Lean construction精益建设.doc

Lean constructionFrom Wikipedia, the free encyclopediaJump to: navigation, search Lean Construction is a combination of original research and development in design and construction with an adaption of lean manufacturing principles and practices to the end-to-end design and construction process. Unlike manufacturing, construction is a project based-production process. Lean construction is concerned with the holistic pursuit of concurrent and continuous improvements in all dimensions of the built and natural environment: design, construction, activation, maintenance, salvaging, and recycling (Abdelhamid 2007). This approach tries to manage and improve construction processes with minimum cost and maximum value by considering customer needs. (Koskela et al. 2002)The term Lean Construction was coined by the International Group for Lean Construction in its first meeting in 1993. (Gleeson et al. 2007)Contentshide 1 Historical Development o 1.1 A New Paradigm 2 What is lean construction? 3 Integrated Project Delivery 4 Practical applications 5 Last Planner System 6 Differences between Lean Construction approach and Project Management Institute (PMI) approach 7 Lean Construction FAQs 8 Commercial arrangements that support IPD and Lean Project Delivery 9 LC Networks, Teaching and Research 10 References edit Historical DevelopmentThe seminal work of Lauri Koskela in 1992 challenged the Construction Management community to consider the inadequacies of the time-cost-quality tradeoff paradigm. Another paradigm-breaking anomaly was that observed by Ballard (1994), Ballard and Howell (1994a and 1994b), Howell and Ballard (1994a and 1994b) and Howell (1998). Analysis of project plan failures indicated that “normally only about 50% of the tasks on weekly work plans are completed by the end of the plan week” and that constructors could mitigate most of the problems through “active management of variability, starting with the structuring of the project (temporary production system) and continuing through its operation and improvement.” (Ballard and Howell 2003).Evidence from research and observations indicated that the conceptual models of Construction Management and the tools it utilizes (work breakdown structure, critical path method, and earned value management) fail to deliver projects on-time, at budget, and at desired quality (Abdelhamid 2004). With recurring negative experiences on projects, evidenced by endemic quality problems and rising litigation, it became evident that the governing principles of construction management needed revisiting. In fact, a respondentwho? to the 6th annual Survey of Construction Owners by CMAA (2006) included a comment: While the cost of steel and cement are making headlines, the less publicized failures in the management of construction projects can be disastrous. Listen carefully to the message in this comment. We are not talking about just materials, methods, equipment, or contract documents. We are talking about how we work to deliver successful capital projects and how we manage the costs of inefficiency.edit A New ParadigmKoskela (2000) argued that the mismatch between the conceptual models and observed reality underscored the lack of robustness in the existing constructs and signaled the need for a theory of production in construction. Koskela then used the ideal production system embodied in the Toyota Production System to develop a more overarching production management paradigm for project-based production systems where production is conceptualized in three complementary ways, namely, as a Transformation (T), as a Flow(F), and as Value generation(V). Koskela and Howell (2002) have also presented a comprehensive review of the shortcomings existing management theory specifically as related to the planning, execution, and control paradigms in project-based production systems. Both conceptualizations provide a solid intellectual foundation of Lean Construction as evident from both research and practice (Abdelhamid 2004).Recognizing that construction sites reflect prototypical behavior of complex and chaotic systems, especially in the flow of both material and information on and off site, Bertelsen (2003a and 2003b) suggested that construction should be modeled using chaos and complex systems theory. Bertelsen (2003b) specifically argues that construction could and should be understood in three complimentary ways, namely, as a project-based production process, as an industry that provides autonomous agents, and as a social system. With more developments in this line of thinking, it is very likely that the Lean Construction governing paradigm will change to it. And so, the process will keep on repeating!edit What is lean construction?Lean construction is a “way to design production systems to minimize waste of materials, time, and effort in order to generate the maximum possible amount of value (Koskela et al. 2002).” Designing a production system to achieve the stated ends is only possible through the collaboration of all project participants (Owner, A/E, Constructors, Facility Managers, End-user) at early stages of the project. This goes beyond the contractual arrangement of design/build or constructability reviews where constructors, and sometime facility managers, merely react to designs instead of informing and influencing the design (Abdelhamid et al. 2008).Lean Construction recognizes that desired ends affect the means to achieve these ends, and that available means will affect realized ends (Lichtig 2004). Essentially, Lean construction aims to embody the benefits of the Master Builder concept (Abdelhamid et al. 2008).Lean construction supplements traditional construction management approaches with (Abdelhamid 2007): (1) two critical and necessary dimensions for successful capital project delivery by requiring the deliberate consideration of material and information flow and value generation in a production system; and (2) different project and production management (planning-execution-control) paradigms.While lean construction is identical to Lean Production in spirit, it is different in how it was conceived as well how it is practiced.The common spirit flows from shared principles: Whole System Optimisation through Collaboration and systematic learning o continual improvement/pursuit of perfection involving everyone in the system o a focus on delivering the value desired by the owner/client/end-user o allowing value to flow by systematically eliminating obstacles to value creation and those parts of the process that create no value o creating pull production The differences in detail flow from a recognition that construction is a project based production where the product is generally a prototype.As Sowards stated (2004) the priority for all construction work is to:1. keep work flowing so that the crews are always productive installing product; 2. reduce inventory of material and tools and 3. reduce costs. While Lean Constructions main tool for making design and construction processes more predictable is the Last Planner System (see below) and derivatives of it, other lean tools already proven in manufacturing have been adapted to the construction industry with equal success. These include: 5S, Kanban, Kaizen events, quick setup/changeover, Poka Yoke, Visual Control and Five Whys (Mastroianni and Abdelhamid 2003, Salem et al. 2005).In lean design set based design, design structure matrices and target value design strategies are proving valuable.One can think of Lean Construction in a way similar to mesoeconomics. Lean Construction draws upon the principles of project-level management and upon the principles that govern production-level management. Lean Construction recognizes that any successful project undertaking will inevitably involve the interaction between project and production management. (Abdelhamid 2007)edit Integrated Project DeliveryIntegrated Project Delivery (IPD) - a registered business mark by Lean Construction Institute with the US PTO - is a delivery system that seek to align interests, objectives and practices, even in a single business, through a team-based approach. The team primary Team Members would include the Architect, key technical consultants as well as a general contractor and key subcontractors.IPD is a clever solution to the tough organizational and contracting problems faced in todays market. It relies on careful participant selection, transparency and continuing dialog. Construction consumers might consider rethinking their contracting strategies to share more fully in the benefits.(Matthews and Howell 2005)IPD is a Relational Contracting approach that aligns project objectives with the interests of key participants. It creates an organization able to apply the principles and practices of the Lean Project Delivery System. (Matthews and Howell 2005)edit Practical applicationsThe examples and perspective in this article deal primarily with the United Kingdom and do not represent a worldwide view of the subject. Please improve this article and discuss the issue on the talk page. (September 2010)In the UK, a major R&D project, Building Down Barriers, was launched in 1997 to adapt the Toyota Production System for use in the construction sector. The resulting supply chain management toolset was tested and refined on two pilot projects and the comprehensive and detailed process-based toolset was published in 2000 as the Building Down Barriers Handbook of Supply Chain Management-The Essentials. The project demonstrated very clearly that lean thinking would only deliver major performance improvements if the construction sector learned from the extensive experience of other business sectors. Lean thinking must become the way that all the firms in the design and construction supply chain co-operate with each other at a strategic level that over-arches individual projects. In the aerospace sector, these long-term supply-side relationships are called a Virtual Company, in other business sectors they are called an Extended Lean Enterprise.The UK Building Down Barriers Handbook of Supply Chain Management-The Essentials states that: The commercial core of supply chain management is setting up long-term relationships based on improving the value of what the supply chain delivers, improving quality and reducing underlying costs through taking out waste and inefficiency. This is the opposite of business as usual in the construction sector, where people do things on project after project in the same old inefficient ways, forcing each other to give up profits and overhead recovery in order to deliver at what seems the market price. What results is a fight over who keeps any of the meagre margins that result from each project, or attempts to recoup negative margins through claims, The last thing that receives time or energy in this desperate, project-by-project gladiatorial battle for survival is consideration of how to reduce underlying costs or improve quality.edit Last Planner SystemThe Last Planner System (LPS) improves both design and construction schedule/programme predictability work completed as and when promised. It is a system of inter-related elements full benefits come when all are implemented together, over time. Based on simple paper forms, it can be administered using Post-it notes, paper, pencil, eraser and photocopier. A spreadsheet can help.LPS begins with collaborative scheduling/programming engaging the main project suppliers from the start. Risk analysis ensures that float is built in where it will best protect programme integrity and predictability. Where appropriate the process can be used for programme compression too. In this way, one constructor took 6 weeks out of an 18-week programme for the construction of a 40 bed hotel. Benefits to the client are enormous.Figure 1: intense discussion during a programme compression workshopBefore work starts, team leaders make tasks ready so that when work should be done, it can be. Why put work into production if a pre-requisite is missing? This MakeReady process continues throughout the project.Figure 2: part of a MakeReady form for documenting the process of making tasks ready (this one for use in design)There is a weekly work planning (WWP) meeting involving all the last planners design team leaders and/or trade supervisors on site. It is in everyones interest to explore inter-dependencies between tasks and prevent colleagues from over-committing.Figure 3: part of a Weekly Work Plan form used by trade foremen on site or design team leaders to prepare for the WWP meeting.This weekly work planning processes is built around promises. The agreed programme defines when tasks should be done and acts as a request to the supplier to do that task. The last planners (that is the trade foremen on site or design team leaders in a design process) only promise once they have clarified the conditions of satisfaction and are clear that the task can be done.Figure 4: the promise cycle (after Fernando Flores)Once the task is complete the last planner responsible declares completion so that site management or the next trade can assure themselves that it is complete to an appropriate standard.A key measure of the success of the Last Planner system is PPC. This measures the Percentage of Promises Completed on time. As PPC increases. project productivity and profitability increase, with step changes at around 70% and 85%. This score is measured site-wide and displayed around the site. Weekly measures are used by the project and by individual suppliers as the basis for learning how to improve the predictability of the work programme and hence the PPC scores.A key part of the continual improvement process is a study of the reasons why tasks promised in the WWP are delivered late. The following chart shows typical reasons:Figure 5: example of a reasons Pareto chartRecording the reasons in a Pareto chart like the one above makes it easy to see where attention is most likely to yield the most results. Using tools like 5 Why analysis and cause-effect diagrams will help the team understand how they can improve the clarity of information and ensure that there are sufficient operatives.Last Planner benefits dont stop at project predictability, profit and productivity; it contributes to positive changes in other industry KPIs. Danish researchcitation needed shows almost half the accidents and up to 70% less sickness absence on LPS managed sites.The Lean Construction Institute developed the Last Planner System, and allows owners, clients or their construction companies to use is to improve their design and construction performance. LCI makes no charge for this and places no limits on its use within a company. LCI encourages companies that find it useful to become contributors to the Lean Construction Institute.LCI retains a Trademark on the term and Copyright in the idea and materials to prevent people who misunderstand or misrepresent the system from using it in trade. Consulting companies or individuals wishing to use the Last Planner System in trade (commercial offering of service) must first be approved by LCI. Consultants are expected to make financial and other contributions to LCI in recognition of the work and effort LCI put into developing Last Planner.Last Planner System development continues under the direction of Lean Construction Institute Directors Professor Glenn Ballard and Greg Howell with support from users around the world. For more information about the development process see Ballard (1994, 2000) and Ballard & Howell (2004) for exampleFor a more detailed description and list of benefits see here For more on Learning how to implement Last Planner see hereedit Differences between Lean Construction approach and Project Management Institute (PMI) approachThe differences between lean approach and PMI approach are listed below: Managing the interaction between activities and combined effects of dependence and variation, is a first concern in lean construction because their interactions highly affects the time and cost of projects(Howell,1999);in comparison, these interactions are not considered in PMI. In lean construction optimization efforts focus on making work flow reliable (Ballard, LPDS,2000 ); in contrast PMI focuses on improving productivity of each activity which can make errors and reducing quality and result in rework. The project is structured and managed as a value generating process (value is defined as satisfying customer requirements) (Howell, 1999), while PMI considers less cost as value. In lean approach, downstream stakeholders are involved in front end planning and design through cross functional teams (Ballard, LPDS, 2000); on the other hand PMI doesnt consider this issue. In lean construction, project control has the job of execution (Ballard, PhD thesis, 2000); whereas, control in PMI method relies on variance detection after-the-fact. In lean method, pull techniques are used to govern the flow of materials and information through networks of cooperating specialists (Ballard, PhD thesis, 2000); in contrast, PMI uses push techniques for releasing the information and materials. Capacity and inventory buffers are used to absorb variation(Mura). Feedback loops are included at every level, to make rapid system adjustments, (Ballard, PhD thesis, 2000); in comparison, PMI doesnt consider adjustments. Lean construction tries to mitigate variation in every aspect (product quality, rate of work) and manage the remaining variation, while PMI doesnt consider variation mitigation and management. (Ballard, PhD thesis, 2000) Lean approach tries to make continuou