Reasearch On Vibration Isolation Of High-rise Isolated Structure

Isolation is a rapidly development technology of structural vibration control. Withbeing a simple and effective shock absorption technology it is applied to high-risebuilding increasingly in recent years. At present, there are many high-rise buildingswhich adopt isolation technology in foreign countries (such as America, Japan, NewZealand and so on), which is not widely carried out in our country. It is mainly because：(1) Uniform understanding of the damping mechanism of high-rise isolated structure islacked of in our country, in the meanwhile, the damping effect of high-rise isolatedstructure suffers question;(2) High-rise isolated structure is apt to the risk ofoverturning;(3) Relevant research on vibration control of high-rise isolated structureunder wind load in our country is not sufficient;(4) Understanding of torsion control ofhigh-rise isolated stucture is lack of in our country;(5) The isolation technology appliedin high-rise structure has not yet become complete standard which design andconstruction could follow. In view of the above points, the major work has beencompleted in this thesis are:(1) High-rise frame-shear isolation building model and multi-story frame isolationbuilding model are established, seismic waves are input into the two modelabove-metioned, and the isolation layer accelerations of time-procedure are extracted,which are considered as seismic waves and input into the original seismic structure.With making a comparison of the acceleration response spectrum of the two modelsabove before and after the isolation technique is applicated, the comparison of dampingmechanism of the two kinds of isolated structure is made to elaborate the dampingmechanism of high-rise isolated structure finally, the results show that the effectivenessof multi-vibration mode isolation for multi-story isolated structure is low, in themeanwhile, isolation mechanism is mainly on the first-order vibration mode isolationwhile the high-order vibration modes isolation of high-rise isolation structure iseffective, which lead to the multi-vibration mode isolation.(2) Three-particle equivalent model of high-rise isolated structure is deducedaccording to the rules that the first two frequency and vibration mode of thesub-structure which is upper the isolation layer is similar to free vibration of thecantilever uniform section bar, with which the analysis of dynamic response characteristics and top response prediction of high-rise isolated structure are carried out,the results show that the equivalent model which is deduced in this paper has highprecision on storey shearing and storey bending-shearing high-rise isolated structure.(3) To consider the impact of higher modes and overall bending of high-riseisolated structure, with simplified equivalent model of high-rise isolated structure in thesecond work the calculation formula of high-width ratio limit value is derived, and therecommendated limit value of high-width ratio of high-rise isolated structure is given,which is verified by two examples. The changes of the high-width ratio are furtherdiscussed when the basic period is not equal to the critical period, and it is found thatwhen the basic period is less than the critical period the limit of height-width ratio dosenot significantly reduce, and when the basic period is greater than critical period thelimit of height-width ratio reduce obviously.(4) Fluctuating wind speed time history is simulated by employing auto-regressivelinear filtering method, with which average wind speed is translated into fluctuatingwind load and input into the high-rise isolated structure, then in the case that a certaindamping effect is ensured, discussion on vibration effect and its control of high-riseisolated structure under wind load is done, the results show that with enduring50-yearreturn period wind load, it’s difficult to keep isolation layer unyield while the excellencein the earthquake energy absorption properties of the isolated structure is kept.Therefore, it’s proposed in this essay that to keep isolation layer unyield with enduring20to30year return period wind load could be considered; and the acceleration of thetop of the isolated structure can generally meet the human comfort degree index.(5) With Etabs software a high-rise seismic structure and4high-rise isolatedstructures of spatial model which have different torsional property are established andcomparative seismic response analysis of which is done to validate the principle that“the coincidence of upper structure mass center and the isolation layer rigidity center” isthe the key factor of inhibition of isolated structure torsion. Then the torsional effectof high-rise isolated structure under accidental eccentric seismic action was observed inthe case that upper structure mass center and the isolation layer rigidity center could notbe coincident, the results show that as the earthquake decreases, torsion effect is farsmaller than the original seismic structure and the isolation itself has better inhibitoryeffect to torsion than the princeple; the isolation rate of torsion is greater than theisolation rate of translation(6) On the basis of analysis of various issues in the last jobs, isolated structuredesign procedure and method are formed, and based on Etabs finite element analysissoftware the proposed design process of high-rise isolated structure is described withrelevant standards and regulations being considered as a reference, the results show thatthis method is convenient and effective.