Adaptive design of formworks for building renovation considering the sustainability of construction in BIM environment – case study

Progressive technologies and practices are shifting the possibilities of building design and improving work efficiency. Constantly changing site conditions require different procedures and designs that take into account these changing conditions, whether it is a design solution, a change in environmental conditions, or just sustainability factors. Adaptive building design offers opportunities to cope with changing factors to achieve the highest possible level of building quality. This case study deals with the topic of adaptive formwork design for building renovation, taking into account sustainability. Aim of the article is an investigation and demonstration of the building information modelling (BIM) environment used for the adaptive design of formwork elements for the building renovation in the context of sustainability. The object of the case study is a building in the center of Kosice, Slovakia. BIM environment allows prompt and correct adaptation of the formwork design to changing conditions of lighting, ventilation, heating and temperature during the design of the building.

for increasing the efficiency of construction, from the design of the building and its structural elements to the implementation and use of the building. A high degree of adaptability of building design increases the success of a construction project, environmental impact and sustainability. The impact of building design on living conditions can be large. Many, for example, according to studies [8], in China, buildings have consumed almost 28% of the country's total energy in terms of the life cycle [9]. For this reason, too, adaptability in the design phase of a construction project is crucial. As other authors state [10], technological and design solutions must be based on the interrelationship between building organizations and the environmental system.
Foundation is an important process, so it must be well planned. Construction planning begins with the design itself, and this part of the project should also take into account all factors and aspects of the impact, such as weather and environmental conditions. Ensuring a high degree of adaptability in this phase is very important in terms of impacts and possible changes in the project. Since the degree of adaptability is minimal to none during the implementation itself, in the design phase there is room to take into account all the conditions and thus adapt the construction of the building based on these changing facts. As the authors of the study state [11], the designers of the formwork design must also address the issue of increasing the demand for the criteria of the formwork structures. These are, for example, higher construction loads, construction of formwork at high heights, cramped conditions, adherence to a schedule that is borderline for formwork work, adherence to the shape and quality of the surface, economic accessibility and environment conditions.
Given the above facts, the scientific question arises here, what is the use of the BIM environment for the adaptive design of formwork elements in the reconstruction of a building in the context of sustainability?

Formwork and Designing in Adaptive Architecture
The technological process of removal is an important process in the construction of concrete structures. The term removal expresses the process of making the formwork, which will temporarily form the shape of the considered object filled with fresh concrete [12]. The formwork produced (such as supporting structures and molds) must be highly reliable and should not be subject to the overall load due to the weight of the fresh concrete. Improper construction or under sizing of such structures may change the parameters of the final concrete structure to such an extent that it is not technologically permissible. Formwork must be planned and designed with regard to the conditions of the building and its surroundings. This design is in 2D or 3D rendering. Experts must be able to read 2D drawings and assemble a reinforcement cage in 3D to place reinforcements in a reinforced concrete (RC) formwork [13]. After this step and installation, another important task before pouring the concrete in terms of static performance and construction is to check the position and dimensions of the formwork and reinforcements. Formwork is a significant cost factor in reinforced concrete construction [14][15][16]. Therefore, his proposal is a feedback judgment also with the management of the costs of a construction project, which leads to the need to use information technology enabling a new connection in the design and budgeting of buildings [17][18]. According to studies, formwork can account for up to 15% of construction costs and 33% of concrete structure costs [19]. As the authors further point out, the disorganized management and handling of formwork systems can result in an inefficient construction schedule and a consequent impact on the overall construction budget [20]. Formwork plays an important role in projects and civil engineering, while it is important to use technologies for their simulation and design according to needs, experts say [21]. The construction of the formwork consists of a mold, a support system, a support system, connecting elements and auxiliary work platforms. To create the desired shape of the concrete structure, a form of formwork is used, for the production of which mainly wood from coniferous trees is used, but also wood-based materials such as fiberboard and plywood. The main function of the formwork structure support system is to stabilize the mold, distribute the load to the surrounding environment and to the loadbearing parts of the building. We use connecting elements to connect the structural parts of the formwork. Fasteners include threaded rods, screws, steel wedges, etc. Workers use auxiliary work platforms to store and compact fresh concrete. The basic division of the formwork is shown in the table Tab. 1 and is divided into single and multiple according to use [23]. Designers of formwork design need to pay more attention to the issue of increasing the demand for formwork structures, such as: higher structural load, formwork construction at high heights, cramped conditions, adherence to the timeline, which is borderline formwork work, adherence to shape and surface quality, economic availability. Companies place more emphasis on safety at work [11]. The choice of formwork can be affected by several parameters. Adaptive architecture and design bring opportunities to transfer these changing parameters to the virtual environment during the design itself. At the outset, it is necessary to set design criteria and set a priority. The choice of formwork depends on the criteria set by the contractor, but also on the conditions and specifications of the building itself, the environment [22]. The choice of the formwork type corresponds to the required technological, environmental and economic criteria [24].
In the design and dimensioning of the formwork elements, it is necessary to take into account all the loads that will act on it at a given time of use. The structural formwork system must be designed and constructed to withstand the effects of gradual construction [11]. When designing and dimensioning formwork components for individual concrete structures, it is necessary to take into account the adaptive factors that affect the formwork load. These considerations [25]: • self-weight, reinforcement and concrete loading, • the properties of fresh concrete affect the magnitude of the pressure action on the formwork structure, • site loads (workers, technical equipment, etc.), including the static and dynamic effect of the laying, compaction and secondary transport of fresh concrete, • environmental aspects (snow and wind loads, wheatear conditions, and so on).
Design and dimensioning of the system formwork structure should take into account the processed static data for the individual formwork construction systems. These are the so-called static characteristics of the system elements of the formwork, which have been processed in tabular form on the basis of verification by means of tests. These are also affected by environmental impacts, such as geographical location and associated normal weather conditions, in particular aspects such as temperature, seasons, wind, rainfall and others. Dimensioning and design of elements must be based on current applicable standards. Most formwork manufacturers provide static tables containing accurate data, which greatly simplifies the design and dimensioning of formwork. This design must be adapted to the current conditions of a particular building. Emphasis on sustainability also places demands on the adaptability of the solution design and the possibility of customization to the specific requirements of the construction project.

Building Information Modelling and Adaptive Design of Formwork
The building information modelling (BIM) can be defined as a process through which the collection of information about a building is ensured during its entire life cycle [4;26]. This means from design to design through construction and operation of the construction to its liquidation [27]. The database of information created in this way allows all project participants to take into account possible errors and shortcomings, changing factors that could cause possible financial, technological and environmental problems in individual phases [28]. This can also have other economic implications [29][30]. Through BIM, it is possible to identify these problems at an early stage, thus preventing their occurrence [31]. The information model of the building created already in the preproject phase allows the investor to make a decision based on the available information and set specific goals. It will allow the designer, investor and end user to cooperate in the project phase in creating the design and in implementing any changes in the project. Reducing the impact and eliminating errors can be prevented by comprehensive integration of components in the implementation phase with the help of the designer, implementer and suppliers [32]. BIM allows the creation and management of digital information, represents the physical, functional and geometric parameters of the object [33]. The difference between classical 2D design and BIM modeling can be observed in the creation of project documentation and work with it. The basis for the design and implementation of the building is not only obsolete procedures in the form of 2D documents created using CAD software, but gradually moving to 3D, 4D and multidimensional models [34].
Advances in information technology bring changes in design in construction. Manufacturers of building materials are also involved in the new way of designing BIM, contributing by creating digital libraries, initially only for designers and architects. The created BIM objects are carriers of information that the designer needs in the design phase of the project. If he did not have this information, he would have to obtain it via the Internet or from a specific manufacturer, which will significantly increase the time of completion of a given phase of the project and the BIM model will not have the required level. There are databases where it is possible to download the necessary BIM objects into the project, from a specific manufacturer and with the necessary level of LOD detail. BIM objects are made as 2D, 3D. Libraries should contain certified products. Leading manufacturers who produce certified products also insert the logo of the given certification into BIM objects, if the parameter of the certified element changes to another parameter that is not certified, in which case the certification logo disappears [35].
In the catalog documents intended for BIM objects, the manufacturer can state material construction-physical characteristics, which can be used for easier use in individual designed models. These constants simplify the definition of created models. These constants include, for example [36]:

Materials and Methods
Variable environmental conditions of buildings are already evident in the design of buildings. Design of buildings is not only focused on the design of structural, technical, static and sustainable building conditions. During the design of the construction, it is necessary to consider the construction, technological, time, economic and safety conditions of the construction processes. An important part of the construction process of reinforced concrete structures is formwork. The formwork design should also have adapted to the changing conditions of the building design. This is possible through building information modelling (BIM) environment for formwork design.
Aim of article is an investigation and demonstration of the building information modelling environment use for the adaptive design of formwork elements for the building renovation in the context of sustainability.

Research Material
Research focuses on the possibility of formwork design in the BIM environment will be demonstrated through a case study.

Object of Case Study
The object of the case study is a building in the center of Kosice, Slovakia. Renovation of the building includes demolition work and reconstruction of load-bearing and non-load-bearing elements of the building and a superstructure of two floors ( Figure 1).  Demolition works involve the demolition of partitions, perimeter infill masonry, part of the foundation strips, foundation slab, part of the reinforced concrete ceiling slab and roof structure ( Figure 2).
The superstructure of two floors connects to existing reinforced concrete skeletal structure which will be preserved. The building is based on concrete foundation strips, th. 600mm; vertical loadbearing structures are masonry, th. 440mm; and newly built horizontal load-bearing structures are formed by reinforced concrete ceiling slabs, th. 265mm.

Software Tools for Adaptive Design of Formwork
An integral part of the concreting works of reinforced concrete structures is formwork. Design of formwork elements in BIM environmental has to be supported by software tools in three directions: Currently, there is a wide portfolio of software support for BIM design. The most used programs in the Slovak and Czech construction practice are developed by Graphisoft, Autodesk, Tekla, Allplan, particularly ArchiCAD, Autodesk Revit and Tekla Structures ( Figure 3). Building modelling works on the principle of modeling elements to create a realistic virtual model of the building. An indisputable advantage of software supporting BIM design is a sharing information among the various stakeholders involved. Each software has its own tool for project collaboration, information sharing and document management: ArchiCAD 22 -Teamwork, Autodesk Revit 2020 -Worksharing, and Tekla Structures -OpenAPI [37][38][39][40][41].   [42,43].
PeriCAD is a tool for experienced CAD users to design professional system formwork. It allows users to create perfect 3D models for professional drawing documentation. The software is suitable for designing all types of formwork and scaffolding from company. The software speeds up preparatory work of construction process by the detailed drawing of details and an accurate list of formwork elements [42]. DokaCAD software was developed for efficient design of Doka formwork systems. It is basically an extension of the AutoCAD program, which is used for 2D and 3D design and construction of various elements or objects. The disadvantage of software AutoCAD is that the separate software does not include automated formwork insertion. DokaCAD, which is used for designing of formwork drawings, makes this possible. The DokaCAD software contains a number of pre-modeled formwork elements offered by Doka. The use of this software facilitates and speeds up the work of designers. Barrier of this software is that it is not possible to use automatic placement of elements in the whole range for more complex constructions and for this reason it is necessary to model the elements manually [43].
The significant point of software support for formwork design use is their connection with software support for BIM design. Data packet Peri containing the complete catalog of formworks element is possible to insert into the Autodesk Revit. The packet contains a number of functions to simplify the correct design of individual components in the formwork system, allows to automatically connect individual elements of the formwork. Moreover, the result of the formwork design can be a detailed visualization of the formwork model [42]. Tekla Structures supports connectivity with software for formworks design of Doka and Peri [44].  [47,48]. Visualization of information model of building is possible through virtual, mixed or augmented reality [9]. Virtual reality (VR) is used to simulate a computer-generated 3D model in a virtual environment in real time. 3D model display technologies include VR headsets, which use a smartphone to display a 3D model in virtual reality [45]. An application BIMx is used for virtual display of 3D models created in ArchiCAD. The generated BIMx information can contain the entire drawing documentation and its various 3D views (visualizations, load-bearing structure, truss, construction details, etc.) [46]. Augmented reality AR is the connection of the virtual environment with the real world [47]. The Doka AR application is used to display 3D models of formwork in augmented reality ( Figure 5). The application allows you to view different types of formwork systems, e.g. Framax Xlife, Dokadek and others. The user gets a real view of the 3D formwork system [48].

Research Methods
Research of the BIM environment use for the adaptive design of formwork elements will be carried out through a case study. A case study method presents the form of qualitative analysis of particular issue. The quantitative information is not collected [48]. The proving design the adaptive design of formwork elements possibilities is proposed in four steps: Flowchart of adaptive design of formwork elements in BIM environment ( Figure 6) describes the processing of this issue as a case study. The object of the case study has to be a building that contains concrete or reinforced concrete elements. Formwork is part of the construction work of these elements. Buildings that do not contain concrete or reinforced concrete elements cannot be the subject of a case study. The construction design must be processed in software that supports the BIM environment. Therefore, the next step in the case study is to select a suitable software tool for building information modelling. The selected tool must cooperate with the software for formwork design. Also, selected software tool for formwork design must cooperate with the software BIM. Their mutual cooperation and interactivity represent a prerequisite for the creation of adaptive design of formwork elements.
The adaptability of the design lies in the possibility of changing the construction project in the BIM environment. During the design phase of the construction, the construction project may change. Project changes can have various causes: change of layout, change of technical requirements of the construction, change of legislative requirements, change of demands on time, quality or construction costs [48]. Changes can be initiated from all project participants (investor, architect, designer, structural engineer, MEP engineer, contractor, authorities, etc.) [49]. Construction design changes will be developed in the BIM environment. The design of the formwork elements will also respond to these changes.

Results and Discussion
Formwork presents an auxiliary process of concreting of construction elements. It inseparably belongs to the construction process and its design is very complex. The formwork design is affected by many critical requirements which are related to the design of concrete or reinforced concrete elements of the building [50]. The possibilities for more efficient design of the required formwork are allowed by new information technologies. These information technologies enable faster and more accurate formwork design with the minimization of possible failures that could crucial affect the realized formwork. Formwork design can be visualized through virtual, mixed or augmented reality by the created 3D model before it is actually implemented in the construction process taking into account the sustainability of construction in all its aspects.
The object of the case study, the building located in Košice, was chosen correctly. The renovation of the building consists of the superstructure of two floors including the reinforced concrete ceiling slabs, beams, columns, staircase and lift shaft. The 3D model of the load-bearing parts of a building is possible by many software. Modelling of selected renovated building was implemented through two software -Autodesk Revit a ArchiCAD. Software ArchiCAD was used to process the BIM model of formwork structures of case study´s object. Ensuring software compatibility between software for construction design in BIM environment and software for formwork design has been made using the software BIM6x which imported digital formwork elements into ArchiCAD software. At the same time, software BIM6x creates a virtual reality environment for proving the potential and using the created 3D model of building with inserted 3D formwork elements.
The following documents are required to create a 3D model of the load-bearing parts of the examined building and the subsequent insertion of the elements of the formwork system: • Documents for the creation of the load bearing construction 3D model (project documentation), • Documents relating to technological process for construction of the auxiliary structureformwork (technological instructions, technological standard by particularly provider of formwork elements) • Data from the digital library of 3D elements of the formwork structure Project documentation of renovated building was originally created in a software tool ArchiCAD; provided all relevant information concerning specific reinforced concrete elements. The correct design and modeling of the 3D model of the formwork system is possible through documents which are given by the producers of complex formwork systems. The adaptive design of formwork was processed using the Doka system. Specifically, two auxiliary formwork system solutions for the construction of structural elements (ceiling slabs, columns and walls). Dokadek system was used for the ceiling slab formwork, and the Framax Xlife system was used for columns and walls formwork.
An essential part of the adaptive formwork design in a BIM environment is library of system formwork elements (Figure 7). The selected formwork elements must correspond to the technical and technological requirements for the formwork construction of selected structural elements of the solved building. An important aspect in creating a 3D model is the purpose of the created model. The creation of 3D models uses a method of technical modeling, which is characterized by a certain degree of accuracy. The 3D model for the purpose of the formwork design was processed with the level of detail LOD 300 (LOD -level of development). The 3D model of the load-bearing structure is an actual state model of the renovated object, which includes structural elements (foundation strips, columns and ceiling slab). Since this is a renovation of the building (superstructure), the next step is to model the new state of the building, which includes the creation of floors containing the structural elements: columns, gutters, ceiling slab, perimeter masonry, load-bearing walls, partitions, lintels, windows and doors (inserted as empty holes) (Figure 8). 3D construction elements are in the ArchiCAD´s library. The next step is the modelling of the formwork elements. When inserting and modeling formwork objects, it is necessary to import downloaded libraries with 3D formwork elements into ArchiCAD. Only Doka has freely accessible formwork elements´ library. Therefore, a formwork systems Dokadek 30 and Framax Xlife (Figure 8) were chosen to solve the case study. The designed formwork model can be generated in 2D and 3D view (Figure 9).  BIMx application (Figure 11a) allows display the necessary information such as floor plans, sections and details. The application has a spatial 3D display of the model, where movement is allowed. The insert 3D model of the solved construction in the BIMx application can also be presented as a virtual reality with the use of special glasses that support VR, e.g. Samsung Gear VR. BIMx application with VR glasses allows walk in virtual space of the 3D model of the building (Figure 11b).
Information systems are slowly becoming more and more domestic in construction. In addition, more and more companies are gradually implementing these systems into their technological process. The increased investment costs of information systems are profitable in the long term. These technologies are also suitable for smaller construction projects on which groups of more professions are working. Collaboration of professions requires information sharing. Access to always updated data is key. Information systems enable such data availability for every stakeholder who, according to their assignment, finds the exact data they need. Information technologies simplify work mainly in the design, implementation and management of the building and its elements. Design tools can save time, resources, money and make the construction process much more efficient. Information systems combined with mixed reality can effectively control the observance of technological procedures, control of the time schedule against the real progress of work, which results in a reduction in the possibility of failures. One such information system is the BIM system, which together with the mixed reality make it possible to increase the efficiency of the construction process. Design of formwork in 3D model by innovative information tool enabled speed up the formwork design and reduce the design errors. Case study proved the advantages and disadvantages of the design of formwork elements for the building renovation.
Advantages of formwork construction design through 3D modelling: Higher level of skills with individual modeling software Sharing information in a BIM environment is a great benefit in adaptive building design. Each participant in the construction project has timely access to the 3D model. When changing the design of a part of the structure, or HVAC, etc., the change is recorded in the model, and each participant in the construction can adapt his part to it. This is true at every stage and for most projects. Even in projects focused on the reconstruction of buildings, this is a great benefit. Approach to the BIM model and the opportunity to participate in changes adapt the design solution to current changes, which can be flexibly changed in the design.
Changes in natural conditions, the environment and the effort to achieve the highest degree of sustainability also have an impact on the cost side of construction projects. This is also reflected in the formwork design. The advantage shown by this study is that cost savings have already been noted in the design process when changing the formwork design due to the flexibility and adaptation of this project. The design of the formwork in the BIM environment has been shown in the study to be effective, especially in terms of cost and also the impact on sustainability.

Conclusions
The building design is influenced by several factors. On the one hand, these are unchanged conditions that need to be incorporated into the design of the building. On the other hand, it is more difficult to take into account changing conditions, which also have a significant impact on construction. The adaptive design should be a way to cope with these changing conditions when designing a building. Changing natural conditions (rainfall range, weather conditions, daylight, etc.), environmental conditions, and the emphasis on sustainability throughout the life cycle of a construction project require a change in building design approaches and methods. The adaptive design takes into account these changing conditions and already in the project phase tries to work with a design that can be changed according to the requirements of the environment. Formwork design, as described above, also brings several specifics that affect the result. This case study highlighted the adaptive design of building renovations in a BIM environment that takes into account sustainability elements. The case study helped to clarify several conclusions. The BIM environment also greatly helps in designing the formwork to create a model that can be changed if necessary. The main advantage in simulating the changes required by the environment is the fact that this change is recorded in such an environment on other parts of the structure and project. In fact, in connection with the concept of sustainability, this saves mainly costs and labor. This means a small change, caused by the environment and natural conditions, which must be made, for example, in construction, a change in the formwork design in the BIM environment is quickly incorporated with other necessary changes, resulting in cost savings and laborious designers. In the implementation phase, we work with the most optimal design and possible changes are not an obstacle and a problem for the construction project. On the other hand, it works excellently as a control tool. This was especially confirmed during the specific renovation of the building in the case study. Since it was initially based on the original project documentation, the initial design of the building, as well as the formwork itself, was only 2D in nature. Due to the effort to apply BIM technology to this project and the creation of a 3D model, it brought great benefits in the context of adaptive architecture and design. After revealing the real condition of the original building, it was found that it is different from the original project documentation. There was already the first change of fact compared to the original proposal. Since a 3D model was created from the original project documentation, it was faster and easier to perform the ground and record the actual state of the original building in the BIM environment.
It was also found that the original design of the building and the formwork could not be realized, because the structural elements are in fact, designed differently than expected. Therefore, a change in the proposal was necessary. Constantly changing natural conditions and the fact that it is a renovation of a building located near the historic center, it was necessary to take into account other changes caused by the environment. Here, the great advantage of the BIM environment and modelling of the formwork using 3D tools was demonstrated. Changes that did not need to be made based on the changing conditions mentioned above were easier to make over time. This little result in direct effects on sustainability, especially in the context of the cost savings that the implementation of BIM and the formwork design through information technology has brought. Cost savings in the context of sustainability have been demonstrated several times. First of all, the fact that the original design would require extensive ground, which in 2D design would have to be reworked separately, which would cost a lot of effort and time. On the other hand, planning with the supplier's PERI and DOKA and their software environment resulted in a precise formwork requirement, which resulted in the same material savings and thus no waste.
This case study on the reconstruction of a building near the historic center proved the justification for the use of BIM technology and the environment in the process of adaptive design of the building formwork. Currently, this building is in the implementation phase, and these benefits, which were also described in the design itself, are beginning to be demonstrated. This research demonstrated the implementation of BIM also for adaptive formwork design. Here, several research questions and sub-areas open up, where this research can move. One of them is to verify these facts on several construction projects that require changes in the design and formwork. Also based on demonstration of several projects to create a model when it is appropriate to use these technologies and at the same time create a methodology for quantifying and quantifying the degree of adaptability for the needs of implementing a BIM environment for this purpose.