The Analysis And Investigation Of Secondary Stress Of Suspension Bridge

The main cable, which known as the primary load-bearing component of suspension bridge, is set a higher safety factor to ensure the safety generally, without regarding the secondary stress of main cables. In fact, athough the single wire of main cables is very soft, when it is bypassesed saddle or boot-heel with a small curvature radius will also give rise to bending stress. As the main cable is a flexible structure, when it is loaded vertically or horizontally and with a large deformation, will cause the main cable strands loaded unevenly, and this nonuniformity is strengthened by clamps and wrapped around wire. In addition, the strands will be loaded unevenly because of the error of the main cable wire manufacture and erection, and the structural reasons of structure itself. The bending stress and the stress increment of uneven loaded wire stress above the average stress are taken as secondary stress in the thesis. Where the secondary stress is bigger like spaly-saddle, main-sanddle, the first segment of the main cable close wihe sanddles, boot-heel of AS construction and clamps are analyzed, mainly divided into the following aspects:1,The calculation methods and formula deduction of secondary stresses caused by the following reasons is introduced:the manufacture error of wire length, the erection error of wire length, the difference of elasticity modulus, the bending of saddles and boot-heel, the main cable angel change close with saddles, the main cable section change close with saddles, clamps local rotation, and the main cable curvature change. At the same time secondary stress combination of different locations is given.2,Each secondary stress of different locations of the suspension bridge main cable on the dead load or live load is analyzed. And the relation between span and each secondary stress is discussed.3,Xihoumen large bridge of two-span hanging stiffening girder is taken as the example to analyze the secondary stress changes of side-span and mian-span during the stiffening girder lifting process. A large bridge of main-span hanging stiffening girder is taken as the example to study the secondary stress changes when the stiffening girder is lifted from bridge towers to the mid-span, as well as from the mid-span to bridge towers.4,The probabilistic limit state design method is used to make up each stress of different locations of the suspension bridge main cable, and the combined results are studied to determine the safety reserve of the suspension bridge main cable while considering secondary stress.