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Frequently Asked Questions (FAQ)
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RF-/FOUNDATION Pro is a further development of the RF‑/FOUNDATION add-on module.
The main differences are as follows:
- Design according to Eurocode instead of DIN
- Additional foundation type "Block foundation with smooth bucket sides," see Figure 01:
- Input of a soil profile and settlement calculation, see Figure 02:
AnswerThe error message indicates that there was no option found to define the required reinforcement for the mats and rebars that you have selected.After clicking OK, you will be automatically redirected to Window 1.3. Please select additional mats and/or rebars here, and then perform the design again.
In RF‑/FOUNDATION Pro, you can do this by defining the soil profile.In Window "1.1 General Data," you can find the button that opens the dialog box for defining the soil profile.In the "Soil Profile"dialog box, you can then set the soil level interface PGE and PGL.Important:The profile grade line must not be higher than the profile ground elevation.In the case of a bucket foundation, PGE or PGL refers to the upper edge of the bucket.
The lap length design is performed according to DIN EN 1992‑1‑1, Section 8.7.3 or Section 10.9.6.3 for block and bucket foundations with the profiled bucket surface.You can optionally deactivate the design by using the [Details ...] button.An example of the lap length calculation for a bucket foundation can be found in the RF‑/FOUNDATION Pro manual, which you can download using the following link, or open it directly in the add-on module by pressing the [F1] key.
This is possible in RFEM in an indirect way.The soil pressure, from which the bending moment is determined for the design by using the integration, can be applied as an "external load" in the RFEM initial model.Distribution of Compressive Stress in RF-/FOUNDATION ProThis compressive stress can be applied as a "Free Surface Load" to an equivalent structural system in RFEM.In this case, the equivalent structural system is a rigid surface. The size of the surface depends on the position of the design section set in RF‑/FOUNDATION Pro. In this case, it is necessary to set "In Column Center."With this equivalent structure, it is possible to recalculate the "moment from the distribution of compression stress" determined in RF‑/FOUNDATION Pro.You can download the example described above using the link below and open it in RFEM 5.
AnswerThe theoretical approaches for this can be found in "Leonhardt, Fritz. (1977). Vorlesungen über Massivbau, Drittel Teil, (3rd ed.). Berlin [etc.]: Springer."Special attention must be paid to Chapter 16.3 "Single Foundations for Columns."
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 4,595 kip/ft² in RF‑/FOUNDATION. In RF‑/FOUNDATION Pro, 8,688 kip/ft² has been entered.
- Cohesive soil
- Pure silt - UL
- Stiff consistency
- Embedment depth of the foundation t = 4.92 ft
The design of a block foundation as well as a bucket foundation with smooth bucket sides is performed by analyzing 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.
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Wind Simulation & Wind Load Generation
With the stand-alone program RWIND Simulation, wind flows around simple or complex structures can be simulated by means of a digital wind tunnel.
The generated wind loads acting on these objects can be imported to RFEM or RSTAB.
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