Column Slenderness |
  
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Column Slenderness |
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The Slenderness tab allows you to specify the column bracing, which will be considered in axial capacity calculations. Click here for a video:
It is important to understand that the settings on the Slenderness tab serve double-duty:
•They define bracing to resist column buckling, and
•When the column has applied bending forces, these slenderness settings also define the unbraced compression edge lengths, and therefore they affect the calculation of allowable bending stresses.
In most of the column modules there are two tabs: "X-X" and "Y-Y Axis Column Slenderness". Let's start with the all-important definition of the axis reference for slenderness.
Buckling failure of a column can be thought of as an uncontrolled and excessive deflection in the direction of a particular axis. When defining slenderness, one of the important values is the distance between points that brace the column against movement (or failure) along a particular axis.
The column modules ask you to specify the distance between points of bracing that prevent buckling along the column's local X-X or Y-Y axis.
The X-X axis is always parallel to the "width" dimension of the column. The Y-Y axis is always parallel to the "depth" dimension of the column.
For example, the "X-X" axis of a steel W14 section is parallel to the flanges. The "X-X Axis Column Slenderness" defines the distance between points that prevent the column from buckling along its "X-X" axis.
In ENERCALC SEL, slenderness is entered as the distance between points bracing a member against buckling in the direction of the specified axis.
In the screen capture immediately below, we have selected [Fully braced "X" Axis]. This means that the column is fully braced against buckling along its X-X axis, which is parallel to the width dimension. If this was a steel "W" section, then the column is fully braced against buckling parallel to the flanges.
All materials, column fully braced
This selection sets the column as fully braced, and no slenderness effects will be evaluated.
All materials, typical simple slenderness specification
This selection allows you to enter the unbraced length to use for the column slenderness calculation. Also available are selections for the typical slenderness multipliers ("K" factors) for various end conditions.
Note! End fixity is specified on a different tab in the column modules. These slenderness factors do not alter the end fixity you specified for the column, nor do they get determined automatically by the end fixities that you specified.
All materials, typical slenderness with user-defined slenderness factor "K"
This selection allows you to enter the unbraced height and the slenderness "K" factor to use for the column slenderness calculation.
Note! End fixity is specified on a different tab in the column modules. These slenderness factors do not alter the end fixity you specified for the column, nor do they get determined automatically by the end fixities that you specified.
All Materials, non-sway slenderness calculation by calculating K based on stiffness of adjacent members
There is also an option to Compute K using adjacent members. This advanced selection lets you select the framing condition above and below the column, and using the entered lengths and EI values, it will use standard equations for Non-Sway columns to calculate the effective "K" factor.
Keep in mind that this option is used to define the relative stiffnesses of the framing in the plane of buckling that is being considered. For example, when using the X-X Axis Column Slenderness tab, the plane under consideration is the plane in which the column's X-X axis lies.
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