Automated modification of compound elements for accurate BIM-based quantity takeoff

BIM-based quantity takeoff is faster, more accurate, and more reliable than traditional quantity takeoff. However, the quality of BIM models is a major issue. Quantity takeoff is inaccurate for compound elements such as walls and floors modeled as single model elements with defined material layers because the size and composition of each layer cannot be freely adjusted. Furthermore, overlapping regions of compound elements with other elements result in excess material quantities. Manual inspection and modification of each compound element are time-consuming, cost-intensive, and error-prone. This study proposes a method to automatically modify compound elements in BIM models by separating each layer into an individual model element and eliminating overlapping regions. Accurate material quantities for compound elements can be obtained from the modified BIM models. A prototype system was developed and the proposed method was validated by two case studies. Compared to manual modification, the proposed method successfully modified compound elements in BIM models in much less time, with accurate material quantities. The modified BIM models are also beneficial in the construction phase, which requires greater detail regarding BIM elements.