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 pushover analysis is managed by a newly introduced analysis type in the load combinations. Here, you have access to the selection of the horizontal load distribution and direction, the selection of a constant load, the selection of the desired response spectrum for the determination of the target displacement, and the pushover analysis settings tailored to the pushover analysis.
In the pushover analysis settings, you can modify the increment of the increasing horizontal load and specify the stopping condition for the analysis. Furthermore, it is possible to easily adjust the precision for the iterative determination of the target displacement.
Consideration of nonlinear component behavior using plastic standard hinges for steel (FEMA 356, EN 1998‑3) and nonlinear material behavior (masonry, steel - bilinear, user-defined working curves)
Direct import of masses from load cases or combinations for the application of constant vertical loads
User-defined specifications for the consideration of horizontal loads (standardized to a mode shape or uniformly distributed over the height of the masses)
Determination of a pushover curve with selectable limit criterion of the calculation (a collapse or limit deformation)
Transformation of the pushover curve into the capacity spectrum (ADRS format, single degree of freedom system)
Bilinearization of the capacity spectrum according to EN 1998‑1:2010 + A1:2013
Transformation of the applied response spectrum into the required spectrum (ADRS format)
Determination of target displacement according to EC 8 (the N2 method according to Fajfar 2000)
Graphical comparison of the capacity and required spectrum
Graphical evaluation of the acceptance criteria of predefined plastic hinges
Result display of the values used in the iterative calculation of the target displacement
Access to all results of the structural analysis in the individual load levels
During the calculation, the selected horizontal load is increased in load steps. A static nonlinear analysis is carried out for each load step until reaching the specified limit condition.
The results of the pushover analysis are extensive. On one hand, the structure is analyzed for its deformation behavior. This can be represented by a force-deformation line of the system (a capacity curve). On the other hand, the response spectrum effect can be displayed in the ADRS display (Acceleration-Displacement Response Spectrum). The target displacement is automatically determined in the program based on these two results. The process can be evaluated graphically and in tables.
The individual acceptance criteria can then be graphically evaluated and assessed (for the next load step of the target displacement, but also for all other load steps). The results of the static analysis are also available for the individual load steps.
Do you work with the structural components consisting of slabs? In that case, you have to perform the shear force design with the requirements of punching shear design, for example, according to 6.4, EN 1992‑1‑1. In addition to floor slabs, you can also design foundation slabs in this way.
In the Ultimate Configuration for concrete design, you can define the punching design parameters for the selected nodes.
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.
The Dlubal structural analysis software does a lot of work for you. The input parameters, which are relevant for the selected standards, are suggested by the program in accordance with the rules. Furthermore, you can enter response spectra manually.
Load cases of the type Response Spectrum Analysis define the direction in which response spectra act and which eigenvalues of the structure are relevant for the analysis. In the spectral analysis settings, you can define details for the combination rules, damping (if applicable), and zero-period acceleration (ZPA).
Did you know that Equivalent static loads are generated separately for each relevant eigenvalue and excitation direction. These loads are saved in a load case of the Response Spectrum Analysis type and RFEM/RSTAB performs a linear static analysis.
The load cases of the type Response Spectrum Analysis contain the generated equivalent loads. First, the modal contributions have to be superimposed with the SRSS or CQC rule. In this case, you can use the signed results based on the dominant mode shape.
Afterwards, the directional components of earthquake actions are combined with the SRSS or the 100% / 30% rule.
Automatic consideration of masses from self-weight
Direct import of masses from load cases or load combinations
Optional definition of additional masses (nodal, linear, or surface masses, as well as inertia masses) directly in the load cases
Optional neglect of masses (for example, mass of foundations)
Combination of masses in different load cases and load combinations
Preset combination coefficients for various standards (EC 8, SIA 261, ASCE 7,...)
Optional import of initial states (for example, to consider prestress and imperfection)
Structure Modification
Consideration of failed supports or members/surfaces/solids
Definition of several modal analyses (for example, to analyze different masses or stiffness modifications)
Selection of mass matrix type (diagonal matrix, consistent matrix, unit matrix), including user-defined specification of translational and rotational degrees of freedom
Methods for determining the number of mode shapes (user-defined, automatic - to reach effective modal mass factors, automatic - to reach the maximum natural frequency - only available in RSTAB)
Determination of mode shapes and masses in nodes or FE mesh points
Results of eigenvalue, angular frequency, natural frequency, and period
Output of modal masses, effective modal masses, modal mass factors, and participation factors
Masses in mesh points displayed in tables and graphics
Visualization and animation of mode shapes
Various scaling options for mode shapes
Documentation of numerical and graphical results in printout report
In the modal analysis settings, you have to enter all data that are necessary for the determination of the natural frequencies. These are, for example, mass shapes and eigenvalue solvers.
The Modal Analysis add-on determines the lowest eigenvalues of the structure. Either you adjust the number of eigenvalues or let them determined automatically. Thus, you should reach either effective modal mass factors or maximum natural frequencies. Masses are imported directly from load cases and load combinations. In this case, you have the option to consider the total mass, load components in the global Z-direction, or only the load component in the direction of gravity.
You can manually define additional masses at nodes, lines, members, or surfaces. Furthermore, you can influence the stiffness matrix by importing axial forces or stiffness modifications of a load case or load combination.
As soon as the program has completed the calculation, the eigenvalues, natural frequencies and periods are listed. These result windows are integrated in the main program RFEM/RSTAB. You can find all mode shapes of the structure in tables and also have an option to display them graphically and to animate them.
All result tables and graphics are part of the RFEM/RSTAB printout report. In this way, you can ensure clearly arranged documentation. You can also export the tables to MS Excel.
Do you want your structures to remain upright even in wind and snow? Then rely on the load wizards for plate and frame structures. You can now generate wind loads according to EN 1991‑1‑4 and snow loads according to EN 1991‑1‑3 (as well as other international standards). The load cases are generated depending on the roof shape.
Wind loads are also not a problem in your design. You can automatically generate wind loads as member loads or area loads (RFEM) on the following structural components:
Due to the integration of RF‑/DYNAM Pro in RFEM or RSTAB, you can incorporate numeric and graphic results from RF‑/DYNAM Pro - Nonlinear Time History to the global printout report. Also, all RFEM and RSTAB options are available for a graphical visualization. The results of the time history analysis are displayed in a time history diagram.
The results are displayed as a function of time and the numerical values can be exported to MS Excel. Result combinations can be exported, either as a result of a single time step or the most unfavorable results of all time steps are filtered out.
Calculation in RFEM The nonlinear time history analysis is performed with the implicit Newmark analysis or the explicit analysis. Both are direct time integration methods. The implicit analysis requires small time steps to provide precise results. The explicit analysis determines the required time step automatically to provide the stability to the solution. The explicit analysis is suitable for the analysis of short excitations, such as impulse excitation, or an explosion.
Calculation in RSTAB The nonlinear time history analysis is performed with the explicit analysis. This is a direct time integration method and determines the required time step automatically in order to provide the solution stability.
RF-/DYNAM Pro - Nonlinear Time History is integrated in the structure of RF‑/DYNAM Pro - Forced Vibrations and extended by two nonlinear analysis methods (one nonlinear analysis in RSTAB).
Force-time diagrams can be entered as transient, periodic, or as a function of time. Dynamic load cases combine the time diagrams with the static load cases, which provides high flexibility. Furthermore, it is possible to define time steps for the calculation, structural damping, and export options in the dynamic load cases.
User-defined time diagrams as a function of time, in tabular form, or as harmonic loads
Combination of the time diagrams with RFEM/RSTAB load cases or combinations (enables definition of nodal, member, and surface loads, as well as free and generated loads varying over time)
Combination of several independent excitation functions
Nonlinear time history analysis with the implicit Newmark analysis (RFEM only) or the explicit analysis
Structural damping using Rayleigh damping coefficients or Lehr's damping
Direct import of initial deformations from a load case or combination (RFEM only)
Stiffness modifications as initial conditions; for example, axial force effect, deactivated members (RSTAB only)
Graphical display of results in a time history diagram
Export of results in user-defined time steps or as an envelope