Study On The Seismic Response Of Base-isolated Buildings Including Correlation Effect

Base-isolated technology has won the common acknowledgement by both domestic and foreign academia and engineering industries because of its excellent shock absorption effect, economic strengths, durability and applicability. According to statistics, the area of constructions of the base-isolated buildings in China has exceeded 2 million square meters. The application and development of base-isolated technologies are closely related to the study of mechanical property of vibration isolation system and study process of earthquake response and analytical theories of base-isolated building. In the current studies, however, many objective factors affecting the actual earthquake response of the building are ignored because of the failure in considering the influence of effect of lead rubber bearings. In the various relativities of lead rubber bearings, temperature effect and axial load effect have the most significant influence on the physical property of the bearings. To further optimize the theoretical study of base-isolated technology, this article conducts the researches concerning the temperature effect and axial effect of lead rubber bearings and earthquake response of base-isolated buildings as follows on the basis of bearing quasi-static testing and non-linear time history analyses:(1) Studied the temperature effect and axial load effect of lead rubber bearings systematically, conducted the quasi-static testing of temperature effect and axial load effect of lead rubber bearings and got the bearing hysterical curves in different temperatures and axial loads. Analyzed from the results of the temperature effect tests of lead rubber bearing, environment temperature has significant effect on the physical property of the bearings. The yield-shearing force, yielded rigidity and rigidity before the yield-shearing of the bearings will increase with the decrease of temperature and the changes of bearing physical property are most significant in low temperatures. Analyzed the test of axial load effect, the yield-shearing force and rigidity before the force of the lead rubber bearings will enhance by the increase of axial load pressures while yielded rigidity will decrease with the increase of axial loads. The physical property of the bearings tends to be stable when the axial load of the bearings reaches 6MPa. (2) Deduced the bearing parameter identification methods based on sequential non-linear LS (Least Squares) and identified the parameters of the results of quasi-static testing of the lead rubber bearings. In accordance with the parameter identification results, create the influence coefficient function of changes of physical properties of the bearings (rigidity before the yield shearing force, yielded rigidity and yield-shearing force) with the variations of temperatures and axial loads.(3) Studied the influence of temperature effects of lead rubber bearings on the earthquake response of eccentric and non-eccentric base-isolated buildings. As for the non-eccentric base-isolated buildings, after considering the temperature effects of the lead rubber bearings, the relative displacement will increase with the rise of the temperatures while the variation trends of bearing recoverability is related to the speed acceleration of earthquake stimulation. In low temperature environment, the vibration effect of the base-isolated building will be reduced or even cannot achieve the expected objective for vibration absorption. As for eccentric base-isolated buildings, after considering the temperature effects of the lead rubber bearings, though the isolation layer and the displacement of upper building are similar, calculation results under different temperature environment still has noticeable errors. Temperature effect has significant influence on the speed acceleration of the turning of the upper building. But it has only minute influence on the speed acceleration of the turning of the isolation layer, which is tiny enough to be ignored.(4) To study the influence of axial load effect of lead rubber bearings on the base-isolated building, provide the physical model of axial load effect of lead rubber bearings, implant it into the motion formula of base-isolated building and analyze the earthquake response of base-isolated building in simultaneous horizontal and axial loads. After considering the axial load effects of the lead rubber bearings, the hysterical curve of the bearing is no longer smooth, but appears uneven spots. The relative displacement and horizontal shearing force increase. By the influence of displacement, the upper building shifts entirely. The initial pressure of the bearings has significant impacts of hysterical property of bearings and earthquake response of upper building. The less the initial pressure is, the less will the hysterical force of bearing be filled, the more significant of the axial load effect of the bearings on the earthquake response of the upper building. (5) Analyzed the horizontal hunting earthquake response of base-isolated buildings of high-rise or more spacious buildings by integration of axial load effects of lead rubber bearings. Influenced by structural horizontal hunting motions, the axial load of the bearings will not change with the vibration of the building even though the building only considers the horizontal earthquake stimulation. Therefore, the calculation hysterical curve of the bearings will not become uneven; the peak of speed acceleration of the upper building and the influence of high order mode of the building will become more significant.