Effect Of Freezing Thawing And Corrosion On The Bearing Capacity Of Unbonded Prestressed Beams

In some high humidity and plateau area of our country,because the cold area and air humidity,the reinforced concrete structure often subjected to freezing and thawing and erosion corrosion,resulting in serious adverse phenomenon to many buildings,concrete peeling,bare steel and corrosion etc,the serviceability limit state and carrying capacity limit state of a considerable part of the building are greatly reduced,serious performance deterioration,even had to retire early.At present,the research of prestressed structure under the influence of freeze-thaw cycle and steel strand corrosion is still blank.In this paper,combined with the mountain bridge and tunnel engineering state key laboratory cultivation base(Chongqing Jiaotong University)Open Foundation funded project“consideration of environmental conditions damage in the mountainous area PC bridge structural performance cracking research(project number: CQSLBF-Y14-13)”,through development of freezing and thawing circulation and corrosion of steel strand coupling effect of unbonded prestressed concrete component test,to explore the deterioration law of unbonded prestressed concrete beam flexural behavior.The main research contents are as follows:(1)Fast corrosion test for different corrosion rate of steel wire was carried out,as well as static tensile test.The relationship between the mass loss rate,nominal ultimate strength,yield strength,elastic modulus and corrosion rate of steel wires under various corrosion rate conditions was obtained.The tensile failure mechanism of corroded steel strand was revealed.It provides the basis and reference for the calculation of the load bearing capacity of the prestressed concrete beam with steel strand under the condition of corrosion.(2)The rapid freeze-thaw cycle test of the unbonded prestressed beams under different freeze-thaw cycles was carried out,and the compressive strength test and the elastic modulus test were carried out.The mass loss of concrete freeze-thaw cycles under rate,compressive strength and elastic modulus and the relationship between freeze-thaw cycles were obtained,and the corresponding function relationship establishment.Reveals the deterioration of mechanical properties of concrete after freeze-thaw cycles.It provides the basis and reference for the calculation of the bearing capacity of the non bonded prestressed concrete beam under the condition of freezing and thawing cycles.(3)The freeze-thaw cycle test and the steel strand corrosion test of the non bonded prestressed concrete beam are carried out,and the coupling experiment of the two party was carried out.Compared with the steel strand corrosion and freeze-thaw cycle,the prestress loss of prestressed steel strand.The results show that the prestress loss caused by the non bonding prestressed beam is larger than that of the steel strand corrosion and the freezing and thawing cycles,respectively,which are produced under the coupling condition of the two party.(4)Flexural loading test of prestressed concrete beams under different test conditions was carried out.Get the following results:First,the corrosion of the steel strand can cause the failure characteristics of the prestressed beam with few tendons,and the freeze-thaw cycle can cause the failure characteristics of the non bonded prestressed beams.Second,the size of the corrosion rate of steel strand is very large,but the number of freeze-thaw cycles has little influence on the deflection of the beam.Third,the crack height of non bonded prestressed concrete beams with different corrosion rate and freeze-thaw cycles increased with the increase of load,and the development speed of the crack appeared in the early stage,and then slowed down.Fourth,the calculation formula of the bearing capacity of the non bonding prestressed beam is only affected by the corrosion rate under the condition of the corrosion of the steel strand;Fifth,unbonded prestressed beams only in the freeze-thaw cycle under the condition of bearing capacity of freezing and thawing cycles of formula;Sixth,the bearing capacity calculation formula of the influence of the corrosion rate and the number of freeze-thaw cycles of the non bonded prestressed beams under the condition of freeze-thaw and corrosion.At the same time,the relative magnitude of the influence of the steel strand corrosion and freeze-thaw cycles on the bearing capacity of the non bonded prestressed beams is compared.