Study On The Three Dimensional Creep Stress On The Contact Surface Of Twice-prestressed Composite Beam

As a new style of structure, twice-prestressed composite beam is one of the newstructures that the prestressed concrete technique used in the bridge structure. Thebridge used in high-speed railway have the high requirement of deformation control,ordinary prestressed concrete became of no advantage. Because of the goodperformance in crack resistance property and deformation control property, thetwice-prestressed composite beam is worth to be populared in high-speed railway.Due to the particular construction technology, the two part of concrete in thetwice-prestressed composite beam have different dead load and concrete age. Thisdifference will make the creep deformation of longitudinal fibers different. The creepdeformation of longitudinal fibers in the twice-prestressed composite beam restrictsinteractionally, this cause stress which is called stress redistribution caused byeffects of creep. In this paper, we calculate the twice-prestressed composite beam’sstress redistribution caused by effects of creep, by using the liner creep theory andaging theory as well as the the curvature changes compatibility condition, accordingto the internal force equilibrium conditions. The strain increment and the curvatureincrement also could be calculated then. By using the curve fitting theory,twice-prestressed composite beam’s creep camber formula could be obtained. Bycomparing with the experimental result, we can know the formula used to calculatethe twice-prestressed composite beam’s creep camber is feasible. By comparing theresult of the twice-prestressed composite beam and ordinary concrete beam, we canknow that the twice-prestressed composite beam could reduce the creep camber.External loads and effects of creep can cause the stress on the contact surface.Method for calculating the stress on the contact surface is composed of two: the finiteelement method and energy method. In this paper, we can take the age-adjustedmodulus replace the modulus of concrete, take the equivalent load replace the effectsof creep. Based on ANSYS, the finite element method using plane42(2D unit) andSolid65(3D unit) can calculate the contact surface creep stress. By comparing theresults, can we find that the development trend of stress and the calculation results arebasically the same. Stress on the contact surface caused by effects of creep distributeat the end part of the twice-prestressed composite beam. The main parameters ofinfection could be discussed as follows: the stress of contact surface increasing as the first step prestressing force went up, as the precast beam’s loading concrete agedecreased, as the distance between the first step prestressing force tensioning andfield-cast beam casting reduced, as annual mean humidity fell, as concrete gradediminished, as the concrete age of the second step prestressing diminished. At lastusing quadratic polynomial describe the creep stress on the contact surface, accordingto minimum excess principle, basing on the deformation compatibility, the stress onthe contact surface could be calculated.