On Some Issues Of Construction Control And Seismic Response Of A Three-Tower Suspension Bridge

Recently, sea-crossing and river-crossing bridge engineering has become a hot topic, and suspension bridges with multi-towers and multi-spans seem to be more advantagious over other bridge types. Among the specific configurations of suspension bridge, the two-main-span suspension bridges are highly favored by bridge engineers. The three-tower suspension bridges can reduce the length of main span and the tension of main cable, and their overall performance is better than the twin-tower suspension bridges with the same span length.The first part of this paper discusses some issues of construction control of towers of a three-tower suspension bridge, and the second part addresses the free vibration and seismic responses of the suspension bridges under uniform support excitation and the impact of traveling-wave effect. The main work contains the following aspects:(1) Based on the forward calculation method, the entire process of the construction of the side tower is simulated to track the stress and deformation of the tower and temporary supporting structures. This serves as the basis for the design and construction of the tower and falsework which in turn ensure the intermediate state of construction state to meet the design specifications and the design requirments.(2) The finite element model of the suspension bridge is developed to analyze the characteristics of the free vibration of the three-tower suspension bridge. The first ten natural frequencies and mode shapes are analyzed and compared with those for the same type of suspension bridge.(3) Under uniform support excitation, three types of seismic waves are discussed in this thesis, which contain longitudinal wave plus vertical wave, lateral wave plus vertical wave and all three directions together. Then the characteristics of response of the briges to the seismic waves in all three directions are invesstigated. It is well shown that lateral stiffness of the girder is weaker than those in the longitudinal and vertical directions, and the internal forces of middle tower are from 2 to 3 times bigger than that of the side tower.(4) Finally, the impact of traveling-wave effect on seismic responses of the three-tower suspension bridge with the apparent velocity of 360m/s to 2160m/s is studied. It is found that the effect of the traveling-wave is highly dependent on the apparent velocity, and selection of the apparent velocity should be relevant to the site geological conditions.