Introduction
At the beginning of this text let us define what the application is for. In the current version, we developed tools and verified the solution only for anchoring steel structures in simple reinforced concrete blocks.
The following text is divided into two parts: limitations of the application and method itself, and limitations of the import from IDEA StatiCa Connection.
Limitations of the application
Reinforced concrete
The 3D CSFM is not designed for plain concrete or lightly reinforced concrete. In this case, the result of the calculation can lead to misleading results or divergence of the non-linear calculation.
You can read more in Theoretical background.
The main reason why only reinforced concrete elements need to be modeled in the application is that the tensile strength of concrete is negligible. All tensile stress must therefore be transferred by reinforcement.
The second reason is: In IDEA StatiCa Detail 3D, fracture mechanics is not used. The model does not simulate explicit crack propagation, nor does it employ fracture-mechanics parameters of concrete (G_f, K_IC, shape of the fracture surface). Concrete is modeled as a ductile material with a horizontal plastic branch in compression – once the limiting compressive stress is reached, the stress remains constant, and only the strains continue to increase up to a prescribed limit. As a consequence, Detail 3D can capture plastic redistribution of stresses and strains in D-regions, but it does not explicitly model brittle failure mechanisms governed by fracture mechanics (e.g., pure shear failure of plain concrete, unstable propagation of a single dominant crack, etc.).
To wrap it up, your models shall comply with the definition of reinforced concrete as presented in international standards. Follow the detailing rules and obtain correct results.
Ultimate Limit State
All the calculations and code checks are implemented for ULS only. The definition of materials and the way of calculation itself must be different for SLS. You can see this difference in the Detail 2D.
Compression softening
At first, let's define what compression softening is: Concrete in compression loses strength and stiffness when it is simultaneously heavily cracked in tension, i.e. when large transverse tensile strains are present.
In cases where the resistance is governed by a compression strut (compression diagonal) running through heavily cracked concrete, Detail 3D tends to overestimate the capacity (i.e., to be slightly non-conservative) if the result is interpreted directly as the actual ultimate capacity.
For these reasons, the 3D module is suitable to use only for verifying the strength of anchoring in simple reinforced concrete blocks.
Although it is possible to model, for example, a pile cap using supports on a small area, the verification is not reliable because the softening effect becomes significant, particularly in punching-related problems. The same situation may occur in the case of a thin slab with a column placed on it, and in other similar cases.
For these situations, it is necessary to implement concrete softening, which is currently available only in the 2D module. Therefore, the 3D module can be used only for checking failures where this effect has no influence.
Anchor check
The element of the anchor is defined as being able to transfer normal tensile or compression forces as well as shear forces also considering the bending stiffness as described in the Theoretical background.
We support code-based checks according to the relevant standards (EN only), therefore IDEA StatiCa Detail can be used indepently for anchor assessment (anchors, reinforcement, concrete).
Implemented codes: EN 1992-4, EN 1993-1-8, EN 1994-1-1
For verifying other joint components (welds, plates, etc.), you need to use IDEA StatiCa Connection, where you can also perform the full anchor check for plain concrete. The anchorage in Connection —together with the applied forces—can be exported in Detail for additional design of reinforcement.
For ACI and Australina code the code-checks of anchors in shear and in shear and tension are not implemented yet, therefore it is always necessary to use both aplication for comprehensive code-checks of anchors.
Overturning
If the load input causes overturning of the model, the model will calculate until the divergence or reaching of a criterion. This usually takes a long time and you receive the following result:
The percentage of the transferred load is displayed. Moreover, in Auxiliary results extreme deformation is shown.
Workaround: It is recommended to calculate any model first with the Multiplier of default mesh size set to a high value (4-5). This multiplier can be found in Settings -> Mesh settings. The calculation will be quick and you will be able to see if the overturning is the problem or not.
It is necessary to check whether the self-weight of the concrete block is included, as it can prevent the model from overturning. Note that when importing from the Connection application, the self-weight is not automatically entered into the model — see the text below for details.
Limitations of import from Connection
Contacts
Generally, the import of forces acting on the base plate through contact with another steel plate is not supported. This applies to both the edge-surface contact and the surface-surface types of contacts. Read more in this article.
Anchoring by member
Only models anchored via the base plate can be correctly imported to the Detail application. For models, where members are connected to concrete blocks directly, the connecting plate of the member with anchors is imported without loads.
Self-weight is not added automatically
The self-weight is not automatically calculated/added. It must be manually included in the project for the Detail. This can mainly affect the verification of anchoring to the foundations, where failure to consider the self-weight could lead to the foundation overturning, as mentioned in the paragraph above.
Unsupported anchoring types for export
Hooked anchors are not supported in Detail. A waher plate will be used instead in the exported file.
The washer plate is modeled as a plate-shell element directly attached to the anchor shank, transferring load to the concrete exclusively through compression contact. The plate itself is modeled linearly, without plasticity, and is not subjected to resistance checks. Since the shank has zero bond strength, the entire load is transferred to the concrete through the washer plate. More about anchor types can be found in the article: Single anchor definition.
Unsupported combinations for anchor types
The Detail app does not support combining headed studs or reinforcement with other anchor types. These anchor types will not be included in the output. More about plate options can be found in the article: Anchoring plates options.
Imported loads and user-input loads combination
Imported loads and user-input loads cannot be combined within one model. Because of the reasons described in the Theoretical background. Anchors are imported disconnected from the base plates. If you create a user-defined load case, it is obvious that the load will not be transferred correctly.
Workaround: Copy the imported Project item, delete all imported loads, interconnect all anchors with the base plate, and then you can input your user-defined load case.
More concrete blocks
Only one concrete block is supported in Detail. However, the concrete block can be modified using the Negative volume, Cutting plane, and the Cut operation. So it is possible to model more complex shapes such as pedestals, foundation strip extensions, anchoring next to openings, etc.
It is also possible to import two independent concrete blocks from Connection, which are imported into Detail as two model entities that can be further modified using the cut operation.
More than one base plate in one block
Exporting of more base plates in one block is supported, although it is not recommended to import so-called edge anchoring.
In the Connection application, concrete is modeled in a simplified manner using Winkler's subgrade. On the other hand, the model of the steel part above the concrete block is modeled in detail, including the plasticity of materials. For a more detailed verification of reinforced concrete under the base plate, it is possible to export the base plate, anchors, and loads to the Detail application. There, the concrete is modeled plastically.
The anchors are exported axially disconnected, and the load between them is replaced by a pair of equal but opposite forces (precisely because of the lack of stiffness of the steel part above the base plate). Therefore, it is not possible for the axial forces in the anchors to change if the covering layer in the corner of the concrete block becomes plastic. Similarly, the welds of the base plates are exported disconnected, with the connection replaced by equal but opposite forces. Therefore, there can be no change in the stress on the weld in the event of plasticization of the concrete corner.
It follows that after export, although all forces acting on the base plates are in equilibrium, the deformation conditions will not be met.
It applies to the current version 25.1.2. It may differ in previous versions, as we are gradually working to remove these limitations. You can find more information about each version in the release notes.