Study On Secondary Stress Of Cable In Suspension Brage Based On The Theary Of Layering Slip

As the span of suspension bridge gets longer and longer,people in China have constructed numerous suspension bridge with larger and larger cable stay,which is made up with thousands of independent parallel wire strand.Cable has suffered the dead-load and traffic-load,and each of the wires are contacted together randomly.The partial bending of the cable will be caused by the error of wire production,the rotation of the saddle and the pressure caused by the clamp,and it can be the possibility of causing higher secondary-stress in cable.Under the small load of rotation and axis stress of cable,we take cable as a whole to calculate its bending stress.As the rotation of cable gets higher and higher,there will be tremendous shear for the secion.If the shear force is higher than the maximun shear resistance,there will be the layer slipped of cable at the secion.Taking the parallel steel wires of the main cable of the suspension bridge as the research object,the thesis considering the slip between nearby cable layers,carries out the research deeply in the cable bending stress.The main researching content,methods and results are as follows:After tighten of the clamp,the rate of gap inside the cable will decrease dramatically,wires in outer layer will cause apparent bending stress.As for the cable model of tightening clamp,firstly based on the tested data,we fit a curve to describe the material named MELAS with non-liner feature in stiffness.We design a finite element model with the tighten of clampcable to calculate the radial stiffness of the cable.Considering the anisotropy and nonlinearity of the main cable,we establish the hoop layered model of the main cable,it is possible to study the distribution of compressive stress of the main cable at the outlet of the cable clamp after the clamp is tightened.Finally the formula of the secondary stress in cable is comes out,comparing it to the measured data could verify the feasibility of the measure.The slip between the wires could destroy the intergrity of the cable,that will make the section assumption unbelievable and cause a much smaller bending stress.Based on the cablestrand-wire layered slip model,through the segment differential equation,taking the friction between the layers into account,the calculation formula of the ultimate shear stress of the cross-section is calculated.It could be the judgment of whether the laminated beam has slipped.The main cable rotation angle is applied gradually,and we calculate the shear force distribution of the main cable section with the aid of the transfer matrix method and MATLAB.The physical properties of the section would be modified if the shear force overs the shear resistance,and then we iterate over state of the main cable slip and secondary stress distribution.Combined with the actual bridge test on site,the layered slip model of the cable was established at the same time,which takes the bending characteristics of the cable strands and the axial force into considerration,thus the rationality of the layered slip modulus was verified.Based on the ANSYS with the contact of clamp-cable to emulate the tighten of clamp,the analysis shows that the change of porosity is in good agreement with the measured data,which can reflect the radial stiffness of the main cable more reasonably.At the same time,based on the layered cable model,the axial and radial stiffness of the main cable can be taken into account.Thus the radial displacement of the cable clamp outlet along the axial direction could be calculated,and then the secondary stress calculation formula is compared with the measured one.After the main cable section produces layered slip,its section moment will decrease sharply.Based on the layered slip theory,the secondary stress calculation method is compared with measured values in site,that verifies the rationality of its theoretical methods.