## 6 Evaluation
### Case Study  
This paper highlights a small case study that assumed a unit price contract between a general contractor and a subcontractor (application scenario 2). The subcontractor was contracted for the execution of shell construction work. The four-story office building had a gross floor area of 4500 m\({}^{2}\), two staircases, and two large roof terraces. The accounting was based on unit prices for the finished construction works. The subcontractor documented the work carried out, e.g., with a quantity survey, which had to be confirmed by the general  
Figure 11: Listed billing units and configuration of billing arrangements.  
Figure 10: Visualization of the imported billing container (linked IFC model, BoQ with QTO and billing plan) in the BIMcontracts application.  
contractor. Moreover, it was assumed that both contracting parties were registered to the proposed system and had received their blockchain identities.  
As part of the tendering procedure, the execution drawings were provided as a BIM model (Version IFC2x3) with a detailed BoQ (Figure 10). The IFC model contained all necessary semantic and geometric information of the foundations, walls, beams, slabs, stairs, and columns. A high level of detail in the model was a prerequisite for a correct link to the work items. The model differentiated the walls according to the various types of construction and component thicknesses: semi-precast facade elements, prefabricated facade elements, hollow-chamber walls, and cast-in-place concrete walls. The foundation consisted of strip and single foundations, as well as a floor slab with lowerings in certain areas to accommodate the ground structure in the outdoor facilities. The shafts for the building services and elevator underpasses were also created. Under- and overlays, as well as the attic edging, were modeled as beams. If semi-precast elements were involved, they are provided with appropriate properties. The stair landings (precast elements) and intermediate platforms (in situ concrete) were modeled separately. Recesses were provided in the components where necessary; otherwise, they were produced with core drillings. The BoQ contained all relevant details for each item of work, as well as the agreed-upon net price per item, and was linked with the IFC model using unique identifiers. The billing plan had the highest possible level of detail, where each quantity was assigned to the billing unit.  
The next step was to specify the execution details for the billing units and other contractual agreements (Figure 11). The billing arrangements were configured so that completed work could be reported and invoiced every 14 days. The client had seven days to check the completion and release it for payment. In addition, a security deposit of 10% per billing unit was agreed upon. Since the billing units were defined at the level of single quantities, a high level of granularity was ensured, and agreement on partial payments was not necessary. This configuration was applied to all billing units; however, an adjustment per billing unit was also possible, as demonstrated in Figure 11. Next, the smart contract could be generated and deployed, as described in detail in the previous sections. As an exemplary smart contract interaction, the client's contract approval and the corresponding transaction are shown in Figure 12. To demonstrate the billing and payment functionalities, it was assumed that the first completion reports would be provided after 14 days from the contractual start date. After a check, the client confirmed the completion, which triggered an automatic payment of 90% of the agreed amount for these billing units at their bank.