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Abstract

The Next Generation Attenuation (NGA) relationships for shallow crustal earthquakes in the western United States predict a rotated geometric mean of horizontal spectral demand, termed GMRotI50, and not maximum spectral demand. Differences between strike-normal, strike-parallel, geometric-mean, and maximum spectral demands in the near-fault region are investigated using 147 pairs of records selected from the NGA strong motion database. The selected records are for earthquakes with moment magnitude greater than 6.5 and for closest site-to-fault distance less than 15 km. Ratios of maximum spectral demand to NGA-predicted GMRotI50 for each pair of ground motions are presented. The ratio shows a clear dependence on period and the Somerville directivity parameters. Maximum demands can substantially exceed NGA-predicted GMRotI50 demands in the near-fault region, which has significant implications for seismic design, seismic performance assessment, and the next-generation seismic design maps. Strike-normal spectral demands are a significantly unconservative surrogate for maximum spectral demands for closest distance greater than 3 to 5 km. Scale factors that transform NGA-predicted GMRotI50 to a maximum spectral demand in the near-fault region are proposed.

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... These new generation attenuation relationships estimate ground motion values associated with a geometric mean of the horizontal spectral demand, lower than the maximum demand in the near field region affected by forward directivity. As a result, further investigation has been conducted in order to associate the predicted spectral values with this maximum spectral demand (Huang et al, 2008). Up to now this investigation has been undertaken for events with moment magnitude greater than 6.5. ...
... The ratios between maximum and mean spectral demands have been evaluated for different period ranges. According to Huang et al (2008), for most periods the strike normal component of the forward directivity records can be considered to represent the maximum spectral demand. Furthermore, for strong forward directivity and for periods 1.0 and 3.0 seconds, spectral ratios of 1.5 to 2.0 have been estimated. ...
... These amplification values refer to the period range between 1 and 2 sec, where quite a lot of existing structures have their larger natural period. The amplification values given by Huang et al (2008) to estimate forward directivity spectra through new generation attenuation relationships range from 1.5 to 2. This discrepancy could be attributed to the fact that amplification factors for those studies are computed from earthquakes with moment magnitudes larger than 6.5. For such earthquakes the pulse period is expected to be larger than 2 seconds. ...
Conference Paper
In this paper the moderate earthquake event of 1999, which affected the large urban area of Athens, is presented as a case study for the evaluation of the effects of strong directivity in the near field region for small to moderate events. Ground motion records at a distance from the causative fault are analyzed in order to estimate crucial characteristics associated with the event, as possible directivity pulses and their predominant period. Ground motions recorded at rock sites are scaled up to new generation attenuation models of characteristic spectra, accounting for either mean, near field, acceleration amplification or possible directivity related velocity pulses. These ground motions are used as input at the bedrock of typical soil deposits in order to obtain surface ground motions accounting for different soil profiles at various distances from the causative fault in the near field region. Inelastic spectra are generated and the difference between mean and strong, directivity affected, ground motion is established. For ground motions affected by forward directivity it is concluded that even for medium events seismic coefficients, provided by aseismic codes are inadequate for safe structural design. Seismic zonation coefficients must be re-examined and most likely upgraded in order to account for near field directivity, even in the case of moderate earthquake events.
... The matched acceleration spectra for 5% damping at the INL (LANL) site are presented in Fig. 4a and b ( Fig. 5a and b). (3) Scale the amplitudes of the two horizontal components in each set by factors to provide maximum direction-minimum direction (maxmin) ground motions that recover the geometric mean (Huang et al., 2008b(Huang et al., , 2009a. Amplitude scale factors F h and F 1/ h are applied to the two horizontal components in each set, and were selected by a Latin Hypercube procedure from a lognormal distribution with a mean, θ, of 1.3 and a logarithmic standard deviation, β, of 0.13 (see Huang et al. (2008b) for details). ...
... (3) Scale the amplitudes of the two horizontal components in each set by factors to provide maximum direction-minimum direction (maxmin) ground motions that recover the geometric mean (Huang et al., 2008b(Huang et al., , 2009a. Amplitude scale factors F h and F 1/ h are applied to the two horizontal components in each set, and were selected by a Latin Hypercube procedure from a lognormal distribution with a mean, θ, of 1.3 and a logarithmic standard deviation, β, of 0.13 (see Huang et al. (2008b) for details). The max-min ground motion acceleration spectra for 5% damping at the INL (LANL) site are presented in Fig. 4c and d (Fig. 5c and d). ...
... SPRA methodology(Huang et al., 2008b(Huang et al., , 2011a. ...
Article
The implementation of seismic base isolation can substantially reduce horizontal seismic demands on structures, systems, and components (SSCs) in a nuclear facility, potentially providing significant benefits in terms of increased safety (smaller seismic risk) and reduced capital construction cost. Although increased safety of SSCs has been demonstrated previously, the possible reduction in their capital cost has not been explored. To quantify the reduction in risk enabled by isolation, nonlinear response-history analysis of a conventionally founded and a base-isolated model of a generic nuclear facility (GNF) is performed at the sites of the Idaho National Laboratory and the Los Alamos National Laboratory: sites of moderate and high seismic hazard, respectively. Seismic probabilistic risk assessment is performed to compute the mean annual frequency of unacceptable performance. The seismic risk is reduced by 7 to 8 orders of magnitude by the implementation of isolation. The costs of addressing seismic loadings are estimated for the GNF in both the conventionally founded and base-isolated GNF. The possible reductions in the required seismic ruggedness and in the cost of SSCs in the isolated GNF are quantified at both sites. A reduction in cost enabled by isolation is possible at nearly all sites of nuclear facilities in the United States, with the greatest benefit at sites of high seismic hazard, such as LANL. Two risk-calculation procedures are used in the assessment: a simplified method based on Boolean mathematics and a rigorous method based on Monte Carlo analysis. The simplified procedure, which is suitable for implementation with preliminary design calculations, produces accurate estimates of risk unless the mean annual frequencies of unacceptable performance are very small, measured here as smaller than 10-10. The sensitivity of the calculated risk in the conventionally founded GNF, to the choice of anchor period for the seismic hazard curve, is investigated and found to be insignificant over the range considered: 0 to 0.10 second.
... Over the past two decades, directionality effects have received considerable attention. Research has been performed to assess these effects on recorded ground motions Pinzón et al., 2018a), intensity measures and their influences on the development of ground motion prediction equations Boore et al., 2006;Pinzón et al., 2018b), seismic demands of buildings (Rigato and Medina, 2007;Pinzón et al., 2019a;Fujii, 2016;Athanatopoulou, 2005;Cantagallo et al., 2012;Lagaros, 2010), probabilistic damage assessment (Vargas-Alzate et al., 2018), directivity effects in near-fault regions (Gordo-Monsó and Miranda, 2011;Huang et al., 2008;Garini and Gazetas, 2013), horizontal-to-vertical spectral ratios (Matsushima et al., 2017;Pinzón et al., 2019c;Stanko et al., 2017), seismic risk assessment of highways (Torbol and Shinozuka, 2014), and the performance of bridge foundations (Soltanieh et al., 2019). ...
... Therefore, a specific ground motion can have a greater effect on the performance of a building, depending on the orientation of these axes with respect to the action. Thus, the demand on the structure may strongly depend on the orientation of the building with respect to the direction in which the maximum intensity of the seismic action occurs, that is, depending on the azimuth of the building [see for instance Huang et al. (2008) and Vargas-Alzate et al. (2018)]. Figure E7b illustrates how the impact of a unitary force varies depending on the orientation of the building. ...
Thesis
Earthquakes are defined as a "violent shaking of the Earth’s crust and mantle, caused by forces acting inside the Earth". In most cases, these forces are caused by an energy release process generated from the contact of the Earth’s tectonic plates. Other less common causes are the human-induced earthquakes or those generated through volcanic activity. In either case, the energy is released in the form of multi-directional waves, which reach the surface, causing different effects. However, the intensity of an earthquake is not uniform in all its propagating directions. Many times, the motion is polarized due to the type of fault and/or the proximity to it, causing higher intensities in specific directions, depending on the dynamics and geometry of the rupture. This is what is known as the directivity effect. Furthermore, both the intensity and the shape of the wave vary depending on the propagation medium. Ground motion prediction models deal with the spread of the released energy from source to site. Local site effects, both soil effects and topographical effects, are also important. Rigid media, such as rocky and stiff soils, do not tend to amplify the seismic motion, while soft soils amplify specific frequencies depending on local sub-soil geology and on the motion characteristics. Directionality effects refer to the strong motion in a specific site. This thesis deals with two important issues related to directionality. The first one refers to the orientation of the sensors recording the seismic actions; the second one refers to the expected damage in buildings depending on the directions of their strong and weak main axes. It is worth to mention that nowadays, directionality effects are not considered in most structural regulations. In this thesis, special attention is paid to the directionality and soil effects. Since 2008, around 360,000 earthquake fatalities have been reported. This evidence demonstrates the need to develop more and better ways to assess and to prevent seismic risk. Therefore, the main objective of this thesis is to identify and evaluate the strong-motion directionality and the soils’ effects on the seismic hazard and risk, with applications to strong-motion data sets and soils’ in urban environments. This thesis is divided into three principal blocks: I) directionality effects, II) Soils effects, site classification and other seismic risk-related issues and, III) relevant case studies related to the previous two blocks. In the first block, directionality effects have been considered in the expected strong seismic actions, through the estimation of intensity measures using databases from Italy and Costa Rica. Also, in the assessment of the expected damage of buildings through non-linear dynamic analyses, a simplified approach has been proposed to consider directionality effects. In the second block, microzonation and soil-building resonance effects in the city of Barcelona are studied. In addition, a seismic site classification is defined for the Spanish strong-motion network. The dynamic soil-structure interaction, considering directionality effects and, the proposal of a new drift-correlated intensity measure, appeared as supplementary subjects in this block. Finally, in the third block, other relevant contributions were included to complement this dissertation. The results demonstrate 1) that directionality effects in expected seismic actions are significant and should be considered in Probabilistic Seismic Hazard Analysis (PSHA) and in seismic risk assessments; and 2) they confirm the relevance that site effects (soil effects), has both in seismic hazard studies and in the assessment of the expected damage. This PhD thesis wants to be an additional step towards the assessment, prevention, and reduction of the risk due to earthquakes.
... Project 07 [Kircher et al. (2010)], a joint effort of BSSC, FEMA and USGS resulted in three significant changes to design ground motions: (1) "probabilistic ground motions are now defined in terms of uniform risk, rather than uniform hazard, (2) ground motion intensity is now defined in terms of the maximum spectral response in the horizontal plane, and (3) The risk coefficients to convert from uniform hazard to uniform risk [Luco et al. (2007)] are used along with conversion factors to convert from the geometric mean to the maximum direction with 1.1 for 0.2s and 1.3 for 1s to obtain the MCER ground motion values. Several researchers in the past have studied the ratio of geometric to maximum direction ground motion definitions (Beyer and Bommer (2006); Watson-Lamprey and Boore (2007); Campbell and Bozorgnia (2008); Huang et al. (2008)). The maximum direction spectra are constructed by finding the spectral response trace at each oscillator-period of the two horizontal ground motions. ...
... The maximum direction spectra are constructed by finding the spectral response trace at each oscillator-period of the two horizontal ground motions. To setup up the spectral trace, time history analysis is performed using the two horizontal ground motions assuming equal period in both the directions [Huang et al. (2008)]. The response time histories are plotted together simultaneously assuming the time axis to be out of plane, resulting in the spectral trace. ...
Thesis
Full-text available
The definition of hazard-consistent ground motions for seismic design has been an active area of research in the past few decades. With the advancements in computing power we have taken giant steps in performance based seismic design (PBSD). At the heart of PBSD is performing non-linear response history analysis to verify the performance of a structural design. Among the challenges faced by engineers conducting response history analysis is the selection/generation of a set of ground motions that are compatible with a target spectrum that is representative of the seismic demand of the structure of interest. There are several ways to obtain spectrum compatible records. One can do scaling of the ground motions to closely match the response spectrum of an individual record to the design target spectrum. Another method is based on time or frequency domain modifications of the recorded acceleration time series to make them spectrum compatible. The focus of this study is to use spectral matching techniques to represent bi-directional demands accurately. The code spectrum represents bi-directional demand, which is quantified by either geo-mean spectrum (ASCE 7-05) or the maximum direction spectrum (ASCE 7-10). For 3-D analysis, the structure must be subjected to a pair of ground motions accounting for the bi-directional demand of the code spectrum. Although the present code provisions indicate that the RotD100 (Maximum direction) spectra of the individually matched motions be at least 110% of the design spectra, the values are well over 110% according to the analysis presented herein. The primary objective of this study is to propose a spectral matching method that captures the bi-directional demand of the structure and is compatible with design code requirements, named the “Match and Scale” approach. 398 pairs of ground motion records are considered to compute the mean and standard deviation of the scaling factors across oscillator periods. The proposed scaling factors represent the mean of the ratio of RotD100 spectral value of the individually matched motions to the spectral ordinates of the design target spectrum across all periods. Furthermore, another method to simultaneously match pairs of ground motions RSPmatchBi by Grant (2011), is explored for comparison purposes. The accuracy of the proposed method is assessed by performing non-linear time history analysis for bi-directional input and evaluating the variation in structural response as a result of considering different orientations of the input ground motion. The median structural response results from the proposed method is compared with the median response obtained with RSPmatchBi. The median responses fall in the same range, thus validating the proposed method.
... At the same time, efforts have been made to develop GMPEs based on the rotated definitions such as GMRotDxx and GMRotIxx. A number of similar studies have been reported, but mostly to modify the prediction of GMPEs based on GMRotI50, 36,37,38,39 Some structural designers consider RotD100 is better definition for structural design among the all as it intends to capture the maximum demand imposed by a single component over all possible rotations but GMPEs were developed on the basis of RotD50. 40 Shahi and Baker 26 reported possible modification through prediction of the ratio of RotD100 to RotD50. ...
... Alternatively, a much efficient construction is generally followed 38 and for which, one may write ...
Article
Orientation of a structure in a site is generally known but not the direction of maximum shaking during a future seismic event. Two different types of intensity measures (IMs) are usually used to approximately account for this directionality effect, namely, the rotation dependent such as RotDxx and GMRotDxx and the rotation independent such as RotIxx and GMRotIxx. Rotation dependent IMs are presently constructed by performing time history analysis for all possible orientation (usually @ 1 degree) of the input ground motion set followed by picking the xx‐percentile spectral ordinate. In other words, the construction of RotDxx spectrum requires a set of 180 time history analysis of an oscillator per spectral ordinate. Similarly, the construction of GMRotDxx requires time history analysis of an oscillator against 90 pairs of orthogonal components per spectral ordinate. This paper presents a framework that enables the construction of rotation dependent IMs by performing time history analysis against a pair of as‐recorded components with some nominal supplemental processing. This reduces the computational cost more than 90% when compared with the state of the art. Rotation independent IMs are defined through finding out the rotation that minimizes the error (often termed as the penalty function) with respect to the target spectra of associated rotation dependent IM as the benchmark. Resulting rotation independent IMs show somewhat sensitivity on the maximum time period used in spectral representation. This paper presents an alternate definition (involving scaling and rotation) for rotation independent IMs that nearly eliminates such sensitivity.
... Also, they did not find any dependency on the most common directivity factors for the ratio of SA RotD100 =SA GMRotI50 . Huang et al. (2008) investigated the relationships between strike-parallel, strike-normal, geometric mean, and maximum spectral demands using a subset of the NGA-West2 database, including 147 records from near-field earthquakes with moment magnitude M of 6.5 and greater, and rupture distances of 15 km and less. They developed scaling factors to transform SA GMRotI50 to SA RotD100 , which ranged from 1.2 at a period of 0 to 1.3 at a period of 4.0 s, similar to the Beyer and Bommer (2006) results. ...
... For greater distances, there is approximately a 40%-50% probability that the strike-normal demands are equal to or fall below the strikeparallel demands. Huang et al. (2010) expanded the Huang et al. (2008) results by adding 165 pairs of western United States far-field ground motions with the moment magnitudes M 6.5 and greater, and the closest site-to-source distances between 30 and 50 km. They also added 63 pairs of ground-motion records from 19 earthquakes that occurred generally in CENA and provided the median ratio of SA RotD100 =SA GMRotI50 for each dataset separately. ...
Article
Full-text available
A single ground-motion intensity measure, typically spectral acceleration (SA), is required as the main input in deriving empirical ground-motion prediction equations (GMPEs). Traditionally, a single horizontal orientation has been used in calculating SA for all periods. The spectrum changes with orientation, and using a single orientation to represent 2D ground motions leads to loss of useful information regarding the variation of SA with orientation. Different techniques have been proposed in the literature to combine the two horizontal components of ground motions into a scalar horizontal definition. The ratios between different definitions of the horizontal component of ground motions have been studied because of the urgent need to use multiple GMPEs combined in a logic-tree framework in the preliminary stages of performing probabilistic seismic hazard analysis, or at further stages in which the uniform hazard response spectrum is required to be converted to another spectrum for a different horizontal definition. Although the most recent studies produced similar results using different subsets of the Next Generation Attenuation-West2 Project (NGA-West2) database, it is possible that such directionality results may differ for other earthquake datasets and is region specific. The purpose of this study is to derive ratios between median values and the associated standard deviations for different definitions of the horizontal component of ground motions in central and eastern North America using a subset of the NGA-East database. The computed median ratios are similar to the ratios provided in recent studies for other regions with a shift in some period ranges with noticeable differences between the standard deviations. The results of this study fulfill the engineering requirements of considering the maximum direction elastic response spectrum for design of structures.
... Seismic isolation is a viable strategy for protecting safetyrelated nuclear structures, including nuclear power plants, from the effects of extreme earthquake shaking (e.g., Huang et al. [1], Kammerer et al. [2]). For large light water reactors, the isolation system will likely be installed in a horizontal plane immediately below the basemat and above a foundation, as shown in Fig. 1. (For small modular and advanced reactors, isolators may be used to protect an entire plant but be placed at multiple levels below grade, or protect individual structures, systems and components within the plant; see [3] for details.) ...
... The two orthogonal horizontal components of recorded earthquake ground motions are consistently different (e.g., [1,20,21]) and the orientation of the maximum-direction shaking is random at a distance of more than approximately 5 km from the causative fault [22]. To accommodate this difference in the amplitude of the two horizontal components, a maximum-direction spectrum was developed and introduced into ASCE/SEI Standard 7-10 [14]. ...
... However, in the case of seismically isolated buildings with plan irregularities, their nonlinear responses depend on the direction of seismic loading. In addition, near-fault pulse-like ground motions observed in past earthquakes have been characterized by large directivity (e.g., Somerville et al., 1997;Bray and Rodriguez-Marek, 2004;Baker, 2007;Huang et al., 2008;Shahi et al., 2014). Because some near-fault pulse-like ground motions may cause large responses in structures with long periods (e.g., Hall et al., 1995;Güneş and Ulucan, 2019), the influence of the direction of incidence of such pulse-like ground motions to the response of seismically isolated irregular structures is an important issue. ...
Article
Full-text available
In general, isolators and dampers used in seismically isolated buildings are designed to be isotropic in any horizontal direction. However, in the case of buildings with plan irregularities, their nonlinear responses depend on the direction of seismic loading. To discuss the influence of the angle of seismic incidence (ASI) on the nonlinear response of irregular building structures, it is important to define the angle of the critical axis of the horizontal ground motion. One possible choice is the “principal axis of ground motion” proposed by Arias (A measurement of earthquake intensity, 1970). However, because this principal axis is independent of the natural period of a structure, it could be complicated to use for seismically isolated structures with long natural periods. In this study, the influence of the ASI of long-period pulse-like seismic input on an irregular base-isolated building is investigated. First, the angle of the principal axis of ground motion is defined in terms of the cumulative energy input. Then, a nonlinear time-history analysis of a five-story irregular baseisolated building is performed using 10 long-period pulse-like ground motion records considering various ASIs. The results show that, compared with the principal axis of ground motion proposed by Arias, defining the principal axis of ground motion in terms of the cumulative energy input is more suitable for discussions concerning the influence of the ASI on the response of an irregular base-isolated building.
... However, in the case of seismically isolated buildings with plan irregularities, their nonlinear responses depend on the direction of seismic loading. In addition, near-fault pulse-like ground motions observed in past earthquakes have been characterized by large directivity (e.g., Somerville et al., 1997;Bray and Rodriguez-Marek, 2004;Baker, 2007;Huang et al., 2008;Shahi and Baker, 2014). Because some near-fault pulse-like ground motions may cause large responses in structures with long periods (e.g., Hall et al., 1995;Güneş and Ulucan, 2019), the influence of the direction of incidence of such pulse-like ground motions to the response of seismically isolated irregular structures is an important issue. ...
Preprint
Full-text available
In general, isolators and dampers used in seismically isolated buildings are designed to be isotropic in any horizontal direction. However, in the case of buildings with plan irregularities, their nonlinear responses depend on the direction of seismic loading. To discuss the influence of the angle of seismic incidence (ASI) on the nonlinear response of irregular building structures, it is important to define the angle of the critical axis of the horizontal ground motion. One possible choice is the “principal axis of ground motion” proposed by Arias (1970). However, because this principal axis is independent of the natural period of a structure, it could be complicated to use for seismically isolated structures with long natural periods. In this study, the influence of the ASI of long-period pulse-like seismic input on an irregular base-isolated building is investigated. First, the angle of the principal axis of ground motion is defined in terms of the cumulative energy input. Then, a nonlinear time-history analysis of a five-story irregular base-isolated building is performed using 10 long-period pulse-like ground motion records considering various ASIs. The results show that, compared with the principal axis of ground motion proposed by Arias, defining the principal axis of ground motion in terms of the cumulative energy input is more suitable for discussions concerning the influence of the ASI on the response of an irregular base-isolated building.
... However, in the case of buildings with plan irregularities, their nonlinear responses depend on the direction of seismic loading. In addition, near-fault pulse-like ground motions observed in past earthquakes have been characterized by large directivity (e.g., Somerville et al., 1997;Bray and Rodriguez-Marek, 2004;Baker, 2007;Huang et al., 2008;Shahi and Baker, 2014). Because some near-fault pulse-like ground motions may cause large responses in structures with long periods (e.g., Hall et al., 1995;Güneş and Ulucan, 2019), the influence of the direction of incidence of such pulse-like ground motions to the response of seismically isolated irregular structures is an important issue. ...
Preprint
Full-text available
In general, isolators and dampers used in seismically isolated buildings are designed to be isotropic in any horizontal direction. However, in the case of buildings with plan irregularities, their nonlinear responses depend on the direction of seismic loading. To discuss the influence of the angle of seismic incidence (ASI) on the nonlinear response of irregular building structures, it is important to define the angle of the critical axis of the horizontal ground motion. One possible choice is the "principal axis of ground motion" proposed by Arias (1970). However, because this principal axis is independent of the natural period of a structure, it could be complicated to use for seismically isolated structures with long natural periods. In this study, the influence of the ASI of long-period pulse-like seismic input on an irregular base-isolated building is investigated. First, the angle of the principal axis of ground motion is defined in terms of the cumulative energy input. Then, a nonlinear time-history analysis of a five-story irregular base-isolated building is performed using 10 long-period pulse-like ground motion records considering various ASIs. The results show that, compared with the principal axis of ground motion proposed by Arias, defining the principal axis of ground motion in terms of the cumulative energy input is more suitable for discussions concerning the influence of the ASI on the response of an irregular base-isolated building.
... In the forward directivity, the PGA in the fault-normal direction can be much greater with a longer period velocity pulse-like dimension than the fault-parallel (Gerami and Abdollahzadeh 2012). The geometric mean spectral level is generally used in the PSHA (Huang et al. 2008), where its value is determined by only the square-roots of the product between the spectral in x-direction and y-directions, accordingly, and the directivity effects should be taken into account. However, sometimes it used the biggest spectral between 2-direction records (Bradley and Baker 2014; Boore 2010). ...
Article
Full-text available
The objective of this study is to ascertain the causes of damage to buildings that occurred due to an earthquake near its source, particularly in the Pleret sub-district in Yogyakarta Special Province Indonesia. This study was conducted because a large percentage of human fatalities and structural collapse occurred during the Yogyakarta earthquake of May 27, 2006. Since the earthquake records on the site are not available, another way to obtain synthetic ground motions can be done in ways suggested by Bulajic and Manic (Motion records as a seismological input for seismic safety evaluation engineering structures, 2005), Rezaeian and Kiureghian (Earthq Eng Struct Dyn 39:1155–1180, 2010). Towards these ends, this research applied the Total Probability Theorem in the Seismic Hazard Probability Analysis (PSHA) with 3-D seismic sources. In this case, the PSHA analysis was carried out based on a 10% probability exceeded for 50 years building life time. The obtained uniform hazard spectrum (UHS) was then transferred to the risk targeted Maximum Credible Earthquake MCEr through the directivity factor Df and risk targeted factor Rf with an average increase of 8.13% to UHS. Three earthquake records were selected, and after spectral matching, the high ranging bedrock accelerations were obtained from 0.254 to 0.289 g. After conducting site response analysis, peak ground accelerations on the ground surface varied from 0.398 to 0.412 g. Furthermore, acceleration site amplifications between 1.401 and 1.426 were obtained, which are higher than the spectral site amplification between 1.215 and 1.385. Since the site amplification is still in the normal category, building damage is mostly caused by relatively high levels of ground acceleration and shaking to relatively old buildings with low material and construction quality. Although the study is still in its early stages, there are indications of fling effects on the site even though the intensity is relatively small.
... The ground motion intensity is not uniform in all orientations and can be significantly stronger in one orientation. 7,8 This is often referred as "directionality" of a ground motion. As one of the first steps towards understanding the failure mode of Wall D5-6, the directionality (earthquake loading pattern) of two of the major earthquakes that hit the GCH building was investigated (i.e., 4 September 2010 and 22 February 2011). ...
Article
On 22 February 2011, one of the main structural walls of one of the tallest buildings in Christchurch, New Zealand (Grand Chancellor Hotel), had an extremely brittle and unusual failure that significantly damaged the building, severely compromising its structural stability. To this date, this peculiar failure mode has not yet been fully investigated and understood. Moreover, currently, it is not possible to identify and assess walls that are prone to this failure mode. Following recent findings based on experimental investigations, this failure mode was identified as out‐of‐plane shear‐axial failure. A Finite Element (FE) model was developed in DIANA to capture this failure mode, and through a numerical parametric study, the key parameters that contribute to the development of this failure mode in rectangular reinforced concrete (RC) walls were identified. Solid elements were used for the concrete material and embedded truss elements for the steel reinforcement. Bar buckling was not included in this investigation due to the limitation of DIANA in implementing the bar buckling and Menegotto‐Pinto models together, among which the latter was found to be more influential on the behaviour of RC walls investigated in this study. Based on the numerical and experimental studies conducted, an analytical method is proposed to: (1) identify rectangular walls prone to out‐of‐plane shear‐axial failure as a first‐level check for both design and assessment purposes; and (2) determine the out‐of‐plane drift capacity of rectangular walls prone to out‐of‐plane shear‐axial failure. Design recommendations are provided for rectangular walls prone to out‐of‐plane shear‐axial failure.
... In addition, some relationships among various measures for the bidirectional demand are reviewed. The ratio RotD100/GMRotI50 was found to be period-dependent and ranging between 1.2 and 1.3 in the period range between 0 and 4 seconds for earthquakes in the near fault region, based on the study of Huang et al. 28 That study also found that the maximum-direction spectrum can substantially exceed the strike-normal spectral demand in the near-fault regions. Watson-Lamprey and Boore 29 provided the conversion factor from the GMRotI measures to the rotated elastic spectral value of a randomly chosen direction. ...
Article
Full-text available
In this study, the effects of the degree of directionality on critical seismic performance assessment are investigated from two aspects: the bidirectional seismic demand represented by maximum‐direction spectrum and the performance indices obtained from nonlinear time‐history analysis. Firstly, typical representations of the bidirectional demand of ground motions are reviewed and compared, in seismic design practices (e.g., ASCE 7‐16, Eurocode8, and JRA). Statistical analysis using 83 ground motions underlines the implication of the spectrum‐compatible condition that has not been fully considered in past studies investigating the bidirectional effects. In the second part, a series of spectrum‐compatible bidirectional ground motions with various degrees of directionality are generated as inputs. The corresponding seismic performance assessment results of a base isolation building with the friction pendulum system are investigated. According to the simulation results, the current design practices could introduce unconservative assessment on the maximum bearing displacement due to the omission of the directionality effect included in the design ground motions, particularly, when the directionality parameter is at a large value (less directionality). The cases with nondirectionality always tend to result in a nearly constant envelope of the maximum interstory drift and the maximum floor acceleration assessment for the full directionality case, over all incident directions. For the critical seismic performance assessment, the two extreme cases, namely the full directionality and nondirectionality cases, are recommended to be considered.
... return periods are given for geometric mean and maximum rotated inTable 3. The maximum direction spectral ordinates are obtained by modifying Sa GM with period-dependent factors proposed in Huang et al.[47]. These factors are also suggested in the 2009 edition of the National Earthquake Hazard Reduction Program[48], provisions (BSSC, 2009), and the ASCE/SEI 7-10 (ASCE, 2010) document. ...
Article
The size and importance of maritime transportation in world trade are well known. The number of ports, which is one of the most important elements of maritime transportation, is increasing day by day not only in our country but also throughout the world. Many active fault systems in our country are located at sea. In the Marmara Region in particular, most active branches of the North Anatolian Fault system pass through the Sea of Marmara. When offshore structures such as ports are constructed in high-seismicity zones such as the Sea of Marmara, conducting site-specific seismic hazard studies is necessary to reduce the seismic risk of offshore structures. In 2007, the first Turkish Seismic Design Code for Port Structures was published, which introduced new design concepts in the seismic design of offshore structures. According to this code, the design can be finalized in three basic steps: assessment of regional seismicity, estimation of geotechnical hazards, and soil-structure interaction analysis of offshore structures. Nowadays, the first Turkish Seismic Design Code for Port Structures is on the verge of a major update, which was published as a draft report in May 2019. In this manuscript, site-specific probabilistic seismic hazard analysis is needed to determine the seismic hazard associated with typical port sites. Considering this new draft code as a guideline document, we developed consistent seismic hazard studies for offshore structures within the Haydarpaşa Port sites. Unlike the old one, this new document identifies four different levels of ground motion: minimum damage level earthquake (TR=72), limited damage level earthquake (TR=144), controlling damage level earthquake (TR=475), and maximum considered earthquake (TR=2.475).
... 3 relationships gives maximum direction response spectral acceleration of the 110% of 5% damped at short period and 130% at 1 second period. [11]. ...
Article
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The primary objective of the study is to analyze the effect of the horizontal definition in the ground motion selection, in which, how the target spectra of DBE and MCE resulted from the geometric mean method and NGA West-2 Sa RotD100 , the maximum direction method is different from each other. The analysis of the seismic performance of the building is the secondary aim of the research. The linear design methods of equivalent lateral force analysis, response spectrum and seismic response history analysis are performed based on the Myanmar seismic design code to figure out and compare the building responses such as story displacement, story drift, story base shear, and story overturning moment. In this study, the irregular shaped RC building structural responses are also explored with equivalent lateral force analysis (EQLF), response spectrum analysis (RSA) and linear response history analysis (LRHA). The recent ground motion definition response shows great potential in improving the performance-based design of considered structures.
... For example, the target spectrum of the ASCE 7-10 code (ASCE, 2013) represents the maximum direction spectral acceleration for any possible orientation (RotD100), whereas the target spectrum of the Italian Building Code NTC08 represents the maximum spectral acceleration between two orthogonal directions (Max NS-EW ). When selecting accelerograms for the analysis of 3D structures, the use of the maximum direction spectrum is suggested since it automatically takes into account the bidirectional effects of ground motion (Huang et al., 2008;NIST, 2011). Therefore, the maximum direction spectrum of each pair of orthogonal accelerograms should be computed and then the average of the n selected maximum direction spectra should be compared with the target spectrum. ...
Chapter
It should be widely taken to heart that the continued practice of PSHA for determining earthquake resistant design standards for civil protection, mitigation of heritage and existing buildings and lifelines, and community economic well-being and resilience... is in a state-of-crisis. And alternative methods, which are already available and ready-to-use, like NDSHA, should be applied worldwide. The results will then be twofold: (1) not only to extensively test these alternative methods; but (2) to prove that they globally actually perform more reliably and safely than PSHA.
... Spectral matching as detailed in [7] is used to obtain MCE spectrum compatible ground acceleration, and the results are shown in Figure 2 for horizontal spectra. Since maximum rotated (MR) spectra should be used for the isolator design of base isolated structures, MR spectra is also obtained from geometric mean (GM) spectra using factors provided by [8]. These factors are shown in Figure 3. ...
Conference Paper
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This paper presents the structural and seismic design of two data centers with Tier III and Tier IV class resilience levels that are located in a region with high seismicity. The first project is a commercial facility that will be one of the largest data center of Turkey and intended to have Tier III rating. During the design of this project, it is observed that tier requirements for structural and seismic design of data centers are not given in detail in the related IT standards. A detailed design basis, which is presented in the first paper of this study, is developed by authors to facilitate the design after a thorough multidisciplinary design process. As the key objectives, operational level performance is set for the structural and nonstructural components for the design basis and maximum considered earthquake levels. Acceleration limits are set for sensitive computer equipment based on the feedback from IT professionals. Seismic base isolation of the complete building with high-performance friction pendulum isolators is utilized to achieve stringent design objectives. Superstructure is comprised of a steel structure with large spans resting on a thick reinforced concrete isolation slab, which allows large white spaces and future modifications. Substructure is comprised of short columns and mat foundation that provides ample maintenance space. Fundamental results of the design including the structural member sizes, isolator parameters, isolation displacements, isolation and first floor shears, floor accelerations are presented. Design of nonstructural components, anchorages and other components are reviewed and representative details are provided. The second data center is a confidential project with Tier IV class resilience, and a similar design basis is utilized. Structural and base isolation systems of the second project are similar to the first project, and basic results for this project are presented. It is shown that the seismic design of the data centers satisfy the requirements of the design basis and provide a seismic safety suitable for Tier III and Tier IV operational resilience. ABSTRACT This paper presents the structural and seismic design of two data centers with Tier III and Tier IV class resilience levels that are located in a region with high seismicity. The first project is a commercial facility that will be one of the largest data center of Turkey and intended to have Tier III rating. During the design of this project, it is observed that tier requirements for structural and seismic design of data centers are not given in detail in the related IT standards. A detailed design basis, which is presented in the first paper of this study, is developed by authors to facilitate the design after a thorough multidisciplinary design process. As the key objectives, operational level performance is set for the structural and nonstructural components for the design basis and maximum considered earthquake levels. Acceleration limits are set for sensitive computer equipment based on the feedback from IT professionals. Seismic base isolation of the complete building with high-performance friction pendulum isolators is utilized to achieve stringent design objectives. Superstructure is comprised of a steel structure with large spans resting on a thick reinforced concrete isolation slab, which allows large white spaces and future modifications. Substructure is comprised of short columns and mat foundation that provides ample maintenance space. Fundamental results of the design including the structural member sizes, isolator parameters, isolation displacements, isolation and first floor shears, floor accelerations are presented. Design of nonstructural components, anchorages and other components are reviewed and representative details are provided. The second data center is a confidential project with Tier IV class resilience, and a similar design basis is utilized. Structural and base isolation systems of the second project are similar to the first project, and basic results for this project are presented. It is shown that the seismic design of the data centers satisfy the requirements of the design basis and provide a seismic safety suitable for Tier III and Tier IV operational resilience.
... Design spectra should be obtained using both geometric mean (GM) and maximum rotated (MR) measures. MR spectra can be obtained from GM spectra using literature on historical near-field earthquakes such as Huang, Whittaker [8]. Table 5. ...
Conference Paper
Full-text available
This paper proposes a seismic design basis for Tier III and Tier IV class data centers to achieve consistent levels of seismic resilience. Many organizations heavily rely on the operational continuity of data centers for everyday operations. As such, design of data centers is based on a paradigm that has resilience at its focal point. To quantify, standardize and compare the resilience with objective measures, a four-level tiered classification system is being used. However, structural and seismic focus of these tiers are provided in a brief format, and there are some inconsistencies between prescriptive and performance-based requirements. In overall, a sound design basis with clear details should be established to have consistent levels of resilience. To propose a design basis, first, a brief summary and critique of the structural tiering reference guide provided by the main standard for data center design and tiering, TIA-942-A, is given. Then, structural and seismic design challenges associated with the requirements of this standard and data centers in general are discussed. A design basis that addresses these challenges and satisfy the baseline criteria provided by TIA-942-A is proposed based on an intense multidisciplinary study. The design basis set the intent and include criteria for but not limited to the design and performance evaluation of structural and nonstructural elements, acceleration limits, inclusion of vertical ground motion and base isolation. Emphasis is given to base isolation since conventional structural systems are known to have difficulty to achieve the high levels of required performance with reasonable cost. Criteria for base isolation include displacement and axial load capacity of isolators, use of geometric mean and maximum direction spectra for isolator and superstructure design, scaling or spectral matching of historical ground accelerations to a design spectrum including the vertical ground motion. It is considered that proposed design basis establishes a sound ground for seismic design of data centers that is compatible with available tier classification. ABSTRACT This paper proposes a seismic design basis for Tier III and Tier IV class data centers to achieve consistent levels of seismic resilience. Many organizations heavily rely on the operational continuity of data centers for everyday operations. As such, design of data centers is based on a paradigm that has resilience at its focal point. To quantify, standardize and compare the resilience with objective measures, a four-level tiered classification system is being used. However, structural and seismic focus of these tiers are provided in a brief format, and there are some inconsistencies between prescriptive and performance-based requirements. In overall, a sound design basis with clear details should be established to have consistent levels of resilience. To propose a design basis, first, a brief summary and critique of the structural tiering reference guide provided by the main standard for data center design and tiering, TIA-942-A, is given. Then, structural and seismic design challenges associated with the requirements of this standard and data centers in general are discussed. A design basis that addresses these challenges and satisfy the baseline criteria provided by TIA-942-A is proposed based on an intense multidisciplinary study. The design basis set the intent and include criteria for but not limited to the design and performance evaluation of structural and nonstructural elements, acceleration limits, inclusion of vertical ground motion and base isolation. Emphasis is given to base isolation since conventional structural systems are known to have difficulty to achieve the high levels of required performance with reasonable cost. Criteria for base isolation include displacement and axial load capacity of isolators, use of geometric mean and maximum direction spectra for isolator and superstructure design, scaling or spectral matching of historical ground accelerations to a design spectrum including the vertical ground motion. It is considered that proposed design basis establishes a sound ground for seismic design of data centers that is compatible with available tier classification.
... Huang et al. [39] utilized a ratio (�1.0) of the maximum spectral value to strike-normal spectral demand to examine the effectiveness of the strike-normal direction as representative of the maximum spectral direction. The ratio shows a clear dependence on the period of vibration and closest site-to-fault distances. ...
Article
The ground motion pulse-like effect depends on its orientation, it is thus necessary to identify the direction of the ground motion with the strongest pulse. A simple yet efficient method to identify the strongest pulse over all orientations in multicomponent ground motions is presented in this study, through rotating the ground motions to the orientation associated with the maximum peak ground velocity (PGV). It is demonstrated that the pulse-like ground motion components in the orientation with the maximum PGV value have the potential to produce the largest mean/median ductility than the components rotated to all remaining orientations. A comparison of the proposed methodology with an existing method is also performed, further demonstrating that the proposed maximum PGV methodology can accurately identify the strongest pulse. The determined strongest pulse can be utilized in engineering practice to estimate the maximum seismic demands on structures.
... Later, in another paper, he [1] worked on the response spectra of near-fault ground motions. Huang et al. [10] evaluated the maximum seismic spectral demand in the near-fault region. Shahi and Baker [11], did a regression analysis to find the probability density function for estimating the occurrence probability of velocity pulse in the near-fault area. ...
Article
This research attempts to study the pulse-like ground motions, recorded on the Iranian plateau, and propose predictive equations for simulating the main features of this type of signal. In this regard, firstly, the statistical characteristics of pulse-like records of the Iranian database, containing 770 events and 1206 accelerograms, are statistically investigated. The probability density function of facing a pulse-like signal, for a given location, is obtained, and the main features of acceleration and velocity spectra of these signals are evaluated for the horizontal and vertical directions. Interestingly, the mean value of vertical to horizontal ratio of spectral acceleration of signals reaches above one in many cases. In the next part, a set of ground motion prediction equations are presented for simulating the major properties of velocity pulse itself, including the amplitude, period, and the occurrence time during the recorded time series. Besides to these equations, another set of GMPEs is proposed for generating the 5% damped spectral acceleration of the horizontal and vertical pulse-like ground motions simultaneously considering their component's correlation. These newly developed equations are compared and validated with the existing GMPEs of the Iranian plateau. All of the suggested equations are applicable for the magnitude between 4.0 and 6.5, the site-to-source distance of 2 km–100 km, the focal depth of 2–40 km, and the shear wave velocity of underlying soil varying between 200 m/s to 900 m/s.
... Some studies [56][57][58] investigated the seismic responses of the structures subjected to the near-fault ground motions. Several investigations [59][60][61][62][63][64][65][66][67][68][69] on the strength reduction factors of the common structures with the corresponding models (including Elasto-perfectly plastic (EEP) model, Bilinear model, degradation model and pinching model) under near-fault motions were also carried out for the structural seismic design. However, these studies did not account for the self-centering structure with self-centering model, especially for the near-fault ground motions with pulse-type. ...
Article
Full-text available
This paper focuses on the strength reduction factor spectra for self-centering (FS) model subjected to near-fault ground motions with pulse-type based on nonlinear dynamic analysis of single degree of freedom (SDOF) system. In order to investigate the influence of the the FS model on the strength reduction factor, the ratio of the strength reduction factor of the FS model and that of Elastic-Perfectly-Plastic (EPP) model is evaluated and discussed. The ratio is larger than 1.0 and the maximum value can reach 1.35 during medium and long period. This result indicates that it is conservative for the structural design of the self-centering structure when the strength reduction factor for EPP model is used. The investigations of the effects of the post-yielding stiffness ratio and the energy dissipation ratio of the self-centering model on the strength reduction factor are also carried out.
... Common choices of target spectra include the Uniform Hazard Spectrum (UHS) and the Conditional Mean Spectrum (CMS) [8]. We choose to study the UHS rather than a Uniform Risk Spectrum [6] because applying the "risk adjustments" [9] tends to negate the effects of transforming the horizontal component to "maximum direction" [10]. ...
Conference Paper
Full-text available
The Conditional Mean Spectrum (CMS) is often employed to select ground motions for intensity-based assessments of tall buildings. However, the seismic demands determined by response history analyses with ground motions from a single CMS may be unconservative because multiple vibration modes often significantly influence the response of tall buildings. Existing solutions to this problem include analyzing the building with: (i) a Uniform Hazard Spectrum (UHS), (ii) multiple CMSs conditioned on different vibration periods, and (iii) a complete risk-based assessment. To minimize computational effort while preserving accuracy, we propose an alternative target spectrum that combines features from both the CMS and the UHS (referred to as the CMS-UHS Composite Spectrum). Results from a realistic case study suggest that this engineering solution provides seismic demands that are as accurate and precise as those obtained from analyzing the building with multiple CMSs while simultaneously reducing the computational effort by a factor of two or more. ABSTRACT The Conditional Mean Spectrum (CMS) is often employed to select ground motions for intensity-based assessments of tall buildings. However, the seismic demands determined by response history analyses with ground motions from a single CMS may be unconservative because multiple vibration modes often significantly influence the response of tall buildings. Existing solutions to this problem include analyzing the building with: (i) a Uniform Hazard Spectrum (UHS), (ii) multiple CMSs conditioned on different vibration periods, and (iii) a complete risk-based assessment. To minimize computational effort while preserving accuracy, we propose an alternative target spectrum that combines features from both the CMS and the UHS (referred to as the CMS-UHS Composite Spectrum). Results from a realistic case study suggest that this engineering solution provides seismic demands that are as accurate and precise as those obtained from analyzing the building with multiple CMSs while simultaneously reducing the computational effort by a factor of two or more.
... is arbitrary for fault distances greater than approximately 3-5 km (Campbell and Bozorgnia, 2008). At closer fault distances, however, the azimuth of this component tends to align with the strike-normal orientation (Huang et al., 2008). Ground motions are usually recorded at two arbitrary orientations that are not necessarily the orientations of the strongest (FD) and weakest (PD) pulses. ...
Article
Full-text available
This study evaluates primarily the effectiveness of seismic isolation for structures with intermediate and relatively long non-isolated periods (e.g., bridges with tall piers) subjected to near-field (NF) and far-field (FF) excitations. The inelastic response spectrum approach is used to systematically evaluate the effects of the two fundamental aspects of seismic isolation, i.e., period lengthening and lateral-strength reduction on the force and displacement demands on isolated structures. To validate the results, the real-world isolated Rudshur bridge with a relatively flexible (long-period) substructure is studied. Additional isolated and non-isolated variants of the Rudshur bridge with different initial periods are also developed. 20 FF (non-pulse) and 20 NF (pulse type) ground motions are used for nonlinear response history analyses. The results illustrate that when designed properly, seismic isolation can effectively reduce the mean base shear and acceleration responses of structures with relatively long non-isolated periods under FF excitations. For these structures, seismic isolation does not significantly increase the mean displacement responses under FF excitations, and even for particular cases, can reduce them. For the NF excitations, seismic isolation can significantly reduce the mean base shear responses of intermediate- to long-period structures. In some cases, this reduction is more significant than that for FF excitations. However, when the initial period of the isolated structure is relatively long (e.g., greater than 2.5 s), NF excitations can impose significantly large mean displacement demands on the superstructure (i.e., as great as 1.0 m for the studied cases). For NF excitations, a range of initial period (e.g., 1.5-2.5 s for the studied ground motions) and lateral yield-strength (e.g., 10-15% of the seismically effective weight) exists for the isolation system parameters that can noticeably reduce mean acceleration and base shear responses while mean displacement responses of the isolated superstructure remain within ranges used in practice. The inelastic-spectrum approach as used in this paper can reasonably predict these isolation system parameters.
... Over the past two decades, directionality effects have received considerable attention. Research has been performed to assess these effects on recorded ground motions [4,5], intensity measures and their influences on the development of ground motion prediction equations [6][7][8][9], seismic demands of buildings [10][11][12][13][14][15][16], probabilistic damage assessment [17], directivity effects in near-fault regions [18][19][20], horizontal-to-vertical spectral ratios [21][22][23], seismic risk assessment of highways [24], and the performance of bridge foundations [25]. ...
Article
The paper investigates directionality effects of ground motions in the context of dynamic soil-structure interaction (DSSI) analyses. The problem addressed corresponds to a nonlinear soil deposit, overlaying firm ground, where the input motion was derived from an acceleration time history recorded at a rock outcrop. A simplified procedure is proposed to incorporate directionality effects. The main objective is to identify in advance the incidence angle producing the maximum response of a structure for a given earthquake. Results from the simplified procedure were evaluated by comparison with what is called here the complete rotational approach, where the behaviour of the structure, as a function of the incidence angle of the input motion, is derived through a large number of nonlinear dynamic soil-structure interaction analyses. The obtained results show the importance of considering directionality effects in DSSI analyses. The maximum response of the system was reasonably captured with the simplified approach.
... For example, the hazard for the H components of GM has been defined in terms of the ''arbitrary'' component of GM, ''geometric mean'' component of GM, or variations of the geomean definition (Baker and Cornell, 2006c;Boore et al., 2006). Among the many different definitions for the H components of GM (see, for example, Beyer and Bommer, 2006;Boore and Kishida, 2017;Watson-Lamprey and Boore, 2007), modern ground motion prediction models (GMPMs) commonly define the H components of GM using a summarizing metric such as RotD50 (Boore, 2010) or RotD100 (Huang et al., 2008). To define the hazard for the V component of GM, two main types of GMPMs are available: (a) those for the V component of GM (e.g. ...
Article
Full-text available
This paper develops a methodology for selecting, scaling, and orienting three orthogonal components of ground motion (GM) when conducting intensity-based assessments of structures. Target spectra for selecting multicomponent GMs are critically examined and strategies for selecting hazard-consistent GMs are investigated. The CMS-UHS Composite Spectrum is proposed as an alternative to several Conditional Mean Spectra for selecting multicomponent GMs when conducting intensity-based assessments of complex 3D structures. To ensure hazard consistency, multicomponent GMs should be selected using: (i) the target spectrum for the vertical component of GM, (ii) a wide range of vibration periods, and (iii) scale factors that are constrained. With constrained scale factors, all three components of a GM can be reasonably scaled either by the same scale factor or different scale factors.
... For example, the target spectrum of the ASCE 7-10 code (ASCE, 2013) represents the maximum direction spectral acceleration for any possible orientation (RotD100), whereas the target spectrum of the Italian Building Code NTC08 represents the maximum spectral acceleration between two orthogonal directions (Max NS-EW ). When selecting accelerograms for the analysis of 3D structures, the use of the maximum direction spectrum is suggested since it automatically takes into account the bidirectional effects of ground motion (Huang et al., 2008;NIST, 2011). Therefore, the maximum direction spectrum of each pair of orthogonal accelerograms should be computed and then the average of the n selected maximum direction spectra should be compared with the target spectrum. ...
... Therefore, the paper first takes the strong earthquake record as the base [4], which is based on the ratio of PGA, the ratio of acceleration segment and the ratio of energy, and then studies the sectional statistical characteristic of the ratio of ground motion intensity [5]. Secondly, based on the results of the piecewise statistical characteristics, and based on the three-dimensional vector of the ground motion, two horizontal component strength packages are proposed. ...
... Other studies focused instead on providing modification factors to already available GMPEs to account for the pulse effects. 1,5,6 To include these GMPEs in probabilistic seismic hazard analysis of near-fault sites, many researchers 5,[7][8][9][10][11][12][13] have tried to obtain the probability of occurrence of pulse-like records at a specific site depending on the geometry of the site with respect to the likely rupture orientation in nearby faults. But how often do pulses occur in near fault recordings? ...
Article
Pulse‐like records are well recognized for their potential to impose higher demands on structures when compared with ordinary records. The increased severity of the structural response usually caused by pulse‐like records is commonly attributed to the spectral increment around the pulse period. By comparing the building response to sets of spectrally equivalent pulse‐like and ordinary records, we show that there are characteristics of pulse‐like records beyond the shape of the acceleration response spectrum that affect the results of nonlinear dynamic analysis. Nevertheless, spectral shape together with the ratio of pulse period to the first‐mode structural period, Tp/T1, are confirmed as “sufficient” predictors for deformation and acceleration response metrics in a building, conditioned on the seismic intensity. Furthermore, the average spectral acceleration over a period range, AvgSA, is shown to incorporate to a good proxy for spectral shape, and together with Tp/T1, form an efficient and sufficient intensity measure for response prediction to pulse‐like ground motions. Following this latter route, we propose a record selection scheme that maintains the consistency of Tp with the hazard of the site but uses AvgSA to account for the response sensitivity to spectral shape.
... Therefore, a specific ground motion can have a greater effect on the performance of a building, depending on the orientation of these axes with respect to the action. Thus, the demand on the structure may depend strongly on the orientation of the building with respect to the direction in which the maximum intensity of the seismic action occurs, that is, depending on the azimuth of the building (see e.g., Huang et al., 2008;Vargas-Alzate et al., 2018). Figure 7b illustrates how the impact of a unitary force varies depending on the orientation of the building. ...
Article
We analyze the case of a building that collapsed in a multifamily complex of Tlalpan borough in Mexico City during the 19 September 2017 Central Mexico earthquake. Despite having similar materials and similar structural and geometric properties, this was the only building that collapsed in the complex. A structural analysis of the building and a study of the soils’ predominant periods indicated that resonance effects, if any, would not be significant. However, phenomena related to the anomalous performance of buildings in dense urban areas such as geological soil, soil–structure interaction, and soil–city interaction effects were also investigated. A detailed analysis of the directionality of seismic actions recorded at nearby accelerometric stations and of the azimuths of sound and damaged buildings indicates that directionality effects were responsible for the collapse of the building. Subsequently, a set of 58, two‐component acceleration records of the earthquake was used to perform a thorough directionality analysis. The results were then compared with the foreseen uniform hazard response spectra and the design spectra in the city. Seismic actions in the city due to this earthquake were stronger than those corresponding to the uniform hazard response spectra. In addition, although design spectra have been significantly improved in the new 2017 Mexican seismic regulations, they were exceeded in 11 of 58 analyzed spectra. In 4 of these 11 cases, the design spectra were exceeded due to directionality effects. These results confirm the necessity of considering directionality effects in damage assessments, strong‐motion prediction equations, and design regulations.
... Unless a more substantiated analysis is utilized to assess the effects of pulses and/or maximum orientation at the MCE level (see Almufti et al. 2013), a reasonable approach would be to use 84th percentile Maximum Spectral Demand factors published in Table C21.2-1 of NEHRP (2009) instead of the median Maximum Spectral Demand factors which are used in ASCE 7 -10 maps. These are based on a study by Huang et al. (2008) for near-fault ground motions but NEHRP indicates that they can be used for far-fault ground motions as well. For long periods consistent with isolated structures, the table indicates that the 84th percentile Maximum Spectral Demand is 1.9x higher than that currently used for design. ...
Method
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The REDi guidelines provide owners, architects and engineers a framework for resilience-based earthquake design to achieve "beyond-code" resilience objectives..
... Common choices of target spectrum include: Uniform Risk Spectra (URS), Uniform Hazard Spectra (UHS), or Conditional Mean Spectra (CMS; American Society of Civil Engineers 2016, Baker 2011). We choose to study the UHS instead of the URS for simplicity, as applying the "risk adjustments" to UHS (Luco et al. 2007) tends to counteract the modifications for the "maximum direction" (Huang et al. 2008). For nonlinear RHAs, the H1 and H2 components of each selected GM pair are applied, respectively, to the x-and y-axes to approximately achieve random orientation of the GM pair for far-field sites . ...
Article
Full-text available
The current practice for selecting bidirectional ground motions (GM pairs) to conduct nonlinear response history analysis (RHA) of multistory buildings is restricted to those with a symmetric plan. To overcome such limitations, we propose selecting GM pairs to be consistent with a pair of target spectra defined along the structural axes, enabling a unique azimuth to be determined for each GM pair. We develop two new target spectra: (1) the s-GCMS for two horizontal components of GM and (2) the CMS-UHS Composite Spectrum. Based on nonlinear RHAs of buildings with both symmetric and unsymmetric plans, the CMS-UHS Composite Spectrum is shown to be the best alternative to the current practice of utilizing multiple CMSs, because it provides accurate demands with minimal computational effort and can be easily constructed using existing PSHA tools.
... Relative difference between the maximum displacement through all orientations and the displacement in the orientation of maximum optimal ground motion parameters for different types of ground motions. [9,17,19,20,36,43]). Therefore, examinations on the orientations of the maximum-displacement direction are performed separated for nearfault directivity-pulse (NF-P) and ordinary ground motions. ...
Article
Earthquake ground motions can vary in different horizontal directions. These directional variations need to be included in the earthquake-induced landslide hazard assessment. This paper examines the influence of ground motion directionality on the probabilistic seismic displacement hazard of slopes. The distribution of the orientation of the maximum sliding displacement direction are analyzed, and the optimal ground motion parameters are provided by which the displacement in the orientation of maximum ground motion parameters can be used to represent the maximum sliding displacement over all orientations. Predictive relationships of orientation-independent sliding displacements are developed for different types of ground motions (i.e., forward-directivity pulse and non-pulse ground motions). The proposed relationships for sliding displacement are based on ground motion parameters for which there are available ground motion prediction equations (GMPEs), hence allowing for fully compatible hazard analyses with existing GMPEs. Probabilistic assessment of earthquake-induced landslide hazard is performed for hypothetical slopes, and the seismic landslide hazard maps and the ground-motion selection procedure for site-specific analysis of slopes are presented by including the effects of ground motion directionality in different types of ground motions.
Article
The probability distributions have been comprehensively modeled for natural logarithm of the ratios of every pair of ground motion intensity measures (IM’s) defined from orthogonal horizontal components of seismic waveforms; modeled are maximum values of each component (NS, EW), geometric mean (GM), larger value (Larger), maximum value obtained by axial rotation (rot100). Basically, normal distribution was employed for ratios among “(NS, EW), ” “GM” and “Larger, ” and Gamma distribution was employed for ratios related to “rot100.” Accelerograms recorded by K-NET, velocity waveforms obtained by their time integration and response waveforms of SDOF with 5% damping were used for the analysis. The proposed models agree well with the histograms of ratios. Period-dependent characteristics of the ratios were also discussed. Distribution of the inverted ratio can be derived as axially symmetric distribution of the original ratio. In addition, the models related to median value obtained by axial rotation (rot50) were modified from the previous study (Nojima and Yokoyama, 2021). The proposed comprehensive models enable one to convert an arbitrary pair of various IM’s in a probabilistic manner using the exceeding level.
Article
Earthquake response spectral ordinates vary significantly with changes in orientation within the horizontal plane. This variation is characterized probabilistically in this study using a large database of recorded earthquake ground motions. For each ground motion record, response spectral ordinates are computed in all horizontal orientations as a function of the rotation angle with respect to the azimuth of maximum response and then normalized by (1) the maximum and (2) the median spectral ordinate from all these orientations. Nonlinear regression models are then fitted to the means, standard deviations, and correlations of both ratios, as a function of rotation angle. To achieve a more complete probabilistic description, probability distributions are fitted to both ratios at each rotation angle. These results can be used for several probabilistic seismic hazard computations, such as the sampling of response spectral ordinates at specific orientations within the same site.
Article
Near‐fault pulse‐type ground motions have characteristics that are substantially different from ordinary far‐field ground motions. It is essential to understand the unique effects of pulse‐type ground motions on structures and include the effects in seismic design. This paper investigates the effects of near‐fault pulse‐type ground motions on the structural response of a 3‐story steel structure with nonlinear viscous dampers using the real‐time hybrid simulation (RTHS) testing method. The structure is designed for 75% of the code‐specified design base shear strength. In the RTHS, the loop of action and reaction between the experimental and numerical partitions are executed in real time, accurately capturing the velocity pulse effects of pulse‐type ground motions. A set of 10 unscaled pulse‐type ground motions at the design basis earthquake (DBE) level is used for the RTHS. The test results validated that RTHS is a viable method for experimentally investigating the complicated structural behavior of structures with rate‐dependent damping devices, and showed that the dampers are essentially effective in earthquake hazard mitigation effects involving pulse‐type ground motions. The average peak story drift ratio under the set of pulse‐type ground motions is 1.08% radians with a COV value less than 0.3, which indicated that structural system would achieve the ASCE 7–10 seismic performance objective for Occupancy Category III structures under the DBE level pulse‐type ground motions. Additionally, a nonlinear Maxwell model for the nonlinear viscous dampers is validated for future structural reliability numerical studies involving pulse‐type ground motions.
Article
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The goal of this work is to propose a new strategy for automatically quantifying the high-pass cut-off frequency of digital ground motion (GM) records. In previous studies, the high-pass filter cut-off frequency of GM records was often identified by visual inspection. For this, this article proposes a simple and efficient method to detect a correct cut-off frequency where the displacement waveform exactly does not change significantly. The displacement change is delineated as the change rate of the displacement at the ending of padded record with respect to the cut-off frequency. Based on the Short-Term-Average to the Long-Term-Average (STA/LTA) method, detecting the ratio of calculated average energy in two consecutive moving-time windows above a threshold, a critical frequency where the ending displacement starts deviating from zero level can be identified. Nevertheless, the cut-offs may be affected by GM intensities even though meticulous setting for window length or trigger threshold is adopted. In this paper, a new characteristic function (CF) on the basis of a modified cumulative envelope function is proposed. It has an appealing advantage to detect the critical cut-off frequency based on the CF shape and free of considering the intensity difference among GM records. Finally, the comparison of results with the cut-off frequencies of GMs from the 2008 Wenchuan mainshock calculated by the proposed method and those derived from two traditional methods is presented. Influence of the cut-off frequency on ground motion displacement, elastic, and inelastic spectrum is also studied.
Article
A new measure of ground motion intensity in the horizontal direction is proposed. Similarly to other recently proposed measures of intensity, the proposed intensity measure is also independent of the as-installed orientation of horizontal sensors at recording stations. This new measure of horizontal intensity, referred to as MaxRotD50, is defined using the maximum 5%-damped response spectral ordinate of two orthogonal horizontal directions and then computing the 50th percentile for all non-redundant rotation angles, that is, the median of the set of spectral ordinates in a range of 90°. This proposed measure of intensity is always between the median and maximum spectral ordinate for all non-redundant orientations, commonly referred to as RotD50 and RotD100, respectively. A set of 5065 ground motion records is used to show that MaxRotD50 is, on average, approximately 13%–16% higher than Rot50 and 6% lower than RotD100. The new measure of intensity is particularly well suited for earthquake-resistant design where a major concern for structural engineers is the probability that the design ground motion intensity is exceeded in at least one of the two principal horizontal components of the structure, which for most structures are orthogonal to each other. Currently, design codes in the United States are based on RotD100, and hence using MaxRotD50 for structures with two orthogonal principal horizontal components would result in a reduction of the ground motion intensities used for design purposes.
Article
Several kinds of intensity measures (IM) can be defined from orthogonal horizontal components of seismic waveforms; they are maximum values of each component (NS, EW), geometric mean (GM), larger value (Larger), rotation-independent measures such as maximum (rot100) and median (rot50) obtained by axial rotation. In this study, mutual relationships among such IM’s were probabilistically evaluated. Using accelerograms recorded by K-NET, the distributions of each IM normalized to corresponding rot50 were represented by kernel density. The ratio of NS and EW to rot50 were newly derived as uniform-Rayleigh compound distribution, and on this basis, those for GM and Larger were derived. Bilinear model was adopted for rot100. Period-dependent distributions for each IM were also derived for absolute acceleration, velocity and displacement response waveforms of SDOF with 5% damping.
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Earthquake ground motions (GMs) may display distinct characteristics in all directions within the horizontal plane. However, the causes of GM polarization are still not fully understood. Structural designs use maximum rotated intensity measures (IMRotD100) to accommodate variations of the GM with orientation, but the orientation associated with IMRotD100, β, is not easily predictable. This study investigates the influence of linear site response to observed GM variability with direction. We analyze GMs recorded at the surface and at depth from four stations in the Japanese database, KiK-net. Selected events have moment magnitudes ranging 3–5, and rupture distances within 100 km. Findings provide evidence that site effects contribute to GM directionality, and that directional resonance can be observed at sites lacking significant topographic features. Additionally, values of β at depth are not correlated to the orientation corresponding to their expected polarization (from S-wave radiation patterns), which provides evidence of non-negligible path contributions to GM directionality observed at our study sites.
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The most commonly used intensity measure of ground motion in earthquake engineering is the 5% damped spectral ordinate, which varies in different directions. Several different measures have been proposed over the years to combine the intensity of the two horizontal recorded ground motions to derive ground-motion models as well as for design purposes. This study provides the relation to seven previously used measures of horizontal ground motion with respect to a recently proposed orientation-independent measure of horizontal ground-motion intensity referred to as MaxRotD50. This new measure of horizontal intensity is defined as the median value of the maximum spectral ordinate of two orthogonal directions computed for all possible nonredundant orientations. The relations are computed using 5065 pairs of horizontal ground motions taken from the database of ground motions recorded in shallow crustal earthquakes in active tectonic regions developed as part of the Pacific Earthquake Engineering Research Center’s Next Generation Attenuation-West2 project. Empirically derived period-dependent relations are presented for three quantities that permit transforming any of the seven other definitions of horizontal ground-motion intensity to MaxRotD50, namely, (1) geometric mean of the ratio of MaxRotD50 to any of the seven other measures of intensities, (2) standard deviation of the natural logarithm of the ratio of MaxRotD50 to any of the seven other measures of intensities, and (3) the correlation between the natural logarithm of the ratio of MaxRotD50 to the other measures of intensities and the natural logarithm of the other measure of intensity. In addition, the influence of site class at the recording station, earthquake magnitude, and distance to the horizontal projection of the rupture is examined on the geometric mean of the ratio of MaxRotD50 to the median intensity of all nonredundant orientations (i.e., RotD50), showing negligible influence of site class and only a relatively small influence of magnitude and distance.
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Design philosophy refers to a set of assumptions and procedures, which are used to meet the conditions of serviceability, safety, economy, and functionality of structures. The application of the current introduced “Risk-targeted maximum considered earthquake” ground motion maps enables engineers to incorporate a more consistent and better-defined level of seismic safety into their building designs. It requires that buildings be designed to provide the same level of seismic performance, meaning that they will be equally (un)likely to collapse in earthquakes. The new maps are referred to as risk-targeted because the likelihood of collapse is known as the seismic risk level. The main aim of this thesis is to undertake a comparative study on representative buildings to discuss the current state of design philosophies and applied/considered limit states for different international seismic standards and with respect to modern risk-targeted seismic design analysis.
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Rupture directivity effects cause spatial variations in ground motion amplitude and duration around faults and cause differences between the strike-normal and strike-parallel components of horizontal ground motion amplitudes, which also have spatial variation around the fault. These variations become significant at a period of 0.6 second and generally grow in size with increasing period. We have developed modifications to empirical strong ground motion attenuation relations to account for the effects of rupture directivity on strong motion amplitudes and durations. The modifications are based on an empirical analysis of near-fault data. The ground motion parameters that are modified include the average horizontal response spectral acceleration, the duration of the acceleration time history, and the ratio of strike-normal to strike-parallel spectral acceleration. The parameters upon which the adjustments to average horizontal amplitude and duration depend are the fraction of the fault rupture that occurs on the part of the fault that lies between the hypocenter and the site, and the angle between the fault plane and the path from the hypocenter to the site. Since both of these parameters can be derived from the hypocenter location and the fault geometry, the model of rupture directivity effects on ground motions that we have developed can be directly included in probabilistic seismic hazard calculations. The spectral acceleration is larger for periods longer than 0.6 second, and the duration is smaller, when rupture propagates toward a site. For sites located close to faults, the strike-normal spectral acceleration is larger than the strike-parallel spectral acceleration at periods longer than 0.6 second in a manner that depends on magnitude, distance, and angle. To facilitate the selection of time histories that represent near-fault ground motion conditions in an appropriate manner, we provide a list of near-fault records indicating the rupture directivity parameters that each contains.
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We present a new empirical ground motion model for PGA, PGV, PGD and 5% damped linear elastic response spectra for periods ranging from 0.01-10 s. The model was developed as part of the PEER Next Generation Attenuation (NGA) project. We used a subset of the PEER NGA database for which we excluded recordings and earthquakes that were believed to be inappropriate for estimating free-field ground motions from shallow earthquake mainshocks in active tectonic regimes. We developed relations for both the median and standard deviation of the geometric mean horizontal component of ground motion that we consider to be valid for magnitudes ranging from 4.0 up to 7.5-8.5 (depending on fault mechanism) and distances ranging from 0-200 km. The model explicitly includes the effects of magnitude saturation, magnitude-dependent attenuation, style of faulting, rupture depth, hanging-wall geometry, linear and nonlinear site response, 3-D basin response, and inter-event and intra-event variability. Soil nonlinearity causes the intra-event standard deviation to depend on the amplitude of PGA on reference rock rather than on magnitude, which leads to a decrease in aleatory uncertainty at high levels of ground shaking for sites located on soil.
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The geometric mean of the response spectra for two orthogonal horizontal components of motion, commonly used as the response variable in predictions of strong ground motion, depends on the orientation of the sensors as installed in the field. This means that the measure of ground-motion intensity could differ for the same actual ground motion. This dependence on sensor orientation is most pronounced for strongly correlated motion (the extreme example being linearly polarized motion), such as often occurs at periods of 1 sec or longer. We propose two new measures of the geometric mean, GMRotDpp, and GMRotIpp, that are independent of the sensor orientations. Both are based on a set of geometric means computed from the as-recorded orthogonal horizontal motions rotated through all possible nonredundant rotation angles. GMRotDpp is determined as the ppth percentile of the set of geometric means for a given oscillator period. For example, GMRotD00, GMRotD50, and GMRotD100 correspond to the minimum, median, and maximum values, respectively. The rotations that lead to GMRotDpp depend on period, whereas a single-period-independent rotation is used for GMRotIpp, the angle being chosen to minimize the spread of the rotation-dependent geometric mean (normalized by GMRotDpp) over the usable range of oscillator periods. GMRotI50 is the ground- motion intensity measure being used in the development of new ground-motion prediction equations by the Pacific Earthquake Engineering Center Next Generation Attenuation project. Comparisons with as-recorded geometric means for a large dataset show that the new measures are systematically larger than the geometric-mean response spectra using the as-recorded values of ground acceleration, but only by a small amount (less than 3%). The theoretical advantage of the new measures is that they remove sensor orientation as a contributor to aleatory uncertainty. Whether the reduction is of practical significance awaits detailed studies of large datasets. A preliminary analysis contained in a companion article by Beyer and Bommer finds that the reduction is small-to-nonexistent for equations based on a wide range of magnitudes and distances. The results of Beyer and Bommer do suggest, however, that there is an increasing reduction as period increases. Whether the reduction increases with other subdivisions of the dataset for which strongly correlated motions might be expected (e.g., pulselike motions close to faults) awaits further analysis.
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We present a model for estimating horizontal ground motion amplitudes caused by shallow crustal earthquakes occurring in active tectonic environments. The model provides predictive relationships for the orientation-independent average horizontal component of ground motions. Relationships are provided for peak acceleration, peak velocity, and 5-percent damped pseudo-spectral acceleration for spectral periods of 0.01 to 10 seconds. The model represents an update of the relationships developed by Sadigh (1997) and incorporates improved magnitude and distance scaling forms as well as hanging-wall effects. Site effects are represented by smooth functions of average shear wave velocity of the upper 30 m (V-S30) and sediment depth. The new model predicts median ground motion that is similar to Sadigh (1997) at short spectral period, but lower ground motions at longer periods. The new model produces slightly lower ground motions in the distance range of 10 to 50 km and larger ground motions at larger distances. The aleatory variability in ground motion amplitude was found to depend upon earthquake magnitude and on the degree of nonlinear soil response, For large magnitude earthquakes, the aleatory variability is larger than found by Sadigh (1997).
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Accurately characterizing near-source ground motion is an important consideration for dam safety in California. Near-source ground motion can contain velocity pulses that are amplified by directivity, which is the constructive interference of S waves radiated by a propagating rupture front. Accordingly, Somerville et al. (1997) developed an empirical model for predicting fault-normal (maximum) and fault-parallel (minimum) spectral acceleration for periods > 0.5 sec. We compiled near-source ground motion records representing significant directivity and rotated them to the component with maximum overall spectral acceleration for common periods of directivity amplification (and importance to dam stability analyses, 0.5≤T ≤3.0 sec), which we call SA MAX. As expected, SA MAX correlates with the orientation of a strong velocity pulse in the directivity record. Comparing the amplitude and orientation of SA MAX to Somerville's predictions, we find that strong velocity pulses produced by strike-slip faulting are reasonably aligned with the fault normal, and their corresponding SA MAX is satisfactorily predicted by Somerville's model as modified by Abrahamson. However, the orientations of strong velocity pulses in reverse-faulting records can depart significantly from fault normal, and their corresponding SA MAX can exceed Somerville's predictions appreciably.
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Using a database of 655 recordings from 58 earthquakes, empirical response spectral attenuation relations are derived for the average horizontal and vertical component for shallow earthquakes in active tectonic regions. A new feature in this model is the inclusion of a factor to distinguish between ground motions on the hanging wall and footwall of dipping faults. The site response is explicitly allowed to be non-linear with a dependence on the rock peak acceleration level.
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This paper contains ground-motion prediction equations (GMPEs) for average horizontal-component ground motions as a function of earthquake magnitude, distance from source to site, local average shear-wave velocity, and fault type. Our equations are for peak ground acceleration (PGA), peak ground velocity (PGV), and 5%-damped pseudo-absolute-acceleration spectra (PSA) at periods between 0.01 s and 10 s. They were derived by empirical regression of an extensive strong-motion database compiled by the "PEER NGA" (Pacific Earthquake Engineering Research Center's Next Generation Attenuation) project. For periods less than 1s , the analysis used 1,574 records from 58 mainshocks in the distance range from 0 km to 400 km (the number of available data decreased as period increased). The primary predictor variables are moment magnitude M, closest horizontal distance to the surface projection of the fault plane RJB, and the time-averaged shear-wave velocity from the surface to 30 m VS30. The equations are applicable for M =5-8 , RJB 200 km, and VS30= 180- 1300 m / s. DOI: 10.1193/1.2830434
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The geometric mean of the response spectra for two orthogonal hori-zontal components of motion, commonly used as the response variable in predictions of strong ground motion, depends on the orientation of the sensors as installed in the field. This means that the measure of ground-motion intensity could differ for the same actual ground motion. This dependence on sensor orientation is most pro-nounced for strongly correlated motion (the extreme example being linearly polarized motion), such as often occurs at periods of 1 sec or longer. We propose two new measures of the geometric mean, GMRotDpp, and GMRotIpp, that are independent of the sensor orientations. Both are based on a set of geometric means computed from the as-recorded orthogonal horizontal motions rotated through all possible non-redundant rotation angles. GMRotDpp is determined as the ppth percentile of the set of geometric means for a given oscillator period. For example, GMRotD00, GMRotD50, and GMRotD100 correspond to the minimum, median, and maximum values, respectively. The rotations that lead to GMRotDpp depend on period, whereas a single-period-independent rotation is used for GMRotIpp, the angle being chosen to minimize the spread of the rotation-dependent geometric mean (normalized by GMRotDpp) over the usable range of oscillator periods. GMRotI50 is the ground-motion intensity measure being used in the development of new ground-motion pre-diction equations by the Pacific Earthquake Engineering Center Next Generation Attenuation project. Comparisons with as-recorded geometric means for a large dataset show that the new measures are systematically larger than the geometric-mean response spectra using the as-recorded values of ground acceleration, but only by a small amount (less than 3%). The theoretical advantage of the new measures is that they remove sensor orientation as a contributor to aleatory uncertainty. Whether the reduction is of prac-tical significance awaits detailed studies of large datasets. A preliminary analysis contained in a companion article by Beyer and Bommer finds that the reduction is small-to-nonexistent for equations based on a wide range of magnitudes and dis-tances. The results of Beyer and Bommer do suggest, however, that there is an increasing reduction as period increases. Whether the reduction increases with other subdivisions of the dataset for which strongly correlated motions might be expected (e.g., pulselike motions close to faults) awaits further analysis.
Effects of rupture directivity on probabilistic seismic hazard analysis
  • N A Abrahamson
Abrahamson, N. A., 2000. Effects of rupture directivity on probabilistic seismic hazard analysis, Proceedings, 6th International Conference on Seismic Zonation, Palm Springs, CA.