Default buckling parameters

For parameters for EN-EC read chapter Member check parameters for EC-EN.

The default buckling parameters are used whenever a new 1D member is input into your project. By default, the new member takes these default parameters. If required, you may later alter these default values and assign specific values to the particular member.

Buckling systems relation

zz

System length for buckling around the local zz axis (weak axis). This is usually the length between the points braced in the direction of the local yy axis.

yz

System length for torsional buckling. This is the length between the restraints for torsion.

Both EC3, DIN18800, ONORM4300, NEN6770, SIA263, AISC-ASD and AISC-LRFD take account of torsional buckling.

lt

System length for lateral-torsional buckling. This is usually the length between the points braced in yy direction (= length between the lateral restraints).

The buckling lengths for the calculation are always of the following form :

l = L * k

where

l

effective buckling length for calculation

L

system length

k

k factor

Relative deformation systems relation

def y

System length for deformation in the direction of local yy axis (strong axis).

def z

System length for deformation in the direction of local zz axis (weak axis).

 

ky factor

Calculate

The value of the ky factor is calculated by the program.

Factor

The user defines the value of the factor.

Length

The user inputs the buckling length directly.

kz factor

ditto for kz factor

Influence of load position

This field is relevant for lateral-torsional buckling check. It provides for consideration of destabilising loads in moment factors for LTB.

(See Steel Code Check Theoretical Background, Calculation of moment factors for LTB).

Destabilising loads are loads that act above the level of the beam’s shear centre and are free to move sideways with the beam as it buckles (and produce a disturbing effect)

For a theoretical explanation about the calculation of buckling ratios ky and kz, see Steel Code Check Theoretical Background, Calculation of buckling ratios.

For a member with variable height, the value of ky ratio has no meaning. Buckling properties are calculated using the critical Euler force for this member (see Steel Code Check Theoretical Background, Calculation of critical Euler force for VARH elements). However, the user can choose to define a not-calculated buckling ratio which is used in each intermediate point of the member.

The procedure to adjust the buckling defaults

  1. Open service Steel:

  1. either using tree menu function Steel,

  2. or using menu function Tree > Steel.

  1. Select function Beams >Setup and open it.

  2. In the dialogue that appears on the screen, select tab Buckling defaults.

  3. Type required values and select appropriate options.

  4. Confirm with [OK].