Research On Inelastic Performance Of Upt Continuous Beams Under Cyclic Loading

So far,many researches on mechanical behavior,failure mode and design method of UPT beams under monotonic load have been carried out.However,relatively few studies on inelastic performance of continuous beams were made.Due to the complexity of friction of unbonded tendons from indeterminate structure,it is necessary to do further research and analysis on inelastic performance of UPT continuous beams.The experimental study on inelastic performance of UPT continuous beams under cyclic loading is carried out,by using three types of strands as unbonded tendons and the steel bar of HRB400 as non prestressing reinforcement.Several failure modes and crack development are summarized.Based on the basic parameters of reinforcement index and with or without anti-corrosive grease,the recovery capability is analyzed by residual deformation.The curvature ductility factor which can be expressed as the ratio of ultimate curvature and the curvature while non-prestressed tensile longitudinal reinforcement yielding,and the energy ductility factor which can be expressed as the ratio of ultimate deformation energy and the deformation energy while non-prestressed tensile longitudinal reinforcement yielding both decrease with the increase of reinforcement index.Low reinforcement index is advantageous to improve the ductility of prestressed concrete beams with unbonded strand of large diameter,and improve the rotation capacity of plastic hinge.Beams with anti-corrosive grease have better ductility than those without anti-corrosive grease.Therefore,not only can the anti-corrosive grease protects unbonded strands from corrosion,but also enhance the ductility of test beams.Through analyzing the viscous damping coefficients and the curve between energy consumption and deformation,it is concluded that the anti-corrosive can provide more energy consumption capability.The differential equation on the motion of unbonded tendons is derived and solved.An energy consumption calculation method of the relative movement of tendons is established.Based on the bearing capacity equation of the normal section,the formula of the ultimate stress of the unbonded tendon with the basic parameters of reinforcement index and prestressing reinforcement index is derived and relative coefficients are determined according to the results.