Numerical study of the effect of fatigue on impact performance of RC beams

Some existing concrete structures not only face threats of possible explosions and impact, but also suffer from long-term fatigue loads induced by traffic or vibration of machines. Researchers have conducted extensive investigations on concrete structures against highly dynamic load, e.g., blast or impact. However, the fatigue damage and performance deterioration of flexural members due to long-term cyclic loads throughout the service life have not been considered in the analysis of structures against highly dynamic loads. Studies have proven that fatigue damage resulted in degradation of concrete strength and modulus of elasticity (MoE), as well as a reduction in the strength of steel bars. The deteriorated materials caused a reduction in the residual capacity and stiffness of reinforced concrete (RC) structures under quasi-static loads. Therefore, ignoring the effect of fatigue may result in an overestimation of the performance of existing structures against blast or impact loads. This study numerically investigates the effect of fatigue on the impact performance of RC beams. The grid section method (GSM) is proposed to simulate RC beams with fatigue damage. The GSM is applied to divide the RC beam into compressive and tensile zones and assign deteriorated strength and MoE of concrete to corresponding zones according to the stress level. Numerical models of the RC beam with fatigue damage are established using LS-DYNA and validated against experimental results. The effect of different factors, including fatigue cycles, reinforcement ratio, concrete strength, and impact energy, on the impact behavior of RC beams is examined. Based on the results, the correction method is proposed to take into consideration of the fatigue damage in the estimation of RC beams against highly dynamic load.