3.0 MODULAR SUPPORT SYSTEM 3.1.2 MT BEAM AND COLUMN LOAD TABLES
Modular Support Systems Technical Guide , Edition 1
Column Design Fundamentals Column Support Conditions
Columns are structural elements that resist applied loads primarily in axial compression along their length .
A column ’ s capacity is based on its unbraced length ( noted as “ height " in load tables ), support conditions , cross-sectional properties , material properties , and load location ( i . e . whether applied at the column ’ s center of gravity or at the face of the profile ).
A column ’ s allowable load capacity depends considerably on its support ( end ) conditions . Variations in support conditions for a column are addressed via an Effective Length Factor , K , which modifies a non-pinned-end column ’ s unbraced height to represent that of an equivalent pinned-end column . Accordingly , the K value for a pinned-end column is 1.0 . See the figure below for applicable K values to be used for certain column support conditions .
Column Unbraced Length
The unbraced length of a column represents the distance between braced locations . Braced locations along a column are restrained against lateral movement ( perpendicular to the length of the column ). The larger the unbraced height of a column , its ability to resist applied loads is decreased . The tendency for a column to buckle about an axis under consideration is highly dependent on its slenderness ratio , KL / r , where K is the effective length factor ( explained to the right ), L is the unbraced length of the column , and r is the radius of gyration for the cross section . The AISI S100-16 / CSA S136-16 Specification recommends that such ratios not exceed 200 for compression members . Buckling must be considered in both principal directions for a column , with the smaller buckling load controlling the design . Remember that for members that are not doubly symmetric ( e . g channels ), the radius of gyration will be different for each principal direction .
Column Loading - Concentric
A load applied at the center of gravity , C . G ., of a column cross section is considered concentric . Such a load does not induce a bending moment in the column at the point of load application .
Column Loading - Eccentric
A load applied away from the center of gravity , C . G ., of a column cross section is considered eccentric ( e . g . a load at the slotted face of an MT channel ). Such a load induces a bending moment in the column at the point of load application and , consequently , results in a lower allowable column load compared to a concentrically loaded condition . Columns with higher slenderness ratios are particularly sensitive to eccentrically applied axial loads .
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