Flexural performance of round-ended concrete-filled steel tubular specimens

Round-ended concrete-filled steel tubular (CFST) columns have numerous benefits, including easy construction, aesthetic appearance, and variable section arrangement. This study experimentally and numerically investigated the flexural behavior of round-ended CFST columns. The six testing results showed that as the aspect ratio increased from 1.38 to 1.86, the flexural resistance and stiffness increased by 82.0% and 159.9%, respectively. Every round-ended CFST specimen had excellent ductility. Concrete can be adequately confined by the round-ended steel tube. Mechanistic and parametric analyses were carried out using a finite element model. Mechanistic analysis demonstrated that the round segment of the steel tube can effectively confine the concrete, resulting in a considerable strength gain near the edge of the compression zone. The parametric analyses showed that as the concrete strength increased from 24 to 110 MPa, the flexural resistance increased by average 20.4%; as the steel strength improved from 235 to 700 MPa, the flexural resistance increased by average 155.4%; as the steel ratio enhanced from 0.05 to 0.2, the flexural resistance increased by average 179.7%; and as the aspect ratio increased from 1 to 3, the flexural resistance of the major (minor) axis increased (decreased) by about 59.9% (36.5%). The analysis showed that the flexural stiffness of this composite specimen can be accurately predicted by AISC 360–2016. Finally, a simplified model was proposed for estimating the flexural resistance of the round-ended CFST specimens.