Plastic shell
FEM-Design 23 introduces a new analysis method for computing 3D shells made of reinforced concrete and structural steel in an elasto-plastic manner. The method is called the Layered plastic shell model. The shell core contains layers from 1 to N, and if reinforcement is present, there are four additional layers for reinforcement (bottom x’, bottom y’, top x’, and top y’). Material models are handled using a layer-wise method.
⭳ Download the Theory of Plastic Shells
With the new analysis method, you can:
1. Analyse material non-linearities of reinforced concrete with/by:
- Non-linear stress-strain relation of concrete based on EN 1992-1-1:2004 (E):
- Considering tension stiffening and calculating concrete cracking, taking into account the various effects caused by cracking:
- Considering elasto-plastic behaviour of reinforcement.
2. Perform plastic simulation with structural steel shells using the Von-Mises theory.
Using the new method, the utilization of individual structural elements can be estimated more accurately, which potentially enables the use of less material or more slender structures. The following figure illustrates an example showing the results of a plate calculated with the new analysis. The analysis of plastic shells is available under Material properties of selected structural elements.
With the following options, you can control the elasto-plastic behaviour of plates and walls:
- Elasto-plastic behaviour: the main controller determining whether the plastic behaviour can be considered for the selected structural shell or not.
- Plastic hardening: controls the plastic hardening behaviour of concrete. With plastic hardening of concrete, the parabolic material model is considered. Without plastic hardening, the linear elastic perfectly plastic material model is considered.
- Crushing: determines whether the ultimate crushing strain of concrete is taken into account or not. The biaxial model type (Crisfield/Cervera/Hinton/Prager) for it can also be selected.
- Tension strength in plastic flow rule: controls whether the concrete tension strength is taken into account in the flow rule or not.
- Tension stiffening: controls whether the concrete tension stiffening is taken into account after cracking or not. The tension stiffening model (Hinton/Vecchio/Linear/Cervera) can also be selected.
- Reduced compression strength in case of lateral cracking: and the rule for the efficiency factor on concrete compression strength (Vecchio 1/Vecchio 2/Cervera/Model Code 2010) can be considered.
- Reduced transverse shear stiffness in case of cracking
- Ultimate strain in rebars: determines whether the ultimate tearing strain of rebars is taken into account or not.
Based on the results, a new result can be achieved under Plastic shell condition, which displays the condition of each integration point for every finite element, layer-by-layer. Conditions can be Elastic, Plastic, One-directional crack, Two-directional crack or Crushing/Fracture, and are visualized using a colour palette schema.
The next figures illustrate the Plastic shell condition analysis result for a clamped reinforced concrete shell example.
- Analytical model, and the Plastic shell condition results of the bottom and top concrete layers:
- Plastic condition in the top x’ and y’ directional reinforcements:
- In the individual result diagrams, crack directions can also be displayed. For colour palette result display, there is a separate switch for this, while in symbolic display, crack directions represent the colours of the condition types.
Starting from FEM-Design 23.00.002, stress and strain results are available for plastic shell calculation:
To reduce calculation time and result file size, stress and strain calculation can be switched off at Calculation options of Analysis:
