Study on Structural Stiffness of Three-pylon PC Cable-stayed Bridge with Large Sidespan-to-Midspan Ratio and Without Auxiliary Pier
To solve the low structural stiffness of three-pylon PC cable-stayed bridge with large sidespan-to-midspan ratio and without auxiliary pier,the Xijiang Grand Bridge was taken as the study background,5 commonly used methods(i.e.,setting auxiliary piers,optimizing structural systems,increasing cable pylons'height,increasing stiffness of main beams and stay cables,and stiffening cable systems)were selected to improve the structural stiffness of three-pylon cable-stayed bridge.Based on the parameter sensitivity analysis,the measures for improving structural stiffness were selected according to the factors of flood control,navigation,ship collision and old bridge position.The result indicates that setting an auxiliary pier at sidespan significantly improves the structural stiffness and stress;however,the installation of auxiliary piers on sidespan is affected by the factors of Xijiang embankment alignment,the alignment of new and old bridge piers,and the water resistance ratio.Therefore,it is not recommended to use auxiliary pier schemes to improve the bridge stiffness.The installation of auxiliary cables on both sides of central pylon does not significantly improve the deflection and stress of the sidespan main beam;however,setting auxiliary cables on both sides of side pylon significantly improves the deflection and stress of the main beam.Combining with middle pylon consolidation and side pylon semi-floating constraint system can effectively suppress the pylon top deflection,reduce the bending moment effect at the cable pylon root,and improve the structural stiffness.The consolidation of central pylon also improves the favorable conditions for the cantilever pouring construction of main beam.Increasing the height of cable pylon can only reduce the main beam deflection,and has limited influence on the main beam stress.Simultaneously,increasing the pylon height will bring a rapid increase in costs,and increase the construction difficulty.It is recommended not to adopt the scheme of increasing pylon height.The use of DP section with flange plates is more reasonable in terms of stress than a conventional DP section.It can effectively improve the overall stiffness of cable-stayed bridge with a lower cost.Therefore,it is recommended to adopt the scheme of setting two pairs of auxiliary cables on both sides of side pylon,DP section main beam with flange plates,middle pylon consolidation,and side pylon semi-floating constraint system.
bridge engineeringwithout auxiliary pierlarge sidespan-to-midspan ratiothree-pylon PC cable-stayed bridgestructural stiffness
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