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 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.