Study On Dynamic Problems For Self-anchored Cable-stayed Suspension Bridge

As a new type of bridge, self-anchored cable-stayed suspension bridge has not only some advantages of traditional cable-stayed suspension bridge, but also is more adaptive to being built in deeper sea and soft soil base owing to canceling giant anchor block, so is highly competitive under bad geologic conditions and has been adopted by engineering filed so far. However, there is little research on dynamic behavior for the type of bridge from the documents that have existed. Combined the scientific research question, i.e. the study on cable-stayed suspension bridge-which is scientific and technological item of Ministry of Communciation for traffic construction of west region with the engineering background of Dalian bay across sea bridge, some dynamic problems such as pile-soil-structure interaction, ductility analysis are investigated in this dissertation, the main research work covers the following aspects:(1) Based on Large-displacement Non-linear Elastic Generalized Variational Principle, coupling effect of axial and flexural action, shearing strain energy, torsional strain energy of stiffening girder being considered, the large-displacement incomplete generalized potential energy functional of space coupling free vibration of a three-span self-anchored cable-stayed suspension bridge is presented. By constraint variation, fundamental differential equations of vertical flexural vibration, lateral flexural vibration, longitudinal vibration and torisional vibration are formulated, also presented the equations for the main tower with respect to longitudinal and lateral vibration. The linear free vibration differential equation is obtained when the nonlinear items are discarded. In this paper, a self-anchored cable-stayed suspension bridge with the main of span 100m is an example for the analytic solution of frequency of vertical free vibration. Compared with numerical solution, the results inosculate well. This approach provides theoretical basis for analysis of natural vibration character of self-anchored cable-stayed suspension bridges.(2) The system's dynamic characteristics and seismic response based on rigid foundation is different from under pile-soil-structure interaction which mainly to extend nature vibration period, increases damping and changes internal forces and displacement. Consider the pile-soil interaction effects, pile groups model is established with actual length and equivalent embedded length separately, compared the seismic response result to the consolidation model from response spectrum and time-history analysis, the force and displacement response on controlling section of stiffening girder, main tower and piers were obtained and effect rules were discussed. Seismic response value of structure is close between the mode with actual length and equivalent embedded length by compared the results, therefore, pile foundation could be simulated by equivalent embedded length in place of actual length in engineering. (3) Considering geometric nonlinearity and material nonlinearity, the elastic-plastic time-history analysis had been done for self-anchored cable-stayed suspension bridge by using fiber model. Compared to the results of elastic time-history analysis showed that in elastic-plastic stage, the displacement of controlling node had a obviously increase because of the generation of plastic hinge, meanwhile, the internal force of controlling section were reduced significantly, for semi-floating self-anchored cable-stayed suspension bridge, the longitudinal displacement of controlling node may be increasing by generation of plastic hinge, mainly appeared on top of tower and main span of stiffening girder.(4) Based on the results of elastic-plastic analysis, introduced viscous-damper, Analysis of passive energy dissipation for structure had been done by considering boundary non-linear in elastic and elastic-plastic stage. Results showed that the force of controlling had slightly changing, but the longitudinal displacement of controlling node had obviously reduced by considering viscous-damper. The reason of this condition was that plastic hinge had dissipated some energy from earthquake input in elastic-plastic stage.(5) The lead-rubber bearing has favorable shearing property of rubber and damping characteristics of lead. From analyzing some plans with setting lead-rubber bearing among side pier, tower and stiffening girder showed that the displacement of controlling node and force of controlling section have been reduced, because of energy that inputted to superstructure decreased under earthquake.(6) The multi-level and multi-objective fuzzy optimization model of self-anchored cable-stayed suspension bridge selection is built based on fuzzy decision theory, which combines binary comparison method. The model coordinates the complex relationship among the factors, which are divided into several levels. Fuzzy method is adapted to calculate the weight vector, which can overcome the limitation of linear method. Base on the analysis of the model, energy dissipation by viscous-damper is the most suitable type for dynamic caculation.