Study On Spectrum Characterization Of Long-period Ground Motions And Seismic Performance Of High-rise Building Structures Subjected To Long-period Earthquake Records

Multiple earthquake damage shows that long-period ground motions have an amplification effect on the dynamic response of long-period structures and they are likely to cause serious damage to long-period structures.At present,with the rapid development of economic construction in China,long-period structures of high-rise and super high-rise buildings have been widely used.However,the current code for seismic design of buildings in China can not ensure the seismic safety of long-period structures because it can not consider the resonance effect of long-period ground motions.Therefore,the seismic design of long-period structures considering the effect of long-period ground motions is an urgent problem to be solved in the aseismic field of structural engineering.This paper mainly focuses on two types of long-period ground motions,namely near-fault pulse-like ground motions and far-field harmonic ground motions,and a series of research work is carried out from two aspects of the spectrum characterization of long-period ground motions and the seismic performance of high-rise frame-core wall building structures subjected to long-period earthquake records.The main research contents and conclusions are as follows:（1）The comparative analysis of basic characteristics and strength parameters between the long-period ground motions and common ground motions are made.The influence on the basic strength parameters affected by the focal mechanism,earthquake magnitude,epicenter distance and site condition of long-period ground motions are analyzed.The conclusions are that near-fault pulse-like earthquake has high amplitude intensity and far-field harmonic earthquake has a small peak of acceleration,velocity,displacement.The frequency distribution of long-period ground motions is concentrated in a relatively low-frequency（0.1¹.0Hz）band and common ground motions is concentrated in a relatively high-frequency（1.0².3Hz）band.Near-fault pulse-like earthquake has short strong-shock duration and its energy release is intense,while far-field harmonic earthquake has long strong-shock duration and its energy release is mild.（2）A near-fault pulse-like earthquake record of TCU052-NS,a far-field harmonic earthquake record of YMN010-NS and a common earthquake record of ELC180 are taken as examples,and the predominant frequencies,center frequencies and average periods of all IMF（Intrinsic mode function）components after the EMD（Empirical mode decomposition）decomposition of three earthquake records are statistically calculated.It is suggested that the energy-weighted average period can be taken as a typical period of earthquake records.Based on the energy characterization of HHT（Hilbert-Huang transform）method,a simplified method for low-frequency time history of long-period ground motions is proposed and verified.It is concluded that the larger the proposed energy-weighted average period of ground motions is,the more obvious the long-period characterization of earthquake records is,and the weaker the other.（3）The comparative study between the fitted normalized acceleration spectra of long-period ground motions and the design response spectra of current code in China are made.Based on the weighted average value of acceleration magnification factor spectra,the quantitative boundary method to define common ground motions and long-period ground motions are proposed.The conclusions are that the period corresponding to the inflection point in the peak region of normalized acceleration spectra about far-field harmonic ground motions is shifted to the long-period direction,and it is suggested that the long-period part of normalized response spectra should not be segmented and the attenuation index should be always taken as 0.9.The fitted platform value under near-fault pulse-like and far-field harmonic ground motions are lower than the platform value 2.25 of seismic design spectra in current code,while the fitted characteristic period under near-fault pulse-like and far-field harmonic ground motions exceed the characteristic period of seismic design spectra in current code.The proposed weighted average value in this paper,as a quantitative boundary parameter to define common ground motions and long-period ground motions,would provide the theoretical basis and quantitative criteria for the selection and evaluation of long-period ground motions during the seismic response analysis for high-rise and super high-rise buildings.（4）Taking a high-rise building structure of typical and regular reinforced concrete（RC）frame-core wall with a long fundamental period as the research object,the nonlinear dynamic response analysis of the structure subjected to long-period earthquake records are made.The spectral acceleration of main horizontal components about TCU052,YMN010 and ELC earthquake records is scaled to 200 cm/s².The conclusions are that,at the same amplitude of spectrum acceleration,the structure enters a high degree of plastic deformation under near-fault pulse-like ground motions,followed by the common ground motions,and the far-field harmonic ground motions is the smallest.Near-fault pulse-like earthquake easily leads to the first beyond displacement destruction of the structure,and far-field harmonic earthquake easily leads to the cumulative damage destructions of the structure.（5）The incremental dynamic analysis and seismic fragility analysis of high-rise RC frame-core wall building structures are carried out.The three-level seismic vulnerability matrix of the structure based on the spectral acceleration of S_a（T₁,5%）is obtained,and it realizes the probability-based seismic performance evaluation of the structure.The conclusions are that the structural damage of high-rise frame-core wall buildings caused by two types of long-period ground motions is larger than that by common ground motions,no matter whether the earthquake intensity levels（8 degree0.2g）are frequent earthquake,basic earthquake or rare earthquake.In addition,the bidirectional inputs of long-period ground motions need to be taken into account when the seismic behavior of high-rise RC frame-core wall building structures is evaluated by the method of IDA-based seismic fragility analysis.The research results in this paper will make up for the shortcomings of current code for seismic design of buildings and provide a theoretical reference for seismic design in these areas with long-period earthquake damage hazards,and it will promote the development and improvement of seismic design theory about high-rise frame-core wall building structures.