDEL HADY HOSNY 3 and ADEL ELDOSOUKY 4 1 Faculty of Engineering, Mansoura University, Mansoura, Egypt 2 Department of Civil Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 3 Faculty of Engineering, Ain Shams University, Cairo, Egypt 4 Faculty of Engineering, Tanta University, Tanta, Egypt Received 27 August 1999; accepted 15 February 2001 The appropriate layout of temporary facilities on a construction site has a large impact on construction safety and productivity. For the duration of a project the site layout may need to be efciently re-organized at various intervals to satisfy the schedule requirements and to maintain site efciency. This paper presents a practical model for schedule-dependent site layout planning in construction. The proposed model uses a combination of articial intelligence tools (knowledge-based systems, fuzzy logic, and genetic algorithms) to generate, optimize, and re-organize the site layout plan at frequent intervals during the project. The model incorporates exible representation of irregular site shapes and several options for placing facilities. Based on the proposed model, an automated system is developed, fully integrated with widely used scheduling soft- ware. At each schedule interval, the system recalculates the space requirements and, for the convenience of congested sites, can utilize parts of the constructed space to accommodate temporary facilities. Details of the schedule-dependent model are described, and its application in an actual case study project is presented to demonstrate its capabilities. Keywords: Site layout, quantitative evaluation, material ow *Author for correspondence. e-mail: tarek@uwaterloo.ca Construction Management and Economics ISSN 0144–6193 print/ISSN 1466-433X online © 2001 Taylor & Francis Ltd http://www.tandf.co.uk/journals DOI: 10.1080/01446190110066713