The Project Manager is installed by default when installing RFEM and RSTAB and it manages all projects and calculation files. In the Project Manager, you can link different projects to have a clear overview of the program files.
Structures are naturally three-dimensional. However, because it was impossible to perform calculations on three-dimensional models easily in the past, the structures were simplified and broken down into planar subsystems. With the increasing performance of computers and related software, it is often possible to do without these simplifications. Digital trends such as Building Information Modeling (BIM) and new options for creating realistic visualized models reinforce this trend. But do 3D models really offer an advantage, or are we just following a trend? The following text presents some arguments for working in 3D models.
CFD calculations are in general very complex. An accurate calculation of wind flow around complicated structures is very demanding on time and computational costs. In many civil engineering applications, high accuracy is not needed and our CFD program RWIND 2 enables in such cases to simplify the model of a structure and reduce the costs significantly. In this article, some questions about the simplification are answered.
For stress calculations, some standards use the "wall thickness analysis". We get the wall thickness by subtracting corrosion, abrasion allowance, manufacturing allowances (threading, grooving, and so on), and mill tolerances from the nominal wall thickness. All necessary values can be entered in the "Piping Cross‑Section" dialog box, "Stress Analysis Parameters" tab.
Spreadsheet programs like MS EXCEL are very popular with engineers because they allow you to simply automatize your calculations and quickly output the results. Therefore, combining MS EXCEL used as a graphical interface with Dlubal's WebService API is an obvious choice. By using the free xlwings library for Python, you can control EXCEL, and read and write values. The functionality is described in the following, using an example.
Under Options II in the Help Assistant tab of the program options, you can define the limit values for warning messages that appear after a successful calculation.
In RFEM, you can modify stiffnesses for materials, cross-sections, members, load cases, and load combinations in many places. There are two options in RF‑DYNAM Pro for considering these modifications when determining the natural frequencies.
If the calculation of a member model according to the second-order analysis is terminated with an error message, this instability is often caused by failed tension members: As soon as compressive forces appear in a tension member during a calculation step, this member is no longer considered in the following iterations. Thus, the model can become unstable.
In order to use internal forces from average regions also for the design of concrete surfaces, you have to activate them in the module. For this, click the [Details] button in the "Tools" tab and select the option "Apply the averaged internal forces in the defined average region for the ULS calculation and for the analytic method of SLS calculation."
The most common causes of unstable models are failing member nonlinearities such as tension members. As the simplest example, there is a frame with supports on the column footing and moment hinges on the column head. This unstable system is stabilized by a cross bracing of tension members. In the case of load combinations with horizontal loads, the system remains stable. However, if it is loaded vertically, both tension members fail and the system becomes unstable, which causes a calculation error. You can avoid such an error by selecting the exceptional handling of failing members under "Calculate" → "Calculation Parameters" → "Global Calculation Parameters".
Buckling analysis according to the effective width method or the reduced stress method is based on the determination of the system critical load, hereinafter called LBA (linear buckling analysis). This article explains the analytical calculation of the critical load factor as well as utilization of the finite element method (FEM).
You can apply nominal temperature‑time curves in RFEM or RSTAB using RF‑/STEEL EC3. For this, the standard time-temperature curve (ETK), the external fire curve and the hydrocarbon fire curve are implemented in the program. Based on these temperature curves, the add‑on module can calculate the temperature in the steel cross‑section and thus perform the fire design using the determined temperatures. This article explains the thermal behavior of structural steel, as this has a direct impact on the calculation of component temperatures in RF‑/STEEL EC3.
In this article, a heavy cargo box is calculated according to the guidelines of the German Bundesverband Holzpackmittel (HPE). The load cases for Handling by Crane and Sea Transport are calculated.
The stresses in the cross‑section of the member are calculated in the stress points. These points are set at locations in the cross‑section where extreme values for the stresses due to the loading types can occur in the material.
In SHAPE-THIN, the calculation of stiffened buckling panels can be performed according to Section 4.5 of EN 1993-1-5. For stiffened buckling panels, the effective surfaces due to local buckling of the single panels in the plate and in the stiffeners, as well as the effective surfaces from the entire panel buckling of the stiffened entire panel, have to be considered.
The previous post on this topic describes instabilities that may occur when using tension members. The example shown refers primarily to wall stiffening. Now, instability error messages can also refer to nodes within the range of supports. Truss girders and support trusses are especially susceptible to this. What causes the instability here?
Shoring braces usually obtain the "tension member" type. There are a few specifics to note because in the case of uniform, symmetrical structures and solely vertical loads, an error message often appears as follows: "The model is unstable in node No. 20. Free movement around Y-direction."
In RFEM, structures can be modeled and analyzed in a spatial environment. The permanent 3D visualization helps you to better understand complex models and to represent the force flux. However, you can switch from a spatial mode to a planar sheet mode in the documentation of a calculation. To do this, you have to describe the spatial calculation of the structure with all the necessary properties on "flat" paper pages for an independent reader. Usually, you try to display the load actions and the corresponding results by using an orthogonal view of the substructure of the entire structure. Obviously, the load symbols depicted in the 3D mode in a view perpendicular to the load become unrecognizable due the missing expansion. In order to still be able to create a clear representation of all information, the corresponding adjustments are available in RFEM.
Just as in the RFEM Display Navigator, you can set the distribution of internal forces in surfaces in RF‑STEEL Surfaces. Since deformations are always the result of the FEM calculation, the corresponding forces will be recalculated. This means that the internal forces on an FEM element are calculated depending on the composition (triangular or square) in three or four places. In order to obtain continuous internal forces and thus a smoothed distribution, these internal forces have to be interpolated. Interpolation is done by selecting the "Distribution of internal forces" option in the surfaces.
Critical load factors and the corresponding mode shapes of any structure can be determined efficiently in RFEM and RSTAB, using the RF-STABILITY or RSBUCK add-on module (linear eigenvalue solver or nonlinear analysis).
Cross-section properties in RFEM and RSTAB include different types of shear areas. This technical article explains the calculation and meaning of various values.
For the serviceability limit state design according to Section 6.6 of Eurocode EN 1997‑1, settlement has to be calculated for spread foundations. RF-/FOUNDATION Pro allows you to perform the settlement calculation for a single foundation. For this, you can chose between an elastic and a solid foundation. By defining a soil profile, it is possible to consider several soil layers under the foundation base. The results of the settlement, foundation tilting, and vertical soil contact stress distribution are displayed graphically and in tables to provide a quick and clear overview of the calculation performed. In addition to the design of the foundation settlement in RF-/FOUNDATION Pro, the structural analysis determines the representative spring constants for the support and can be exported to the structural model of RFEM or RSTAB.
In the calculation parameters, you can set the number of member divisions for result diagrams. The effect of this setting option is shown in the following images.
If you want to design structural components in an RFEM or RSTAB add‑on module, several National Annexes are available in some add‑on modules. In the case of structures that are to be analyzed mainly according to a specific National Annex, the add‑on modules provide the option to set a default value. Thus, it is unnecessary to select the NA again for each new model.
This article will show you how to use the Combination Wizard in RFEM 6 to reduce the number of load combinations to be analyzed, thus reducing the calculation effort and increasing the calculation efficiency.
When evaluating line support forces, implausible diagrams sometimes arise at first glance. In particular, for variable loads at locations that also have a nodal support, at division points and edge locations of supported lines, the results sometimes show unexpected support reactions. Using the function of the linear smooth distribution in Project Navigator – Display does not always lead to the expected result diagram.
The efficient design of prestressed structural components requires a few additional steps that go beyond the standard reinforced concrete design, from modeling tendons to the calculation of equivalent loads to the cross-section resistance design. Therefore, it is important that the software for prestressed concrete design is structured and the navigation is possible in the program. RFEM 5, with two add-on modules, RF-TENDON and RF-TENDON Design, fulfills these requirements and allows engineers to carry out the complete design of prestressed beams, frames, plates, buildings, and bridges according to EN 1992‑1‑1 with National Annexes and SIA 262.
The results of an FEM calculation are usually documented by means of isobands and isolines in the graphical display of results. In the following, we will look at creating the results graphic for the black-and-white printout.
Extensive calculations may result in vast amounts of data. Of course, current hard drives and SSDs are measured in terabytes. Therefore, you expect this to be no problem for current computing technology. This is true, in fact, but as often happens, the devil is in the details.