The influence from steel bar on concrete fracture behavior under different impact velocities

摘要

Three-point bending tests on notched plain concrete beams and lightly reinforced concrete beams were carried out with a drop-hammer impact instrument. The shape of the specimen followed the RILEM recommendation, that is, 150 mm x 150 mm in cross section, 800 mm in length, and span was kept constant 600 mm. And only one conventional steel bar was placed in the lightly reinforced concrete beam. The high-speed camera and digital image correlation (DIC) technology were applied to catch the fracture process under dynamic loads. And the reaction force, mid-span deflection, crack velocity, the horizontal strain of concrete at the notch root, and the strain of steel bar midpoint were measured over three impact velocities (i.e., 9.89 x 10(2), 1.71 x 10(3), and 2.21 x 10(3) mm/s). The test results showed that the dynamic fracture energy for plain concrete and reinforced concrete increased with the increase of the impact velocity. When the impact velocity reached 2.21 x 10(3) mm/s, the steel bar reached yielding, which resulted in the influence from reinforcement on fracture energy weakened. Both of the dynamic fracture toughness for plain concrete and lightly reinforced concrete increased linearly as the growth of impact velocity. Furthermore, the crack extended with a decreasing speed for plain concrete and reinforced concrete. And the first-stage crack velocity in concrete was inhibited effectively by steel bar, but the inhibitory effect declined as the increase of impact velocities.