Frequently Asked Questions (FAQ) - Search term: Unit load...

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.

Turbulence modeling is a critical aspect of computational fluid dynamics (CFD) that seeks to predict the behavior of turbulent flows. Turbulence models are essential for designing efficient and safe engineering applications, such as wind-structure interaction in order to structural analysis and design. Among the various approaches to turbulence modeling, three popular models are the Reynolds-Averaged Navier-Stokes (RANS), Unsteady Reynolds-Averaged Navier-Stokes (URANS), and Delayed Detached Eddy Simulation (DDES). Each model has its own unique features and applications.

RANS (Reynolds-Averaged Navier-Stokes)

The RANS approach is one of the most common methods used in turbulence modeling. It involves averaging the Navier-Stokes equations over time, which effectively smooths out the fluctuations of turbulence to provide a steady-state solution. This method simplifies the computational requirements significantly and is particularly useful for applications where the flow is steady or mildly unsteady. RANS models are extensively used in industrial applications due to their robustness and low computational cost. However, they can be less accurate in predicting complex flows with significant separation or strong unsteadiness.

URANS (Unsteady Reynolds-Averaged Navier-Stokes)

URANS extends the RANS approach by allowing for time-dependent changes in the flow field, making it capable of capturing unsteady phenomena. It still utilizes the Reynolds averaging of the Navier-Stokes equations but does not average the flow in time as strictly as RANS. This means URANS can model larger-scale transient flow features and oscillatory behaviors, which are typical in many practical engineering systems, such as vortex shedding from building corners. While URANS improves upon RANS in terms of capturing unsteadiness, it still employs eddy-viscosity models that may not adequately resolve finer turbulent structures.

DDES (Delayed Detached Eddy Simulation)

DDES is a hybrid approach that combines RANS and Large Eddy Simulation (LES) methodologies. In regions of the flow where the boundary layer is attached, DDES behaves like a RANS model, providing computational efficiency. In regions where the flow detaches and larger turbulent structures dominate, DDES switches to an LES mode, which resolves these structures more accurately. This method is particularly useful in complex flows involving flow separation, reattachment, and wake regions, such as building edges and corners. DDES offers a good balance between computational expense and accuracy, particularly in simulating high Reynolds number flows with significant unsteady and separated regions.

Conclusion

Choosing the right turbulence model depends largely on the specific requirements of the problem at hand, including the flow characteristics, accuracy needs, and available computational resources. RANS models are suitable for simpler, steady flows, while URANS provides better handling of unsteady phenomena. DDES, although computationally more demanding than RANS or URANS, offers superior accuracy in cases involving complex, unsteady separated flows. Each of these models has contributed significantly to advancements in fluid dynamics simulations, supporting engineers and researchers in developing more effective and efficient technological solutions.

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.

Yes, you can control the load distribution by setting the limit stresses for tension as very high or small.

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.

The CFD simulation (Computational Fluid Dynamics) is a valuable tool for various areas of engineering, design and research. In the following, we present some of the most important advantages of CFD simulations in more detail.

Cost Efficiency

Using CFD simulations in large or complex structural systems is much more cost-effective than performing physical experiments. For example, the digital wind simulation eliminates the costs for the production of prototypes, securing test facilities, and the use of special equipment

Saving Time with CFD Simulations

You can also save some time in the analysis process by using a CFD simulation. The setup and execution are quick and easy, requiring only a few clicks, which saves you a lot of time compared to setting up a physical test. As an engineer, you can thus benefit from iterative analysis processes. Test your designs in a virtual environment to perfect all aspects digitally before deciding on a physical prototype.

Detailed Visualization

For example, CFD provides you with flow patterns, pressure distributions, and other relevant physical phenomena that would be difficult or impossible to demonstrate experimentally. This additional information gives you an even better insight into the technical data of your project.

Scalability in CFD Simulations

Another advantage of the CFD simulations is the arbitrary scalability without great effort. Do you want to analyze different sizes or configurations of an analysis? In the digital flow tunnel, this is easily possible without any physical changes or new prototypes. A CFD simulation provides you with a wider range of scenarios and analysis parameters.

Sustainability Due to CFD Simulations

Another benefit of the CFD simulation is that it requires fewer physical prototypes and experiments. Lower energy consumption and lower waste production is ideal for achieving sustainability goals, such as reduced material costs and addressing environmental concerns.

Complexity and Precision

A digital wind tunnel gives you the opportunity to accurately model complex geometries and fluid interactions. This would be difficult to replicate in an experimental setup. The precision of CFD allows you to analyze subtle effects and interactions in a controlled environment. At the same time, the program provides you with complex insights that enhance the comprehension and optimization of structural systems.

The CFD simulations are especially useful if you have a thorough comprehension of the underlying models and assumptions. In most cases, it is best to use a combination of CFD simulations and experimental tests to achieve comprehensive results. This gives you the opportunity to fully understand the behavior of your structures in flow situations.

Are you looking for a way to carry out CFD simulations for your projects? The powerful RWIND is a stand-alone program that allows you to perform flow simulations in various situations. Find more information about the latest program generation here: RWIND 2 .

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.

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.

Both features known from RFEM 5, "Area Load on Members via Planes" and "Area Load on Members via Cells", can be found in RFEM 6 in the load wizard "Member Loads from Area Load". You can either define planes via nodes (marked in green in the image) or select the cells (marked in blue in the image).

The Structure Stability add-on is not dependent on the settings made in the Steel Design add-on. It is a global stability analysis of the entire structure according to how the model is created. The setting of boundary conditions is only used for the design in the Steel Design add-on.
If you want the top flange to be supported, for example, we recommend using objects from Types for Members → Member Supports → Shear Panel. These objects are reflected in the results of the add-ons for dynamic and stability analysis.
In order to take into account the shear panel, it is necessary to activate this option of structural modification for the selected load cases or load combinations.

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:

There are no technical differences between the student, trial, and full versions. The scope of functions is only controlled by the authorization.

Simply log in with your email address and password to use your student license.

First, it is worth taking a look at the "Load Transfer" tab when editing the surface. If the load transfer direction is set to "Isotropic | FEM", the loads are not displayed until the load case or load combination has been calculated, as they must be calculated in a sub-model first. So make sure the results are available there.

When creating a new model in RFEM, it is not possible to import the templates from any path. It is necessary to create a project.

When accessing a template in Revit or Rhino/Grasshopper, an error message often appears if the path of the template file used is not linked to a "Template Project" in the Dlubal Center.

Open the Dlubal Center and check whether there is a "template project" for the folder with your template file.

If not, you can add the path of the template file as a project. In the FAQ video, the Downloads folder has been created as a template project, as it contains the template file.

This action category no longer exists in RFEM 6 and RSTAB 9.
It is necessary to create the imperfection cases separately and assign them to the corresponding load case or load combination:

To create an imperfection load case, use the Data navigator (Imperfections → Imperfection Cases → right-click: New Imperfection Case) or directly in the "Load Cases and Combinations" dialog box; see the image.

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.

For parametric cross-sections, the definition is in meters, as Grasshopper refers to the SI units.

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.

Both RFEM and RSTAB are available for the structural analysis and design of temporary structures, such as carousels, roller coasters, stages, or grandstands. There are add-ons available for both main programs that you can use to design steel, aluminum and lightweight structures according to various standards. If you also want to analyze membrane and cable structures, RFEM is your tool of choice.

Main Programs RFEM and RSTAB

The main programs RFEM and RSTAB are used to define the model with its properties and actions. RFEM proves to be the more versatile option, as it can be used to analyze structures with surface components, such as membranes, in addition to pure member structures.

Available Standards

For the design of steel beam and cable structures, the following standards are available:

• EN 1993 (Eurocode 3)
• BS 5950 (British standard)
• AISC 360 (US standard)
• SIA 263 (Swiss standard)
• IS 800 (Indian standard)
• GB 50017 (Chinese standard)
• CSA S16 (Canadian standard)
• AS 4100 (Australian standard)
• NBR 8800 (Brazilian standard)
• SP 16.13330 (Russian standard)

Aluminum structures can be designed according to the following standards:

• EN 1999 (Eurocode 9)
• ADM (US standard)
• GB 50429 (Chinese standard)

Analysis and Design Add-ons

Design add-ons supplement the functionality of the main programs. In the design add-ons Steel Design and Aluminum Design, you can perform the ultimate and serviceability limit state design, as well as the stability analysis according to the standards listed above.

In the case of membrane and cable structures, the Form-Finding add-on facilitates your task to determine the shape of member and surface models subjected to axial forces. On the other hand, you can use the RWIND program to perform simulations in the digital wind tunnel for complex structures and to transfer the generated wind loads to RFEM.

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 solution for temporary structures, our sales team will be happy to assist you.

The Form-Finding add-on is available for the structural FEA software RFEM, which you can use to search for the shape of a tensile membrane structure before the actual design.

Once you have modeled a supporting structure or a substructure in RFEM and defined membrane surfaces, you can analyze the global model according to the large deformation analysis.

Programs and Add-ons

Use the main program RFEM to define the model, including the properties and actions.

The Form-Finding add-on allows you to determine a shape of the member and surface models subjected to axial forces.

Use the RWIND program to perform simulations in the digital wind tunnel for complex structures and to transfer the generated wind loads to RFEM.

Depending on the design, you can use the add-ons Steel Design and Aluminum Design to design the structure.

If a seismic or vibration analysis is required, the Dynamic Analysis add-ons are the perfect tools for this.

In case of any questions about the Dlubal solution for tensile membrane structures, our sales team will be happy to assist you.

Both RFEM and RSTAB are ideally suited for modeling and analysis of cable and tensile structures, including substructures. You can decide whether to consider the prestress of cables.

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, you can also use RFEM to model plate, wall, and shell structures. Thus, RFEM proves to be the more versatile option.

Add-ons for Cable Structures

Various add-ons supplement the functionality of the main programs. In the design add-ons Steel Design and Aluminum Design, you can perform the ultimate and serviceability limit state design, as well as the stability analysis according to various standards.

The Form-Finding add-on for RFEM provides you with the option to perform form-finding for cable and membrane systems before the actual design.

In case of any questions about the Dlubal solution for cable and tensile structures, our sales team will be happy to assist you.

The unit symbol for axial and shear strain shown in Image 01, o/oo, represents "per mille" which means part per thousand.

This is not to be confused with %, which represents parts per hundred.
Example: 1 o/oo would equal 1/1000 or 0.001.

For the Isotropic load transfer (LT) surface, RFEM uses the finite element method and creates a submodel. In the FEA submodel, the LT surface is substituted by a rigid surface where all the structural elements that are integrated in the surface are substituted by rigid supports. In a future implementation, users will have the ability to adjust the support conditions. The support reactions in the FEA submodel are then converted into member loads after running the calculation.

To display the load separately as member loads after running the calculation, activate the "Loads from Distribution Surface" option in the Display Navigator.

The Earthquake Limit State (with and without overstrength) only provides a result for members with an assigned Seismic Configuration.
The Strength Limit State is used to design all members, including the members that are not part of the seismic force-resisting system (SFRS). Therefore, both Earthquake and Strength Limit States are required.
The Serviceability Limit State is also available.

Image 01 is an example of the required design situations for the LRFD Design.

Notes:
1) The web ductility check per Table D1.1 of AISC 341‑16 (RFEM EQ 1100) is applicable to all load combinations, including non-seismic COs. Therefore, the Earthquake Limit State is also applied to Equations 1 to 5 (Design Situation DS5 in Image 01).

2) For the Combination Wizard, the “Result Combinations” is required when using the response spectrum analysis.

For open structures that consist only of members, such as lattice towers, the load acts only on the member cross-sections.

To apply area loads such as snow or wind to an open structure, select Load Wizards → Member Loads from Area load to create a new area load. Under the Geometry tab, select "Empty, on members only" for the Area of load application.

The area load can be displayed on individual members by right-clicking the load and selecting Display separately.