Research On Fatigue Bahavior In Normal Section Of P.P.C Beam With Mixed Reinforcement

In recent years, the mixed reinforcement partially prestressed concrete (P.P.C) has been widely used in the engineering structure, especially in great size structures. However, the fatigue problem of P.P.C flexural members with mixed reinforcement is more prominent due to its special reinforcement details and mechanical behavior in comparison with conventional reinforced or prestressed concrete members.In this paper, fatigue failure pattern of flexural member is analyzed by experimental research on fatigue behavior of P.P.C beams with mixed reinforcement. Fatigue strength, reinforcement stress,crack width and fatigue deformation are mainly addressed.First of all, the horizontal section assumption is feasible according to experimental results and deformation modulus calculation formula is put forward. The two types of steel bar stress growths is not synchronous, the normal stress of reinforcement grows much faster. The calculation formula of two types of steel bar in beams was deducted by reinforcement stress analysis. Upon the observation of experimental courses and the analyses of experimental results, steel bar rupture is a mainly cause of beam destruction. The fatigue strength calculation formula is set up according to stress range and stress ratio, of which compared with the fatigue strength in the air.Then recommended values in fatigue strength design of ordinary steel bar are proposed.Secondly, the cracks development of P.P.C beams under fatigue loads is analyzed on the basis of thses experimental results, and the influencing factors are discussed . Then argument cause of crack width under fatigue loads is investigated, fatigue crack calculation method based crack width under static loads and concrete strain in the compression zone is mainly discussed under fatigue loads. The calculation formula is also set up by the initial crack width and smagnified coefficent ,which is available through regression analysis to experiment data, and the calculated values fit favorably with the test results.Finally, the deformation rule of P.P.C beams under fatigue loads is analyzed according to experimental results. Then, the calculation methods of residual deflection and loading deflection are discussed. The calculation formula of the total deflection is obtained.