Research On Bearing Capacity Of Acid Rain Corrosion Prestressed Concrete Beam And Existing Prestress Test

Prestressed concrete structure is widely used in various engineering fields because of its good crack resistance and high stiffness.Prestressed concrete structures are prone to damage accumulation due to load,corrosion and fatigue during service,which leads to structural resistance attenuation.When the prestressed reinforcement of the prestressed concrete structure is corroded,it may lead to the sudden destruction of the prestressed structure without obvious symptoms,which threatens the service life and safety of the engineering structure,and even leads to serious engineering accidents.At present,there are relatively few studies on the influence of prestressed reinforcement corrosion on the durability of prestressed concrete structures in China and abroad.At the same time,since China has become one of the three major acid rain pollution areas in the world,acid rain corrosion will undoubtedly affect the strength of prestressed reinforcement,thereby affecting the bearing capacity of prestressed concrete.In addition,the loss of prestress will also lead to the decrease of bearing capacity of concrete beams,so it is necessary to measure the existing prestress of concrete structures.Therefore,in order to study these two aspects,this paper combines the characteristics of acid rain in Jiangxi Province,the effects of corrosion time on the failure mode,section strain,crack width,cracking moment and ultimate moment of prestressed concrete beams were analyzed by simulating acid rain environment,electric accelerated corrosion test,bending test and theoretical calculation of bearing capacity.In addition,the ring hole method is used to measure the existing prestress of prestressed concrete beams.The rules of drilling depth,strain and release rate are studied,and the factors affecting the accuracy of existing prestress test are analyzed.Results indicated that the ductility of the test beam is affected by the corrosion time,and decreases with the increase of corrosion time;When the corrosion time is long,due to the pitting stress concentration effect and section weakening effect of steel strand,When the corrosion time is long,due to the stress concentration effect of pit corrosion and the weakening effect of cross section on the steel strand,the ductility of the test beam decreases greatly,and the failure mode of the prestressed concrete beam changes from the initial ductile failure to the brittle failure without obvious signs.Before the cracking of the test beam,the neutral axis of the midspan section of the test beam moves upward,and the reinforcement is in the elastic stage.There is a good linear relationship between the concrete strain at different heights in the mid-span,indicating that the concrete section conforms to the plane section assumption.Within a certain range of corrosion,corrosion has no significant effect on the distribution area,number and width of cracks;When the corrosion time is longer,the crack width increases with the increase of corrosion time.The effect of corrosion time on the cracking moment of prestressed concrete beams is not significant,and the effect is within 7 %.With the passage of corrosion time,the ultimate bending moment of prestressed concrete beams decreases,and the trend is more obvious,compared with the uncorroded beam,the ultimate bending moment of accelerated corrosion 30 days and 45 days decreased by 13.2 %and 33.3 % respectively.Based on the bending test results of test beams and the design code for concrete structures,the calculation method of bearing capacity of corroded prestressed concrete beams was proposed with the section area and yield strength loss of prestressed reinforcement after corrosion as the variation parameters,and the calculation formula of bearing capacity of prestressed concrete beams under acid rain corrosion was established.The calculation results are compared with the existing experimental results to verify the accuracy of the calculation method.When the ring-hole method is used to measure the existing prestress,the release rate increases linearly with the increase of borehole depth.Take a drill with an inner diameter of100 mm for drilling,When the borehole depth exceeds 40 mm,the release rate increases;When the drilling depth is 50mm-60 mm,the stress is released completely.Therefore,under similar test conditions,50-60 mm can be used as the best hole depth to measure the existing prestress of prestressed concrete structure.The average error between the existing prestress calculated by the ring-hole method and the actual prestress of the steel strand is less than 9 %.It can be seen that the existing prestress of the prestressed concrete structure measured by this method has high accuracy.Vibration and heat generated by drilling and environmental temperature will affect the accuracy of existing prestress measurement.