## 4 Master Digital Model for a Suspension Bridge
### Creation of the Initial Master Digital Model
#### 4.2.3 Assembly of the Master Digital Model  
The master digital model, identical to the general BIM model, is an alignment-based object-oriented model. Based on the bridge alignment, each individual 3D digital member for a structure is mapped to the appropriate location and orientation. On the other hand, the related metadata is also linked to that digital model through the specified ID (see Figure 9). In addition, for suspension bridges, almost all the structural members are prefabricated. Each member is a separate entity; however, in the entire bridge system, the member-to-member relationship always involves some constraints. Therefore, in the digital model, it is necessary that each structural member has an individual priority index (PI); it is used with the aims to better manage the bridge alignment, avoid disagreements during assembly, and clarify its importance in the entire bridge structure system. Normally, the member PI can be defined following the assembling order of the structure during the construction stage. For example, a suspension bridge project starts with the construction of the pylon and earth anchorage. Subsequently, the main cable and hunger cable is assembled. This process culminates with the assembly of the stiffening girders. The pylon, earth anchorage, main cable, hanger cable, and stiffening girder have a PI of 1.0, 2.0, 3.0, 4.0, and 5.0, respectively. By adding this index, the engineer can easily monitor the change in the bridge alignment when a higher PI member undergoes transposition, leading to a change in the deformation and structural behavior of all the lower PI members. It should be noted that the opposite does not occur, i.e., a lower PI member can be changed without affecting the higher PI members. In particular, for concrete members, to avoid disagreement or duplication at the intersection of structures, such as the pylon and its crossbeam, the PI assists engineers in determining the structure to which the overlapping portion belongs. In this case, the overlapped volume is attributed to the higher PI structure, i.e., the pylon; therefore, the engineer can extract the exact volume of both the pylon and its crossbeam to the quantity reports.  
Figure 11: Example for creation of a typical pylon digital model in an open-source design API.  
The advantages of data-driven design and alignment-based parametric modeling lie in their capability to update and synchronize data according to the change in the input database. Within a short interval after finishing the generation of the master digital model, the design \"optioneering\" can be performed and the digital model can be optimized to match the additional requirements of all the stakeholders. Although it requires additional resources and time for model creation, after a master digital model is finished, it proves significantly helpful to engineers in saving more resources in terms of releasing the design revision of the digital model, as compared to the traditional document-based model. Digital models with multiple uses include domain knowledge through the construction project because the engineer experience design changes to solve every problem. Then by that way, the accumulated digital inventory for a suspension bridge is a valuable digital asset. In terms of guarantee the credibility of information flow throughout the project lifecycle, including any design revision or as-built update from the construction stage, the digital model demonstrates a superior ability to archive information, allowing engineers to access any state of the digital model. In addition, the mechanical model can be extracted anytime from the updated model, which significantly supports engineers in monitoring the actual behavior of the bridge structure system. To this end, the interoperability of the design platform should be considered. This is further explained in the subsequent section.