Seismic behaviour of dams to near fault and far fault ground motions: A state of the art review

A Multi Record Based Artificial Near Fault Ground Motion Generation Method

Seismic Response of Base-Isolated Structures with LRB and FPS under near Fault Ground Motions

Ground motions in the vicinity of the source caused severe damage to structures as evidenced during the past earthquakes (Loma Prieta 1989; Kobe 1995; Chi-Chi 1999). Near fault ground motions are characterized by long period velocity pulse as reported in literature (Somerville, 2005). This pulse type of motion is produced due to forward directivity where fault rupture propagates towards the site at a velocity close to shear wave velocity, causing most of the seismic energy to arrive at the site within a short time. Such impulsive motion subjects structures to high input seismic energy at the beginning of the record. In this study, near fault ground motion for M w 6.0 has been simulated in Delhi region . The high frequency ground motion has been simulated using specific barrier model, combined with long period velocity pulse. As reported in literature, strong ground motion with long period pulse can increase the demand on medium and high rise structures.

A composite source model has been used to simulate a broadband strong ground motion with an associated fault rupture process. A scenario earthquake fault model has been used to generate 1000 earthquake events with a magnitude of Mw8.0. The simulated results show that, for the characteristic event with a strike-slip faulting, the characteristics of near fault ground motion is strongly dependent on the rupture directivity. If the distance between the sites and fault was given, the ground motion in the forward direction (Site A) is much larger than that in the backward direction (Site C) and that close to the fault (Site B). The SH waves radiated from the fault, which corresponds to the fault-normal component plays a key role in the ground motion amplification. Corresponding to the sites A, B, and C, the statistical analysis shows that the ratio of their aPG is 2.15:1.5:1 and their standard deviations are about 0.12, 0.11, and 0.13, respectively. If these results are applied in the current probabilistic seismic hazard analysis (PSHA), then, for the lower annual frequency of exceedance of peak ground acceleration, the predicted aPG from the hazard curve could reduce by 30% or more compared with the current PSHA model used in the developing of seismic hazard map in the USA. Therefore, with a consideration of near fault ground motion caused by the rupture directivity, the regression model used in the development of the regional attenuation relation should be modified accordingly.

Linear and nonlinear time history analyses have been becoming more common in seismic analysis and design of structures with advances in computer technology and earthquake engineering. One of the most important issues for such analyses is the selection of appropriate acceleration time histories and matching these histories to a code design acceleration spectrum. In literature, there are three sources of acceleration time histories: artificial records,synthetic records obtained from seismological models and accelerograms recorded in real earthquakes. Because of the increase of the number of strong ground motion database, using and scaling real earthquake records for seismic analysis has been becoming one of the most popular research issues in earthquake engineering. In general, two methods are used for scaling actual earthquake records: scaling in time domain and frequency domain. The objective of this study is twofold: the first is to discuss and summarize basic methodologies and criteria for selecting and scaling ground motion time histories. The second is to analyze scaling results of time domain method according to ASCE 7-05 and Eurocode 8 (1998-1:2004) criteria. Differences between time domain method and frequency domain method are mentioned briefly. The time domain scaling procedure is utilized to scale the available real records obtained from near fault motions and far fault motions to match the proposed elastic design acceleration spectrum given in the Eurocode 8. Why the time domain method is preferred in this study is stated. The best fitted ground motion time histories are selected and these histories are analyzed according to Eurocode 8 (1998-1:2004) and ASCE 7-05 criteria. Also, characteristics of both near fault ground motions and far fault ground motions are presented by the help of figures. Hence, we can compare the effects of near fault ground motions on structures with far fault ground motions\' effects.

이 논문에서는 안정대륙권역(Stable Continental Regions, SCRs)에서의 중규모 지진에 의한 근단층지반운동(Near Fault Ground Motion, NFGM) 모델을 처음으로 제시한다. 근단층지반운동은 큰 진폭의 장주기 속도 펄스를 갖는 특징을 가지고 있다. 이 속도 펄스를 모델링하기 위해서는 그 주기와 진폭을 지진의 규모와 단층거리의 함수로 표현할 수 있어야 한다. 그런데 안정대륙권역에서는 관측 자료가 빈약하여 지진데이터로부터 이 관계식을 직접 유도하는 것은 어렵기 때문에 이 연구에서는 간접적인 접근법을 채택하였다. 속도 펄스의 주기와 진폭은 단층파열의 상승시간과 파열속도의 함수임이 알려져 있고 활성구조권역(Active Tectonic Regions, ATRs)에 속하는 미국 서부지역에서는 실험적 공식이 확립되어 있다. 안정대륙권역에서의 상승시간과 단층파열속도의 지진규모에 대한 함수관계는 WUS와 CEUS에서의 자료를 비교하여 도출하였다. 이 관계식들로부터 안정대륙권역에서의 NFGM의 속도 펄스의 주기와 진폭을 지진규모 및 단층 거리에 대한 관계식으로 유도하였다. 안정대륙권역에서의 NFGM의 가속도 시간이력은 추계학적으로 생성된 원역지진지반가속도에 새로운 관계식에 의한 속도 펄스를 중첩하여 얻어진다. 적용 예제로서 탄소성 단자유도 시스템의 근단층지반운동에 대한 응답을 분석하였다. This paper proposes a method for modeling new fault ground motion due to moderate size earthquakes in Stable Continental Regions (SCRs) for the first time. The near fault ground motion is characterized by a single long period velocity pulse of large amplitude. In order to model the velocity pulse, its period and peak amplitude need be determined in terms of earthquake magnitude and distance from the causative fault. Because there have been observed very few new fault ground motions, it is difficult to derive the model directly from the recorded data in SCRs. Instead an indirect approach is adopted in this work. The two parameters, the period and peak amplitude of the velocity pulse, are known to be functions of the rise time and the slip velocity. For Western United States (WUS) that belongs active tectonic regions, there art empirical formulas for these functions. The relations of rise time and slip velocity on the magnitude in SCRs are derived by comparing related data between Western United States and Central-Eastern United States that belongs to SCRs. From these relations, the functions of these pulse parameters for NFGM in SCRs can be expressed in terms of earthquake magnitude and distance. A time history of near fault ground motion of moderate magnitude earthquake in stable continental regions is synthesized by superposing the velocity pulse on the for field ground motion that is generated by stochastic method. As an demonstrative application, the response of a single degree of freedom elasto-plastic system is studied.

In this study, a new mathematical model is developed composed of two parts, including harmonic and polynomial expressions for simulating the dominant velocity pulse of near fault ground motions. Based on a proposed velocity function, the corresponding expressions for the ground acceleration and displacement time histories are also derived. The proposed model is then fitted using some selected pulse-like near fault ground motions in the Next Generation Attenuation (NGA) project library. The new model is not only simple in form but also simulates the long-period portion of actual velocity near fault records with a high level of precision. It is shown that the proposed model-based elastic response spectra are compatible with the near fault records in the neighborhood of the prevailing frequency of the pulse. The results indicate that the proposed model adequately simulates the components of the time histories. Finally, the energy of the proposed pulse was compared with the energy of the actual record to confirm the compatibility.

<p>Near fault ground motion (NFGM) is a single long period velocity pulse of large magnitude. These earthquakes have caused severe and impulsive damage on various infrastructures because the epicentre is close to the urban area. These characteristics are unique compared to the far-fault ground motion (FFGM), upon which nearly all seismic design criteria are based. The objective of this study is to explore the shake table response of reinforced concrete bridge piers and to investigate near-fault ground motion effects on reinforced concrete bridge piers compared to those by the far fault ground motion. The seismic performance of two RC bridge piers under near-fault and far fault ground motions was investigated on the shake table. In addition, comparative tests were made for RC bridge piers subjected to Pseudo-dynamic loadings and Quasi-Static loadings. Test results showed that NFGM generally induced worse seismic performance than FFGM.</p>

In violent earthquakes, ground motion is considered to change dramatically in the process of spatial propagation. Strong spatially varying exists in ground motion near fault area, and it can cause the large-span and large stiffness structure to be damaged. In this paper, a typical long-span steel box arch bridge is selected as an engineering case. In order to simulate the spatial variation of near fault ground motion accurately, the records that sampled in former earthquake are used as ground motion input. The shaking table experiment and finite element analysis are used as analysis means. Through the analysis of the internal force and displacement response of the key position of the arch rib, it is found that the spatially varying in the near fault ground motion can bring severe seismic response. If the spatially varying is ignored, the damage of the bridge will be seriously underestimated.

In this paper, the seismic collapse probability of special steel moment-resisting frame (SSMRF) structures, designed to 4th edition of Iranian seismic design code, under near fault pulse-like and far fault ordinary ground motions is evaluated through fragility analysis. For this purpose, five sample frames with 3 to 15 stories are designed and imposed to the ground motion excitations with different characteristics. Fragility curves are derived for the sample frames using the results of incremental dynamic analyses. Three sets of near fault ground motion records with different range of pulse period and one set of far fault ordinary records are used in dynamic analyses. Each record set involves ten acceleration time histories on soil type III. Based on the obtained results, it was found that pulse-like motions with medium- and long-period pulses are significantly more destructive than other types of ground motions. Fragility analysis reveals that the average collapse probability for the case study frames under the far and near fault ground motions at the intensity of 0.35g equals to 4.3% and 10.3%, respectively. These values are 15.9%and 38.6%, for PGA of 0.53g. It is also found that the increase in the height, leads to increase in higher modes effect to transfer drift demands toward upper stories.

In common structural design codes, behaviour factor (R factor) is used to reduce earthquake design loads by taking advantage of nonlinear behaviour of structure during seismic events. There are some analytical approaches to evaluate behaviour factor using the results of incremental dynamic analysis (IDA) method. Using such methods, the variation of R factor values for different types of ground motions (near-fault and far-fault) can be investigated. Regarding the effect of near fault ground motions on ductility capacity of structures, R factor values are expected to be sensitive to the type of earthquake record. This issue is investigated through evaluation of R factor for three buckling-restrained braced frames (BRBF) for two sets of ordinary and near-fault ground motions. The results demonstrate that behaviour factor of BRBF structures is considerably lower for near-fault ground motions, compared to ordinary records. This is very critical for design of structures in near fault regions.

Seismic fragility analysis of containment structure subjected to near fault ground motions

Effect of supplemental damping on seismic response of base isolated frames under near & far field accelerations

Damping reduction equation for the equivalent linear analysis of seismic isolated structures subjected to near fault ground motions

Damage performance based seismic capacity and fragility analysis of existing concrete containment structure subjected to near fault ground motions