Study On Performance-based Seismic Design Of RC Frame Structures Based On Ground Motion Input

Ground motion is the key to input in seismic design,and it is an important content of performance-based seismic design.However,the relevant provisions on ground motion in Chinese Code for Seismic Design of Buildings are difficult to be implemented by engineers and technicians.In Chinese Code for Seismic Design of Buildings,earthquake action is calculated based on the elastic response spectrum of seismic precautionary intensity to realize the calculation of seismic bearing capacity,which is not directly related to the seismic performance level.In view of the above problems,the studies on selection of ground motion records,synthetic ground motion,seismic intensity measures,quantization parameter of seismic performance levels,and performance-based seismic design of reinforced concrete structures were conducted.The main study contents are as follows.(1)A method of constructing ground motion records alternative database was proposed.The primary principles of record selection were established according to magnitude,epicentral distance and site conditions.The matching between record response spectrum and design response spectrum was controlled in the characteristic period and the structure basic period,under considering the ground motion characteristics,seismic environment and structure characteristics.The sectionalized-dual-band method of ground motion records selection was proposed.And the ground motion records alternative database was set up.The validity of records in the alternative database was verified by time history analysis.The selection range of records can be narrowed by using the records alternative database.And the problem of selecting records one by one due to the structure change can be solved.(2)A method of synthesizing ground motion of main control sections was proposed.The main control section of natural ground motion was extracted based on the design response spectrum.Then the main control sections were serialized into acceleration time history curve in periodic order.And the ground motion with natural factors was synthesized,which was adjusted by strength envelope function and corrected by zero line drift.The synthetic ground motion of main control sections was compared with common artificial ground motion and natural ground motions on spectral analysis and structural time history analysis.The synthetic ground motion containing spectrum features of natural records realized the whole period matching between synthetic response spectrum and design response spectrum.A synthetic ground motion record can be used for multiple engineering structures,which has high robustness.(3)The correlation,efficiency and sufficiency between seismic intensity measures(IMs)and engineering demand parameters(EDPs)were studied.At present,most of the researches on IMs and EDPs focused on the correlation,but few considered the efficiency and sufficiency at the same time.In addition,the number of samples and the input of ground motion records of similar models were limited.Therefore,the above effects were considered comprehensively.Based on 15 structures of five layers and three fortification intensities,120 ground motion records were selected to do 1800 times of nonlinear dynamic history analysis.The correlation,efficiency and sufficiency between 28 seismic intensity indexes and 4 key engineering demand parameters were evaluated.The optimal IMs were selected for the research on performance-based seismic design of RC frame structures.(4)The quantization parameters of seismic performance levels under performance-based seismic design were determined.The earthquake design level and performance level of major countries were compared and analyzed.The experimental data of 56 concrete frames and 440 concrete columns,collected from the published literature at home and abroad,was statistically analyzed.Combined with the Chinese Code for Seismic Design of Buildings and the Technical Specification for Concrete Structures of Tall Buildings,six performance levels were determined and the six performance levels were quantified,which laid a foundation for the performance-based seismic design.(5)A method for calculating the earthquake action of structures based on the performance level was proposed.In Chinese Code for Seismic Design of Buildings,the earthquake action is calculated by using the seismic effect coefficient corresponding to the seismic precautionary intensity,which does not correspond to the performance level.So a method to calculate earthquake action based on performance level was proposed,and the above research results of ground motion were applied into the method.The method can be used as a supplement to the existing calculation of seismic action based on seismic precautionary intensity,so as to meet the requirements of designers to select suitable objectives for design according to the owners,and also to deal with the occurrence of extreme earthquakes with ultra-intensity.The innovations are as following.(1)In order to improve the accuracy and efficiency of ground motion records selection,the sectionalized-dual-band method was proposed,and the ground motion records alternative database was set up.(2)The method of extracting the main control section of natural ground motion record was proposed,and the record containing natural factors was synthesized,which can satisfy multiple structures.(3)The method for calculating the earthquake action of structures based on the performance level was proposed,which can be used as a supplement to the existing calculation of seismic action based on seismic precautionary intensity.