The Members | Stability tab is available if the “Perform stability design’' check box is selected in the Members | Main tab. Here, you can configure additional settings for the stability analyses.
The “Design parameters” are divided into several categories, which differ depending on the design standard. The following sections describe the parameters for these standards:
EN 1995
Stiffness Reduction
This category is relevant for the time-dependent behavior of compression members with large permanent load components: According to the German National Annex NCI NA.5.9, the creep effect shall be taken into account for compression-loaded structural components in service classes 2 and 3 if the design value of the permanent and quasi-permanent load components exceeds 70% of the design value of the total load. This may be considered by reducing the stiffness by a factor of 1/(1 + kdef).
Position of Load Application
In the Effective Lengths dialog box, you can specify how the ideal elastic critical moment Mcr is determined. With the Eigenvalue Method, the load application point can significantly influence the critical moment for lateral-torsional buckling: A load acting on the top chord of a bending beam in the direction of the shear center has a destabilizing effect. If, on the other hand, the load pulls on the bottom chord, it has a stabilizing effect. Use the selection boxes to specify the ‘‘Vertical position.”
For members with a constant cross-section, the load application point also influences the definition of the equivalent member lengths, according to the footnote in [1] Table 6.1.
Settings for Eigenvalue Method
The “Activate warping stiffness” check box is relevant when the ideal elastic critical moment Mcr is determined using the eigenvalue method. This allows you to control whether the warping resistance Iω should be taken into account for lateral-torsional buckling. In the analytical equations of the standard for determining the critical lateral-torsional buckling moment, the effect of warping stiffness is neglected on the safe side.
NDS
Representative Dimension of Section for Tapered Compression Members Acc. to 3.7.2
In this category, you can specify which equation should be used to determine the representative cross-section dimensions of tapered compression members:
- Eq. 3.7-2: for specific standard support conditions
- Eq. 3.7-3: for all other support conditions
Position of Positive Transverse Load Application
In the Effective Lengths dialog box, you can specify how the ideal elastic critical moment Mcr is determined. When using the Eigenvalue Method, the load application point can significantly influence the critical moment for lateral-torsional buckling: A load acting on the top chord of a bending beam in the direction of the shear center has a destabilizing effect. If, on the other hand, the load pulls on the bottom chord, it has a stabilizing effect. Use the selection boxes to specify the "Vertical position".
Settings for Eigenvalue Method
The “Activate warping stiffness” check box is relevant when the ideal elastic critical moment Mcr is determined using the eigenvalue method. You can use it to control whether the warping resistance Iω should be taken into account in the lateral-torsional buckling analysis. In the analytical equations of the standard for determining the critical lateral-torsional buckling moment, the effect of warping stiffness is neglected on the safe side.
CSA O86
Position of Positive Transverse Load Application
In the Effective Lengths dialog box, you can specify how the ideal elastic critical moment Mcr is determined. With the Eigenvalue Method, the load application point can significantly influence the critical moment for lateral-torsional buckling: A load acting on the top chord of a bending beam toward the shear center has a destabilizing effect. If, on the other hand, the load pulls on the bottom chord, it has a stabilizing effect. Use the selection boxes to specify the "Vertical position".
Strong Buckling Axis of Built-up Compression Members
The “Omit strength reduction factors acc. to 6.5.5.4.7” check box allows you to control whether the strength reduction factors for buckling in the major axis of the lamellas, specified in Sections 6.5.5.4.2 through 6.5.5.4.5, may be omitted.
Settings for Eigenvalue Method
The “Activate warping stiffness” check box is relevant when the ideal elastic critical moment Mcr is determined using the eigenvalue method. This allows you to control whether the warping resistance Iω should be taken into account for lateral-torsional buckling. In the analytical equations of the standard for determining the critical lateral-torsional buckling moment, the effect of warping stiffness is neglected on the safe side.
