Calculation of Cost Estimation Based on Building Information Modeling in Construction Projects

BIM (Building Information Modeling) is currently a concept that can include important information in planning. This study aims Kosmetika Global Helath Indonesia, Ejip Area, Cikarang. In this research, 3D modeling of steel structures was carried out based on shop drawing documents from the research location. Next, calculate the quantity take-off for the estimated cost of steel structure work using Autodesk Revit software. It can be concluded that using Auusingit software can optimize the 2D modeling process into the 3D form so that the quantity take-off calculations can be more detailed and accurate and reduce material waste. It also already supports BIM 5D to help calculate estimated costs. The results of calculating estimated costs using Autodesk Revit software are 3.45% smaller than conventional calculations. It is because conventional methods are calculated manually based on 2D images, which allow for differences due to lack of detail.


INTRODUCTION
The population growth that occurred in Indonesia has had an impact on the growing number of construction builders. Many projects include housing, shops, hotels, bridges, and so forth (Khamistan, 2018;Liman, Adianto, & Wimala, 2020). It is hoped that these projects will be carried out with optimal processes and consider sufficient construction funds so that there will be no shortage of funds, resulting in stalled building construction (Haider, 2020;Laorent, 2019). Communities as owners of land and buildings are expected to be smart in choosing and managing the construction processes and methods used to suit the objectives and available costs (Agustapraja & Affandy, 2017;Saputra, Hasbullah, & Sukono, 2020) However, in development planning activities, most construction actors in Indonesia still use conventional methods (Muhammad & Yunus, 2020;Umam, Erizal, & Putra, 2022). Of course, this conventional method is quite behind in terms of time efficiency because the process of processing this conventional method cannot be done simultaneously, and it takes quite a lot of time to make a development plan (Dewi, Yana, & Susilawati, 2019;Jawat & Suwitanujaya, 2018). Along with technology development, technology in the construction field is also growing. The presence of BIM (Building Information Modeling) is currently a concept that can include important information that can make it easier to carry out a plan to be built (Troncoso-Pastoriza, López-Gómez, & Lara, 2018;Zahro, Ratnaningsih, & Hasanuddin, 2021). So the quality of the planning will be better. Modeling methods in BIM can also generate 4D, 5D, 6D, and 7D models in addition to 2D and 3D (Mardhani, Ratnaningsih, & Arifin, 2022;Setiami & Maulana, 2021). BIM provides facilities such as 3D for object-based parametric modeling, 4D to provide scheduling information or it can be called a time element, 5D to provide integrated cost estimates from 3D design, 6D to be able to analyze energy in a building, up to the top BIM level, namely 7D, 7D is facility management in a building, this 7D BIM level is for the maintenance stage, and these facilities are already integrated with accurate data (Husin, Sihombing, Kussumardianadewi, & Rahmawati, 2020;M. N, Wang, Wei, Chi, & Ni, 2021). One of the software based on BIM is Autodesk Revit.
Autodesk Revit is software for modeling architectural, structural, mechanical, electrical, and plumbing (MEP) projects. In addition to presenting 2D design working drawings, users can build a building by modeling each component in 3D ( Danny Laorent, Nugraha, & Budiman, 2019;Ramadhan & Maulana, 2020). Users can also simulate planning for scheduling or assigning execution phases for each building component while providing schedule details and being able to provide cost estimates (Anjani, Bayzoni, Husni, & Niken, 2022;Rosmyanto, 2022). Therefore, in this study, image modeling was carried out up to the cost estimation stage using Autodesk Revit software. This study aims to carry out 3D modeling to calculate estimated costs with the help of Autodesk Revit software. In this study, the modeling to calculate cost estimation in terms of the steel structural elements of the PT. Global Health Cosmetics Indonesia EJIP Area, Cikarang.

METHODS
Data collection was carried out at PT. Global Health Cosmetics Indonesia EJIP Area, Cikarang. The material used is in the form of shop drawing documents. In this study, the implementation of 3D BIM was carried out by modeling the steel structure of the building and calculating estimated costs for implementing 5D BIM with the help of Autodesk Revit software. The outline of this research can be seen in Figure 1.

Figure 1. Research Flowchart
The available data is in the form of shop drawing documents of PT. Global Health Cosmetics Indonesia EJIP Area, Cikarang. Furthermore, 3D image modeling was carried out until the implementation of 5D BIM with the help of Autodesk Revit software. The results of modeling and cost calculations are compared with conventional methods. Conclusions are drawn based on differences in estimated cost estimates between BIM and conventional manual calculation methods.

Result
3D modeling was carried out based on documents obtained from the case study site. The structural elements of the building being modeled were steel structural work on columns, beams, and steel roofs. The results of 3D modeling using the Autodesk Revit software are shown in Figure   The types of steel columns used are IWF steel 400x400x21x13 for K1-K78 main columns and IWF steel 150x150x7x10 for KG1-KG7 Gable Columns. The total number of columns used is 85 columns. 78 main columns and 7 gable columns.  Namely steel IWF 400x400x21x13 for the rafter, C 200x75x20x2.3 for purlin, and D16 concrete iron for the brace. The total steel in the roof structure is 58 steel, 34 rafters, 24 purlins, and 40 D16 concrete iron for the brace. Based on the 3D BIM image above, it can be concluded that BIM-based modeling can provide important information related to the modeling, information such as the identification of the structural elements used and the coloring of each structural element to make it easier for construction workers to identify each work in carrying out a project development. After the 3D modeling is complete, the application of BIM 5D is carried out. BIM 5D is a cost estimate that has been combined with the 3D object design and can estimate the flow of costs that may be incurred. To find volumes in modeling, Revit already provides a standard BIM software schedule feature for identifying objects or structural elements to make volume calculations easier. As shown in Figure 6.

Figure 6. Schedule Identification of Structural Objects
The picture above shows the stages of making a schedule for identifying structural objects whose volumes will be searched. Then input the unit price in the modeling by preparing the AHSP document for steel structure work. AHSP document table data for steel structure work can be seen in Table 1. The AHSP data above is input for each steel structure work item. Then make a formula or formula on the parameters added in the structure object identification schedule. The parameter filled in the formula is the cost parameter to get the value of the total cost of the work. As shown in Figure 7. After that, the total price value for each job will automatically appear. The total cost value for each steel structure work can be seen in Figure 8. From the image data above, it is known that the total cost of the steel column structure work was found to be Rp. 1,400,753,951.55. Then the results of the total cost of the steel roof structure work can be seen in Figure 9. From the image data above, it is known that the total cost of the beam structure work was found to be Rp. 718,613,197.54. Then the total cost data on steel column structure work can be seen in Figure 10. The steel roof structure is IWF steel 400x400x21x13 for the rafter, C 200x75x20x2.3 for purlin, and D16 concrete iron for the brace. The total steel in the roof structure is 58 steel, 34 rafters, 24 purlins, and 40 D16 concrete iron for the brace. Next is data recapitulation of the total cost of steel structure work which can be seen in Figure 11.

Figure 11. Price Recapitulation
The recapitulation of prices for steel structure work found a value of Rp. 3,101,976,320.11. This value is based on the sum of the structural work of columns, beams, and steel roofs. It can be seen that the results of price recapitulation on steel structure work found a value of Rp. 3,101,976,320.11. While the total cost of steel structures using conventional calculations based on the case study documents can be seen in Table 2. The total steel structure cost in the estimation table above is Rp. 3,212,716,087.85. The volume value in conventional cost estimates is larger. It is because conventional calculations are done manually, and there may be some differences due to less accuracy, which makes the volume value larger. Based on the results of the cost estimation generated by BIM and the conventional method, it can be seen that there is a difference in the total cost value generated by the two methods. The results of calculating the estimated cost of the conventional method are found to be Rp. 3,212,716,087.855, while calculating the estimated cost using Revit, found a value of Rp. 3,101,976,320.11. there is a difference between Rp. 110,739,767.74. which means that calculations using BIM assisted by Revit software are 3.45% smaller than conventional method calculations.

Discussion
BIM (Building Information Modeling) is currently a concept that can include important information that can make it easier to carry out a plan to be built (Novita & Pangestuti, 2021;P, Adhi, Hidayat, & Nugroho, 2016). So the quality of the planning will be better. Modeling methods in BIM can also produce 4D, 5D, 6D, and 7D models in addition to 2D and 3D. BIM provides facilities such as 3D for object-based parametric modeling, 4D to provide scheduling information or it can be called a time element, 5D to provide integrated cost estimates from 3D design, 6D to be able to analyze energy in a building, up to the top BIM level, namely 7D, 7D is facility management in a building, this 7D BIM level is for the maintenance stage, and these facilities are already integrated with accurate data (Rizqy, Martina, & Purwanto, 2021;Suasira, Tapayasa, & Santiana, 2021). One of the software based on BIM is Autodesk Revit. Autodesk Revit is software for modeling architectural, structural, mechanical, electrical, and plumbing (MEP) projects (Pratama & Witjaksana, 2022). In addition to presenting 2D design working drawings, users can build a building by modeling each component in 3D. Users can also simulate planning for scheduling or assigning execution phases for each building component while providing schedule details and being able to provide cost estimates (Marizan, 2019;Pratiwi & Wirawan, 2022). Therefore, in this study, image modeling was carried out up to the cost estimation stage using Autodesk Revit software.

CONCLUSION
Based on the results and discussion above, it can be concluded that the use of Autodesk Revit software can optimize the 2D modeling process into the 3D form so that the quantity take-off calculations can be more detailed and accurate and can reduce material waste and already supports BIM 5D to help calculate estimated costs. The results of calculating estimated costs using Autodesk Revit software are 3.45% smaller than conventional calculations. It is because the conventional method is calculated manually based on 2D images, allowing for differences due to lack of detail.