Page 6 - ZSi-Foster Channel Loads

Column - Design Fundamentals

Columns are structural members that are loaded parallel to their length. Support Conditions - Pinned Top –
Most columns are vertical and are used to carry loads from a higher level to
a lower level. However any member subjected to compression loads, such Fixed Bottom
as a diagonal or prop brace, is a column. The top is restrained against lateral movement (translation)
A column fails by “buckling”, which is a sudden loss of straightness and but is allowed to rotate The bottom is restrained against
subsequent collapse Allowable column load is dependent on: rotation and lateral movement
(a) the length of column, This is a common support condition and is used to K=0.80
construct the allowable column load applied at the Slot
(b) the type of loading,
Face tables
(c) the support conditions, and
(d) the column’s cross-sectional shape and material
Column Length
The column length is measured from braced point to braced point A braced
point is where the column is restrained from lateral movement (translation) Support Conditions - Pinned Top –
in all directions Pinned Bottom
Column Loading – Concentric Loading Both ends are restrained against lateral movement
Loads applied to the center of gravity of the column cross-section are (translation) but, are allowed to rotate
considered concentric A beam that passes over and rests on the top of a
column is an example of concentric loading K=1.00
Column Loading – Eccentric Loading
Any load which is not concentric is eccentric The amount of eccentricity (in
inches) has a major effect on the load-carrying capacity of any particular
column A load that is transmitted to a Unistrut Metal Framing column using
a standard fitting bolted to the slot face is considered eccentric
The load tables give allowable loads for both concentric (loaded at C G )
and certain eccentric (loaded at slot face) loading Allowable loads for other Support Conditions - Fixed / Free Top –
eccentric loading must be determined by a qualified design professional Fixed Bottom
Support Conditions The top is restrained against rotation but is allowed to move
Based on the support conditions, an appropriate "K" value is selected This laterally The bottom is restrained against rotation and lateral
“K” value, which mathematically describes the column end conditions, is movement (translation)
used in the column design equations The most common support condition K=1.2
combinations are as follows:
Support Conditions - Fixed Top –
Fixed Bottom
Both ends are restrained against rotation and lateral Cross-Sectional Shape
movement (translation)
The cross-sectional shape of a column member determines the value of
its “Radius of Gyration” or "r" In general, a member with a large "r" makes
K=0.65
a better column than a member with a small "r" Each axis of a column has
a different "r" Typically the axis with the smallest "r" determines the final
design

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