Page 6 - ZSi-Foster Channel Loads
P. 6

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
                                                               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

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