# Errata, 1st Edition

Page 201

Margins for Buckling are shown as being calculated by:

M.S.(Buckling) = Allowable EV / Buckling EV – 1

With Allowable EV corresponding to the required Eigenvalue by a program and Buckling EV corresponding to the lowest Eigenvalue reported by Nastran. This should instead read:

M.S.(Buckling) = Buckling EV / Allowable EV – 1

Example 1. If an engineering development program required a buckling Eigenvalue against limit loads of 1.5, and the first Eigenvalue discovered by Nastran was 0.8, then the Margin of Safety is calculated:

M.S.(Buckling) = 0.8 / 1.5 – 1
M.S.(Buckling) = -0.46

Explanation: This is logical because the structure is expected to buckle at only 80% of limit load, the Margin of Safety is appropriately negative.

Example 2. If an engineering development program required a buckling Eigenvalue against limit loads of 1.5, and the first Eigenvalue discovered by Nastran was 1.6, then the Margin of Safety is calculated:

M.S.(Buckling) = 1.6 / 1.5 – 1
M.S.(Buckling) = +0.07

Explanation: Because Nastran predicted it would take a factor on limit load of 1.6X to buckle, and the requirement was only 1.5, there is a positive Margin of Safety against buckling.