15

CHAPTER 2 BUILDABILITY AND CONSTRUCTABILITY: A LITERATURE REVIEW

2.1. Introduction

Buildability (constructability) is a huge area of study in the construction industry. The

purpose of this literature review is to study areas that have relevance to developing the

decision support system for buildable designs. The review of the literature first places

an emphasis on buildability principles and conceptual guidelines for buildability

implementation since these principles and guidelines are important ways of

transferring construction knowledge to designers. Then, the review of the literature

concentrates on knowledge management in buildability with respect to how

buildability related knowledge and information was classified, acquired, represented

and utilized during the life cycle of a project. Finally, the review of the literature

focuses on how to apply the available buildability knowledge and information for

quantitative and formal buildability review and evaluation.

Section 2.2 elucidates the definitions of buildability. Section 2.3 briefly describes the

evolution of buildability concepts. Section 2.4 reviews principles (concepts) and

organizational approaches to implement buildability. Section 2.5 introduces knowledge

management in buildability. Section 2.6 presents the approaches to quantifying

buildability. At the end of this chapter, a summary is given.

2.2. Definitions of buildability

The two definitions of buildability, which are most widely accepted in research and

practice, were developed by the Construction Industry Research and Information

Association (CIRIA) in the UK and the Constructability Task Force of the

16

Construction Industry Institute (CII) in the USA, respectively. The CIRIA defined

buildability as follows:

“Buildability is the extent to which the design of a building facilitates ease of

construction, subject to the overall requirements for the completed building (CIRIA,

1983:6)”.

The Constructability Task Force defined constructability as follows:

“Constructability is the optimum use of construction knowledge and experience in

planning, design, procurement, and field operations to achieve overall project

objectives (CII, 1986:2)”.

Other researchers also derived their definitions based on their commitment to

conceptual assumptions and ways to studying buildability. A selected sample of these

definitions is given as follows.

Illingworth (1984) defined buildability as design and detailing which recognize the

assembly process in achieving the desired result safely and at least cost to the client.

Moore (1996:31) modified Illingworth’s (1984) definition as a “design philosophy,

which recognizes and addresses the problems of the assembly process in achieving the

construction of the design product, both safely and without resort to standardization or

project level simplification”.

Ferguson (1989:1) defined buildability as “the ability to construct a building

efficiently, economically and to agreed quality levels from its constituent materials,

17

components and sub-assemblies”. Similarly, Williams (1982) defined buildability as

the most economic and efficient way of putting a building together.

The Construction Industry Institute in Australia (CIIA) (Griffith and Sidwell, 1997:29)

defined constructability as “a system for achieving optimum integration of

construction knowledge in the building process and balancing the various project and

environmental constraints to achieve maximization of project goals and building

performance”. More specifically, Lueprasert (1996:5) defined constructability as “an

important feature of a structural design and the construction project site conditions,

which determines the level of complexity of executing the associated structural

assembly tasks”.

Some researchers believed that constructability differs markedly from buildability in

terms of its much wider boundaries (e.g., Griffith and Sidwell, 1997). The difference is

seen mainly in that buildability is a design-oriented concept but constructability is

concerned with the whole project process. Others believed that there is no difference

between the two concepts, except that buildability is usually used in the UK but

constructability is often used in the USA. Generally, although there is a different

nuance in their connotation, the two concepts are used interchangeably in most

situations. Thus, this research does not make any difference between the two concepts.

Further, buildability has been adopted in this research since it is an official term used

in Singapore.

18

For the purpose of this research, the CIRIA’s definition is used as the working

definition since it focuses more specifically on design and consequently is more

consistent with the aim of this research.

2.3. Evolution of concepts of buildability

2.3.1. Development of concept

The awareness of buildability can be traced back to a UK governmental report in the

early 1960’s (Emmerson, 1962). This report implied that vertical fragmentation of the

project process has led to many problems in the construction industry and

recommended the improvement of coordination and communication among the

architects, consultants and contractors. A subsequent report (Banwell, 1964) further

suggested that design and construction must be considered together and that the

contractor is too far removed from the design stage in the traditional contracting

situation, at which his/her specialized knowledge and techniques could be put to

invaluable use. The report also highlighted that integration of design and construction

leads to clearly defined client requirements, promotion of cooperation between

designers and contractors, and improved interdisciplinary relationships.

Following the Banwell (1964) Report, several further studies (Economic Development

Council, 1967; National Economic Development Office, 1975, 1983) suggested that

alternative forms of contractual arrangements, such as design and build, construction

management, and design and management, should be sought to implement the

recommendations made in the Banwell (1964) report. These reports also further

recommended that design has to facilitate progress on site, take account of buildability

19

and obtain contributions from specialist consultants, the contractors, subcontractors

and suppliers.

Based on the above-mentioned reports, the members of CIRIA (1983), who were

building contractors, initiated a study to investigate what they regarded as the main

problems of building practices. The research interests concentrated on buildability,

which implied that building designs did not enable the industry’s clients to obtain their

best value for money in terms of efficiency with which the building was carried out.

The CIRIA (1983) report defined buildability (see Section 2.2) and gave two

implications of the definition, which include that, firstly, buildability is a dynamic

concept, which exists on a scale from very good to very bad, and secondly, every

building has overall requirements that may necessitate the acceptance of less than very

good buildability.

Compared with the development of buildability in the UK, the concept of

constructability emerged in the late 1970’s as a result of research into promoting

quality efficiency, productivity and cost effectiveness in the construction industry of

the USA (Construction Management Committee, ASCE Construction Division, 1991).

A relevant report (Business Roundtable, 1982) concluded that the benefits to be gained

from good constructability throughout the building process are approximately ten to

twenty times the costs to achieving them. The conclusion stimulated the establishment

of the Construction Industry Institute (CII) based at the University of Texas at Austin

in 1983 in the USA (Griffith and Sidwell, 1997). The CII constructability concept

emphasized the optimum use of construction knowledge and experience in planning,

design, procurement, and field operations to achieve overall project objectives, and the

20

constructability program was also extensively implemented in practice in the USA (see

Section 2.4).

2.3.2. Design for Buildability

In order to change and enhance the fragmented design and construction process, new

production philosophies were recently applied to improve and innovate the project

delivery process (e.g., Koskela, 1992; Low and Chan, 1997; Egan, 1998). Compared

with the concept of design for manufacture (DFM) or design for manufacture and

assembly (DFMA) in the manufacturing industry, design for buildability, which is also

termed as design for construction (DFC) or design for constructability method

(DFCM), is adopted as an element of new production philosophies in the construction

industry (e.g., De la Garza, et al., 1994; Skibniewski and Arciszewski, 1997; Egan,

1998; Luiten and Fischer, 1998; Fox, Marsh and Cockerham, 2001).

For instance, Skibniewski and Arciszewski (1997) proposed a two-stage method of

design for constructability and suggested that information technology has provided a

foundation to implement and develop the design for constructability method in

construction. Luiten and Fischer (1998) described a framework that helped researchers

and practitioners to approach computer-aided design for construction systematically.

They further argued that information technology provides a promising opportunity for

the building industry to integrate design for construction into its linear facility delivery

process and to approach a more cyclical process. Fox, Marsh and Cockerham (2001)

stated that it was possible to apply the fundamental principles of design for

manufacture, such as standard production design improvement rules and standard

production design evaluation metrics, to all buildings and building components. A

21

recent report (Egan, 1998) pointed out that a design for construction concept should be

developed in the construction industry as an equivalent concept of design for

manufacture in the manufacturing industry to achieve an annual reduction of 10% in

construction cost and construction time.

2.3.3. Phases of development in concepts

Generally, the development of buildability concepts can be divided into three phases

(Fig. 2.1). In the early phase, buildability is regarded as a design rationale that

narrowly focuses on providing design rationalization for ease of construction and

improving site productivity (e.g., CIRIA, 1983). In the developing phase, buildability

is regarded as a total project concept that embraces the whole life cycle of a

construction project (e.g., CII, 1986; CIIA, 1993). In its present phase, buildability is

integrated with new production philosophy, for instance, as design for construction

(Egan, 1998). This concept is integrated with the developed methodology of new

production philosophies, such as total quality management (TQM) (Anderson, Fisher,

and Gupta, 1995; Russell, et al., 1994).

Design rationale As a narrowly focused concept with emphasis on

design for ease of construction and site productivity

A life-cycle concept As a total project concept, embracing the planning, design,

procurement, field operations, and maintenance

A methodology of new production philosophy Integration with philosophies, such as lean construction, concurrent construction and TQM

Fig. 2.1 Evolution of buildability concepts Source: Author

22

2.4. Buildability implementation

With the development of the buildability concept, various buildability concept

guidelines and principles were developed to integrate construction knowledge and

experience into different phases of a project development process. The practical

implementation of buildability was subject to the “push” and “pull” aspects that may

vary from one organization to another. The “push” aspect or the organizational aspect

(Section 2.4) placed the emphasis on management systems and the team-based

approaches. The “pull” aspect or the technical aspect focused on the IT-based

approaches (Sections 2.5 and 2.6) and attempted to combine these approaches with

organizational approaches to help design and construction organizations to fully

benefit from buildability implementation.

Various approaches and models were constructed to facilitate its implementation in

practice. Empirical studies were also conducted to examine the benefits and barriers to

implement the buildability concept guidelines, principles, approaches and models in

the practices developed, as well as gaps between potential and realized benefits of

buildability implementation.

2.4.1. Concept guidelines and principles

The CIRIA’s report (1983) identified seven categories of buildability principles in the

form of provisional design guidelines and as the basis for further research, discussion

and development. These principles included carrying out thorough investigation and

design; planning for essential site production requirements; planning for a practical

sequence of building operations and early enclosure; planning for simplicity of

assembly and logic sequences; detailing for maximum repetition and standardization;

23

detailing for achievable tolerances; and specifying robust and suitable materials.

Adams (1989) further developed the seven principles above into sixteen more definite

ones, which included: thorough investigation; considering access at the design stage;

considering storage at the design stage; designing for minimum time below ground;

designing for early enclosure; using suitable materials; designing for the skill

available; designing for simple assembly; planning for maximum

repetition/standardization; maximizing the use of plant, allowing for sensible

tolerances; allowing for practical sequence of operations, avoiding return visits by

trades; planning to avoid damage to work and subsequent operations; designing for

safe construction; and communicating clearly.

The CII of the USA conducted three research studies to investigate the ways that

construction knowledge and experience can enhance constructability during the

conceptual planning phase of a project (Tatum, Vanegas and Williams, 1986), the

engineering and procurement phase of a project (O’Connor, Rusch and Schulz, 1986a),

and the field operations phase of a project (O’Connor and Davis, 1988). Based on the

three studies, the CII of the USA (CII, 1987a) published fourteen constructability

concepts, which included the following across the three phases:

• Constructability concepts during the conceptual planning phase, including

constructability programs are made an integral part of project execution plans;

project planning actively involves construction knowledge and experience; the

source and qualifications of personnel with construction knowledge and experience

varies with different contracting strategies; overall project schedules are construction

sensitive; basic design approaches consider major construction methods; and site

layouts promote efficient construction.

24

• Constructability concepts during the engineering and procurement phase, including

project constructability is enhanced when design and procurement schedules are

construction sensitive; designs are configured to enable efficient construction;

constructability is enhanced when design elements are standardized; project

constructability is enhanced when construction efficiency is considered in

specification development; constructability is enhanced when module/preassembly

designs are prepared to facilitate fabrication, transportation and installation; designs

promote construction accessibility of personnel, material and equipment; and designs

facilitate construction under adverse weather conditions.

• Constructability concepts during the field operations phase, including

constructability is enhanced when innovative construction methods are utilized.

The Construction Industry Institute, Australia (CII Australia) also developed twelve

constructability principles within the Australian context with the help of the CII of the

USA (CII Australia, 1993). These principles included: integration, construction

knowledge, team skills, corporate objectives, available resources, external factors,

program, construction methodology, accessibility, specifications, construction

innovation, and feedback.

Generally, the review of principles and guidelines provides the practical background

and general knowledge for developing the decision support system for buildable

designs.

25

2.4.2. Organizational approaches to buildability implementation

2.4.2.1.Total buildability management system

The CII of the USA (CII, 1987b) developed a total constructability management

system, which emphasized the commitment and adoption of a constructability program

and cost curve for the implementation of a constructability program. The total

constructability system includes three parts – a constructability program, the cost-

influenced curve and the constructability concepts. Within this system, the cost-

influenced curve emphasizes that the constructability program has to be started as early

as possible. The constructability program is the application of a disciplined, systematic

optimization of the construction-related aspects of a project during the planning,

design, procurement, construction, test, and start-up phases by knowledgeable,

experienced construction personnel who are part of the project team (Construction

Management Committee, ASCE Construction Division, 1991). This program

comprises of seven components: self-assessment, policy, executive sponsor,

organization, procedure, appraisal and database.

2.4.2.2.Program assessment, barriers and benefits

O’Connor and Miller (1994a) identified fifteen significant corporate and project

parameters that reflect effective constructability program implementation and further

developed a Constructability Program Evaluation Matrix that defines five distinct

levels of project maturity – no program, application of selected supports, informal

program, formal program, and comprehensive formal program. O’Connor and Miller

(1994b) also identified eighteen prevalent barriers to implementing a constructability

program at both the corporate and project level and provided a three phase cycle,

including identification, mitigation, and review, to treat constructability barriers.

26

Russell, Gugel and Radtke (1992a) conducted a comparative analysis of three different

approaches, which were used by clients to implement constructability programs. This

study concluded that the four elements, including client involvement and support, early

incorporation of construction knowledge and experience, contracting strategy and team

building are keys to successfully implementing constructability programs. This study

resulted in the development of a framework, which can calculate a cost/benefit ratio

reflecting the effectiveness and/or maturity of a constructability program, to measure

costs and benefits from implementing constructability.

2.4.2.3.Implementation guide

Based on the previous studies (O’Connor and Miller, 1994a, 1994b; Russell, Gugel

and Radtke, 1992a, 1992b), CII (1993) developed a constructability implementation

roadmap. The roadmap offered nineteen constructability implementation tools to aid in

acquiring early client commitment and support, developing efficient and effective

teamwork, and building and sustaining effective constructability management systems.

2.4.2.4.Other studies

Apart from the above-mentioned CII research, the National Cooperative Highway

Research Program of the USA also initiated a research to develop a systematic

approach and methodology for constructability review for transportation facilities. A

constructability review process (CRP) was developed by the IDEF0(1) modeling

technique (Anderson, Fisher and Rahman, 2000). Twenty-seven selected tools and

twenty-one constructability functions were integrated into the final CRP model and

(1) IDEF0 is a structural analysis and design technique.

27

road maps were provided to indicate the linkage between basic and future tools and the

constructability functions these tools support (Fisher, Anderson and Rahman, 2000).

Glavinich (1995) discussed the use of design-phase scheduling and in-house design-

phase constructability review to increase the efficiency of a design and achieve

improved constructability. Low and Abeyegoonasekera (2001) used ISO 9000 quality

management systems as a working platform for implementing buildability principles at

both the design and construction stage of a project.

2.4.3. Surveys on implementation

Vardhan and Yates (1992) concluded that the methods of buildability were minimally

practiced by the building industry and the need for the use of constructability has not

yet been fully realized. However, most of the research showed that buildability

concepts and approaches were practiced and their practical implementation had

reported a variety of benefits. An early survey by the University of Wisconsin of 56

contractors indicated that 71% had a buildability program and estimated savings of

6.4% (CII Australia, 1993). Uhlik and Lories (1998) found that contractors applied

buildability concepts and participated in the earliest phase of the projects more often

than is thought. Eldin (1999) implied that adopting buildability concepts has the

potential for significantly reducing the project delivery time, for instance, up to 30%

without overall cost increase. Eldin (1999) also identified success factors,

implementation barriers and lessons learned for buildability implementation in

practice.

Previous studies also examined the gaps between the viewpoints of buildability

concepts and their practical applications. Nima, et al. (2001) revealed that the

28

Malaysian construction professionals had a wide understanding of the majority of

buildability concepts but they seldom applied these concepts in practice. Jergeas and

Van der Put (2001) indicated that the gaps between potential and realized benefits of

buildability implementation existed in the involvement of contractors in the design

phase, building mutual trust, respect and credibility between project planners,

designers, and contractors, willingness to adopt approaches that bring contractors into

the project from the very beginning, and willingness to try new approaches in the

interest of achieving significant gains in project cost, schedule, performance, and

safety. They further implied that significant gains in project costs, schedule,

performance, and safety could be achieved when the above gaps are filled.

2.5. Knowledge management in buildability

The studies reviewed in section 2.4 placed emphasis on concept guidelines and

principles, management systems, teamwork, client involvement and provision of tools

and methods. Along with these studies, recently researchers have focused much of

their research on the applications of information technology (IT) in practical

buildability implementation (e.g., Skibniewski and Arciszewski, 1997; Luiten and

Fischer, 1998; Yu and Skibniewski, 1999a, 1999b). In particular, IT is able to aid in

knowledge management in construction through acquiring, processing and utilizing

buildability knowledge and information (Skibniewski and Arciszewski, 1997). Thus,

research in this domain is divided into and reviewed as four topic areas: knowledge

classification, knowledge acquisition and knowledge representation and computerized

systems for knowledge management.

29

2.5.1. Knowledge classification

Knowledge classification is the starting point of knowledge management in

buildability. Several knowledge and information classification systems were developed

in this area with different emphasis.

In the arena of construction technology, Tatum (1988) proposed a classification system,

which includes the four major components: material and equipment resources;

construction-applied resources; construction processes; and project requirements and

constraints. Each of these components is further defined by elements and attributes.

This classification system provides a useful tool to measure technological change and

analyze specific operations for potential improvement. Ioannou and Liu (1993)

developed the Advanced Construction Technology System (ACTS). This technology

system provided classification of new technologies based on the Construction

Specification Institute’s CSI Master format in a database with facilities for searching

keywords.

In the arena of structural designs, Fischer (1991) and Fischer and Tatum (1997)

developed a framework of constructability factors for preliminary design of reinforced

concrete structures. These factors are grouped into endogenous and exogenous factors.

Endogenous factors were related to design variables (e.g., the dimensions of a beam)

and were under the control of the designer. Exogenous factors are beyond the control

of the designer (e.g., route restrictions of site). To make the design-relevant

constructability knowledge available to designers at the right time during design

development, Fischer (1991) and Fischer and Tatum (1997) further divided this body

of knowledge into the following five groups: application heuristics, layout knowledge,

30

dimensioning knowledge, detailing knowledge, and exogenous knowledge. Lueprasert

(1996) and Skibniewski, Arciszewski and Lueprasert (1997) developed a knowledge

classification space for conceptual structural design. The knowledge was classified into

two major categories: (1) structural data, which was further classified into three

categories, structural (e.g., dimensions, reinforcement ratio), relational (e.g., position,

orientation, relationship), and others (e.g., identification, physical characteristics,

differences between connected members, main connection’s characteristics); and (2)

preliminary construction conditions, which included equipment availability, material

availability, crew availability, and construction period.

More broadly, Hanlon and Sanvido (1995) developed a comprehensive

Constructability Information Model (CIM) for the whole life cycle of a construction

project. The resulting CIM is a hierarchical breakdown of constructability concept

attributes grouped into categories and attributes. The major categories include design

rules, lessons learned, external constraints, resource constraints, and performance

information.

2.5.2. Knowledge acquisition

Acquisition of buildability knowledge within a proper classification system is the key

to effectively managing and applying buildability knowledge (Fischer and Tatum,

1997). The conventional knowledge acquisition techniques, including voluntary

survey, questionnaires, interviews, pre-construction meeting notes, and final project

reports, were discussed and analyzed by O’Connor, Larimore and Tucker (1986b). In

particular, O’Connor, Larimore and Tucker (1986b) recommended that the interview is

an effective approach to identifying ways in which designs may become more

31

construction-sensitive. The conventional knowledge acquisition techniques were used

by researchers (e.g., Fischer, 1991; Malek, 1996) to acquire buildability knowledge.

Knowledge acquisition is the major bottleneck for computerized buildability analysis

(Skibniewski, Arciszewski and Lueprasert, 1997). In order to remove the knowledge

acquisition bottleneck for computerized buildability analysis, automated knowledge

acquisition techniques were adopted by researchers (Lueprasert, 1996; Skibniewski,

Arciszewski and Lueprasert, 1997) to acquire buildability knowledge. For instance,

Lueprasert (1996) and Skibniewski, Arciszewski and Lueprasert (1997) developed an

inductive learning system through the learning for examples program called AQ15 to

acquire and generate formal buildability knowledge. Yu and Skibniewski (1999a)

described a methodology for automotatic knowledge acquisition of construction

technologies through combing the neuro-fuzzy network-based approach with genetic

algorithms.

2.5.3. Knowledge representation

After the buildability knowledge is acquired, the knowledge should be organized in a

format desirable to its future use. The development of knowledge representation can be

divided into two phases. Early research focused on representing the general

buildability knowledge as design principles and concept guidelines that were intended

to stimulate designers’ thinking about buildability and how to make it work (see

Section 2.4.1). Recent research organized and represented buildability knowledge in

various formats that support computerized applications.

32

For instance, Fischer (1991) represented the constructability knowledge in the form of

explicit constructability knowledge in a way that is suitable for input to the design

process. The knowledge was represented through three main steps: formalization and

organization of constructability knowledge, development of a product model in the

form of a three-dimensional object-based CAD system to represent project data, and

integration of the product model with the constructability knowledge.

IF/THEN rules were also used to represent buildability knowledge in the knowledge

base. Lueprasert (1996) and Skibniewski, Arciszewski and Lueprasert (1997)

represented constructability knowledge in the form of decision rules. The knowledge

was represented as a collection of attributes and their values that were used to

characterize decisions regarding the problem under consideration. The typical decision

rule was exemplified as:

“If the following conditions are met:

(1) Reinforcement ratio of the beam is low.

(2) The second column-to-beam reinforcement ratio is low.

(3) Number of walls attached to the slab is one.

Then constructability evaluation of a beam is expected to be excellent.”

Malek (1996) represented the constructability knowledge as the Modus Ponens format.

The typical rule was exemplified as:

“If the acquisition cost of the construction system under consideration is low, Then the

constructability is high.”

33

2.5.4. Computerized systems for knowledge management

Computerized systems were developed to automatically manage and process available

buildability knowledge and information. Based on their various functions, the

developed systems can be grouped into four categories.

The first group used a database to manage known constructability knowledge (Navo,

Shapira and Shechori, 2000). For instance, CII Australia (1993) built a constructability

database, which contained examples of constructability savings on some Australian

projects. Individual companies can use the database to record their experiences so that

constructability can be improved in the future.

The second group attempted to integrate constructability knowledge and information

within automated design systems (Navo, Shapira and Shechori, 2000). For instance,

Alshawi and Underwood (1996) developed an integrated object-oriented system. Their

system was proposed to recommend the appropriate exterior cladding and lining type,

the gird layout, the column sizes, the floor to ceiling height and the beam sizes, check

the tolerance compatibility for the recommended exterior cladding and lining type, and

establish the optimum lining element for each cladding element, based on specific

information of the project. However, the system does not diagnose a given design

(Navon, Shapira and Shechori, 2000).

The third group analyzed existing design solutions from the executive perspective

(Navo, Shapira and Shechori, 2000). For example, Fischer (1991) developed the

prototype system COKE (COnstructability Knowledge Expert). The system can reason

about the geometrical and topological forms of a given design through constructability

34

heuristics and provide feedback on the constructability of the structural design of a

reinforced concrete building structure.

The fourth group provided two important functions of constructability analysis,

namely, to detect potential constructability problems in the early phase of a project and

then to find solutions for them (Yu and Skibniewski, 1999b). For instance, Navon,

Shapira and Shechori (2000) modeled a system to automatically diagnose potential

rebar-related constructability problems and offer solutions to the problems discovered.

Udaipurwala and Russell (2002) proposed a comprehensive decision support system.

The system can store and access construction domain knowledge through an intelligent

representation structure and formulate and access a project plan.

2.6. Buildability evaluation and reviews

A buildability review is a comprehensive analysis and assessment of all factors related

to the feasibility of a project through the reasonable use of available buildability

knowledge and information. Previous research has attempted to provide qualitative and

quantitative approaches to buildability reviews and evaluation. These approaches are

reviewed and discussed below.

2.6.1. The regression analysis approach

Touran (1988) used the regression analysis approach to measure the effects of

elements’ irregularities on formwork productivity. The following equation was used:

1

n

ij i ji

A X Y=

=∑ 2.1

Where: A = Area of the beam; X = Productivity rate; Y = Total man-hour; n = Total

number of known productivity rate; j = Floor number.

35

However, the use of the above approach for constructability evaluation has serious

limitations. The major weakness is that it is difficult to imagine a situation in

construction where productivity rates remain absolutely constant for every floor

(Malek, 1996). Touran (1988) also stated that the regression analysis was not

successful on the first few floors because there were too many variations.

2.6.2. The expert system approach

An expert system is an information system that follows human lines of reasoning,

expressed in rules (e.g., IF/THEN rules), to arrive at a conclusion from known facts

(Mallach, 1994). The approach is extensively used to solve the problems in the

construction industry, as well as in buildability reviews and evaluation. For instance,

Alkass, Jergeas and Tyler (1992) developed a PC-based prototype expert system,

called Constructability Assessment for a Detailed Design system to evaluate the

constructability of a design detail. Fischer (1991) also developed a prototype expert

system to aid designers in achieving a more constructable reinforced concrete

structural system.

However, the classical expert system techniques have their inherent drawbacks, which

include: they cannot solve the problems that involve our subconscious use of “common

sense” that does not map well into production rules of expert system techniques; their

domain of expertise is usually narrow; they are brittle at their limits; and, they may be

costly to develop, in terms of the total time of the human experts and other people

involved in the process of development. In addition to the above-mentioned

drawbacks, production rules in conventional expert systems are deemed to be either

applicable or not applicable. However, most practical buildability problems depend

36

heavily on intuitive thinking and professional expertise that usually have a large

variation of shades of gray as opposed to black and white colors (Malek, 1996). Thus,

the classical expert system techniques have their limitations in solving problems in the

buildability domain.

To overcome the inherent drawbacks of the traditional expert system technique, the

decision support system was developed by combining three techniques, namely QFD,

fuzzy set theories and fuzzy systems. QFD provides a framework to broaden the

expertise by integrating the different disciplines into the decision-making processes of

buildable designs. Fuzzy set theories were used to capture the “common sense”

involved in buildable designs. Fuzzy systems provide a more flexible, economical and

reliable way to utilize the knowledge and experience in buildable designs.

2.6.3. The artificial neural network approach

Artificial neural networks (ANNs) were developed to mimic the biological neural

systems in learning, association, and generalization from training patterns or data (Yu,

1996). Based on the fuzzy ANN approach, Yu and Skibniewski (1999a, 1999b)

developed a prototype computer system, named Construction Technology Selector, for

constructability analysis and improvement of construction technologies. The system

has two basic functions. Firstly, the system can automatically acquire the buildability

knowledge through the combination of fuzzy logic with the learning abilities of neural

networks and genetic algorithms. Secondly, the system can evaluate construction

technology alternatives through a neuro-fuzzy knowledge-based multi-criterion

decision support system.

37

ANNs, especially the neuro-fuzzy approach, are promising methods to solve

knowledge acquisition problems in buildability reviews and evaluation (Yu, 1996; Yu

and Skibniewski, 1999a). However, the methods have several limitations and these

include: ANNs are black-box methods; ANNs are prone to having overfitting problems

due to their typical, large parameter set to be estimated; tedious experiments and trial-

and-error procedures are often used in ANNs; ANNs usually require more data and

computer time for training; and ANNs are data-driven and model-free and hence they

may be too dependent on a particular sample observed (Zhang, Patuwo and Hu, 1998).

For constructability evaluation and reviews, the decision makers want to know not

only how buildable a project is, but also why it is not builable. However, ANNs fall

short in answering the latter question due to its drawbacks (Yu, 1996). Moreover,

ANNs are also difficult in providing a structured mechanism for buildability reviews.

2.6.4. The fuzzy approach

Fuzzy set theories, introduced by Zadeh (1965), are widely used to solve the ill-

structured design and construction problems as well as buildability problems. For

instance, Malek (1996) developed a constructability assessment model for selecting the

optimum construction system for project execution. Chao and Skibniewski (1998)

developed a fuzzy-logic based risk-incorporating approach to evaluating new

construction technology. Generally, the fuzzy approach is a feasible and promising

approach for buildability reviews and evaluation (Malek , 1996; Yu, 1996; Chao and

Skibniewski, 1998). In particular, the fuzzy approach can be used to develop a

structured approach for formal buildability reviews and evaluation. A further

description of fuzzy set theories is given in section 4.2.

38

2.6.5. The Buildable Design Appraisal System (BDAS)

The Singapore Buildable Design Appraisal System (BDAS) was developed by the then

Singapore’s Construction Industry Development Board (CIDB) with the help of

various government agencies, leading local and foreign contractors, consultants and

product manufacturers, and employed the productivity data inputs supplied by them

(CIDB, 1993). The three principles, namely, standardization, simplicity and single

integrated elements were adopted by the system for buildability assessment (CIDB,

1993). Depending on the extent to which the three principles are adopted, the appraisal

system awards a set of parameter values or indices for each type of structural and

architectural system and other buildable design details (Poh and Chen, 1998).

The appraisal system employs equation 2.2 to compute a buildable score.

BS = 50[ (As Ss)] + 30[ (Aw Sw)] + N× × 2.2

Where: As =Asa / Ast, and Aw =Awa / Awt; As = Percentage of total floor area using

a particular structural design; Ast = Total floor area which includes roof (projected

area) and basement area; Asa = Floor area using the particular structural design; Aw =

Percentage of total external and internal wall areas using the particular wall design;

Awt = Total wall area, excluding perimeter wall of the basement; all internal walls in

the basement are to be considered; Awa = External and internal wall areas using the

particular wall design; Ss = Labor saving index for structural design, Sw = Labor

saving index for external and internal wall design; N = Buildability Score for other

buildable design features.

The Buildability Score of a project, which may consist of more than one building, is

computed by equation 2.3.

39

( )( )

Ast buildingBS project=Sum of BS building × Ast project

2.3

Generally, the appraisal system provides a feasible quantitative method to assess the

potential impact of design on labor usage during the construction process. However,

the appraisal system was criticized for its internal shortcomings. These shortcomings

mainly include: the appraisal system does not consider any project-related and site-

related factors that can affect site productivity; the appraisal system also does not

consider unit construction costs (Poh and Chen, 1998).

2.7. Summary

In this chapter, the state-of-the-art buildability and constructability was described and

discussed. It is noted that the theme that runs through the various studies completed

was to provide tools, methods and ways to integrate construction knowledge and

relevant information into all phases (planning, procurement, design, construction and

use) of the project lifecycle in order to achieve optimum project goals and building

performance.

The research aims at developing a decision support system for buildable designs. The

review of the principles and guidelines for buildability implementation provides the

theoretical foundation to develop the knowledge management model for buildable

designs (KM-BD, see Section 5.4). The review of knowledge management in

buildability provides the ways for organizing the buildability knowledge and

information into a manageable format. The review of knowledge management also

reveals the suitable functions of the proposed system. An examination of buildability

40

reviews and evaluation shows the advantages and disadvantages of the various possible

approaches to developing the proposed system.