Study Of The Effect Of Near-fault Ground Motion On Structural Seismic Design

Earthquake is one of the most serious natural disasters to human lives and properties in sudden burst mode. Especially, in the past decade several large earthquakes caused infrastructure damage, casualty and property loss, which shocked all the people around the world. After nearly 60 years of study, scholars of different countries come to a common understanding that the complicated and special feature of the near-fault (near-field/source) ground motion is an important factor that causes the structure damage. Subsequently, many studies related to the near-fault ground motion arose, mainly including simulation of near-fault ground motion, setting up attenuation relationship of near-fault ground motion, analyzing the damaging effect of near-fault ground motion on structures and finding reasonable methods of vibration isolation or energy dissipation under near-fault ground motion. However, till now no systematical method and theory are proposed for structure design and structure reinforcement to consider the influence of near-fault ground motion, especially in China.During the process of designing or reinforcing structures, firstly, it is necessary to judge whether the building is located in the near-fault region, and then we need to decide which structure design scheme is to be used, the last step is to choose a computational method, that is to decide the design spectrum and input ground motion. To solve the previous problems, this paper proposes the definition of near-fault region and analyzes the effect of near-fault pulse-like ground motion on the design spectra of China Seismic Code, and then puts forward a synthetic method to simulate the near-fault pulse-like ground motion. The effect of the parameters of near-fault ground motion on structure damage is analyzed. It is given that structure design scheme considering the effect of near-fault pulse-like ground motion and how to select this type of ground motion for time history analysis. The main objectives and results of this study are shown as following:(1)Based on damage potential parameters, a method for near-fault region zoning is proposed. When defining the near-fault region, a concept of Normalized Rupture Distance (NRD) is established, and this distance is defined as the ratio of rupture distance to moment magnitude (dr/Mw). Depending on the PEER strong ground motion database, the variation of damage potential parameters with NRD is analyzed, and then the near-fault region is defined according to some appropriate parameters. The rationality of zoning result is proved to some extend by the distribution range of ground motions, which embodies directivity and hanging/ foot wall effect.(2)The features of elastic, inelastic response spectra of near-fault pulse-like ground motion, near-fault non-pulse-like ground motion, far-field pulse-like ground motion and far-field non-pulse-like ground motion are compared, and their effects on design spectrum of China Seismic Code and inelastic displacement of structures are analyzed. It shows that the near-fault pulse-like ground motion mainly affects the design characteristic period of ground motion, and has no special influence on the spectral function and the maximum value. A suggestion for modifying the design spectrum is also provided, which takes the near-fault pulse-like ground motion into account. Additionally, the result shows that the method adopted in China Seismic Code for inelastic displacement calculation tends to be unsafe when the near-fault pulse-like ground motion is considered, and therefore the time history analysis is needed as a complement.(3)The insufficiency of the previous equivalent velocity model is analyzed, and a new model of equivalent velocity pulse is put forward. The limitation of existing methods for identifying pulse period and pulse amplitude is given. A new criterion is provided, which firstly uses the Hanning Window to smooth the pulse-like ground motion, and then identifies the pulse period and pulse amplitude parameters. And the rationality of the identification method is proved. The previous method used for synthesizing near-fault ground motion is improved as well.(4)The effects of every element of near-fault ground motion on elastic and inelastic spectra, reinforced concrete frame structure and reinforced concrete frame-shear wall structure are deeply analyzed. The deficiency of different parameters used to represent damage potential of near-fault ground motion is pointed out, including energy density (Eρ), maximum increment velocity (ΔVmax), improved effective peak acceleration (IEPA), improved effective peak velocity (IEPV) and ratio of peak horizontal velocity to peak horizontal acceleration (PHV/PHA). The results show that the damage potential of near-fault ground motion can not be represented by a single parameter, while it should be described by peak acceleration, peak pulse velocity and the relationship between pulse period and the natural vibration period of the structure synthetically. (5)Dynamic response and damage mechanism of reinforced concrete frame structure and reinforced frame-shear wall structure under near-fault pulse-like ground motion and far-field ground motion are compared. According to the results, structure design scheme considering the effect of near-fault ground motion is put forward. It is proposed that the near-fault pulse-like ground motion influence area should be evaded with the permission of the engineering background as possible, and the distribution of the number of near-fault ground motion along the rupture distance is counted as well, which can be used as the reference for deciding the preventing area.(6)The practicability of different seismic design methods considering the effect of near-fault pulse-like ground motion is discussed, including force based seismic design method, energy based seismic design method, and displacement based seismic design method. It is showed that only the force based seismic design method is practicable for current seismic design method. Based on the analysis results of the damage potential parameters, the method of selecting near-fault pulse-like ground motion is given for time history analysis.