In recent years,several disastrous near-fault earthquakes,such as the Wenchuan earth-quake in China,the Chi-Chi earthquake in Taiwan,the Kobe earthquake in Japan,and the Northridge earthquake in the United States,have occurred.A large amount of near-fault pulse-type earthquake data from all these earthquakes has been recorded,and has attracted close scruti-ny and extensive research.This seismic record contains obvious long-period velocity pulses.Near-fault ground motions not only cause serious damage to buildings,but also cause slope instability and damage to infrastructure,These disasters have a serious impact on the economic infrastruc-ture and safety of people.Therefore,understanding the response of structures to near-fault ground motions is necessary.This allows for more reliable and efficient seismic design.Different ground motion records contain different types of information such as peak acceleration,peak velocity, peak displacement,and duration of ground motions.Near-fault ground motions have prominent features and destructive force and their velocity response spectra are significantly different from the velocity response spectra of far-fault ground motions.This study used 30 near-fault earthquake records from the Pacific Earthquake Engineering Research Center’s strong motion database;the records contain magnitude,fault mechanism,soil layer shear wave velocity,and fault distance in-formation.First,a motion equation for a single degree-of-freedom system was established.Then,a state-space method and MATLAB was used to change the motion equation to a state equation. Next the equation was solved to obtain the velocity response of a single degree-of-freedom system and based on the velocity response,the velocity response spectra of the single degree-of-freedom system was obtained.Because the velocity response is related to the acceleration response and the displacement response,the velocity response of structures are analyzed in the present study.The features of the velocity response spectra were obtained by normalizing and averaging,and then the 30 near-fault earthquake records selected from the PEER strong motion database were divided in-to different groups based on the period corresponding to the peak velocity.A velocity design spec-tra was established using a piecewise linear fitting method.The reasonableness of the velocity de-sign spectra was verified by comparing the velocity design spectra and the velocity average spectra of different groups.The results show that the velocity response spectra of near-fault ground mo-tions consist of four stages:ascent segment,peak segment,depression segment,and horizontal segment.The damping ratio of the structure has no influence on the spectral shape of the velocity response spectra,but the damping ratio of the structure can affect the spectra peak of the velocity response spectra.When the damping ratio of the structure is different,the maximum relative error of the velocity response spectra peak is 1 6.68% after pairwise comparison.%近断层地震动是一种特点明显且破坏力巨大的地面运动，其速度反应谱与远场地震动的速度反应谱有显著不同。本文从美国太平洋地震工程研究中心(PEER)强震数据库选取具有特定震级、震源机制、土层剪切波速和断层距的30条近断层地震记录作为输入；运用状态空间法，利用MATLAB 进行地震动作用下单自由度体系的运动方程计算得到体系的速度反应谱；通过标准化、求均值的方法研究速度反应谱的特征；按照速度反应谱峰值对应的周期对所选的30条地震记录进行分组，并用分段线性拟合方法建立了设计速度反应谱；通过不同组的设计速度反应谱与速度反应谱平均值的对比，验证本文提出的设计速度反应谱的合理性。研究结果表明，近断层地震动下的速度反应谱谱形包括四个阶段；结构的阻尼比对速度反应谱的谱形没有影响，但是会影响速度反应谱的谱峰值，结构阻尼比不同时，两两比较后的最大相对误差为16.68%。
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