Comparison Of P.C Beams Between Constant Amplitude Fatigue Experiment And Variable Amplitude Fatigue Experiment

With increasing economic strength in past decades,China is striving to develop public transportation system to meet the growing trend of travel demands.However,along with the incremental improvement,potential safety implications are increasing as well.Damage of heavy traffic on bridges is one of the most impending risks.Within the service lifetime,bridges are keep being damaged from overloading over a long period.Thus,researching on fatigue behaviors of bridges under the repeated overloading is becoming the priority.Based on the reliable experiment data,this paper analyses the fatigue behavior of partially prestressed concrete beams in order to give some references for future researches and engineering.In order to do an in-depth research on the fatigue damage of bridge structures under the repeated load,seven partially prestressed concrete scale model beams that based on real engineering of a bridge in structure factory were applied in this experiment.Constant amplitude fatigue experiment and variable amplitude fatigue experiment were conducted in the laboratory.A conclusion was drew based on the experiments: partial prestressed concrete beams fatigue damage is started in the fatigue fracture of non-prestressed steel;the partial prestressed concrete beam that doesn't destroyed in fatigue load becomes not only weaker but also more durable;the fatigue life of non-prestressed steel has a linear relationship with stress amplitude(S-N curve).This paper creatively compared the results of constant amplitude fatigue experiment with the results of variable amplitude fatigue experiment,and got many conclusions among fatigue life,deflection change,crack propagation and the law of strain of concrete.For example,under two level variable amplitude fatigue load,the load sequence has a great effect on the fatigue life of prestressed concrete beam.If suddenly increase the upper limit of secondary fatigue load,it may dramatically decrease fatigue lifespan.This conclusion proved that a random variable amplitude fatigue load will cause greater damage to beams.Because under the random variable amplitude fatigue load,the structure is going through the process of load change from low to high at any time.And the actual engineering of the bridges are more close to the random variable amplitude fatigue load,so designers should focus on it particularly.In addition,this paper also estimate the fatigue damage cumulative theory Miner Criterion and Revised Miner Criterion.By estimation separately and comparing with experimental results,it is proved that the estimation Miner Criterion of the fatigue life has larger error and more dangerous,but the estimation by Revised Miner Criterion of the fatigue life is more precision and conservative.The stiffness degradation law of prestressed concrete beams are analyzed,and the calculation formulas are deduced.