Research On Base-isolation Of Long-span Prestressed Concrete Continuous Rigid-frame Bridge

PC continuous rigid-framed bridge has the advantages of large bending stiffness along vertical bridge and the torsional stiffness along the horizontal Bridges and traffic smoothly. Additionally,it has simple constructruction and low maintenance cost. So it was relatively rapid developed in the past 40 years. The span has been developed from about 100m to over 300m around the world. PC continuous rigid-framed bridge has become one kind of the long-span bridge structure in the Gulf, the ravine,and large river.However, the project of building Long-Span PC continuous rigid-framed bridge, with bigger selfweight, stiffness and smaller natural vibration period, in high seismic intensity areas was seldom used because of its worse earthquake-resistant behavior comparing with same span cable-stayed bridge or suspension bridge.Based on this situation, combining with characteristics of continuous rigid-framed bridge under loading and relevant principles of base isolation, the base isolation of long-span PC continuous rigid-framed bridge was setup and feasibility of its scheme was studied by finite element simulation analysis. It is hoped that the desired objectives are achieved expected goal under limited increase construction cost by related measures.In another words, long-span PC continuous rigid-framed bridge which is dealed with base isolation is not only safe and steady in the event of high frequency earthquake, but also withstands the examination in rare earthquake.The following three aspects were mainly studied:1. ShuiTu Jialing River Bridge was taken as engineering background. Base isolation method and location were chosed firstly. Base isolation devices were arranged. Bridge model with base isolation device (name isolated structure for short below) and bridge model without base isolation device (name non-isolated structure for short below) were established by professional bridge software. Displacement, acceleration and principal tensile stress of concerned sections in the two type structure under the event of high frequency earthquake were compared by analyzing the calculation results. The behavior and performance of isolated structure were discussed.2. Good stability must be ensured in any bridge structure. Long-span PC continuous rigid-framed bridge belongs to a long-strip structure. Its whole stability will be affected greatly after base isolation devices were installed. So, the stability of isolated structure must be analyzed. The analysis results that the isolation structures under the event of high frequency earthquake still work in linearly elastic stages. The first type stability of insolation structures were analyzed only in the paper. Insolation structures were improved and optimized intently in order to get a good stability by analyzing the front several bands of buckling modes and the eigenvalues of isolated structure.3. According to the seismic resisting principle——"the structure are not damaged under modreate earthquakes, they are repaired under major earthquakes and they are not fallen under great earthquakes ". In the high intensity region, it is not enough for the structure to resist the seismic forces in the event of high frequency earthquake, and can also resist the seismic forces in rare earthquake. The deformation and stress of isolated structure under rare earthquake were analyzed in order to provide theortical b ases for evaluation the reliability of this type structure. Further more, isolated structures of ong-span continuous rigid frame bridge are optimized in order to work at linearly elastic stages in infrequent earthquake.