Comparative Study in Bill of Quantity Estimates on Reinforcement Works of Pile Cap, Single Pier and Double Pier of Flyover Between Conventional Methods and BIM (Building Information Modelling)

One of the construction materials with a high level of demand is steel rebar. Globally, the demand for steel rebar has quadrupled from 1960 to 2005—and this increase is predicted to double by 2050. In one project, steel rebar accounts for 16% to 60% of the total project budget. Therefore, if the volume of steel rebar is not estimated correctly it will have an impact on project budget wastage and swelling. The project budget wastage is indicated by the large volume of material remaining, while the budget swelling is indicated by the procurement of additional steel rebar because the material requirement is greater than the initial estimate. To minimize this, a comprehensive understanding of volume estimation is required. Currently, the method of estimating the reinforcement volume that is widely used is the conventional estimation method and the BIM (Building Information Modeling)-based estimation method. The conventional method is done manually based on the BBS (Bar Bending Schedule) as a reference. Meanwhile, the BIM-based method used in this study is the Allplan Engineering 2021 software and is a more modern estimation alternative because it is considered more practical, fast and efficient. Although these two methods are widely used, there are limitations and advantages that are taken into consideration when choosing the most appropriate method. Therefore, a study is needed to prove and compare the accuracy of the estimation of reinforcement volume between the conventional method and the BIM-based method. This study also highlights the advantages and limitations of the two methods for comparison. The conventional method is more transparent in terms of the estimation formula used because it is done manually. This can help the estimator track the estimation process to ensure the accuracy of the results. Whereas, the BIM-based estimation method is superior in terms of work automation and accuracy compared to the conventional method. Furthermore, the limitations of the conventional method are that it does not have a 3D visual model and requires a relatively long time to complete if there is a revision of the plan drawing. On the other hand, the BIM-based estimation method offers convenience in the form of data input using 3D drawings. The practical data input process is proven to provide accurate results. However, the main limitation of the BIM-based method, especially for the software used in this study, is that the estimation formula cannot be traced because it relies more on three-dimensional modeling. This causes the estimator to be unable to ensure the accuracy of the estimation results. However, this limitation may differ from other BIM software products outside of this study.