Problems in Determining the Buckling Loads of Slender Full-Scale Concrete-Filled Tube Specimens

This paper describes the methodology for post-processing experimental data related to the axial strength of slender full-scale concrete-filled tubes. Although utilizing a state-of-the-art testing system, the results obtained during testing needed to be corrected to account for the compliance, frictional forces, resolution and capacity limits of the testing system, as well as the initial imperfections of the specimens. A complex load protocol, aimed at determining the buckling load capacity of CFT columns, a set of points in the P-M interaction diagram of CFT beam-columns, and the torsional strength of CFT members, was used. This load protocol consisted of a set of load cases applied sequentially: (1) pure compression, (2) uniaxial and biaxial bending combined with different constant axial load levels, and (3) torsion with and without constant compression loading. Successful post-processing of the data required the application of different techniques to correct, filter and extrapolate the measured experimental response. In addition, these efforts required that behavior of the loading system be characterized through integration of data from different sensors and computational simulations using stiffness and displacements obtained directly from the test.