Study On Base Isolation Design Method For Single Tower Cable Stayed Bridge With Consolidation System

Single tower cable-stayed bridges with consolidation system are widely used.However,these bridges have been found some defects during earthquake,such as insufficient strength and limited ductility.It is an urgent issue that the seismic performance of the above bridges should be improved to reduce the probability of seismic damage.Base isolation design method was proposed to solve the above problem for single tower cable-stayed bridge with consolidation system.A practical bridge was taken as the research object.Design method research on base-isolation design of single tower cable-stayed bridge with consolidation system was done by ways of theoretical analysis,detailed design,numerical simulation,and development of a new seismic-isolation device.The main works were as follows:(1)The design scheme of base isolation was proposed.For single tower cable-stayed bridge with consolidation system,tower cap was divided into two parts in the vertical direction,where the base isolation layer composed of seismic-isolation devices was installed.Models of seismic-isolation devices were initially determined according to vertical bearing capacity.Structural measures design was done to achieve some necessary functions,such as displacement limitation of base isolation layer,replacement of seismic-isolation devices,and waterproof of isolation basement.Effects of base isolation design on normal operation of single tower cable-stayed bridge was investigated by static and stability analysis.The results indicated that: as the base isolation layer was located in the middle of the tower cap,it could make full use of the projection plane of the bridge and enhance the stability of the foundation;harmful displacement of base isolation layer could be avoided by the displacement limitation design;serviceability of bridge could be improved by the replacement design for seismic-isolation devices;durability of base isolation layer could be enhanced by the waterproof design;although bridge stiffness was slightly deduced by base isolation design,the effects on stability and mechanical properties such as dead weight,vehicle braking force,and transverse wind load were very small.As a result,the base isolation design for single tower cable-stayed bridge with consolidation system was preliminary feasible.(2)The seismic performance of base isolation bridge was studied.6 base isolation design schemes were employed for single tower cable-stayed bridge with consolidation system,the seismic performance of which was respectively investigated.Optimization for seismic-isolation devices was done by parameter analysis,and reasonable base isolation design schemes for bridge were selected afterwards.The results indicated that: bridge stiffness was reduced by each base isolation design schemes,resulting in increase of seismic displacement and decrease of seismic forces;bridge damping was respectively increased by LRB,FPS,FVD,and PSD,resulting in the further decrease of seismic displacement and forces;as the criterion of the maximum seismic response value and seismic isolation devices' energy dissipation efficiency,FVD + RB scheme,LRB scheme and FPS scheme were adopted as the base isolation design schemes for single tower cable-stayed bridge with consolidation system(3)The influence of complex factors on the base isolation bridge was studied.Seismic design scheme for transition pier and displacement-limitation design scheme were chosen as two complex factors,the effects of which on seismic performance of bridge were separately determined.The results indicated that: the combination of sliding bearing and FVD was recommended for seismic design scheme for transition pier,as it could dramatically reduce seismic force of transition pier and seismic relative displacement between beam and transition pier,without increasing seismic force of tower;displacement-limitation design scheme could restrict the seismic displacement of base isolation layer,but the seismic force of tower was fairly increased;as a result,displacement-limitation design scheme should be used for the situation with high demand of displacement.(4)A new type of seismic isolation device was developed.Steel wire rope and rubber bearing were assembled as a whole called a new type of seismic isolation device.Theoretical and experimental studies were done to determine the load-displacement relationship and its application effects in bridge.The results indicated that: relative displacement between superstructure and substructure could be limited by the device,which could protect the bearing and reduce the risk of beam falling;seismic response of pier might be increased by the device,while the seismic performance of pier could still be met the demand by choosing suitable parameters of steel wire rope;initial gap and elastic stiffness were the main parameters of steel wire rope;initial gap should meet the requirements of normal operation and earthquake;elastic stiffness could be determined by seismic response of pier and the bearing itself.