Experiment And Numerical Simulation Study On Reinforced Concrete Beam Under Impact Loading

Over the past decade, social security, people’s lives and property were often exposed tothe threat of terrorist attacks. Eathquakes, tsunamis, landslides and other natural disasters, aswell as their secondary disasters which caused severe damage to structures had been reportedfrequently. The probability of reinforced concrete structures exposed to the impact loading,explosion shock and other non-design loading is increasing. Therefore, to carry out the studyof the impact resistance of reinforced concrete structures is very important and necessary.1. Concrete material under high strain rate loading is demonstrated the strong nonlinearcharacteristics, which is a barrier to study the impact resistance performance of reinforcedconcrete structures. In addition, dynamic data acquisition is still a challenging issue forresearchers. However, for improving the measurement accuracy, a new Polyvinylidenefluoride (PVDF) based stress gauge is developed to measure concrete stresses under impactloading. Calibrated on a split Hopkinson pressure bar (SHPB), the PVDF gauge was then usedto establish dynamic stress-strain curves of concrete cylinders from a series of axial impacttesting on a drop-hammer test facility.2. A series of numerical simulations were conducted to FE model of concrete cylindersby explicit finite element program ls-dyna. Using the dynamic stress-strain curves measuredby PVDF gauges, parameters of concrete continuous cap model (CSCM) had been optimized.The simulation results shown that, by using the optimized parameters of CSCM model, thesimulation results coincided with test results pretty well.3. In order to study the anti-collapse performance of hinged RC beams, a series of staticloading tests were carried out. During the tests, load-carrying capacity, mid-span displacement,absorbed energy, failure types and crack propagation pattern have been recorded. The heightvariation of the concrete compression zone at mid-span cross-section and the axial force ofthe RC beams were calculated and analyzed, failure mechanism of hinged RC beams understatic loading was also discussed. The static test results showed that: at the beginning of theloading process, compressive arch action within hinged RC beams had been quickly formedwhen the test RC beams exceeded the elastic stage. Subsequently, with the development ofmid-span displacement, the stress state of the hinged RC beams gradual transition to catenaryaction stage. During the loading process, hinged RC beam showed good energy absorptionperformance because external load can be effectively delivered to the nearby support by axialforce and external input energy also can be dissipated by large deformation and cracking of hinged RC beams. By using optimized CSCM model, the numerical simulation analysisresults of loading process also confirmed this.4. A series of impact tests on hinged RC beams which have the same sizes andreinforments with the static loading beams are carried out on the large-scale drop-hammer testfacility at Hunan University. During the test, signal of impact force, mid-span displacement,strain of concrete and reinforced bars at supports have been measured. The failure process ofhinged RC beams during the test have been captured by high-speed camera. Thisexperimental study aimed at better understanding of the dynamic behavior of hinged RCbeams under impact loading. These data can also be very helpful for improving thecalculation accuracy of the numerical simulation for RC beams under impact loading. Anumerical simulation are carried out on hinged RC beams subjected to impact loading.Results from the simulations showed acceptable accuracy of optimized CSCM model inlow-speed impact range. By changing the reinforcement ratio of the finite element beamsduring numerical simulations, the critical failure energy of hinged RC beams under impactloading had been captured. Base on the simulation results, a simplify calculation formulaabout hinged RC beam under impact loading had been derived. Meanwhile, a resistancehysteresis model of Hinged RC beam has been proposed. With the resistance hysteresis modeland the load vs mid-span displacement curves measured from static test of hinged RC beams,the impact loading process have been analysed by using single degree of freedom method.