Research On Fatigue Property Of Prestressed Concrete Beam In The Freeze-thaw Environment

The prestressed concrete structure has gradually become the mainstream structure in the building and transportation field since 1950 s.Because prestressed concrete bridge is an important link in transportation field,international scholars have paid attention to the durability of prestressed concrete structure.Bridge structure is exposed to nature chronically during the period of normal service,which is subjected to the continuing traffic cyclic loading,at the same time,which also inevitably is subjected to the external environment such as carbonation,chloride ion erosion and freezing and thawing multiple effects.The effects of freezing and thawing cycle have been confirmed as one of the important factors which effect the durability of bridge structure.So it is very necessary to study the durability degradation mechanism and fatigue characters under the condition of freezing and thawing cycle and traffic loading of the prestressed concrete bridge,at the same time,it is also the precondition to correct evaluation of health condition and residual fatigue life.Based on the freezing and thawing cycle test,fatigue loading experiment and analogue simulation,the change rule of fatigue properties of prestressed concrete beam under the action of freeze-thaw cycle is researched and analyzed.The main research contents are as follows:1.Experimental study on the static and dynamic properties of prestressed concrete beam under freeze-thaw cyclesAccording to the specification of concrete durability test,A new kind of test method of freezing thawing for large concrete structure component was put forward,the freeze-thaw experiment of prestressed concrete hollow beam and concrete specimens were carried out.Based on the apparent phenomenon,compressive strength,dynamic elastic modulus of the specimens were subjected to different number of freeze-thaw times(0,50,75,100 times),then we got the influence of freeze-thaw cycles on mechanical property.A static and dynamic experiment onprestressed concrete beam suffering different freeze-thaw cycles was carried out,based on the stress and displacement of static and dynamic experiment,the static and dynamic mechanics performance changes of the prestressed concrete beams under freeze-thaw cycles was studies.2.Experiment study on fatigue loading performance of prestressed concrete beam suffering different number of freeze-thaw cyclesThe loading test of these beams which subjected to different times of freeze-thaw cycles was implemented.The loading cycle was 500000 times,and a static and dynamic loading experiment were done once 500000 of fatigue loading cycles,then it continued,the deflection,strain,fundamental frequency and dynamic displacement were collected every time.By monitoring the change of fatigue performance and evaluating the deterioration degree of structure,the fatigue life prediction formulas of prestressed concrete beams under freeze-thaw cycle were built.3.Numerical simulation analysis of the mechanical property of prestressed concrete beam under freeze-thaw cyclesBased on the above research results,the beam models were built by the FEA which was produced by Midas company,and the mechanical property of prestressed concrete beam under freeze-thaw cycles was analyzed.The study on linear static performance changes and nonlinear fracture mainly to illustrate the attenuation law of mechanical performance of beams was performed.And then numerical simulation was compared with experiment,an analytical method of mechanical performance of prestressed concrete beam under freeze-thaw condition was put forward.