Complete code-check of anchors and concrete block with IDEA StatiCa

The Eurocode specifies several methods of failure of anchors and concrete footings and further divides them according to the loading type. In IDEA StatiCa Connection, we have been able to assess the anchors up to now, but with some limitations, assessments had to be done manually. 

At the same time, reinforcement for concrete blocks was impossible to account for. This is now changing with IDEA StatiCa Detail 3D, which adds more possibilities. IDEA StatiCa Detail 3D does not offer assessments as we are used to in the standard that defines them for plain concrete. However, with FE analysis, we can verify that reinforced concrete will satisfy the specified load, and here, it will prevent the failure of the concrete, which would correspond to those conditions. The apps work independently and can be used separately, but thanks to the link between Connection and Detail, it is also possible to use Detail only as a supplementary calculation. 

Now, let's go through the Eurocode conditions one by one and the possibilities the applications offer us. 

Tensile force

Eurocode divides the first type of load (tensile force) into 6 possible cases of anchor or concrete block failure (a, b, c, d, e, f) and two more for reinforced footings (g, h). 

The figure below schematically shows which type of failure you can assess with the Connection app and what behavior can be covered by using reinforced concrete and, therefore, the analysis in Detail. IDEA StatiCa Connection uses empirical formulas from Eurocode ( EN 1992-4-7.2.1) for anchor design (CBFEM), while IDEA StatiCa Detail is based completely on the finite element method (3D CSFM). Some assessment options are, therefore, overlapping in both applications, but always with a different method. 

By the nature of the methods implemented in the software, only plain concrete can be considered in Connection, while only reinforced concrete footing can be considered in Detail. 

The main assumptions and limitations of the analysis for the IDEA StatiCa Detail 3D are mentioned in the article Known Limitations. 

a) Steel failure 

Steel failure of tension-loaded anchors alone is verified in both applications. Anchor tensile resistance is checked in Connection according to the following formula:

In Detail, the anchors are checked like the regular reinforced bars according to the stress-strain diagrams defined for particular materials while using the value of limit strain  maximally 5% (calculated based on tension stiffening effect read more in TB)

b) Concrete cone failure 

Concrete cone failure can be verified in Connection. However, at Connection, the app can only consider plain concrete. 

Therefore, in case the concrete cone fails, it is appropriate to proceed to IDEA StatiCa Detail, where an analysis of the entire reinforced block is provided. The tensile strength of the concrete is conservatively neglected, which means the bearing capacity for cone failure is, to a considerable extent, determined by the specified amount of reinforcement. In the picture below, you can see the directions of the principal stresses that indicate the shape of the cone mentioned above. In the right part, you can see the values of the concrete stresses, which are assessed with the limit values. 

 c) Pull-out failure

This code-check is in Connection only for certain cases (see the first picture in that article). An additional assessment is necessary for post-installed mechanical anchors. 

In Detail, it is possible to set up so-called adhesive anchors and specify the design bond strength according to their technical parameters. The anchors will then be verified based on these parameters. (Applicable only for reinforced concrete.)

d) Combined pull-out and concrete failure of bonded fasteners

This failure can only be detected in Detail, where the concrete stresses and the anchorage areas are assessed using 3D CSFM. The Combined pull-out and concrete failure mechanism is in Detail based on principles defined above, and its assessment is part of the concrete strength and anchorage check. (Applicable only for reinforced concrete.)

e) Concrete splitting failure

It is not possible to assess in Connection. For Detail, Splitting failure is usually a problem of plain concrete, where the use of reinforcement prevents it from occurring. At the same time, it is possible to see the stresses and strains of both the reinforcement under compression or tension and the concrete under compression in the Detail app. 

f) Concrete blow-out failure 

For plain concrete, empirical code-check according to Eurocode in Connection is possible. 

For reinforced structural members, it is possible to use Detail. Concrete blow-out failure is covered in the concrete strength analysis. Where the tensile stresses are transferred only by the reinforcement (as mentioned several times above).

Additional checks for reinforced concrete blocks:

For reinforced footings, an additional reinforcement assessment is required. Steel failure of reinforcement and anchorage failure of reinforcement is part of the reinforcement assessment in Detail. 

g) Steel failure of reinforcement

h) Anchorage failure of reinforcement

Shear load

Eurocode divides the second type of load (shear force) into 4 possible cases of anchor or concrete block failure (a, b, c, d) and two more for reinforced footings (e, f). 

The figure below shows schematically which type of failure you can assess with the Connection app and also what behavior can be covered by using reinforced concrete and, therefore, the analysis in Detail.  IDEA StatiCa Connection uses empirical formulas from Eurocode ( EN 1992-4-7.2.2) for anchor design (CBFEM). All types of failure caused by shear force can be covered in the Connection app.  

In the IDEA StatiCa Detail 3D, shear can be transferred by friction, anchors or shear lug. It is important to say that only the footing is assessed. Anchors/shear lug need to be checked in Connection or somewhere else. Again, it must be emphasized that only reinforced concrete is required.

a) Steel failure without lever arm

Steel failure without the lever arm of shear-loaded anchors is verified only in Connection. Anchor shear resistance is checked in IDEA StatiCa Connection according to the following formula:

The assessment is not possible in Detail.

b) Steel failure with lever arm

Steel failure with the lever arm of shear-loaded anchors is verified only in Connection. Anchor shear resistance is checked in IDEA StatiCa Connection according to the following formula:

The assessment is not possible in Detail.

c) Concrete pry-out failure

Concrete pry-out failure of shear-loaded anchors is verified only in Connection. Anchor shear resistance is checked in IDEA StatiCa Connection according to the following formula:

The shear capacity of the concrete through the base plate is then assessed in the Detail application. 

d) Concrete edge failure

Concrete edge failure of shear-loaded anchors is verified in Connection only for plain concrete. Anchor shear resistance is checked in IDEA StatiCa Connection according to the following formula:

Concrete edge failure can be checked in the Detail (reinforced concrete only). 

Additional checks for reinforced concrete blocks:

For reinforced footings, an additional reinforcement assessment is required. Steel and anchorage failure of reinforcement is part of the reinforcement assessment in IDEA StatiCa Detail. 

e) Steel failure of supplementary reinforcement

f) Anchorage failure of supplementary reinforcement

Conclusion

The most significant advantage can be found in examples such as anchoring close to an edge and other cases where plain concrete does not meet the required load. Note that, anchors and shear lugs need to be further assessed in Connection, but together, these two software tools provide a comprehensive solution.

Due to the method and the way the application is designed, the Detail application is only suitable for reinforced footings.