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Evaluation of the reliability of BIM-based quantity take-off processes in construction projects

Eroğlu, Emre
Quantity take-off (QTO) process is a significant part of construction projects. Outputs of this process are used in many phases of the projects such as resource planning, scheduling, budgeting etc. Commonly, quantities are calculated by using 2D CAD drawings and CAD tools but this process requires too much time and effort as well as it is prone to errors due to numerous variables. For instance, there is a risk of double counting, missing elements, probable errors when moving data between 2D drawings. Nowadays, Building Information Modeling (BIM) software programs are started being widely used as an alternative to the traditional methods for quantity take-off process. Studies in literature show that BIM ensures benefits in terms of time and accuracy of quantities due to its automated processes. However, studies commonly concentrate on acquiring quantities in standard conditions and there is not enough research regarding challenges in obtaining quantities of some problematic construction items such as formwork. Therefore, reliability of quantities extracted from BIM models is still a research subject. For this purpose, a case study is carried out by modeling selected construction items of a building with Autodesk Revit program and the quantities obtained are compared with the quantities extracted from Allplan model which was created by a construction company. Results indicate that formwork area quantities obtained from Revit by using a formwork area tool is not reliable however quantities of other items considered in the scope of this study which are obtained from Revit and Allplan models are consistent when appropriate modeling approaches for QTO are implemented. The modeling approaches required for different construction items and detailed analyses of QTO results are contributions of this study.