Research On The Design Of Anti Slide Between Main Cable And Saddle Of Three-Pylon Suspension Bridges

Because of the "middle tower effect", the requirements of driving comfort (ratio of deflection to span) and the anti-sliding safety of main cable are incompatible in the three-pylon suspension bridge, which makes the anti-sliding design of main cable and main saddle become one of the main design elements in the three-pylon suspension bridge. There are many factors that affect the anti-sliding safety of main cable such as the general layout, the stiffness of middle tower, the nominal friction coefficient of main cable and saddle, the size of dead loads and live loads, and the constraint systems of main girder, etc. Effects of these factors on anti-sliding safety of main cable need to be studied and analyzed more deeply.The research progresses of main mechanical properties of the three-pylon suspension bridge and anti-sliding safety of main cable were introduced briefly. Ignoring the stiffness of stiffening girder, horizontal component of tension of main cable, alignment of main cable, and tension of main cable can be calculated by using superposition principle under the most unfavorable loading mode of anti-sliding safety. And then the estimated formulas of the main cable anti-sliding safety factor was established. Good agreements between formula-results and FEM-results were found. The effects of main span, rise span ratio, stiffness of middle tower, dead loads and live loads on anti-sliding properties of the main cable were studied by the method.The friction behavior between main cable and saddle was analyzed by using the finite element method in the dissertation. Based on the large-scale finite element software ANSYS, the contact model of single strand and saddle groove was built. Through simulating single strand condition in the main cable and saddle friction model test, the relationship of cable force and displacement in the sliding process was obtained, and then the nominal friction coefficient between single strand and saddle groove could be calculated besed on FEM analysis.Taking an 800m main span three-pylon suspension bridge project as example, the constraint systems of main girder in the flexible tower scheme and rigid tower scheme were studied respectively. The anti-sliding safety coefficient of the main cable, the stress in the tower and girder, the displacement results of the stiffening girder which were caused by load under different constraint systems of main girder were compared. The advantages and disadvantages of various constraint system were analized. Based on that, researches on the three-pylon suspension bridge with inclined cable system and inclined vertical combination systems were conducted. The effects of constraint systems of main girder on the anti-sliding safety of main cable were researched under inclined cable system and inclined vertical combination system.