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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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:
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:
Some materials have multiple limit stress limits for compression, tension, and so on. For these materials, the limiting stress must be input manually by the user.
The limit stress values are listed under the Material Values tab.
These values can be added in the Member/Surface Configurations under the User limit stress type.
All members when using the Design Add-ons for serviceability checks are considered supported at the end nodes by default. If the member is instead a cantilever or includes an internal support for a combination of both a cantilever and supported at both ends member type, a new Design Support should be defined under the member details.
The Design Support option can be found under the member dialog box under Design Supports & Deflection tab. Supports can be added to any nodes detected along the member length such as the member start, member end, or internal nodes.
Under the New Design Support dialog box, you can set the type of support from the drop-down including general, concrete, or timber. The "general" will give the program guidance on the deflection member type and which limiting deflection ratio to reference from the Serviceability Configurations whether cantilever (e.g., L/180) or supported on both ends (e.g., L/360). The alternative types "concrete" and "timber" will also influence the deflection design, but have additional strength design options incorporated such as moment and shear internal force modification for concrete design and a stress perpendicular to grain check for timber design.
For additional detailed information on this new setting in RFEM 6 including a "timber" type design support, refer to the webinar listed below under Links at time 51:05.
Yes, you can also export the response spectra from RFEM 6 and import them into RFEM 5 as a user-defined response spectrum. Please note that export and import via Excel may also have different columns/descriptions due to different versions.
Export your data in RFEM 6 to Excel.
If you want to import this table directly, you will get an error message. RFEM 5 expects a different worksheet description and two columns only.
As soon as you adjust the name in Excel and delete the column with the frequency results, you will be able to edit the response spectrum in RFEM 5.