Study On Middle Towr Effect And Suitable Stiffness Of Double-cable Multi-pylon Suspension Bridge Based On Integral Saddle

As a new form of suspension bridge structure,double-cable suspension bridge has attracted wide attention in recent years.Compared with the traditional single-cable multi-tower suspension bridge,the structure stiffness has been greatly improved due to its special cable arrangement.However,the anti-slip safety of the main cable at the top of the middle main tower restricts the development of the structure.A new type of double-cable multi-tower suspension bridge with integral saddle is expected to solve the anti-slip safety problem of double-cable suspension bridge.Double-cable multi-tower suspension bridge is significantly different from traditional single-cable multi-tower suspension bridge in force.Based on the integral saddle,the "middle tower effect" of double-cable suspension bridge and the influence of main design parameters on structural stiffness and anti-sliding safety of main cable are studied by finite element method,which has theoretical and practical significance.The main research contents are as follows:(1)Based on the evaluation method of main cable anti-slip safety proposed from the point of view of structural resistance,a new limit value of main cable anti-slip safety factor is determined.This limit is a key control index,which paves the way for the next study on the reasonable value of main structural design parameters of double-cable multi-tower suspension bridge.(2)Taking a typical long-span highway suspension bridge as the background,the spatial finite element model of double-cable multi-tower suspension bridge is established.The "middle tower effect" of double-cable multi-tower suspension bridge with separated saddle and double-cable multi-tower suspension bridge with integral saddle is preliminarily discussed.The results show that when the sag difference between top and bottom cables is large,the structural stiffness is very large.At this time,the double-cable multi-tower suspension bridge don’t have the problem of "middle tower effect",but when the sag difference between the top and bottom cables is small,the structural stiffness is small,and the double-cable suspension bridge will show a certain "middle tower effect".The anti-slip safety of the main cables of the double-cable multi-tower suspension bridge with separated saddles is prominent,and the integral saddle mentioned in this thesis can effectively solve the anti-slip safety of the main cables in the double-cable suspension bridge.Double-cable multi-tower suspension bridge with integral saddle has broad application prospects.(3)Taking a double-cable multi-tower suspension bridge with integral saddle as the research object,the effects of the stiffness of tower,the dead load distribution ratio of the top and bottom cables and the rise-span ratio,on the structural stiffness and the sliding safety factor of the main cable are further analyzed.The new limit of anti-slip safety factor and the limit of deflection-span ratio of stiffened beams are used as key control indexes to study the reasonable selection of design parameters.