Research On Longitudinal Tendon Layout Design For Prestressed Concrete Continuous Rigid Frame Bridges

The number of long-span continuous rigid frame bridges is increasing,but with the passage of time,the problems faced by long-span continuous rigid frame bridges are gradually emerging.Most of the long-span continuous rigid frame bridges at home and abroad have cracks in the main beam and a decline in structural stiffness during use,resulting in an increasing trend of mid-span deflection over time.In order to achieve a reasonable state of bridge completion under long-term deflection control of continuous rigid frame bridges,this paper focuses on a continuous rigid frame bridge on a certain expressway and takes the prestressed tendon layout design of the bridge as the research object,with the following research:(1)By reviewing existing literature and materials,the development history and future trends of prestressed concrete continuous rigid frame bridges are systematically summarized and analyzed.Typical diseases of current continuous rigid frame bridges are described,and the research status of domestic and international prestressed reinforcement design for these diseases is elucidated.(2)A calculation model of an unequal-span continuous rigid frame bridge is established using Midas/Civil,and the stress and deformation of the bridge under the maximum cantilever state before closure during the construction stage and the completed bridge state are analyzed.A method to reduce the long-term deflection of prestressed concrete continuous rigid frame bridges,i.e.,increasing the moment ratio,is derived.In addition,it is found that the contribution of the web tendons in the balanced moment is not as important as that of the top tendons,and their influence on the main beam’s bending resistance is relatively small.(3)The application of "constant load zero moment" in the configuration of top tendons is explained,and the influence of the tendon layout method based on "constant load zero moment" on internal forces and deflections is analyzed through a simple case.To ensure a good displacement state at the mid-span position,more external loads need to be balanced by the bottom tendons.Based on the load balance theory,the design principles and calculation formulas of the initial bottom tendons are determined.The feasible domain of prestress is determined according to the stress limit requirements of prestressed concrete specifications.(4)The longitudinal prestressed tendon layout design of prestressed concrete continuous rigid frame bridges is carried out using the tendon layout design method proposed in this paper.The tendon layout method is applied and a tendon layout program design is carried out based on Python,and the initial tendon layout results are finally checked.The Midas/Civil is used to compare the internal forces,deflections,and stresses with the original design,verifying that the tendon layout results basically meet the characteristics of a reasonable state.(5)An entity model of the zero block is established through Midas/FEA,and the stress distribution of the zero block under the maximum cantilever during the construction phase,the completed bridge state,the maximum negative moment,and the maximum shear force during the operation phase are obtained in the four working conditions.The results show that the zero block is in a state of compression under the four working conditions,and the stress state is reasonable.This further verifies the rationality of the tendon layout results.