Study On Stress Behavior Of Unbonded Partially Prestressed Concrete Beams With HRB600 Bars

When the rebar graded HRB600 is used in the bridge structure as the tensile non-prestressed steels,it can effectively improve the bearing capacity and durability of the beam and will make significant economic benefits, so it will be the development trend of the bridge structure. At present, the test research of unbonded partially prestressed concrete beam with HRB600 steel bars is still belong to blank, so it is necessary for us to make systematic study in order to expand its scope of application.In this paper, five unbounded partially prestressed concrete beams are tested in order to fully understand the effect of prestress degree and Steel strength grade. Then we analyze the beams cracks, stiffness and deformation, the normal section carack resistance property, the ultimate flexural capacity, ductility, recovery performance and prestressed reinforcement limit stress increment.The results show that: HRB600 rebar can effectively improve the beams ultimate flexural properties, recovery performance, utilization rate of the prestressed steel and reduce the ductility of the test beam, but it has little effect on the normal section crack resistance property and deflection. Enhancing the prestress degree can effectively improve the beams normal section crack resistance property, ultimate flexural properties, stiffness, recovery performance and reduce the ductility, utilization rate of the prestressed steel, therefore, we must limit the prestress degree in order to improve utilization rate of the prestressed steel. When HRB600 rebar is used in the unbonded partially prestressed bridge component, its cracking load, ultimate flexural capacity, stiffness after cracking should use JTG D62-2004 given calculation formula to calculate, but for the average crack spacing, stiffness before cracking, we recommend using GB50010-2010 to calculate. Based on test data, we get the stress increment and deflection’s fitting formula which is different before cracking and after cracking,finally we recommend the HRB600 steel bar’s yield strength to take 500 MPa.