In the world of structural analysis, engineers are constantly faced with choices.
One of your first choices is: do you create a 2D or a 3D model?
Diamonds, structural analysis software, allows you to do both. But what is the best approach? When is a 2D model sufficient and when does a 3D model offer added value?
In this article, we will guide you through the practical considerations, with the aim of helping you work more efficiently, accurately and with a view to the future.
What is a 2D calculation?
In 2D calculation, you typically model structural elements in the plane: beams (1D) and slabs or plates (2D) are represented in their cross-section or plane.
Example: 2D model
The Mundo-A office building in Antwerp stands above an underground metro station. In order to create a clear passageway and because it was not possible to transfer loads to the metro station, this building was designed as a bridge. The bridge structure was conceived as three trusses made of laminated wood.
Rather than developing one large calculation model for the entire structure, the engineering firm preferred to split it into separate calculation models for the different trusses.
(Photo: Ilse Liekens)
Advantages of 2D calculations
An important advantage of 2D calculation is the speed and efficiency of the calculations. Because the model contains fewer unknowns and the stiffness matrices are smaller, the calculation times are considerably shorter. This makes it particularly suitable for iterative design, where quick and repeated adjustments to cross-sections or material properties can be made without excessive calculation times.
In addition, 2D calculation provides a clear interpretation of the results. Internal forces (moments, axial forces, shear forces), reactions and displacements are easy to visualise and check. This makes the model transparent, not only for the designer himself, but also during project meetings or when creating reports.
Accessibility is also a plus. Because 2D models require less computing power, fewer expensive software licences are needed and limited hardware can be used. This makes this approach particularly suitable for small to medium-sized projects. Moreover, a basic knowledge of the Finite Element Method (FEM) is usually sufficient for the correct setup and interpretation of 2D calculations.
Disadvantages of 2D calculations
However, 2D calculations also have limitations. Complex geometries, such as three-dimensional nodes or buckling shapes, are difficult to model. This requires simplifications in the model, for example by estimating the stiffness of nodes, which approximate reality but cannot fully capture it.
Furthermore, the interactions between different structural elements, such as beams, plates and shells, become blurred. The mutual interactions must be entered into the model manually or via simplified couplings (for example via rigid links). This increases the risk of inaccuracies, especially when rotations or torsion play a role.
Finally, 2D calculations are less suitable for dynamic analyses. Since natural vibration modes (eigenmodes) often occur in three dimensions, it is difficult to model them correctly with a 2D approach. This makes this method less than ideal for applications where behaviour under seismic loading or wind analysis is central, as these require a full 3D analysis.
What is a 3D calculation?
In 3D calculation, you model all structural elements in a three-dimensional space: beams, columns, slabs and plates together form the ‘actual’ geometry of the building.
Example: 3D Model
The observation tower in the Lommel Sahara was deliberately modelled in 3D because the tower has a unique, non-standard architectural shape. The forces at work in such shapes are difficult to describe using a 2D model.
Advantages of 3D calculations
3D calculations make it possible to model complex joints and continuities with a high degree of accuracy. Phenomena such as torsion, rotation and spatial interactions are automatically included in the calculation, providing a realistic and complete picture of the structural behaviour.
3D calculation enables advanced analyses to be performed, including seismic analysis and wind effects in all directions.
An important advantage is the direct link to BIM models, such as those from Revit or Tekla. This allows geometry and loads to be automatically exported to the calculation model. In addition, 3D calculation makes it possible to use a single model for various types of analyses, including statics, dynamics and stability.
Disadvantages of 3D calculations
But all that functionality comes at a price: a 3D model is less transparent. You have to rely on the software and your own insight to interpret the results correctly. An imperfection in the geometry or a forgotten load can have major consequences and is less likely to be noticed due to the complexity.
Creating a 3D model requires setting many parameters. The most important (but unfortunately also the most underestimated) is the boundary conditions: what forces can the structural elements exchange with each other? This must correspond to reality if you want the 3D model to be representative of the building you want to design.
Because 3D models are often large, this leads to longer calculation times and places high demands on the hardware used. Moreover, interpreting the results requires a certain amount of experience.
Is there a future for 2D calculations?
Yes, absolutely! As long as repetitive, simple structures exist, 2D remains the fastest way to calculate. Think of preliminary studies, second opinions, repetitive structural elements such as frames and halls.
What’s more, 2D also allows you to continue working didactically: it forces you to understand. What happens to the moment when I move that support? Where does the shear force come from?
The future lies in hybrid models: a good engineer switches between 2D and 3D like a driver switches between gears. And Diamonds makes that switch child’s play.
Example: hybrid model
Both 2D and 3D models were created for the design of the SKY One tower (see cover photo of this article) in Ostend.
- The 3D model was used for load deduction, checking the horizontal stability and reinforcing walls, floors, beams, and columns.
- The 2D models were used to determine the minimum thickness of the cantilevered terraces, as well as for the design of the façade and the dimensioning of wall openings.
Conclusion
Both calculation techniques have their own purpose. 2D calculations excel in speed, overview and cost efficiency for simple structures and early design phases. 3D calculations offer ultimate accuracy and advanced analysis options, essential for complex, dynamic and large projects.
Diamonds combines the best of both worlds:
- An intuitive 2D module for quick design checks and plate structure calculations.
- A fully-fledged 3D environment with automatic meshing, BIM links and non-linear analysis options.
- Flexible licensing models for calculation capacity tailored to your needs.
With Diamonds, you can complete your projects more efficiently, while retaining full control over results and risks. Contact us today for a no-obligation demonstration and discover how you can take your calculations to the next level!
