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Updated:
05/17/2013

Cross-References

Related programs


 
RF-STEEL
 RFEM add-on module for stress analysis of surfaces and members
RF-STEEL EC3
 RFEM add-on module for design of members and sets of members acc. to EC 3
RF-STEEL AISC
 RFEM add-on module for design of members acc. to ANSI/AISC 360-05
RF-STEEL SIA
 RFEM add-on module for design of members acc. to SIA 263
RF-STEEL IS
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RF-STEEL BS
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RF-STEEL CS
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RF-KAPPA
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RF-FE-LTB
 RFEM add-on module for lateral torsional buckling design acc. to second-order analysis (FEA)
RF-EL-PL
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RF-C-TO-T
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Products - Overview

RF-LTB 5.xx

Lateral-Torsional Buckling Analysis
by Equivalent Member Method  
RF-LTB is not a stand-alone program but an add-on module that is integrated in the graphical user interface of the main program RFEM. Due to the integration, all structure-specific input data and internal forces are automatically available in the module.

In return, you can evaluate RF-LTB results in the RFEM work window graphically and include them in the global printout report. RF-LTB performs the design for safety against lateral torsional buckling for members and sets of members subjected to actions due to uniaxial and biaxial bending with or without axial force. The analysis is based on the equivalent member method according to

 DIN 18800-2:1990-11.

Take advantage of RF-LTB to design your structural systems efficiently. The program determines and applies stiffness-increasing effects conforming to standard, such as rotational restraints, shear panels, warp stiffenings, plastic cross-section resources or specific support conditions. The determination of the moment coefficient z and thus of the ideal elastic critical moment Mcr follows different approaches.

Note: For the design according to Eurocode 3, the add-on module RF-STEEL EC3 is required.

Features


  • Full integration in RFEM with import of all relevant internal forces
  • Smart presettings of design parameters specific for lateral torsional buckling
  • Determining the distribution of internal forces automatically including classification according to DIN 18800 part 2
  • Consideration of rotational restraints and shear panels by means of integrated tools for determining the corresponding factors conforming to standard
  • Integrated libraries with corrugated sheets provided by major manufacturers
  • Determination of moment coefficient z and thus of the ideal elastic critical moment Mcr
  • Different support types considering warp springs for different stiffening and connection situations
  • Cantilever design
  • Option for calculation according to Vogel/Heil
  • Consideration of lateral restraint by determining Mcr and Ncr according to Wittemann
  • Output of fastener forces due to rotational restraint for trapezoidal cross-sections and purlins
  • Optimization of cross-sections
  • Parts list by member and by set of members
  • Option to export all results directly to MS Excel or OpenOffice.org Calc
Graphical result representation
 

Input 


When RFEM has finished the calculation of the structure, you can open the RF-LTB add-on module. First, you create at least one design case in the module for which you define the members and sets of members that you want to design. In addition, you determine the load cases or load combinations that are required for the design. 

Take advantage of the RFEM graphic tools to select the members and sets of members easily. The materials and cross-sections used in RFEM are already preset in the module but can always be modified and completed. Furthermore, RF-LTB provides comprehensive libraries for the selection of materials and cross-sections. 

Moreover, RF-LTB allows you to optimize cross-sections.
Cross-section Library
 

Design Parameters


The specifications for the lateral torsional buckling design are defined separately for members and sets of members. The following parameters can be set:

Support Type / Buckling Load

  • You can select pinned supports, pinned supports that are built-in and cantilevers.
  • Special supports can be specified by the degree of restraint bz and the degree of warping restraint b0. By defining geometrical dimensions, the degree of warping restraint can also take into account an elastic warping support for an end plate, a channel, an angle, a column connection or a cantilevered beam.
  • Alternatively, it is possible to enter the lateral buckling load Ncr or the effective length scr.

Shear Panel

  • The shear panel can be defined by a trapezoidal sheeting, a truss or by a combination of both.
  • Alternatively, it is possible to enter the shear panel stiffness Sprov directly.

Rotational Restraint

  • You can select either a continuous or a discrete rotational restraint.

Load Application Point

  • You can define the z-coordinate of the load application point freely in a specific cross-section graphic (upper flange, lower flange, centroid).
  • Alternatively, it is possible to specify the value by graphical selection or manual data input.

Beam Type

  • The following beam types are available for common cross-sections: rolled beam, welded beam, castellated beam, notched beam or tapered beam (web or flange welded).
  • For special cross-sections, it is possible to define the beam coefficient n, the reduced beam coefficient n or the reduction factor kM directly.
Assigning Zeta Coefficient to Moment Diagrams
 

Design


Generally, RF-LTB performs the analysis according to the equivalent member method described in DIN 18800, part 2. A separate dialog box allows you to define detailed settings for the design:

Calculation According to Vogel/Heil

You can apply this method to determine the
  • required shear panel stiffness Sreq
  • critical lateral buckling force Ncr
  • critical bending moment Mcr.

This plastic-plastic method of calculation is only applicable for pinned supports with uniaxial bending together with a load introduction on the upper flange. If the requirements are not fulfilled, for example in case of biaxial bending, RF-LTB displays an error message. Furthermore, it is possible to set the reduction factor kM for the bending moments My to 1.0 by conservative assumption if a rotational restraint is available. 

Non-Designable Internal Forces

It is possible to neglect non-designable internal forces to exclude them from the analysis if the quotient of design force and plastic capacity falls below a certain value. In this way, you can ignore for example a low moment about the minor axis to avoid applying the method for biaxial bending.

Application Rule According to DIN 18800 Part 2, Element (320) and Element (323) 


Automatic Determination of z 

If you want to determine the factor used for the determination of the ideal elastic critical moment Mcr automatically, you can select one of the following options:
  • Numerical solution of elastic potential
  • Comparison of moment distribution diagrams
  • Australian code AS 4100-1990
  • U.S. standard AISC LRFD 
When comparing the moment distribution diagrams, you can take advantage of the library with more than 600 diagrams listed in tables.   
Detailed settings
 

Results


Subsequent to the design, RF-LTB displays the results sorted by cross-sections, members, sets of members or x-locations in clearly arranged results tables. The result values in the tables are shown always together with the corresponding cross-section graphic. In the RFEM analysis model, the values are highlighted by different colors. In this way, you can easily detect difficult or oversized structural components. The colors and values assigned can be modified.

Diagrams showing the result distribution on the member or set of members allow for a specific evaluation. It is also possible to represent every intermediate value.

The masses determined during the design are displayed by member as well as by set of member in the form of parts lists.

Finally, you can export all tables to MS Excel or OpenOffice.org Calc or in a CSV file without any problems. All specifications required for the export are defined in a special transfer menu.
Printout report
 

Note

You can find more information about RF-LTB here:

> Hotline
> Training


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Price Information

Net prices in USD
For use in United States
First License
RF-LTB 1,029.56
Next License
RF-LTB 463.30
> Webshop
1.1 General Data
1.1 General Data
1.2 Materials
1.2 Materials
Material Library
Material Library
1.3 Cross-Sections
1.3 Cross-Sections
Units and Decimal Places
Units and Decimal Places
1.5 Parameters - Sets of Members, Support Type
1.5 Parameters - Sets of Members, Support Type
1.5 Parameters - Sets of Members, Shear Panel
1.5 Parameters - Sets of Members, Shear Panel
1.5 Parameters - Sets of Members, Rotational Restraint
1.5 Parameters - Sets of Members, Rotational Restraint
2.1 Design by Cross-section
2.1 Design by Cross-section
2.2 Design by Set of Members
2.2 Design by Set of Members
2.4 Design by x-Location - Sets of Members
2.4 Design by x-Location - Sets of Members
Result Diagram on Member
Result Diagram on Member
3.1 Parts List by Member
3.1 Parts List by Member
Export settings for MS Excel
Export settings for MS Excel
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