Energy consumption and carbon emissions assessment of integrated production and erection of buildings’ pre-fabricated steel frames using lean techniques

Journal of Cleaner Production 253 (2020) 120045

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Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro

Energy consumption and carbon emissions assessment of integrated production and erection of buildings’ pre-fabricated steel frames using lean techniques Gholamreza Heravi*, Milad Rostami, Majid Fazeli Kebria School of Civil Engineering, College of Engineering, University of Tehran, 16 Azar Ave., P.O. Box 11155-4563, Tehran, Iran

a r t i c l e i n f o

a b s t r a c t

Article history: Received 30 July 2019 Received in revised form 25 November 2019 Accepted 7 January 2020 Available online 8 January 2020

The growing development of the building industry and the significant contribution of the construction industry to global energy consumption and CO2 emissions demonstrate the need to apply techniques such as lean techniques aimed to reduce environmental impacts by reducing wastes. The present study, using lean techniques has tried to improve the processes of production, transportation, and erection of pre-fabricated steel frame (PSF) components in terms of the energy consumption and CO2 emissions. In this regard, value stream mapping (VSM), just in time (JIT), continuous flow, and total productive maintenance (TPM), as four lean techniques, are used aimed to identify and eliminate processes’ wastes and improve the resource efficiency. To assess the impact of applying lean techniques, the life cycle assessment (LCA) methodology outlined in the ISO 14040 is used. The results indicate that the energy consumption and CO2 emissions are reduced by 9.2% and 4.4%, respectively, that shows the ability to improve the environmental performance of the installation of PSFs by using lean techniques. © 2020 Elsevier Ltd. All rights reserved.

Handling editor: Zhen Leng Keywords: Life cycle assessment Lean techniques Value stream mapping Embodied energy consumption CO2 emissions Pre-fabricated construction

1. Introduction With the development of industrial construction, the environmental impacts of implementing industrial processes in comparison with conventional methods have been assessed in recent years (Ortiz et al., 2009). Now it is crucial to improve the performance of industrial construction methods by applying innovative methods such as lean techniques in order to achieve a more favorable environmental effect. The construction industry, with 40% of the total global energy consumption and 33% of environmental pollutant emissions, has excellent potential for reducing environmental impacts (Ouldboukhitine et al., 2011). Industrial construction is a suitable way to reduce the environmental impacts of construction processes according to its ability to improve construction performance by employing lean techniques compared to conventional methods (Aziz and Hafez, 2013). In this regard, industrial construction using lean techniques can be one of the best

* Corresponding author. E-mail addresses: [email protected] (G. Heravi), (M. Rostami), [email protected] (M.F. Kebria). https://doi.org/10.1016/j.jclepro.2020.120045 0959-6526/© 2020 Elsevier Ltd. All rights reserved.

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ways for reducing environmental impacts and embodied energy consumption of the construction phase (Jin et al., 2018). Industrial construction is a system that uses more innovative techniques and processes in which the structural components are manufactured in a factory, transported to the final location and assembled there, that would be an acceptable alternative for reducing energy consumption by eliminating wastes (Mroueh et al., 2001). Lean techniques include a set of techniques that are aimed at improving the current mode of industrial construction by eliminating wastes and increasing resource efficiency and equipment (Womack and Jones, 2005). Lean construction by reducing energy dissipation causes improvement in construction efficiency by increasing the rate of resource utilization and reducing idle time of processes through implementing processes at the right time with the right quantity (Heravi and Firoozi, 2017). LCA is a technique for assessing the environmental effects related to all the stages of a product’s life, which include raw material extraction, materials processing, production, transportation, use, repair, maintenance, and disposal or recycling (Li and Chen, 2017). The building industry in Iran, with 30 percent of the total economy and 40 percent of energy consumption, has a significant role in the economic and environmental status of Iran

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(Abbasianjahromi and Talebian, 2018). Also, the construction industry has the potential for significant improvements because of its easy access to natural resources for the production of materials and the low cost of materials compared to other countries. However, due to the low energy cost and the lack of incentives to develop new construction techniques, the energy consumption at the construction stage is five times higher than the global average, which is a result of little attention given to the efficiency of the construction industry (Road, Housing & Urban Development research center, 2019). Consequently, in Iran, like most other countries, using innovative techniques to reduce energy waste in the building industry is recognized as a crucial need. Considering the extended use of different techniques such as industrial construction and their significant environmental impacts compared to conventional methods, now it is crucial to improve the performance of the industrial construction in order to achieve a more favorable environmental effect. The purpose of this study is to investigate the effect of applying lean methods, including VSM, JIT, continuous flow, and TPM in order to reduce the environmental impact of production, transportation, and erection of PSF components of a residential building. The lean methods are implemented at an eight-story residential building located in Tehran to integrate the production, transportation, and erection processes aimed at reducing the processes wastes. Considering the production, transportation, and erection processes as a continuous flow of activities provides the opportunity to adjust the processes above based on their capabilities and requirements, which lead to efficient use of resources. Installation of the PSFs of residential buildings is selected as the target of this study because: (1) market share of steel structures in the construction industry in Iran is significant (Noorzai et al., 2016); (2) implementing lean techniques for industrial construction is feasible due to its process-based nature; and (3) the impacts of implementing lean techniques for the production, transportation, and erection of PSFs can be assessed using simulation techniques (Heravi and Firoozi, 2017). In order to evaluate the effects of applying lean techniques, all activities are evaluated into two different modes, including current and lean modes. The current mode is the common processes of the production, transportation, and erection of PSFs. In the lean mode, the lean techniques improve the current mode through two following phases after implementing VSM technique to integrate the production and erection processes as follow: (1) first lean phase: using JIT technique based on outputs of implementing VSM technique to improve the production process as well as integrate the production and erection processes, and (2) second lean phase: implementing TPM and continuous flow techniques to improve the erection process based on the integrated flow created in the first lean phase. In order to evaluate two modes, discrete event simulation (DES) is used. Finally, two modes are compared to assess the results of implementing lean techniques. In the current study, the LCA framework, which is recommended in the international standard organization (ISO) 14040 standard, is used to assess and compare the proposed modes in production, transportation, and erection of PSFs. The ISO 14040 standard assesses the life cycle of processes in four main stages, including goal and scope definition, life cycle inventory (LCI), life cycle impact assessment (LCIA), and interpretation (ISO, 2006). Due to the multi-stage construction processes of a building, LCA is a practical tool for evaluating the environmental impact of the construction processes (Ortiz et al., 2009). This paper structured as follows. It starts with a literature review and identifying the gap of knowledge in applying lean techniques for improving industrial construction processes. Then the next section provides the methodology used in the research. The article continues to implement the proposed method in a

residential building as a case study. Finally, the paper closes with conclusions in the last section. 2. Literature review Considering the importance of reducing the embodied energy consumption of construction processes of buildings, many studies have been focused on assessing embodied energy consumption during the life cycle of construction projects to reduce energy consumption and environmental impact of construction processes (Heravi and Qaemi, 2014). Some of them have tried to assess the effects of using modern construction methods, such as industrial construction or the use of innovative techniques such as lean techniques. However, the simultaneous use of lean techniques and industrial construction has been less considered. As a result, integrating innovative methods such as lean techniques and using appropriate construction methods such as industrial construction is known as a gap of knowledge. Relevant studies to the current research may be classified into the following three categories: 2.1. Using suitable construction systems Some of the recent studies focused on evaluating impacts of building materials from the environmental perspective. Wu and Sui Pheng (2011) evaluated the environmental effects of precast concrete columns in Singapore. They also stated that by recognizing the embodied CO2 emissions of different materials using the carbonlabeling program, the construction industry could move toward sustainability. Some studies evaluated the total embodied CO2 emissions of construction materials. Zhang and Wang (2016) assessed the embodied CO2 emissions of building construction. Their results indicate that materials of construction account for 80%e90% of the total embodied emissions. Also, some studies evaluated the environmental impact of optimizing the supply chain of materials. Gursel and Ostertag (2017) showed that environmental impacts reduced about 10e34% by importing materials from a nearer source. They performed a detailed LCA of concrete manufacturing in Singapore. Moreover, some studies compared the environmental impact of constructing concrete and steel structures as conventional building structures. Guggemos and Horvath (2005) showed that in the construction phase, concrete constructions have fewer pollutant emissions compared with steel frame constructions. Heravi et al. (2016) showed that the embodied energy consumption of concrete frame constructions in the construction phase is 27% less than steel frame constructions. Besides that, some studies evaluated the environmental impact of using sustainable materials during the construction phase. Sandanayake et al. (2017) showed that using sustainable materials like fly ash and blast furnace concrete reduces greenhouse emissions by about 12%. Soares et al. (2017) showed that using light steel frame (LSF) and thermal insulators, in addition to considerable operational energysaving, embodied energy did not show much increase. Some recent studies assessed the environmental impact of using pre-fabrication and industrial construction methods during construction processes. The results of these studies indicated the effect of using pre-fabricated and industrialized methods on reducing energy consumption and pollutant emissions (Mao et al., 2013; Monahan and Powell, 2011). Some studies evaluated and compared the wastes of different industrial construction systems. Firoozi and Heravi (2013) showed that insulating concrete forms have the lowest and steel frames with bolt and nuts have the highest wastes at the construction phase. Moreover, many studies have compared the environmental impacts of using industrial construction methods in comparison with conventional construction methods. Kawecki (2010) showed that the CO2 emissions of

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construction processes are reduced by up to 30% using the modular construction system. Monahan and Powell (2011) showed that by using a novel off-site panelized modular timber frame system, CO2 emissions reduced up to 51% compared with conventional masonry methods. Also, Mao et al. (2013) investigated the impacts of using PSFs on greenhouse gas emissions in comparison with conventional methods. They showed that by using PSFs, greenhouse gas emissions reduced up to 8%. Wen et al. (2015) compared the environmental effect of industrial construction method with conventional methods. They carried out a compatible LCA between two case studies; the results showed that the industrialized building system has more advantages in terms of reducing embodied energy and global warming potential (GWP). As a result, it can be seen that the application of industrial construction techniques, in comparison with conventional methods, reduces the environmental impacts of construction processes. Therefore, in addition to the need of evaluating the embodied energy of the different construction methods, which in recent research has been identified as a limitation and gap of knowledge (Wu and Sui Pheng, 2011), investigating ways to improve the performance of existing construction methods such as PSF and precast concrete construction is also very important. 2.2. Using lean techniques In recent years, some studies tried to implement lean techniques to reduce embodied energy consumption and CO2 emissions of the construction processes. Some studies tried to reduce the environmental impact of construction processes by using the VSM technique. Rosenbaum et al. (2012) used the VSM technique in the production phase of a hospital in Chile. They detected and quantified the source of environmental wastes and provided some suggestions for reducing wastes. Later, Rosenbaum et al. (2013) used a quantitative model of VSM to evaluate the execution phase of concrete construction. To reduce the waiting time and depot, they suggested lean techniques such as First-in and First-out. Roosen and Pons (2013) showed the use of the VSM technique at the production phase of a manufacturing plant. Fu et al. (2015) compared the environmental impacts of using lean techniques during the production phase of steel components. They used partial LCA framework to evaluate the environmental impact of the production phase. Wu (2014) evaluated the environmental effects of lean techniques on the erection stage of precast concrete sites. The results indicated that the lean techniques reduced the CO2 emissions in terms of removing wastes and inappropriate erection arrangement. Heravi and Firoozi (2017) evaluated the effect of using VSM on the production process of PSFs in a factory as a case study. They showed that by using the VSM technique, lead time of the production process might be reduced by 34%. Tommelein and Li (1999) used JIT technique in order to improve the supply chain of the construction phase of a concrete structure building. Also, Tommelein and Weissenberger (1999) drew on examples of typical structural steel supply chains from the industrial and building construction sector. Also, some studies tried to reduce the environmental impact of the production phase by using JIT technique. Kong et al. (2018) evaluated the impacts of using JIT technique for supply chain management of precast construction. Their results indicate the considerable effect of applying JIT technique on the environmental impact of construction processes. Also, some studies tried to focus on the fundamental elements for adopting offsite construction in different studies. Mostafa et al. (2016) tried to analyze and integrate existing knowledge from various literature. The results of their study indicated that limited attention was paid to lean principles and simulation integration within the off-site construction concepts. Moreover, Mostafa and Chileshe (2018) investigated the effects of client order on the performance of off-

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site manufacturing using DES. They developed and validated their DES model through interviewing. According to some recent studies, as well as some recent reviews (Jin et al., 2018), integrating industrial construction processes and using lean techniques to improve the environmental performance of industrial construction are recognized as the requirement, which has been introduced for further study. As a result, attention to improving the performance of industrial manufacturing processes through the integration of processes, as well as the application of different lean methods can be recognized as the gap of knowledge. 2.3. Integrating lean techniques with other techniques Some studies tried to evaluate the capabilities of using different lean methods and also the capabilities created by integrating lean techniques with other approaches, such as green building systems and sustainability development. Mostafa et al. (2015) tried to adopt lean principles and collectively integrate them into the maintenance processes. According to their research results, they found that the performance of a maintenance department can create more improvement opportunities. Henao et al. (2019) tried to evaluate the current trends concerning the effect of lean manufacturing on sustainable performance. The results of their review identified some knowledge gaps in using lean techniques aimed at promoting the manufacturing performance industry in the area of sustainable development. Moreover, some studies attempted to integrate pre-fabrication construction and building information modeling (BIM). Li et al. (2017) integrated lean construction principles, information technology, radio frequency identification, and building information modeling to reduce the uncertainties and remove the constraints of pre-fabrication housing production (PHP). Recently, Li et al. (2019) proposed a conceptual framework for the integration of BIM and PHP, reviewing 65 papers from 2005 to 2017. Saieg et al. (2018) tried to combine building information modeling, lean techniques, and sustainability to fill the gap targeting the architecture, engineering, and construction industry. Also, they conducted a literature review to understand the relations that have recently been explored by researchers between these fields (Saieg et al., 2018). Leon and Calvo-Amodio (2017) evaluated lean and sustainability approaches using literature review, more especially by using systems, relations, and the perspectives theory. Moreover, some studies evaluate the interactions of lean and green methodologies. Farias et al. (2019) systematized the relations between the green and lean methodologies to identify the relation of lean and green methodologies with performance criteria and how they could be integrated. Verrier et al. (2016) intended to enhance the previous studies by giving an implementation structure to lean and green methodologies based on seeking and eliminating wastes in production processes. Also, some studies tried to compare the performance of off-site construction techniques to conventional techniques. Jin et al. (2018) studied the performance of off-site construction compared to that of conventional construction approaches. Also, they reviewed the recent studies gaps in integrating off-site construction with either emerging construction concepts. They concluded that further studies are needed to integrate digital construction technology, project delivery methods, lean construction, and issues related to the sustainable development of off-site construction. Due to the gap in the previous studies on assessing the environmental impact of the integrating PSFs construction processes as well as the desirable results of previous studies on the simultaneous use of various techniques such as lean techniques, BIM, and information technology (Li et al., 2017, 2019), the environmental impact assessment of the use of lean techniques in the PSFs construction processes is useful to the profession.

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3. Methodology Lean techniques, through considering the waste elimination approach, are proper tools for reducing the environmental impacts of the modular and industrial construction processes. In this study, the main focus is on integrating production, transportation, and erection processes of PSF components through the application of the VSM, JIT, Continuous flow, and TPM techniques. Then, through using the LCA, the environmental effects caused by implementing this new construction method are assessed. The environmental impacts of the production, transportation, and erection processes are studied in current and lean modes. The current mode consists of conventional processes of production, transportation, and erection of PSF components. The lean mode includes the output of using the VSM technique to draw the current state map to identify the capabilities for further improvement. Then, in the first lean phase, the JIT technique is implemented in order to integrate the production and erection processes. The reason for applying JIT, as the first lean phase, is the need for an integrated flow to coordinate the production and erection stages. In other words, due to the need to adjust the erection processes based on the capabilities of the production stage as well as to adjust the production processes according to the requirements of the erection stage, the JIT technique is applied in the production stage, as the first lean phase. Then, in the second lean phase, TPM and continuous flow techniques are implemented to improve the current state map based on the integrated flow created by applying the first lean phase. ISO has issued a standard for environmental management in the 14000 series and published LCA methodologies (Finkbeiner et al., 2006). The LCA is a comprehensive tool and has been the base of many recent studies. Also, by adopting this standard, the LCA has found useful in the construction industry (Ortiz et al., 2009). The methodology of this study is consisting of the following three major stages:
Goal and scope definition: (1) goal definition involves the definition of objectives and application of the VSM, JIT, continuous flow, and TPM techniques, as well as LCA method; and (2) scope definition includes the definition of the product groups, the production, transportation and erection systems, defining boundaries, and the categorizing of input and output data.
Applying lean techniques: First, using the VSM technique tried to visualize the current mode aimed to identify the processes’ wastes. Based on the results of applying the VSM technique, in the lean mode the production processes must be adjusted based on the needs of erection processes. So, it is first and foremost to integrate the production and erection processes. As a result, the first lean phase is tried to adjust the production line of PSFs by placing some supermarkets between production stations as well as integrate the production and erection stages by placing a supermarket between these two stages. The Supermarket is an icon with a specific capacity to have a mean of giving accurate production instruction to the upstream process (Duggan, 2012). Due to the nature of each process and the ability to move human resources between stations, one can set up a supermarket between some processes. In the second lean phase, after creating an integrated flow between the production and the erection stages by placing a supermarket, the continuous flow technique is applied to carry out the erection processes simultaneously. Also, the TPM technique is implemented to group the human resources and equipment of the erection stage aimed to increase resource efficiency and reduce the wastes of equipment operations in the erection stage. Fig. 1 shows the implementation steps of the VSM, JIT, continuous flow, and TPM techniques.

Fig. 1 shows that implementing of lean techniques first begins using of the VSM technique to identify wastes; then, in two steps, first by implementing the JIT technique in the first step, and then by implementing the TPM and Continuous flow techniques, in the second step, while reducing the process wastes, the production, transportation and erection processes of the PSFs are integrated. ARENA simulation software is used to get the desired outputs of each process based on its inputs as well as to calculate the working and idle times of each process in different modes based on DES. In order to assess the impact of the using lean techniques, the energy consumption and CO2 emissions during the production, transportation, and erection of PSFs through the LCA framework are evaluated according to the following steps: Life cycle inventory: Inventory analysis involves collective and calculative actions in order to quantify relevant inputs and outputs of a product system (ISO, 2006). In this stage, inputs of resources and environmental outputs are aggregated for each activity. After identifying the LCI of the current mode (i.e., conventional methods of production, transportation, and erection of PSFs), the LCI of lean mode (i.e., lean modes of the production, transportation, and erection processes of PSFs), is identified for assessment and comparison in the next stage. Life cycle impact assessment: This phase of LCA using the LCI results tried to evaluating the significance of potential environmental impacts (ISO, 2006). The significance of the potential environmental impacts of a product system based on LCI results is evaluated by using LCIA. In this study, between various environmental impacts, CO2 emissions have been considered based on the importance of reducing CO2 emissions. According to international obligations, environmental protection and reducing the greenhouse gas emission, especially CO2 emissions, is considered as a global concern. The construction industry has excellent potential for environmental improvement due to its significant share of energy consumption and pollutant emissions, as well as the high capability of developing and applying eco-friendly methods. (Ouldboukhitine et al., 2011). In this regard, at this stage, both current and lean modes are examined to assess the impact of the use of lean techniques in reducing energy consumption and CO2 emissions. Interpretation: Interpretation is the last phase of LCA aimed to analyze the findings from the inventory analysis and the impact assessment together or only the inventory analysis. The results of the LCIA should be interpreted based on the objectives and scope of the study. In order to evaluate the results, the following steps are followed: Assessing the improvements of environmental performance: LCA is a practical instrument which is using for environmental improvement, strategic environmental planning, and making ecolabeling; so, it would be a proper tool for quantifying environmental impacts of the built environment and brings opportunities for reducing the environmental impact of the construction industry (Crawford, 2011). So, in this study, the LCA is used based on the results of the former stages, after integrating production, transportation, and erection processes of PSFs by implementing lean techniques in order to assess the reduction of energy consumption and CO2 emissions of the production, transportation, and erection processes of PSFs. Comparing results with previous studies: For validating the method of integrating production, transportation, and erection processes of PSFs using lean techniques, the produced results are compared to previous studies. Fig. 2 shows the study algorithm. As shown in Fig. 2, based on the LCA framework, first, the goal and the scope of the project are marked. Then, after implementing lean techniques, the next three steps of the LCA framework, including LCI, LCIA, and interpretation are applied in sequence. So,

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Fig. 1. Steps of Lean techniques.

using LCA framework is so useful due to its ability to be used simultaneously with the lean techniques, ability to consider different project stages (i.e., production, transportation, and erection processes) without location constraints, and considering a wide range of activities that increase the accuracy of the environmental analysis (Curran, 2012). 4. Application The project consists of an 8-story residential building with a total building area of 3720 m2, which is located in Tehran, Iran. The present study tried to assess the environmental impacts of using

lean techniques on energy consumption and CO2 emissions of the processes of production, transportation, and erection of PSFs of floors 5 to 8 with a total building area of 1610 m2 (112 tons of PSFs). The selected case is a standard sample of the residential buildings constructed in Tehran. The widespread use of this construction method for residential buildings helps the authors to generalize the obtained results to the residential buildings with steel frames constructed in Tehran. Floors 5 to 8 were built by a contractor responsible for production and erection stages. Due to the simultaneous implementation of the process of production and erection of PSFs by a single responsible company, improvement of the production and erection processes by integrating production,

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Fig. 2. The study algorithm.

transportation, and erection processes of PSFs is pursued seriously. Of course, due to the repetitive nature of the production and erection processes, extending the results is possible. The primary assumption of the present study is that the production factory is worked solely on this project and also in the DES; the duration of each activity is a fixed value.

4.1. Goal and scope definition In the present study, the impacts of the application of the lean techniques are evaluated to reduce the energy consumption and CO2 emissions, which are examined in the form of two current and lean modes (i.e., conventional methods and lean mode of the production, transportation, and erection processes of PSFs). The LCA data will be used to indicate the effectiveness and application of lean techniques to reduce the energy consumption and CO2 emissions during the production, transportation, and erection processes and compare two different modes.

4.1.1. Scope of the production processes at the factory Based on some previous studies, case study is a useful instrument for assessing “real world” examples and one of the best ways of providing detailed explanations of “best practices” (McCutcheon and Meredith, 1993; Ellram, 1996). In a case study, case selection and defining case design have a highly critical role (Yin, 2003). In this regard, in order to conduct a case study successfully after the literature review and defining the research question and selecting the research methodology, the case selection criteria should be clarified in order to choose a proper case based on the research €hko € nen, 2011). method (Ka The pre-fabrication factory is located in the western suburbs of Tehran. The factory is located in Safadasht industrial town, which includes most of the pre-fabrication factories in Tehran. This factory is selected because (1) its 20 years of experience in the production and erection of PSFs; (2) its responsibility for the production and erection of the PSFs for a typical building project in Tehran during this research time frame; (3) providing the ability to study the integrated production, transportation and erection processes of the PSFs; and (4) being an excellent example of a common prefabrication plant in Iran. Also, based on the different case designs that is defined (Yin, 2003), the current case design is a single case with a holistic perspective because of the focus of current research on implementing the lean techniques on production, transportation, and erection processes of PSFs as a single unit of analysis on a one typical residential building project as case study. The reason for selecting a single case with holistic approach is that the current study is focused on evaluating the environmental effects of implementing lean techniques on production, transportation, and erection of PSFs, which is a critical case to test a formulated theory and the selected case is a unique and previously inaccessible phenomenon, especially in Iran (Voss et al., 2002). Moreover, the current research is tried to reduce the limitations of using single case by using face-to-face interviews with multiple respondents, including several experts in the field of industrial construction and lean techniques, as well as factory officials in order to gather highly efficient and reliable data. The selected factory consists of one main production line, and only the welding processes of beams and columns are performed by using different welding rectifiers in two separate stations. Moreover, before transporting to the erection site, fabricated components have been checked by quality control department in order to fix the plausible defects. The related information to production line stations, human resources, and equipment used at each station are depicted in Table 1. Table 1 presented the human resources and equipment of production, transportation, and erection processes. Also, the power consumption of the equipment is presented in Table 4. 4.1.2. Scope of the transportation process The distance between the pre-fabrication factory and the erection site is 67 km. The average time to transport by 20-ton truck is 1.5 h, and the average fuel consumption of loaded trailers are 20 lit per 100 km. As depicted in Table 1, for loading and transporting PSFs, three trucks are used, and the components have been transported to the erection site in 10 trips as follows: columns in 4 trips; beams in 5 trips; and rolled steel profiles as braces in 1 trip. 4.1.3. Scope of erecting processes on site The on-site erection processes of PSFs are performed through five main stations. The related information to erection stations, human resources, and equipment used at each station are depicted in Table 1.

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Table 1 Stations, human resources and equipment of production, transportation, and erection processes. Process Production Cutting main parts Initial assembly Cutting and drilling Welding of columns Welding of beams Final assembly Drilling of main components Cleaning fabricated components Painting the fabricated segments Transportation Transporting components Erection Lifting and moving Pre erecting Bolting Plumbing Permanent connection a

Human resourcea

Equipment

2 4 3 3 3 2 3 2 1

One Flat cutting machine, one Computer numerical control machine, and one shearing machine Two Strapping, and two tack welding machine One Cutting machine, and two magnet drilling machine Four Shield metal arc welding (SMAW) machine Four Gas metal arc welding (GMAW) machine One CO2 welding rectifier Two Magnet drilling machine One Shaping machine One Airless machine

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Three Trucks

2 4 4 5 6

One tower crane, and one mobile crane One tower crane One elevator e Two impact spanner

Human resources are included ordinary worker, ordinary welder, skilled worker, skilled welder, painter, foreman, erection worker, and bolting worker.

4.2. Implementing lean techniques The VSM technique is used in the following three steps: (1) choosing production family; (2) drawing current state map; (3) and drawing a future state map. 4.2.1. Choosing product family First of all, the product families (i.e., groups of products produced through the same processes and use the same resources and equipment) that are studied in this research should be specified. In this study, three kinds of production families have been detected, which include columns, beams, and braces. 4.2.2. Drawing current state map One of the major types of waste is overproduction, which means production at each stage is more than the next stations’ requirement. In order to reduce these wastes, all production stations should be integrated. In this stage, after choosing production families, in order to reduce the wastes of the production processes of PSFs in the factory, the current state map is drawn. The current state map of production and erection processes are drawn by using information such as the number of processes, process times, and the resources in each process. In the current mode, the push production system has been used. The reason for using the push production system in the studied factory is the prevalence of this method for industrial plants in Iran, focusing solely on production with the highest capacity and applying earliest start approach to reduce the delay risks. The current state map represents the lead time, idle time, working time and the depot number for each station. Depending on the information obtained from the current state map, none-value-added processes are identified. None-valueadded processes are the processes with a high rate of idle time that increase energy consumption. The current state map of production and erection processes are depicted in Fig. 3. In the current state map, in addition to specifying the relationship between the stations, the processing time of each station for each of the product families is identified. Moreover, DES has also been used to calculate the idle and working times of production and erection processes. For instance, Fig. 4 shows the simulation of the production processes in the current state map. Considering the ability of the ARENA to simulate the industrial construction processes, the DES application is an appropriate tool for simulating industrial manufacturing processes. After drawing

the current state map to reduce wastes, some lean techniques are implemented through two phases. After applying the VSM technique, in the first lean phase using the JIT technique, one supermarket has been placed between the production and erection stages, in order to create a link between these two stages and leading the production progresses based on the requirements of the erection site by integrating production and erection stages. This supermarket creates an integrated pull production system. Then, in the second lean phase using the continuous flow and the TPM techniques, some of the erection processes are performed simultaneously, and the erection equipment is grouping according to their functions, which reduces the idle time of the erection stage processes. The aim of using the TPM technique is to reduce idle times and maximize resource efficiency by grouping the erection equipment. Moreover, using the continuous flow aims to reduce the total duration of the erection stage.

4.2.3. Drawing future state map In the current mode, conventional methods of production, transportation, and erection of PSFs are performed based on the push production system. The push production means production with maximum capacity and in mass terms, regardless of the level of customer demands. Also, the pull production system means production based on the demands of the customer and not based on the highest production capacity. In the lean mode, production, transportation, and erection processes are improved by implementing lean techniques. As a result push production system converts into a pull production system through placing supermarkets between production stations, and also production and erection stages are integrated by placing a supermarket between these stages based on the JIT technique. Applying the first lean phase, cause improvement in the idle time and depot of each process. Moreover, the future state map is tried to improve the erection stage in the second lean phase by applying continuous flow and TPM techniques. Fig. 5 illustrates the lean mode of integrated production and erection processes of PSFs. As shown in Fig. 5, in the lean mode, seven supermarkets are placed between the production stations in order to create the pull production system. The logic of the supermarkets which are located between the production stations are based on the ability of these stations to relocate human resources. According to this, seven supermarkets are placed between production stations, but there is no supermarket placed between the erection stations.

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Fig. 3. Current state map of production, transportation, and erection of PSFs.

After drawing the future state map, the idle time, Working time, and the depot of the production, transportation, and erection processes are computed for the assessment of the environmental impacts of the implemented lean techniques (Tables 2 and 3). As depicted in Table 2, the production processes are mostly affected by applying the JIT technique. In this regard, the idle time, working time, and depot of the production stage show significant improvement after implementing the JIT technique; however, according to Table 3, applying JIT (first lean phase) does not affect the erection processes. As depicted in Table 3, the erection processes are mostly affected by TPM and continuous flow techniques. The working time of the erection processes improved significantly after implementing TPM and continuous flow techniques (second lean phase). Also, according to Tables 2 and 3, the cleaning process, with 79% improvement, is mostly affected by implementing the JIT technique (first lean phase) and the bolting process, with 38% improvement, is mostly affected by implementing TPM and continuous flow techniques (second lean phase).

4.3. Assessing energy consumption and CO2 emissions Due to the development of the construction industry, the environmental impact of these processes is also increasing. CO2 is known as the most important pollutant released in recent years (Bilec et al., 2009). Consequently, CO2 is considered as the most important emitted pollutant in the present study. In order to evaluate the environmental effects of industrial construction using lean techniques, according to the methodology outlined in ISO 14040, the following steps are taken:

4.3.1. Life cycle inventory (LCI) The electrical consumption of the equipment used in the production line of PSFs at the factory is assessed in idle and working modes of each device using rules for three-phase alternating current circuits (Eq. (1)): Power ¼ I  3phase voltage  Power Factor  √3

Fig. 4. The DES model of the production in the current state map.

(1)

G. Heravi et al. / Journal of Cleaner Production 253 (2020) 120045

9

Fig. 5. Integrated stream of processes in lean mode.

Where, Power ¼ the power level of the equipment in the production stage (W); I ¼ input electric current of equipment (A); 3Phase voltage ¼ 380 (V); and Power Factor ¼ 0.7. The conversion relationships of electricity (KWh) (the average power output of Iranian power plants is 33%), and diesel fuel energy to GJ are as follows: 1 KWℎ ¼ 0.0036  3 GJ ¼ 0.0108 GJ

(2)

1 Lit gasoline ¼ 0.0386 GJ

(3)

GWP is a relative measure of the heat that greenhouse gas is stored in the atmosphere. This parameter compares the amount of heat constrained by a given amount of gas to the constrained heat by the same amount of CO2. It expresses in a scale of “tons of equivalent CO2” for the time interval of 20, 50, and 200 years. Given the values provided by the Intergovernmental Panel on Climate Change (IPCC), the GWP index for each Kwh of electricity produced by the power plants is equal to 696 g of CO2 equivalent (IPCC, 2013). The pollutant emissions per liter of consumed fuel are calculated

Table 2 The idle time, working time, and depot of the production process. Production processes Current mode

Using TPM & Continuous flow

Using JIT

Improvement (%)

Idle (day) Working (min) Depot (No) Idle (day) Working (min) Depot (No) Idle (day) Working (min) Depot (No) Idle Working Depot Cutting Initial assembly SMAW Welding GMAW Welding Sectioning Final assembly Drilling Cleaning Painting

49 20 5 4 9 11 39 24 0

197 303 300 40 428 312 227 212 130

124 42 3 16 19 17 87 55 0

19 7 3 1 4 6 15 3 0

189 232 180 30 428 312 170 141 130

40 15 2 5 7 17 32 7 0

19 7 2 1 2 6 15 5 0

189 232 180 30 428 312 170 141 130

40 14 1 3 4 17 32 12 0

61 65 60 75 78 45 61 79 0

4 23 40 25 0 0 25 33 0

68 67 67 81 79 0 63 78 0

Table 3 The idle time, working time, and depot of the transportation and erection processes. Transportation and erection processes

Loading Transporting Pre-erection Bolting Brace erection Plumbing Permanent connection

Current mode

Using JIT

Using TPM & Continuous flow

Improvement (%)

Idle (day)

Working (min)

Depot (No)

Idle (day)

Working (min)

Depot (No)

Idle (day)

Working (min)

Depot (No)

Idle Working Depot

0 0 25 0 0 15 0

60 90 77 8 15 960 10

0 0 60 0 0 236 0

0 0 25 0 0 15 0

60 90 77 8 15 960 10

0 0 60 0 0 236 0

0 0 25 0 0 15 0

60 90 62 5 14 630 7

0 0 60 0 0 236 0

0 0 0 0 0 0 0

0 0 19 38 7 34 30

0 0 0 0 0 0 0

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G. Heravi et al. / Journal of Cleaner Production 253 (2020) 120045

as follows: First, Brake Specific Fuel Consumption (BSFC) is calculated for each equipment, which means the fuel consumed by the engine per unit of power produced in 1 h: BSFC ¼ 239.89  PEngine

Table 5 Energy consumption in the production processes of PSFs. Equipment

Working Current mode SMAW rectifier Shaper Magnet drill Flat cutting Airless Guillotine MIG rectifier Seven-work Welder Overhead power Total Lean mode SMAW rectifier Shaper Magnet drill Flat cutting Airless Guillotine MIG rectifier Seven-work Welder Overhead Total

(4)

Where, P is the power of the engine in KW, and BSFC is according to gr per KWh. Then the CO2 emissions of equipment can be obtained as follows: CO2 ¼ 3.67  BSFC  Carbon precent in fuel

Time (h)

(5)

Where, CO2 is the level of CO2 emissions in gr, and the residual CO2 in fuel based on the National Iranian Oil Refining and Distribution Company is 0.1 percent (IFCO, 2018). Table 4 depicts the power consumption of all electrical and diesel engine equipment used in production, transportation, and erection processes. As depicted in Table 4, the CO2 emissions factor for each Kwh of electricity produced in Iran’s power plants is equal to 696 gr/Kwh (IPCC, 2013; IFCO, 2018). Moreover, the CO2 emissions factor for diesel engines is calculated according to Equations (4) and (5). The LCI of production, transportation, and erection processes of PSFs evaluated through the following three steps:
Producing PSFs at the factory: After calculating the working and idle times of each process according to the results of the DES using ARENA software as well as using the power consumed by each equipment (Table 4), the energy consumption for producing PSFs at the factory is evaluated. By using lean techniques, the production of PSFs has been improved by creating a pull production system that leads to reducing the idle time of each station. Table 5 depicts the total energy consumption of the production processes of PSFs at the factory. Table 5 shows the significant improvement in the production stage, which caused 42.9% and 4.6% improvement in the idle and the total energy consumptions, respectively.
Loading and transportation of PSFs to erection site: Based on the described scope of transportation process in section 4.1.2, the energy consumption in this process is as follows: (1) total

Energy consumption (KWh) Idle

Working

Idle

Total

1174.3 121.6 211.8 122 98 296.6 356.8 36.9 85 e 2503.0

0.15 28.56 53.99 0 63.81 14.48 0 5.83 8.31 176.45 351.58

5731.9 115 273 74.1 1345.6 4663.7 1741.8 402.9 816.5 e 15164.5

0.1 13.1 49.7 0 735 146.8 0 42.9 9.5 850.7 1848

5732 128.2 322.8 74.1 2080.6 4810.5 1741.8 445.8 826 850.7 17012.5

1173.2 121.1 211.8 122 98 296.6 357.1 36.9 85 e 2503

0.15 29.57 33.96 40.82 21.81 12.52 2.15 0.63 2.54 125.01 269.15

5727 115.5 273 74.1 1345.6 4663.7 1743.4 402.9 816.5 e 15161.7

0.1 13.6 31.3 18.8 251.2 126.9 1.4 4.6 2.9 602.7 1053.6

5727 129.1 304.3 93 1596.7 4790.6 1744.9 407.5 819.4 602.7 16215.3

fuel consumption is 269.48 Lit, and (2) total energy consumption is 10.4 GJ.
Erection processes of PSFs on site: After calculating the required time for each station in the erection stage of the PSFs and calculating the operation time of the equipment in both working and idle modes, the energy consumption and the CO2 emissions at this stage are evaluated considering Table 4. The erection processes are mostly affected by the TPM and continuous flow techniques, which improves the rate of resource utilization by applying the TPM technique and also creates the possibility of performing some of the erection processes simultaneously by applying continuous flow techniques. Table 6 shows the energy consumption of erection processes according to the working and idle times of the equipment. Table 6 depicts that by using lean techniques, the fuel consumption of the erection equipment is reduced significantly,

Table 4 The power consumption of the electrical and diesel engine equipment used in production, transportation, and erection processes. Equipment Production MIG rectifier Submerged arc welding machine SMAW rectifier Flat cutting Guillotine Shaper Magnet drill Airless painter Seven-unit machine Overhead power Transportation Truck Lift truck Erection Crane Impact Spanner Elevator Overhead Power a

Working power (KW)

Idle time power (KW)

Fuel Consumption

Emission factora

13.82 27.64 13.82 0.92 27.64 1.98 2.07 18.42 18.42 4.82

0.69 1.15 0.69 0.46 10.13 0.461 0.921 11.51 7.37 4.82

e e e e e e e e e e

696 696 696 696 696 696 696 696 696 696

371 68

277 50

0.20 (Lit/Km) 6.56 (Lit/h)

209.3 41.7

200 1.61 2.76 0.10

149 0.46 1.84 0.10

37.12 (Lit/h) e e e

120.6 696 696 696

The unit of emission factor is gr/Kwh for electrical equipment and gr/h for diesel engine equipment.

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Table 6 Energy consumption in erection processes of PSFs. Equipment

Time (h) Working

Current mode Crane Elevator Impact spanner Overhead power Total Lean mode Crane Elevator Impact spanner Overhead power Total

Idle

Energy consumption

Total energy consumption

Working

Electricity (KWh)

Fuel (Lit)

Energy (GJ)

Idle

55 15 75 39 184

8 1 5 e 14

2042 (L) 41.46 (KWh) 120.97 (KWh) 23.4 (KWh) e

297 (L) 1.84 (KWh) 2.30 (KWh) e e

e 43.3 123.3 23.4 189.98

2339 e e e 2339

90.29 0.468 1.331 0.252 92.34

44 14.2 48.7 34.4 141.3

6.4 0.9 3.2 e 10.5

1633 (L) 39.38 (KWh) 157.26 (KWh) 20.62 (kWh) e

237 (L) 1.64 (KWh) 2.99 (KWh) e e

e 41 160.3 20.6 221.9

1870 e e e 1870

72.19 0.44 1.73 0.22 74.58

although electricity consumption has been slightly increased. Finally, the total energy consumption in the erection stage is reduced by 19.2% compared to the current mode.

4.3.2. Life cycle impact assessment (LCIA) In this stage, after calculating energy consumption in different processes, the environmental impact due to reducing energy consumption is evaluated. Table 7 depicts the effect of lean techniques on the production, transportation, and erection processes of PSFs based on a reduction in energy consumption. As shown in Table 7, the power consumption in the idle mode is significantly reduced based on applying lean techniques. Finally, the reduction in energy consumption and CO2 emissions are 9.2% and 4.4%, respectively. The results indicate that the impact of using lean techniques on the energy consumption and CO2 emissions by the processes of production, transportation, and erection of PSFs. In addition to reducing the energy consumption and CO2 emissions, the total time and cost of the processes of production, transportation, and erection of PSF components are reduced by 42.3% and 17.1%, respectively. The primary cause of the improvements in the reduction of wastes (idle times) as well as integrating the production and erection processes using lean techniques. 4.3.3. Interpretation In order to interpret the results, the first step is to select the operational unit appropriately. In the discussion of energy consumption, the expression of the results as energy per unit area of the construction (GJ/m2) is one of the most widely used operational units. Also, regarding the CO2 emissions, the global warming effect or kilogram equivalent CO2 emitted is a common and standard indicator. Expression of results in terms of unit building area

eliminates the effect of the building’s size and allows comparisons between similar models with common LCI but with different sizes. Accordingly, the selected units for the results in the present study are GJ/m2 for energy consumption and kilogram equivalent CO2 per m2. Considering the average annual number of constructed steel structure buildings in Tehran, which equal to 2,804,550 m2 (Statistical Center of Iran, 2018), the annual energy consumption and CO2 emissions are shown in Fig. 6. Fig. 6 shows that due to the application of the lean techniques, the annual energy consumption and CO2 emissions in Tehran can be reduced by 45,988 GJ and 932 tons, respectively. Also, according to the information stated in the energy balance sheet of Iran, the pollutant emissions per kWh are specified (IFCO, 2018). Based on the achieved improvements in the use of electrical power-operated equipment, the environmental improvements from this equipment are depicted in Table 8. The emission factors presented in Table 8 are based on the published statistics in the energy balance sheet of Iran (IFCO, 2018). Also, due to the significant energy consumption in the production processes of steel material, applying lean techniques to the steel production processes will have a significant impact on the total embodied energy consumption of production, transportation, and erection processes of PSFs. Due to the reasons such as repeatable nature of the production and erection processes of PSFs, the prevalent use of pre-fabrication methods for residential buildings in Tehran, and similarities of the dimensions of the studied buildings with the common examples implemented in Tehran the results of this study could be extended with a moderate confidence level. Also, for validating the results of DES tried to compare the outputs, inputs, and simulation model with the actual processes carried out in the production factory and erection site. Regarding the validity of the evaluated model, one of the most suitable ways

Table 7 Total energy consumption and CO2 emissions. Process

Current mode Production Transportation Erection Total Lean mode Production Transportation Erection Total a

Electricity consumption (KWh)

Fuel consumption (Lit)

Total energy (GJ)a

Total CO2- eq. GWP (Kg)a

Working

Idle

Total

Idle

Idle

Total

15165 e 185.8 15326

1848 e 4.15 1852

17013 e 190 17178

e 269.48 2042 2311.48

e e 297 297

e 269.48 2339 2608.48

183.73 10.4 92.34 286.5

11845 3.2 140 11988.2

15162 e 217.3 15379.3

1054 e 4.64 1.58.6

16215 e 221.9 16436.9

e 269.48 1613 1882.48

e e 237 237

e 269.48 1870 2139.48

175.12 10.4 74.58 260.1

11289 3.2 160.8 11453

The amounts are evaluated for the building area of 1610 m2.

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Fig. 6. The annual energy consumption and CO2 emissions of both modes.

to validate the model is to compare the model results with the actual results of the production and erection processes. Consequently, the results from the simulation of the current mode were compared with the actual results recorded at the factory. The results indicate the acceptable accuracy of the simulation model. Also, based on the recommendation of some recent studies (Mostafa and Chileshe, 2018) in order to face validate the results of lean mode simulation, the results of the simulation model were validated through an interview with several experts in this field as well as factory officials. Also, according to a comparison of the improvement achieved during the current study with some of the previous studies (Nahmens and Ikuma, 2011; Yu et al., 2011; Heravi and Firoozi, 2017), the overall improvement rate is at an acceptable level. Some studies tried to reduce energy consumption and

pollutant emissions of the construction processes. Reviewing some of the previous studies, Table 9 depicts some conventional methods used to reduce the energy consumption and pollutant emissions of the construction processes (Pomponi and Moncaster, 2016). As depicted in Table 9, the application of the methods, such as the use of less energy-consuming materials, has the potential to reduce the amount of energy during the construction process to an acceptable level, so using innovative techniques such as lean techniques can increase the amount of the achieved improvement. A comparison of the results of this study with the results of other methods demonstrates the desirability of the simultaneous application of pre-fabrication method as well as lean principles. Also, considering some criteria such as executive capabilities, required infrastructure, operational complexity, and initial capital

Table 8 Environmental impact improvement of electrical equipment using the lean method. Pollutants

Emission factor (gr/Kwh)

Current mode (gr)

Lean mode (gr)

Improvements (gr)

NOx SOx CO CH SPM

0.906 0.906 0.001 0.024 0.088

15585.3 15585.3 17.2 412.8 1513.8

14892.1 14892.1 16.4 393.5 1446.5

693.2 693.2 0.8 19.3 67.3

Table 9 Comparison of the results of commonly used methods in previous studies to reduce the environmental impacts. Method Use of low-energy materials

Results of previous studies

Using the steel-concrete structure compared to the masonry-concrete structure, the energy consumption is reduced by 4.2% (You et al., 2011). Better design It reduces direct and indirect energy consumption by 1.6% and 20%, respectively (Acquaye et al., 2011). Modern methods and The use of tools such as BIM and energy simulation soft wares creates a balance between the embodied energy consumption and the methodologies operational energy used of the operation phase. Utilization of the recycled materials By utilizing recycled materials, the environmental impacts are reduced by 46% (Intini and Kühtz, 2011). The increasing use of local The use of local materials reduces the effects of the transportation stage and also increases the economic benefits of the national materials economy (Crishna et al., 2011). More efficient construction This method contains more efficient manufacture of building materials, applying processes with less waste and idle time in the processes construction phase. There are several innovative ways to reduce the environmental impacts of construction processes, but there are limited studies on this method’s impact. The increasing use of preThis method is liked to more efficient construction processes method. The results of some studies indicate a 3.2% decrease in pollutant fabricated elements emissions compared with conventional methods (Mao et al., 2013). There is also the ability to combine this method with other methods like innovative and lean methods. Increasing the use of renewable Increasing the use of renewable energy self-supply in order to reduce environmental impacts (Qaemi and Heravi, 2012). energy

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requirement, the use of innovative techniques such as lean techniques and its combination with pre-fabrication method can bring the possibility of further improvements considering the possibility of extensive implementation of these methods. Despite small improvements due to the application of lean techniques, considering the multiplicity of residential building construction as well as the possibility of implementing these techniques on a large scale, the application of these techniques could have a significant impact on the annual energy consumption and pollutant emissions.

analysis, Investigation, Resources

5. Conclusions

Abbasianjahromi, H., Talebian, R., 2018. Identifying the most important occupational diseases in the construction industry: case study of building industry in Iran. Int. J. Constr. Manag. https://doi.org/10.1080/15623599.2018.1518657. Acquaye, A., Duffy, A., Basu, B., 2011. Embodied emissions abatementda policy assessment using stochastic analysis. Energy Policy 39 (1), 429e441. Aziz, R.F., Hafez, S.M., 2013. Applying lean thinking in construction and performance improvement. Alexandria Eng. J. 52 (4), 679e695. Bilec, M.M., Ries, R.J., Matthews, H.S., 2009. Life-cycle assessment modeling of construction processes for buildings. J. Infrastruct. Syst. 16 (3), 199e205. Crawford, R., 2011. Life Cycle Assessment in the Built Environment. Routledge, UK. Crishna, N., Banfill, P.F.G., Goodsir, S., 2011. Embodied energy and CO2 in UK dimension stone. Resour. Conserv. Recycl. 55 (12), 1265e1273. Curran, M.A. (Ed.), 2012. Life Cycle Assessment Handbook: a Guide for Environmentally Sustainable Products. John Wiley & Sons. Duggan, K.J., 2012. Creating Mixed Model Value Streams: Practical Lean Techniques for Building to Demand. Productivity Press. Ellram, L.M., 1996. The use of the case study method in logistics research. J. Bus. Logist. 17 (2), 93e138. Farias, L.M.S., Santos, L.C., Gohr, C.F., de Oliveira, L.C., da Silva Amorim, M.H., 2019. Criteria and practices for lean and green performance assessment: systematic review and conceptual framework. J. Clean. Prod. 218, 746e762. Finkbeiner, M., Inaba, A., Tan, R., Christiansen, K., Klüppel, H.J., 2006. The new international standards for life cycle assessment: ISO 14040 and ISO 14044. Int. J. Life Cycle Assess. 11 (2), 80e85. Firoozi, M., Heravi, G., 2013. A lean approach to industrialized and modular homebuilding: identification and assessment of wastes in mass-housing proal, QC, jects. In: Proc. 4th Construction Specialty Conference CSCE. Montre Canada. Fu, F., Sun, J., Pasquire, C., 2015. Carbon emission assessment for steel structure based on lean construction process. J. Intell. Robot. Syst. 79 (3e4), 401e416. Guggemos, A.A., Horvath, A., 2005. Comparison of environmental effects of steeland concrete-framed buildings. J. Infrastruct. Syst. 11 (2), 93e101. Gursel, A.P., Ostertag, C., 2017. Comparative life-cycle impact assessment of concrete manufacturing in Singapore. Int. J. Life Cycle Assess. 22 (2), 237e255.  mez, I., 2019. Lean manufacturing and sustainable perHenao, R., Sarache, W., Go formance: trends and future challenges. J. Clean. Prod. 208, 99e116. Heravi, G., Firoozi, M., 2017. Production process improvement of buildings’ prefabricated steel frames using value stream mapping. Int. J. Adv. Manuf. Technol. 89 (9e12), 3307e3321. Heravi, G., Qaemi, M., 2014. Energy performance of buildings: the evaluation of design and construction measures concerning building energy efficiency in Iran. Energy Build. 75, 456e464. Heravi, G., Nafisi, T., Mousavi, R., 2016. Evaluation of energy consumption during production and construction of concrete and steel frames of residential buildings. Energy Build. 130, 244e252. Intini, F., Kühtz, S., 2011. Recycling in buildings: an LCA case study of a thermal insulation panel made of polyester fiber, recycled from post-consumer PET bottles. Int. J. Life Cycle Assess. 16 (4), 306e315. IPCC, 2013. The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Iranian Fuel Conservation Company IFCO, 2018. Iranian balance sheet. www.ifco.ir. ISO 14040, 2006. Environmental management-life cycle assessment-principles and framework. Int. Stand. Organ. Jin, R., Gao, S., Cheshmehzangi, A., Aboagye-Nimo, E., 2018. A holistic review of offsite construction literature published between 2008 and 2018. J. Clean. Prod. 202, 1202e1219. €hko €nen, A.-K., 2011. Conducting a case study in supply management. Oper. Ka Supply Chain Manag. Int. J. 4 (1), 31e41. Kawecki, L.R., 2010. Environment Performance of Modular Fabrication: Calculating the Carbon Footprint of Energy Used in the Construction of Modular Homes. Ph.D. thesis. USA Arizona State University. Kong, L., Li, H., Luo, H., Ding, L., Zhang, X., 2018. Sustainable performance of just-intime (JIT) management in time-dependent batch delivery scheduling of precast construction. J. Clean. Prod. 193, 684e701. Leon, H.C.M., Calvo-Amodio, J., 2017. Towards lean for sustainability: understanding the interrelationships between lean and sustainability from a systems thinking perspective. J. Clean. Prod. 142, 4384e4402. Li, X., Shen, G.Q., Wu, P., Yue, T., 2019. Integrating building information modeling and prefabrication housing production. Autom. ConStruct. 100, 46e60. Li, X., Shen, G.Q., Wu, P., Fan, H., Wu, H., Teng, Y., 2017. RBL-PHP: simulation of lean construction and information technologies for prefabrication housing production. J. Manag. Eng. 34 (2), 04017053.

Increasing energy consumption and pollutant emissions have been led to further attention to developing novel methods to reduce the environmental effects of the construction sector. Given the effectiveness of applying industrial construction techniques to energy consumption and CO2 emissions compared with traditional construction methods, for more performance improvement, upgrading industrial processes using innovative methods is necessary. Several studies have been done to improve the performance of the pre-fabrication process, but the integration of production and erection processes using lean techniques and considering their effects on each other have not been studied comprehensively. In the present study, the environmental effects of applying lean techniques including VSM, JIT, continuous flow, and TPM on the energy consumption and CO2 emissions have been studied during the processes of production, transportation, and erection of PSFs using the methodology outlined in ISO 14040. By simultaneously applying the lean techniques as well as considering the production and erection processes as an integrated flow, the amount of energy consumed and CO2 emitted during the production and erection processes were reduced up to 9.2% and 4.4%, respectively. Also, the methods used in the present study have high applicability in all building projects with pre-fabricated steel frames due to the ease of implementation and no need for additional resources, which in addition to saving money, reduce the environmental impacts of construction processes. For example, with the estimation carried out in Tehran, the annual energy consumption and CO2 emissions of the production and erection processes of steel frames could be reduced by 45,988 GJ and 932 Tons, respectively. The main reason for reducing energy consumption and thus reducing CO2 emissions is to eliminate the waste of production and erection processes, adjust the production processes based on the needs of the erection processes, and reduce the idle time of the processes. Considering the significant reduction in environmental impacts of applying pre-fabricated method in comparison with traditional techniques (Mao et al., 2013; Monahan and Powell, 2011; Kawecki, 2010), the application of various lean techniques to integrate the production, transportation, and erection processes of pre-fabricated components can enhance the performance of the pre-fabricated methods. Also, considering the duration of the processes as fixed-value, limitation on the use of other lean techniques such as 5S due to the factory limitations, the limited numbers of steel frame production factories that could take over the responsibility of the erection processes of PSFs, and the lack of development of lean techniques in Iran due to the widespread application of push production systems are considered as the main limitations of the current study. Author contribution statement Gholamreza Heravi: Conceptualization, Methodology, Validation, Supervision, Project administration. Milad Rostami: Data curation, Writing- Original draft preparation, Writing - Review & Editing, Visualization. Majid Fazeli Kebria: Software, Formal

Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References

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