In the first quarter of this year, Hrdlička processed a pilot order for the Czech Road and Motorway Directorate (ŘSD) for the passporting of bridges and culverts in the form of BIM models. The contract was awarded in connection with the legislative changes to be introduced in the documentation of constructions, in particular the Digital Technical Map of Regions according to Decree 393/2020 Coll. as amended (DTM) and the forthcoming Act on Building Information Model, Information and Digital Modelling, the so-called BIM Act, which envisages the creation of information models during the individual phases of the construction life cycle (milestones).
The contract primarily seeks to assess the possibilities of maximising the use of the data obtained in the bulk data collection during the mapping of the transport infrastructure of the Regional Transport Directorate, which will be carried out due to the need to populate the spatial data of the Regional Transport Directorate into the DTM. It also seeks to assess the advantages and laboriousness of passporting using standard BIM objects, compared to the current method of keeping documentation in 2D according to the B2/C1 directive.
A change to Directive B2/C1 will be necessary as the DTM data standard already requires the acquisition of data in a simplified 3D form, including the addition of database attributes to individual elements according to the DTM Uniform Interchange Format (JVF DTM). At the same time, the State Fund for Transport Infrastructure (SFDI) is developing a Building Information Modelling (BIM) code that introduces a data standard for transport infrastructure structures.
With the introduction of this code, the Railways and the Railway Administration will receive the actual designs directly in the form of BIM documentation. The B2/C1 code will also have to respond to this change.
It would not make sense to create a spatial BIM model on its own without linking it to the existing operational systems of the CRD, so the contract also addressed the scope of the data to be recorded and the possibility of linking it primarily to the Bridge Management System (BMS) and the Central Defects Register (CDR). In addition, available documentation and supporting documents provided by ŘSD prior to the start of the work were used to create the BIM models.
For the pilot contract, four objects were selected by the RMD: a 37 m long single highway beam bridge on the D11 highway, a 13 span, 465 m long double highway bridge on the D3 highway, a culvert on the D4 highway (structurally consisting of a spillway bridge), and a pipe culvert on the I/18 highway.
All objects were processed in the form of BIM documentation, 3D CAD documentation in the form of a wire model, 2D documentation according to the B2/C1 directive and in the formats Spatia-Lite and Shapefile, whose structure corresponded to the JVF DTM data model version 1.3.
Bulk data collection was performed by laser scanning using Trimble X7 and Trimble SX10 instruments. The measurements were made in the JTSK coordinate system and the Bpv elevation system. Connection to the national systems was made from the existing bridge baseline network supplemented with points determined by GNSS-RTK technology. The standard deviation of the connection points is less than 0.03 m in position and height. The processed and cleaned point cloud served as a basis for the creation of individual documents. The modelling was performed at the LOD 300 level of detail. The BIM models of the bridges were prepared by Strabag, which has extensive experience in BIM modelling of bridges. CAD documentation in 2D and 3D was prepared in the scope of B2/C1 guidelines.
On one of the bridge structures, an evaluation of the resulting accuracy of each type of documentation was carried out at selected control points. The produced documentation in the form of 3D and 2D CAD drawings meet the accuracy specified in B2/C1 and the BIM models meet accuracy class 2 due to the required degree of generalization of the model parts.
The contract has yielded many interesting findings. First of all, it turned out that the creation of a BIM model from the acquired point clouds is not significantly more laborious than the acquisition of 3D CAD documentation; on the contrary, in the case of typified objects, of which there is a large number in the possession of the Regional Directorate of Transport, significant time savings can be achieved thanks to BIM libraries of individual parts of objects. In addition, BIM documentation can contain a large number of additional attributes that can be shared with other operating systems of the RDC. As new objects under construction or refurbishment will be submitted in the form of BIM documentation, the ideal target state is to have data on new or refurbished objects in the same format and structure as data on existing objects, so that working with all data is uniform, clear and simple.
It was clearly confirmed that 2D map documentation is no longer sufficient for today's user requirements. Therefore, 3D documentation is becoming a standard, and BIM documentation has a great added value in the form of possible linking to other documentation of the Regional Directorate. Therefore, it is confirmed that documenting bridges and selected culverts as 3D BIM models is the right direction for the documentation of these structures. At this point, it remains to define the BIM data standard by SFDI so that the passporting of the selected structures of the RDS is extended in this direction and resp. based on this data standard.
During the inspection days during the implementation of the contract, it also became clear that the transition to BIM documentation of objects such as a bridge, a structurally complex culvert or a DUN makes sense, but it is not necessary and even with today's technical means it is not appropriate and effective to keep comprehensive BIM documentation of all objects of the RDSD. Therefore, the result should be a combination of selected objects maintained in the BIM model and the remaining objects maintained according to the modified B2/C1 directive in the 3D GIS of the Regional Directorate.
When presenting the outputs to the RDSD staff, the resulting BIM models were appreciated mainly for their clarity, which would enable the passports to be worked with by a wider technical public. It remains to be seen whether the RDC will be interested in continuing this method of documentation.
Ing. Jan Floriánek
