Columns and Other Compression Members

1. Columns and Other Compression Members • The strength of steel compression members is usually limited by their tendency to buckle. • The load at which a compression member becomes unstable is the buckling load. • The buckling load depends on the length, cross-section, and end conditions of the column and the stiffness of the material.

2. Buckling Load • Pcr is the load at which the compression member becomes unstable • E is modulus of elasticity of steel = 29,000 ksi • I is moment of inertia of the cross section • L is the length of the compression member • K is the effective length factor

3. Effective Length Factorsfor Braced Frames L K=1 K= K=

4. p. 16.1 – 189 LRFD

5. Strength of Steel Compression Members • Design Equations p. 16.1 – 27 • Tabulated in Table 4-2, p.4-21→ 4-151 • Strengths given in table are for buckling about the y-axis z z P P y x x y

6. 1st Column Design Example p. 63 notes A column in a braced frame building is 22 ft tall, with no intermediate lateral support in any direction. The construction is such that is may be considered pinned at each end, in all directions. Select the lightest possible A992 steel column to support an axial live load is 225 kips and dead load of 220 kips.

7. 2nd Column Design Example p. 63 notes In order to reduce the size of the column in the previous example, it is to be supported against weak axis buckling at mid-height. z z x y