Nonlinearity And Reliability Of Long Span Cable-stayed Bridge

In the recent decades,cable-stayed bridges have become one of the most popular types of bridges,as the provide an economical solution for medium to long span bridges and possess excellent structural characteristics and aesthetic appearance.As the bridge span increases,the high strength material have been used and the bridge becomes more flexible and ,as result,more susceptible to nonlinear behavior. Geometrically nonlinear behavior, load-carrying capacity and reliability analysis of cable-stayed bridges are the subjects of this study.The sources of geometric nonlinearity are cable sag effect,axial force-bending moment interaction in the bridge deck and in pylons,and large displacement effect.CR formulation is discussed intensively which can remove the restriction of small rolations and accumulative error accomplished by using CR coordinate to eliminate the rigid body motion accurately and computing the internal forces based on the total equilibrium condition but not on incremental equilibrium condition of the problem.The precision and efficiency of CR formulation is very high.Flexibility-based fiber-model beam-column elements takes the postulate of element section force field as starting point of element to be built.For Beam-columns depending mainly on axial and bending deformations,the postulate usually is able to obtain exact satisfaction and not influenced by nonlinear behavior of element.Even to strong nonlinear problem that elements have come into soften phase later,element interior equilibrium condition is still able to get exact satisfaction.An essential ingredient in finite element reliability analysis is accurate, consistent and efficiently computed response sensitivities. Using the direct differentiation method, a unified formulation of finite element response sensitivities with respect to material, load and shape parameters is developed and implemented. The first-order reliability method are used for computing probabilities for structure.These analytical methods is Incorporated into a computer programe BSNAS. Tower and deck segments are modeled with muti-slice fiber beam-column elements base on flexibility method.A shallow cable element appropriate for modeling cable-stays .Nonlinear material constitutive models are used for concrete,reinforcing steel,prestressing steel and cable-stay steel.Reinforce creep models are used for concrete.Nonlinear geometric effects include in all structural element.The developed programe can trace the response of segmentally erected reinforce and prestressed concrete cable stayed bridges due to either immediate or sustained loads;the analysis incorporates the effects of both material and geometric nonlinearity.,temperature effects ;The response of concrete structures can be tracked both before and after cracking,throught the inelastic range and past the peak resistance throught strain softening behavior;The programe can also analy reliability of structure.All of above-mentioned theories,methods and programes were synthesized to apply to the nonlinear analysis and reliability analysis of two cable-stayed bridges:one is Fourth Bridge across the HanJiang river in WuHan,the others is the BaDong Bridge across Yangtse River.The result show that the research of this dissertation can be as a guide for the design,the construction and the safety evaluation of cable-stayed bridges.