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Frequently Asked Questions (FAQ)
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AnswerNonlinear material models are only available in the 3D environment. Please make sure that the model type is set to '3D' (see Figure 02).
AnswerSimilarly to surfaces, there are various smoothing options for displaying the results of support reactions. For a nonlinear support, you should always select the actual distribution to display the results.
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 provide a suitable solution. In addition to Eurocode 2, the international standards, such as ACI 318, CSA A23.3, SIA 262, or GB 50010, are also available for the design in both programs.
With the add-on modules for designing columns or foundations, or for punching shear designs, it is possible to quickly and reliably calculate the structural components.
Main Programs RFEM or RSTABThe main programs RFEM or RSTAB are used to define structures, materials, and actions.
For reinforced concrete structures, RFEM is clearly the first choice as it allows you to also create structural systems consisting of plates, walls and shells in addition to spatial frame structures. RFEM is the more diverse variant as it can be equipped and extended with the corresponding add-on 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 the 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 it is necessary to perform seismic analysis or vibration designs of a building, the RF‑/DYNAM Pro add-on modules provide special tools for determining natural frequencies and mode shapes, for an analysis of forced vibrations, a generation of equivalent loads, or for a nonlinear time history analysis.If you have any question about the Dlubal Software programs, please do not hesitate to contact the sales department.
For surface supports, this option is only available if there is also the nonlinearity defined in the local z direction (failure if contact stress in z is negative/positive). In the dialog box where you can edit the nonlinearity, you can find the "Friction in plane xy" option.
This option works as shown in the graphic dialog box: The support in the x and y direction is fully accepted only when reaching the contact stress Tau (contact stress Sigma multiplied by the friction coefficient). It is necessary to reduce this linearly in advance.
In order to use this option, a support must be in the horizontal directions. It can be defined as fixed or with an elastic spring. If the spring is defined with 0, no support is considered even though a friction coefficient has been entered.
Friction is a nonlinearity and can therefore only be modified via the interface to the member hinge.
For this, it is first necessary to create the member hinge, if not already available. Then, the IMemberHinge interface is brought to the member hinge and then to the nonlinearity (here IFriction). Then, you can use the methods GetData and SetData to modify the data (here Friction):Sub SetMemberHingeFriction ()Dim model As RFEM5.modelSet model = GetObject(, "RFEM5.Model")model.GetApplication.LockLicenseOn Error GoTo eDim data As IModelDataSet data = model.GetModelDataDim hinge(0 To 0) As RFEM5.MemberHingehinge(0).No = 1hinge(0).RotationalConstantX = 1hinge(0).RotationalConstantY = 2hinge(0).RotationalConstantZ = 3hinge(0).TranslationalConstantX = 4hinge(0).TranslationalConstantY = 5hinge(0).TranslationalConstantZ = 6hinge(0).Comment = "Member Hinge 1"hinge(0).TranslationalNonlinearityX = FrictionATypedata.PrepareModificationdata.SetMemberHinges hingedata.FinishModification' get interface for member hingeDim imemhing As IMemberHingeSet imemhing = data.GetMemberHinge(1, AtNo)' get interface for nonlinearity 'friction'Dim iFric As IFrictionSet iFric = imemhing.GetNonlinearity(AlongAxisX)' get friction dataDim fric As Frictionfric = iFric.GetDatafric.Coefficient1 = 0.3' set friction datadata.PrepareModificationiFric.SetData fricdata.FinishModificatione: If Err.Number <> 0 Then MsgBox Err.Description, , Err.SourceSet data = Nothingmodel.GetApplication.UnlockLicenseSet model = NothingEnd Sub
In the case of the friction Vy + Vz, the Coefficient2 is used to set the second coefficient. The spring constant in the Friction dialog box is controlled by the translational spring of the member hinge. In this particular case, this is TranslationalConstantX for the X‑direction (see Figure 01).
AnswerWhen defining nonlinearities, such as support failure under tension, it may happen that some load cases cannot be calculated. If these are the loads that cannot exist without other stabilizing loads, the problem resolution is simple: You can set the load cases to "Not To Be Calculated." As a result, the load combinations are only considered in the "Calculate All" option of the calculation process. This is possible because some loads can never appear without a dead load, for example.In the attached example, it is clearly evident that the structural system would buckle in the Wind load case, and thus no convergence is found. In contrast to this, it is possible to calculate the load combination, where the dead load and the wind are combined without any problem because the dead load stabilizes the system.
AnswerEven if the program does not calculate a nonlinear material, it may calculate a nonlinear algebraic equation according to the second-order or large deformation analysis. Therefore, the design is not only nonlinear because of the geometrical material nonlinearities, but also because of the nonlinear physical analysis method.The attached video shows that if the nonlinear behavior of the tension beam is not considered during the calculation, a linear analysis is displayed in load cases and a nonlinear analysis is displayed in load combinations. The reason for this is the nonlinear design according to second-order analysis in the load combination.
In this case, it is recommended to use the definition of slippage. For this, select Partial Activity as a "Nonlinearity" in the "Edit Nodal Support" dialog box. In the "Nonlinearity - Partial Activity" dialog box, you can define the slippage in the respective zone. For checking purposes, there is a diagram, see Figure 01.
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 after the load relief.
In the case of the Isotropic Plastic 1D material model, 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 in both models to define the distribution after the last step.
The Isotropic Nonlinear Elastic 1D material model allows for the anti-symmetric input of the stress-strain diagram (different for the positive and negative zone), whereas the isotropic Plastic 1D model only allows for symmetric input.
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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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