Experimental Research On Prestress Loss And Mechanical Property Of Prestressed Concrete Beam After Freeze-thaw Cycles

Normally, concrete structures are subjected to various kinds of environment erosion, such as carbonization, freeze-thaw, corrosion, etc. Because of these effects concrete members are liable to deteriorate, which eventually make the whole structure nondurable. In cold regions of the North of China, freeze-thaw damage is reported to be the main effect that accounts for nondurable concrete structures. When freeze-thaw cycle is applied to prestressed concrete member. Prestress loss will happen. Then the crack resistance and bearing capacity will reduce gradually, which affect the durability of the whole structure. Thus, it is of great importance and applicable value to improve the design method through research on mechanical property of prestressed concrete structure after freeze-thaw cyclesCombined with the NSFC(Natural Science Foundation of China) project, uniaxial prestressed member and prestressed beam with prestress on one side were chose on the basis of previous research results.6uniaxial prestressed members which only subject to freeze-thaw cycles, and48prestressed beams which subject to static loading test after freeze-thaw cycles, were cast. The freeze-thaw effect on prestress loss and mechanical property of prestressed members were analyzed, and the results could provide basis for freeze-thaw durability research of prestressed structures.Based on the freeze-thaw effect on prestressed members, this paper had done work as follows:1.The freeze-thaw resistance of uniaxial prestressed members and prestressed beams of different concrete strength grade, different steel line shape and different bonding situation were investigated. Prestress losses of both were analyzed.2.A useful method of calculating the prestress loss was proposed based on the elastic modulus of concrete reducing after freeze-thaw cycles, and the theoretical results were compared with the actual results.3.Static loading test was applied to prestressed beams after freeze-thaw cycles. Factors, such as concrete strength, line shape of prestress steel, bonding situation, which affect the freeze-thaw resistance, were analyzed by using orthogonal experiment and intuitive analysis, and the optimal design scheme was presented.4.Based on the results of static loading test, the calculation methods of prestressed beam under service loads were analyzed, and a helpful method of computing the deformation of prestressed beam with curved prestress steel was suggested.5.Based on the change of stress-strain curve of concrete during freeze-thaw cycles, getting flatter every cycle, a method of calculating the ultimate bending load was proposed considering the decrease in strength and increase in plasticity of concrete. And the coefficient α1of concrete strength grade in common use under different freeze-thaw cycles was listed.Results show that line shape of prestress steel and concrete strength affect the freeze-thaw resistance most. High concrete strength, curved prestressed steel and grouting will make the beam resistant to freeze-thaw cycles. Results calculated by methods proposed in this paper coincide with the results got in experiments.