Research on a Buckling Detection Technique for Rectangular Concrete-filled Steel Tubular Columns based on Grating Projection

<p>The surface buckling of concrete-filled steel tubular (CFST) columns under axial compression was observed in real time by using fringe projection, and pre-set fringes with phase information were projected onto the surface of the member. The buckling information (the size and shape of drum buckling) and its evolution were obtained by analysing the buckling images during the loading process. Nine images of key moments during the experiment were obtained by a technique of obtaining the actual measurements synchronously, and the position of the bulge on the whole side of the steel pipe was obtained by unwrapping. The shape and evolution of the drum buckling of the steel pipe developed symmetrically before point C (the ultimate bearing capacity) and evolved from 2 to 3 peaks. After passing through point C, the buckling deformation was asymmetrical. The deformation near the loading end increased gradually, and the buckling deformation increased with loading. The fastest growth stage was between points C and F, and the load displacement curve showed a rapid reduction in the load. These experimental results show that this noncontact measurement method based on fringe projection is effective in detecting the buckling of rectangular CFST column surfaces.</p> <p>&nbsp;</p>