1. Effective Length Coefficients
by Bart Quimby, P.E., Ph.D
UAA School of Engineering
CE Steel Design
Fall 1994
(last updated 10/5/06)

2. Braced vs. UnBraced Frames
Consider everything in the plane of buckling.
Upper portion of this frame is UNBRACED.
Lower portion of this frame is BRACED.

3. Effective Length Coefficient
Theoretical Values: SCM pg
The theoretical values assume that joints are completely fixed against rotation or totally free to rotate.
Reality is usually somewhere in between. This affects the value of K.
A method accounting for rotational stiffness of joints is given on SCM pg through 243.

4. Alignment Charts
Two Charts are presented. One for braced frames (sidesway inhibited) and one for unbraced frames (sidesway uninhibited).
To use these charts you must determine the rotational stiffness, G, of each joint in the plane of buckling being considered.

5. Rotational Stiffness at Joint
Look at stiffnesses that resist rotation in the plane.

6. Typical Framed Joint

7. I to use for each plane

8. Sample Problem
Determine the Axial Capacity of the column shown

9. Strong Axis Buckling, Kx
Compute Gtop & Gbtm.
Determine Kx from the UNBRACED frame nomograph.

10. Weak Axis Buckling, Ky Compute Gtop & Gbtm.
Determine Ky from the BRACED frame nomograph.

11. Determine Column Capacity