Fatigue Life Evaluation Of Corroded Rc Beams Based On The Fatigue Crack Propagation Of Reinforcement

Reinforced concrete bridges suffered from repeated vehicle loads during service life.Meanwhile,steel bars in bridges are easily corroded in the deicing salt or coastal environment.Steel corrosion will accelerate the fatigue cumulative damage and clearly decrease the service life of structure.It is reported from most experimental researches and engineering accidents that fatigue fracture of structure can both be attributed to fatigue break of reinforced materials.Therefore,the commonly used HRB400 reinforced materials in engineering is taken as research objects in the paper to investigate the fatigue crack propagation and microscopic microstructure of standard compact tension C(T)specimens,based on different specimen orientation and different stress ratio.The main work is as follows:(1)Fatigue crack propagation rate test of C(T)specimens of reinforced materials was carried out under different orientation and stress ratio,which investigated influence of specimen orientation and stress ratio of C(T)specimen on fatigue crack propagation life and fatigue crack propagation rate for rebars.(2)Stress ratio has important effect on fatigue crack propagation property.Fatigue crack propagation life and fatigue crack propagation rate both increase with the increase of stress ratio,in addition,fatigue crack propagation property of axial C(T)specimen is more relevant with stress ratio.Fatigue crack propagation property of HRB400 reinforced materials shows apparent relevance with C(T)specimen orientation.Resistance for Radial C(T)specimens to fatigue crack propagation is apparently stronger than that with same stress ratio.(3)With different specimen orientation and different stress ratio,observation and comparative study of the fracture morphology and microstructure for C(T)specimens were carried out.It is reported that the vertical section of HRB400 reinforced materials significantly showed ferrite/pearlite bands characteristics,fatigue crack perpendicular to ferrite/pearlite bands(namely the radial orientation),mainly the transgranular failure,showed obvious crack branching and more bendy crack propagation path,fatigue crack parallel to ferrite/pearlite bands(namely the axial orientation),mainly the intergranular failure,showed no crack branching.(4)On the basis of fatigue crack propagation,prediction model of fatigue life of corrosion RC beam was established.According to the equivalent initial crack(EIFS),electrochemical theory,linear elastic fracture mechanics,with comprehensive consideration of corrosion pit increase,fatigue crack propagation of steel bar and influence of stress-focusing effect aroused by steel corrosion on fatigue crack propagation rate,prediction model of fatigue life of corrosion RC beam was established using method of comparing corrosion pit growth rate with fatigue crack propagation rate and gradually translating into single propagation mechanism analysis for fatigue crack,Monte Carlo method was used for analog computation and parameters analysis.