Analytical And Experimental Research On Three-Dimensionally Isolated Bridge

Characteristics of near-fault earthquake different from far-filed seismic motions and its effects on engineering structures are present research focus. Vertical earthquake is prominent in high intensity and near-fault regions, so vertical seismic motions and its effects on engineering structures attract many scholars'attention. Bridge isolation based on horizontal isolation technology provides an effective approach to improve seismic performance of bridge, but present horizontal isolation technology is invalid for vertical isolation problem. Vertical or three-dimensional (3D) isolation technology will be a promising trend for the vertical vibration sensitive structures. But, substantial progress on development and implementation of 3D isolation technology was not achieved by now at home and abroad. Theory and experiment research are performed on characteristic of near-fault horizontal and vertical seismic motions, 3D seismic responses, 3D isolator and its isolation effect, analysis and design methodology of bridge engineering. the main research of this dissertation are as follows:1. Abundant earthquake records including quite a number of near-fault seismic records are collected; an attenuation model of peak ground acceleration considering magnitude and distance-to-fault is proposed and compared with other models. The influence of distance-to-fault, site condition, magnitude and fault rupture mechanism on vertical-to-horizontal spectral ratio are investigated. Seismic records in Wenchuan earthquake released recently are adopted to analyze the peak ground acceleration attenuation character and response spectrum, the influence of spatial distribution of seismic motions on building damage in Dujiangyan city is discussed. Anlysis results indicate that the proposed model can reflect the attenuation relation of seismic motions, vertical-to-horizontal spectral ratio is remarkably affected by distance-to-fault, spectral period, site condition and fault rupture mechanism.2. Dynamic characteristic analysis is carried out for large-span cable-stayed bridge, several group of strong earthquake records with different seismic property are adopted for dynamic time history analysis to investigate the influence of near-fault three-dimensional seismic motions on seismic responses of these bridges. Analysis results show that near-fault seismic motions will impose obvious effect on large-span flexible bridges. 3. An invention of three-dimensional isolation bearing is proposed, design method of constructional design and mechanics parameters are also introduced. Mechanics property experiments are carried out on every main part and holistic device of the 3D isolator. Numerical simulation analysis of lumped mass-single pier model is applied to validate horizontal and vertical isolation effectiveness of the 3D isolation bearing. Experimental and analytical results indicate that the proposed 3D isolator possess reasonable structure and explicit force-transmission mechanism and appropriate 3D isolation stiffness and damping, simplified model analysis reveal that it has favorable horizontal and vertical isolation effectiveness.4. Finite element model of a full-scale three-span continuous girder bridge is established, horizontal and vertical mechanical property parameters of the proposed 3D isolation bearing are designed. horizontal and vertical isolation effectiveness for the continuous girder bridge are validated and the influence of seismic excitation property, lateral stiffness of pier, yield strength of lead-rubber bearing, stiffness of combined disc spring and rhombic steel plate damper on horizontal and vertical isolation effect. Analytical results reveal favorable horizontal and vertical isolation effectiveness and rhombic steel plate damper can evidently improve vertical isolation effectiveness.5. A 1/25 scale three-span continuous girder beam and single span girder bridge are designed according to the prototype bridge, seismic excitation input, experimental case and disposal of measurement instrument are designed, shear performance experiment is carried out for the natural laminated rubber bearing and proposed 3D isolator. Horizontal and vertical shaking table test are performed to validate the isolation effectiveness of the 3D isolation bearing. Experimental results show that the 3D isolator is effective for horizontal and vertical isolation, but the laminated rubber bearing is invalid for vertical isolation, even adverse effect on vertical seismic responses.6. Design principle and method of 3D isolation system and 3D isolated bridge are summarized and discussed for girder Bridges. Taking a three-span continuous girder bridge for an example, conceptual design and MDOF elastic response spectrum analysis and design are performed for the proposed 3D isolation bearing and 3D isolated bridge.