الزامات مورد نیاز برای مدل سازی اطلاعات ساختمان بر اساس سیستم های مدیریتی تولید ناب جهت ساخت و ساز

Smooth flow of production in construction is hampered by disparity between individual trade teams' goals and the goals of stable production flow for the project as a whole. This is exacerbated by the difficulty of visualizing the flow of work in a construction project. While the addresses some of the issues in Building information modeling provides a powerful platform for visualizing work flow in control systems that also enable pull flow and deeper collaboration between teams on and off site. The requirements for implementation of a BIM-enabled pull flow construction management software system based on the Last Planner System™, called ‘KanBIM’, have been specified, and a set of functional mock-ups of the proposed system has been implemented and evaluated in a series of three focus group workshops. The requirements cover the areas of maintenance of work flow stability, enabling negotiation and commitment between teams, lean production planning with sophisticated pull flow control, and effective communication and visualization of flow. The evaluation results show that the system holds the potential to improve work flow and reduce waste by providing both process and product visualization at the work face.

Construction projects typically involve multiple discrete organizations working simultaneously on congested sites. They suffer from waste that is manifested in waiting time for crews, rework, unnecessary movement and handling of materials, unused inventories of workspaces and of materials, etc. Achieving smooth work flow with minimal waste requires not only appropriate construction planning, but also effective production management. Lean thinking applied to construction has led to development of planning and control systems and other practices that improve matters. Koskela's ‘Transformation-Flow-Value’ (TFV) conceptualization of production in construction [1] provides a theoretical basis for appreciating the flow and value aspects of construction in addition to the well established transformation view. Applied research using discrete event simulation has clearly shown the adverse impact of variation in production and delivery rates [2] and [3] and the benefits of pull flow of trade teams according to information maturity [4]. In practice, the Last Planner System™ (LPS) [5] and adaptations of it are increasingly applied to reduce variation, improve coordination and work flow, and thus to reduce various forms of waste in construction projects. While a detailed explanation of the LPS is beyond the scope of this paper, we list the principles that underpin it as they are the foundation for much of what follows. Koskela [6] outlined five principles for a production control system: • assignments should be sound regarding their prerequisites (i.e. constraints must be released) • the realization of assignments is measured and monitored (in LPS the percent plan complete measure serves this purpose) • causes for non-realization are investigated and those causes are removed • a buffer of unassigned tasks which are sound for each crew is maintained • in look ahead planning, the prerequisites of upcoming assignments are actively made ready. In his definitive work on the LPS [5], Ballard added the following: • Variability must be mitigated and remaining variability managed • The traditional schedule-push system is supplemented with pull techniques • Production control facilitates work flow and value generation • The project is conceived as a temporary production system • Decision making is distributed in production control systems • Production control resists the tendency toward local sub-optimization. The LPS was designed to be applied with minimal, if any, information technology support. Nevertheless, effective production management in construction projects with large numbers of essentially independent work teams and extensive distinct spaces (such as office towers, shopping malls, etc.) remains difficult to achieve. A number of factors make coordination between the trade contractor teams, material and equipment suppliers, construction management personnel, and designers and inspectors difficult. Among them: • physical dispersion of the teams within the building or across the site, where they are usually hidden from one another by the structure itself; • contracting relationships with remuneration terms that encourage local optimization and work against overall project optimization [7]; • complex variations in productivity rates [8], which makes it very difficult to predict short-term progress; • lack of effective real-time reporting of progress, despite multiple research efforts aimed at automating this aspect of project control [9]; • dependence on key individuals to obtain and communicate critical information regarding constraint status to the look ahead and last planner functions; • reliance on paper documents to communicate product information, with the limitations of design documentation errors, lack of clarity and potential obsolescence of information [10]; While the LPS reduces variation by improving the reliability of short-term planning, it does not achieve pull flow in the pure sense in that it does not prioritize tasks in relation to signals from downstream demand. In lean production in manufacturing settings, pull flow is implemented using ‘Kanban’ systems [11]. In manufacturing plants, process visualizations are used to provide flow signals to workers and to empower them to adjust flow to suit the overall system pace [12]. On construction sites, where work teams, not products, move, it is very difficult to visualize the flow of the work in progress and to communicate its status to the teams and individuals involved. The amount of buffered work in progress (WIP) accumulated between work teams cannot be seen by the naked eye in the same way that piles of products that constitute WIP can be seen accumulating between processing stations in a manufacturing plant [13]. Another problem is that the most common cycle time used with the LPS is one week (called ‘weekly work planning’). The weekly response time is too long to avoid waste in the case of tasks whose constraints are only resolved within days prior to their execution. For example, the maturity of building finishing works that have short task durations and multiple and varying dependencies on information, preceding tasks and equipment, cannot be guaranteed in advance of a one-week window. Where the LPS is used with a shorter planning window (e.g. [14]), it has been done on projects where work is narrowly focused and all participants can easily see the process status, unlike the case of finishing works in large buildings. Finally, as implemented in practice, the weekly work plans do not make any a priori provision for structured experimentation that could facilitate continuous improvements; rather, the percent plan complete measure is compiled, which enables retrospective learning from failure, but not planned learning from success. Although the formulators of the LPS envisioned that it would support learning from success, the pressures of day-to-day construction make recording of success for learning (both within and beyond the current project) impractical. A computerized system with automated recording and reporting might obviate this difficulty. To address these issues, we propose that production management systems for construction should be based on BIM platforms and introduce Kanban style pull process flow and Andon alerts. We call this concept ‘KanBIM’. We hypothesize that a software system that supplements the LPS by providing ubiquitous access to 3D visualizations of process status and future direction, delivered to all on site and enabling real-time feedback of process status, including Kanban card type pull flow control signals and Andon alerts, can empower people to manage the day-to-day flow of construction operations with greater reliability and less variability than can be achieved without such a system. The following sections of this paper outline the state of the art, describe the goals and method of a research program underway to develop the KanBIM concept, and establish the requirements for the modes of operation of future KanBIM type software systems.

A set of guiding requirements for implementation and operation of a BIM-based lean production management system for construction has been compiled through development of the KanBIM concept. The requirements were derived through research in which a system was specified, prototype interfaces were implemented and tested using a touch-screen unit for site communications, and in which the approach was evaluated with construction companies. The key requirements concern issues of visualization of the construction process and its status; visualization of the construction product and work methods; support for planning, negotiation, commitment and status feedback; implementation of pull flow control; maintenance of work flow and plan stability; and formalizing production experiments for continuous process improvement. The requirements emphasize the role of a KanBIM system in supporting human decision making, negotiation among trade teams to coordinate weekly work plans, reduction of the granularity of planning to a daily level, real-time evaluation of task constraints to compute task maturity, and implementation of the language/action perspective. The primary contribution of the KanBIM concept is that it provides visualization not only of the construction product, but of the production process. It extends the LPS by providing the information infrastructure to reduce the granularity of planning coordination from weekly to daily. It enables negotiation between parties affected by changes and informs – and thus empowers – all others on and off site of any changes agreed to the plan in real-time. As such, it can contribute to relieving the need for construction managers to ‘fight fires’ and enable them to focus on establishing the production systems, setting policy and continuous improvement. If used with the priority pull flow index, it will also extend the LPS's ability to stabilize plans by enabling implementation of a CONWIP production system. The qualitative feedback resulting from the discussions and questionnaires used in the three workshops indicates that practitioners were generally supportive of the system and its aim to improve management in construction but they agreed that the system requires careful addressing of potential problems. According to the received feedback site conditions, security and human behavior are among the most serious problems that could affect the implementation of the system. Project team integration by means of sub-contractors’ involvement in the detailed planning process and the need to better visualize production/process information were all found to be highly significant for the successful production management. However, adequate testing on site in order to establish to what extent technical difficulties can impact upon the usefulness of the system and behavioral investigation of its use have been identified as prerogative before the system could see the full scale application in the industry. This paper has outlined the concept and defined the requirements and presented a system design for a BIM-enabled lean production management system for construction. Evaluation to date has identified the value of the system concept, but also shortcomings in the interface designs. Clearly, further research is needed before a full scale KanBIM system can be built. Future work will include testing of the algorithms for calculation of work package and task maturity, development of the pull flow index and its computation, experimentation to explore the feasibility for guiding teams’ progress through projects using the touch-screen or other interfaces, and the information technology challenges of maintaining an updated construction process model within a construction BIM tool.