Shear Behavior of U-Shaped Steel–Concrete Composite Beams with Positive and Negative Loading

This paper studies the shear behavior of U-shaped steel–concrete composite beams (USCCBs), which include eight full-scale beam specimens with different loading directions, loading positions, and shear span ratios. The USCCB is composed of reinforcing bars, encased concrete, U-shaped steel plate, headed studs, and novel dumbbell-shaped connectors. The three-point loading tests were carried out to confirm the shear failure mode and force-transfer mechanism of a concentrated load. The diagonal compression failure of encased concrete, welding fracture and local buckling of U-shaped steel plate, and cracking and spalling of concrete slab were observed in the experiments. The displacement ductility factor of eight specimens was between 1.55 and 3.61, and a rapid drop of the load did not occur in this study. The concrete slab reached ultimate compressive strength, the U-shaped steel plate mainly reached yield strength, and the steel–concrete relative slip or separation did not occur before the load reached peak value. The loading direction and shear span ratio have more effect on the bearing capacity of specimens. The novel connector controls the buckling range of the steel plate, but it has less effect on the bearing capacity. The transfer path of the shear load was measured and analyzed by strain data, and the included angle was between 33.5° and 49.2°. The calculation method of shear capacity for USCCB specimens was proposed, and the average ratio of calculation/test was 1.04.