[en] The main object of this work is related to the effect of cyclic straining (like cyclic thermal stress) on the buckling of mechanical structures. It is known that cyclic straining can produce progressive distortion. Therefore initial geometrical imperfections can be strongly increased by cyclic straining. There is a ratcheting effect and the buckling load can be reduced. In order to obtain a sound design it is necessary to be able to appraise the value of this critical load reduction. In other words, it is intended to furnish indications on the effect of cyclic secondary stress (like cyclic thermal stress) on the buckling phenomenon. Hence experimental tests have been undertaken in order to obtain a better understanding of the effect of secondary cyclic stress on buckling. Those tests are similar to the tests made in the frame of the progressive distortion program. Columns of tubular cross section are submitted to constant axial compressive load and to a cyclic straining which is created by cyclic twisting of the columns. Test device and test procedure are described and test results are given. It appears that initial geometrical imperfections are progressively magnified by cyclic straining, the consequence being a progressive deflection till instability happens (progressive buckling)