Studies On The Connection Mechanism Between Clamp And Suspension Bridge Main Cable And Anti-slip Analysis Method

Main cable clamps are important connection members used in suspension bridges.The clamps are tightened on the cable through pre-stressed bolt group to produce resistance.When the resistance is insufficient,the clamp will slip or separate from the cable,which is harmful to the connection safety.Once the clamp slipping happens in service period,it is difficult to repair.Currently,empirical equations to evaluate the friction resistance for the clips or clamps used in cable structural buildings or suspension bridges are provided by the Structural Eurocode 3 and the Chinese specifications of highway suspension bridge.In these equations,the friction resistance of the clamp is determined by the Coulomb friction law,however,the calculation of the contact compression force on the cable-clamp interface is unclear.This problem is associated with poor knowledge about the mechanism of the fastening connection between the relative rigid clamp and the main cable composed of discrete steel wires.In addition,particular transverse compressed behavior of the cable section under the clamping force increases uncertainty in clamp bolt group assembly as well as its pre-stress maintenance,due to the cross talk effect and the time dependent relaxation.At present,rare in-depth studies are reported about these issues.Therefore,a series of theoretical and experimental studies are made trying to search preliminary law about the fastening connection mechanism of the cable-clamp.Some novel models and methods aiming at better dealing with cable-clamp connection issues including resistance evaluation,bolt group assembly,cable internal pressure tests,and bolt relaxation prediction are proposed.The main research work is as follows:(1)Experimental research was made to observe the nonlinear transverse compression deformation of main cables with 0.6?1.3 m diameter under the clamping force.Logarithmic composite strain-stress function was fitted by the tests data to express the transverse stiffness of main cable.Then corresponding finite element modeling(FEM)method on the base of a nonlinear constitutive model of main cable was devised.That is used in subsequent numerical studies.A pressure sensor which is suit for internal pressure measurement for the main cable was invented.It is applied in a full-scaled model experimental test,and the internal pressure state of the cable under clamping force by the clamp was revealed.(2)Analytical clamp slip resistance formula was derived based on force equilibrium principal.The formula comprehensively considers the influence of clamp structural type(pinned connection and grooved connection),pre-tightening force by clamping bolt,hanger load,and orthotropic cable-clamp interface friction on the connection system.Then FEM analyses were also conducted.The FEM results and the analytical results reveal the same law:for the pinned connection clamp,added hanger load will decrease the compression force between the lower part of clamp and the cable,even lead to separation in the interface,which is unfavorable to the anti-slip of the clamp;while for the grooved connection clamp,added hanger load will increase compression force on hanger rope-clamp and cable-clamp interfaces,thus being favorable to the anti-slip of the clamp.(3)Experiment tests were carried out to study the slip resistance issue of the cable clamp.Based on the theoretical and experimental research work,a cable clamp anti-slip analysis method is proposed and it considers multi-factors which affect the connection system.Formulas which resolve critical residual bolt tension force or hanger load in specific anti-slip limit states are provided.(4)The cross talk(interaction)effect on the bolt group assembly for the cable clamp was studied through experiments and FEM analyses.The studies prove that the side-to-centre bolts tightening sequence is advisable.Furthermore,an optimization method,which is based on bolt over-tighten control and a FEM simulation program,is devised,trying to raise the certainty and efficiency of the bolt assembly for cable clamp.(5)Model experiment and in-suit experiment were carried out to study time-dependent bolt relaxation behavior of the cable clamp.For the full-scaled model experiment,the clamping bolt tension had been recorded for a year.The test data was used to establish a timedependent function and an axial creep function to portray and to predict the relaxation behavior of the bolt.The experiment in-directly proves that the long-term transverse compression creep deformation of the main cable is an important reason for the relaxation of the clamp bolt.