Experimental Study On Fatigue Performance Of Reinforced Concrete Beams In Marine Environment

As the service life of bridges increases,reinforced concrete bridge structures are getting older,and long-term service bridges are increasingly affected by adverse environmental effects.Especially in recent years,the rapid increase of traffic flow has made the corrosion degree of steel bars in concrete bridges in coastal areas gradually deepen,and the fatigue stress amplitude and the number of fatigue actions have also increased simultaneously,and a large number of bridge structures urgently need to perform structural performance degradation analysis under the combined action of corrosion and fatigue.Based on the calculation of the stress state of the actual bridge under the load of highway I-level vehicles,this thesis carries out the fatigue performance experiments of reinforced concrete beams under different stress amplitude conditions,analyzes the experimental phenomena,summarizes the experimental results,establishes the stiffness degradation models of fatigue beams and corrosion-fatigue coupled beams and compared with the finite element numerical simulation results,in order to extend the numerical model to practical bridges.Mainly carried out the following work:(1)Experimental design of fatigue performance of reinforced concrete beams.A fatigue-related test plan is formulated,and the test conditions mainly include fatigue test,corrosion-fatigue coupling test,and post-corrosion fatigue test,and the test method and device are innovated for the coupling conditions of test beam corrosion and fatigue load.(2)Fatigue performance test of reinforced concrete beams.Including material performance test,static load test and fatigue performance test.On the basis of the fatigue calculation of highway class I vehicle load,the fatigue performance tests of reinforced concrete under seven different stress amplitudes were carried out,and the variation laws of cracks,stiffness,steel strain and fatigue life of the test beams were compared and analyzed.(3)Performance degradation test of reinforced concrete beams under the combined action of corrosion and fatigue.Considering the performance degradation of reinforced concrete bridge structures in coastal areas due to the combined effect of corrosion and fatigue,the corrosion fatigue coupling test and post-corrosion fatigue test under the same stress amplitude were carried out,and the influence law of stress level and marine environment on the crack,deflection,steel strain,fatigue life and failure form of the test beam was compared and analyzed.Based on the stiffness degradation law of the test beam,the stiffness degradation models of the fatigue beam and the corrosion fatigue coupled beam was established.(4)Introduce the influence of fatigue and corrosion on parameters such as the constitutive relationship of concrete and steel bars,and realize the finite element simulation of the fatigue performance of corroded reinforced concrete beams by ABAQUS software,and further reveal the influence law of corrosion and fatigue on the bearing capacity of reinforced concrete beams.The test results show that: under the same stress amplitude,the failure area,crack development and stiffness degradation of the corrosion fatigue coupling test beam are the most serious in the three test conditions;when the fatigue failure occurs,the cross section of the corrosion fatigue coupling beam steel bar is uneven and inclined.The tear shape of the cross-section is completely different from the smooth cross-sectional characteristics of the fatigue beam,and the corrosion distribution of the steel bars tends to be more natural "point-like" corrosion;When the corrosion and fatigue are coupled together,the two factors will mutually promote the expansion of the fatigue crack of the steel bar,thereby reducing the fatigue life.