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#002 Why 3D Models in Structural Design?
New Technology and New Models
Structures, such as bridges or office blocks, are three-dimensional in reality. In the past, it was not possible to calculate three-dimensional models and structures, which is why the structures had to be simplified and broken down into planar subsystems. However, thanks to powerful PCs and software, these simplifications can now be dispensed with. A calculation of 3D models is possible and can be supported by digital trends, such as BIM or new options for models visualized close to reality.
In structural engineering, the structural concept is important: How do I prepare structural analysis and how do I structure the entire structural project? At the beginning, there are considerations about how the structure works, how the respective load directions run, whether all loads can be transferred into the foundations, what distance between the respective columns and secondary beams is necessary, and so on. A 3D model is suited for this very well, and it is used to better read out and understand the respective forces.
Stability also plays a major role in the calculation. In 2D structural analysis, it is often ignored, because idealized models are used. This can be a problem, especially in the case of more complex structures. But what is stability anyway? For example, when people talk about stability in the media, they actually mean sustainability. You can imagine stability as a long ruler. You can bend it slowly, which it can withstand for some time until it finally breaks. Structures deform, which is normal to a certain extent, as long as the critical point is not exceeded. In 3D, you can see much better where problems arise in terms of stability, and you can counteract them. A global stability failure as a conclusion is so much easier to understand.
BIM Models
BIM provides such well-idealized 3D models as a basis for structural design, which can be used for the calculation from the very beginning. Ideally, a BIM 3D model is supplied directly from the architect's CAD model, which saves a considerable amount of time. This model is a helpful method of preliminary design and assessment of the correct structure for the structural analysis.
Why is it not possible to continue using the BIM models right away? Here is another trend: a complete coupling of parametric design engineering with architecture software that allows you to use it directly. The data exchange processes in BIM are not yet working properly, but they are getting better and better.
What are the advantages of 3D models?
Many building structures cannot be described and calculated well in 2D if the geometry and structure are more complex. Examples are freeform structures or membrane structures, such as the Olympic Stadium in Munich, Germany. Using 2D, increased safety is expected. However, a 3D model allows for much more efficient calculation.
Another important factor in the calculation is a wind load. Structural engineers apply loads to buildings for their analysis. This includes permanent loads, such as a floor structure or traffic loads. Snow loads are still relatively clearly regulated, but in the case of wind loads, the standards only give the instructions for simplified shapes and geometries. In the case of wind load calculations, the question is how to correctly apply the respective load introductions. In conventional structural analysis, a gradually increased load introduction has been used so far in order to stay on the safe side. However, there are now software tools with digital wind tunnels for more efficient calculations. They only work with a 3D model.
Another point is dynamic analysis. Seismic design also works almost exclusively with 3D models. Mode shapes, vibrations, and frequencies are the results that a structural engineer has to consider in order to assess whether a structure can withstand the given seismic loads.
Due to 3D models, you can also flexibly respond to the changes that occur repeatedly in the design process. In the construction process, it is important to be clear about what is structurally feasible and what changes have been or must be made.
Nowadays, a complete 3D structural model is carried out automatically and the modified forces in the structure are immediately transferred from one component to another. If you let the program recalculate it, the model is always up to date and everyone can access it. Thus, the additional effort due to entering all values carefully is compensated.
In the past, a positional structural analysis was used. In this case, the individual components of a structure are identified and then calculated. Supporting elements, such as walls and so on, are "positions" that a structural engineer analyzes in the structural calculations, identifies them, and specifies the corresponding dimensions and cross-sections that are then used by a construction company.
3D models are also advantageous for a detailed structural analysis. This includes the connections in steel structures, where several members or connections extend from a point or a node. FEA software facilitates such difficult calculations and nodal points while providing much more efficient results.
Other side effects of 3D models are clearer results, even for people who are not familiar with the subject. A complete model in 3D is easier to understand than a multitude of partial models. Deformations, stresses, and forces are also visualized. 3D models convey a professional impression to all parties involved: Structural engineers gain a good image and clients have more confidence in them.
It is also possible to estimate costs and determine dimensions on 3D models. You are very flexible in optimizing the model in terms of shape, function, and weight, and it can be done quickly. For complex construction projects and more complicated geometries, 3D models provide clear advantages.
However, 2D and 3D structural analysis should not stand in the way or compete, but complement each other. Each is well suited for different calculations. In the end, the choice is up to the engineer.