In the Modal Analysis add-on, you have the option to automatically increase the sought eigenvalues until reaching a defined effective modal mass factor. All translational directions activated as masses for the modal analysis are taken into account.
Thus, it is possible to easily calculate the required 90% of the effective modal mass for the response spectrum method.
The modal relevance factor (MRF) can help you to assess to which extent specific elements participate in a specific mode shape. The calculation is based on the relative elastic deformation energy of each individual member.
The MRF can be used to distinguish between local and global mode shapes. If multiple individual members show significant MRF (for example, > 20%), the instability of the entire structure or a substructure is very likely. On the other hand, if the sum of all MRFs for an eigenmode is around 100%, a local stability phenomenon (for example, buckling of a single bar) can be expected.
Furthermore, the MRF can be used to determine critical loads and equivalent buckling lengths of certain members (for example, for stability design). Mode shapes for which a specific member has small MRF values (for example, < 20%) can be neglected in this context.
The MRF is displayed by mode shape in the result table under Stability Analysis → Results by Members → Effective Lengths and Critical Loads.
The Concrete Design add-on allows you to perform the seismic design of reinforced concrete members according to EC 8. This includes, among other things, the following functionalities:
Seismic design configurations
Differentiation of the ductility classes DCL, DCM, DCH
Option to transfer the behavior factor from a dynamic analysis
Check of the limit value for the behavior factor
Capacity design checks of "Strong column - weak beam"
Detailing and particular rules for curvature ductility factor
Detailing and particular rules for local ductility
The Ponding load type allows you to simulate rain actions on multi-curved surfaces, taking into account the displacements according to the large deformation analysis.
This numerical rainfall process examines the assigned surface geometry and determines which rainfall portions drain away and which rainfall portions accumulate in puddles (water pockets) on the surface. The puddle size then results in a corresponding vertical load for the structural analysis.
For example, you can use this feature in the analysis of approximately horizontal membrane roof geometries subjected to rain loading.
Have you already discovered the tabular and graphical output of masses in mesh points? That's right, this is also part of the modal analysis results in RFEM 6. This way, you can check the imported masses that depend on various settings of the modal analysis. They can be displayed in the Masses in Mesh Points tab of the Results table. The table provides you with an overview of the following results: Mass - Translational Direction (mX, mY, mZ), Mass - Rotational Direction (mφX, mφY, mφZ), and the Sum of Masses. Would it be best for you to have a graphical evaluation as quickly as possible? Then you can also graphically display the masses in mesh points.
As you've already learned, the results of a Modal Analysis load case are displayed in the program after a successful calculation. You can thus immediately see the first mode shape graphically or as an animation. You can also easily adjust the representation of the mode shape standardization. Do that directly in the Results navigator, where you have one of four options for the visualization of the mode shapes available for the selection:
Scaling the value of the mode shape vector uj to 1 (considers the translation components only)
Selecting the maximum translational component of the eigenvector and setting it to 1
Considering the entire eigenvector (including the rotation components), selecting the maximum, and setting it to 1
Setting the modal mass mi for each mode shape to 1 kg
You can find a detailed explanation of the mode shape standardization in the OnlineManual here.
Do you want to consider other loads as masses in addition to the static loads? The program allows that for nodal, member, line and surface loads. For this, you need to select the Mass load type when defining the load of interest. Define a mass or mass components in the X, Y, and Z directions for such loads. For nodal masses, you have an additional option to also specify moments of inertia X, Y, and Z in order to model more complex mass points.
It is often necessary to neglect masses. This is particularly the case when you want to use the output of the modal analysis for the seismic analysis. For this, 90% of the effective modal mass in each direction is required for the calculation. So you can neglect the mass in all fixed nodal and line supports. The program automatically deactivates the associated masses for you.
You can also manually select the objects whose masses are to be neglected for the modal analysis. We have shown the latter in the image for a better view. A user-defined selection is made the and the objects with their associated mass components are selected to neglect the masses.
When defining the input data for the modal analysis load case, you can consider a load case whose stiffnesses represent the initial position for the modal analysis. How do you do that? As shown in the image, select the "Consider initial state from" option. Now, open the "Initial State Settings" dialog box and define the type Stiffness as the initial state. In this load case, as of which is the initial state taken into account, you can consider the stiffness of the structural system when the tension members fail. The purpose of all of this: The stiffness from this load case is considered in the modal analysis. Thus, you obtain a clearly flexible system.
You can already see it in the image: Imperfections can also be taken into account when defining a modal analysis load case. The imperfection types that you can use in the modal analysis are notional loads from load case, initial sway via table, static deformation, buckling mode, dynamic mode shape, and group of imperfection cases.
Did you know? You can easily define structural modifications in load cases of the Modal Analysis type. This allows you, for example, to individually adjust the stiffnesses of materials, cross-sections, members, surfaces, hinges, and supports. You can also modify stiffnesses for some design add-ons. Once you select the objects, their stiffness properties are adapted to the object type. In this way, you can define them in separate tabs.
Do you want to analyze the failure of an object (for example, a column) in the modal analysis? This is also possible without any problems. Simply switch to the Structure Modification window and deactivate the relevant objects.
Is your goal to determine the number of mode shapes? The program offers you two methods for this. On the one hand, you can manually define the number of the smallest mode shapes to be calculated. In this case, the number of available mode shapes depends on the degrees of freedom (that is, the number of free mass points multiplied by the number of directions in which the masses act). However, it is limited to 9999. On the other hand, you can set the maximum natural frequency the way that the program determined the mode shapes automatically until reaching the natural frequency set.
Is the calculation finished? The results of the modal analysis are then available both graphically and in tables. Display the result tables for the load case or the load cases of the modal analysis. Thus, you can see the eigenvalues, angular frequencies, natural frequencies, and natural periods of the structure at first glance. The effective modal masses, modal mass factors, and participation factors are also clearly displayed.
You have several options available to define masses for a modal analysis. While the masses due to self-weight are considered automatically, you can consider the loads and masses directly in a load case of the modal analysis type. Do you need more options? Select whether to consider full loads as masses, load components in the global Z-direction, or only the load components in the direction of gravity.
The program offers you an additional or alternative option for importing masses: A manual definition of load combinations as of which are the masses considered in the modal analysis. Have you selected a design standard? You can then create a design situation with the Seismic Mass combination type. Thus, the program automatically calculates a mass situation for the modal analysis according to the preferred design standard. In other words: The program creates a load combination on the basis of the preset combination coefficients for the selected standard. This contains the masses used for the modal analysis.
Compared to the RF-FORM-FINDING add-on module (RFEM 5), the following new features have been added to the Form-Finding add-on for RFEM 6:
Specification of all form-finding load boundary conditions in one load case
Storage of form-finding results as initial state for further model analysis
Automatic assignment of the form-finding initial state via combination wizards to all load situations of a design situation
Additional form-finding geometry boundary conditions for members (unstressed length, maximum vertical sag, low-point vertical sag)
Additional form-finding load boundary conditions for members (maximum force in member, minimum force in member, horizontal tension component, tension at i-end, tension at j-end, minimum tension at i-end, minimum tension at j-end)
Material types "Fabric" and "Foil" in material library
Parallel form-findings in one model
Simulation of sequentially building form-finding states in connection with the Construction Stages Analysis (CSA) add-on
Compared to the RF-/STEEL Warping Torsion add-on module (RFEM 5 / RSTAB 8), the following new features have been added to the Torsional Warping (7 DOF) add-on for RFEM 6 / RSTAB 9:
Complete integration into the environment of RFEM 6 and RSTAB 9
7th degree of freedom is directly taken into account in the calculation of members in RFEM/RSTAB on the entire system
No more need to define support conditions or spring stiffnesses for calculation on the simplified equivalent system
Combination with other add-ons is possible, for example for the calculation of critical loads for torsional buckling and lateral-torsional buckling with stability analysis
No restriction to thin-walled steel sections (it is also possible to calculate ideal overturning moments for beams with massive timber sections, for example)
Compared to the RF‑/DYNAM Pro - Natural Vibrations add-on module (RFEM 5 / RSTAB 8), the following new features have been added to the Modal Analysis add-on for RFEM 6 / RSTAB 9:
Preset combination coefficients for various standards (EC 8, ASCE, and so on)
Optional neglect of masses (for example, mass of foundations)
Methods for determining the number of mode shapes (user-defined, automatic - to reach effective modal mass factors, automatic - to reach the maximum natural frequency)
Output of modal masses, effective modal masses, modal mass factors, and participation factors
Masses in mesh points displayed in tables and graphics
Various scaling options for mode shapes in the Result navigator
Compared to the RF‑/STABILITY (RFEM 5) and RSBUCK (RSTAB 8) add-on modules, the following new features have been added to the Structure Stability add-on for RFEM 6 / RSTAB 9:
Activation as a property of a load case or a load combination
Automated activation of the stability calculation via combination wizards for several load situations in one step
Incremental load increase with user-defined termination criteria
Modification of the mode shape normalization without recalculation
Once you activate the Form-Finding add-on in the Base Data, a form-finding effect is assigned to the load cases with the load case category "Prestress" in conjunction with the form-finding loads from the member, surface, and solid load catalog. This is a prestress load case. It thus mutates into a form-finding analysis for the entire model with all member, surface, and solid elements defined in it. You reach the form-finding of the relevant member and membrane elements amid the overall model by using special form-finding loads and regular load definitions. These form-finding loads describe the expected state of deformation or force after the form-finding in the elements. The regular loads describe the external loading of the entire system.