Evaluating the function of prefabrication in high-rise buildings Evaluación de la función de la prefabricación en edificios de gran altura

Prefabrication in a high-rise building can reduce construction waste. In this research, high-rise construction companies in Iran were studied, and the advantages and disadvantages of prefabrication were identified; then the development strategies of this industry were reviewed. For this purpose, the questionnaires were used to select the proper sub-systems for prefabrication. Delphi Snowball method was applied according to experts 'opinion, and these questionnaires were identified and adopted. Then the effect of prefabrication on non-structural components was examined on the extent of waste reduction. Consequently, the investigation results of waste production on a high-rise building revealed that prefabrication can reduce the cost of waste to 97.54%, and the total cost of the project would be reduced by 5.06% . luego se revisaron las estrategias de desarrollo de esta industria. Para ello se utilizaron cuestionarios para seleccionar los subsistemas adecuados para prefabricación. A partir de la opinión de los expertos se aplicó el método Delphi Snowball para identificar y adoptar los cuestionarios adecuados. Luego, se examinó efecto


Introduction
Sustainable development refers to the proper use of natural resources and environmental principles, and it can prevent problems such as degradation of natural resources and ecosystems, reduce in justice and environmental pollution, and enhance the quality of life. In construction, a reasonable use of energy and reducing the production of construction waste are considered to be the characteristics of eco-efficiency. Natural resource scarcity is no longer merely a remote possibility and governments increasingly seek information about the global distribution of resource use and related environmental pressures (Teixidó-Figueras et al., 2016).
One of the largest consumers of non-renewable resources is buildings, and many natural materials are being constructed around the world. At the same time, large quantities of waste from the construction or demolition of old buildings are being produced. While demand for construction increased, waste generation has become a major threat to the environment. Therefore, building management is necessary to reducing the production and recycling of construction waste. Extensive research has been conducted on various construction projects in this regard. markets and supports builders with financial support and focus on prefabrication and reform of laws (Mahpour, 2018); (Hong et al., 2018).
Prefabrication is an innovative construction method designed to minimize the construction activities on-site and transfer many activities to the factory to ensure about the development of a product with higher quality, safety, and a shorter project delivery time (Chauhan et al., 2019). The major difference between a prefabricated system and a conventional building system is that a large part of the building components is produced outside the construction site in the prefabricated system (Arif and Egbu, 2010); (Neill and Organ, 2016), and prefabrication is also safer and more environment-friendly compared to conventional construction, so This technology suits different types of construction projects (Steinhardt et al., 2019). Prefabrication is a highly beneficial approach with numerous advantages such as the short project delivery time, higher quality, higher control over the construction activities, workers' safety and improvement, environment-friendliness, and lower project costs (Lu, 2009). The construction industry can support prefabrication technology in many ways to improving productivity and performance (Tam et al., 2007), and there are numerous suggestions for improving productivity and the industry performs with the aid of the advantages of prefabrication technology over the conventional construction system (Bell, 2009). Various researchers defined productivity as the measurement of availability of resources for the attainment of a predetermined goal (Durdyev and Ismail, 2019); (Ghasemi Poor Sabet and Chong, 2019); (Ranasinghe et al., 2011). In addition, cost and time are known as the factors influencing the training of human forces in the prefabrication industry (Arashpour et al., 2018); (Wang et al., 2018), and economic advantage is one of the major reasons mentioned by the stakeholders involved in the construction process, so it is expected to considerably increase the delivery of prefabricated buildings. Besides, financial support can promote prefabrication technology, optimize the integration of prefabricated buildings, and improve market maturity in comparison with the traditional construction system (Hong et al., 2018). Although many studies have reported the advantages of prefabrication such as its simplicity, speed, and cost-effectiveness, but one of the reasons for the reduction in the market share in the construction industry is the limited diversity of the design of prefabricated buildings in the current condition (Kasperzyk et al., 2017).
The descriptive statistics tests of data were processed in Iran and the results showed that 53,445 ton of waste are annually generated in the city of Yazd, and the amount of cement and concrete, bricks, tile and ceramic (TC), ferrous metals, non-ferrous metals, glass, plastic, and wood are approximately 38%, 20%, 14%, 11%, 6%, 5%, 3%, and 3%, respectively. Regarding to the high volume of waste generated and a remarkable part of the recyclable waste, urban planners should pay attention to the implementation of waste reduction and recycling programs (Ansari and Ehrampoush, 2018).
As the main gap identified in the studied literature, the previous researches have mainly examined the benefits of prefabrication while its disadvantages, which could be an obstacle to future development, have not been assessed. Also, the impact of prefabrication on various components has not yet been studied; therefore, the study aimed at checking the waste indicators and related costs.
In this research, the feasibility for construction of components of buildings is analyzed, and the advantages and disadvantages of prefabrication and the possibility of its development are investigated. Then the amount and cost of building waste are compared with those of two methods of prefabrication and traditional method in a case study.

Material and Methods
In this research, the questionnaires were used at two phases. In the first step, the advantages, disadvantages, and the functional programs for the development of dry systems were checked, and in the second step, the proper subsystems for prefabrication were selected. Then by using Delphi Snowball method and according to experts' opinion, the questionnaires were identified and adopted. To prepare the two questionnaires, 10 experts with high professional backgrounds and degrees were employed, and the Likert range was used to prioritize the options.
From 4500 mass producers as the statistical population of the first questionnaire, 351 mass producers were sampled according to the Morgan table. The questionnaires were distributed by simple random method, and they were collected by the researchers. The questionnaires were distributed among the samples of the statistical population, and 228 questionnaires(65%)were answered (21 questionnaires were incomplete and 207 were completed). The prepared questionnaires include the advantages of prefabrication with 8 questions, the disadvantages of prefabrication with 10 questions, and prefabrication development applications with 7 questions; besides, experts were asked to determine which methods were chosen between the traditional, partially-prefabricated, prefabricated and modular to implement different components of a high-rise building. Finally, the waste cost was estimated in a case study of a high-rise building according to the information obtained. In this study, after studying the relevant sources, content validation method was used to determine the validity of the questionnaire; then the initial plan of the questionnaire was prepared, reviewed, and revised by several professors and experts; afterward the desired comments were applied, and the final questionnaire was compiled. Cronbach's alpha method was used to evaluate the reliability of the questionnaire. This method is used to calculate the internal coordination of the measurement tool that measures different characteristics. To calculate Cronbach's alpha coefficient, the variance of the scores of each subset of the questionnaire and the total variance was calculated. The closer the percentage is to 100%, the more reliable the questionnaire is; moreover, the amount of Cranbach's alpha obtained should be above 0.7 to ensure the reliability of the questionnaire so the Cronbach's alpha that was calculated for each research variable can be seen in (Table 1) and (Table 2). The results show that the all variables are acceptable.

3.Data Analysis
Before analyzing the questionnaires, the experts were questioned about the impact and value of the respondents on their professional experience records, educational level, and drying experience, and the impact factors were determined according to 10 experts' opinion. Experts valued the opinion of experts with a professional background of less than 5 years, 5-10 years, 10-15 years, 15-20 years, and a significant number of people with over 20 years, and their impact factors were 1, 1.1, 1.2, 1.3, and 1.4, respectively; furthermore, for the degree of education, the impact factors of 0.8, 1, 1.2, and 1.4 were proposed for associate diploma, bachelor's, master's, and doctoral degrees, respectively. The respondents with high prefabrication experience were known 50% greater than the subjects without prefabrication experience.
Among participants, 50 have associate diploma, 76 have a bachelor's degree, 56 have master's degrees, and 25 had doctorate degree, and all of these people were active in the field of construction and familiar with prefabrication; moreover, some of these people were contractors and had high executive experience in this field (106 people). A number of respondents also were designers in the field of construction, and they were not directly involved in prefabrication but had sufficient and necessary knowledge (101 people). In the following, the results, which have been extracted based on the questionnaire, are presented on the advantages, disadvantages, and solutions of prefabrication development.

Prefabrication Advantages
The advantages of using prefabrication in the building industry were arranged according to the Likert Table  pattern in the form of questions with five answers provided for the respondents. In (Table 3), the value of the opinions of the respondents was averaged, and the answer to each question was compared with the total average; furthermore, in the column of average value, the value was recorded, and the ranking was determined based on the average value in the last column. For ranking, any advantage with a higher average value number is ranked first up to the eighth in the final column, respectively. (Table 3) indicate that, with regard to the advantages of prefabrication , the experts ranked the shortened construction time with the average value of 1.15 as the top priority, followed by the increased ease and efficiency of the construction using modular repetitive parts with an average value of 1.08. Then improved environmental performance and minimizing construction waste with average value of 1.07, and better monitoring and improving the quality of work with an average value of 1 were ranked forth and fifth, respectively. Definitely, despite its many advantages, prefabrication has some disadvantages, which will be discussed further.

Disadvantages of prefabrication
According to (Table 4), the disadvantages of prefabrication were identified and prioritized. The participants responded to the importance of each item in this table, and the respondents' opinion values were summed up and averaged, meaning that with the answer to each question further compared to the average. The ranking of each disadvantage of prefabrication is presented in the last column, where the importance of each of the disadvantages was determined according to the experts. According to (Table 4), the lack of experience of local contractors; higher initial investment; lack of demand for prefabrication; lack of research information due to the novelty of this technology, and the lack of proper flexibility in design due to the presence of modular dry parts with ratings of 1.1, 1.07, 1.05, 1.03, and 1.02, respectively, were the most important disadvantages of prefabrication from the experts' perspective.
Considering the fact that prefabrication is one of the ways of eco-efficiency in construction, and the production of waste resulting from construction will be minimized with this technology; furthermore, functional programs for the development of prefabrication can support the sustainability of construction.

Functional programs for the development of prefabrication
According to the experts, important cases in the development of prefabrication in a high-rise buildings were determined by Delphi Snowball method; then the participants responded to each question according to (Table 5). In the ranking of future functional programs for prefabrication in high-rise buildings, the average number, which shown in (Table 5) for each program, represents the importance of each program in the development of prefabrication . The most important program according to the experts' opinion for the development of prefabrication in high-rise buildings was acquiring the knowledge of localization of the dry parts with an average value of 1.08, followed by making incentive decisions to expand the prefabrication with an average value of 1.06; then developing culture for protecting the environment in educational centers and governmental agencies using prefabrication with an average value of 1.04, and training and holding specialized courses in the design and implementation of dry parts with an average value of 1.02" accordingly. In adopting prefabrication, it is of particular importance to choose the appropriate dry system, which deals with the environmental problems stably to be implemented. This point is discussed further.

Selection of proper dry systems
Based on review of the feasibility study on various projects regarding the use of dry part production technologies, in recent years, designers and executives have shown a greater willingness to use industrial construction. In traditional ways of construction of buildings, the impact of human factors has been considerable while it has reduced the quality of the implementation of buildings. Industrial building techniques and the use of prefabrication lead to increased quality requirements; indeed, due to the mass production of parts in industrial methods, the efficiency of building production has increased, so the final product has a higher quality.
Expert opinions on the adoption of a dry method in the components of high-rise buildings are as follows; Prefabrication minimizes the construction activities on-site and transfer many activities to the factory to ensure higher quality and safety as well as a shorter project delivery time; in fact, the major difference between a prefabricated system and a traditional building system would be a large part of the building components produced outside of the construction site in the prefabricated system. In the Modular system, the building is installed as prefabricated volumetric parts.
In these questionnaires, each of the different components of the building includes traditional, partiallyprefabricated, prefabricated, and modular methods were investigated, and the respondents commented on the selection of implementation method of various components in high-rise buildings can be seen in (Table 6). The selection of the method for implementing the work in various components and sub-elements was asked from experts in the form of a questionnaire, and each expert chose one of the four methods for each sub-element. Then the number of respondents to each method in a particular element was divided by the total number of respondents, and the weight value of each method was obtained for different components. According to experts showed in (Table 6), the facade of the building, the execution of interior partition walls, tiling, masonry, flooring and plastering as prefabricated and partially prefabricated is the most appropriate method of execution. In the following, the cost of waste reduction in the prefabricated method compared to the traditional method is examined. (Figure 1) reveals the relationship between each method for a specific component.

Experts believe that the foundation and skeletons in the traditional form are much appropriate in Iran for highrise buildings, and the use of modular systems was not welcomed by experts. They showed a great deal of interest for using prefabrication for building installation systems, and the Partially-prefabricated exterior of the building was recommended along with the use of internal walls and plastering in dry and Partially-prefabricated conditions; in addition, experts believed that tiling in the kitchen and bathroom should be done in Partially-prefabricated manner.
Based on the results of ( Figure 1) as a case study, the cost estimation of waste in a high-rise building has been investigated further.

Estimating the cost of waste in a high-rise building
This section investigates the effect of prefabrication on high-rise buildings waste. For this purpose, in a case study, the cost of preparation of materials and the implementation of various components of a concrete structure (Twin Tower of Yazd) was specifically estimated. First, the volume and cost for various components such as concrete, fittings, non-structural parts, installation pipes, internal and external walls, plastering, flooring, tiling, and stoning were estimated; then given the exact recording of construction waste information in each section of the project, the cost of waste in various components that can be reduced by prefabrication were determined according to (Table 6). In a building, which has an area of 36000 m 2 of infrastructure and has been implemented in 22 stories in a traditional way, about 2800 tons of wastes are produced (based on the manufacturer's documentation), and (Table 7) provides the various components of the building, the amount and volume of materials consumed, the unit price of consumables, the average level of waste in the traditional and dry state, the percentage reduction in construction waste in the dry state, and the total amount of waste in dry and traditional states for various components; in addition, the waste costs in the traditional and dry states as well as the waste cost reduction in the case of prefabrication and the waste cost reduction in dry state were determined.  Based on the calculations in (Table 7), the following result is considered with prefabrication: While the total cost of the project is reduced by 5.06%, the most effective component was plastering (2.43%), and the lowest one was tiling and stoning (0.22%) (Figure 2).

Figure 2. Cost reduction in the use of prefabrication in various non-structural components
The highest environmental efficiency in the use of prefabrication is related to plastering with 99.2%, and the lowest efficiency in using prefabricated buildings with 95.03% is related to tiling and stoning (Figure 3).

Figure 3. Ecoefficiency in the use of prefabrication in various non-structural components in the study
In the studies, the foundation and the skeleton as well as ceiling are considered as traditional form while the non-structural components are regarded as the dry state. The results of ( Table 7) indicate that if the skeletons and ceilings are traditionally executed according to experts (Table 6) and the rest are implemented in prefabrication states, the cost of waste would be reduced by 97.54%.
In prefabrication, the plaster board for walls and ceilings, AAC blocks for interior and exterior partition walls, and ceramics with mechanical connections for building facades are used. In the prefabrication, estimation of materials is more accurate than traditional construction, and quality of construction is better and change of maps is a little; hence, the amount of construction waste is few. In the current study, the total cost of the project was reduced by 5.06%, and environmental efficiency in the background for the reduction of construction waste production was determined to be 99.2%.

Conclusion
Reduction or conversion of construction waste in the construction industry is an important issue. In this regard, prefabrication is one of the ways to reduce construction waste, and there is still a problem in the construction of building in a dry method, yet the adoption of prefabrication can reduce both the waste and construction costs. In this research, the advantages, disadvantages of prefabrication, and its development strategies were determined. For this, waste costs in both traditional and prefabrication was determined by adopting prefabrication in non-structural components of high-rise buildings, so the waste cost would be reduced to 97.54%, and it can probably prevent problems such as degradation of natural resources and ecosystems; reduce environmental pollution; and enhance the quality of life. In construction, a reasonable using of energy and reducing the production of construction waste are considered to be the characteristics of eco-efficiency; therefore, the total cost of the project was reduced by 5.06%, and environmental efficiency for the reduction of construction waste production was determined to be 99.2%.