Experimental verification of buckling-mode interaction in intermediate-length composite columns

Column buckling is a major design concern for pultruded composite columns. Interaction between the local (¯ange) and global (Euler) buckling modes occurs in intermediate length thin-walled columns with near coincident buckling loads. The interaction of more than one buckling mode induce an unstable tertiary post-buckling path, causing imperfection sensitivity and premature failure. In this work, the existence of buckling-mode interaction is experimentally veri®ed for intermediate length pultruded wide-¯ange columns subjected to uniaxial compression. Characterization of the interaction mode is done using both conventional testing techniques and the shadow moire optical technique, allowing for non-contact, full ®eld measurement of the buckling modes.