Study On The Reasonable Seismic System And Energy Dissipation Measures Of Low Pylon Cable-Stayed Bridge

Long span bridges represent transportation hub and lifeline engineering, and their failures under strong earthquakes may cause tremendous loss of human life and property. It is very important to guarantee the seismic safety of long span bridges by selecting reasonable structural systems and implementing energy-dissipation design.In this study, the seismic performance of low-pylon cable-stayed bridges with special reference to the Rongjiang Bridge with a main span of 380 m is studied. The main work is summarized as follows:1. A variety of theory ranging from proportional amplitude method to time-domain superposition method for generating seismic motion are introduced, and their advantages and disadvantages are compared. It was found that time-domain superposition method retains all the phase characteristics and the time-varying spectral characteristics of the actual acceleration records. In most cases, it is capable of reproducing the non-stationary property and natural integral relations of the original input motion record. It is a relatively accurate method for fitting the original motion.2. A narrow band time history inversion method based on the time domain superposition is proposed for the fitting of response spectra of seismic input. In this method, the relationship between a narrowband time history and the inverting input time history is derived by the steady-state response of single degree of freedom system in the frequency domain. The fitted spectra of artificial wave are found in good agreement with the target response spectrum. Five natural seismic waves, representative of the site condition of the Rongjiang cable-stayed bridge, are adjusted to have the same goal response spectrum, and they are used for the nonlinear time history seismic response analysis. This method can be used for reference of seismic design of similar bridges.3. After a review of energy dissipation mechanism of steel dampers, the author have designed the sliding bearings with steel damper and investigated its feasibility for its use on the general bridge to dissipation the seismic energy. The combined control scheme of the steel damper in series with velocity locking devices for dissipating the seismic energy were proposed and applied for seismic response mitigation of cable-stayed bridges. It is found that the steel damper has a good performance for the seismic energy dissipation on both the general bridges and cable-stayed bridges.4. In order to improve the effective stiffness of stay cables as well as reducing the axial forces in bridge girder of the low- pylon cable-stayed Rongjiang Bridge, the stay cables are arranged in quasi radial type and anchored at the top of the pylon. The concentrated anchorage within an overall steel anchor room is one of the technical innovation, and at the same time it reduce the fundamental period of longitudinal motion, which is helpful for seismic performance.5. A comparative study concerning the dynamic characteristics and seismic response of the pylon pier beam consolidation system(RS) and the semi floating system(FS) were carried out for the Rongjiang Bridge. Analysis results indicate that the seismic performance of the FS system outperforms RS system.And on the basis of seismic absorption mechanism of cable-stayed bridge, the vertical and transverse seismic response mitigation scheme of Rongjiang bridge is proposed. By the parameter sensitivity analysis, the optimal parameters for the longitudinal viscous damper, damper of steel and transverse steel damper are determined.6. The shaking table test of 1:20 scale whole model of Rongjiang bridge was conducted. Test results indicate that the energy dissipation system based on viscous dampers in the longitudinal direction, the steel damper in transverse direction can effectively reduce the displacement of the key points and the strain of key section. And with the increase of earthquake intensity, the shock absorption effect is more obvious.