Behavior of RC Beams under Variable Amplitude Fatigue Loading

Passenger and freight collinear railway bridges (PFCB) are commonly used in the infrastructure of the existing railroad system and play an important role. Due to the rapid development of railway system, these old bridges are faced with train speed and weight increase for many times. However, the influence mechanism of the early low stress service history on the later static and fatigue behavior of the bridge is not clear. The innovation of this paper is to investigate the influences of the low-level variable amplitude cyclic fatigue loading on capacity reinforced concrete (RC) beams in terms of the static and fatigue loading. Five RC beams were tested subjected to different combinations of static and cyclic loading, and the cyclic load was variable amplitude fatigue load. The results are shown in terms of the failure mode, the evolution of stiffness and detailed sectional strains. Finally, it is found that the early low stress loading only makes a difference of 1.6% (0.64 kN·m) on the static loading capacity of the beams. However, the static failure mode of the beam has changed. At the same time, the fatigue lives of the two beams BF1 and BF2 are 1,903,451 cycles and 2,268,798 cycles, respectively, which indicates that the early low stress loadings have limited influence on the fatigue behavior of the RC beams. Combined with the field test, the presented results are useful in evaluating, maintenance and upgrading of the existing bridges infrastructures.