Input of intermediate supports for the lateral support of members and sets of members

Technical Article on the Topic Structural Analysis Using Dlubal Software

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The support conditions of a beam subjected to bending are essential for its resistance to lateral-torsional buckling. If, for example, a single-span beam is held laterally in the middle of the span, the deflection of the compressed flange can be prevented, and a two-wave eigenmode can be enforced. The critical lateral-torsional buckling moment is increased significantly by this additional measure. In the add-on modules for member design, it is possible to define different types of lateral supports on a member using the "Intermediate supports" input window.

Differences between nodal support and intermediate support

The differences between these two variants can only be found in the input. In general, an intermediate support can only be defined between the start and end points of a member. It is not necessary to divide the member at this point, and you can quickly enter several similar intermediate supports.

A nodal support is always defined on a node. The member must, therefore, be divided at this point in order to define the support. The effect of an intermediate support in the y-direction and a nodal support with a restraint of uy is identical in the calculation.

However, the nodal support offers more options for user-defined input than the intermediate support, depending on the add-on module. In most of the add-on modules, the intermediate support is applied as a fork support with a restraint of the lateral displacement and a rotation restraint around the longitudinal axis. In the RF-/STEEL EC3 and RF-/STEEL AISC add-on modules, however, it is also possible to distinguish between a hinged support on the upper or lower flange, a fork support, or a user-defined lateral support.

Selection of the input option

Depending on the design format, a certain input option may be specified. Thus, the nodal supports are not offered in the RF-/STEEL EC3 add-on module for the equivalent member method because the boundary conditions are defined by the effective lengths. Thus, it is only possible to use the intermediate support. For the designs according to the General Method or with RF-/STEEL Warping Torsion, the nodal supports and the intermediate supports are available. They are then used depending on whether a node is already defined in the main model or not. Some add-on modules, such as RF-/ALUMINUM, offer the choice between a member-like input with intermediate supports, or a set of member-like inputs for nodal supports.

Example

For a single-span beam, the lateral-torsional buckling analysis in RF-STEEL EC3 is performed with the equivalent member method and an intermediate support in the middle, and compared with a design according to the general method and a central nodal support.

The expected two-wave mode shape results for both input variants.

Author

Dipl.-Ing. Oliver Metzkes

Dipl.-Ing. Oliver Metzkes

Product Engineering & Customer Support

Mr. Metzkes is responsible for the development of the add-on modules for steel structures and provides technical support for our customers.

Keywords

Intermediate lateral restraint Support Stabilization Lateral-torsional buckling Stability

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  • Updated 07/15/2021

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Price of First License
1,480.00 USD
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Design of aluminium members according to the American standards ADM 2010, ADM 2015 and ADM 2020

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RSTAB
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The structural engineering software for design of frame, beam and truss structures, performing linear and nonlinear calculations of internal forces, deformations, and support reactions

Price of First License
2,550.00 USD
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Price of First License
760.00 USD
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Price of First License
1,480.00 USD
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Price of First License
1,480.00 USD
RSTAB
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Price of First License
1,480.00 USD
RSTAB
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Price of First License
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Price of First License
1,480.00 USD
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Price of First License
1,480.00 USD
RSTAB
STEEL HK

Add-on Module

Design of steel members according to Code of Practice for the Structural Use of Steel 2011 (Buildings Department - Hong Kong)

Price of First License
1,480.00 USD
RSTAB
STEEL IS

Add-on Module

Design of steel members according to the Indian standard IS 800:2007

Price of First License
1,480.00 USD
RSTAB
STEEL NBR

Add-on Module

Design of steel members according to the Brazilian standard ABNT NBR 8800:2008

Price of First License
1,480.00 USD
RSTAB
STEEL NTC-DF

Add-on Module

Design of steel members according to the Mexican standard NTC-DF 2004

Price of First License
1,480.00 USD
RSTAB
STEEL SANS

Add-on Module

Design of steel members according to the South African standard SANS 10162-1:2011

Price of First License
1,480.00 USD