A Beginner's Guide to the Steel Construction Manual, 13^th ed. (old)

Chapter 7 - Concentrically Loaded Compression Members

© 2006, 2008 T. Bartlett Quimby

Section 7.7

Compression Member Summary

Last Revised: 11/04/2014

Compressive strength is limited by:

• Material Strength
• General Buckling
• Local Buckling

Strength Limit States:

All strength limit states take the form:

The STRENGTH of a Column is computed by:

The nominal capacity of the column, P_n = F_cr A_g

• F_e = p² E / (KL/r)² = Euler Critical Buckling Stress

• Q =1 for compact and non-compact sections

• Q = Q_s Q_a for slender sections

• Q_s:  Slenderness factor for unstiffened elements (SCM E7.1).  A function of the slenderness (b/t) of the unstiffened element.
• Q_a:  Slenderness factor for stiffened elements (SCM E7.2).  Different equations for flanges of square and rectangular sections, circular sections, and other uniformly compressed elements.
• KL = Effective Length

Slenderness Limit State (SCM E2)

This serviceability limit state is not binding, but a good suggestion:   (KL/r) < 200

Computing Effective Length (SCM Commentary C2)

Principles of Mechanics are used to determine the effective length of columns.  The effective length is a function of the overall member length, length between lateral braces, end support condition, and the arrangement of these factors relative to each principle axis. 

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