Frequently Asked Questions (FAQ) - Search Term: Forces li...

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*54.1
Material: S235
Material 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.

In programming, flags should be regarded as switches or switch positions. In this specific case, the flags provide information about the section type from which the result comes. Here is an overview of all the flags and their meanings:

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.

According to EN 1993‑1‑1, 6.3.4 (1), the general method allows for the lateral-torsional and torsional-flexural buckling analysis of individual structural components, which are subjected to loading in their principal plane and include any single-symmetric cross-section, a variable height, and any boundary conditions, as well as the analysis of entire planar structures or partial structures consisting of such components. Therefore, the design of structural components with an asymmetric cross‑section is not possible using the general method. Steel Design reports a failed design and shows the corresponding error message.

The stability analysis may be performed as section design according to EN 1993‑1‑1, 5.2.2 (7) a, provided that a spatial calculation according to the second-order analysis is performed with the global and local imperfections applied. In order to model the lateral-torsional buckling, it is necessary to determine the internal forces according to the geometrically nonlinear torsional buckling analysis with regard to warping torsion. Then, it is only necessary to perform the section design, as all stability effects are covered by the calculation. Therefore, this design method is applicable to all cross‑sections subjected to any loading.
Considering the cross-section warping as an additional degree of freedom is possible using the Warping Torsion add-on.

In RFEM 6, you can only design reinforced concrete members and surfaces. To do this, use the Concrete Design add-on. This is used to carry out the design for the ultimate limit state, stability, and serviceability limit state.

Reinforced concrete solids cannot be designed directly in RFEM 6.

However, it is possible to create solids with the "Concrete" material and determine the stresses within the solid, for example. Optionally, you can also insert a result beam into the solid, with which the results of the solid are converted into member internal forces. You can then design this result beam in the Concrete Design add-on.

The following programs and add-ons are particularly suitable for structural timber projects.

Main Program

To model your structure and determine the internal forces, you need one of the main programs. Depending on the application area, you can use RFEM 6 or RSTAB 9.

• RSTAB: Analysis of planar or spatial frame & truss structures
• RFEM: Finite element analysis of plate, wall, shell, and member structures

If your model has surface components, such as plates and walls, in addition to membe elements, you need RFEM. This program is the only one with the capability to analyze laminate or cross-laminated timber elements and curved objects.

Timber Design Add-on

Use the Timber Design add-on to design the timber components of your model. The design checks in compliance with specific standards cover both members (bending beams, columns) and surfaces (plates, walls). For columns, the stability analysis according to the equivalent member method or the second order analysis is performed.

You can perform the ultimate and serviceability limit state design checks, as well as the fire resistance design according to the following standards:

• EN 1995 – including National Annexes
• SIA 265
• NTC
• NDS
• CSA O86
• GB 50005
• AS 1720

In the fire resistance design, the charring of a cross-section is taken into account for both the stiffness and the design.

Multilayer Surfaces Add-On

With the Multilayer Surfaces add-on for RFEM, you can analyze laminate and sandwich structures with user-defined layer structures. This allows you to design cross-laminated timber panels, for example.

If certain layers have nonlinear material behavior, you can assign the appropriate properties to them. Furthermore, this add-on allows provides you with the option to analyze curved surfaces.

Additional Add-ons

In case of special requirements for your timber structure, we recommend further add-ons and additional programs to help you solve the task.

If you need to perform seismic or vibration analysis, the dynamic analysis add-ons provide you with powerful tools for your structural analysis and design. The Modal Analysis add-on enables the calculation of natural frequencies, and in combination with the Response Spectrum Analysis add-on, you can also perform seismic analysis according to numerous standards.

If you are designing a building with a complicated shape, so that the determination of wind loads according to the relevant standards reaches its limits, the RWIND RWIND program will help you: Using a CFD analysis, you can determine the wind loads even for highly complex building shapes.

If the construction stages affect the final internal forces in a structure, or if the governing internal forces for the structural design result from certain construction stages, you should consider the modeling using the Construction Stages Analysis add-on. The Building Model add-on allows you to easily enter large multi-story timber structures.

Please note that the enveloping results are usually shown when displaying the results of design situations or result combinations.

There are three options to graphically display the results of deformations, internal forces, and support forces: Max and Min-values can be displayed separately. To display both envelopes from the extreme values on the model, select Max and Min-values.

In the standards, no torsion is taken into account in the stability analysis for the equivalent member method or the general method. The warning message is a reminder to the user of this fact.

First of all, the magnitude of the torsional stress or moments should be analyzed. Very small torsional moments in the members to be designed often prevent certain design formats. In order to neglect them and suppress the warning, you can change the limit values in the Ultimate Configuration. There is no normative basis for this limit value and therefore, no general specification. Find more information here:
Neglecting Torsion

In the case of open cross-sections, it can generally be assumed that the acting torsional moments are not transferred by primary torsion, but by secondary (warping) torsion. In RFEM 6 and RSTAB 9, the internal forces are initially only determined with six degrees of freedom without considering warping. For small acting torsional moments, it seems obvious to neglect the torsional stresses in the design. For large torsional moments, however, a calculation should be carried out with seven degrees of freedom in order to also consider the influence of the warping moment and the secondary torsional shear stresses. For this, you can use the Torsional Warping (7 DOF) for RFEM 6 / RSTAB 9 add-on, for example.

We usually release a new version of RFEM 6 / RSTAB 9 every Monday; means, four versions per month.

You are informed about a new version on the Extranet and in the Dlubal Center. There you will also find the links to download the versions.

In RFEM 6 and RSTAB 9, the calculation parameters are no longer managed in a dialog box of the same name, but in the form of Static Analysis Settings in the Load Cases and Combinations category in the navigator.

There are tree analysis types preset:

• Geometrically linear
• Second-order (P-Δ)
• Large deformations

You can adjust the parameters of these analysis types or create more types.

In the "Load Cases & Combinations" dialog box, you can then assign the relevant static analysis setting (SA) to the load cases and load combinations.

The stiffening can be modeled using line releases as follows:

• Create a line with the planned beam dimensions.
• Open the "Edit Line" dialog box and assign a member with the cross-section of the planned stiffening to the line.
• Create a New Line Release in the "Special Objects" subfolder by right-clicking it.
• A dialog box appears where you can select the previously created line and then the created member (see the image).
• Create a new Line Release type and enter the appropriate support conditions in the dialog box according to your planned stiffening and fasteners.

• Select the original line and repeat Steps 2 through 5 to create a second reinforcement (for unsymmetric cross-sections, the corresponding section should be arranged with an angle of 180°).
• Assign the cross-section of the main beam to the original line.
• Now, you can assign a corresponding eccentricity to the stiffening beams.

Another option for applying stiffening is described in the following FAQ:

You can find another article on the subject of flexible timber joints on our website:

In RFEM 6 or RSTAB 9, you can use plastic hinges to simulate the nonlinear behavior of steel structures subjected to a load. You can model a plastic hinge by arranging a hinge with nonlinear properties on a member end. Proceed as follows:

• Select the member or members to which you want to assign the hinge.
• Open the "Edit Member" dialog box by double-clicking the member or using the member shortcut menu.
• Select the Hinges option in the "Main" tab.
• In the "Hinges" tab, click the button for the member start or the member end, to define a new hinge type.
• In the "New Member Hinge" dialog box, select one of the four plastic options for the relevant degree of freedom in the Nonlinearity list; for example, a plastic hinge according to FEMA 356 or a bilinear hinge according to EN 1998‑3.

• In the second tab, you can specify the yield properties, acceptance criteria, and yield strengths. The parameters are set by default based on the member properties and standards. If necessary, adjust it to describe the behavior of the hinge; for example, the bilinear yield curve including the yielding and hardening regions.

• Click OK to save the hinge.
• Clicking OK again in the "Edit Member" dialog box to assign the hinge to the member end.

In order to specify a uniaxial load transfer for a plate, you can assign orthotropic properties to the surface. This way, you can control the stiffnesses for specific directions so that the loads are mainly transferred in one direction. You have two options.

Orthotropic Thickness for Isotropic Material

• Double-click the surface to open the dialog box for editing the slab.
• In the Thickness with Material section, click the button to the right, to create a new thickness.
• In the "New Thickness" dialog box, select the Shape Orthotropy thickness type.

• Switch to the "Shape Orthotropy" tab. The Effective Thicknesses orthotropy type is set by default.
• For the uniaxial load transfer, enter the effective thicknesses as orthotropic properties in such a way that the stiffness is very high in the desired main support direction and very low in the other direction.

• To consider the self-weight, you can apply a user-defined fictitious thickness that corresponds to the full surface thickness.
• Click OK to save the thickness.
• Click OK again in the "Edit Surface" dialog box to assign the thickness to the plate.

Orthotropic Material Model for Constant Thickness

• Double-click the surface to open the dialog box for editing the slab.
• In the Thickness with Material section, click the button to the right, to create a new material.
• In the "New Material" dialog box, select the material from the library as usual. However, change the material model to Orthotropic | Linear Elastic (Surfaces) (1). Also, activate the User-defined material option (2).

• Switch to the "Orthotropic | Linear Elastic (Surfaces)" tab.
• For a uniaxial load transfer, change the modulus of elasticity of the secondary load direction to a very small value. You can also specify very small values for the shear moduli in the secondary support direction. Furthermore, set the Poisson's ratios to zero.

• Click OK to save the material.
• Click OK again in the 'Edit Surface' dialog box to assign the material of the plate.

If a Rhino surface cannot be created by using the geometry type, it will not be transferred. This is the case, for example, of curved surfaces with more than four boundary lines. In the Rhino command history (_CommandHistory or the F2 key combination), you can find a list of warnings and errors displayed during the transfer process:

The following programs and add-ons are perfectly suitable for your reinforced concrete projects.

Main Program

To model your structure and determine the internal forces, you need one of the main programs. Depending on the application area, you can use RFEM 6 or RSTAB 9.

• RSTAB: Analysis of planar or spatial frame & truss structures
• RFEM: Finite element analysis of plate, wall, shell, and member structures

If your model has surface components, such as plates and walls, in addition to membe elements, you need RFEM.

Concrete Design Add-on

Use the Concrete Design add-on to design the reinforced concrete components of your model. The design checks according to specific standard include not only members (bending beams, columns) and surfaces (plates, walls), but also surfaces susceptible to punching shear. For columns, the stability analysis according to the nominal curvature method is integrated in the add-on.

You can specify user-defined reinforcement or determine it by using the program. With these basic conditions, you can perform the ultimate and serviceability limit state design checks according to one of the following standards:

• EN 1992, including National Annexes
• ACI 318
• CSA A23.3
• SP 63.13330

The add-on also allows for deformation analyses for cracked reinforced concrete surfaces (state II) using the approximation methods described in the standards. Tension stiffening as well as creep and shrinkage can be taken into account.

Additional Add-ons

If you have special requirements for the reinforced concrete structure, we recommend further add-ons and additional programs to help you solve the task.

To use a cross-section that is not included in the extensive cross-section library of RFEM 6 or RSTAB 9, the RSECTION program helps you when modeling the cross-section including reinforcement. You can then design this cross-section as usual in the Concrete Design add-on.

If you need to perform seismic or vibration analysis, the dynamic analysis add-ons provide you with powerful tools for your structural analysis and design. The Modal Analysis add-on enables the calculation of natural frequencies, and in combination with the Response Spectrum Analysis add-on, you can also perform seismic analysis according to numerous standards.

If you are designing a building with a complicated shape, so that the determination of wind loads according to the relevant standards reaches its limits, the RWIND RWIND program will help you: Using a CFD analysis, you can determine the wind loads even for highly complex building shapes.

If the construction stages affect the final internal forces in a structure, or if the governing internal forces for the structural design result from certain construction stages, you should consider the modeling using the Construction Stages Analysis add-on. The Building Model add-on allows you to easily enter large multi-story concrete structures.

Basic Add-ons

If you design steel structures, you need the following add-ons in addition to RFEM or RSTAB:

• Steel Design
• Stress-Strain Analysis
• Stability
• Steel Joints

The Steel Design add-on allows you to perform stability analysis (lateral-torsional and torsional-flexural buckling) in addition to the normal cross-section design.

The Stress-Strain Analysis add-on calculates not only stresses, but also strains in members, surfaces, and solids.

Steel structures are usually slender structures so the stability plays an important role. Use Structure Stability add-on to calculate the effective lengths and critical load factors for a precise stability analysis.

Model the connections between members precisely and flexibly using the Steel Joints add-on that is based on FEA. The connections need to be loaded not only in the main load-bearing plane. Even if the connection is loaded about the "minor axis", you can dimension the connection using this add-on.

Additional Add-ons

If you have special requirements for steel design checks, there are other add-ons and additional programs available to support you in solving your special tasks.

To use a cross-section that is not included in the extensive cross-section library of RFEM 6 or RSTAB 9, the RSECTION program helps you when modeling the cross-section and calculating the section properties.

If you want to analyze the lateral-torsional buckling with the more accurate and cost-effective method with 7 degrees of freedom, you will need the Torsional Warping (7 DOF) add-on.

If it is necessary to consider the plastification of the material when determining the internal forces, you can use Nonlinear Material Behavior add-on.

The Modal Analysis add-on enables the calculation of natural frequencies, and in combination with the Response Spectrum Analysis add-on, you can also perform seismic analysis according to numerous standards.

If you are designing a building with a complicated shape, so that the wind load calculation according to the relevant standards reaches its limits, then the RWIND program will help you: Using a CFD analysis, it can determine wind loads even for the most complicated building shapes.

If the construction stages affect the final internal forces in a structure, or if the governing internal forces for the structural design result from certain construction stages, you can model this using the Construction Stages Analysis add-on.

The Building Model add-on allows you to easily enter large multi-story concrete structures.

For your design of lightweight steel structures, containing cables and membranes, the Form-Finding add-on can help you to determine the shape of the structure.

The "Beam Panel" element will allow you to model entire buildings or only certain areas using surfaces for timber shear wall panels.
By introducing the necessary line hinges in the rigid couplings, the "Beam Panel" element was also released, which will now be further optimized step by step in order to achieve the goal mentioned above.
Currently, the application is limited to very simple structures. However, we are strongly focused on improving the application as quickly as possible. The current state of development is summarized in this FAQ:

Current State and Planned Development:

• Modeling of single, independent surfaces
• Boundary lines orthogonal to each other and not interrupted (four boundary lines, except across surface cells)
• Openings possible via surface cells
• Automatic connection stiffness calculation according to EN 1995‑1‑1 (linear) for nails and fasteners
• More convenient input and extension for all standards (in development)
• Rotation orthotropy direction of sheathing (in development)
• Semi-rigid coupling of adjacent elements (in development)
• Different cross-sections for boundary members in the positive and negative directions (in development)
• Optional no definition of boundary members (in development)
• Connections of panel joints (corners, T-joint, wall-slab) (in development)
• Integration of modeling tools (drag and drop, copy...) (in development)

There can be several reasons for this error.

Missing Surface Reinforcement

In the surface with the punching nodes is no reinforcement available.

You can find out how to create surface reinforcement here: Surface Reinforcement

Missing Dimensions

In RFEM 6, the geometry of punching nodes is usually determined using the cross-section of the connected structural component (wall, column). If a slab or a plate is designed separately within a 2D positional analysis and thus no walls or columns in the form of surfaces or members exist in the model, RFEM cannot automatically determine the structural component dimensions. In this case, it is necessary to manually enter the dimensions:

Not Supported Nodes

In the case of punching nodes that are not supported by a nodal nor linear support, the dimensions of the connected components can be defined via the ultimate configurations.

More information can be found here: Ultimate Configurations (Punching)

Supported Nodes

In the case of punching nodes that are supported by a nodal nor linear support, which represent a connected component, you can specify the dimensions in the support settings.

More information can be found here:
Fictitious Columns (Nodal Supports) | Fictitious Wall (Line Supports)

Not Valid Nodes

In the punching nodes are located in the middle of a line load or a line support, no punching shear occurs. Therefore, these nodes are indicated as not valid.

Navigation to the "New Member Hinge" Dialog Box
To connect a member as hinged in RFEM 6 or RSTAB 9, you need to define a member hinge first. You can open the "New Member Hinge" dialog box by using the menu bar, the navigator, the table, or the "Edit Member" dialog box. The following video shows all four options.

Creating New Member Hinge
When defining a new member hinge, select your reference coordinate system first. By selecting the hinge conditions, you release the corresponding degree of freedom. In the image below, the member hinge has been defined, for example, in such a way that free rotation about the local y- and z-axis of the member is possible. Furthermore, you can define spring constants and nonlinearities.

More information about defining a member end hinge can be found in the online manual of RFEM 6 / RSTAB 9:
Online Manual RFEM 6 – Member Hinges

Connecting Member Ends with Hinges
In the "Edit Member" dialog box, you can define member hinges for the selected members. For this, select the "Hinges" option in the "Main" tab.

In the "Hinges" tab, you can separately select the member end hinges defined previously for both member ends.

No, it is not possible to deactivate the Mia assistant. However, if the avatar is in a distracting position, you can simply move it by using the mouse.

Our AI assistant is continuously being developed. In the future, Mia will become much more integrated in RFEM and it is learning new things every day. Our goal is to make your work with RFEM even more intuitive and easier.

Mia provides you with the opportunity to use the capabilities of large language models (LLM) for the structural analysis and program operation of RFEM 6 and RSTAB 9.

Mia already offers a number of advantages:

Support 24/7, including weekends

Perhaps you know this situation, too: a project that still needs to be finished. Shortly before the end, problems arise for which you urgently need support, and the phone support has already closed.

Mia can help you to find a solution to your problem in this situation.

Better work efficiency

You will get the answers to your problems directly. You don't need to interrupt your work until the support has responded to your question.

Communication in almost any language

Mia has an integrated translation function. Communicate in the language that is easiest for you.

Easy access to information

You don't need to search through long articles to finally get the information you are looking for. Instead, you get exactly the information that is relevant to your question.

Easy to use

Simply describe your problem in natural language. It's no longer necessary to formulate complicated Google search queries and to search in countless documents for the results.

User friendliness

The AI function of Mia is directly integrated into the program interface of RFEM 6 and RSTAB 9; that is, exactly where the questions arise. It is no longer necessary to switch to the browser and open a specific website.

Free access

With Mia, you get free, fast access to the support team.

In the shortcut menu, you can find some important functions that support you when working with RFEM 6 and RSTAB 9.

Test Mia yourself. The answers are not always perfect, but are often amazingly good and effective. By the way, Mia also has a sense of humor.

More Information About Mia:

The most important functions for using RFEM are described in the online manual. It also includes a short theoretical chapter on finite elements. Useful information about modeling and result evaluation for calculations according to the Finite Element Method can also be found in the technical articles of our Knowledge Base.

Of course, the documentation cannot replace the technical literature. To help you get started with finite elements, here are some recommended readings:

• Barth, Christian, & Rustler, Walter. (2013). Finite Elemente in der Baustatik-Praxis. (2nd ed.). Bauwerk. (➥ Amazon)
• Werkle, Horst. (2021). Finite Elemente in der Baustatik. (4th ed.). Springer Vieweg. (➥ Amazon)
• Nasdala, Lutz. (2015). FEM-Formelsammlung für Statik und Dynamik. (3rd ed.). Springer Vieweg. (➥ Amazon)
• Němec, Ivan. (2010). Finite Element Analysis of Structures – Principles and Praxis. Shaker-Verlag. (➥ Amazon)
• De Souza Neto, Eduardo A. (2008). Computational Methods for Plasticity – Theory and Applications. Wiley. (➥ Amazon)
• Rombach, Günter. (2000). Anwendung der finiten Elemente im Betonbau. Ernst & Sohn. (➥ Amazon)

This list is only a small selection of the recommendations. You can also find further technical literature in the references of the mentioned works.

In RFEM 6 and the "Concrete Design", the fiber-reinforced concrete design can be carried out according to DIN EN 1992‑1‑1 in conjunction with the DAfStB guideline "Fiber Reinforced Concrete".

To activate the surface or member design using steel fiber reinforced concrete, it is sufficient to assign a material of the corresponding material type to the surface or member.

To do this, create a new material of the "Fiber Concrete" material type.

The concrete and lightweight concrete are designated with the "P1/P2" extension, which stand for Performance Class 1 and Performance Class 2.

The performance classes L1 and L2 are initially preset with the values 1.20 and 0.90 (see Image 02).

In order to be able to adapt these performance classes, you can activate a "user-defined material" in the "Main" tab of the material under the "Options".

Thus, the text boxes for L1 and L2 become accessible, so you can adjust the performance classes.

If you now perform the design with the material of the "Fiber Concrete" type in the "Concrete Design" add-on, the design checks modified or completed in the DAfStB guideline for the "fiber-reinforced concrete" design are adjusted. This modification of the design process can be found in the "Design Details", including the reference to the DAfStB guideline.

Note

For this type of design, it is necessary to specify "normal reinforcement" (member reinforcement for a member, area reinforcement for a surface), otherwise the surfaces cannot be designed. This means that you can only add steel fibers to already reinforced components.

To calculate a slab with fiber-reinforced concrete only (without reinforcing steel), use the "Damage 2D/3D" material model.

The process of creating temporary supports in RFEM 6 has changed since RFEM 5. In RFEM 5, they were created using the support function. In RFEM 6, you have two different options.

The first option is the definition of structural modifications; it is easier with the Construction Stages Analysis / RF-FORM-FINDING (see Link Describing Form-Finding Add-on for RFEM ) for more information about considering construction stages).

A detailed explanation of the temporary support definition has been given in the online manual.
Definition of Temporary Supports for Form-Finding

You can also find there a detailed description of the entire form-finding process.
Detailed Description of Form-Finding Process in RFEM 6

Furthermore, you can watch a free webinar about this.
Link to Internal Webinar on Form-Finding and Calculation of Membrane Structures

Using the cross-section library, it is possible to display the unit stresses at the individual stress points of cross-sections. If you know the internal forces of the respective cross-section, you can quickly find a suitable cross-section without starting the stress calculation of the entire model.

Yes, you have to activate the "Nonlinearity" tab in the "New Member/Edit Member" dialog box; see Image 01.

In the "Nonlinearity" tab, you can then define a new member nonlinearity; see Image 02.

Yes, such solids are rigidly connected by default.

To implement another type of connection, you can use surface releases.

It is possible to transfer the login data via the command line parameters. Then, the login window will no longer appear when starting the program.

It looks like this, for example:

RFEM6.exe --email [email protected] --password Trurvzrf_Cnffjbeg

You can add these parameters directly to the links to RFEM on the desktop:

Please pay attention to using quotation marks in the link because of the spaces in the path. Therefore, you need to enter the link target as follows:

"C:\Program Files\Dlubal\RFEM 6.05\bin\RFEM6.exe" --email [email protected] --password Trurvzrf_Cnffjbeg

Accuracy of RWIND Results and Ratio of Accuracy Versus Cost

The RWIND program was designed to quickly and easily calculate wind flow around buildings in order to obtain pressure values on their surfaces and generate load forces. In order to meet this main goal, a number of compromises had to be made, such as allowing the use of a simplified model or a relatively coarse computational mesh. It is obvious that these simplifications affect the accuracy of the results. Increasing the accuracy of the results using a finer mesh and other user settings in RWIND is possible, but this process may not be easy and requires sufficient experience with CFD simulations. An important question here is what is the acceptable ratio of effort and cost to the improvement in accuracy achieved. We recommend reading the CFD Project Accuracy vs. Effort article which deals with this issue in detail.

RWIND Error E315

When increasing the mesh density, memory and performance requirements do not grow linearly, but with the 3^rd to 4^th power (we have three spatial dimensions and also a reduction of the time step is necessary). This not only leads to a significant slowdown of the calculation, but also various problems can start to appear, which are usually related to the fact that the program approaches its limits or the limits of the hardware used. These problems also include error E315 which indicates a general failure inside the OpenFOAM© calculation modules – such as memory allocation failure, loss of numerical precision, and so on. The specific reasons for the failure can be different. More detailed information can be found from the relevant Log File.

RWIND Customer Support and its Limits

Dlubal customer support always tries to help RWIND users who encounter any problems. However, numerical simulations of wind flow can be very complex and results cannot generally be guaranteed. This is due to the fact that there is still no mathematical proof of the existence and uniqueness of the solution of the Navier-Stokes equations that describe this flow and which RWIND solves numerically using the finite volume method. Although the calculation converges to the correct solution in most cases, a failure of the calculation cannot be excluded. In the event that a calculation failure occurs in a large and complex project, assistance can be very time-consuming. If you are interested in additional extended assistance, please Contact Our Sales Team.

The choice between steady-state (by using RWIND Basic) and transient simulation (by using RWIND Pro) depends on the specific requirements of the wind analysis, the level of accuracy needed, and the computational resources available. Steady-state simulations are suitable for simpler, time-invariant analyses, while transient simulations are necessary for capturing the dynamic behavior of wind flow and its impact on structures over time, and are more accurate than steady-state simulation.

Parapets present a unique challenge in the analysis of wind loads on buildings due to their positioning and the complex flow patterns they generate. Their interaction with wind loads is influenced by several factors that contribute to their complicated behavior:

Height and Exposure

Parapets extend above the main roof level, exposing them to higher wind velocities and different flow patterns compared to lower parts of the building. This exposure means they can experience significantly different wind pressures, including uplift forces.

Geometry and Shape

The shape of the parapet—whether it is flat, crenellated, or has other architectural features—can affect how wind flows over and around it, leading to complex patterns of vortices and turbulence. These flow patterns can alter the distribution and magnitude of wind pressures on the parapet and adjacent roof areas.

Interaction with Building Shape

The overall shape of the building influences how wind flows around it, which in turn affects the wind loads on the parapet. For instance, wind flowing over a streamlined, aerodynamic building will behave differently from wind encountering a building with a more bluff body. This interaction can lead to areas of higher pressure or suction on the parapet that are difficult to predict without detailed analysis.

Vortex Shedding

Tall parapets on high-rise buildings can experience vortex shedding, where alternating vortices are shed from either side of the parapet, leading to oscillating pressures that can cause structural vibrations. These effects are highly dependent on the wind speed, parapet shape, and the building’s orientation to the wind.

Gust Effect

Parapets can be subjected to gusting effects, where short-duration increases in wind speed cause fluctuating loads. These transient effects are particularly important for the structural design of parapets to ensure they can withstand sudden wind load increases without failure.

Given these complexities, advanced simulation techniques such as computational fluid dynamics (CFD) are often employed to accurately predict the wind loads on parapets. Both steady-state and transient simulations play a role, but transient simulations provide a more detailed understanding of how parapets respond to varying wind conditions over time in RWIND 2 Pro. These simulations can capture the instantaneous effects of gusts, the development of vortices, and the impact of turbulent flow, which are critical for designing parapets to be both functional and safe under wind loading.

In the RSECTION program, you can analyze general steel or aluminum cross-sections and determine the effective section properties. For this, you need the Effective Sections program extension of RSECTION. If you have licensed this add-on, you can activate the Effective Section option for the calculation in the Base Data of the cross-section.

Then, define the standard according to which the calculation should be performed. Currently, the following options are available:

• EN 1993-1-1 and EN 1993-1-5
• EN 1993-1-3 (Cold Formed)
• EN 1999-1-1 (Aluminum)

The effective section properties depend on the internal forces of the cross-section. Therefore, create a load case and define one or more internal force constellations.

After the calculation, the effective section properties are displayed in the table. In the graphic, you can check the stresses on the effective section.

Once you have saved the cross-section, you can import it into RFEM or RSTAB to use it for further analyses.

The webinar Determination of Section Properties and Stress Analysis in RSECTION shows the modeling and calculation of a cold-formed section. You can find further information there.