Research On Seismic Performance And Design Method Of Base-isolated Reinforcement With An Integrated Base Plate Of Adjacent Structures

Base isolation used in seismic retrofitting of structures achieves reduction of the seismic response by lengthening the structural fundamental vibration period.However,the separation distance between existing adjacent superstructures may not be sufficient to accommodate the relative motions under seismic excitation as the top displacement tends to increase when the isolation bearings are added.Therefore structural damage due to pounding becomes a major constraint in the consideration of seismic retrofit by means of base isolation.One possible way to reduce the risk of pounding in seismic base isolation is to connect the base layer of adjacent structures to form a single large plate in the base-isolation construction procedure.This would ensure that the seismic motions at the isolated base layer are in phase,and together with the base isolation mechanism the condition against pounding would improve.Compared with the method of shifting the whole buildings to increase the separation distance,coupling the translational and torsional motions at the isolation layer of the adjacent structures is much easier.However,the actual dynamic responses in the adjacent buildings with an integrated base-isolation layer are complicated With the increase of the complexity of the structure,the increase of the eccentricity of the superstructure makes the control of the structural torsion effect more difficult.On the other hand,the torsional effect makes the integrated base plate connection in the two-way force state,the plate is easy to produce large additional internal force,resulting in local damage to the plate.Therefore,it is necessary to give the design method of base-isolated adjacent structures with an integrated base plate(BIASIBP)and analyze the structural seismic performance.In this paper,performance and design method of the BIASIBP for retrofitting of existing adjacent frame structures is studied.Based on the basic structure design of the additions of the natural rubber bearing and the lead rubber bearing,a series of related researches have been done,including the design of isolation layer of BIASIBP,top displacement difference of superstructures of BIASIBP,the torsional motions of the structures and the complex stress state of the integrated base plate.The main results are as follows:(1)Summarizing the research progress and present application situation of the base isolation for retrofitting of existed structures,the advantages of base isolation reinforcement compared with the traditional reinforcement method are put forward.The research progress on the relative seismic displacement of adjacent structures and solutions to the decrease the relative displacement are reviewed and summarized.Based on the different analysis objectives,the finite element analysis model of seismic isolation structure from simple to complex is given,which can be used to analyze the dynamic indexes of the BIASIBP.(2)The actual buildings are modeled as individual single degree of freedom(SDOF)structures,parametric study on the influences of varying the superstructure dynamic properties and the characteristics of the ground motions on the relative displacement of the BIASIBP,common base-isolated structures and fixed-supported structures are analyzed.The results show that the relative displacement of the BIASIBP is roughly 10%to 20%of the other two systems.The effect of the stiffness and damping of the isolation layer on the displacement difference of the superstructures are analyzed for the BIASIBP.A method based on random vibration theory and mode superposition scheme to estimate the relative displacement of the superstructures is presented.(3)The influence of the dynamic characteristics of the superstructure and the isolation layer on the torsional effect of the BIASIBP is analyzed by using the "tandem plate" model for the structural difference of the superstructure and the structural torsional effect caused by the irregular plane and the complex stress of the bottom plate.The results show that the torsional response of the whole isolation structure is about 50%?60%of the other two systems,and the torsional resistance of the structure is enhanced.This paper explores the influencing factors and distribution law of the stress level of the large floor of the isolation layer under the bi-directional earthquake record,and the design method of the isolation layer for the BIASIBP is given.(4)Based on an actual engineering structure,the isolation layer design method of double objective including the elimination of torsional displacement and the relative displacement of superstructures is presented,apart from two indicators,which are the force and the displacement.The combined base-isolated structure using the design method of double objective achieves the same reduction of the seismic response compared with the commom base-isolated structures.It proves that the integrated design method of the base-solation structure based on energy is practical,effective,and reliable.