BIM Workflow – Data Exchange and Interfaces

You can listen to the full episode here: #007 BIM Workflow – Data Exchange and Interfaces

BIM has already been discussed in a number of our podcast episodes. It provides users with clear advantages and facilitates their work. The problem with it is that it does not quite work in practice as it does in theory.

The biggest hurdles are the different architecture and structural analysis programs. There is another program for TGA. You need to be able to import the model into each of these programs again during your design planning. However, the different types of software sometimes cause difficulties in exchanging data via interfaces.

What does an efficient data exchange look like?

Two points are particularly important for the data exchange scenarios: openness and continuity. There are different methods or approaches that can be used in BIM-based planning: Little BIM, BIG BIM, Open BIM, and Closed BIM.

Little BIM

In the case of Little BIM, there is only one software solution to be used in a design office. This is also referred to as an island solution. Using the software program, a digital building model is created from which all plans and data are derived. Then, it is sent on to the other parties involved. The disadvantage of this is that this model cannot continue to be used and other planners must continue to work with derived plans. Exchange with other programs is also impossible. Therefore, Little BIM does not provide the best approach to communication. For example, if an architect is modeling their building with a program, they can do a cost analysis or quantity surveying for themselves. However, it is not possible for the structural engineer to access these data, because other programs are used. Thus, the architect has to have plans generated especially for the structural engineer, which is then used to develop his/her own models.

BIG BIM

BIG BIM is a continuous exchange scenario. Here, the focus is on communication and collaboration between the truss designers, whose access is ensured over the entire life cycle of the building through digital building models. Interdisciplinary work is possible and different software tools are used. Technical designers can extract the data they need from the architect's model. In contrast to Little BIM, the communication is no longer done solely via 2D plans. Furthermore, the intelligence of the data is retained and can continue to be used by the technical designer.

Teamwork is the top priority for BIM.

Closed BIM

In the case of Closed BIM, all the planners work on a construction project using the same software solution in order to enable an exchange of data with the fewest errors. There is no loss of information due to identical file formats.

This is a good option for well-established partners and teams working on a common theoretical basis. However, one disadvantage is that not every technical designer has this program. This results in limited flexibility in the external technical disciplines, because no compatible solutions are available. Each engineering office follows its own path and has its own criteria when using different programs. Therefore, as a result of uniform engineering software, no trade-specific model requirements can be represented.

Direct interfaces can also be connected with Closed BIM. This means that two software solutions are linked directly. Information is transmitted via necessary APIs (Application Programming Interfaces) – interfaces provided by the software system to integrate the data in another program. The data are exported from Program A and then immediately imported into Program B as a native object. Then, the model is created there.

The advantages of a direct interface are that the data are not lost, as all conversion steps are omitted and only the conversion process from A to B is necessary. Missing definition structures are also irrelevant.

The disadvantage is that direct interfaces are user-dependent. You need the corresponding program and have to program the APIs individually there. The providers cannot be changed at will. However, some engineering offices have their own processes for the customized program interfaces. The prerequisite for this is that the program pairs have the APIs available and that program documentation is available. This is a customized interface: The effort involved in creating it is manageable, but the design process has a much higher degree of automation. This creates enormous potential for saving time and money and avoiding errors. The structure depends on the parameters in the design phase.

Open BIM

As the name suggests, the focus of this BIM variant is on openness. Here, neutral and producer-independent exchange formats are used, which can be integrated openly and transparently into the programs of various software companies. This promotes the future-oriented idea of interdisciplinary cooperation between all project participants in a BIM process. In this way, the building model data can be exchanged across all trades, regardless of the software used.

Unfortunately, this process does not yet work properly in practice and is often susceptible to errors. More research is needed in this area. Moreover, common guidelines and agreements are necessary on how these exchange scenarios should ultimately work, as well as the corresponding handover routines of the respective technical designers.

IFC

Another important aspect with regard to open data exchange is the IFC interface. IFC is a producer-independent and open data structure that is defined by the buildingSMART organization. It can be used, among other things, for collision checks, as well as for quantity surveys or cost estimations. A big advantage of the IFC file is that it allows the data to be exchanged among all software programs. In practice, however, the quality always depends on the respective software producer. The software has a converter that allows for reading/writing the files. The result is translated into the native data of the respective program. IFC is a text-based file that contains the respective information that can be read by the program. To do this, however, it has to be interpreted in such a way that the relevant object can be created in the corresponding program. In IFC, there are views, as mentioned in a previous podcast. The coordination view describes a model with its physical properties, while the structural analysis view describes it in an idealized and simplified way. Not every program can read, write, and output both views. Therefore, architects and structural engineers have to deal with these views and determine which programs they can use for the IFC exchange. This currently makes it relatively difficult to implement the continuous data exchange between CAD and structural analysis software.

Therefore, it is necessary to start at a higher level: What philosophies should be used in the future when it comes to implementing these IFC interfaces? It should be clarified how the programs have to be set up and how the communication between architects and structural engineers should work in order to make the data exchange via IFC work smoothly. The respective software producers are also in demand here.

Rethinking is an important part of future developments.

Synchronization with Changes

What happens if you change something in a structural analysis model? Is it automatically changed in the other models, or do you have to do this separately?

Structural calculations are already carried out in work phases 1-3: basic analysis, concept design, and preliminary design. Structural engineering is important from the very beginning to optimize the structural design and specify the section sizes. Usually, several drafts are considered, and the architectural draft and structural design are coordinated with each other. The aim is to integrate the structural design in the BIM software and then to transfer the calculations of the entire model or the submodel to the structural analysis software. There are possible changes in the structural analysis, such as the stiffening concept or other cross-sections. The programs can communicate with each other digitally and this is how the changes are made.

For example, you can make cross-section changes in RFEM, because other cross-sections are needed, so that whole model remains stable. Then, you add or supplement other components in the design model. When updating, these changes are applied via a direct interface to Revit or Tekla.

BIM requires interdisciplinary coordination throughout all work phases. Therefore, it makes sense to feed BIM models with structural data; for example, with results, such as deformations or internal forces, that would be useful for an early assessment of feasibility, completeness, or further processing of results in other companies.

Structural engineers can also add structural position plans to the BIM model. In an architect's plan, various positions are identified by numbers, often with a letter in front of them. A component is marked here that is also found in the structural calculation because a structural analysis has been performed for it.

For reinforced concrete structures, you can also transfer certain test results to the respective Revit or other corresponding program with the complete building model, from the structural analysis program to the global software program. Afterwards, the test can be drawn automatically in the CAD program and later plotted or issued for utilization on a construction site.

The following episodes of the podcast will also deal with BIM and the opportunities and difficulties associated with it. Listen and read to find out more about this trend-setting development!