Introduction

Concrete formwork systems are temporary framework systems which are used for the cast-in-situ or precast construction (providing structural shape and texture of the plastic concrete on hardening) of Reinforced Cement Concrete (RCC) structures. It plays a paramount role in the construction of RCC structures, precisely, the cost of formwork construction (forming cost) and construction time pertaining to erection and assembly of formwork systems (forming time) contributes to 10 and 50% of the overall cost and overall time of the entire construction project, respectively (Hanna 1999; Peurifoy and Oberlender 2010; Jha 2012; Hurd 2005). Besides both forming cost and forming time, other associated attributes like forming quality, forming safety and environmental sustainability, significantly influences the concrete formwork systems (Kannan and Santhi 2013a).

These intrinsic and interdependent characteristics which influence the profitability of formwork construction can be fragmented into five major criteria as cost, time, quality, safety and environmental sustainability. These five criteria are instantiated using a phenomenal construction project management technique known as ‘Constructability’.

Constructability

Construction Industry Institute (CII) (1986) defined constructability as “a system for achieving optimum integration of construction knowledge and experience in planning, engineering, procurement and field operations in the building process and balancing the various project and environmental constraints to achieve overall project objectives”. ASCE, Construction Management Committee (1991) defines constructability program as “the application of a disciplined, systematic optimization of the construction-related aspects of a project during the planning, design, procurement, construction, test and start-up phases by knowledgeable, experienced construction personnel who are part of a project”. Constructability is the only project management technique designed and developed solely by the construction industry for the construction industry (McGeorge et al. 2012). The concept and scope of constructability and buildability are synonymous similar and are used interchangeably by many researchers, however, for the sake of clarity, the term ‘constructability’ is monologously considered and used throughout this research. To integrate constructability efficiently and efficiently into overall phases of the project, a specialized classification system incorporating all the attributes or factors that influences constructability are to be identified and listed in a logical sequence (Hanlon and Sanvido 1995).

Constructability information model

Many researchers developed single-user classification systems for categorizing and storing the constructability information (Hanlon and Sanvido 1995). The classification systems developed by some of the researchers are highly unique (domain specific and predilection in the classification format) and does not cover the overall phases of the project comprehensively (Hanlon and Sanvido 1995). Hanlon and Sanvido (1995) described the prominence of the constructability information classification system that covers over all phases of the project since it is the prelude for constructability assessment. They developed a sophisticated framework called as Constructability Information Model (CIM) through which constructability information is classified, stored and retrieved accurately and efficiently throughout the project. The CIM comprises two parts, first is the categories of information and its associated attributes and other is the storage format of attributes (Hanlon and Sanvido 1995). To ease the process of the constructability, the classification of various concrete formwork systems augmenting this research is illustrated in Fig. 1 and ensnared schematically in Table 1, also, the constructability information scheme adapted for this research incorporating all the attributes traversing the concrete formwork construction is illustrated in Fig.  2 and tabulated in Table 5 of Appendix ‘Constructability information scheme for concrete formwork systems’.

Fig. 1
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Distinct classification of concrete formwork systems

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Table 1 Nomenclature of concrete formwork systems
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Fig. 2
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Constructability information classification schema

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Constructability Assessment of Concrete Formwork Systems

The appreciable work on implementing the concept of constructability in concrete formwork design was initially carried out by Touran (1988). O‘Connor and Davis (1988) and CRSI Report No. 32 (1989) depicted the importance of interaction between formwork contractor and Engineers for attaining rapid construction cycle by virtue of performance-oriented specifications of formwork construction such as selection of suitable formwork systems (Gang formwork system and flying truss formwork system) for rapid cycle, strength and serviceability consideration of formwork systems and choice of shore-replacement methods: backshoring, reshoring and preshoring. Meanwhile, Fischer (1991) realized the importance of incorporating constructability even in the formwork planning phase for reinforced concrete construction projects. He also emphasized the importance of selection of appropriate construction crew for specialized formwork systems like self-climbing formwork, etc., as they are generally complex in nature requires highly skilled and qualified personnel and mostly custom-made systems demands a higher degree of planning garnering space adequacy, access for materials transport and crew during construction (Hanlon and Sanvido 1995) etc. Generally, to achieve these details, a well-documented framework or guide comprising set of rules/criteria developed by expert members are employed. For this research, a comprehensive overview of all the constructability criteria pertaining to concrete formwork construction for performing constructability analysis, the promulgated ideas and information pertaining to the global concrete formwork construction by various experts are recorded through an intriguing mechanism known as ‘Constructability Survey’.

Constructability survey

ASCE, Construction Management Committee (1991) emphasized that to enhance constructability into construction projects ‘experienced construction personnel need to be involved with the project from the earliest stages to ensure that the construction focus and experience can properly influence the owner, planners, and designers, as well as material suppliers’. Experienced personnel mean persons having a full understanding of the nature of the project from start-to-finish and acquired knowledge from the previous and similar projects (Kartam and Flood 1997) which was done earlier rather than sticking with the project for a long period of time. More importantly, the experienced personnel should have deeper knowledge on modern or innovative construction process or methods (O’Connor and Miller 1994). These skills are generally acquired through a process called ‘Constructability Survey’.

Kannan and Santhi characterized constructability survey as ‘a process to acquire the knowledge and experience by adequate hands-on-training in a project (similar to the proposed project) for a particular period of time, in collecting work samplings, gathering information on work sequencing, productivity, contractual procedures and material handling function, etc., from the construction personnel/industry actually involved in the project’ (Kannan and Santhi 2013b). For performing constructability analysis of concrete formwork systems, 173 residential construction projects was surveyed. The template used for the survey are given in Table 6 of Appendix ‘Constructability survey template’. From the constructability survey, the weights assigned to compute constructability score of each concrete formwork systems are calculated using a technique known as Relative Importance Index (RII). Researchers characterize RII as a measure of the extent to which each variable contributes to the prediction of the criterion individually and in combination with the other variables contributing to the prediction (Johnson and LeBreton 2004; Somiah et al. 2015). It is also termed as ‘relative weight’ and is calculated using the expression as shown in the Eq. 1.

$$\begin{aligned} {{\hbox {RII}} = \dfrac{\sum \limits _{i=1}^{{N}}w_i}{w_h\ \times \ {N}} (0 \le {\hbox {RII}} \le 1)} \end{aligned}$$
(1)

where, \(w_i\) is the rating or weight of each factor (0–10), \(w_h\) is the highest rating or weight allocated to each factor (i.e., 10 for 0–10 rating scale, 11 point Likert scale) and N is the total number of responses recorded. For instance, RII for Forming cost, \(C_i\) is calculated as shown in the Eq. 2.

$$\begin{aligned} {{\hbox {RII}}\ =\ \dfrac{\sum \limits _{i=1}^{173} w_i}{9.21\ \times \ {173}}\ =\ \dfrac{8.23\ +\ 6.45\ +\ \cdots \ +\ 9.21\ +\ 7.71}{9.21\ \times \ {173}}\ =\ 0.9450\ \approx 0.95} \end{aligned}$$
(2)

Where, \(\sum \nolimits _{i=1}^{173} w_i\) is the values of the forming cost, \(w_h\) is the highest rating of forming cost (9.21), N is the total number responses (173). Similarly, the RII value of other constructability criteria are determined, the sum of all the RII values is 4.0. The weight of each constructability criteria is calculated using Eq. 3

$$\begin{aligned} {w = \dfrac{{\hbox {RII}}}{{\hbox {Total RII}}}} \end{aligned}$$
(3)

For example, the weight of the constructability criteria, Forming cost, \(C_i\) is calculated as shown in Eq. 3 using Eq. 4.

$$\begin{aligned} {w\ =\ C_i\ = \dfrac{\hbox {RII}}{\hbox {Total RII}} = \dfrac{0.95}{4.0} = 0.2375\ \approx 0.24} \end{aligned}$$
(4)

Similarly, the weights for other constructability criteria are also calculated using Eq. 3. The overall RII value and weight for each constructability criteria was calculated and ranked based on the higher value of the RII values as shown in the Table 2.

Table 2 RII value and weight for each constructability criteria
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The application of RII in determining weights of these criteria is portentous than computing through commonly used statistical measures, i.e., median and mode of the sample distribution. Thus, the Constructability Score (CS) for concrete formwork systems can be computed using Eq. 5.

$$\begin{aligned} {{\hbox {CS}}\ =\ \dfrac{0.24 \times \sum \limits _{i=1}^{8}C_i\ +\ 0.23 \times \sum \limits _{j=9}^{16}C_j\ +\ 0.20 \times \sum \limits _{k=17}^{24}C_k\ +\ 0.17 \times \sum \limits _{l=25}^{32}C_l\ +\ 0.16 \times \sum \limits _{m=33}^{40}C_m}{8}} \end{aligned}$$
(5)

The constructability score of a comprehensive concrete formwork system (project specific system) and optimum constructability score (optimal constructability score obtained using Linear Programming) for individual formwork system that are used in the 173 projects are tabulated in Tables 3 and 4 respectively.

Table 3 Constructability survey report
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Table 4 Constructability score for different formwork systems from the constructability survey
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Constructability rating

Constructability scoring or rating of concrete formwork systems for determining optimal constructability score for simpler constructions can be performed manually and more accurately without any difficulties, but for the heavy construction projects due to its inherent difficulties and complexities associated with the projects, performing constructability rating is quite perplexing rather challenging and hence additional guides and tools are required. Many researchers developed computerized solution for constructability implementation for concrete formwork construction starting from integrated microcomputer packages (Christian and Mir 1987; Tah and Price 1997), 2D CAD and 3D CAD models to sophisticated ‘Enterprise Design/Data Management’ (EDM) and Building Information Modeling (BIM) for developing nD models (Kannan and Santhi 2013b; Kannan and Knight 2012; Lee et al. 2009; Kannan and Santhi 2013a, 2015; Jun and Yun 2011; Meadati et al. 2011; Neto and Ruschel 2015) and collaborative construction process using customized software tools (Multimedia constructability tool 1998; Ganah et al. 2005; Hijaji et al. 2009).

Building information modeling

BIM is a digital representation of physical and functional characteristics of the buildings developed in the pre-construction stage or even during the conceptual stage (pre-design stage) of the project which provides provision for the participation of client, stakeholders, engineers and contractors in a single platform so as to eliminate all the possible errors that could probable occur in a project even at the beginning of the project so as to produce flawless diagrams and could be readily updated at any point of time, generally this features is called as ‘parametric-change characteristics’.

The parametric change characteristics of 3D BIM formwork module was visualized and portrayed in detail by Kannan and Knight (2012). The parametric change capabilities of 3D BIM formwork module were further extended to account for the automatic layout and simulation of concrete formwork systems and to perform 4D and 5D constructability analysis by Kannan and Santhi (2013a). A detailed retrospective assessment of constructability analysis of three major types of climbing formwork systems, namely, crane-independent climbing formwork system, semi-dependent climbing formwork system and automatic climbing formwork system traversing the cost, time, attributes using 3D BIM was carried out by Kannan and Santhi (2013b). The 3D BIM formwork module proves to be an essential tool in checking for clashes with the associated 3D BIM architectural, structural and MEP models in the pre-construction stage of the construction project, which is commonly termed as ‘clash detection’ (Kannan and Santhi 2015) to identify and eliminate obstacles or prevent error, delays and cost over-run that could probably occur during construction. Thus, the interoperability characteristics of BIM plays a vital role in incorporating the constructability criteria of formwork construction (Kannan and Santhi 2013b, 2015; Hijaji et al. 2009; Kim and Cho 2015). In this research, the implementation of BIM for constructability assessment of concrete formwork systems is portrayed for the pre-construction visualization and decision-making phase of a project

This is achieved by developing an unique add-in functionality for Autodesk Revit known as ‘CONSTaFORM’.

CONSTaFORM

For developing a comprehensive add-in for Constructability assessment of Concrete formwork systems in Autodesk Revit, a detailed formulation and fragmentation of unified 3D BIM Model (3D Structural BIM + 3D BIM Formwork Module) is necessitated and the manoeuvring process involved in accomplishing the same are delineated in the Figs. 3, 4, 5, 6, 7, 8 and 9. The detailed convoluted procedures are elaborated as follows: initially, 3D BIM Structural Model of a 20-storied building is created using the 2D BIM structural floor plan as in Fig. 3 and 2D BIM structural elevation as in Fig. 4 then, convert the solid 3D BIM Model as in Fig. 5, into wireframe 3D BIM model as shown in Fig. 6, which acts as a reference for 3D BIM Formwork Family insertion. Then 3D BIM Formwork Module are created separately as Component Family File, i.e., a type of Revit Family that is available for all the Revit projects and gets loaded into the projects when necessary as in Figs. 7 and 8. The detailed process of integration of the 3D BIM Structural Model and 3D BIM Formwork Module is illustrated in Fig. 9 (Kannan and Santhi 2013b, a, 2015).

Fig. 3
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Typical 2D structural floor plan of a 20-storied building

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Fig. 4
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Typical 2D structural elevation of a 20-storied building

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Fig. 5
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Typical 3D BIM model of a 20-storied high-rise building

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Fig. 6
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Conversion of solid 3D BIM to wireframe 3D BIM model

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Fig. 7
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3D BIM wall formwork Revit family file depicting a system wall formwork

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Fig. 8
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3D BIM formwork accessories Revit families

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Fig. 9
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Sequence representing the process of integration of 3D BIM formwork family with 3D BIM structural model, incorporation of a wall formwork, b column formwork, c beam formwork, d slab formwork, e formwork supporting element and f formwork accessories

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The constructability score of each concrete formwork system from Table 4 is incorporated directly into its” respective 3D BIM formwork family file as ‘shared parameters’ (information of the parameters stored explicitly in each 3D BIM family file for accurate retrieval) is shown in Fig. 10.

Fig. 10
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Incorporating respective constructability score into the 3D BIM wall formwork family as shared parameter

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This unified 3D BIM Model plays a key role in the development of ‘CONSTaFORM’, an Add-in for Autodesk Revit to perform constructability assessment of concrete formwork systems using BIM. This can be achieved through a cutting edge methodology known as ‘API-fication’.

API-fication

API is a short form of ‘Application Programming Interface’ is an all-embracing term related to computer programming, which is a set of protocols and tools used by developers for building application software and also in many cases, it used to enhance the functionality of the existing application software. Thus, the process of revamping the application software architecture by modification or alteration to enhance additional functionality is termed as API-fication. In this research, the CONSTaFORM Add-in is developed by customizing Revit API through both Revit Macro Manager (MM) as shown in Fig. 11 and Visual Studio software using C# language in .Net Framework (Rudder 2013). The detailed description of the development environment of the CONSTaFORM Add-in is given in the Algorithm 1.

figure a

The detailed description of the steps involved in the Algorithm 1 are as follows. To create CONSTaFORM add-in for Autodesk Revit, the initial process is to create a application, invariably to create a module named ‘CONSTaFORM’ using Revit Macro Manager (MM) as shown in Fig. 11. The programming language used in this research is C# language in .Net Framework, however, the customization can also be done using other programming languages like Ruby and Python. The customization of the Revit Macro can be done using the Revit’s in-built Script, but for enhancing the versatility of the code editing, Visual Studio is used in this research. Initially, the two important libraries known as RevitAPI.dll (database library) and RevitAPIUI.dll (user-interface library) are referenced into the project with marking Copy Local to False, i.e., any customization of these libraries will not modify the parent or existing library files (Rudder 2013). Using, the referenced libraries, the class of elements known as namespace elements such as Autodesk.Revit.DB and Autodesk.Revit.UI are imported respectively, and then, a new class file, CONSTaFORM.vb is created in the Visual Studio. Then using the Autodesk.Revit.UI user-interface namespace, user-interface elements such as TaskDialog Box, Ribbon Panel and PushButtons are created for the CONSTaFORM Add-in. A sample 3D BIM formwork family file is loaded into a 3D BIM Structural Project, the details of the shared parameters corresponding to 3D formwork family is obtained using get ElementInfo. This process is carried out for other 3D BIM formwork family, to find out the 3D BIM formwork family files with missing parameters, provided ElementInfo = Null in the code, for displaying the missing parameters. For missing parameters, values are entered manually as in Fig. 10.

Fig. 11
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Screenshot of the process of creating CONSTaFORM add-in using Revit Macro Manager (MM)

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When all the 3D BIM formwork families are verified, the process of assembly of all the formwork systems required for a sample project is done as in Fig. 9 to get the information pertaining to the overall formwork systems using GetObjectFromReference. Using the pick surface function, the details of each formwork systems are obtained. Then, using pick surface for the entire project, selects the overall formwork systems used in the entire project, this is used to compute the overall constructability score of formwork systems used in the entire project. To be precise, the values of the formwork systems are initially stored in a directory as a relational database and the computation of the constructability score is carried out like in the Fig. 12 using Eq. 5. The output of the constructability score is visualized in a dialog box as shown in Fig. 13.

Fig. 12
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Relational diagram for constructability assessment of concrete formwork system

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Fig. 13
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Output of CONSTaFORM depicting the overall constructability score for the integrated 3D BIM Model

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Results and discussion

From Fig. 13, we infer that, the CONSTaFORM Add-in provides a vivid display of the overall constructability score of concrete formwork systems used in the entire project, however, the CONSTaFORM Add-in should be checked for reliability of the final constructability scores, this is actually performed using an important functionality of BIM, known as parametric change characteristics as in Figs. 14 and 15.

Fig. 14
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Schematic illustration of parametric change characteristics of BIM

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Fig. 15
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Output of CONSTaFORM depicting the overall constructability score for the integrated 3D BIM Model after the parametric change

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The parametric change characteristics of the BIM not only accommodates the effective modification of the 3D BIM formwork families but also provides a semi-intelligent markup, i.e, when changing the 3D BIM system wall formwork family to 3D BIM conventional wall formwork family as in Fig. 14, the associated formwork accessories of the 3D BIM system wall formwork family are deleted instantaneously. This brings down some of the major complexities associated with the formwork planning. Moreover, for a greater understanding of the clashes between different 3D BIM Formwork families and 3D BIM structural model, a sophisticated process known as ‘clash detection’ is carried out using the same integrated 3D BIM model in a separate software, say, Autodesk Navisworks. Then, after resolution of the clashes in the integrated 3D BIM Model, it is then transferred to Autodesk Revit for performing the constructability rating.

One of the advantages of the CONSTaFORM Add-in is that the outputs, i.e., the overall constructability scores as well as the constructability scores of each concrete formwork system can be exported to Microsoft Excel, MySQL and other database management systems for further data analysis.

In addition to the capabilities of incorporating parametric change characteristics, it should be incorporated in a real-time construction projects for actual advocacy and validation.

Validation

For validating the CONSTaFORM Add-in, an ad hoc testing in a real-time project is carried out. The following are some of the salient features of the real-time construction project considered for the analysis.

  • 14-storied residential building as in Fig. 16

  • Modular aluminium formwork system is used for the construction as illustrated in Fig. 17

Fig. 16
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Architectural elevation of the proposed high-rise residential building

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Fig. 17
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Integrated 3D BIM model of the proposed high-rise residential building

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The overall constructability score of concrete formwork systems for this project, obtained from the CONSTaFORM Add-in is shown in Fig. 18.

Fig. 18
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Output of CONSTaFORM depicting the overall constructability score for the integrated 3D BIM Model for validation perspective

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Conclusion

The CONSTaFORM Add-in developed in this research is an innovative automated constructability rating framework system for assessing constructability of different concrete formwork system. The developmental procedure adapted for CONSTaFORM Add-in, in this research, is based on various possible techniques and tools by trial and errors. From Figs. 13, 15 and 18, we infer that, the CONSTaFORM Add-in is capable of adapting in all the situations traversing from the 3D BIM models to a real-time project.

Further research

This research promulgates the interoperability of BIM for constructibility assessment of concrete formwork systems, withal this concept can be extended to incorporate in other modern reality technologies such as virtual reality, augmented reality and mixed reality so as to enhance and explore further functionalities of BIM (Boga et al. 2018). Additionally, the capabilities of BIM can be further enhanced by coupling with the open source graphical software like Dynamo (Griendling 2016), blender and so on. Additionally, the clash detection process of the 3D Integrated BIM Model (3D BIM structural + 3D BIM formwork module) is carried out externally using Autodesk Navisworks, thus, the API-fication process (customizing Navisworks API) can be incorporated in Autodesk Navisworks to synchronize with Revit API to perform the clash detection process of the integrated 3D BIM Model intermediately or simultaneously.