Study On Different Design Methods For Reinforced Concrete Base-isolated Moment Resistant Frame Structures And Research On Their Seismic Performance

Isolated structures have been widely applied all over the world after decades of theoretical research and earthquake simulating shaking table tests.Isolated structures refer to setting isolation layer in structures with small shear stiffness,which extend periods of sturctures so as to reduce horizontal seismic action of upper structures and lead to higher safe level.At present,there are some isolated structures survived the test of actual earthquakes.Up to now,the design method of “frequent earthquake-separated” based on the code for seismic design of buildings is adopted in the actual engineering design of isolated structures,which takes the structure above the isolation layer to carry out the design,and needs repeated design and adjustment to get satisfactory design results.The design method of “medium earthquake-unitary” proposed on the code of design for seismic isolated buildings was published in 2018.This method considers the medium earthquake and take into account the whole structure,but research results of structures designed according to this method are not published,and the performance of these structures under the condition of rare earthquake are not clear.In order to compare the difference of design level and the difference between “separation” and “unitary” design method,this article holds that it is necessary to propose the “frequent earthquake-unitary” design method and investigate its seismic performance.This paper has researched the present situation of isolated structures,the design method of codes and actual engineering design method of isolated structures.And then,this paper systematically introduces and compares the “frequent earthquake-separated” design method,the “frequent earthquake-unitary” design method and the “medium earthquake-unitary” design method based on a actual engineering of RC moment resistence frame structure in 8 degree(0.30g)area.Finaly,this paper investigates the performance of the isolated structure designed by each design method under the condition of rare earthquake.The key conclusions of the thesis are:(1)comparing with the “frequent earthquake-separated” design method and the “frequent earthquake-unitary” design method,the “medium earthquake-unitary” design method raise the design level of horizontal earthake action,which increase cross section of structure’s members while the amount of reinforcement decreases.So the “medium earthquake-unitary” design method won’t significantly improve the cost of materials in engineering.(2)The “separated” design method used in engineering design now selects appropriate ground motion records at the elastic design stage because of the requirement of the calculation the horizontal seismic decrease coefficient.While the practical wave selection method in the existing engineering needs to meet the site conditions first.Secondly,it should meet the PGA requirement of the non-isolated model and the isolated model at the main periodic point at the same time.Finally,the base shear check must be carried out.Therefore,it is difficult to select adequate and suitable ground motion records.(3)under the medium qarthquake,the calculation result of the horizontal seismic decrease coefficient of the inelastic model is obviously larger than the result of the elastic model used in the design.It is shown that the state of the superstructure under earthquake affects the ratio of the shear force and then affects the isolation effect.And as an important parameter of the “separated” design method,horrizongtal seismic decreses coeffient does not reflect the actual isolation effect of the isolated structure.(4)Under the rare earthquake,the deformation and bearing capacity of three schemes are satisfied.And maximum drift of three schemes are at different floor location,but all do not exceed the limit value accordingly.The isolated structure designed according to the “frequent earthquake-separated” design method and the “frequent earthquake-unitary” design method performs well under rare earthquake with beams are damaged or destroyed in varying degrees and few column members damaged.And few beam is damaged and no column is damaged in the isolated structure designed according to the “medium earthquake-unitary” design method.Therefore,the “medium earthquake-unitary” design method can effectively improve the performance of the structure under rare earthquake,and it can basically achieve the performance target of “rare earthquake repairable” in the code of design for seismic isolated buildings.(5)Under the extremely rare earthquake,according to the isolation model designed by the “medium earthquake-unitary” design method,beam members are damaged in varying degrees with a few beams are seriously damaged while most of column members are still in good condition.Therefore,the “medium earthquake-unitary” design method can effectively improve the performance of the structure under the extremely rare level,and it can basically achieve the performance target of “extremely rare earthquake can not knock down” in the code of design for seismic isolated buildings.(6)Generally,the “frequent earthquake-separated” design method can be considered as an approximate design method for the isolated structure in the case of the previous design software conditions that can not consider the isolation bearing while the actual project does have the need.With the development of computer and design software,the “frequent earthquake-unitary” design method is considered to be a more reasonable design plan considering the influence of isolation bearings.And the “medium earthquake-unitary” design method is a design plan that may be adopted along with social progress and economic development,which improve the seismic performance standard of building structures.The main innovation points in this paper are:(1)Combined with the existing code and the code of design for seismic isolated buildings,three design schemes of “frequent earthquake-separated” design method,“frequent earthquake-unitary” design method and “medium earthquake-unitary” design method are systematically introduced based on a practical engineering of RC moment resistence frame structure.(2)Based on the deformation of the component,the performance state of the isolation model of three design schemes in the rare earthquake and the “medium earthquake-unitary” scheme under extramly rare earthquake are investigated.