LOCAL INSTABILITY OF SYMMETRICAL RECTARGULAR TUBES UHDER AXIAL COMPRESSION

A chart is presented for the coefficient in the for-mula for the critical compressive stress at which cross-sectional distortion begins in a thin-mall tube of rec-tangular section symmetrical about fts two principal axes. The energy method of Timoshenko was used in the theoreti-cal calculations required for the construction of the chart. The deflectfon equation used in this method was selected to give g00a accuracy. The exact velues given by solution of the differential equation were calculated for a number of cases and it was found that tie energy solu-tion was correct to within a fraction of 1 percent. The calculation of t?te critical compressive stress at stresses above the elastic range is also discussed. In oraer to demonstrate the use of the formulas and the chart in engineering calculations, several illvlstrative problems are included