In addition to our technical support (e.g. via chat), you’ll find resources on our website that may help you with your design using Dlubal Software.
Frequently Asked Questions (FAQ)
Customer Support 24/7
AnswerIn a short overview, creating hold down elements involves modeling rigid links and adding in nodal supports with non-linearity settings that allows the supports to take only tension forces. A line support is added at the bottom of the wall that only takes compression forces. The individual nodal supports connected with rigid members only take tension forces.
A more detailed look on how these elements can be model can be seen in the video below.
AnswerBoth RFEM and RSTAB are available as solutions. In addition to Eurocode 2, international standards such as ACI 318, CSA A23.3, SIA 262 or GB 50010 are also available for the designing in both programs.
With additional modules for columns, foundations, or punching shear designs, it is possible to calculate the components quickly and reliably.
Main Programs RFEM or RSTABThe main programs RFEM or RSTAB are used to define structures, materials, and Actions.
RFEM is clearly the first choice for solid structures, since in addition to the possibility of creating spatial frame structures, structural systems consisting of plates, walls and shells can be created as well. RFEM is the more diverse variant, as it can be equipped and extended with appropriate additional modules for all materials and designs.
- Eurocode 2 (EN 1992-1-1)
- SIA 262
- ACI 318
- CSA A23.3
- GB 50010
- RF-/CONCRETE Columns
Reinforced concrete design according to the model column method or nominal curvature method
- RF-PUNCH Pro
Punching Shear Designs of Surfaces
- RF-/FOUNDATION Pro
Design of Single, Bucket and Block Foundations
- RF-CONCRETE Deflect (RFEM)
Analytical deformation analysis
- RF-CONCRETE NL
Realistic deformation analysis of surfaces and members
Dynamic AnalysisIf earthquake calculations or vibration analysis of the building are necessary, the RF-/DYNAM Pro Add-on Modules provide suitable tools for determining natural frequencies and shapes, forced vibration analysis, generation of equivalent loads or also for nonlinear time history analysis.If you have any further questions on the Dlubal programs, please do not hesitate to contact the sales department.
AnswerWhen defining non-linearities, for example, failure of support under tension, it may happen that some load cases cannot be calculated. If these are loads that cannot exist without other stabilizing loads, solving the problem is simple: You can set the load cases to 'Not To Be Calculated'. As a result, only the load combinations are considered in the option 'Calculate All' of the calculation process. This is possible because, for example, some loads can never appear without having a self-weight.In the attached example, it is clearly evident that the system would buckle in the load case wind, and thus no convergence is found. In contrast to this, it is possible to calculate the load combination in which self-weight and wind are combined without a problem because the self-weight stabilizes the system.
AnswerEven if the program does not calculate nonlinear material it may calculate a Nonlinear algebraic equation according to II. or III. Order analysis. Therefore, the design is not only nonlinear because of geometrical material nonlinearities but also because of the nonlinear physical analysis method.In the attached video it can be seen that if the nonlinear behavior of the tension beam is not regarded during the calculation in the load cases linear design is displayed and in the load combination nonlinear design is displayed. The reason for this is the nonlinear design according to II. Order Theory in the load combination.
The difference between both material models is as follows:
In the Isotropic Nonlinear Elastic 1D material model, no plastic deformations are considered. This means that the material returns to its initial state when the load is released.
Whereas in the case of the material model Isotropic Plastic 1D, the plastic deformation is considered.
For both material models, the nonlinear properties are defined in an additional dialog box. When entering data by means of a diagram, it is possible to define a distribution in both models after the last step.
For the material model Isotropic Nonlinear Elastic 1D, it is possible to enter the stress-strain diagram (different for the positive and negative zone) in an anti-metrical way, whereas for the model Isotropic Plastic 1D, only symmetric input is possible.
When using a diagram in the program, the first strain is always given. (Initial strain). It depends on the output modulus of elasticity and cannot be controlled directly. There is a trick in the program to nevertheless adjust the first strain to the desired value. To do this, you have to calculate the initial modulus of elasticity and enter it in the material parameter. In this case, the following procedure would be used.
AnswerDifferences resulting from the determination of the deformation in the cracked state can have different causes. The following points should be checked for deviations:
Is the same calculation method applied?
RF-CONCRETE Deflect uses an analytical analysis approach according to EN 1992-1-1 7.4.3.RF-CONCRETE NL uses a physically nonlinear analysis approach.More detailed information about the calculation methods can be found, for example, in the RF-CONCRETE Surfaces Guide in Chapter 2.7 and 2.8.
Is the same initial structure available?
The results of the linear calculation provide the best tool for consideration if the underlying system should be taken for equivalent. The linearly determined deformation of the underlying combination should be approximately equal. Any possible differences in the linear deformation may be increased in the cracked state in connection with the deformation analysis.
Are the same effects taken into account?
When performing a comparison, make sure that the same effects as for example creep and shrinkage are taken into account (Figure 02).
Are the same input values available?
Furthermore, it should be checked in connection with the deformation analysis if the same input values are available. In this case, it is necessary to pay particular attention to whether the applied reinforcement (Figure 03) and the lever arm or concrete cover are the same.
If not having found the cause after the fundamental examination, please contact our hot line.
AnswerIf nodal supports are modeled on supported lines, this may lead to problems and incorrect definitions. Therefore, the following warning message appears in the plausibility check.Internally, line supports and nodal supports are treated on each FE node. If a nodal support is located on a line support, an FE node thus receives several support definitions. If the defined directions of the supports do not match, this is not critical and the warning message can be ignored. If the same directions are defined several times, contradictions may occur.In case of line support which is failing on the tension and nodal support on this line, the tension force thus results in the FE node which however counts to the line support and to the nodal support.To avoid this behavior, it is possible to insert a short line without support definition in the area of each nodal support. It may also be useful to model the tension bracket using a newly defined member. The force transmission can then be adjusted by means of the support of the member, the member type itself, and the member end hinge.In general, the support stiffenings should be estimated realistically; in the example, rigid supports were assumed as a simplification.
The differences between the two modules are explained in this FAQ .
In general, you should also calculate the same results for both add-on modules if the settings are identical. However, this does not apply to existing nonlinearities. This is because no nonlinearities are considered in the RF-/DYNAM Pro add-on module. If the results are output via the Forced Vibrations add-on module, all nonlinearities are ignored. In contrast to this, the equivalent loads are calculated on a linear system, but the exported load cases are then calculated on the real system, that is, with all nonlinearities in RFEM or RSTAB . This may lead to inconsistent results.
If you deactivate the nonlinearities for the exported load cases, they should have identical results.
The way of considering nonlinearities in the response spectrum analysis is described using the tension members in this FAQ.
AnswerIf the load-bearing capacity of the wall surface is neglected and only applied to the ceiling as a load by using a line load, it would result in very large deformations.
If the nonlinear property of the masonry is not considered, it would result in very small deformations.
In principle, there are three options available in RFEM.
- Line release: Vertical compression forces are only transferred. In this case, the nonlinear property is only applied for the force transmission directly to the connection line of both surfaces.
- Nonlinear material "Isotropic Masonry": In this case, the tension stresses in the x- and y-direction (that is, vertical and horizontal) are reduced iteratively to the specified limit values by reducing the stiffness. Using this model, it is possible to represent the behavior of a masonry wall that is closest to reality, because the tension stresses are reduced in the direction of the mortar joints. This requires the RF‑MAT‑NL add-on module.
- Nonlinear surface stiffness type "Membrane without tension": In this case, the tension stresses in the principal stress direction are reduced iteratively by reducing the stiffness.
Did you find your question?
If not, contact us via our free e-mail, chat, or forum support, or send us your question via the online form.
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.
“Thank you for the valuable information.
I would like to pay a compliment to your support team. I am always impressed how quickly and professionally the questions are answered. I have used a lot of software with a support contract in the field of structural analysis, but your support is by far the best. ”