All design results and design checks are displayed in detail and in a comprehensible manner. An error log indicates non-designable situations or failed recommendations. Due to the permanent integration in RFEM/RSTAB, subsequent modifications in the structural system and in loading are automatically taken into account for the connections to be checked.
If one of the designs could not be fulfilled, the corresponding line is highlighted in red. The output appears in a short or a long form in the global printout report of RFEM/RSTAB. Furthermore, you can easily export all result tables to MS Excel or in a CSV file. A special transfer menu defines all specifications required for the export.
In accordance with DIN 18800, Part 2, the designs are carried out separately for flexural buckling and lateral-torsional buckling to simplify the calculation. Generally, the flexural buckling design is performed in the framework plane using the stress analysis of the planar structure according to the second-order analysis, considering design loads and pre-deformations.
The lateral-torsional buckling design is performed on an individual member detached from the entire structure by using defined boundary conditions and loads in accordance with the elastic-elastic method.
RF-/FE-LTB searches for the governing failure mode by means of the critical load factor which describes flexural, torsional, and lateral-torsional buckling, or the combination of all failure modes, depending on the model and load applied. Then, the module performs recalculation to obtain the required operands.
Detail settings control whether the critical load factor is calculated due to loss of stability (providing the material is defined by infinitely elastic properties), or with stress limitation.
If necessary, you can adjust the size of the finite elements. You can also modify the partial safety factor γM. In RF-/FE-LTB, iteration parameters are preset appropriately to calculate all common models, but can be adjusted individually.
Comprehensive and easy options in the individual input windows facilitate the representation of the structural system:
Nodal Supports
The support type of each node is editable.
It is possible to define a warp stiffening on each node. The resulting warp spring is determined automatically using the input parameters.
Elastic member foundation
In the case of elastic member foundations, you can manually enter spring constants.
Alternatively, you can use the various options to define the rotational and translational springs from a shear panel.
Member End Springs
RF-/FE-LTB calculates the individual spring constants automatically. You can use the dialog boxes and detailed pictures to represent a translational spring by connecting component, a rotational spring by a connecting column, or a warping stiffener (available types: end plate, channel section, angle, connecting column, cantilevered portion).
Member Hinges
If there are no member hinges defined in RFEM/RSTAB for the set of members, you can define them directly in the RF-/FE-LTB add-on module.
Load Data
The nodal and member loads of the selected load cases and combinations are displayed in separate windows. There you can edit, delete, or add them individually.
Imperfections
RF-/FE-LTB automatically applies the imperfections by scaling the lowest eigenvector.
In RF‑/LTB, the design is usually performed according to the equivalent member method according to DIN 18800, Part 2. However, you can specify extensive detailed settings for the design in a separate dialog box:
Design according to Bird/Heil
Optionally, it is possible to apply the method according to Bird/Heil in the program
the required shear stiffness Sreq
the lateral-torsional buckling load Nki
the critical buckling moment Mki
.
This plastic-plastic calculation method is only valid for lateral and torsional restraints with simple bending with simultaneous load introduction on the upper flange. Further requirements that must be met can be found in the program manual. In case of invalid conditions (for example, biaxial bending), RF-/LTB displays the corresponding error message. In addition, the reduction factorκM for the bending moments My can be set to 1.0 if a restrained rotation axis is present.
Non-Designable Internal Forces
It is possible to neglect non-designable internal forces and thus exclude them from the design if the quotient of the internal force and the fully plastic internal force falls below a certain value. This way, you can neglect, for example, a small moment about the minor axis, thus avoiding the method for biaxial bending.
Allowance according to DIN 18800, Part 2, Element (320) and Element (323)
Automatic determination of ζ
If you want the factor for the determination of the ideal elastic critical moment Mcr to be determined automatically, you can select one of the following types:
Solving the elastic potential numerically
Comparison of moment diagrams
Australian Standard AS 4100-1990
US standard AISC LRFD
When aligning the moment distributions, you can use the library which contains more than 600 moment distributions in tables.
The details for the lateral-torsional buckling analysis are defined separately for members and sets of members. The following parameters can be set:
Support Type/Lateral-Torsional Buckling Load
Available options are Lateral and torsional restraint, Lateral and torsional restraint or Cantilever
Special supports are possible by specifying the degree of restraint βz and the degree of warping restraint β0. In this section as well, you can consider the elastic warping restraint of an end plate, a channel section, an angle, a column connection, and a beam cantilever by specifying the geometry dimensions.
As an alternative, it is also possible to enter the lateral-torsional buckling load NKi or the effective length sKi directly
Shear panel
A shear panel can be defined from a trapezoidal sheeting, bracing, or a combination of these
Alternatively, you can enter the shear panel stiffness Sprov directly
Rotational restraint
Choose between continuous and discontinuous rotational restraint
Position of Positive Transverse Load Application
The z-coordinate of the load application point can be freely selected in a detailed cross-section graphic. (upper chord, lower chord, centroid)
Alternatively, you can specify the data by selecting them or entering the data manually.
Beam Type
For standard sections, the rolled beam, welded beam, castellated beam, notched beam, or tapered beam (web or flange welded) options are available
For special cross-sections, it is possible to directly enter the beam factor n, the reduced beam factor n, or the reduction factor κM
After the calculation, the deformations, internal forces, support forces, and stresses are displayed. Since the module considers warping torsion, the diagrams of the warping bimoment, as well as of the primary and the secondary torsional moment, are also available. Stability analysis uses the imperfections during the calculation and determines the critical load factors that can be used to determine Mki and Nki.
In addition to the result values in tables, the corresponding cross-section graphic is shown. In RFEM/RSTAB, various results are highlighted in different colors on the member model. You can modify the colors and values assigned.
Result diagrams of a set of members provide targeted evaluation. It is also possible to represent all intermediate values. Finally, it is possible to export all tables to MS Excel or in a CSV file. A dialog box includes the necessary export data.
After the design, the results are displayed in different windows sorted by cross-sections, members, sets of members, or x-locations. The corresponding cross-section graphic is always displayed with the result values in tables. In RFEM/RSTAB, they are highlighted by different colors in the structural model. Critical or oversized components can be identified at a glance. You can modify the colors and values assigned.
Result diagrams of a member or a set of members ensure targeted evaluation. It is also possible to represent all intermediate values.
The masses determined during the design are displayed in parts lists for both members and sets of members.
Furthermore, you can export all result tables to MS Excel or in a CSV file. A special transfer menu defines all specifications required for the export.
In a separate dialog box, you can specify extensive detailed settings for the design:
Design Method According to DIN 18800
Design Method 1 According to El. (321)
Design Method 2 According to El. (322)
Analysis method
Elastic-Plastic according to DIN 18800
Elastic-elastic according to a publication by Kretschmar, J./Österrieder, P./beirow, B.
Limit loading of general sections
General sections – these include all cross-sections that cannot be assigned to single or double symmetric I-sections, box sections, or pipe sections – can also be designed according to the equivalent member method against flexural buckling. In this case, however, the plastic cross-section properties are determined without interaction conditions. The allowable application limits for this consideration depend on the ratio of the existing internal force to the fully plastic internal force. Five text boxes provide the option for user-defined control.
Check of limit (c/t)
In this dialog section, you can activate or deactivate the check of c/t ratios.
Treatment of Result Combinations
When designing a result combination, a result set is obtained due to the result superposition on each member location, which makes it impossible to clearly determine the moment factors. In this section, you can thus freely specify a global moment factor for a result combination design. The predefined values are on the safe side, regardless of the design method.
After entering the model in RFEM/RSTAB, it is possible to open the RF-/FE-LTB add-on module. Here you can define continuous members and load cases or combinations to be designed in a design case.
The continuous members can be selected graphically as well. The materials and cross-sections used in RFEM/RSTAB are already preset but can always be adjusted, if necessary. Extensive libraries are available for this purpose.
Full integration in RFEM/RSTAB including import of all relevant internal forces
Intelligent presetting of flexural buckling-specific design parameters
Automatic determination of the distribution of internal forces and classification according to DIN 18800, Part 2
Optional import of buckling lengths from the RF-STABILITY/RSBUCK add-on module. For this, a comfortable graphical selection of the relevant buckling mode is possible
Optimizing Cross-Sections
Optional calculation according to both design methods of DIN 18800, Part 2
Automatic determination of the most unfavorable design location, also for tapered members
Check of c/t-limit values according to DIN 18800, Part 1
Design of any thin-walled RFEM/RSTAB or SHAPE-THIN section for compression and bending without interaction according to the elastic-plastic method
Design of I-shaped rolled and welded sections, I-like sections, box sections, and pipes subjected to bending and compression with iteration according to the elastic-plastic method
Clearly arranged, comprehensible design checks with all intermediate values in the short and long forms
Full integration in RFEM/RSTAB with import of relevant internal forces
Design checks for the elastic-elastic and elastic-plastic methods
Graphical selection of members and sets of members for design
Analysis for several load and design cases
Design based on the buckling field parameters integrated in the cross-section library for the cross-section parts supported on one and both sides
Optional determination of shear stresses according to comment on El. (745)
Possibility to consider the weld thickness in the design of welded cross-sections, which has the effect of a shortening of the cross-section part width
Cross-section optimization with the option to export modified cross-sections