2.1 Construction systems

The increase in competitiveness among construction companies is growing throughout Brazil. This competition requires business strategies that allow a greater use of resources and rationalization of processes (^{Milan, 2011}). In this context, ^{Marcos and Yoskhioka (2015)} point out that a possible alternative towards rationalization and industrialization of civil construction processes is the use of new constructive technologies.

The reasons for such a significant use of masonry in the country refer to: non-qualified workforce¹, cheap and available throughout the country; familiarity with the raw material, which consists of ceramic or concrete blocks, which is also easily accessible and used in various works, and finally, the cultural aspect: Brazilians value the construction in masonry, as it ensures comfort both in winter and summer (Ferreira, 2014).

However, it can be seen that this constructive process, based on structural masonry, is still essentially artisanal, and presents significant flaws such as low productivity and high waste of material resources (^{Santiago and Araújo, 2008}). ^{Mello (2007)} further emphasizes that this construction system provides unsatisfactory quality and productivity, unwillingness for modifications, employment of low-skilled workers and consequent high turnover.

In addition to the aforementioned characteristics, sector studies of ^{SEBRAE (2008)} show that there is a small share of formal employment in the total number of workers employed in the construction sector, which favors high turnover rates.

Based on this reality, the civil construction sector in Brazil has been looking for alternatives, in order for constructive systems to become more effective and less environmentally harmful. Prefabricated building systems, such as Light Steel Framing (LSF) and Light Wood Framing (LWF) are an alternative to traditional systems, since control of planning and design within the industry contributes to avoid material waste and slow production processes (^{Vivan, 2011}).

According to Ferreira (2014), industrialization in the civil construction sector provides several advantages. Among them, one could highlight faster completion of the project, elimination of indirect costs that are difficult to account, higher quality of final product, replacement of part of the workforce by equipment, process traceability, cleaner and more organized construction site.

The LWF system is composed of structural wood components, covered by panels such as: OSB boards, and cement boards, which act as bracing elements, and gypsum board. The LWF consists of an industrialized, fast-running construction system. According to ^{Molina and Calil junior (2010)}, ^{Cardoso (2015)} and Kobunbun 2014 the industrial environment allows for several activities to be carried out simultaneously resulting in shorter delivery times and lower costs.

Another advantage related to works with the LWF system is that the raw material is renewable. However, not all wood can be used for this processing. According to ^{DATec 020-A (2015)} the wood used for LWF must be properly treated. Said wood must present good quality (without defects) and with considerable dimensions to be industrialized in the design of structural panels.

According to data from the Brazilian National Forestry Information System (^{SNIF, 2017}), lumber, i.e. sawn wood used for construction, has been increasingly used in recent years, with a growth of 48% from 2013 to 2014.

Because it is considered a new constructive method in Brazil, there are only a few suppliers and manufacturers of specific products such as cement boards, waterproof membrane, etc., which adds costs to building (^{Cardoso, 2015}). Another important factor is the issue of skilled labor. ^{Kokubun (2014)} emphasizes that skilled labor is essential for this type of constructive system, for operations of panel manufacturing and structure assembly and disassembly. This labor force, in turn, becomes less available, given the need to train these employees and bring these professionals from the timber industry.

Besides these aspects that must be considered, the system suffers with cultural barriers. Wood is still considered a poor-quality material and many are afraid that it's use will involve deforestation, says ^{Cardoso (2015)}. For ^{Dias (2005)}, the main problem related to the cultural barrier is the lack of knowledge and technological development in the area.

The LSF system has similar characteristics to the LWF. The main difference is in the use of raw material, which in this case is steel and not wood. The Light Steel Framing pieces are galvanized, cold formed, designed to withstand building loads and work together with other industrialized subsystems (^{Sousa and Martins, 2009}).

Being an industrialized system, it demands more qualified workforce, as well as the LWF. (Ferreira, 2014).

The LSF is a more expensive construction system in terms of raw material: galvanized steel (Ferreira, 2014). However, direct and indirect costs may be lower compared to reduced construction time and the absence of common losses in conventional construction.

According to ^{Gomes et al. (2013)}, this system presents a time reduction of 1/3 in construction periods when compared to the conventional construction methods in masonry. Therefore, the system is more used when the construction time factor is more important than the costs.

It should be emphasized that the choice of construction systems should take into account environmental, economic and social aspects. According to ^{Jadid and Badrah (2012)}, the choice of an input material, and consequently a constructive system, is related to several criteria which include, but are not limited to:

This information must be available for selection of the constructive system most appropriate to that situation. For this purpose, it is essential to create a database in which this information is available during the design phase of the project. This can be created in partnership with suppliers and designers who already work in the area and who can inform about the aspects listed above (^{Jadid and Badrah, 2012}).

2.2 Analytic Hierarchy Process (AHP)

The Analytic Hierarchy Process (AHP) developed by ^{Saaty (1990)}, is based on three fundamental principles: the decomposition of the structure, the comparison of the judgments and hierarchical priorities composition. The decomposition of the decision problem facilitates the construction of hierarchies of criteria to determine the importance of each criterion. These criteria, defined by experts, are analyzed and compared, two by two, independently. For this purpose, concrete data of subjective alternatives or judgments can be considered.

Once the hierarchy is structured, the alternatives are systematically evaluated by means of comparison, two by two, according to each of the criteria and a numerical scale is assigned to each pair of n alternatives (Table 1). These numerical scales are used for comparisons of pairs between the alternatives according to their impact on an element placed at a higher level of the hierarchy (^{Saaty, 1990}).

The sequence of the method calculations can be found in detail in ^{Saaty (1990)}. This method further allows for the ranking obtained by calculating the consistency index.

Among the advantages of AHP are the ease of use and ease of adjustment of its hierarchical structure to deal with problems of different dimensions (^{Velasquez and Hester, 2013}).

2.3 Building Information Modeling (BIM)

According to Eastman et al. (2014), BIM is a modeling technology and an associated set of processes for producing, communicating and analyzing construction models, including information related to design, simulation and operation through the use of different integrated tools.

During project design, BIM can support project detailing, providing specific information on the structure of the project, the execution processes and even on the choice of the most appropriate building system (^{Jalaei and Jrade, 2014}).

According to ^{Jalaei et al. (2015)}, the great advantage of using BIM for selection of constructive systems is its function of information integration and interoperability. BIM allows to include detailed descriptions of a single building or set of buildings may be important to make accurate analyzes of the project.

In addition, several studies have assessed the integration of BIM with environmental sustainability in Brazil. ^{Oliveira et al. (2015)}, for example, highlights BIM as a resource that allows for a lifecycle approach (LCA) of the building, enabling analysis during the design phase of the project; ^{Marinho (2014)} highlights BIM as a tool to help optimize, for example, energy, water and materials use in integrated analyzes. ^{Carvalho and Scheer (2015)} demonstrate the characteristic of BIM in the anticipation of problems and prevention of project inefficiency. For them, prevention of mistakes that are often noticed only at the construction site can lead to a reduction in the costs of construction and the expense of materials, providing gains in work quality and resource savings, favoring sustainability of the buildings.

2.4 Related Papers

To better understand the practical problem and to examine the potential of the topic under study, a search was carried out to identify recent and related works published in the last five years. The search was carried out in the reference databases - ScienceDirect and CAPES Journals.

Several papers related to this topic were identified. Papers that came closest to the analysis of constructive systems using BIM and / or the decision-making tool were the four described below.

^{Marcos and Yoshioka (2015)} wrote about how they used BIM as a tool to assist managers in the choice of inputs with the least environmental impact, comparing two construction systems: masonry and light steel frame. Its focus was specific on environmental impact.

The research of ^{Jadid and Badrah (2012)} created a decision-making method for material selection during the design phase of an architectural project. This paper focused on multicriteria method within the architectural projects.

The research of ^{Jalaei et al. (2015)} brought together the two subjects, the BIM platform software (Revit) and the decision-making method. The authors created a plug-in within BIM to assist in choosing inputs that would provide a lower environmental impact, analyzing more specifically the material life cycle. Again, this paper addresses environmental aspects.

For ^{Jobim et al. (2006)}, the choice of construction systems is not only characterized from a technical or professional view but must take into account the context in which the project is inserted, user requirements, available resources, physical conditions, environmental conditions and aspects relating to cost improvement.

The novelty of this paper lies in the proposition to analyze not only a relevant factor for the construction system choice, but also some of the main factors, such as the environmental aspect related to the inputs, the financial cost and operational factors, such as availability of labor and materials.

In this way, this subject, besides being relevant and researched by other authors, is fundamental, as it enables the unfolding of the new constructive systems and helps to expand the incorporation of BIM in the production chain of civil construction in Brazil.

4.1 Deployment and tests for the solution

The chosen residence is a 42 m² house, consisting of two bedrooms, living room, kitchen and bathroom. It was also considered that the housing scenario would be the region of Curitiba, in the state of Paraná.

Using Revit, the residence was modeled in the three constructive systems (structural masonry, LSF and LWF). The LSF and LWF systems were modeled from the plug-ins Timber Framing (from Autodesk) and Metal Framing Wall + of AGACAD (version 1.0.0.6), respectively. The use of plug-ins makes modeling faster, which allows the designer to model the project only once. The plug-ins allow conversion of any type of wall into a wall of LSF or LWF almost instantly, which increases productivity in the modeling process. The plug-ins also make possible to make changes in the new frame, according to the designer's preferences, since the types of profiles as well as their dimensions, the distances between the uprights and the details of the openings and connections can be changed.

The data highlighted in Table 2 were added to the parameters of the modeled walls.

Then, using Revit documentation resource, which is one of the advantages of BIM software, the list of materials with the values ​​for the walls of the three construction systems was automatically obtained (Table 3).

In the next step, the AHP method was used to help structuring the problem of choosing a constructive system. In this way, the criteria were first identified in the literature (Figure 2).

Figure 2 Hierarchy of criteria and alternatives of the case study, for use of the AHP method. 

Subsequently, from the hierarchical structure of this case study and the data obtained through Revit, the abovementioned experts evaluated the constructive systems, following the structure of the AHP method, using the scale presented in Table 1. The expert evaluations were implemented in the software SuperDecisions. Thus, the weights stipulated by the experts for each criterion can be visualized in Table 4.

It can be seen from Table 4 that the weights indicated by the experts for each criterion of constructive system selection were very discrepant, i.e., there was no consensus among them. For experts A and B, for example, the weight of choice was the environmental impact. While for experts C, D and E, the most striking criterion is the financial value of work.

This analysis proves in fact that the choice of constructive system depends on the interests of each user / constructor. According to ^{Jobim et al. (2006)}, the analysis of alternatives for constructive systems and materials available, regardless of whether the technology is considered innovative, should be analyzed under different criteria and in particular meet certain performance requirements, such as performance standard 15.575 (^{ABNT - Brazilian Association of Technical Standards, 2013}).

From the stipulated weights for each criterion it was possible, with the help of the software SuperDecisions, to identify which building system is most suitable for each expert. The percentage preference for the construction system (ranking) is shown in Table 4.

It can be seen from Table 5 that the most appropriate constructive system in the evaluation of experts is Light Wood Framing.

The experts were consulted to analyze the integration of BIM with the MCDM method. As they also know the construction systems, because they work in the field of civil construction, they also contributed to create the preference ranking of construction systems.

This option was the most promising especially for the advantages that the system presents when compared to structural masonry in matters of: time, cost and environmental impact and with respect to the system Light Steel Framing, in matters of: cost, raw material and environmental impact.

It is noteworthy that the scenario elaborated took into consideration the construction of this house in the region of Curitiba in the state of Paraná, where companies are known to work with the three construction systems. It is also worth noting that the proposal of the article is to show the established scenarios and not which system is the most appropriate, since considering other factors, a system can be more promising in some situations and not so much in others.

4.2 Evaluation of the solution applicability

In order to evaluate the applicability of the proposed solution, the experts were asked about the relevance of the information extracted from Revit to choose the most appropriate construction system. On a scale of 1 to 5, in which 1 means nothing relevant and 5 very relevant, the average score of the experts was 3.2, i.e., in general they consider that the use of a BIM platform software contributes to the choice of construction system.

They also described how they believe BIM can contribute to the use of new constructive systems, which could also contribute to address some social barriers.

Expert A considered that, from the moment a professional is aware of the BIM tool, it may be essential to assist in their work. However, he warns that misuse of such tool may represent only a misleading view of the actual state of a project.

Expert B reported that the use of BIM platform software during the design phase is extremely satisfactory and stressed that this can help users choose more sustainable buildings.

Expert C, in agreement with expert B, considered the tool satisfactory for the comparative process, provided the extracted sources are reliable. Expert D also pointed out that BIM helps ensure that the same project will be edited, modifying construction systems in an easy and simple way allowing for efficient comparison between systems and a more reliable choice for the most appropriate option.

The expert also understood that BIM allows for greater detailing of a project which makes processes more accurate and with less waste of raw material and manpower.

4.3 Identification and analysis of theoretical contributions

Based on the case study and the evaluation carried out with the experts, it is believed that the use of BIM, as in this case, Revit and the AHP method have contributed in a promising way to assist in the choice of constructive method, since through this integration it was possible to compare criteria and have a better view from the BIM modeling, the 3D design, as well as easily extract quantitative data.

It is also considered that comparing is the way for more users to know other constructive systems and to implant them in their constructions.

As BIM incorporates a data library for information storage, said library can be used by managers during the design process of projects, contributing to the choice of the most appropriate building system. In addition, the information added can be updated depending on the project by the suppliers of inputs and contractors themselves. For example, LWF inputs are still being tested and physical tests and other inputs are being developed. In this situation, the input supplier could pass this information on to the project offices to show the new information and inputs, in order to update the data and present the novelties with respect to that construction system. Another advantage is the tool's practicality in modeling several different constructive systems in an easy and fast way, this being one of the resources to assist in the choice, which, together with the automatic obtaining of project documentation, can make project design a faster/efficient.