Analysis Of Seismic Response Of Base-isolated Structures With Prestressed Rubber Bearings

To overcome the shortages of the existing rubber bearing(RB),a new type of isolator named "prestressed rubber bearing"(PRB),is proposed in this paper.PRB has many properties such as horizontal displacement limited,vertically isolated and tension-resistant.Based on the previous research,the seismically isolation capacity of PRB and its influencing factors are further studied in this paper.It mainly includes:(1)Establish two analytical models—horizontal "limitation of displacement on both way" and "pounding" for isolated structure with PRB,and correspongding horizontal motion equation is derived.On the basis,analyse how the cross sectional area of flexible cable and its reserve length affect the horizontally seismic response of isolated structure with PRB.The results show that,due to the work of the flexible cable in PRB,compared to common isolated structure,the horizontal acceleration of isolated structure with PRB increases and its displacement decreases.(2)According to the different choice of flexible cable's tensile stiffness and its reserve length,establish three different analytical models,named vertically "free vibration","limitation of displacement on single way" and "pounding",then corresponding vertical motion equation is derived.Study the transformation among above three models while the flexible cable's tensile stiffness and its reserve length are differently chosed.On the basis,analyse how the cross sectional area of flexible cable and its reserve length affect the vertically seismic response of isolated structure with PRB.Results show that,PRB has apparent capacity of vertically seismic isolation,and its flexible cable can effectively resist tension inside the bearing under rare occurrence earthquake.Only when the flexible cable's tensile stiffness is reasonably chosed,will the transformation be avoided from vertically "limitation of displacement on single way" to"pounding".(3)In this paper,it is studied how the flexible cable's impulse force affect the acceleration response of upper structure under vertical earthquake.The relationship between the flexible cable's cross sectional area,its reserve length and the intensity of flexible cable's impulse force is investigated.The results show that,the intensity of flexible cable's impulse force increases with its cross sectional area increased and its reserve length decreased.Moreover,the acceleration response of isolated structure is in direct proportion to the intensity of flexible cable's impulse force,and in inverse proportion to genenalized mass,genenalized period of structure's each order natural vibration mode.(4)In order to study the work mechanism of how the bearing's swing affacts the isolated structure's horizontally seismic response,establish a single freedom system about linear structure named "shear-swing" analytical model,and corresponding motion equation is derived.The results show that,the work mechanism of swing is mainly increasing the vibration period of linear structure and decresing horizontal seismic force exerted to the structure.(5)Establish the analytical model of the isolated structure with PRB considering bearing's swing,and corresponding motion equation is derived.Then,it is analysed how the PRB's rotational stiffness k?,y and reserve angle ?0 affact the acceleration,displacement response of upper structure.The results show that,while considering bearing's swing,the relative acceleration of the isolated structure with PRB decreases and its relative displacement increases under earthquake;The much more difference value between the PRB's rotational stiffness k?,y and k?,TRB will apparently increase swing acceleration of upper structure,but has little affection to relative acceleration;The variation of ?0's value has little affection to swing acceleration and relative acceleration of upper structure;The max relative displacement of upper structure gradually decreases with ?0 decreased and k?,y increased,gradually approaching the situation without considering bearing's swing.