Study Of The Corrosion Damage Performance Of Unbonded Prestressed Concrete Beam

Unbonded prestressed concrete structure is an important compo-nent part of prestressed concrete structures. As the unbonded prestressed concrete structure has a lot of good mechanical properties, simple construction and so on, which has been widely used in engineering construction. Compared with the prestressed concrete structures, the unbonded prestressed concrete structures are more prone to corrosion damage, which lead to structural durability failure, and the use of structural safety hazards. Since the research on the issue of domestic and still in its infancy, so this paper mechanical properties of unbonded prestressed concrete corrosion occurs after injury has been explored, the research results will provide important reference value for the bridge structure durability design and assessment of complex environments, the main contents are as follows:①Through the static tensile test, the static behavior of corroded strand is studied.The results show that the mechanical properties of the corroded strand are deteriorated,the plastic property, the elongation, the nominal ultimate strength and the nominal elastic modulus decrease with the corrosion rate increased and attenuation. Based on statistics analysis of experimental data, a constitutive relation of corroded strand were established in monaxial tensile tests. In this paper, the fracture criterion of corroded wire is put forward for the corrosion test. The reliability of strand wire was analyzed based on the corroded strand cross section, and the failure probability density function of strand was obtained.② After considering the relevant factors reasonably, a series of unbonded pre-stressed concrete beams for the corrosion damage research are designed. The effect of the corrosion damage on the static behavior of the beams is studied by the static loading tests of the same group of beams. The static test results showed that the failure mode of the unbonded prestressed concrete beams with corroded strand is gradually over to the brittle state from the ductile state, The cracking load and the ultimate load of the test beam gradually decrease with the increase of corrosion rate, and the amplitude of the ultimate load decreases more significantly, the load deflection curves of the beams under different corrosion rates are different, and the index of curve turning point decreased with the increase of corrosion rate.Under the action of the external load, the corrosion has no obviously effect on the stress increment of unbonded prestressed tendons before the test beam arises the crack. But after cracking of the beams,thecorrosion has some effect on the stress increment of the unbonded prestressed tendons,under the same load, the stress increment increases with the corrosion rate. The crack width, height and the average spacing of the same group of test beams increases with the corrosion rate.③ According to the test results,mechanical performance of partial unbond prestressed concrete beams with corroded strand are analyzed. After considering the corrosion factor, the calculation formula of cracking load,ultimate load, deflection and short term stiffness after cracking is established.By comparing the theoretical values with the test values, the calculation formula of the difference of the ultimate load is modified, and the modified results are in accord with the actual values.