Seismic Response And Damage Evaluation Of High-rise Isolated Structure

With the acceleration of urbanization, construction quantity of high-rise building structurebecomes increasingly pronounced in our country. However, the1999chi-chi earthquake and the2010Chile earthquake damage events show that the seismic performance of high-rise buildingstructure is facing a severe test. After wenchuan earthquake and ya’an earthquake in our country,in order to reduce the damage of high-rise building structure seismic action, the application ofhigh-rise isolated structure in China is developing rapidly. There is an important practicalsignificance on studying high-rise isolated structure seismic response and damage mechanism.Because of the uncertainty of the ground motion, some problems of adopting reasonable andeffective seismic intensity to evaluate the high-rise isolated structure seismic performance state,predicting seismic response and evaluating damage performance of high-rise isolated structurehave become obstacles in high-rise isolated structure engineering application and technicaldevelopment. To solve the problems, considering the complexity of earthquake ground motionand the vibration characteristics of high-rise isolated buildings, the effective seismic intensitymeasure, seismic response prediction theory and seismic damage behavior evaluation methodcaused by collision are proposed.The main researches and achievements are as follows:(1) Strong seismic records selection procedure for dynamic elastic-plastic time historyanalysis of high-rise isolated structure was proposed based on a combination of fuzzy clusteringmethod(FCM) and seismic intensity measure (IM) index evaluation method. Comparative analysisabout correlation of six kinds of IMs were done for simplified equivalent single degree-of-freedom(SDOF) model and three dimensional high-rise isolated structure dynamic elastic-plastic timehistory method. Six IMs are PGA, PGV, PGD, PGA/PGV, acceleration spectrum and equivalentspeed spectrum. Superstructure storey deformation, roof acceleration and isolation layerdisplacement were choosen as Engineering Demand Parameters (EDP). The optimal IMs wereused for earthquake wave samples. The earthquake wave samples were classified based on fuzzy clustering algorithm. The effectiveness of fuzzy clustering algorithm was proved through thecomparison of responses of unclassified earthquake set and selected subset.(2) The Single-degree-freedom (SDOF) system with bilinear model was analyzed bynonlinear time history analyses, total energy spectrum analysis and hysteretic energy spectrumanalysis under44far field ground motions and20near-field and high-speed pulse seismic waves.A hysteretic energy spectrum model for long-period elastic-plastic structure was establishedaccording to constant ductility criterion. A new index based on characteristic hysteresis energycoefficient considering relationship of hysteretic energy, ductility and strength is proposed.Equivalent speed spectrum of total energy for single degree freedom (SDOF) system isestablished. Based on equivalent speed spectrum and energy balance，the maximum displacementof SDOF is predicted. Akiyama energy balance formula, Leelataviwat energy balance formulaand proposed energy balance formula are compared by using a SDOF example. The suitabilityand calculation accuracy of proposed model and method are verified. The application of energyspectrum model is described by using a10stories high-rise isolated structure engineeringexample. The results show that the calculation process using the proposed method is easy andefficient, and results are acceptable.(3) Aiming at two-mass simplified model of high-rise isolated structure, the pure massmodel method (PMM) which can be utilized to calculate earthquake responses quickly forhigh-rise isolated structures is proposed in the paper. Firstly, transformational relation andparameters of two mass simplified model and archetype are established according to equivalentcriteria for base shear and energy. And then, two key parameters: stiffness transformationalcoefficient and mass ratio were obtained to determine seismic responses. Envelop responsescalculation formulas of simplified model were proposed based on energy balance method in thestudy. Energy balance methods and models transformational relations were used to analyze theseismic response envelop values of every layer of archetype. At first, the22stories high-riseisolated structure of engineering example was transformed into two-mass simplified model.Thereafter, the suitability and calculation accuracy of pure mass model method were verified. Itis shown that computational results of new method are similar to the results of multi-mass model time history analysis method. The calculation amount of the method proposed is less, andparameters determination is clear and convenient. The calculation method can be applied toanalyze the earthquake responses of high-rise isolated structures. To extend the method tohigh-rise isolated structure considering rocking effect of the isolation layer, simplified analysismodel considering the effect of rocking is established, the angle prediction formula of isolationlayer is proposed, and based on the simplified method, the vertical force response of isolationbearing is predicted. The accuracy of the proposed prediction formulas was validated by high riseisolated structures with2.5and5.0aspect ratio shaking table tests.(4)108isolation bearing damage test results have been investigated. The relationship ofultimate shear strain, shape coefficient and diameter of bearings is analyzed. Damage values forsimplified single mass isolation model and simplified isolation model of two degrees of freedomvibration under60near fault pulse-like records (pulse period is0.69-5.9s) are calculated. Theeffects of bearing yield force coefficient (2.8%,5%,10%,5%), hardening of the displacement(150%,200%,250%,200%) on bearing damage, and the effects of superstructure yield forcevalues on the structure damage were examined. Based on elastoplastic damage constitutive ofconcrete and steel ductile damage, a15-storey steel frame-core wall high rise isolated structuralfinite element model was established. Dynamic elastoplastic damage evolution and yield stressof the core tube, floor slab and steel frame of high-rise isolated structure under standard seismicwave and near fault pulse-like ground motions were analyzed by using a explicit dynamicexplicit finite element method (FEM) analysis. The calculation results show that, compared toconventional seismic input, near fault pulse-like earthquake-induced damages in isolationbearing and the upper structure are more serious. Based on material damage level, componentdamage level and storey damage level, high-rise isolated structure damage performance assessmethod was proposed. The global damage index of the15-storey steel frame-core wall high riseisolated structural was determined with the damage model proposed here. The method canprovide reference for damage performance assess of similar engineering structure.(5) In order to study the equivalent linear stiffness value of impact model, based on equatingenergy dissipation and maximum collision compression deformation of isolated structure with the Hertz model and Kevin model in the process of collision, formula of the equivalent linearstiffness of the collision was derived, and the rationality and accuracy of the proposed stiffnessmodel were validated by numerical analyses, balls impact experiment and shaking table tests.Damping coefficients of long-period seismic isolation structure displacement spectrum undernear fault and far source ground motions were studied. Damping coefficient formulationsstipulated in Chinese Code for seismic design of buildings (GB50011-2010), JPN2001,FEMA368and Euro Code-8were compared. The damping coefficient stipulated in GB50011-2010will be too conservative for the structure with period (<6s). However, comparedwith the damping coefficients for near-fault ground motions, the values provided by JPN2001,FEMA368and Euro Code-8codes are lower. Based on simplified two degrees of freedom Modeland22stores high-rise frame shear wall structure model under long period ground motion, theeffect of impact on acceleration, displacement response of structure, the displacement ofisolation layer, and the hysteretic energy dissipation were studied. It is shown that seismicisolation displacements under near fault earthquakes are smaller than that under far sourceearthquakes, but it causes more serious damage to the superstructure. Impact effect will not onlyinduce higher order modes of the high-rise isolated structure, but also can cause more hystereticenergy dissipation and structural damage in the main structure.