CHAPTER 6 RESULTS AND DISCUSSION (OBJECTIVES 1 TO 3)
6.7.1 Importance of the factors, criteria and attributes
The t - test results show that the selection of structural frames is significantly affected by the economic sustainability (EC), environmental sustainability (EN), and constructability (CP) performance of the structural material (see Section 6.3.1). Therefore, all of the three factors (EC, EN, and CP) in the first level of the hierarchy tree (see Figure 5.3) are significantly important and should be considered when making a decision on the selection of structural materials.
This result confirms the relevance of the theory of the firm and rational choice theory (see Section 4.2) in the selection of structural materials, as economic sustainability is a significant indicator to be considered when managers making decisions. In addition, it is found that the two theories do not fully apply to those projects (including HDB projects) because pursuing profits maximization is not the only target for those projects. Developers and contractors also care about environmental sustainability and productivity.
This result also supports the theory of corporate social responsibility (DTI, 2004), which states that private sector organizations should contribute to sustainable development goals (Section 4.3). The result in Section 6.3.2 shows that environmental sustainability is a significantly important factor to be considered when selecting structural material. However, it should be pointed out that Singaporean contractors currently do not exhibit strong ‗CSR‘
although many of them already started to recognize the importance of this issue because of the lack of incentive from government or clients, and may incur additional cost.
Furthermore, this result confirms the relevance of constructability (Section 4.4) in the selection of structural materials.
According to the t-test on the importance of criteria and attributes in Section 6.3.2, it was reported that six (EC3.2, EC4, EC5.3, EN1.2, EN1.4 and EN2) out of the 20 attributes are not significantly important when selecting structural material, while the remaining 14 attributes are significantly
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Under the factor of economic sustainability (EC), four out of the five criteria proposed in the conceptual framework are significantly important. They are structural costs (EC1), maintenance costs (EC2), non-construction costs (EC3), and additional incomes (EC5).
The end of life costs (EC4) is not significantly important for two reasons. The first reason is that the end of life costs of current projects is normally not paid by the clients, but by other future clients who buy these projects for redevelopment many years later. Thus the end of life costs is not important for the current clients when he has to choose between a SS frame and RC frame.
The other reason is that a building generally exists for more than 50 years, and it is hard to predict the costs for demolition at the end of building‘s life.
Corporate tax (EC3.2), an attribute under EC3, is not significantly important because the use of SS frame or RC frame does not really affect the amount of corporate taxes. Although using SS frame causes higher initial costs than RC frame (EC1), a SS framed project might bring in more incomes (EC5).
Therefore, the amount of corporate tax is not related to the structural frame material, but is dependent on corporate profit.
Possible incentive from BCA (EC5.3), an attribute under EC5, is not significantly important for the reason that none of investigated project had earned any incentive from BCA by using RC or SS frame.
Under the factor of environmental sustainability (EN), two attributes (EN1.2 and EN1.4) under material consumption (EN1) and one criterion (EN2) are identified as not significantly important.
The reuse rate of structural material (EN1.2) is not significantly important because it is not common to directly reuse structural elements derived from old projects in Singapore‘s construction industry. This might be because it is difficult to find old structural elements which have perfect size matched with the current project. Even if such structural elements were found, many stringent tests should be conducted to check whether the materials to be reused
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Reusability of structural material (EN1.4) is not significantly important for the similar reason described above. As it is hard to directly reuse the structural elements in future projects, both RC elements and SS elements are normally recycled instead of reused after the building is demolished.
CO2 emission during construction (EN2) in this study refers CO2 produced by constructing structural elements. EN2 is currently not significantly important for two reasons. The first reason for EN2 being not important in current decision process is that in the latest version of BCA Green Mark, points associated with reduction of CO2 emission are earned by saving on energy consumption during operation stage of a project, and no points could be given to reduction of CO2 emission during construction. However, it should be noted that its absence in the Green Mark Scheme is not because it is not important, but because the benchmark to measure and evaluate the extent of reduction of CO2 emission have not been established. The second reason is that the study on CO2 emission during construction is still in its infancy stage so the industry and the government do not have sufficient knowledge to build an inventory about CO2 emission during construction. This also explains why the benchmark for CO2 emission during construction has not been established.
However, given the current trend, this criterion will become more important for the reason given in Section 7.2.1. In addition, during the survey, nine experts pointed out that EN2 will become important for decision on selection of structural materials in the near future when information about CO2 emission during construction is available. Therefore, EN2 is kept in the DSSSSM for future application.
Under the factor of constructability (CP), all of the four criteria (labor consumption, construction duration, construction safety, and construction quality) are significantly important for selection of structural material. This finding support the principles of constructability given by O‘Connor et al.
(1986) and Trigunarsyah (2007), which highlighted efficient construction and accessibility of manpower. This result is also consistent with the findings by Ugwu et al. (2004), which pointed out construction safety and quality are
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implied in constructability concept. The importance of constructability is consistent with the many schemes such as BDAS, CAS, and CONQUAS that are implemented in construction projects in Singapore.