Determination of Buckling Loads from Triaxial Load Tests of Slender Concrete-filled Tube Beam-columns

This paper briefly describes efforts at determining buckling loads of slender concrete-filled tube beam-columns. Although utilizing state-of-the-art equipment and controllers, unexpected difficulties were encountered on extracting buckling loads for the specimens due to (a) frictional forces in the actuators, (b) large initial bidirectional imperfections, (c) initial stresses due to construction and (d) correlating data from different sensors. In addition, the complex load histories used required that all of these phenomena be carefully accounted for in all the simulation studies. Successful extraction of buckling loads required that behavior of the loading system be characterized through integration of data from different sensors and simulations using stiffness and displacements obtained directly from the test. Calibration of advanced simulation tools well into the late stages of the load history have also been preliminary documented.