In Figure P12.8, columns AB and CD have pinned ends, are made of an aluminum alloy (E = 72...

In Figure P12.8, columns AB and CD have pinned ends, are made of an aluminum alloy (E = 72.0 GPa), and have equal rectangular cross sections of 20 mm by 30 mm. Determine the magnitude of P that will first cause one of the columns to buckle. Assume elastic conditions.

FIGURE P12.8