Effects of Low-Cycle Fatigue Fracture of Longitudinal Reinforcing Steel Bars on the Seismic Performance of Reinforced Concrete Bridge Piers

Earthquakes, which can cause tremendous local stress and strain on infrastructure, can cause reinforced concrete (RC) bridges to collapse due to the concrete cracking and fracture of the steel reinforcement rebars. The fracture of longitudinal reinforcing steel due to low-cycle fatigue is one of the main causes of failure in RC structures under earthquake loading. The purpose of this research is to include the effects of low-cycle fatigue fracture of longitudinal reinforcing steel bars on the seismic performance of reinforced concrete bridge piers. To obtain a greater understanding of low-cycle fatigue failure of steel reinforcement of RC bridge piers subjected to seismic loadings, its properties were studied by considering the slenderness ratio to observe its effects on the behaviors of the steel material. The slenderness ratio are functions of unsupported length, diameter of the circular cross section of the longitudinal reinforcing bars, and the spacing of transverse reinforcing bars. The seismic performance of RC single-column pier-supported bridges with flexural failure under near-fault ground motion were assessed with the use of damage indices. The damage indices can numerically assess the damaged state of RC bridge piers and show the gradual accumulation of damage. Four numerical models are developed with fiber-based nonlinear beam-column elements to simulate the damage accumulation on RC bridge piers under seismic loadings, considering variables such as low-cycle fatigue, tensile strain damage, global buckling of longitudinal steel bars, the cracking and spalling of cover concrete, and the bond-slip between concrete and longitudinal steel bars. Bond-slip is related to the interaction between the longitudinal steel rebars and the concrete for load bearing and coordination deformation. The four numerical models were developed with different considerations of low-cycle fatigue and bond-slip: Model 1 (without bond-slip and without fatigue), Model 2 (without bond-slip and with fatigue), Model 3 (with bond-slip and without fatigue), and Model 4 (with bond-slip and with fatigue). The models underwent nonlinear time-history analyses. The results were compared with experimental testing results. All four numerical models are optimal to assess the seismic performance of RC single-column pier-supported bridges. The proposed damage indices can reasonably reflect the damage states in accordance with the experimental results. The proposed models can reasonably predict the damage states and seismic behavior of RC bridge columns and could be available to the structural engineering community for non-linear analysis and performance assessment of RC bridge structures.