The most complete level of interoperability is achieved using an intelligent 3D model connection – as opposed to a drawing representation – in which the building model being exchanged represents 3D structural objects (slabs, walls, columns, beams, windows, roofs etc.), each with specific, defined attributes and properties.
Model-based exchange between the architect and the structural engineer can follow one of two concepts:
The reference model concept ensures the “security” of the architectural model and the structural model files, since each office remains responsible for his/her own model. Thus, the structural engineer receives a file from the architect, but does not modify it; he/she uses the architectural information as a basis for building up his own structural model. This occurs manually, using the tools of his own software, but automatic element conversion utilities also exist to speed up the process. Similarly, the architect leaves intact the file received from the structural engineer, while taking into account its suggestions for modeling load-bearing elements. This way, each discipline’s own file is independent of the one received as a reference.
The other approach to model-based exchange is to convert the other party’s model elements into the native format of one’s own application. The converted model is transformed according to the specifications of the recipient, so the original version of the model is not preserved. This approach is most typical of data exchange between architectural and analysis programs.
ARCHICAD can combine the advantages of both approaches. The 3D model obtained from the structural engineer – regardless of the method used to import it – is always transformed into native ARCHICAD elements. At the same time, it is possible to use the imported elements as a reference, since they can be automatically placed onto their own, protected layers (which are locked to prevent editing). This reference-model approach is also supported by the Merge and Link workflows. Since the incoming elements or modifications are converted into native format, they become an active part of the architectural model, while retaining their properties (e.g. material, profile) assigned in the structural model.
The 3D models exchanged between the architectural and structural disciplines can be considered in three categories:
The architect works on the architectural model, based on her own design and on the client’s requirements. Already during the design phase, the architect should keep in mind that the model will later be exchanged with a structural engineer. For example, she can define the building elements’ structural function; define initial materials to be used; choose columns and beams with standard profiles; define the load bearing core of composite elements. In addition to this preparatory work, she can filter the model so as to narrow down the data to be exchanged: this way, only the structural model, containing just structural elements, will be exported. Naturally, the architect can export the entire architectural model, if the structural engineer’s program is capable of filtering and collecting the model data that he/she needs to work with.
Exporting a structural model from ARCHICAD is sufficient for data exchange with most structural applications (the “management” and “detailer” types). However, analysis and design softwares require the so-called Analysis model in order to run their calculations. These applications can often convert the structural model to Analysis model themselves, or they can use the Analysis model converted by a management/detailer program as the input. An Analysis model is a 2D or 3D representation of the structural model that includes not only planes (in the case of wall, slab, roof elements) and axes (columns and beams) of elements, but also their structural characteristics (e.g. stiffness, material, profile). The simplified analysis model also differs geometrically from the structural model: for example, curved surfaces are represented as a collection of planes; element intersections may be modified.
The export and import of 3D model data often takes place using a standard known as IFC (Industry Foundation Classes), which is actively supported by many design applications. In addition, many applications provide native Add-Ons for data exchange with other specific programs. Some engineers or applications (especially analysis applications) will just exchange data at the most basic level: they import CAD drawings (that is, the lines and points representing floor plans, sections and elevations), and use them as a reference for building the analysis model.
Models and drawings are often accompanied by other documentation, such as suggestions or reports; the most commonly used format for these is PDF. ARCHICAD contains a number of techniques for displaying the structural model and for differentiating it from the architectural design. In addition, ARCHICAD can interpret and store the imported structural data, such as the proposed or utilized materials, and the properties of profile elements.