They are combined and the overlapping regions are removed before extracting their surfaces.
The RC elements, which are foundations, columns, beams, slabs, walls, and stairs, are imported from a BIM model. This paper presents a method that automatically calculates the quantities of concrete formwork from the surfaces of reinforced concrete (RC) elements. The quantity of concrete formwork is the surface area of the formworks that are used as molds. This makes quantity takeoff of the concrete formwork difficult and time-consuming because construction practitioners have to calculate its quantity manually or have to create a specific BIM model that has concrete formwork for the quantity extraction. Concrete formwork is a building element that is usually absent from the BIM model because it is a temporary component used during a construction process to form a concrete structure. However, if building elements do not exist in the BIM model, the material quantities cannot be extracted from them. Quantity takeoff using building information modeling (BIM) gains more popularity in recent years because of its speed, reliability, and accuracy over the traditional 2D-based method. The results indicate that the proposed new framework automatically identifies the semantic errors in BIM models and obtains code-compliant quantities. Subsequently, linguistic-based approaches are developed to automatically audit the BIM model integrity for QTO purposes, with QTO algorithms developed and used in a case study for demonstration. It begins with domain knowledge modeling, taking into consideration QTO-related information, semantic QTO entities and relationships, and SMM logic formulation. This paper presents a new knowledge model-based framework that incorporates the semantic information and SMM rules in BIM for automatic code-compliant QTO. Furthermore, conventional BIM models do not contain all the required information for automatic QTO and the results do not follow the descriptive rules in the standard method of measurement (SMM). The results of quantity take-off (QTO) based on building information modeling (BIM) technology rely heavily on the geometry and semantics of 3D objects that may vary among BIM model creation methods. Ongoing research is focused on the extension of the tool to automate the creation of formwork models for 4D modeling for the construction stage, including the aspects of scheduling and clash detection in the context of open-BIM. Consequently, accurate and faster formwork quantification results and generic formwork models are automatically obtained.
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A case study is presented, and the results obtained from the presented algorithm are verified with the manual operation of the BIM quantification features as well as manual calculations for some elements. Therefore, this publication describes how the extraction of formwork quantities and the creation of formwork models can be automated with Autodesk Revit Dynamo. Moreover, automated formwork generation is not supported by the majority of BIM tools although it is also a time consuming task and necessary for construction phase planning, visualization, and interference check.
It is important to note that QTO is needed during several phases of the design and construction process, with differing requirements and available information. This is mainly due to lack of modeling conventions, agreed workflows, and classification, together with modeling errors like overlapping structural elements and limitations of BIM software. According to literature, the accurate, automated calculation of formwork areas from BIM remains still problematic. Therefore, the use of BIM for QTO is increasing. However, obtaining accurate QTOs from 2D traditional drawings is tedious and time-consuming. Quantity take-off (QTO) is an indispensable part of construction projects since it is used for scheduling and cost calculation.
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