BIM-based wall framing calculation algorithms for detailed quantity takeoff

Although an automated quantity takeoff using building information modeling (BIM) is proved to be faster and more reliable than the traditional quantity takeoff method, the information and geometries in a BIM model must be input correctly. Drywall is a wall type that consists of wall framings as a core structure layer and drywall sheets as finish layers. During a tendering phase, the area of each layer of drywall is used for cost estimation. However, during a construction phase, the material quantity of wall framings must be calculated in length in order to purchase the materials effectively. If the wall framings do not exist in the BIM model, construction practitioners have to create them or calculate their length manually. Creating wall framing elements in a BIM model is a time consuming and error-prone task, especially in a large scale project. The increased geometries in a BIM model also affect the working performance of the software. This research proposes a method that automatically calculates the lengths of vertical and horizontal members of wall framings from the extracted
wall surfaces and the input spacing values. The method also eliminates the region of walls that overlap with structural elements such as columns and beams. The validation is done by using an interior construction project as a case study. It showed that the proposed method provides an accurate wall framing quantity when compared with the quantity results from the BIM model that has wall framings and the quantity results from the manual calculation methods. With this method, the wall framing elements do not need to be created in a BIM model for quantity takeoff. The modeling time can be saved while construction practitioners can get an accurate wall framing quantity for purchasing material during a construction phase.