The Fatigue Performance Of The Prestressed Concrete Under Bending Loads In The Freeze-thaw Environment

Prestressed concrete structure is widely used in civil engineering, transportationengineering and hydraulic engineering, which has obvious superiority compared to thereinforced concrete structure. As the same as the other structures, Prestressed concretestructure also will occure durability failure under the effect of erosion environment for along time, the problem of the durability of prestressed concrete structure in erosionenvironment has been a focus in structure engineering research.In the point of view from the climate condition, our country has quite a large area incold zone,some investigation show that in northeast of China, many freeze-thaw damageshappened of reinforced concrete structure or prestressed concrete structure in hydraulicstructures and bridge engineering, which results in huge economic loss. Freezing andThawing action is the most important factor in structure durability of the prestressedconcrete structure in cold environment for a long time, the freezing resistance has led tocommon concern in the engineering field. On the other hand, prestressed concrete structurebear static and frequent repeated loads in its service life, such as structure weight, vehicleload and random wave force, which will bring resistance of prestressed concrete structuregradually attenuated and the structure becomes function degradation or failure with thedamage accumulation.It is the urgent problem to evaluate and analize the durability of current and newprestressed concrete structure at present, around above-mentioned problems; on the basis ofthe above, The National Natural Science Foundation of China “The study on durability Testand life prediction of prestressed concrete structure under Two-indexes erosionenvironment” was produced, Through the prestressed concrete members in thefreeze-thawing and thawing and fatigue load under the action of alternating experimentalstudy of prestressed concrete members, analyzes the fatigue performance of prestressedconcrete member in the freeze-thawing environment,the main work and achievements arelisted as follows:1．Experiment studies were carried out through sixteen prestressed concrete members,discussing the change rule of specimen’s appearance shape, dynamic elastic modulus,mid-span deflection, strains of concrete and steel bar considering the effect of the concretestrength, degree of prestress, the ratio of alternating frequency of freeze-thawing and fatigue load.2．The attenuation rate of dynamic elastic modulus with the effect of the ratio of alternatingfrequency of freeze-thawing and fatigue load, maximum fatigue loads, degree of prestresswas studied through orthogonal test; it shows that there is centain interation interactioneffect among freeze-thawing and fatigue load in the degradation of dynamic elasticmodulus.3．Based on the fatigue damage accumulation theory and damage index of dynamic elasticmodulus, a new damage model was developed for freeze-thawing and fatigue load, it showsthat this damage is quite match with the experiment results.4．Analysis the specimen section stress after the freeze-thawing and load fatigue and thetheoretical value with the test value contrast5．The life prediction model were established based on the attenuation of dynamic modulusand the fatigue fracture of ordinary bar.This topic investigated the durability of prestressed concrete member under thefreeze-thawing and fatigue load,research results has high theoretical significance andpractical value for our country the north cold region has built and new construction offreeze-thawing environment of fatigue durability evaluation.