Research On Selection And Applications Of Ground Motion Records Based On Code Design Spectrum And Scenario Spectrum In Seismic Areas

In the process of time-history analysis of structures,selection and scaling of ground motion records is a crucial step.At present,the basic requirements for the selection of ground motion records in various countries are to match the target spectrum while taking the seismic parameters into account,but the specific procedures in terms of the scaling method of ground motion records,the selection and construction of the matched target spectrum,and the degree of matching between the records and the target spectrum are not clearly described.There have no clear principles in selection and scaling of ground motions for engineers and researchers to make seismic design of structures.It has been known that the influences of selection of ground motion records on the results of structural time-history analysis cannot be ignored.Unreasonable ground motion selection will overestimate or underestimate structural responses,resulting in a large deviation between the results obtained from seismic design of structures and actual structural responses when real earthquakes occurr.There are hidden dangers to safety of people's lives and properties.Therefore,the rational procedures of selecting and scaling ground motion records require more in-depth research.In view of the above reasons,this thesis is focusing on selection and scaling of ground motion records based on Chinese seismic design codes,which is also a key issue involved in performance-based seismic design.The definitions of ground motion parameters used in the seismic design process are discussed and analyzed,and the various design details of the ground motion selection process are compared and analyzed,including the scaling method,matching period range,determination of seismic parameters,construction of target spectrum,etc.It is hoped to summarize a reasonable method of ground motion selection for practical seismic design.In order to achieve the above research goals,this thesis takes the selection and scaling of ground motion records as the main line,takes single-degree-of-freedom(SDOF)systems and multi-degree-of-freedom(MDOF)reinforced concrete frame structures as the research objects,and evaluates the selection and scaling methods of ground motion records through the variations of structural seismic responses.The research route of this thesis is as follows: determination of target ground motion parameters ? preliminary selection conditions of ground motion records ? comparison of preferred methods of ground motion records based on code design spectrum ? construction of scenario spectrum in seismic areas based on ground motion prediction equations ? consideration of statistical uncertainty ground motion records to evaluate seismic performance of structures.The main research contents of this theses are as follows:(1)The effective peak acceleration(EPA)of the target ground motion intensity parameter is studied,the controversial parameter values in the EPA calculation formula are discussed,and a regression fitting formula is proposed to explore the statistical relationship between the EPA and peak ground acceleration(PGA),then the conversion relationship between the two parameters is found.Based on the EPA values given in Chinese seismic design code,combining with the determined parameter values,the target ground motion parameters EPA and PGA values are modified.Based on the modified target ground motion parameters,the preliminary selection conditions of ground motion records are investigated.Based on the intensity prediction equation(IPE)and ground motion parameter prediction equations given in the 5th generation ground motion parameter zoning map of China,the seismic parameters(magnitude,distance,site category)of preliminary selection are calculated,and the corresponding mappings between the seismic parameters and the design earthquake categories in the seismic design code are established to facilitate the usage of these conditions in practical seismic design.(2)Taking the horizontal seismic influence coefficient curve of the 2010 version of Chinese seismic design codes as the target spectrum of ground motion selection and scaling,various conditions that affect the results of record selection in the process of ground motion selection and scaling are discussed.Unfer the same fortification requirements and with the same target spectrum,different scaling methods,different matching period ranges,different order of scaling and selection,and different structural funamental periods are compared and analyzed.Based on these analyses,relatively reasonable selection and scaling method is proposed.It has been found that the period range around the fundamental period of a structure does have a greater impact on the structural response.It is recommended to use the Sa(T1)scaling method and the matching period range [0.2T1,2T1] in selecting and scaling ground motion records in practical seismic design based on code design spectrum.(3)Based on the ground motion parameter PGA prediction equations and the acceleration response spectrum Sa(T1)prediction equations,the target PGA value is determined according to the seismic design requirements of each fortification level and site condition.Substituting the values of the given earthquake magnitude and the shear wave velocity of the soil layer at different sites for the senario earthquake magnitudes into the PGA prediction equations,the corresponding distance parameters are determined.And then,the obtained magnitude and distance pairs are taken as the scenario seismic parameters.The acceleration response spectrum for the senario earthquakes corresponding to the ground motion prediction equations in different seismic areas are constructed for the median value of the target response spectrum under the corresponding scenario earthquakes and design requirements.Since theprediction equation itself has probabilistic significance,the standard deviation values can also be obtained at the same time.On this basis,the scenario spectrum distribution composed of the obtained median value and standard deviation is taken as the target spectrum,the seismic records and the target distribution are matched to select and scaling the ground motion records.The ground motion records recommended for seismic design and the corresponding scaling factor under each design situation for different seismic areas are then given.(4)The aforementioned results of seismic motion records selection and scaling are input into RC frame structures for elastic seismic response analyses under frequent earthquakes,as well as elastoplastic seismic response analysis under rare earthquakes.The 84% fractile of the average distribution of the maximum inter-storey displacement angles(ISDA)of structures as the engineering demand parameters(EDP)are considered in order to consider the statistical uncertainty with regard to the number of the selected seismic records.It has been shows that the variations of the structural responses to three records are higher than the theoretical responses of the structures.It is recommended to select 7 or more seismic records and use the empirical coefficient formula to calculate the 84% fractile of the average values of the structural responsess as the design response parameters.Based on this investigation,the results of the base shear and the ISDAs of the structures satisfy the code limiting values,and the seismic performance of the structures under consideration is evaluated to well fulfil the requirements,which also verifies the rationality of the aforementioned methods of selecting and scaling ground motion records.