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Frequently Asked Questions (FAQ)
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This discrepancy is often caused by changing DIN 1054 to EN 1997.In the 'old' DIN 1054, the design was performed by using the characteristic values on the action side and the allowable stress on the resistance side. The actions were used without partial factors and compared with certain allowable stress. In this case, the 'eta' resistance was completely included in the allowable stress.In the predecessor module of RF‑FOUNDATION Pro, which performed the calculations according to DIN 1054, there was a special tab 'Ground Failure Analysis (Service Loads)' for this purpose.In the Eurocode, the ground failure design is performed in a different way.Here, a partial factor is applied to the action and the resistance side. Thus, the loading is increased by the factor of 1.35 or 1.5, and the resistance is reduced by the factor of 1.4.With regard to the 'old standard', the 'eta' resistance is completely included in the 'allowable stress sigma_all'.Under the Downloads link below, you can find a model file for RFEM or RSTAB, which clarifies the problem in RF‑/FOUNDATION or RF‑/FOUNDATION Pro. Here, the design has not been performed by using the user-defined entry of the soil pressure, but using the allowable stresses from the standard case tables. There should be the same soil with approximately the same foundation dimensions resulting or the Eurocode and for the old standard.The following assumptions for the foundation have been made in both add-on modules:
When using the all. soil resistance according to DIN EN 1997‑1 from the standard case tables, the factor of 1.4 is already included. The base values Sigma‑R,d(B) of the soil resistance also differ by the factor of 1.4 compared to the allowable soil pressure 'sigma_all' (DIN 1054).Results of the comparison:Ground failure design according to DIN 1054 in RF‑/FOUNDATION (old):Ground failure design according to EN 1997‑1 in RF‑/FOUNDATION Pro:In spite of different input values, the results from DIN 1054 and EN 1997‑1 are comparable.If you want to recalculate the foundation in RF‑/FOUNDATION Pro, which has already been designed with RF‑/FOUNDATION (old), you would have to apply twice the soil pressure Sigma_R,k:Sigma_R,k (input in RF‑/FOUNDATION Pro) = 1.40 (partial factor for ground failure) x 1.35 (resistance on the load side in the example) x Sigma_all (from RF‑/FOUNDATION (old)).In the attached file, this has been done in CA2 in both add‑on modules. In this case, the allowable soil pressure has been entered as 220 kN/m² in RF‑/FOUNDATION. In RF‑/FOUNDATION Pro, 416 kN/m² has been entered.
- Cohesive soil
- Pure silt - UL
- Stiff consistency
- Embedment depth of the foundation t = 1.50 m
The design of a block foundation as well as a bucket foundation with smooth bucket sides is performed by analysing the horizontal components Ho and Hu.
In this case, the restraining moment at the column base is converted into a horizontal component on the upper side (Ho) and on the bottom side (Hu).
For block and bucket foundations with smooth bucket sides, no vertical component is calculated to be used for the design of anchorage.
See Figure 01 and Figure 02.
A different situation is with block and bucket foundations with rough bucket sides. In this case, you can activate the design of the lap length of bucket reinforcement in Details.
First, the impact load if defined as a load case in RFEM or RSTAB. This load case is then considered in a load or result combination, for which the support forces are determined.
In the design, RF‑/FOUNDATION Pro always uses the support forces from RFEM or RSTAB. This applies for all designs and cannot be controlled separately.
It is only possible to completely deactivate a certain support force for the designs.
Figure 01 - Deactivating Support Loads for Foundation Design
If you do not want to consider a load for geotechnical designs, for example, because the foundation is otherwise constructively stabilized with regard to the impact load, it is possible to deactivate the load in the setting shown in the figure.
However, if it is necessary to consider the impact load for bending design (for example, design of bucket walls), you should copy the design case and include the impact load again.
The foundation evaluation would then be performed using two design cases in the module.
In the case of a ground failure analysis or soil contact stress analysis, the 'equivalent surface' is determined in RF‑/FOUNDATION Pro in order to calculate the soil contact stress.If the foundation dimension is smaller than twice the load eccentricity 'e', the 'equivalent surface' or the 'effective foundation' cannot be determined. In this case, you receive the corresponding error message.In most cases, the problem is that a user has entered too small dimensions of the foundation plate.To remedy the problem, you can manually set greater dimensions. Or select the 'Dimensioning' feature.
AnswerFirst, set 'DIN' as National Annex.Thus, the 'For standard case acc. to DIN EN 1997‑1, A6.10' option becomes available (see Figure 01).You can set here whether there is the 'cohesive' or 'non-cohesive' soil. In 'Details', you can then enter further settings for the standard case tables, such as the values for allowable soil pressure (see Figure 02).It is not possible to modify the values in the standard case table.
AnswerThe design of lifting loads is performed in RF‑/FOUNDATION Pro under the name of 'Uplift limit state design'.In this case, it means not only the uplift of the foundation with regarg to the groundwater level, but also the presence of the lifting or negative support forces.The uplift limit state design can be activated in 'Details' of the add-on module or it is activated by default when creating a new design case (see Figure 01).If the dimensions of the foundation should be designed, the program increases the foundation dimensions iteratively until the uplift limit state design is fulfilled.
AnswerPlease check the load.The foundation base is probably not overpressed due to the lifting load.In this case, RF-/FOUNDATION Pro displays the design criterion of '-' with the note 'Design not required'.
Yes, it is possible.For this, open the '1.3 Materials' dialog box. Here you can deselect the 'Available Reinforcing Steel Mats' and select the reinforcing bars that should be considered for the reinforcement of the foundation.Alternatively, it is also possible to specify an alternative reinforcement concept for the foundation plate in dialog boxes 2.4 or 2.5 after the calculation performed previously, while this concept would not take into account the mat reinforcement, for example.After you change the reinforcement concept in dialog boxes 2.4 and 2.5, it is necessary to calculate the result again. If you switch to another dialog box after modifying the reinforcement, a message appears saying that the recalculation of results is required.
AnswerAs you have correctly mentioned, there is the design according to EN 1992‑1‑1 or EN 1997‑1 available in RF‑/FOUNDATION Pro.The reinforced concrete design according to DIN 1045‑1 or DIN 1045, or Geotechnical designs according to DIN 1054 can be performed in the predecessor module RF‑/FOUNDATION.You can find the RF‑/FOUNDATION add‑on module in the Data navigator under the add-on modules and in the menu under 'Add-on Modules' → 'Foundations'.In the detailed settings (see Figure 02), you can specify the standard according to which the reinforced concrete design should be performed.
AnswerYes, it is possible. If a nodal support is arranged at a certain angle in RFEM or RSTAB, the geometry of the foundation at the node also follows this coordinate system (see Figure 01).
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