Formwork system selection model using structural equation modeling and rough multi criteria decision-making methods

Abstract

The formwork system (FWS) is a temporary structure which provides the required geometry and strength to the cured concrete. In addition, the FWS may be the most critical aspect in building construction projects since it may significantly affect the time, cost, quality, safety, and sustainability performance of a building construction project. Therefore, selecting the most appropriate FWS may significantly improve these performance factors in reinforced concrete (RC) construction projects. This dissertation is planned as a cumulative work consisting of five published scientific articles and is framed within the FWS selection problem for RC building construction projects. The main goal of this dissertation is to develop a FWS selection model for building construction projects. For this purpose, the first article (Chapter 2) intends to identify and analyse the different industrial FWS supply chain configurations (SCCs) to minimize lead time and time waste in building construction projects. In addition, the selection of the FWS may depend on several criteria. Therefore, the objective of the second article (Chapter 3) is to identify and summarize the FWS selection criteria in a single body of knowledge by conducting a critical review of the literature. Based on the findings of the second article, the third article (Chapter 4) provided validation and applicability of the previously identified FWS selection criteria in the Turkish building construction sector through a questionnaire study. Furthermore, in the third article, the most important FWS selection criteria were determined, and the perception and perspectives of different construction professionals regarding the importance level of the FWS selection criteria were revealed. Based on the findings of the third article, the fourth article (Chapter 5) utilized a structural equation modeling (SEM) approach to identify the underlying FWS selection criteria groupings and their quantitative relationships. The fifth article (Chapter 6) proposed an integrated multi criteria decision-making (MCDM) model to solve the FWS selection problem, based on the findings of the preceding chapters. In addition, the effectiveness of the proposed approach is validated through a real-life case study. Finally, the dissertation was completed with conclusions derived from the results of these articles and recommendations for further research (Chapter 7). The first article identifies and analyses industrial FWS SCCs using value stream mapping (VSM). The roles and responsibilities of the main stakeholders (e.g., engineer, contractor and FWF) can be represented by the different SCCs. First, three SCCs for the industrial FWS in the Turkish RC construction sector were identified and described as process maps. Then, these SCCs were analysed based on data obtained from a real-life case study using VSM, an effective lean tool for identifying and eliminating waste. The findings indicated that the SCC where the FWF was involved early with the engineer and contractor at the design stage of the building construction project had higher performance (i.e., low time waste and less lead time) than the other SCCs. As a result, the study concluded that early involvement of the FWF in the decision-making process for selecting the FWS is critical for minimizing waste and improving project time performance. Numerous studies have been conducted since the early 1990s to identify the FWS selection criteria and/or to develop MCDM methods to solve the FWS selection problem. To date, however, no research has conducted a critical review of previous literature addressing the FWS selection criteria in building construction projects. The second article fills this important knowledge gap by undertaking a critical literature review utilizing an integrated approach. In the scope of the second article, a total of 26 studies were systematically analyzed, and 35 FWS selection criteria were then identified. These 35 criteria were divided into five main categories: structural design, project specifications, local conditions, supporting organization, and FWS characteristics. The study showed that "speed of construction", "type of concrete finish", and "initial cost of FWS" were the most frequently cited FWS selection criteria in building construction projects. Furthermore, the majority of FWS selection criteria under the structural design and FWS characteristics categories are interdependent, according to interviews. Consequently, these interdependent criteria should not be evaluated separately when selecting the FWS. The findings of the second article provide a comprehensive guide for FWS selection criteria in building construction projects, assisting construction professionals and practitioners (e.g., formwork designers) in selecting the most appropriate FWS for their projects. In the scope of this dissertation and future studies, these criteria may also be utilized in MCDM methods to select the most appropriate FWS for building construction projects. The FWS is selected by construction professionals with varying technical and/or administrative backgrounds. Depending on their motivations, the perspectives and perceptions of construction professionals and companies involved in the FWS selection process may differ. Furthermore, several building structural parameters may significantly impact the FWS selection criteria. Most previous studies investigated the FWS selection criteria only from the contractors' perspective, neglecting potential differences in perspectives and perceptions between construction professionals of different backgrounds. The main objective of the third article is to identify the critical FWS selection criteria, as well as the differences in perception and perspectives regarding the relative importance level of FWS selection criteria among construction professionals and companies specialized in different fields. In this regard, the third article is a continuation of the second since it employs the previously identified 35 FWS selection criteria in a questionnaire study of the Turkish building construction sector. The questionnaire data collected from 222 Turkish construction professionals were statistically analyzed. The findings of the third article revealed that the formwork design and/or formwork sales engineers (FD/FSL) group showed significant statistical differences regarding the FWS selection criteria as compared to all other groups. There were statistically significant differences between formwork and scaffolding companies and employees of these companies and the other groups, particularly among structural design and FWS–FWF characteristics-related criteria. Since involving the FWF with other stakeholder groups during the design phase can improve the performance of a building construction project (see findings of the first article), the perspectives and perceptions of the FD/FSL group or the FWF group should be considered alongside other groups of construction professionals and companies. In addition, the "speed of construction", "hoisting equipment", and "labour productivity" in building construction projects were all affected by project size (i.e., total area of building construction) and total building height. As a result, decision-makers and construction professionals may need to include these FWS selection criteria and the appropriate building structural parameters in the FWS selection process to improve the project's performance factors. Finally, it can be concluded that the third article serves as an additional validation of the applicability of the FWS selection criteria identified in the second article. The impacts of FWS selection criteria groupings, such as structural design and local site conditions, on the FWS selection process investigated in the literature are based primarily on expert knowledge, with no quantitative evidence or connection to the identified FWS selection criteria. Furthermore, the impacts of the selected FWS on time, cost, quality, and productivity performance factors have been primarily investigated using case studies' data. As a result, the main objective of the fourth article is to quantitatively identify the relationships and interdependencies among the FWS selection criterion groupings and their quantitative impacts (i.e., direct and indirect effects) on the performance factors. The questionnaire data from the third article were statistically analyzed, and five latent factors were revealed: FWS-FWF characteristics, structural design, local conditions, cost, and performance indicators. Based on these latent factors, a conceptual framework was constructed, and a SEM approach was used to determine the hypothesized effects of the latent factors. The SEM approach supported all hypothesized direct and indirect effects, with FWS-FWF characteristics having the highest direct effect on performance indicators, followed by its direct effect on cost. Furthermore, the structural design had a significant direct effect on FWS-FWF characteristics and indirect effects on performance indicators and cost. In other words, the effects of the structural design and the local site conditions on the FWS-FWF characteristics and the effects of FWS-FWF characteristics on the cost and the performance indicators are quantified in the fourth article. Therefore, it is considered a substantial contribution to the existing body of knowledge on FWS selection criteria in building construction projects. The main objective of this dissertation was to develop a FWS selection model to improve the performance of RC building construction projects. Therefore, the fifth article concludes the dissertation by proposing an integrated MCDM model based on the findings of the preceding articles in this dissertation. Several MCDM methods have been used in the literature to solve the FWS selection problem. However, none have considered the subjectivity and uncertainty that arise from group decision-making. In this regard, the fifth article proposes an integrated approach employing recently developed MCDM methods with rough numbers to fill this knowledge gap. The integrated approach starts with forming a decision-making team to develop the decision hierarchy. The rough analytic hierarchy process (R-AHP) is then used to calculate rough criteria weights. Subsequently, the rough evaluation based on the distance from average solution (R-EDAS) method is employed to rank the FWS alternatives. Finally, the results are compared using other rough MCDM methods to ensure that the proposed approach is consistent. The proposed approach is used to select the appropriate FWS for a real-life building construction project in Turkey. The integrated approach proved to be effective, and it was suggested that it should be employed in future FWS selection problems.