Dynamic Characteristics And Seismic Performance Of Three-tower Suspension Bridges

With comparison to the common two-tower suspension bridge, the main spansof three-tower suspension bridge can be greatly shortened, which leads to significantreduction of the tension forces in cables, the size of anchorages and substructures, andfinally the overall cost, and therefore it becomes a competitive scheme for long andsuper long-span bridges. For three-tower suspension bridge, due to the lack of effectivelongitudinal restraint for the center tower, structural stiffness becomes less than that ofthe common two-tower suspension bridge, and it is considered to be a structural systemwith greater flexibility, and becomes more susceptible to the dynamic action. By takingthe first three-tower suspension bridge in the world with two main spans of1080m-theTaizhou Highway Bridge over the Yangtze River as example, structural dynamiccharacteristic and seismic performance are investigated by MIDAS/CIVIL, and themain work is described as follows.(1) Dynamic characteristics analysis of a three-tower suspension bridge isconduced, and the dynamic property is revealed. Through the analysis and comparisonwith the two-tower suspension bridge with the same main span, differences in dynamicproperty between the three-tower and two-tower suspension bridges are discussed.Finally, the influence of pile-soil interaction on dynamic characteristics is alsoinvestigated.(2) The seismic response of three-tower suspension bridge is analyzed by usingthe response spectrum method and the time history method, the seismic behavior andthe influence of different methods on seismic response analysis are discussed. Theinfluence of pile-soil interaction on seismic response of three-tower suspension bridge is investigated,.and also the difference in seismic property between three-towersuspension bridge and two-tower suspension bridge is revealed.(3) The effects of structural parameters on the dynamic characteristics andseismic response of three-tower suspension bridge are investigated, such as therise-span ratio of main cables, structural stiffness of the center tower, the central buckleand elastic cable etc, and then the key structural parameters and also their favorablevalues are presented.The results show that:(1) three-tower suspension bridge and two-towersuspension bridge have similar dynamic characteristics, the pile-soil interaction haslittle influence on the dynamic characteristics;(2) structural response of three-towersuspension bridge under the transverse earthquake action is remarkable, due to lessstructural stiffness, structural nonlinearity is consequently remarkable, and therefore thenonlinear time-history method should be used to predict accurately structural seismicproperty of three-tower suspension bridge. The pile-soil interaction has little effect onthe seismic response of three-tower suspension bridge.(3) good seismic performancefor three-tower suspension bridges can be achieved by selecting favorable rise-spanratio of main cables, using the center tower with less structural rigidity and setting thecentral buckles between the main cables and the stiffening girder and also the elasticcables between the center tower and the stiffening girder.