Experimental Research On Fatigue Performance Of Reinforced Concrete Beams Under Overload And Corrosion Damage

With the increase of service life, the damage of RC highway bridge influenced by vehicle load and environment accumulates continuously. Two most important forms of damage are caused by overload and corrosion. With the purpose of understanding the fatigue performance of RC beams under these two kinds of damage in a further step, this paper carried out the experimental research on fatigue performance of RC beam under overload and corrosion damage. The main contents included that the effect of overload on fatigue performance of RC beams, the effect of corrosion environment on fatigue performance of RC beams, and the variation of concrete steel corrosion and chloride ion distribution under fatigue load.Based on the investigation report of vehicle loads, appropriate fatigue load amplitude was selected. Then the overloaded variable-amplitude fatigue experiment of RC beams was carried out. Test results showed that, the diagonal sectional fatigue failure occurred on all the beams subjected to overload. Moreover the subsequent fatigue life of beams was closely related to overload recycle ratio; and the excessive number of overload cycles would result in rapid destruction of RC beams. In addition, the mid-span deflection and crack width increase evidently of beams overloaded. With the increase of overload cycles, the variation range of deflection and crack width became larger. The cumulative damage model and life prediction method were built based the attenuation rule of dynamic stiffness of beams overloaded.The corrosion fatigue experiment of RC beams were carried out with the accelerated corrosion method of "Electro osmosis-constant Current-Wet and Dry cycle" during fatigue test. The results indicated that the corrosion environment had less influence on fatigue life, mid-span deflection and concrete strain when the corrosion environment acted in short time compared with the atmospheric environment. However, the corrosion environment would reduce the fatigue life obviously and accelerate the development of deflection and strain when it acted in long time. There were crack source zone, propagation zone and fracture zone in fatigue rupture sections of steel of corrosion fatigue beams. Corrosion fatigue damage was the result of both alternating stress and corrosion and corrosion accelerated the initiation and propagation of fatigue crack of steel. Partial corrosion was the main factor leading to the failure of beams.To grasp the degree of steel corrosion and the distribution rule of chloride under corrosion fatigue, half-cell potential method, concrete resistivity method and RCT method were used. The results indicated that, with the increase of corrosion acting time, corrosion potential and electrical resistivity of concrete present a downward tendency in the mass. In addition, corrosion rate of beam under load was higher than unloaded one. Moreover, with the increase of the fatigue load, the corrosion rate increased significantly. The chloride ion content in the fatigue crack area was much more than the area without crack. And chloride ion accumulation phenomenon would occur in a certain depth of concrete cover.The achievements in this paper could provide further reference for the establishment of cumulative damage model, life prediction and maintenance of RC bridge under overload operating and corrosion environment.