Waste Identiﬁcation in the Operation of Structural Engineering Companies (SEC) According to Lean Management

: Although the architecture, engineering and construction (AEC) industry is highly relevant to national development, it suffers from signiﬁcant productivity challenges. Beneath the design and documentation of structures, a dynamic, complex process is taking place, with constant modiﬁcations and feedback involving numerous professionals from different ﬁelds and their respective approaches and work developed using various computer programs. This diversity of factors converges within an iterative trial-and-error process and does not stop until a reﬁned model is achieved. To understand traditional structural engineering companies (SECs) in Chile involved in building private procurement projects, 25 non-value-adding SEC activities were identiﬁed and classiﬁed according to typical lean management waste categories. These were initially validated by a panel of experts and then conﬁrmed through a survey of 37 companies. The identiﬁed activities reduce the productivity of SEC organizations, contributing to low AEC industry indicators.


Introduction
The architecture, engineering and construction (AEC) industry is known for having low productivity levels, which is worrying in an industry of relevance to a country's development, in terms of its contributions to the gross domestic product and the social welfare that it generates [1]. This is due to several well-known problems: cost overruns and delays, minimal interaction between different actors, poor knowledge management, a focus on routine activities, high fragmentation, poor asset management, design changes during the construction stage and poor planning and scheduling, among others [2]. All these problems are associated with the complexity of AEC industry projects, the high number of processes, professionals and approaches involved in the different stages of the project, the insufficient incorporation of technologies, automation and collaborative work [3].
Fragmentation in the construction industry, considered to be one of the major problems in the sector, is caused by, on the one hand, the separation of the design and construction phases and, on the other hand, the composition and structure of the construction industry. In this regard, it is common to find professionals dedicated to design who fail to anticipate how the company should carry out the construction of the project they have designed, which, in the long run, produces delays, disputes and claims that negatively impact the scheduling of the work [3].
In this context, trends have emerged in the last decade that could contribute to the improvement of these indicators [4]. The term Industry 4.0 refers directly to the current shift towards digitization and automation of the manufacturing environment worldwide. However, this concept has not yet reached unanimous acceptance within the construction industry and it is necessary for the industry to adopt the political, social, economic, technological, environmental and legal implications that Industry 4.0 requires [5].
The desire to introduce digital change into the construction industry has benefited from the irruption of building information modeling (BIM) [6]. Despite this, professionals in the construction industry are frequently involved in situations involving the loss of information necessary for the development of the work. The challenge then centers on enabling the development of systems that facilitate the exchange of information within organizations. It is currently estimated that errors made in the design process cause approximately 30% of the errors that occur during the construction stage and approximately 55% of the errors that are made during the maintenance phase of a project [3]. In this sense, the BIM system can be considered the confluence of digital information necessary to support the design and construction processes, favoring collaborative work and the exchange of information [7].
Lean project management is a methodology designed to achieve three fundamental goals which could address the problems mentioned above: deliver a product, maximize value and minimize waste [8]. In the design phase, the greatest wastes involve the clarification of needs, rework, internal control of activities, interdisciplinary reviews, waiting times and interruption [9]. To maximize value and minimize waste in the design phase, there are some lean design management practices that can be applied, such as involving specialists, designers and builders during early stages; encouraging the active, systematic participation of clients during decision making; and holding meetings to resolve problems, identify waste and define a responsible person to reduce it, among others [10].
Considering the role of structural engineering companies (SECs) in building projects with private procurement [11] and the importance of their efficient work in the initial stages of construction projects [12], this paper seeks to identify and quantify situations and problems that hinder optimal processes in the functioning of traditional SECs in Chile, especially those issues responsible for reducing the productivity of these organizations and that contribute to the low indicators of the AEC industry.
Based on a literature review and validated by a panel of experts, the SEC workflow was identified, detailing roles and processes. According to these interactions and based on a literature review, the non-value-adding SEC activities were studied through the identification of waste according to lean management. Information was collected through a survey of 37 Chilean SECs, studying the frequency with which these activities occur in the work process and the importance that companies give to these activities as hindering the work process. With these results of importance and frequency for each SEC activities that do not add value in the workflows, three indicators were calculated (relative importance index (RII), frequency index (FI), and frequency adjusted importance index (FAII)), with which it was possible to make a ranking of these activities, based on the importance/frequency analysis. In addition, using a Kruskal-Wallis test, it was possible to determine that these trends were maintained regardless of the size of the SEC projects. The research seeks to answer the following questions: • What problems arise in current SEC workflows? • What is the importance that professionals in the field place on these problems? • What is the recurrence of these problems in SECs? • Is there a difference in the presence of problems according to the size of projects executed by companies?

Research Methods
The research methodology is organized into three stages: (1) identification of SEC operation, (2) identification of SEC activities that do not add value and (3) validation of SEC activities that do not add value. Figure 1 specifies the activities, research tools and deliverables for each stage of the research. The research is focused on building projects with private procurement.

Research Methods
The research methodology is organized into three stages: (1) identification of SEC operation, (2) identification of SEC activities that do not add value and (3) validation of SEC activities that do not add value. Figure 1 specifies the activities, research tools and deliverables for each stage of the research. The research is focused on building projects with private procurement. In the first stage, the SEC operation in building projects with private procurement was defined, considering roles and workflows based on the traditional methods currently performed. These SEC processes were validated by a panel of five experts. In the second stage, based on the flowchart of the processes developed in the SECs, 25 activities were identified that do not add value; these were then classified according to the typical waste categories in lean management and then validated by a panel of five experts. In the third stage, the list of SEC activities that do not add value-according to the typical waste categories of lean management-was incorporated into a questionnaire using a scale of 1 to 5, so that 37 SECs could evaluate the importance and frequency of each of the 25 identified wastes. Based on this assessment, the authors analyzed and validated the identified waste and its relevance to SEC workflows.

STAGE
Literature reviews were conducted in stages 1 and 2, considering recommendations from literature review methodologies [13,14]. Figure 2 shows, in simplified form, the steps performed for this purpose. The specific aspects of each search are detailed in Sections 2.1 and 2.2, below. Figure 3(a) shows the distribution of the selected articles in the range of years included in the study. Figure 3(b) shows the "Search criteria" distribution according to selected articles. Figure 4 shows the journal distribution of the selected articles. In the first stage, the SEC operation in building projects with private procurement was defined, considering roles and workflows based on the traditional methods currently performed. These SEC processes were validated by a panel of five experts. In the second stage, based on the flowchart of the processes developed in the SECs, 25 activities were identified that do not add value; these were then classified according to the typical waste categories in lean management and then validated by a panel of five experts. In the third stage, the list of SEC activities that do not add value-according to the typical waste categories of lean management-was incorporated into a questionnaire using a scale of 1 to 5, so that 37 SECs could evaluate the importance and frequency of each of the 25 identified wastes. Based on this assessment, the authors analyzed and validated the identified waste and its relevance to SEC workflows.
Literature reviews were conducted in stages 1 and 2, considering recommendations from literature review methodologies [13,14]. Figure 2 shows, in simplified form, the steps performed for this purpose. The specific aspects of each search are detailed in Sections 2.1 and 2.2, below. Figure 3a shows the distribution of the selected articles in the range of years included in the study. Figure 3b shows the "Search criteria" distribution according to selected articles. Figure 4 shows the journal distribution of the selected articles.

Stage 1: Identification of SEC Operation
A literature review was carried out, based on the methodology proposed by Tranfield et al. [15]. It consists of three parts: a) planning the review, b) conducting the review and c) reporting and dissemination.

Stage 1: Identification of SEC Operation
A literature review was carried out, based on the methodology proposed by Tranfield et al. [15]. It consists of three parts: a) planning the review, b) conducting the review and c) reporting and dissemination.

Stage 1: Identification of SEC Operation
A literature review was carried out, based on the methodology proposed by Tranfield et al. [15]. It consists of three parts: (a) planning the review, (b) conducting the review and (c) reporting and dissemination.

•
In (a), to identify the workflow of the SECs, the following search topics were considered: processes in engineering, engineering design and structural engineering companies. Journals specializing in structural engineering, engineering and construction project management and conference proceedings were considered, based on the Web of Science and Scopus collections. Documents focusing on construction processes and technical aspects of design and/or construction were excluded. For the search, documents from the year 2000 to the present were considered. • In (b), the search was carried out, selecting 47 references on processes and interactions of the design stage and the SECs, with a focus on building projects with private procurement. • In (c), based on the selected references, the SEC workflow was described, detailing its characteristics, professionals and main processes. The SEC operation was defined using a flow chart that shows the processes developed during a structural engineering project linked to seven positions in charge of each of the indicated activities.
This flow chart and the description of its operation was validated by a panel of experts detailed in Table 1. Five experts were selected who met the following requirements: (a) more than ten years of practice and (b) experience as a consultant or researcher in the area of structural engineering and engineering design stages. In a focus group, the experts discussed the proposed processes and flows, finalizing the flowchart of the processes developed in SECs.

Stage 2: SEC Activities That Do Not Add Value
A second literature review was carried out according to the guidelines described above [15]. It again comprised three parts:

•
In (a), to identify activities that do not add value in the SEC workflow, the following search topics were considered: problems in engineering design, interactions in engineering projects, processes in engineering, engineering design and structural engineering firms. Journals specializing in structural engineering, engineering and construction project management and conference proceedings, based on the Web of Science and Scopus collections, were considered. Documents focusing on construction processes and technical aspects of design and/or construction were excluded. Documents from the year 2000 to the present were considered for the search.

•
In (b), the search was performed, selecting 47 references that identify problems within SEC workflows, with an emphasis on construction projects with private contracting. Activities that do not add value were identified based on waste categories according to lean management. Eight types of waste were identified based on the lean management philosophy, which are shown in Table 2. • In (c), from the selected references, a list of activities was identified and classified according to the lean waste categories.
Based on the literature review and the flowchart obtained in Stage 1, activities that do not add value to the processes developed in the SECs were identified. These activities were then classified according to the typical waste categories of Lean Management and then validated by the panel of experts described in Table 1, following the same work dynamics described in Stage 1, thus obtaining a list of 25 SEC activities that do not add value. Table 2. Typical waste categories of lean management [12,16].

W1
Waste of overproduction Producing more than required leading to overstaffing, storage and transportation costs. Causes a significant amount of resource to be tied up, which otherwise could be used for value-adding operations.

W2
Waste of time on hand (waiting) All the time which is not spent for value-adding activities.

W3
Waste in transportation Carrying works which does not add value to final product for customer.

W4
Waste of processing itself (overprocessing) Unnecessary transactions involved in the process.

W5
Waste of movement Any unnecessary movement performed by sources

W6
Waste of stock on hand (inventory excess) Excessive amount of supply stored with respect to customer needs and value.

W7
Waste of making defective products Deviation of products from customer requires or specification.

W8 Unused Employee Creativity
This is a situation of not using the potential efficiently, which makes an organization to benefit less than possible.

Stage 3: Validation of SEC Activities That Do Not Add Value
To validate the list of 25 SEC activities that do not add value, according to typical lean management waste categories, the researchers invited all the SECs involved with the collaborative space of technology, innovation, management and sustainability (TIMS) in civil engineering in Chile to join the research. Thirty-seven interested Chilean SECs were assessed; each company's representative had the following characteristics: (1) more than ten years of experience, (2) basic knowledge about BIM and lean and (3) agreed to provide information about the waste of their SEC.
A survey was given to the 37 Chilean SECs, either online through the SurveyMonkey platform or through personal interviews. The measurement instrument, shown in Table 3, uses a Likert scale of five points, according to two indicators: frequency of occurrence (never = 1, rarely = 2, occasionally = 3, frequently = 4 and very frequently = 5) and importance of the problem as hindering the process (not important = 1, of little importance = 2, moderately important = 3, important = 4 and very important = 5).
Based on the answers of the 37 SECs, the distribution of the response rates with respect to frequency and importance was obtained, based on the Likert scale, for each of the 25 SEC activities that do not add value. In addition, the following analyses were carried out: (1) an analysis to rank the 25 SEC activities that do not add value, based on importance/frequency and (2) a Kruskal-Wallis test to identify if there are differences according to the size of the projects developed by the different SECs.
With the aim of obtaining a ranking of the 25 activities, based on a weighting between importance and frequency, three indicators were calculated [17]:

•
The relative importance index (RII) was used to measure the importance of the different SEC activities. The five-point Likert scale ranging from 1 (not important) to 5 (very important) was implemented. The RII was calculated based on Equation (1): where W is the weight given to each factor by the respondents (1 to 5), A is the highest weight (in this case 5) and N is the total number of respondents (in this case 37). The value of the RII varies from 0 to 1: the greater the value, the higher the importance of each SEC activity.

•
The frequency index (FI) was used to measure the frequency of the different SEC activities. The five-point Likert scale ranging from 1 (never) to 5 (very frequently) was implemented. The FI was calculated based on Equation (2): where W is the weight given to each factor by the respondents (1 to 5), n is the frequency of the responses and N is the total number of respondents (in this case 37). The value of the FI varies from 0% to 100%: the greater the percentage, the higher the frequency of each SEC activity.

•
The frequency adjusted importance index (FAII) was used to rank frequency and importance at the same time. Based on both the FI and RII, the frequency adjusted importance index was calculated according to Equation (3): The value of the FAII varies from 0% to 100%; the greater the value, the higher the importance/frequency ratio of each SEC activity. The SEC activities were ranked based on the values of the FAII. Indicate the size of projects you commonly undertake (less than 500 m 2 , between 500 m 2 and 1000 m 2 , between 1000 m 2 and 5000 m 2 , between 5000 m 2 and 10,000 m 2 , between 10,000 m 2 and 20,000 m 2 , or more than 20,000 m 2 ). Results were quantitatively assessed for differences according to project size via the Kruskal-Wallis test, which is used to determine if the medians of two or more groups differ. As a non-parametric test, it is efficient for studying independent samples obtained from professionals working on different project sizes. For cases where statistical distributions are not precisely known, the test identifies whether or not there are differences in samples. With this technique, each problem raised was verified and the following hypotheses were formulated: • H 0 = there is no difference in the assessment of the problems (in frequency or importance) with respect to the different sizes of projects carried out by the respondents. • H 1 = there is a difference in the assessment of the problems (in frequency or importance) with respect to the different sizes of projects carried out by the respondents.
A significance level of 0.05 was defined and the p-value was obtained for each of the problems raised to determine whether the H 0 or H 1 hypotheses was accepted. If the p-value is greater than the level of significance, the null hypothesis cannot be rejected; otherwise, the null hypothesis is rejected, resulting in H 1 .

Fragmentation in the AECO Industry
Traditionally, companies that are dedicated to the development of structural projects have very well-defined activities that make up their workflow, from the beginning of conceptualization until the detailed engineering of a specific project [18]. To a large extent, the workflow ultimately obeys the technological tools adopted by each company; these include analysis and structural design programs, plan-drawing programs and programs for the preparation of budgets and internal company practices [11]. These tools, even when they can be adapted to each company's way of working, do not offer the possibility of carrying out the integrated work of teams operating from the same platform, which would allow the coordination of the different stages of a structural project. Instead, the existing tools result in a significant fragmentation of the work that affects the quality of the product, the execution time and the cost of the structural project [19]. This last condition is evident in the lack of fundamental methods that would allow adequate BIM interoperability between architectural design and structural analysis [20].
Three characteristics that determine the fragmentation within the industry can be pointed out, namely the isolation of the different disciplines that participate in a project, the lack of coordination between designers and builders and the execution of work in a formal manner. The isolation is undoubtedly due, in part, to the fact that many of the relationships established in the construction industry are of a temporary nature; this also affects the loss of the transfer of knowledge that is generated in individual projects and the actors who participate in them in a formal way [1].
On the one hand, fragmentation can be understood as related to the number of specialist companies or professionals involved in construction projects. This implies a growth in the demand for specialties as the project grows in size and complexity. Additionally, fragmentation can be classified depending on whether it is internal or external [3]. Likewise, one study [2] identified 26 main sources that create interaction problems within the construction industry; among these, employer interference and poor planning and coordination stand out. On the other hand, the interfaces of construction projects have also been identified as the main obstacle to innovation [1]. Of the various interfaces, the interface representing the relationship with customers is recognized as one of the most active, while the interface with suppliers appears to be the most distant.
The consequences of this non-integrated work have been thoroughly studied recently [20][21][22][23][24] and they include the following: lack of precision, delays in the delivery of information, the need for re-correction of tasks, the slowing down of certain demanding processes and errors in the transfer of information, among others. These consequences, from a project management point of view, can be considered losses for the company. Moreover, this is not an exhaustive list, as the construction industry is often identified as not having done its part to mitigate the effects of pollution emissions [25].

BIM and Lean Construction
Industry 4.0 represents a notable increase in the digitization and automation of manufacturing processes, the implementation of which involves notable challenges related to the construction industry's high complexity due to its interdisciplinary work, the uncertainty associated with its processes, a fragmented supply chain, short-term thinking and its cultural roots [5]. Apart from this, the construction industry is perceived as conservative, with little focus on innovation [1] and as having a high impact on the environment [26]. Despite these obstacles, the implementation of Industry 4.0 has various benefits: it improves productivity, increases quality and efficiency and promotes collaboration, security and sustainability, all of which are necessary to improve the image of the construction industry.
Improving efficiency within the construction industry requires new approaches to channel all initiatives related to Industry 4.0. For this reason, Fang et al. [27] propose the implementation of a conceptual framework under a sector innovation system that allows construction work to be simplified, saving time and costs. This proposed conceptual framework is based on a new theory of innovation in construction.
The irruption of new technologies focused on the field of structural engineering, as well as other civil engineering disciplines, has caused a radical change in the way these fields operate [28][29][30]. In this context, it is necessary to mention the impact that has occurred around the appearance of building information modeling (BIM). The transition from the traditional way of producing a structural project to the more integrated approach through the application of BIM has not been without problems and losses associated with work delays.
BIM allows for the efficient, parametrical modelling and management of information in an integrated way throughout the life cycle of a project; however, the effective implementation of BIM within a construction company requires significant technical capabilities, which usually results in resistance to adoption [31]. Reality has shown that the implementation of BIM within the construction industry is led by independent designers or specific design offices.
Since interdisciplinary interaction and collaboration in complex projects seems inevitable, it also seems inevitable that changes will occur in the efficient detection of project modifications that originate during the design and quality control stages [32]. To solve this problem, it has been proposed that large companies and project units of large corporations can use the internal networks of other companies to learn about what has happened in projects of a similar nature in order to gain knowledge [1].
In the case of construction companies that have implemented BIM, it is necessary to keep a reliable record of the changes carried out in the different versions of a BIM model, for which Gu et al. [32] have proposed a modification of the semantic classification of the changes, allowing effective detection in the models. These improvements, carried out within construction companies, will undoubtedly lead to an improvement in the value of BIM models [26].
In the case of companies dedicated to projects involving large structures or singular structures, BIM has allowed advances in the efficiency of the design and detailing processes, since it offers tools for which other platforms, such as the CAD platform, have few development capabilities. In terms of the aforementioned need to produce an adequate transfer of information between the design team and the construction team, this undoubtedly offers an excellent opportunity for improvement, as evidenced in the work of Gu et al. [33]. In this sense, it has been reported that the use of BIM in structural projects manages to reduce by 37% to 48% the number of instructions to modify projects and to eliminate between 43% and 68% of requests for information, although the cost of a project can be increased by up to 31% compared to the cost achieved with traditional processes [34].
In the review of the implementation of BIM within project companies, the use of tools that combine BIM with CAD applications has been found to have negative consequences, especially in the process of information exchange by different disciplines [34].
Another aspect that adversely affects the implementation of BIM in construction companies, apart from the associated costs, has to do with the need to count on the reliable interoperability of the computational tools used within the entire process [26]. Interoperability undoubtedly allows for the automation of the import-export processes that usually occur within interdisciplinary work. In this regard, the intention is to obtain a complete transfer of the model, meaning a complete export of the geometry, the static loads, the boundary conditions and the properties of the model materials. The IFC format (industry foundation classes) usually has associated errors and a loss of information [26].
On the other hand, it is well known that the design stage is one of the stages considered within lean construction, which seeks the continuous improvement of these processes. Despite good intentions, implementation of this approach in the area of structural design has not been an easy task, especially due to the resistance to change that exists in the companies in charge of carrying out such projects. In the identification of case studies in which lean construction was applied for the improvement of structural projects, one case [35] determined that, among several available options, lean construction adapts more efficiently to the processes typical of a company that develops steel structure projects, based on its low cost, focus on quality and integrated continuous improvement process. Although the case focuses directly on the manufacturing processes of structural steel components, these cannot be separated from the structural design activities that must necessarily be carried out in order to guarantee compliance with current national regulatory requirements.
However, the adaptation of Lean construction to projects is not limited to the peculiarities inherent to the typologies or materials used, as it is also useful when facing very complex projects. Such complex projects are very often linked to the poor performance of the constructed building. In their work, Bascoul et al. [36] try to establish the interdependent relationships that exist between the different stages of a complex project (product design, engineering, installation and use). From this perspective, they encourage the teams involved to understand the work process in a collaborative way, instead of continuing to follow the traditional method that involves the accomplishment of certain milestones, usually identified by the expected deliverables. A significant project that satisfies this condition of complexity is the case of the design of a hospital building [37], which involves the introduction of novel technologies, changes in the distribution of the required internal spaces and the performance of the buildings in their entirety. To the abovementioned characteristics must be added the specificity of the staff working in the building and the users who come to request health care services. The authors focus their recommendations on the joint implementation of BIM and lean construction in order to find solutions that meet the expectations of users, together with a series of technical and regulatory specifications applied to the design of this type of building [38].
A recent study [11] addressed the issue of waste generation, focusing specifically on the waste generated by remodeling projects. By applying the interpretive structural modeling (ISM) method, the study proposed that project offices reduce the emission of waste by adopting a series of measures: • Reusable and adaptable design; • A system for construction drawings and information as built; • Integrated planning for waste management work processes; • Development of waste benchmarking for rehabilitation projects.
In addition, thanks to the availability of new technologies applied to construction processes, it has been possible to combine industrialized structural design work using, for example, 3D printing of reinforced concrete elements, allowing the automation of premanufacturing processes [39]. Without a doubt, the synergy generated by working in BIM environments has made it possible to improve production plans, significantly reducing the generation of waste directly linked to the design of structural components. However, this is only possible as long as the BIM processes are adapted to the particular form of the industries, allowing the constant evaluation of the processes in a flexible way and incorporating changes that improve the perception of the different project components, as happens with mixed reality [40] or automation processes [41].
In a study focused on the joint use of BIM and lean construction in building projects [42], the adaptation of the ways companies operate was studied using an approach that considered the roles of the staff, the design methods and the practice of communication between designers. The authors identified, through a series of surveys directed to designers and design directors in three specific case studies, the most frequent problems in the management of structure design and construction in the context of the implementation of the BIM platform within the companies studied. They identified 13 serious problems and six medium-level problems that had to do with the definition of BIM roles, recurrent problems of information exchange between the different disciplines, changes introduced by redesigns, the design director's lack of familiarity with the ways of working with BIM, conflicts in the models generated independently in the different disciplines, long response times between disciplines, clients not familiar with BIM and changes made but not materialized in the delivered documents. The study's authors considered it necessary to introduce changes related to better management of the BIM implementation in the company and made recommendations on the implementation of lean tools, such as big room, nodes, last planner and design based on sets, for the solution of specific problems.
Regardless of the work methodology adopted, it can be affirmed that the digital irruption has had a positive and permanent impact on structural design companies [43], opening the possibility of starting a global transformation in which the losses and waste that currently characterize the construction industry are generally reduced.

Identification of SEC Operation
Structural engineering companies (SECs) develop the design and calculation of structural elements and systems of various civil works as a part of the process chain-including conception, pre-design, design, documentation, planning, construction, operation and maintenance-which continues to converge until the definitive operation and maintenance of the civil work [9]. Although there are many professionals interacting within an SEC, it is convenient to distinguish between two types: internal professionals of the company (stable, permanently hired staff) and external professionals specific to each project (not directly contracted by the company). SECs usually prepare multiple projects in parallel and thus interact with a broad diversity of people (as each project has different teams). The external professionals comprise clients, architects, specialist engineers, review engineers, construction engineers and management engineers. The internal professionals include senior engineers, project engineers (civil engineers) and draftsmen [44].
For any particular building project entering an SEC, the workflow begins with the arrival of the architectural plans, which contain the spatial dimensioning of the work and a preliminary structuring given by the architecture. These plans are reviewed by the senior structural engineer (a civil engineer with experience in the area), who indicates modifications to the architectural structuring and proposes, if necessary, a new preliminary structuring (the arrangement of structural elements, such as walls, beams and columns, that must support the weight of the structure itself, as well as the potential services and loads it will experience during its projected useful life) [45]. This marks the beginning of the iterative design process and from here, the project is passed on to one or more civil engineers who are responsible for carrying out structural analysis models, verifying the structuring, doing the preliminary design, proposing solutions for the correct design and, finally, producing a calculation report containing the theory applied and the regulatory criteria adopted [46].
In parallel to this civil engineering work, a designer does structural detail drawings (documentation). In this phase, a project engineer informs the designer which structural elements (including how many, their location, etc.) must be included in the plans. Thus, another iterative process begins, this time between the designer and the indications made by the engineer, until the final structural design is completed. At this stage, the project engineer consults with the senior engineer on important modifications and decisions and the senior engineer authorizes or optimizes them. With the structural plans completed, the project engineer and the senior engineer carry out the final review. There may be observations and modifications, which mainly seek to optimize costs without harming structural stability and efficiency. If any changes occur, the process returns to the previous stage [47].
The structural design plans are issued by the design office to be reviewed by another external office (qualified according to current regulations and for projects that the regulations indicate). This external office makes observations and questions the design, providing a detailed report of the observations in the structural plans. When the revised draft is returned, the observations are evaluated; if there are any objections, according to design criteria used, such "mistakes" or omissions are re-evaluated. Once there are no more observations to clarify, the project engineer meets the senior engineer to make the modifications indicated. After that, the initial design phase of the cycle is repeated, starting with modelling and draft modifications and the coming and going of information between the drafter and the project engineer restarts [9,48].
Once the structural design is complete (or simultaneously), engineers from other disciplines carry out calculations and installation plans (electrical, sanitary, water, HVAC, etc.). The SEC, the architectural office or a subcontracted entity uses these sets of plans to coordinate the building systems. This process is part of a highly fragmented system [49].
The processes developed in the structural engineering companies, as detailed above, are summarized in the flow chart in Figure 5.

SEC Activities that Do Not Add Value
Based on the process flow interactions developed in structural engineering companies, Table 4 lists the SEC activities that do not add value by the typical waste categories of lean management. Twenty-five SEC activities that do not add value have been identi-

SEC Activities That Do Not Add Value
Based on the process flow interactions developed in structural engineering companies, Table 4 lists the SEC activities that do not add value by the typical waste categories of lean management. Twenty-five SEC activities that do not add value have been identified and classified into three categories of interaction: I-E, situations occurring between internal (I) and external (E) professionals; I-I, situations occurring among internal SEC professionals only; and I-E/I-I, situations involving both of the two previous types of interactions. The set of SEC activities and their classification were validated by the panel of experts. According to lean management, the type of waste with the highest presence in SECs is W2-"Waste of time on hand" (21 SEC activities, 84%), followed by W4-"'Waste of processing itself" (19 SEC activities, 76%), W3-"Waste in transportation" (18 SEC activities, 72%), W5-"Waste of movement" (17 SEC activities, 68%), W7-"Waste of making defective products" (17 SEC activities, 68%) and W8-"Unused Employee Creativity" (16 SEC activities, 64%). Two additional categories had a much lower presence, namely W1-"Waste of overproduction" (six SEC activities, 24%) and W6-"Waste of stock on hand" (four SEC activities, 16%). Figures 6 and 7 show the details of the survey results obtained for each of the 25 SEC activities that do not add value. Figure 6 shows that for 100% of the SEC activities, respondents rated them with a score of 3 (occasionally), 4 (frequently) or 5 (very frequently). Figure 7 illustrates that for 21 of the 25 SEC activities, more than 50% of the respondents rated them with a score of 3 (moderately important), 4 (important) or 5 (very important); the exceptions were (8) "Delays in deliveries due to questioning of calculations based on differences in design criteria between project review offices", 43%; (24) "Large number of spreadsheets (Excel, etc.) that make the design process slow and cumbersome", 43%; (11) "Large number of spreadsheets (Excel, etc.) that make the design process slow and cumbersome", 38%; and (16) "Errors in final structural plans", 38%.    Table 5 shows the distribution of the SECs participating in the study, according to the size of the projects: (I) less than 500 m 2 ; (II) between 500 m 2 and 1000 m 2 ; (III) between 1000 m 2 and 5000 m 2 ; (IV) between 5000 m 2 and 10,000 m 2 ; (V) between 10,000 m 2 and 20,000 m 2 ; and (VI) more than 20,000 m 2 .   Table 5 shows the distribution of the SECs participating in the study, according to the size of the projects: (I) less than 500 m 2 ; (II) between 500 m 2 and 1000 m 2 ; (III) between 1000 m 2 and 5,000 m 2 ; (IV) between 5000 m 2 and 10,000 m 2 ; (V) between 10,000 m 2 and 20,000 m 2 ; and (VI) more than 20,000 m 2 .  Table 6 shows the results of the ranking based on the importance/frequency analysis. The values of RII, FI and FAII have been obtained and based on the latter, the 25 SEC activities have been ranked. It is possible to see, for example, that the two activities with the lowest FAII (importance/frequency rating), N8-delays in deliveries due to questioning of calculations based on differences in design criteria between project review offices and N11-loss of information from central source (architect, client) when passing across the desks of senior engineers, coordinators, up to the executing project engineer, are the direct responsibility of the senior engineer. By contrast, the highest-ranked activity, N25many projects with similar deadlines as all clients want their projects to be completed quickly, does not depend on a direct responsible (specific person) within the company, but on defining the deadlines with external companies.

Validation of SEC Activities That Do Not Add Value
Furthermore, the activities ranked 2nd, 3rd, 4th and 7th for FAII are highly related to each other (N15-large number of reworks by the designing draftsman due to recurring changes; N1-various returns of the projects to architecture; N3-no notification or spec-   Table 6 shows the results of the ranking based on the importance/frequency analysis. The values of RII, FI and FAII have been obtained and based on the latter, the 25 SEC activities have been ranked. It is possible to see, for example, that the two activities with the lowest FAII (importance/frequency rating), N8-delays in deliveries due to questioning of calculations based on differences in design criteria between project review offices and N11-loss of information from central source (architect, client) when passing across the desks of senior engineers, coordinators, up to the executing project engineer, are the direct responsibility of the senior engineer. By contrast, the highest-ranked activity, N25-many projects with similar deadlines as all clients want their projects to be completed quickly, does not depend on a direct responsible (specific person) within the company, but on defining the deadlines with external companies.
Furthermore, the activities ranked 2nd, 3rd, 4th and 7th for FAII are highly related to each other (N15-large number of reworks by the designing draftsman due to recurring changes; N1-various returns of the projects to architecture; N3-no notification or specification of changes in plans from architecture; and N19-changes in analysis models (partial or global) due to project modifications). Iterations with architecture (N1, FAII: 1st) could be directly related to the re-drawing of the project (N15, FAII: 2nd). However, problems in communication channels (N4, FAII: 15th) and lack of meetings in the process (N5, FAII: 23rd) do not seem to affect the workflows in the SEC companies as much as aspects related to the initial coordination of the projects (N6, FAII: 6th) and timely information of changes (N3, FAII: 4th). In addition, the results of the Kruskal-Wallis test, based on the six size categories in Table 5, are shown below. Table 6 shows the hypothesis and results for each issue. There is no difference in perception, for either importance or frequency, with respect to the different sizes of projects carried out by the SEC respondents in all cases.

Limitations
According to the development of the study and the analyses carried out, the research had the following limitations:

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The study considered only structural engineering companies in Chile. The 37 companies evaluated are not a global statistical sample; however, the study establishes trends for this country and provides a guideline for further studies that may examine companies from different countries, by making qualitative and quantitative assessments of the results obtained.

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The activities and workflow described in the SEC operations, together with the problems identified therein, correspond to privately contracted building projects. It is important to note that the results shown may be influenced by the type of projects developed by the companies, which are focused on residential or commercial buildings using a structural typology based on reinforced concrete walls and slabs, designed under the high levels of seismic hazard in Chile.

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The study did not measure the combined effect of the 25 non-value-adding activities identified. Therefore, future research should identify the origin and evaluate the combined impacts of these activities and quantify the individual and combined effects on the processes' performance (both quantitative and qualitative).

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The workflows and non-value adding activities identified are not necessarily all the possible ones that can be presented, as practices associated with specific IT processes, such as the use of BIM or work in the cloud, were not considered. Further studies should evaluate the impact of these methodologies and technologies and the improvement they bring to the processes.

Conclusions
In structural engineering companies (SECs), interactions between professionals both within and outside the organization, and the workflows they follow tend to create situations that decrease productivity, interaction problems among different professionals, inefficient exchanges of information, inadequate communication channels, reworks and recurrent changes. Several authors have described activities and workflows, mainly in the complete design and construction process (not focusing on or detailing the structural design stage) [11,18]. They have shown, based on case studies or macro analyses of the construction sector, several of the problems described in this work concerning fragmentation [1,3], interaction problems [2] and its consequences for the processes [4,[20][21][22][23][24][25], associated with reductions in quality, time efficiency and general management problems. This study collected part of those experiences and focused on and detailed the workflows and issues in the structural design process. Moreover, these diverse situations were categorized into 25 specific activities and evaluated by several professionals in the field in relation to their importance and frequency. Concerning importance, all problems raised were considered shortcomings affecting the correct development of daily tasks, thus damaging optimal SEC workflows. In terms of frequency, 21 of the 25 problems were rated as highly recurring in the daily work of professionals.
In addition, it was found that SEC activities are independent of project size. In other words, in all cases studied, there was no difference in respondent perception, either in importance or in frequency, with respect to the different project sizes. Thus, in light of the results obtained and in view of the professionals involved, it was concluded that SECs present several deficiencies that interrupt the flow of processes and interactions. In general terms, similar problems were found irrespective of the size of the company and the size of the project. Therefore, SECs require methodological and technological restructuring to improve productivity and methodologies such as BIM could help to solve these problems effectively.
The results of this study allow general managers of SECs and their project managers to identify the main types of waste incurred in their projects. The identification of waste allows organizations to diagnose the problem and to propose improvement plans for the systematic mitigation or elimination of waste from the production process. Additionally, this study provides a questionnaire that allows SECs to self-diagnose and to compare themselves with similar companies.
As outlined above, this study had some limitations: the sample size does not allow for making inferences that characterize all structural engineering companies; the study only identifies the waste and not the sources of waste; it focuses on privately contracted building projects; and it does not propose actions, tools or technologies for the improvement of the processes of structural engineering companies. Therefore, for future studies, it is recommended to increase the sample size, to identify the sources of losses and their interactions in the SECs and to propose methods for the improvement of the productivity of the SECs, based on Lean Management and BIM methodologies.