Use a 2D model when your structure is simple, repetitive, or dominated by in-plane behaviour: it calculates faster, is easier to check, and needs less software and hardware. Use a 3D model when the geometry is complex, connections and load paths run in multiple directions, or you need seismic, wind, or BIM-linked analysis. Most engineers end up switching between both, depending on the project. Diamonds supports both approaches, this article walks through when each one earns its place.
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. To create a clear passageway, and because loads couldn’t be transferred to the metro station, the building was designed as a bridge, conceived as three trusses made of laminated wood. Rather than developing one large calculation model for the entire structure, the engineering firm split it into separate calculation models for the different trusses.
(Photo: Ilse Liekens)
Advantages of 2D calculations
- Speed and efficiency. Fewer unknowns and smaller stiffness matrices mean shorter calculation times, well suited to iterative design where cross-sections or material properties change repeatedly.
- Clear interpretation. Internal forces, reactions, and displacements are easy to visualise and check, both for the designer and during project meetings or reporting.
- Accessibility. Less computing power means cheaper software licenses and modest hardware requirements, making this approach a good fit for small to medium-sized projects.
- Lower knowledge barrier. A basic understanding of the finite element method (FEM) is usually enough to set up and interpret 2D calculations correctly.
Disadvantages of 2D calculations
Complex geometries, such as three-dimensional nodes or buckling shapes, are difficult to model directly and require simplifications, for example estimating node stiffness, which approximates reality without fully capturing it. Interactions between different structural elements (beams, plates, shells) also become blurred and must be entered manually or via simplified couplings, raising the risk of inaccuracy where rotation or torsion matters. Finally, 2D is less suited to dynamic analysis: natural vibration modes usually occur in three dimensions, making seismic or wind-driven behaviour hard to capture without 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 of its unique, non-standard architectural shape. The forces at work in shapes like this are difficult to describe with a 2D model.
Advantages of 3D calculations
That functionality comes at a price: a 3D model is less transparent, you rely on the software and your own judgement to interpret results correctly, and an imperfection in the geometry or a forgotten load can have major consequences while being harder to spot. Setting up a 3D model means defining many parameters, the most important, and most underestimated, being the boundary conditions: what forces the structural elements can exchange with each other, which must match reality for the model to be representative. Larger models also mean longer calculation times, higher hardware demands, and results that take more experience to interpret correctly.
Disadvantages of 3D calculations
That functionality comes at a price: a 3D model is less transparent, you rely on the software and your own judgement to interpret results correctly, and an imperfection in the geometry or a forgotten load can have major consequences while being harder to spot. Setting up a 3D model means defining many parameters, the most important, and most underestimated, being the boundary conditions: what forces the structural elements can exchange with each other, which must match reality for the model to be representative. Larger models also mean longer calculation times, higher hardware demands, and results that take more experience to interpret correctly.
Is there a future for 2D calculations?
Yes. As long as repetitive, simple structures exist, 2D remains the fastest way to calculate: preliminary studies, second opinions, repetitive elements such as frames and halls. 2D also keeps you working didactically, it forces you to understand what happens to the moment when a support moves, or where the shear force comes from.
The future lies in hybrid models: a good engineer switches between 2D and 3D the way a driver switches gears, and Diamonds makes that switch easy
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 handled load deduction, horizontal stability checks, and reinforcement of walls, floors, beams, and columns. The 2D models determined the minimum thickness of the cantilevered terraces and were used for the façade design and the dimensioning of wall openings.
Conclusion
Both techniques have their place. 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 both: an intuitive 2D module for quick design checks and plate structure calculations, a full 3D environment with automatic meshing, BIM links, and non-linear analysis options, and flexible licensing models sized to what you need.
FAQ
When should I use a 2D model instead of a 3D model?
Use 2D for simple, repetitive structures where speed, clarity, and low hardware/licensing cost matter more than capturing complex 3D behaviour, think preliminary studies, second opinions, or repetitive elements like frames and halls.
When do I need a 3D model?
When the geometry is genuinely three-dimensional, when connections and load paths interact in multiple directions, or when the analysis itself requires it, seismic behaviour, wind effects in all directions, or a direct BIM link.
Can I combine 2D and 3D in the same project?
Yes, this is the hybrid approach most engineers actually use in practice: a 3D model for global stability and load deduction, 2D models for specific checks like façade design or wall openings. Diamonds is built to support both without switching software.
Next step
Want to see how this works on your own project? Contact us for a no-obligation demonstration.
