The structural analysis software RFEM 6 is the basis of a modular software system. The main program RFEM 6 is used to define structures, materials, and loads of planar and spatial structural systems consisting of plates, walls, shells, and members. The program also allows you to create combined structures as well as to model solid and contact elements.
RSTAB 9 is a powerful analysis and design software for 3D beam, frame, or truss structure calculations, reflecting the current state of the art and helping structural engineers meet requirements in modern civil engineering.
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In the case of the structural analysis of members with a nonlinear material model, an FE mesh is generated on the cross-sectional area and used for the calculation. As of the version RFEM 6.06.0009 and RSTAB 6.06.0009, it is possible to adjust the mesh density for the FE mesh of the cross-sectional area via a refinement factor.
The preset mesh is relatively fine by default, and thus ensures a high degree of accuracy for the calculation results.However, a coarser FE mesh may be completely sufficient in many cases, reducing the calculation time significantly.
You can adjust the FE mesh refinement factor in the "Edit Section" dialog box, the "FE Mesh" tab. The smaller the value, the finer the mesh.The effects of the mesh density of the cross-sectional area on the calculation time and internal forces are shown below, using a simple example. Cross-section: HD 260*54.1Material: S235Material model: Isotropic / Plastic (Members)A vertical distributed load is applied over the entire length of the beam, and it is so large that a plastic hinge is formed above the central support.
Different FE mesh refinement factors between 0.5 and 5.8 will be analyzed. The calculation time as well as the support and sagging moment are evaluated. The relative deviation from the results with an FE mesh refinement factor of 1.0 is shown in brackets.
The table shows that it is reasonable to increase the FE mesh refinement factor for this structural system. In the case of relatively small deviations of internal forces (less than 1%), the calculation time for a structural analysis can be roughly halved.
The most likely cause of the different results is that you have probably not set the same smoothing of the surface internal forces.
This can be set separately in RFEM 6 and in the add-on.
If the smoothing is the same in both settings, the stresses are also the same.
For the CSA O86 and NDS, the Modification and Adjustment factors used in the Timber Design add-on in RFEM 6 can be manually adjusted. The factors are listed under the material properties.
To edit them manually, first open the material(s) being used for timber design and then set them to "User-Defined". Once this is done, navigate to the Timber Design tab where the Modification and Adjustment factors can be entered manually.
The Calculation for Torsion in the NDS Strength Configuration works together with the torsion limit set to ensure the safety of the member and structure. Below, you find a short explanation for each option:
Check torsional limit only:The ratio torsion check is compared to the torsion limit. If the ratio is smaller than the limit, then no further calculation is carried out. If the ratio is bigger than the torsion limit, an error will be shown in the design check. The error is then the most governing design check in the graphical and tabular results.
According to Timber Construction Manual:Torsion design is according to the Timber Construction Manual 4.6, and the result is a typical design ratio based on the calculation.
Ignore torsion:This setting is very similar to the first option. The ratio is compared from the torsion calculation to the torsion limit. If the ratio is smaller than the limit, then no further calculation is carried out. If the ratio is bigger than the limit, then a warning is shown in the design check. This warning will not be a governing design check in the results tables or graphics and serves only as a warning for safety considerations.
To neglect all torsion for the member design check, the limit value for torsion must be increased.
RFEM allows you to perform structural analysis and design of laminate and sandwich structures. The same applies to the cross-laminated timber. Stress and deflection analysis of laminate and sandwich surfaces is performed according to the laminate theory, taking into account the shear coupling.
Programs and Add-ons
RFEM is the main program that you can use to define the model and actions. You can model planar and spatial structures, consisting of plates, walls, shells, and members.
For the stress and deflection analysis, you need the Multilayer Surfaces add-on. It allows you to define and analyze layer structures.
Use the Timber Design add-on to also design the member supporting elements of the structure according to Eurocode 5 or ANSI/AWC NDS, for example.
Dynamic Analysis
If you need to perform a seismic or vibration analysis, the corresponding Dynamic Analysis add-ons are the perfect tools for determining natural frequencies and mode shapes, or for the analysis of external excitations.
In case of any questions about the Dlubal timber design solutions, our sales team will be happy to assist you.
Both RFEM and RSTAB are ideally suited for the structural analysis and design of timber structures.
Main Programs RFEM and RSTAB
The main programs RFEM and RSTAB are used to define the model with its properties and actions. In addition to spatial frame and truss structures, such as halls or space trusses, it is possible to model plate, wall, and shell structures with RFEM. Thus, RFEM is the more versatile variant—especially if you work in other areas, such as solid construction.
Available Standards
Add-ons for Timber Structures
Design add-ons supplement the functionality of the main programs. Use the Timber Design add-on to perform the ultimate and serviceability limit state design checks as well as the stability analysis and fire resistance design according to the standards listed above. In combination with the Torsional Warping (7 DOF) add-on, you can also perform lateral-torsional buckling analysis with up to seven degrees of freedom.
The special-solution Multilayer Surfaces add-on for RFEM is ideally suited for laminate surfaces made of cross-laminated timber (CLT).
The formula to determine the initial section depth di (CSA) or the equivalent square section dimension aeq (NDS) used for the slenderness ratio calculation is as follows:
If no angle can be defined in the "Rotation" column, there is an isotropic material model selected for the material, where stiffnesses are identical in all directions and it is not necessary to define an angle.
If you use materials with anisotropic behavior (for example, timber), it is necessary to ensure that the "Orthotropic | Linear Elastic (Surfaces)" material model is selected.
Note: The "Orthotropic | Timber | Linear Elastic (Surfaces)" material model cannot be currently used in combination with the "Layers" thickness type.
As soon as switching to the orthotropic material model, the individual layers can be rotated accordingly.
To activate the nonlinear material behavior in RFEM 6 or RSTAB 9, the Nonlinear Material Behavior add-on must be activated.
The material model should then be modified from the default setting "Linear Elastic" to the relevant "Plastic" setting in the Material dialog box, depending on whether the element is a 1D member, 2D surface, or 3D solid.
Lastly, the Static Analysis Settings should further be modified to set the number of load increments and to activate the "Save results of all load increments" checkbox.
After the calculation, all results can be viewed in the Navigator - Results panel according to the selected load increment.
The ASCE 7-22 standard provides several types of design spectra. In this FAQ, we would like to focus on the following two design spectra:
The two-period spectrum is implemented in the program as usual. However, based on the data available from the standard, only the horizontal design spectrum / MCER spectrum as well as the modification related to the force and displacement can be offered.
For the multi-period design spectrum, discrete numerical values are specified. ASCE 7‑22 states that these values can be queried on the USGS Seismic Design Geodatabase page. In the current state of development, you have the option to create a user-defined response spectrum with a g‑factor (depending on the mass conversion constant) to use the data from the ASCE 7 Hazard Tool [1], for example.
Please proceed as follows: