Mechanical Mechanism of Pylon and Beam of Multi-pylon Cable-stayed Bridge with Asymmetric Crossed Cables
To improve the structural stiffness of multi-pylon cable-stayed bridges,the optimal arrangement strategy for crossed cable was proposed to enhance the contribution to structural stiffness.Based on the crossed cables'analytic expression of mid-pylon constraint stiffness,the relation between crossed cable longitudinal constraint stiffness and its anchorage position on deck was derived.It was found that when the height-span ratio of multi-pylon cable-stayed bridge was in the range of 0.2-0.3,and when the crossed cable anchorage located at about 0.7 times span-length from mid-pylon,its constraint stiffness to the mid-pylon was the largest.Based on this,the crossed cable asymmetric arrangement was proposed.To verify this theory,the finite element model of three-pylon cable-stayed bridge with crossed cables was constructed.The differences in pylon deformation,main girder deformation and structural stress state were compared and analyzed when the crossed cables were asymmetrically and symmetrically arranged.Under the live load,the mid-pylon top deflections were reduced by 19.92%and 33.99%,the main girder deflections were reduced by 10.02%and 12.60%,and the main girder maximum bending moments were reduced by 17.38%and 25.39%respectively.In addition,the mid-pylon bottom bending moment increased slightly when the crossed cable was arranged symmetrically;while the bending moment at pylon bottom was reduced by 18.23%when the crossed cable was arranged asymmetrically.The result indicates that the three-pylon cable-stayed bridge stiffness can be effectively increased by adding crossed cables to the main-span.The stress and deformation of main girder and pylon under live load can be improved.While maintaining the amount of cable system steel use unchanged,the crossed cable asymmetric arrangement is superior to the symmetrical arrangement in improving the structural stiffness.It provides a new optimization direction for the crossed cables design in multi-pylon cable-stayed bridges.
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