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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