Monday, December 5, 2011

Column Design (Part 5)

From [Column Design (Part 4)], the Euler formula has been introduced. But when the slenderness ratio KL/r is less than the transition value Cc, then column is short, and the J.B. Johnson formula should be used. If we use Euler formula for the short column, it would predict too high critical load than it really is.

The J.B. Johnson formula is as follows:

From the J.B. Johnson formula we can see that the critical load for the short column is affected by the strength of the material (Sy) in addition to its stiffness (E). But for the long column as Euler formula is used, the strength of material (Sy) is not a factor for the critical load.

Let's see how we can make the excel file to help calculate critical load for both short and long columns in the next post.