Research On Fatigue Test Data Of Pre-stressed Concrete After Freeze-thawing Damage

The structures in part or in large areas subjected to different degrees of freeze-thaw damage in north China,especially those in the north cold region,almost are 100%.Frost heave cracking makes the concrete structures' the elastic modulus, compressive strength,tensile strength and other mechanical properties to serious decline.Part of the ordinary concrete structures,after ten years freeze-thaw damage, should not play a role.The pre-stressed concrete structure under normal circumstances,such as crane beam,highway and railway bridges,bear not only complicated and ever-changing natural environment,but also often repeated load and they will happen brittle fracture below the static load strength very likely.In recent years,post-tensioning pre-stressed concrete in structural engineering has been widely used,but particularly in the large size of the structure,its fatigue performances,which are under complex situations,has been relatively little research.Through the analysis of experimental data,this paper uses the fatigue reliability theory,statistics,injury mechanics,probability theory and some other theories and methods.Firstly,this paper combines domestic and foreign antifreeze properties of concrete as the foundation of a series of studies.Through the analysis of the relative dynamic elastic module's changes,it discusses the impacts of component freeze-thaw properties of different pre-stressed degree and different freeze-thawing times. Secondly,it systematically evaluates pre-stressed structure's fatigue working conditions and performance after freeze-thawing damage and also analyzes the freeze-thaw damage coefficient and the development statistically.From existing data and information,it uses the structural reliability analysis method,and set up the fatigue life prediction model of the pre-stressed structure after freeze-thaw damage, and the proposed formula for calculating reliability of real project.This paper considers that pre-stressed level and freeze-thawing cycles on the fatigue performance of pre-stressed concrete structures are obvious.Perhaps because of few freeze-thawing time,high concrete Strength and pre-stressed force,this test does not appear the relative DEM's substantial decline submitted by other documents. Fatigue life of pre-stressed concrete structures in the process of relative dynamic elastic modulus has roughly 2～3 stages.The first stage is the rapid growth phase.The second phase is the stable development stage and its process is about 80%of the whole time.The third stage for the moment is micro-damage phase of predictability. In the second stage,the relative dynamic elastic modulus exists linear relationship with fatigue cycles changes.Through DEM data measured by freeze-thaw test,we can see clearly that the low freeze-thawing time should not damage the pre-stressed structure significantly.In addition,if the freeze-thawing damage is taken as corrosion damage,we can make use of the existing theoretical analysis of the corrosion.From the influence coefficient model,Influence coefficient's power function relationship can be seen with the freeze-thawing frequency and pre-stressed degree and we can calculate the structure component's remaining fatigue life with the reliability after freeze-thawing times.We can found and boldly guess that the high pre-stressed components out of some extent are much easier affected by freeze-thawing effect than the low.The structure's fatigue data after low freeze-thawing times compared with the high number of freeze-thawing case,its reliability does not change significantly,because of pre-stress and high-performance concrete.Low frequency of freeze-thawing does not affect the structural reliability. However,if the components bear relatively higher freeze-thawing times,it can show obvious relationship of the three stages of curve.