Known limitations for Detail 3D

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 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.

So you need to model structures that meet the requirements of the detailing rules defined in codes especially the maximum distance of reinforcement bars. In the following figure, you can see where the method starts to be reliable. The left model does not contain any stirrup leg in the volume around anchors. The model will be calculated successfully, but the results can be misleading because the maximum distance of sturrup legs is far from fulfilled. On the other hand, the right model has this rule fulfilled and the results will be correct.

To wrap it up, follow the detailing rules defined in your code and you will 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

Defining the support over a small area can lead to overestimating the capacity of the compression strut. Decreased strength of the concrete in the strut due to the transversal tensile strains (compression softening) is not taken into account in the calculation.

For this reason, the 3D module is suitable to use only for verifying anchorage. 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 around anchors 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.

Contact stress from Shear

It is possible to transfer shear load from anchors or shear lugs to the concrete volume (and then, of course, to reinforcement, etc.). The contact stress between the concrete and the anchor or shear lug is not checked and is only informative.

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.