Using approximation by a micropolar continuum, the extensional buckling of a multi-story, multibay rectangular frame with rectangular boundary is solved by formulating the problem in terms of a system of six linear ordinary differential equations. The buckling loads must be computed by a trial-and-error procedure because all coefficients of the 6 × 6 determinant to vanish depend on explicitly inexpressible complex roots and eigenvectors of another 6 × 6 determinant which in turn depends nonlinearly on the initial stress. It is shown that for tall frames consideration of long-wave buckling loads is important. Also, the continuum approximation is found to give very accurate results, as compared with the exact solutions of large frames.
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