However, the shape of the bond stress-slip curve was not significantly affected by high strain rates. Jacques and Saatcioglu ( 2019a, 2020) performed beam-end tests and lap splice tests under high strain rates of 0.1–1.0 s −1, and reported that the bond strength increased by 28–47%. The test result also confirmed the increase of bond strength under high-strain rate, and a dynamic increase factor was proposed based on the strain rate effect of tensile strength of concrete to evaluate the bar development length in existing design methods. ( 2019a) conducted drop hammer test on RC beams having longitudinal bars partially bonded at the beam ends to investigate the effects of bar diameter, development length, drop height, and hammer mass on the bond strength. The test results showed that the bar bond stress was increased as the strain rate increased, and the required bar development length under high-strain rate was smaller than or equal to that under static load. ( 2015) performed shock tube testing to investigate the strain rate effect on the bar development length under three simulated blast loads: static, 0.1 s −1, and 0.2 s −1. Solomos and Berra ( 2010) performed dynamic Hopkinson bar tests, and the test results showed that the peak pullout force and bond stress-slip curve under high strain rates were above those of static load. However, the strain rate dependency of concrete in tension and compression are observed to be different. ( 1974) confirmed that the increment of bond strength can be attributed to the increase of concrete strength because the main mechanism of the bond is based on the concrete surrounding the ribs of the steel (or reinforcement). Hansen and Liepins ( 1962) performed pull-out tests of reinforcing bars under impact load, and initially found the increase of bond strength under high-strain rate. The existing studies reported that the bond strength increases as strain rates increase (Shah and Hansen 1963, Rezansoff et al. Thus, understanding the bond between concrete and reinforcement in RC structures under impact load is of great importance. The load transfer from reinforcing bars to adjacent concrete becomes essential for the structural integrity and ductile response. Soroushian and Choi ( 1987) reported that dynamic load increased both the yield and ultimate strength of reinforcing bars. According to Malvar and Ross ( 1998), high-strain rate increases the tensile strength of concrete more than the compressive strength of concrete. Bischoff and Perry ( 1991) reported the increase of 85–100% in compressive strength of concrete under impact load. Impact loads with short duration increase the material properties of concrete and reinforcing bars in different ratio, which change ductile behavior into brittle behavior in RC structures (Yang and Lok 2007). The impact resistance of RC structures depends on the material properties of concrete and reinforcing bars under high-strain rate. To consider the strain rate effect due to impact load on the bar development length, available studies and test results are extremely limited. However, current design codes specify the bar development length based on test results under static load. Particularly, impact damage on the development length of reinforcing bars may deteriorate the structural integrity significantly. In reinforced concrete (RC) structures, impact damage is a critical issue: piers of bridge collided by ships or other vehicles, retaining walls damaged by heavy rocks, and high-rise buildings attacked by aircraft. The prediction of the proposed method agreed well with the tensile strength of bar splices under impact load. Factors related to the strain rate effect of materials, impact damage, and impact energy loss were proposed. On the basis of the test results, existing design equations for the bar development length under static load were modified to consider the impact loading effect on the bond strength. Although the designed bar development length was 31–69% of the requirement of current design codes under static load, the tensile strength of bar splices was greater than the dynamic yield strength when subjected to large impact energy under impact load. The dynamic responses including the impact load history, mid-span deflection history, crack distribution, and strain history of reinforcing bar were evaluated. The test parameters were reinforcing bar diameter, splice length, drop height, and hammer mass. To understand the effect of strain rate on the bond strength of reinforcing bars in RC beams under impact load, drop hammer test was performed on twenty-four simply supported RC beams with lap spliced bars at the mid-span. Impact loading damage of reinforced concrete (RC) members deteriorates bond strength of reinforcing bars.
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