Full-Scale Tests of Slender Concrete-Filled Tubes: Interaction Behavior

This paper presents selected results from an experimental and computational evaluation on the behavior of slender concrete-filled steel tubes (CFTs) under combined axial compression and biaxial flexure. A complex loading protocol was used in the experimental program, including monotonic and cyclic loading that allowed detailed evaluation of the complete beam-column response. This paper principally addresses the experimental determination of the maximum stable axial load-bending moment (P-M) interaction strength. The experimental P-M interaction strengths extracted at incipient instability shows that for very slender specimens, the bilinear interaction diagram proposed in the current design provisions of the AISC is somewhat unconservative. This experimental observation is also confirmed by detailed computational results. However, the results also indicate that current AISC provisions provide an accurate and conservative approach for evaluating axial load-flexural interaction for most practical CFT column sizes and lengths (i.e., composite beam columns with low and intermediate slenderness). (C) 2014 American Society of Civil Engineers.