Analysis And Application Research Of Random Seismic Responses Of Large-Span Multi-Tower Cable-Stayed Bridge

For large estuary or valley terrain that is needed to build the construction of bridge engineering, the girder bridge or arch bridge structure is possibly difficult to meet the demand of crossing these places, in some speical circumstances even cable-stayed bridge and suspension bridge are difficult to cross the river or valley within one-span. In this background, the multi-tower cable-stayed bridge come into being and was gradually applied all around the world. Multi-tower cable-stayed bridge generally refers to the cable-stayed bridge with three main towers or more, two main spans or more. Due to existence of the middle tower, there has linkage between each cable plane and the main beam, which result in difference in the mechanical behavior between multi-tower cable-stayed bridge and two-tower cable-stayed bridge. With the development of society and economy, long-span multi-tower cable-stayed bridge gradually comes into people’s vision. For the multi-tower cable-stayed bridge with each span of over 400 meters, which has a number of five main towers or six more, structural response behavior of it under dynamic load is influencing engineer’focus. Regarding the choice of seismic analysis and calculation methods, random vibration analysis method has greater probabilistic statistical significance than conventional response spectrum analysis method and time history analysis method. So this dissertation use random vibration analysis method to analyze long-span multi-tower cable-stayed bridge’s seismic response. the rms of response has good representation in the sense of probability.Jiashao river-spanning bridge is a six-tower and four-cable-plane cable-stayed bridge, it has a single span of 428 meters, the full length of the bridge is 2680 meters, and it is the world’s longest cable-stayed bridge. In this dissertation, Jiashao river-spanning bridge is taken as the enginnering background, a random vibration analysis of long-span multi-tower cable-stayed bridge on seismic behavior was studied systematically, the main contents are as follows:Firstly the dissertation reviews the development of long-span multi-tower cable-stayed bridge in domestic and international engineering field, elaborates the existing seismic analysis methods of bridge structure. The second section selects the stationary and non-stationary random seismic power spectrum model to be used in the next work of long-span structure analysis. Based on the structural dynamics principle, the stationary random vibration’s conventional algorithms and pseudo excitation method and the theoretical formulas are derived.The basic dynamic characteristics of the long-span multi-tower cable-stayed bridge are researched in this dissertation, in which the differences are gived by comparing with two towers cable-stayed bridge. The forth section imports multi-dimensional multi-point stationary random seismic excitation to long-span multi-tower cable stayed bridge with the advanced kanai’s power spectrum which was proposed by Hu Yuxian and Zhou Xiyuan, the excitations include in one-dimensional and multi-dimensional consistent excitation, as well as inconsistent excitation that is considering seismic spatial characteristics, which involves travelling waves effect, coherency effect and local site effect. The results shows that long-span multi-tower cable-stayed bridge has strong spatial coupling characteristics, especially the vertical excitation’s coupling effects on longitudinal and lateral response can not be ignored; the influence roles of different spatial characteristcs to internal forces and displacements of the structure are various. Thereinto, the travelling wave effect on such a long-span structure with several supports is very obvious, spatial characteristics’influence on each tower is not all the same, it should be analyzed independently. In addition, this section researches the differences and similarities of response’role affected by seismic spatial characteristcs between two-tower cable-stayed bridge and multi-tower one, the results show that the role on two types bridges affected by these three characteriscs are consistent basically, but the degree of the effect is various.The fifth section derives the calculation process of the long-span multi-tower cable-stayed bridge under non-stationary random vibration, gives the formula expreesion of directly solving absolute displacement by large mass method, derives and explains the steps in the program to calculate non-stationary random seismic movement through the use of ANSYS apdl self programming to finish full transient analysis. The displacement and internal force of the key section of main girder and main tower are calculated under multi-dimensional multi-point non-stational excitation. The results show that the calculation results from stationary stochastic seismic calculations will be conservative by 10% to 30% comparing non-stationary stochastic seismic. Internal forces and displacements of Jiashao bridge’s crucial section are calculated under different site conditions, local site effect on responsing parameters of the structure is considered to have a same degree, comparing to stationary random excitation calculation results.In the sixth section the influence of the modulus of elasticity, rigidity of the hinge structure, the selection of power spectrum model, modal number, constraints between tower and beam for structural random seismic response of multi-tower cable-stayed bridge was researched. The results can provide a reference for the design and calculation of similar bridges.Last section calculates and analyzes dynamic reliability of jiashao river-spanning bridge, making use of the results of random sesmic analysis in previous section. The calculation method is checking point method. The result shows that dynamic reliability of jiashao river-spanning bridge is safe; the calculation method used in this section can provide reference for related calculation of homologous multi-tower cable-stayed bridge.