Flexural And Shear Behavior Of External Prestressed Concrete Segmental Girders

External prestressed precast concrete segmental girder(PCSG)was a representative bridge form due to its competitive construction technology of the Accelerated Bridge Construction(ABC).However,the discontinuity of the joints between concrete segments,slip and second-order effects of the external tendons resulted in the more complicated structural mechanical behaviors than the monolithic ones.Especially for the nonlinear loading states with open joints,the differences between them were more significant.Focused on the flexural and shear behavior of PCSGs,some work had been done by the author in the paper,including the resisting mechanism,numerical model,and simplified design methods for external prestressed PCSGs.The main work and results were concluded in the following,(1)In order to analyze the flexural behavior of externally prestressed PCSGs,an analytical model constisted of fiber beam and sliding cable element was proposed and the shear lag effect of box girder,slip and second-order effect of external tendons and discontinuous behavior of joints were all considered.The warping deformation of upper and lower flanges were introduced into the traditional fiber beam element to build the new fiber beam element for box girder with shear lag effects considered.According to the overall coordinated deformation mechanism of external tendons,a sliding cable element was built to describe the mechanical behavior of external tendons with arbitrary geometry types.Aiming at the discontinuous mechanical behavior of joints,a joint element simulation method based on modified concrete constitutive model was proposed.The FE formulas and methods were all integrated into the Open Sees framework as the newly developed elements and a convenient executable program was built for the flexural behavior analysis of external prestressed PCSGs.The effectiveness was fully verified for both the scaled specimens and full-scale bridges.(2)With the established program,the parameter study was done to discuss the primary factors and their influence regularities on the flexural performance of PCSGs.Based on the discovered patterns,the reasonable hypothesis of the deformation pattern and failure criterion of PCSGs under ultimate states were proposed.Then the equations for the traction increments and the effective height reduction of external tendons were built,and the simplified design approach for the flexural capacity prediction of PCSGs was proposed.(3)The static test on six specimens with hybrid prestressed tendons were conducted under combined bending and shear loads.The failure modes,load-deformation curves,ultimate capacities,and strain(for both concrete,steel,and tendons)were all recorded in the tests.The influence of the factors including the joints,shear-span ratio,and tendon arrangements on the shear behavior of PCSGs were compared and analyzed,and the shear mechanism was simply concluded.(4)The FE model with tendon-solid elements were developed and built in the ABAQUS software for the combined bending and shear behavior analysis of PCSGs.In the model,the combined axial-shear behavior of reinforced concrete element was simulated by the UMAT subroutine with the Rotated Angle Softened Truss Model(RASTM),and the external tendons were simulated by the UEL subroutine with the proposed slipping tendon element formulas,and the joints between segments were simulated by the equivalent cohere flat joint with the cohesive contact method.The proposed refined model applied to predicted the behavior of the specimens and the effectiveness was fully verified by comparisons of load-deformation curves and failure modes.The principal stress states under ultimate loading were analyzed with the established model and the Truss-Arch model was employed to discuss the shear mechanism of PCSGs in detail and the simplified calculating method was put forward.(5)Based on the previous study on the numerical model and resisting mechanism of PCSGs,the shear deformation was introduced into the previous flexural analysis model and an improved numerical model for both flexural and shear dominated behavior analysis of PCSGs was built.The FE formula was deduced based on the flexibility-based fiber beam element and programmed in the Open Sees framework as a newly developed element.The new element model was applied to predict the capacity and deformation of the specimens in this paper and beams reported in the literature,the results revealed the good agreements between the model and tests for both flexural and shear failure dominated specimens.