The first cost engineer mentioned that efficiency is the most important criterium during a preliminary design, as long as the accuracy does not deviate too much. The quantities can deviate from the actual quantity, because during preliminary design, a certain deviation is allowed, often 30%. Therefore, the criterium accuracy is the least important criterium. Efficiency is deemed most important, because if you can estimate the quantities very quickly, it is quicker and cheaper to create a cost estimation. Therefore, Arcadis can earn more money and gain more work. The second most important criterium is the traceability of the quantities. It is of importance that the quantities can be verified by the client and by other cost engineers, otherwise it is unknown of what construction object the quantities are and if they are accurate.
Table 28: Importance ratings according to cost engineer 1
Efficiency Accuracy Traceability
100 60 80
Cost engineer 2
The second cost engineer believes accuracy is the most important criterium for a quantity estimation method, because otherwise the estimated total costs are incorrect. Even using a preliminary design, the cost
estimation should be as accurate as possible. The costs can deviate more during preliminary design; however, it is of importance that the cost estimation is as accurate as possible. Traceability is the second most important criterium, because cost engineer two thinks a project should always be clear, traceable and transparent. Efficiency is considered least important.
Table 29: Importance ratings according to cost engineer 2
Efficiency Accuracy Traceability
70 100 80
Cost engineer 3
Cost engineer 3 considers traceability of the quantities the most important criterium, because if the quantities are not traceable, the cost estimation cannot be delivered to the client. The client will reject a cost estimation that is not traceable, because the client cannot verify the quantities. Accuracy is considered second most important, because inaccurate quantities cause inaccurate costs. Efficiency is considered least important, because making a cost estimation takes more time if the estimation must be accurate.
Table 30: Importance ratings according to cost engineer 3
Efficiency Accuracy Traceability
61
Cost engineer 4
Cost engineer 4 considers accuracy by far the most important criterium, because if the quantity estimation process is accurate, the quantities are traceable and there will be worked efficiently. Therefore, according to cost engineer 4, accuracy is significantly more important than traceability and efficiency. Efficiency is not considered important, because if there will be worked quicker, quantities will deviate more from the actual quantities.
Table 31: Importance ratings according to cost engineer 4
Efficiency Accuracy Traceability
25 100 25
Cost engineer 5
The fifth cost engineer is of the opinion that accuracy is the most important criterium, followed by traceability and efficiency. Accuracy is considered most important, because inaccurate quantities lead to inaccurate cost estimations. If the cost estimation is inaccurate, problems arise with the client, because the budget of the client might not be sufficient for the project.
Table 32: Importance ratings according to cost engineer 5
Efficiency Accuracy Traceability
70 100 90
Cost engineer 6
Cost considers accuracy and traceability the most important criteria, because both criteria and important for the client. The client wants a traceable and accurate cost estimation. Efficiency is also of importance; however, it is important for Arcadis itself. When the cost estimation is made quicker, more work can be gained, and more revenue can be made.
Table 33: Importance ratings according to cost engineer 6
Efficiency Accuracy Traceability
80 100 100
Accuracy
In section four, only the deviation was mentioned. This appendix describes the quantities that were
estimated during the workshop. Six cost engineers estimated the quantities of nine cost determining objects. The estimated quantities using the manual quantity estimation method are illustrated in Figure 22. The quantities estimated using the BIM-viewer and BIM-based QTO were equal for all cost engineers and are therefore not displayed in this appendix. Figure 22 displays all measured quantities of the cost determining objects. There can be seen that most quantities do not deviate much from the actual quantity. Furthermore, there can be seen that for most cost determining objects some cost engineers estimated quantities higher than the actual quantity and some cost engineers lower. Therefore, there is no trend line regarding deviating quantities. Different types of mistakes were made during the workshop. Sometimes a cost engineer
estimated the area instead of the volume. Furthermore, a cost engineer used the depth of the piles instead of the length of the piles and a cost engineer forgot to combine all parts of the asphalt and therefore only estimated the quantity of one part of the asphalt. Furthermore, some mistakes were made when measuring quantities and some assumptions were made when measuring quantities of round objects.
Figure 22: Estimated quantities using manual quantity estimation
A histogram was created to display the frequency of the deviation using the three quantity estimation methods. The histogram is displayed in Figure 23. Since all cost engineers estimated the same quantities using the BIM-viewer and BIM-based QTO, obviously the frequency is a multitude of six, the number of participants of the workshop. There can be concluded that estimating quantities using the BIM-viewer or BIM-based QTO deviates less from the actual quantity compared to manual quantity estimation.
Furthermore, manual quantity estimation results in deviations of over 10% in contrast to the BIM-viewer and BIM-based QTO. The quantities estimated using BIM-based QTO or the BIM-viewer deviated 6% for the girders, because Autodesk Revit estimated the gross area and in the detailed cost estimation the net area was used.
Figure 23: Histogram of deviation of quantity estimation methods
0,0 50,0 100,0 150,0 200,0 250,0
Abutments Wing walls Prefab girders Concrete topping Approach slab Asphalt road surface Sidewalk Traffic barrier Piles Q ua nti ty (m 3 /m 2 /m /p c s )
Cost determining object