Study On Reasonable Structural System And Wind Resistance Performance Of Three-tower Suspension Bridge With Unequal-length Main Spans

Multi-tower suspension bridges have extraordinary spanning capacity and excellent economy.Several multi-tower suspension bridges with equal-length main spans have been built in China.If unequal-length main spans are adopted,this bridge type will have better terrain adaptability and wider application scope.Due to the loss of symmetry,the reasonable structural system and wind resistance performance of multi-tower suspension bridge with unequal-length main spans are different from those of multi-tower suspension bridges with equal-length main spans.In this paper,a three-tower suspension bridge with unequal-length main spans is taken as the research object,and the following prospective works are carried out by employing theoretical analysis and numerical simulation methods:(1)Based on the theory of segmented catenary,the shape finding of main cable of three-tower suspension bridge with unequal-length main spans is studied.According to the principle that the length of the shortest suspender in the main span is equal to that in the secondary main span,the tower top elevation of the secondary main span side tower is determined,The thermal effect on the main cable shape,tower displacement and the rotating momentum of splay saddle is calculated.(2)By calculating the main cable shape under live load,combined with the two conditions of "limit value of deflection to span ratio" and "limit value of anti-sliding between main cable and saddle",the analytic formula of reasonable stiffness interval of central tower is derived.The influences of dead to live load ratio and friction coefficient between main cable and saddle on reasonable stiffness interval of central tower are studied.(3)Based on the method of segmented catenary,the analytical algorithm of main cable shape in three states of double-cable suspension bridge(completed bridge state,live load action and free cable state)is derived.Meanwhile,the key construction parameters are obtained,such as the saddle pre-offset and the installation positions of the cable clamps.Finally,the influence of bridge tower stiffness on live load effect of three-tower double-cable suspension bridge and the longitudinal restraint effect of double cables on the central tower are analyzed.(4)Based on the theory of equivalent elastic support,the model of three-tower suspension bridge is simplified to two-tower suspension bridge.Based on the theory of equivalent simply supported beam,the analytical algorithm of gravity stiffness of three-tower suspension bridge is derived considering the central tower stiffness.The influence of rise span ratio,central tower stiffness and cross sectional area of main cable on gravity stiffness is analyzed and verified by the finite element method.(5)Based on the finite element method,the wind-resistance performance of three-tower suspension bridge with unequal-length main spans is studied.The critical wind speed and instability mode of aerostatic stability are calculated by the incremental double iteration method,with optimum iteration.The critical flutter wind speed and the flutter mode are calculated by the full mode method.The wind-resistance performance of the bridge is compared with that of the three-tower suspension bridge with equal-length main spans.