Research On Calculation Theory Of Preflexed Combined Continuous Beam

Preflexed composite beam bridge is a new type of prestressed steel-concrete composite structure with mechanical properties between steel beam and prestressed concrete beam.This structure has broad application prospects,and is applicable to transportation fields such as urban roads,highway projects,and rail transit projects,as well as to civil fields such as port terminals,stations,underground buildings,and high-rise buildings.At present,the research theory and production practice of preflexed composite simply supported beam have been relatively mature,and an independent theoretical norm system has been formed.The industry-recommended standard of the Ministry of Housing and Urban-Rural Development has published “Technical standard for Preflexed composite beam bridges(CJJ/T 276-2018)”,which mainly edited by Southeast University and jointly edited by Jilin University,.In view of the fact that preflexed composite continuous beam in the specification has still research space.For this reason,the paper will carry out further research on preflexed composite continuous beam bridge.The main research work including the following aspects:(1)Based on the classical Dischinger equation method and the Tr?st-Bazant algebraic equation method,the physical equation between the deformation(or displacement)and the force,the static equilibrium equation,the geometrically compatible equations satisfying deformation conditions,and the boundary conditions were established.The calculation process of steel beam and concrete stress redistribution caused by shrinkage and creeping factors in preflexed composite beams was derived.Through comparative analysis,it is recommended to use the Tr?st-Bazant stress-strain algebraic equation elastic calculation method with the aging coefficient approximating 0.8 to solve the creep effect of preflexed composite beam.(2)The creeping secondary internal force of preflexed combined continuous beam is affected by the internal force redistribution of the composite beam,but the creeping secondary internal force changes the section internal force distribution.Using the Tr?st-Bazant stressstrain algebraic equation method and the flexibility method principle,preflexed combined continuous beam with the external constraint and the internal constraint.Remove the redundant constraint and establish the deformation coordination.The creeping secondary internal force of the second-stage concrete and the later period creeping of secondary internal force of the firststage concrete were solved.(3)According to the requirements of the lately issued “Technical standard for Preflexed composite beam bridges(CJJ/T 276-2018)”,the design and calculation methods for normal stress,shear stress,complex stress and ultimate flexural capacity,shear capacity of preflexed combined continuous beam were elaborated in detail in this paper.,aiming to give a practical calculation method which can be applied to the engineering design of preflexed combined continuous beam.(4)Other design problems for preflexed combined continuous beam,including the design of cracking moment of the second-stage concrete bridge deck and crack width in the negative moment region,the design points of the prestress in middle support,and the calculation method of the deflection(deformation)were explained,in order to provide theoretical basis for engineering construction.