Case Study Max Bögl
The case:
As-built analysis and modelling from a point cloud
That the working method BIM (Building Information Modeling) is the future of design and construction is clear to most people who engage with this fascinating field. It is sometimes hard to summarise the methodology in simple, brief words. The reason is that the subject serves several disciplines of the construction industry and offers a multitude of possibilities for sustainable design and construction documentation .
In the spring of this year, one of the largest German general contractors, Max Bögl, contacted us about an interesting project in which we were able to apply our BIM know-how in practice. What the BIM methodology makes possible is explained in more detail in the text that follows.
The brief:
We were able to devote ourselves to the following brief:
STA – Südtiroler Transportstrukturen AG commissioned the consortium of Klapfer Bau, Goller Bögl, Wipptaler Bau and Marx with the construction of a new mobility hub at the station in Brixen, South Tyrol. In this BIM pilot project, Goller Bögl / Max Bögl took on the BIM coordination for the scheme on behalf of the consortium. The station square is intended to serve the town as a “a modern hub of mobility” . On around 20,000 m² , some 200 car parking spaces, around 1,000 cycle spaces, bus turning areas and an adjoining station were built.
The original detailed design was based on a highly detailed BIM model, which consisted of several sub-models from various trades.
The client intended to document the site-specific changes and geometric deviations between the detailed design and the state actually built, and to work them into the construction models. The updated new-build as-built record thus serves the client as a basis for the operating phase of the structure. In addition, an updated model was to be made available to the site managers in charge. In short: a so-called “as-built” model was needed, in order to create a basis for billing. This way of working is intended to spare site managers the tiresome evaluation of slips of paper based on manually entered measurements or billing sheets.
The workflow:
To meet the requirements of this commission, the following workflow was chosen.
Survey by laser scanner (mobile mapping)
First, an as-built capture of the entire facility was to be carried out once construction had been completed. We produce surveys of this scope with the mobile VLX laser scanner from NavVis. For the checking and georeferencing of the point cloud , both the control network already present on site and additional, newly measured control points were used.
This laser scanner allows us to record the whole facility as a raw point cloud within a relatively small window of time while keeping to the agreed measurement tolerances on site. A further particularity was that the capture took place during ongoing operation. The field team needed roughly one working day for setting out the control points and for the capture with the mobile laser scanner.
In order to be able to use the processed data at the same time as a “viewer”, it was decided to create a virtual tour using the Benaco Viewer.
In this, data from a high-resolution camera is matched to the point cloud data while the panoramas from the laser scanner are integrated. Alongside the point cloud, this gives a fully walkable and verifiable virtual tour through the new facility.
The analysis:
Once all the laser scan data had been processed and registered , we had a solid basis on which to begin the main part of the task.
First it had to be established how far the design matched what had been built. For this, the georeferenced point cloud is overlaid directly on the georeferenced model . Tolerances were defined with the client at an early stage so that negligible deviations could be filtered out in advance. The diagram below shows the entire workflow of the as-built process that we agreed on.
The illustration below shows the point cloud produced with the design model overlaid.
On this basis and with the help of a systematic approach , the differences between design and execution could be documented easily. As an interface for the documentation, a so-called “BCF” file was created using the REVIT plug-in “BIM Collab Manager”. In this file, deviations outside the tolerance can be documented component by component , so that the client is able to check and assess individual viewpoints and recorded deviations systematically.
Using the BCF file we supplied, our client was able to import the deviation analysis into his local Revit model and list all elements outside the tolerance in a way that could be followed .
As-built modelling on the basis of the BCF documentation
After analysing the individual trades and producing extensive BCF documentation, it was decided which deviations should actually be worked into the models. Here again it was possible to refer to the BCF documentation and to adjust the component list.
As on every building site, there were of course components that had already been sealed . Among them were, for example, underground cables for electricity pylons. Since these cannot really be reconstructed afterwards without further aids, it was decided to move the cables according to logic and to the offset position of the pylons. Although no hundred-per-cent guarantee of the actual execution can be given here, the model offers a simple method of checking the plausibility of the cables actually installed.
The model serves as a basis for communication and as a data source before, during and after the construction of a structure. Even though this reflects only one part of the BIM methodology and there are many more use cases, this practical example shows a great deal of potential in the sustainable modelling of structures .
Electrical sub-model, existing state compared with the as-built model (Metrika360-Kling & Schrievers Ingenieure AG)
Architecture sub-model, existing state compared with the as-built model (Metrika360-Kling & Schrievers Ingenieure AG)
Structural shell sub-model, existing state compared with the as-built model (Metrika360-Kling & Schrievers Ingenieure AG)
Detail of the electrical sub-model – design (red), as-built (green), overlaid with the point cloud (Goller Bögl/ Max Bögl)
Detail of the architecture sub-model – design (red), as-built (green), overlaid with the point cloud (Goller Bögl/ Max Bögl)
Detail of the structural shell sub-model – design (red), as-built (green), overlaid with the point cloud (Goller Bögl/ Max Bögl)
Detail of the electrical sub-model – design (red), as-built (green) (Goller Bögl/ Max Bögl)