lean design process

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Lean Design Process Chien-Ho Ko 1 and Neng-Fu Chung 2 Abstract: Improper design in the construction industry leads to change orders, rework, decreased constructability, cost overruns, and delays, making it one of the biggest causes of waste. The writers aim to develop a lean design process to enhance design reliability by creating a learning environment using the design correctness ratio. Waste is first identified by analyzing the planning and design processes. A new design workflow is then proposed using lean concepts to smooth design work, reduce unnecessary design errors, and increase design reliability. The proposed process can provide team members with feedback on design status and thus allow for continuous improvement. The lean process is conceptualized using system dynamics to validate applicability. Analysis shows that the proposed lean design process can enhance design completeness and reliability, thus increasing design correctness. Waste due to improper design could be reduced accordingly. The proposed process is one of the first to apply the lean approach to construction-project design. DOI: 10.1061/(ASCE)CO.1943-7862 .0000824. © 2014 American Society of Civil Engineers. Author keywords: Lean production; Lean design; Design correctness; System dynamics; Construction industry; Project planning and design. Introduction Before the industrial revolution, the design and construction phases of a building project were tightly interconnected. However, in- creased specialization and diversification of construction-related professions have since separated design and construction into two distinct phases (Yeh 2004), with architects conducting and con- cluding the design phase based on their knowledge and specialty. However, architects have difficulty completing a comprehensive design involving various professional sectors. Moreover, construc- tion projects are increasing in complexity (Gould and Joyce 2009) such that no single designer can claim comprehensive expertise. Thus, final designs may include hidden problems that appear only in the construction phase (Abdelsalam et al. 2010). Whereas some minor design defects can be resolved by the general contractor in discussions with the architect, more serious problems require a mandatory change order, which may increase both time and cost (Josephson et al. 2002; Günhan et al. 2007). Improper design, indicating design error caused by design and which incurs a change order in the construction phase, is potentially one of the biggest sources of waste in the construction industry (Breit et al. 2008). From beginning to end, the project lifecycle can be roughly divided into phases, including conceptual, planning, design, bidding, construction, operation, maintenance, and decom- mission. After the architect completes the design, design drawings are delivered through the tender process to the construction team. If an improper or unfeasible design is found in the construction phase, the design has to be returned to the architect for correction. This continuously repeated correction-process increase both time requirements and cost (Mendelsohn 1997; Kawamura 2000). In the entire project lifecycle, planning and design have the greatest impact on the whole project (Soibelman et al. 2003), and faulty planning and design can result in significant change orders. Forty percent of design changes result from issues arising in the design phase (S. D. Chang, G. S. Shi, and Y. Chou, unpublished internal report, China Engineering Consultants, 2007). Therefore, finding ways to reduce design errors and minimize cost overruns and schedule delays resulting from change orders is a serious issue in the construction industry (Nylen 1996), focusing attention on ef- fectively coordinating design with construction to deal with design problems before they occur (Riley 2005; Li et al. 2008). Toyota Motor Corporations lean production system is a key fac- tor in the firms competitiveness in the global automotive industry (Liker 2004). Implemented as the 4P and 14 principles, this system has enabled Toyota to establish an organizational culture that emphasizes organizational learning between employees and business partners along with the continuous elimination of waste (Wu et al. 2010). Such concepts and methods could be applied in the design phase to establish an environment conducive to co- operative learning between the design team members and ensure the expertise of each team member is fully used (Freire and Alarc ´ on 2002; Womack and Jones 2003; Ko 2010b). The writersobjective is to adapt the lean production system to enhance design accuracy. Background information on the lean- production system and design correctness is first introduced. A lean design process is then developed based on lean production concepts. Finally, feasibility of the proposed process is validated using system dynamics. The final section presents conclusions and suggestions for future research directions. Background This section introduces methods and concepts used to develop the lean design process. The origin of lean production is first introduced, followed by a review of design correctness in addition to an explanation of simulation tools and system dynamics. 1 Professor, Dept. of Civil Engineering, National Pingtung Univ. of Science and Technology, 1 Shuefu Rd., Neipu, Pingtung 91201, Taiwan (corresponding author). E-mail: [email protected] 2 Research Assistant, Dept. of Civil Engineering, National Pingtung Univ. of Science and Technology, 1 Shuefu Rd., Neipu, Pingtung 91201, Taiwan. E-mail: [email protected] Note. This manuscript was submitted on November 11, 2012; ap- proved on November 21, 2013; published online on February 26, 2014. Discussion period open until July 26, 2014; separate discussions must be submitted for individual papers. This paper is part of the Journal of Construction Engineering and Management, © ASCE, ISSN 0733- 9364/04014011(11)/$25.00. © ASCE 04014011-1 J. Constr. Eng. Manage. J. Constr. Eng. Manage., 2014, 140(6): 04014011 Downloaded from ascelibrary.org by Pontificia Universidad Catolica Del Peru on 06/20/16. Copyright ASCE. For personal use only; all rights reserved.

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Page 1: Lean Design Process

Lean Design ProcessChien-Ho Ko1 and Neng-Fu Chung2

Abstract: Improper design in the construction industry leads to change orders, rework, decreased constructability, cost overruns, and delays,making it one of the biggest causes of waste. The writers aim to develop a lean design process to enhance design reliability by creatinga learning environment using the design correctness ratio. Waste is first identified by analyzing the planning and design processes. A newdesign workflow is then proposed using lean concepts to smooth design work, reduce unnecessary design errors, and increase designreliability. The proposed process can provide team members with feedback on design status and thus allow for continuous improvement.The lean process is conceptualized using system dynamics to validate applicability. Analysis shows that the proposed lean design process canenhance design completeness and reliability, thus increasing design correctness. Waste due to improper design could be reduced accordingly.The proposed process is one of the first to apply the lean approach to construction-project design. DOI: 10.1061/(ASCE)CO.1943-7862.0000824. © 2014 American Society of Civil Engineers.

Author keywords: Lean production; Lean design; Design correctness; System dynamics; Construction industry; Project planningand design.

Introduction

Before the industrial revolution, the design and construction phasesof a building project were tightly interconnected. However, in-creased specialization and diversification of construction-relatedprofessions have since separated design and construction into twodistinct phases (Yeh 2004), with architects conducting and con-cluding the design phase based on their knowledge and specialty.However, architects have difficulty completing a comprehensivedesign involving various professional sectors. Moreover, construc-tion projects are increasing in complexity (Gould and Joyce 2009)such that no single designer can claim comprehensive expertise.Thus, final designs may include hidden problems that appear onlyin the construction phase (Abdelsalam et al. 2010). Whereas someminor design defects can be resolved by the general contractor indiscussions with the architect, more serious problems require amandatory change order, which may increase both time and cost(Josephson et al. 2002; Günhan et al. 2007).

Improper design, indicating design error caused by design andwhich incurs a change order in the construction phase, is potentiallyone of the biggest sources of waste in the construction industry(Breit et al. 2008). From beginning to end, the project lifecyclecan be roughly divided into phases, including conceptual, planning,design, bidding, construction, operation, maintenance, and decom-mission. After the architect completes the design, design drawingsare delivered through the tender process to the construction team.If an improper or unfeasible design is found in the constructionphase, the design has to be returned to the architect for correction.

This continuously repeated correction-process increase both timerequirements and cost (Mendelsohn 1997; Kawamura 2000). In theentire project lifecycle, planning and design have the greatestimpact on the whole project (Soibelman et al. 2003), and faultyplanning and design can result in significant change orders. Fortypercent of design changes result from issues arising in the designphase (S. D. Chang, G. S. Shi, and Y. Chou, unpublished internalreport, China Engineering Consultants, 2007). Therefore, findingways to reduce design errors and minimize cost overruns andschedule delays resulting from change orders is a serious issue inthe construction industry (Nylen 1996), focusing attention on ef-fectively coordinating design with construction to deal with designproblems before they occur (Riley 2005; Li et al. 2008).

Toyota Motor Corporation’s lean production system is a key fac-tor in the firm’s competitiveness in the global automotive industry(Liker 2004). Implemented as the 4P and 14 principles, thissystem has enabled Toyota to establish an organizational culturethat emphasizes organizational learning between employees andbusiness partners along with the continuous elimination of waste(Wu et al. 2010). Such concepts and methods could be appliedin the design phase to establish an environment conducive to co-operative learning between the design team members and ensurethe expertise of each team member is fully used (Freire and Alarcon2002; Womack and Jones 2003; Ko 2010b).

The writers’ objective is to adapt the lean production systemto enhance design accuracy. Background information on the lean-production system and design correctness is first introduced.A lean design process is then developed based on lean productionconcepts. Finally, feasibility of the proposed process is validatedusing system dynamics. The final section presents conclusions andsuggestions for future research directions.

Background

This section introduces methods and concepts used to developthe lean design process. The origin of lean production is firstintroduced, followed by a review of design correctness in additionto an explanation of simulation tools and system dynamics.

1Professor, Dept. of Civil Engineering, National Pingtung Univ. ofScience and Technology, 1 Shuefu Rd., Neipu, Pingtung 91201,Taiwan (corresponding author). E-mail: [email protected]

2Research Assistant, Dept. of Civil Engineering, National PingtungUniv. of Science and Technology, 1 Shuefu Rd., Neipu, Pingtung91201, Taiwan. E-mail: [email protected]

Note. This manuscript was submitted on November 11, 2012; ap-proved on November 21, 2013; published online on February 26,2014. Discussion period open until July 26, 2014; separate discussionsmust be submitted for individual papers. This paper is part of the Journalof Construction Engineering and Management, © ASCE, ISSN 0733-9364/04014011(11)/$25.00.

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Lean Production System

The writers attempted to enhance design accuracy using lean-production systems. Lean production practices were originally de-veloped by Sakichi Toyoda in the design of his automated weavingmachine. The new device was not only faster than existing modelsbut could automatically detect errors and stop operations, thus pre-venting wasteful production of defective products. His son KiichiroToyoda later visited car factories and supermarkets in the UnitedStates, and observed that both enterprises replenish their invento-ries as customers make their purchases. This observation led himto develop the just-in-time manufacturing approach, in which therequired materials are provided to the production line in the re-quired quantities at the required time (Ko 2010a). Later, thismethod evolved into the Toyota Production System, relying on ji-doka (autonomation) and time management to reduce inventory re-quirements, and improve production quality and efficiency. Thisapproach allowed the firm to be profitable even during periods ofslow growth (Hino 2005).

Decades of continually refining its production process allowedToyota employees to continuously update obsolete productionmethods, which are not only applied in Toyota factories but havealso been adopted by the company’s suppliers. These methods werecompiled and organized to create the Toyota production system(TPS) house diagram.

The TPS house diagram is supported by two pillars, as follows(Liker 2004): (1) just-in-time production (producing the rightamount of parts at the right time), and (2) jidoka (stopping produc-tion once a problem is detected to prevent defective products fromleaving the work station). The base of the TPS house diagram iscomposed of standardization, stable work flow, and heijunka (lev-eling), which helps maintain the stability of the production systemand reducing bloated inventories (Liker 2004). The roof of thehouse represents the core TPS philosophy. Finally, the interior ofthe house is composed of human issues, in which employees areencouraged and given support to achieve continuous improvementand waste-reduction. The house metaphor emphasizes that weak-ness in any component results in the fragility of the entire produc-tion system (Liker 2004).

The core goal of TPS is the elimination of waste, defined as anyactivity that fails to meet production standards and anything thatdoes not help create value. The search for waste extends beyondthe production line to product development and other workflows.In 1960, Taiichi Ohno, known as “the father of the Toyota produc-tion system” (Ohno 1988), identified seven activities that failed tocreate value, as follows:1. Waste of overproduction, i.e., producing more than what

the consumers need would lead to other waste, such as over-employment or bloated inventory, ultimately resulting in in-creased costs;

2. Waste of transportation, i.e., transporting products from oneplace to another during the production process or the transportof raw materials, parts, and finished products;

3. Waste of waiting, i.e., time in which the worker has nothingto do while the worker waits between process cycles, or idlingcaused by delays in management decision-making or by com-ponents or equipment not being ready for use;

4. Waste of inventory, i.e., excessive volumes of raw materials,work-in-process goods, or finished products require increasedstorage and lead to increased obsolescence (inventory wastemay also lead to other, hidden issues such as unbalanced pro-duction or idle machinery);

5. Waste of making defective products, i.e., production of defec-tive products or products that require repair before shipping

does not create any value and may even consume additionalcapital in repair operations (these rework and repair activitiesare wasteful as they require additional investments of time,effort, and capital);

6. Waste of movement, i.e., employees engaged in finding, re-trieving, or stashing components or tools are not creating value(walking between work stations is also a form of waste); and

7. Waste of processing itself, i.e., poorly designed tools and pro-ducts result in lead repairs, delays, defects, and inefficient pro-cesses (hence, waste must be eliminated from product design).

In 1926, the Toyota Company was started to manufacture andmarket Sakichi Toyoda’s automatic weaving machine. In 1930, theToyota Motor Company was established. Both companies enduredtwo world wars as well as severe inflation that led to a drasticdevaluation of the Japanese yen and created a severe debt crisis.In 1973, the first oil crisis led to a global recession. In 1990, Japan’sbubble economy burst, leading to more than a decade of stagnantgrowth. Over 8 decades, the Toyota Company has consistentlythrived through multiple crises. In 2003, Toyota became the largestcar manufacturer in the world in terms of sales (Lin 2009).

By 1987, Womack et al. (1990) had realized that the Toyotaproduction concepts were different from conventional mass pro-duction. Krafcik (1988) gave the innovation its generic name whennoting, “The characteristics of this system is to use less effort, lessspace, less defects, less throughput time so that less investment andcapital would be needed at every layer of the production process.When demands are low, this new system would only require lowlevels of input to economically design and manufacture productsthat are relatively reliable. This is ‘lean.’” (Krafcik 1988; Ko et al.2011). Over the past 20 years, as recognition of the advantages ofthe TPS became more widespread, it has transformed manufactur-ing worldwide (Womack et al. 1990).

Design Correctness

The writers’ purpose is to enhance design correctness. Designcorrectness can be regarded as a metric to measure the degree towhich design meets the needs of the user or application. Theconcept has been used in construction, software design, hardwaredesign, and knowledge-engineering projects to enhance designquality (Sandecki 1998; Barrow 1984; Riet 2008; Ekenberg andJohannesson 2004; Barber et al. 2003). The first-time-pass ratio(FTPR) was originally proposed as a standard index for evaluat-ing construction quality and it has the advantages of easy data-acquisition, simple calculation of product quality, and clear displayof product appearance (Lin 2005). Chen (2009) applied FTPR as adesign quality-control method, converting FTPR construction eval-uation items into design projects to calculate the FTPR in design,thus determining the quality of the design process. This allows fordefective designs to be immediately improved rather than waitinguntil the design was completed or in the construction phase. TheFTRP process first requires a detailed planning-inspection andwork schedule, followed by the selection of key tasks and qualityevaluation. Experienced staff members then evaluate the selectedtasks to calculate the FTRP. Accuracy calculations and statisticalanalysis results are represented as the quality of product design,which could be used to provide feedback for design correction andrevision.

System Dynamics

Simulation modeling is frequently used to verify the feasibility ofimprovement plans prior to application in actual projects. Systemdynamics is selected to validate the applicability of the proposed

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Page 3: Lean Design Process

method prior to actual application. System dynamics combinesdecision theory, simulation studies, information feedback, andcybernetics. Forrester (1961) laid out a theory that the world is adynamic system that is mutually interactive and related, with de-cisions leading resulting in certain actions based on current cir-cumstances. The action then changes those circumstances andinfluences new decisions, thus creating a causal loop. System dy-namics primarily solves problems from a macro perspective, thusavoiding the fragmented thinking of the micro perspective, makingit suitable for the modern corporations and social organizations, inwhich it is mainly used to solve issues related to dynamic complex-ity. Causality is the constituting foundation of system dynamics aswell as the simplest means by which to discuss system organiza-tions (Palm 2009). In system dynamics, the causes and effects be-tween variables in a system are indicated by arrows. The modelingof system dynamics is mainly composed of four basic components,as follows: (1) stock, (2) flow, (3) arrows, and (4) auxiliary vari-ables. Arrow and auxiliary variables can be used to interpret thecausal feedback diagram, that is, the presentation of the informationflow of variables (Senge 1990). Using the population-dynamic flowas an example, the population is represented using the stock. Thebirth and death rate are the inflow and outflow, respectively, bothof which are auxiliary variables. System dynamics allows for thedynamic relationship among birth rate, population dynamics, anddeath rate to be depicted.

Lean Design Process

The research reported in this paper adapts the concept of lean-production systems to establish a lean design process. The devel-opment process (Fig. 1) consists of value stream analysis, animplementation process, and verification. Waste is first identifiedby analyzing the current planning and design processes using valuestream mapping. A new design workflow is then proposed usinglean concepts. The design flow is divided into three stages, as fol-lows: (1) preliminary design, (2) basic design, and (3) detailed de-sign. In each stage, design procedures are elaborated to smoothdesign work, reduce unnecessary design errors, and increase designreliability. Finally, feasibility of the proposed method is validatedusing system dynamics. Details about the development process areexplained next.

Value Stream Analysis: Current Design Flow

Design of construction projects can be largely divided into twostages, as follows: (1) preliminary design, and (2) detailed design.Architectural plans for the preliminary and detailed stages areusually completed independently by architects (Fig. 2). Preliminarydesigns are usually prepared for design competitions, with thewinning design plan approved to go to the detailed design stage.Architects make revisions on the winning design plan in accor-dance with the owner’s requirements, whereas the structural por-tions are handed to structural engineers to generate detailedshop-drawings. Once the plans are checked for errors, they aresigned and approved. The relevant engineers conduct facility andequipment analysis, after which the plans are again signed andapproved after checking for errors. The architect then integratesthe prints obtained from these processes. This design workflowmay appear smooth on the surface but it actually hides underlyingissues. Failing to uncover these issues in the design phase not onlyaffects the design process but the actual construction as well.

Lean production aims to promote customer value. The pro-duction process uses flow methods to identify valueless activitiesfor elimination, thereby incrementally increasing customer value(Koskela 1992). The construction process requires considerabletime-inputs devoted to planning, design, construction, and hand-over. Problems frequently arise from the shop drawings, resultingin change orders (Pulaski and Horman 2005; Motawa et al. 2007).Improvements to the design and planning process could help alle-viate some of these issues.

Fig. 2 shows the current design and planning workflow. Withthe exception of the structural and equipment designs, which aredelegated to structural and equipment engineers, every stage of thedesign plan is the responsibility of the architect. To analyze issuesin the current design process, the research reported in this paperillustrates the current-state value stream mapping of the designprocesses. The owner first tasks the project design to the architect,who would then independently complete each part of the designplan (Fig. 3). Structural and equipment engineers must wait untilthe upstream design work had been finished before analyzing,illustrating, and inspecting the designs. The completed work isthen handed over to the construction firm to initiate construction.The completed building is then turned over to the owner. If workis obstructed by design errors or construction issues, the design isreturned to the architect for corrections. Analyzing this processrevealed the following problems:• While waiting for the architect to hand over the relevant prints

for analysis, the structural and equipment engineers did not havethe opportunity to make any design suggestions;

• The design stage of the workflow was independently completedby the architect, and any resulting design problems requirethe plans to be returned to those responsible for the designtasks; and

• The architectural prints include aspects that are likely beyondthe range of the architect’s expertise, making it difficult for thearchitect to produce a complete and error-free plan. Any pro-blems or design changes during the construction stage will ne-cessarily delay project completion and increase cost overruns.

Value Stream Analysis: Lean production Concepts

Applications of Toyota’s lean production system are not restrictedto manufacturing, and many other industries currently use thesystem’s measures and concepts to improve their internal organi-zations and workflows (Ko 2010a, 2011). In lean productionsystems, a product has no value until it has been made. Poorly de-signed products create waste, leading to reduced value and productFig. 1. Development process

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Page 4: Lean Design Process

competitiveness. In other words, poor design is itself a form ofwaste in that it is an obstacle to smooth production. In constructionprojects, 60–95% of costs are determined in the planning phase(Yeh 2004), which means that every decision made in the planningphase significantly affects later stages. Failure to plan adequatelywill require repetitive reviews of the design plan. As a result, about40% of change orders during construction can be traced back tothe designers (S. D. Chang, G. S. Shi, and Y. Chou, unpublishedinternal report, China Engineering Consultants, 2007). Analyzingcurrent workflows revealed that the source of the waste was apoor understanding of the owner’s requirements. For example, timespent by structural and equipment engineers waiting for design-print analysis and approval translated into waste in design inventoryand waiting. Design errors caused by the independent nature of thearchitect’s work would lead to waste through the production ofdefective products (Bynum et al. 2013).

The TPS emphasizes that management should fundamentallyfocus on long-term operations to create value for the consumers(Liker 2004). A system of correct design workflows, producingoptimal design results, can be created after clarifying and definingthe owner’s requirements. Such a system would produce value forthe project, helping to uncover and resolve issues before they be-come serious problems. In addition, providing continuous feedbackon issues from one project to the next will help initiate organizedlearning, which also creates value. This research establishes a de-sign process using the concepts of lean production systems to elimi-nate the types of waste described previously.

Implementation Process: Overview

Product designs undergo numerous reviews and are subjected tocontinuous brainstorming sessions by designers before they are

actually manufactured. These processes are also applied in con-struction. Simply put, architectural designs are organizations ofspace for using material technologies to construct a living envi-ronment for people. Hence, architectural designs are by naturemultidisciplinary efforts, requiring consideration of many aspects,including structural composition, aesthetics, pipes and cables,water drainage, overall environment, and more. Over its lifespan,from construction through maintenance, a building experiencesmany problems. As in the automobile industry, even a single over-sight in the design process can require design corrections andreviews during manufacture, or time-intensive and cost-intensiverepair work.

In the design process proposed in this paper, the architectleads the entire design process and is responsible for communicat-ing with the owner. The architect translates the owner’s ideas andrequirements into an architectural model. The design flow is di-vided into three stages (Fig. 4), as follows: (1) preliminary design,(2) basic design, and (3) detailed design. Preliminary design ismainly a preparation stage, in which designs are submitted to a de-sign competition. The subsequent two stages are initiated once thewinning entry has been confirmed.

Implementation Process: Preliminary Design Phase

The main purpose of the preliminary design phase is to prepare thenecessary documents and illustrations for a design competition.These include the exterior perspective, interior perspective, floorplans, sectional plan, elevation plan, and design report. This phaseof the design process is led by the architect in close consultationwith the owner. The process includes the following steps:• Construct building system conceptual model. The architect

confirms the project type with the owner. Different types of

Fig. 2. Current design workflow

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Page 5: Lean Design Process

buildings (e.g., factories, libraries, or stadiums) require differ-ent considerations. Detailed and in-depth discussions with theowner reveal the project’s conditions (e.g., land area, land-userights, natural environment, and spatial needs), providing infor-mation necessary for analysis and transforming the owner’sideas into a preliminary design.

• Propose structural plan. Structural engineers use the conceptualmodel developed by the architect, and based on an onsite inves-tigation, create a preliminary structural plan, detailing founda-tion type, and roof structure.

• Propose equipment plan. Professional equipment engineers usethe conceptual model, based on the owner’s requirements, tocreate a preliminary equipment plan covering facilities require-ment analysis, water and drainage systems, air conditioning andventilation designs, and emergency evacuation designs.

• Evaluate preliminary design correctness ratio. This step usesTable 1 to verify design project completeness. The entire designteam performs a group check and discusses the proposed designcontents. Any ambiguity in the design is clarified by the re-sponsible member so that all team members have an in-depthunderstanding of the design. Any errors found in the designare delegated to the responsible team member for correction.Designs are only sent to the next stage after they are corrected,completed, and verified to match the owner’s specifications.Rather than numerical rankings, design correctness evaluation

responses in the table are limited to yes, not sure, and no.Eq. (1) formulates an index to evaluate the design correctnessratio (DCR). Applying Eq. (1) to the inspection tables allowsdesign-team members to learn from each other and uncoverproblems early

DCR ¼�Nyes

A

�× 100% ð1Þ

where Nyes = number of inspected items evaluated as yes; andA = amount of inspected items.

• Integrate building-plan model. By integrating the results ofthe preliminary designs, the necessary documents (e.g., exteriorperspective, interior perspective, floor plans, section plans, ele-vation plans, regulatory overview, and planning report) are thencompiled for submission.

Implementation Process: Basic Design Phase

This stage focuses on the detailed analysis of the building planmodel for the design competition’s winning entry, including theplanning for structural reinforcements, structural strength and loadanalysis, water pipe and electrical layout, and emergency evacu-ation routes. This stage includes the following steps:

Fig. 3. Current-state value stream mapping

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• Detail model, i.e., the architect adds further details to theintegrated architectural model, including spatial assignments,flow routes, and construction-cost estimates;

• Analyze structural system, i.e., based on the building planmodel, the structural engineers perform overall analyses forbasic reinforcements, required concrete strength, roof structure,dimensions of beams and pillars, and steel strength loading inaccordance with building regulations;

• Analyze equipment system, i.e., contents of the design plan thathave undergone preliminary design verification can be used todraft analyses for water pipelines, electrical conduits, elevators,and emergency escape routes;

• Evaluate basic design correctness ratio, i.e., in addition toevaluating the basic design correctness using Eq. (1), generalcontractors are invited to conduct conflict inspections andraise issues that may potentially arise during the constructionphase; any errors or ambiguities in the design are returnedto the responsible designer for correction; after the design iscertified to be complete and error-free, it is passed on to thenext phase; and

• Integrate building basic model, i.e., design documents thathave passed the basic design inspection are integrated to pro-vide a more complete blueprint for the development of detaileddesigns.

Implementation Process: Detailed Design Phase

The aim of this stage is to compile all documentation followingthree inspections to reduce design errors. This stage includes thefollowing steps:• Construct detailed building drawing, i.e., components and

equipment in the basic design plan are marked and representedin the design plans (the architect determines the brand, model,and style of the equipment, such as doors, windows, elevators,and air conditioners);

• Construct detailed structure drawing, i.e., details of structuralcomponents are illustrated in the detailed design plan;

• Construct detailed equipment drawing, i.e., details of equip-ment and components are illustrated in the detailed designplan;

Fig. 4. Lean construction design process

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• Evaluate detailed design correctness ratio, i.e., detailed designdrawings are inspected; general contractors work with the de-sign and specialist teams to perform conflict and constructabilityanalyses for each of the resulting plans; inspections are con-ducted using Eq. (1), with the results fed back to the responsibleparties for correction; and

• Complete building system model, i.e., the architect compilesrelevant data and information into the final building systemmodel (the owner then passes the completed prints to the generalcontractor to begin construction).

Process Verification

System dynamics, which play a major role in process verification,primarily solve problems from a macro perspective, thus avoidingthe fragmented thinking of the micro perspective (Karnopp et al.2012). The research reported in this paper uses system dynamicsto validate the feasibility of the proposed lean design process,converting the workflow into conceptual causal-loop diagramsto analyze possible results when implementing the process. Thedesign flow is divided into three phases, as follows: (1) preliminarydesign, (2) basic design, and (3) detailed design. The research re-ported in this paper uses a causal-loop diagram to identify cause-and-effect relationships between variables in the design phasesto analyze the information flow over the duration of the designprocess.

Causal Loop: Preliminary Design System

The aim of the preliminary design system is to understand whetherthe collected information and building concept can meet theowner’s requirements. The architect creates a conceptual buildingsystem after inspecting onsite conditions and obtaining designrequirements. Information from the design concepts then is sent to

the structural and equipment engineers for structural-planning andequipment-planning. The preliminary design correctness ratio rep-resents the degree of correctness of the system’s design. Failure toachieve 100% correctness triggers successive rounds of correctionsuntil the correctness reaches 100%. Fig. 5(a) shows the preliminarydesign causal loop. The preliminary design correctness ratio isenhanced by the completeness of the equipment designs, buildingsystem concept, and structural plans [Fig. 5(a)]. A correct prelimi-nary design can decrease the number of iterations required formodification and corrections for demand, structural, and equipmentplans. The next design stage is only implemented when the currentstage reaches 100%, thus eliminating the need for redesign, whichwould idle other team members and delay work schedules.

Causal Loop: Basic Design System

In this phase, the building system design model is developed basedon previous design phase. At this stage, basic design correctnesscan be obtained using Eq. (1). In this phase, the general contractoralso conducts constructability analyses.

Fig. 5(b) shows the basic design causal loop. Changes to thebuilding model, structural plans, and equipment plans are carriedout based on the design correctness results. With the participationof the general contractor, the first round of corrections is able tocover the constructability analysis, structural analyses, model de-tailing, and equipment analyses. When the basic design correctnessratio has reached 100%, these documents are then sent to the nextphase to complete the detailed designs.

Causal Loop: Detailed Design System

As in the previous system, this phase begins with a basic designmodel with a 100% correctness ratio. Once compiled by the archi-tect, the basic design plans are sent to the structural and equipment

Table 1. Preliminary Designs Inspection

Inspect Item

Results

Architect Structural engineer Equipment engineer

RemarkYes Not sure No Yes Not sure No Yes Not sure No

ArchitectLand-use conceptsLand area and building heightNatural environment investigation and analysisEnvironmental impact analysisHuman environment investigation and analysisCurrent-land use situationSpatial requirement analysis: Spatial content

Spatial requirement analysis: Spatial featuresStructural engineer

Foundation structure: Foundation geology investigationFoundation structure: Foundation typeFoundation structure: Roof structureFoundation structure: Above-ground structureFoundation structure: Underground structureSeismic resistance structural design concepts

Equipment engineerEquipment requirement analysis conceptsElectrical system conceptsLow-current equipment system conceptsWater provision and drainage system conceptsHVAC conceptsEmergency system conceptsAccessibility system concepts

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engineers to illustrate the detailed plans. The architect also makesdetailed changes to the model and assesses design correctness atthis stage in consultation with the general contractor regarding con-structability analyses. In Fig. 5(c), the general contractor conductsa feasibility analysis, whereas the architect in addition to the struc-tural and equipment engineers reference the design correctnessratio to conduct a first round of corrections to the relevant designprints. Subsequent rounds of corrections are conducted until thefinished design is assessed as being 100% correct.

Design Correctness Analysis: PreliminaryDesign System

In the preliminary design causal loop [Fig. 5(a)], the preliminarydesign correctness ratio is affected by completeness of the buildingsystem concept CBSC, completeness of the structural-planning CSP,and completeness of the equipment-planning CEP. The proportionof analyses by the architect in addition to the structural and equip-ment engineers can be obtained (Table 1). A total of 21 items arelisted for correctness inspection, of which the architect is respon-sible for eight (i.e., a proportion of 0.38 or ratio of 8∶21). Using thismethod, the respective weightings for the structural and equipmentengineers are 0.29 and 0.33. The preliminary design correctnessratio is simulated using Eq. (2a). The completeness of the buildingsystem concept is directly impacted by the completeness of thedesign information CDI [Eq. (2b)]. Using Eq. (2c), the complete-ness of the structure plan and equipment plan increases 20% in eachrevision

MIN½ð0.38 × CBSCÞ þ ð0.29 × CSPÞ þ ð0.33 × CEPÞ; 100� ð2aÞ

MINCDI; 100 ð2bÞ

MIN½ðCBSCÞ þ ðCcorr × 20Þ; 100� ð2cÞwhere Ncorr = number of corrections.

Analyzing the preliminary design correctness ratio using sys-tem dynamics shows that the structure and equipment planshave attained 100% completeness by the second week (Fig. 6).However, rate of improvement may be affected by the need toupdate the owner or by the completeness of environmental inspec-tions, as shown in the building system concept (Fig. 6). Thus, thepreliminary design systems required four rounds of corrections(i.e., 4 weeks) to achieve 100% correctness (Fig. 6). At this point,the next step of basic design phase could be performed.

Design Correctness Analysis: Basic Design System

This phase begins with the completeness of the building systemconcept model which, given that the research reported in this paperincludes three design phases, accounts for one-third of project com-pleteness. The basic design system phase involves the general con-tractor conducting constructability inspections in regards to thedesign contents. The basic design correctness ratio could be simu-lated using Eq. (3a). Using the same method used to calculate theparameters in Eq. (2a), the parameters of Eq. (3a) can be obtainedfrom the basic design inspection checklist. The respective inspec-tion weightings for the architect, structural engineer, equipmentengineer, and general contractor are 0.2, 0.4, 0.32, and 0.08. Themodel assumes a 30% increase in completeness for model detailingCMD, completeness for structural analysis CSA, and complete-ness for equipment analysis CEA with each successive revision[Eq. (3b)]. The effects of basic constructability (BC) on basicdesign correctness could be calculated using Eq. (3c)

Fig. 5. Lean construction design causal loops: (a) preliminary design;(b) basic design; (c) detailed design

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MIN½ð0.08 × BCÞ þ ð0.2 × CMDÞ þ ð0.4 × CSAÞþ ð0.32 × CEAÞ; 100� ð3aÞ

MIN

�CBSM þ Ccorr × 30; 100

�ð3bÞ

MINðNcorr × 30; 100Þ ð3cÞThe basic design correctness ratio is analyzed using system

dynamics. Experimental results (Fig. 7) show that model-detailing,structural analysis, and equipment analyses attain 100% complete-ness by week 3. However, as the correctness ratio in this phase isaffected by basic constructability (Fig. 7), the design correctnessratio reaches 100% by day 2 of week 3, as depicted in the basicdesign (Fig. 7). Only then can the next design phase be performed.

Design Correctness Analysis: Detailed Design System

The detailed design is prepared based on the basic design model.Through the previous two phases, the design team members havebecome familiar with the design details. As a result, 70% designcompleteness is assumed for the entire project. Like the previous

phase, this phase also requires the general contractor to conduct aconstructability analysis. Using the same method used to calculatethe parameters in Eq. (2a), the parameters of Eq. (4a) can be ob-tained from the detailed design inspection checklist. The respectiveweightings for the architect, structural engineer, equipment engi-neer, and general contractor are 0.24, 0.44, 0.28, and 0.04. The cor-rectness ratio of the detailed designs is simulated using Eq. (4a).Completeness of detailed modeling CDM, completeness of thedetailed structure plan CDSP, and completeness of the detailedequipment plan CDEP is assumed to increase 40% with each roundof corrections, as formulated in Eq. (4b). The effects of the basicconstructability assessment on basic design correctness are calcu-lated using Eq. (4c)

MIN½ð0.24 × CDMÞ þ ð0.44 × CDSPÞ þ ð0.28 × CDEPÞþ ð0.04 ×DCÞ; 100� ð4aÞ

MIN½CBSM þ ðCcorr × 40Þ; 100� ð4bÞ

MIN½ðCcorr × 40Þ; 100� ð4cÞ

Based on the results shown in the detailed model (Fig. 8), thedetailed structure plan and the detailed equipment plan attain 100%completeness in the week 1. The reduced time required for thedesign period points to the benefits of creating an organizationallearning environment for the design team. However, as shown inthe detailed constructability (Fig. 8), the design correctness ratiois affected by detailed constructability and thus the entire designproject is completed by day 5 of week 2, as shown in the detaileddesign (Fig. 8).

This verification demonstrates how, in the design process, themethod proposed in this paper reduces the likelihood of errorsoccurring during the traditional design-bid-build approach. The tra-ditional approach’s well-known stovepipe approach to disciplinescauses many types of errors (Azhar 2011). The collaborative useof building-information modeling (BIM) and integrated projectdelivery (IPD) are used to prevent errors and increase building qual-ity in current architecture, engineering, and construction (AEC)practices (Grilo and Jardim-Goncalves 2010), which could be re-garded as parallels to the collaborative approach suggested in theresearch reported in this paper.

Fig. 6. Analyzed results in preliminary design system

Fig. 7. Analyzed results in basic design system Fig. 8. Analyzed results in detailed design system

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Conclusions

The research reported in this paper uses lean production perspec-tives to review traditional planning processes in construction proj-ects. Value streaming is applied to ascertain hidden sources ofwaste in traditional workflows. A lean design process is then de-veloped using lean concepts to make the process more pliable to theowner’s needs, i.e., customer’s value. System dynamics is used tovalidate the feasibility of the proposed process, and analysis resultsshow that it can increase design correctness and reliability, thusincreasing value to the owner.

Construction projects require a joint effort of professionals fromdifferent fields. Currently, design plans tend to be completed inde-pendently by the architect, who is responsible for resolving designerrors discovered in the design phase or change orders made in theconstruction phase. Current practice frequently results in scheduledelays or budget overruns. The research reported in this paper es-tablishes an organizational learning environment within the designworkflow. The root cause of design errors can be identified thoughsystematic inspections of design correctness. This approach notonly helps correct the design itself but allows design team membersto learn from errors. In addition, whereas traditional design proc-esses are divided into two stages (i.e., preliminary and detailedplanning), the research reported in this paper seeks to provide proj-ect participants with the opportunity to inspect actual design con-tents by dividing the design process into three phases, as follows:(1) preliminary design, (2) basic design, and (3) detailed design.This three-stage approach, coupled with multiple design-feedbackcycles, builds team consensus and allows for the early detection oferrors, thus optimizing the resulting design plans. The proposedapproach can be applied to construction and civil engineering,in which civil engineers deal with infrastructure elements such astunnels, sewage systems, dams, and water projects.

The writers assume a first-time correctness rate for preliminarydesigns of 80%, with an additional 20% improvement with eachround of correction. In the second phase, basic design systems areprepared based on a 30% completion of the entire project with a 30%improvement gradient in revision. The third, detailed design phaseassumes that the previous stage has completed 70% of the entireproject and that every round of correction can increase correctnessby 40%. The capability or expertise of the actual individuals execut-ing the proposed process largely dictates the quality of the outcome.These parameters differ in accordance with the characteristics ofvarious projects and individuals. Future studies can investigate re-lationships between project characteristics, individual capability,and the correctness ratio. Future work will apply the method pro-posed in this paper to actual projects for performance assessment.

References

Abdelsalam, S. S., Sritharan, S., and Suleiman, M. T. (2010). “Currentdesign and construction practices of bridge pile foundations withemphasis on implementation of LRFD.” J. Bridge Eng., 10.1061/(ASCE)BE.1943-5592.0000118, 749–758.

Azhar, S. (2011). “Building information modeling (BIM): Trends, benefits,risks, and challenges for the AEC industry.” Leadership Manage. Eng.,10.1061/(ASCE)LM.1943-5630.0000127, 241–252.

Barber, K. S., Graser, T., and Holt, J. (2003). “Evaluating dynamic correct-ness properties of domain reference architectures.” J. Syst. Softw., 68(3),217–231.

Barrow, H. G. (1984). “Verify: A program for proving correctness of digitalhardware designs.” Artif. Intell., 24(1), 437–491.

Breit, M., Vogel, M., Häubi, F., Märki, F., and Raps, M. (2008). “4D designand simulation technologies and process design patterns to support leanconstruction methods.” Tsinghua Sci. Technol., 13(1), 179–184.

Bynum, P., Issa, R. R. A., and Olbina, S. (2013). “Building informationmodeling in support of sustainable design and construction.” J. Constr.Eng. Manage., 10.1061/(ASCE)CO.1943-7862.0000560, 24–34.

Chen, H. Y. (2009). “First time correctness ratio–A quality measure appliedon engineering design”, M.S. thesis, National Cheng Kung Univ.,Tainan City, Taiwan (in Chinese).

Ekenberg, L., and Johannesson, P. (2004). “A framework for determiningdesign correctness.” Knowl.-Based Syst., 17(7), 249–262.

Forrester, J. W. (1961). Industrial dynamics, Pegasus Communications,New York.

Freire, J., and Alarcon, L. F. (2002). “Achieving lean design process:Improvement methodology.” J. Constr. Eng. Manage., 10.1061/(ASCE)0733-9364(2002)128:3(248), 248–256.

Gould, F., and Joyce, N. (2009). Construction project management,3rd Ed., Prentice Hall, Upper Saddle River, NJ.

Grilo, A., and Jardim-Goncalves, R. (2010). “Value proposition on inter-operability of BIM and collaborative working environments.” Autom.Constr., 19(5), 522–530.

Günhan, S., Arditi, D., and Doyle, J. (2007). “Avoiding change orders inpublic school construction.” J. Prof. Issues Eng. Educ. Pract., 10.1061/(ASCE)1052-3928(2007)133:1(67), 67–73.

Hino, S. (2005). Inside the mind of Toyota: Management principles forenduring growth, Productivity Press, New York.

Josephson, P. E., Larsson, B., and Li, H. (2002). “Illustrative benchmarkingrework and rework costs in Swedish construction industry.” J. Manage.Eng., 10.1061/(ASCE)0742-597X(2002)18:2(76), 76–83.

Karnopp, D. C., Margolis, D. L., and Rosenberg, R. C. (2012). Systemdynamics: Modeling, simulation, and control of mechatronic systems,Wiley, Hoboken, NJ.

Kawamura, S. (2000). Integrated design and operation of water treatmentfacilities, Wiley, Hoboken, NJ.

Ko, C. H. (2010a). “An integrated framework for reducing precast fabrica-tion inventory.” J. Civ. Eng. Manage., 16(3), 418–427.

Ko, C. H. (2010b). “Application of lean production system in the construc-tion industry: An empirical study.” J. Eng. Appl. Sci., 5(2), 71–77.

Ko, C. H. (2011). “Production control in precast fabrication: Consideringdemand variability in production schedules.” Can. J. Civ. Eng., 38(2),191–199.

Ko, C. H., Wang, W. C., and Kuo, J. D. (2011). “Improving formwork en-gineering using the Toyota way.” J. Eng. Proj. Prod. Manage., 1(1),13–27.

Koskela, L. (1992). “Application of the new production philosophy to con-struction.” Technical Rep., Stanford Univ., Stanford, CA.

Krafcik, J. F. (1988). “Triumph of the lean production system.” SloanManage. Rev., 30(1), 41–52.

Li, H., et al. (2008). “Integrating design and construction through virtualprototyping.” Auto. Constr., 17(8), 915–922.

Liker, J. K. (2004). The Toyota way: 14 management principles from theworld’s greatest manufacturer, McGraw Hill, New York.

Lin, L. H. (2009). “The impact of integration strategy on organisationalinnovation and growth in the global automotive industry.” Int. J. Auto.Technol. Manage., 9(1), 54–68.

Mendelsohn, R. (1997). “The constructability review process: A contrac-tor’s perspective.” J. Manage. Eng., 13(3), 17–19.

Motawa, I. A., Anumba, C. J., Lee, S., and Pena-Mora, F. (2007). “Anintegrated system for change management in construction.” Automat.Constr., 16(3), 368–377.

Nylen, K. O. (1996). “Cost of failure in a major civil engineering project.”Licentiate thesis, Royal Institute of Technology, Stockholm, Sweden.

Ohno, T. (1988). Toyota production system, Productivity Press, New York.Palm, W. J. (2009). System dynamics, McGraw-Hill, New York.Pulaski, M. H., and Horman, M. J. (2005). “Organizing constructability

knowledge for design.” J. Constr. Eng. Manage., 10.1061/(ASCE)0733-9364(2005)131:8(911), 911–919.

Riet, R. P. (2008). “Twenty-five years of Mokum: For 25 years of data andknowledge engineering: Correctness by design in relation to MDE andcorrect protocols in cyberspace.” Data Knowl. Eng., 67(2), 293–329.

Riley, D. R., Diller, B. E., and Kerr, D. (2005). “Effects of deliverysystems on change order size and frequency in mechanical

© ASCE 04014011-10 J. Constr. Eng. Manage.

J. Constr. Eng. Manage., 2014, 140(6): 04014011

Dow

nloa

ded

from

asc

elib

rary

.org

by

Pont

ific

ia U

nive

rsid

ad C

atol

ica

Del

Per

u on

06/

20/1

6. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

Page 11: Lean Design Process

construction.” J. Constr. Eng. Manage., 10.1061/(ASCE)0733-9364(2005)131:9(953), 953–962.

Sandecki, T. (1998). “Innovative approaches to highway geometric designin Poland.” Transportation Research Circular E-C003, TransportationResearch Board, Washington, DC, 1–7.

Senge, P. M. (1990). The fifth discipline: The art and practice of the learn-ing organization, Bantam Dell, New York.

Soibelman, L., Liu, L. Y., Kirby, J. G., East, E. W., Caldas, C. H., andAndlin, K. Y. (2003). “Design review checking system with corporatelessons learned.” J. Constr. Eng. Manage., 10.1061/(ASCE)0733-9364(2003)129:5(475), 475–484.

Womack, J. P., and Jones, D. T. (2003). Lean thinking: Banish waste andcreate wealth in your corporation, Revised and updated, Free Press.

Womack, J. P., Jones, D. T., Ross, D., and Carpenter, D. S. (1990). Themachine that changed the world: The story of Lean production,McGraw Hill, New York.

Wu, S., Blos, M. F., Wee, H. M., and Chen, Y. L. (2010). “Can the Toyotaway overcome the recent Toyota setback? A study based on the theoryof constraints.” J. Adv. Manuf. Syst., 9(2), 145–156.

Yeh, M. H. (2004). “A study on the combination of the interface betweendesign and construction.”M.S. thesis, National Yunlin Univ. of Scienceand Technology (in Chinese).

© ASCE 04014011-11 J. Constr. Eng. Manage.

J. Constr. Eng. Manage., 2014, 140(6): 04014011

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