Constructability and Structural materials selection

2.5.1 Definition and principles of Constructability

The term ―constructability‖ in US and the equivalent concept ―buildability‖ in the UK emerged in the late 1970s. This concept is employed and defined by many organizations.

 The Construction Industry Research Information Association (CIRIA) definition

Constructability is the extent to which the design of the building facilitates ease of construction, subject to the overall requirements for the completed building (CIRIA, 1983).

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 The Construction Industry Institute (CII) definition

Constructability is the effective and timely integration of construction knowledge into the conceptual planning, design, construction, and field operations of a project to achieve the overall project objectives in the best possible time and accuracy at the most cost-effective levels (CII, 1993).

 CIIA definition

Constructability is 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 (CIIA, 1993).

 Singapore BCA definition on Buildability

Buildability is the extent to which the design of a building facilitates ease of construction as well as the extent to which the adoption of construction techniques and processes affects the productivity level of building works (BCA, 2011a).

Although the definition of buildability given by BCA is similar to the definition of constructability given by CIRIA (1983), the implications of buildability and constructability are different. In Singapore, the BDAS focuses on the use of buildable designs during the upstream design process to bring about greater productivity improvements, while CAS is used to tackle improvements in downstream construction methods. Designers‘ attention to buildable designs has to be complemented with builders‘ adoption of labor- efficient construction technologies to bring about greater ease in construction.

It means that BDAS and CAS mainly emphasize labor-efficiency both upstream and downstream. Therefore, neither the buildability concept nor the constructability concept adopted by Singapore BCA is appropriate for this study because the implications are too narrow.

Among all these definitions, the CIIA definition was adopted to explain the

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concept of constructability as it takes environmental constraints into account.

The principles of constructability are given by O‘Connor et al. (1986) and Trigunarsyah (2007):

 Design and procurement schedules are construction driven;

 Designs are simplified to enable efficient construction;

 Design elements are standardized;

 Owner, designer and constructor personnel review specifications in detail;

 Pre-assembly work is scoped in advance and module/pre-assembly designs are prepared to facilitate fabrication, transport and installation;

 Designs promote accessibility of manpower, material and equipment;

 Designs facilitate construction under adverse weather conditions.

Singapore BCA states Standardization, Simplicity and Single integrated elements (3S) are the principles of buildability, which is mainly measured by labor saving. However, other than labor saving, there are several aspects are implied in constructability concept, such as resource accessibility (O‘Connor et al., 1986; Trigunarsyah, 2007), construction quality and safety (Ugwu et al., 2004).

2.5.2 Evaluation of constructability performance 2.5.2.1 Evaluation by Singapore BDAS and CAS

Singapore has pioneered the quantification of buildability based on two schemes known as the Buildable Design Appraisal System (BDAS) (BCA, 2004) and Constructability Appraisal System (CAS) (BCA, 2011a). It has culminated in statutory requirements for building designs to fulfil a Minimum Buildability Score and a Minimum constructability score. Under the Building Control Act, the requirement is a prerequisite for approval of submitted

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The 3 key design principles on which a design is judged for buildability include Standardisation, Simplicity and Single integrated elements.

 Standardisation refers to the repetition of grids, sizes of components and connection details. A repeated layout, for example, will facilitate faster construction regardless of whether formwork or pre-cast components are used. Similarly, columns or external claddings of repeated sizes will reduce the number of mould changes whether on- site or in the factory.

 Simplicity means uncomplicated building construction systems and installation details. A flat plate system, for example, eases formwork construction as well as reinforcement work considerably. Use of pre- cast components reduces many trade operations on site and should improve site productivity, provided the standardisation principles are observed.

 Single integrated elements are those that combine related components together into a single element that may be prefabricated in the factory and installed on site. Pre-cast concrete external walls, curtain walls or prefabricated toilets are good examples of this.

In BDAS and CAS, the Buildability scores and Constructability scores are given according to the relative extent of labor saving that can be achieved by the use of different construction systems. Projects with higher scores are generally more buildable and fewer site workers are needed by the same contractor.

2.5.2.2 Evaluation by other studies

By reviewing the constructability assessment works of CII, Ugwu et al. (2004) concluded that an enhanced constructability process includes:

 Reduction in costs;

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 Enhancement in the quality of the constructed facility;

 Improvements and shortening of the project schedule through encouraging innovative construction techniques;

 Improvements in safety during construction;

 Reduction in change and work orders;

 Reviewing projects during design to identify constructability issues as part of the value engineering process, which leads to significant savings in the project through improved productivity and reductions in claims, disputes and litigation?

2.5.3 Indicators of constructability performance

With reference to the indicators addressed in section 2.5.2, the 7 indicators of constructability performance can be summarized as follows:

 Construction costs saving;

 Labor saving;

 Construction schedule shorting (faster construction speed);

 Construction safety improvements;

 Element standardization, pre-assembly work and prefabrication;

 Accessibility of manpower, material and equipment;

 Ease of transportation and installation of elements.