Ground Motion For Seismic Design Research Articles

Preliminary Evaluation of the Impact of Eurocode 8 Draft Revision on the Seismic Zonation of Romania

This study is focused on the impact of the Eurocode 8 draft revision on the seismic zonation of Romania, one of the countries with the highest hazard levels in Europe. In this study, the design response spectra are evaluated for a number of sites in Romania for which both shear wave velocity profiles and ground motion recordings are available. The impact of the proposed changes on the structural design for structures situated in the southern part of Romania is also discussed. The results show considerable differences between the design response spectra computed according to the Eurocode 8 draft revision and the design response spectra from the current Romanian seismic code P100-1/2013. The differences are larger in the case of the sites situated in the southern part of Romania and those which have large design values for the control period TC. In Bucharest, for instance, it was found that the maximum design spectral accelerations would correspond to those from the 2006 version of the code while the maximum design spectral displacements would be significantly smaller than the levels produced by the 1981 or 1992 versions of the code. The results presented herein show that the differences in the seismic hazard and design ground motions are mainly due to the effects of local soil and site conditions and the associated site amplification proposed in the current Romanian seismic code and EC8 draft revision. Moreover, it has been shown that more analyses are needed to apply the seismic actions proposed in Eurocode 8 revision specifically for the sites in Romania under the influence of Vrancea intermediate-depth earthquakes so as to ensure an increased level of seismic safety for structures designed and built in the future.

Seismic hazard analyses of the Metropolitan Water District Emergency Freshwater Pathway, California

The Sacramento-San Joaquin Delta in central California is particularly susceptible to damage in a large earthquake due to the vulnerability of the levees that protect cities, farms, and infrastructure. The Delta is located adjacent to the seismically active San Andreas fault system and is also subject to strong ground shaking from numerous other seismic sources in central California, including faults within the Delta. We performed a probabilistic seismic hazard analysis (PSHA) to provide seismic design ground motions for the Metropolitan Water District (MWD) Emergency Freshwater Pathway. We have evaluated the appropriateness of the Next Generation of Attenuation (NGA)-West2 ground motion models for use in our analyses of the Delta, evaluated shear-wave velocity ( VS) data in the vicinity of the Pathway, and performed site response analyses. The latter was performed to compute the probabilistic hazard at the top of the peat at five sites along the Pathway. The sixth site was located outside the Delta and on firm soil. The probabilistic hazard for the six sites and for a range of return periods of engineering relevance were computed in the PSHA. For a return period of 2500 years, the peak horizontal ground acceleration (PGA) values on peat ranged from 0.40 g to 0.53 g. The seismic sources that control the hazard at these sites vary as a function of return period and spectral frequency, but in general, the closer the sites are to faults within the San Andreas fault system, the higher the hazard.

Analysis of the risk-targeting approach to defining ground motion for seismic design: a case study of Iran

Modern seismic codes employed the uniform hazard basis for seismic design, which defines design ground motion with a fixed return period for different sites. Seismic design for uniform hazard ground motion does not lead to the goal of uniform structural safety. As a potential solution to address this problem, the risk-targeting approach has been considered in recent years. This study aims to investigate the changes applied by this approach to the current uniform hazard ground motions. For this purpose, hazard curves for Iran from the Earthquake Model of Middle East (EMME14) have been used. The risk-targeting approach has been performed in two cases, once considering GMs with a 475 year return period and then considering GMs with a 2475 year return period. For each case, a generic fragility function for buildings has been defined. A 1% probability of collapse in 50 years was selected as the target risk in both cases. For each case, the map of the distribution of the theoretical collapse risk is presented. It was discussed that by employing a generic fragility function, the risk-targeting could not guarantee to harmonize risk amongst the sites with different hazard levels, but it could have such an impact for the sites with the same design GM but the different slope of hazard curves. Finally, it was found that basing the seismic design on the 2% in 50 years GMs level leads to a more uniform collapse risk across the country.

Vs30 değerine bağlı koherans modeli

Strong ground motion caused by earthquakes at every point of extended structures would not be same. This difference in ground movement has an important effect on the design of these types of structures. Meanwhile, the seismic resistant design has been lead to investigate the variability of earthquake ground motion over last decades. This variability of strong ground motion can define in terms of frequency or time. In this study, frequency domained variability named coherency is considered. Several coherency models have been proposed without considering soil effect. In this context, spatial variation of seismic ground motion based on the average shear wave velocity over the upper 30 m of depth, Vs30 is analyzed. Initially, coherency values are calculated using data triggered during six earthquakes recorded by the Istanbul Earthquake Rapid Response System. Lagged coherency data is considered in the process to get the coherency model. Nonlinear regression analysis is used for the model to obtain a good-fit to observed data. A coefficient is defined based on Vs30 values of the station-pairs. The cohereny model based on this coefficient of Vs30 is derived for EW and NS components. It is expected that coherency function decreases with the increase of frequency and separation distance. The decrease in the coefficient of Vs30 causes decrease in coherency. The variance in the coherency model between EW and NS components is small. This coherency model is used to simulate spatial variable ground motion for the accurate seismic design of elongated structures for the future studies.

Regional-Scale 3D Ground-Motion Simulations of Mw 7 Earthquakes on the Hayward Fault, Northern California Resolving Frequencies 0–10 Hz and Including Site-Response Corrections

ABSTRACTLarge earthquake ground-motion simulations in 3D Earth models provide constraints on site-specific shaking intensities but have suffered from limited frequency resolution and ignored site response in soft soils. We report new regional-scale 3D simulations for moment magnitude 7.0 scenario earthquakes on the Hayward Fault, northern California with SW4. Simulations resolved significantly broader band frequencies (0–10 Hz) than previous studies and represent the highest resolution simulations for any such earthquake to date. Seismic waves were excited by a kinematic rupture following Graves and Pitarka (2016) and obeyed wave propagation in a 3D Earth model with topography from the U.S. Geological Survey (USGS) assuming a minimum shear wavespeed, VSmin, of 500 m/s. We corrected motions for linear and nonlinear site response for the shear wavespeed, VS, from the USGS 3D model, using a recently developed ground-motion model (GMM) for Fourier amplitude spectra (Bayless and Abrahamson, 2018, 2019a). At soft soil locations subjected to strong shaking, the site-corrected intensities reflect the competing effects of linear amplification by low VS material, reduction of stiffness during nonlinear deformation, and damping of high frequencies. Sites with near-surface VS of 500 m/s or greater require no linear site correction but can experience amplitude reduction due to nonlinear response. Averaged over all sites, we obtained reasonable agreement with empirical ergodic median GMMs currently used for seismic hazard and design ground motions (epsilon less than 1), with marked improvement at soft sedimentary sites. At specific locations, the simulated shaking intensities show systematic differences from the GMMs that reveal path and site effects not captured in these ergodic models. Results suggest how next generation regional-scale earthquake simulations can provide higher spatial and frequency resolution while including effects of soft soils that are commonly ignored in scenario earthquake ground-motion simulations.

Spatially correlated vertical ground motion for seismic design

Spatial variation of vertical ground motion may have influence on the response of long span lifeline structures like bridges, pipelines, etc. However, studies specific to the spatial variability of vertical component of ground motion are limited in the literature when compared with the associated horizontal components. Based on the data recorded at SMART1 and LSST arrays, comparison of spatial variability of vertical and horizontal components is explored here using the coherency model reported by the authors elsewhere. Alternatively, Fourier amplitudes of horizontal components are often scaled through an empirical function to estimate that of the vertical components. Ratio of auto-spectral density (ASD) of horizontal to vertical ground accelerations is then investigated using the array recordings. Conditional simulation of spatially varying ground motion (CSSVGM) can be categorized into two different approaches: (i) (evolutionary) cross-spectral density (CSD) based procedures and (ii) auto-spectral density (ASD) based procedure. While the former assumes spatially uniform ASD and accounts only for the phase variability, the latter takes into the account the spatial variability of ASD and thereby accounts for both phase and amplitude variability. These frameworks do not differentiate between horizontal and vertical components. However, the results reported to date by most researchers are based only on the horizontal components. Spatially varying vertical components are next simulated in this paper using both the perspectives and assessed against the array recordings. An attempt has also been made to estimate the SVGM of the vertical components for a future event. Choice of functional form of ASD (of a seed ground motion) on the resulting spatially varying vertical ground motion is also investigated. Finally, empirical forms of vertical to horizontal (V/H) response spectral ratio reported in the prior art do not account for the spatial variability over the footprint of array, which is also investigated here.

The Effect of Soil Type and Different In-situ Test Results on Soil Amplification Analysis

The effect of local soil conditions is taken into consideration in the evaluation of ground motion properties in seismic design of structures. One of the most important effects on the ground surface due to strong ground motion is soil amplification resulted in the structural damage. Soil amplification can be determined both by dynamic analyses performed according to analytical methods based on local site conditions and obtained with investigations based on the results of in-situ testing methods. Therefore, the effects of local site conditions are considered to evaluate the properties of ground motion for seismic design of structure. In this study, soil properties of İnönü district are evaluated based on Standard Penetration Test (SPT) and Multi-Channel Analysis of Surface Wave (MASW) method which is one of the geophysical methods. İnönü is located at the west of Eskişehir surrounded with numerous active fault systems and subjected to very intensive tectonic activities in geological history. The studies related to seismic activity have been made on the basis of probabilistic seismic hazard analyses. Soil amplification analyses are performed with Shake2000 software comparatively by taking into considerations data from in-situ testing methods.

Amplification of thickness and topography of loess deposit on seismic ground motion and its seismic design methods

The Loess Plateau in China is a region with the biggest thickness and most complicated topography of loess deposit in the world, where is affected by strong earthquakes frequently. The seismic amplification effects were discovered in the Plateau during the Wenchuan Ms8.0 earthquake and some other strong events. The field investigations, observations, and analyses indicated that large number of casualties and tremendous economic losses were caused not only by collapse and damage of houses with poor seismic performance, landslides, liquefaction and seismic subsidence, but also amplification effects of thickness and topography of loess deposit on seismic ground motion. In this paper, the characteristics of strong ground motion recorded in the region were analyzed; shaking table tests were performed and numerical analysis was carried out on amplification of thickness and slope of loess deposit on seismic ground motion. Moreover, we also developed site amplification factors of ground motion for seismic design of engineering projects on loess sites. The results showed that the amplification effects are more predominant with increase of thickness and slope of loess deposit. The ground motion may be amplified in seismic intensity by 1–2°, PGA by 1.1–2.2 times, and predominant period by 1.1–1.6 times respectively.

Determination of mean shear wave velocity to 30m depth for site classification using shallow depth shear wave velocity profile in Korea

Abstract The mean shear wave velocity to a depth of 30 m (VS30), established in the western United States, is the current site classification criterion for determining the seismic design ground motion, taking site amplification potential account into. To evaluate VS30 at a site, a shear wave velocity (VS) profile extending to a depth of at least 30 m must be acquired using in situ seismic tests. In many cases, however, the obtained VS profile does not extend to a depth of 30 m due to unfavorable field conditions and limitations of testing techniques. In this study, VS30 and the mean shear wave velocity to depths less than 30 m (VSDs) were calculated using VS profiles of more than 30 m obtained by seismic tests at 72 sites in Korea, and the correlation between VS30 and VSDs was drawn based on the computed mean VS data. Additionally, a method for extrapolating the VS profile from shallow depths to 30 m and bedrock was developed by building a shape curve based on the average data of all VS profiles. These two methods of extrapolating VS30 from shallow VS profiles, using VSDs and a shape curve, resulted in less bias than the simple method in which the lowermost VS value obtained is extended to the depth of 30 m. These two extrapolation methods are useful for VS profiles extending to depths of at least 10 m. Furthermore, the shape curve method developed in this study may be useful in the western United States as well as in Korea.

Comparative study of codes for the seismic design of structures

A general evaluation of some points of the South American seismic codes is presented herein, comparing them among themselves and with the American Standard ASCE/SEI 7/10 and with the European Standard Eurocode 8. The study is focused in design criteria for buildings. The Western border of South America is one of the most seismically active regions of the World. It corresponds to the confluence of the South American and Nazca plates. This region corresponds roughly to the vicinity of the Andes Mountains. This seismicity diminishes in the direction of the comparatively seismically quieter Eastern South American areas. The South American countries located in its Western Border possess standards for seismic design since some decades ago, being the Brazilian Standard for seismic design only recently published. This study is focused in some critical topics: definition of the recurrence periods for establishing the seismic input; definition of the seismic zonation and design ground motion values; definition of the shape of the design response spectra; consideration of soil amplification, soil liquefaction and soil-structure interaction; classification of the structures in different importance levels; definition of the seismic force-resisting systems and respective response modification coefficients; consideration of structural irregularities and definition of the allowable procedures for the seismic analyses. A simple building structure is analyzed considering the criteria of the several standards and obtained results are compared.

설계용 탄성응답스펙트럼으로 규준화된 인공지진동과 기록지진동의 비선형 지진응답

In the nonlinear response history analysis of building structures, the input ground accelerations have considerable effect on the nonlinear response characteristics of structural systems. As the properties of the ground motion, using time history analysis, are interrelated with many factors such as the fault mechanism, the seismic wave propagation from source to site, and the amplification characteristics of the soil, it is difficult to properly select the input ground motions for seismic response analysis. In this paper, the most unfavourable real seismic design ground motions were selected as input motions. The artificial earthquake waves were generated according to these earthquake events. The artificial waves have identical phase angles to the recorded earthquake waves, and their overall response spectra are compatible with the seismic design spectrum with 5% of critical viscous damping. It is concluded that the artificial earthquake waves simulated in this paper are applicable as input ground motions for a seismic response analysis of building structures.

A Method of Determining Strengthening Design Ground-Motion Parameters for the Existing Building

At present, seismic strengthening design reference period of the existing building is usually equal to 50 years in China, sometime this is uneconomic and unreasonable. In this paper, determining principle of seismic strengthening design reference period for the existing building with different importance is presented. The seismic strengthening design level of the existing building is put forward. After the shape factor of intensity probability distribution function is used to represent the seismic hazard characteristic of different areas, the seismic hazard curve formula of design acceleration Amax and earthquake influence coefficient αmax are deduced according to the seismic hazard curve of intensity. The seismic strengthening design ground motion parameter for the existing building with different importance is researched in detail by use of hazard curve formula of seismic ground motion parameter based on seismic hazard characteristic zone. At last, the method and the calculation step are explained by a calculation example. The result shows that for the existing building with different design reference period, using same design parameter is unreasonable in different seismic hazard characteristic zone, and the method is more scientific than the code method.

A preliminary study on seismic design criteria of offshore platforms in Bohai Sea of China

This paper analyzes the seismicity in Bohai Sea, introducing a shape factor K to characterize the seismic risk distribution in sub-regions of the sea. Based on the seismic design ground motions for 46 platforms located in the Bohai Sea, a statistical analysis was performed for different peak ground acceleration (PGA) ratios at two different probability levels. In accordance with the two-stage design method, a scheme of two seismic design levels is proposed, and two seismic design objectives are established respectively for the strength level earthquake and the ductility level earthquake. By analogy with and comparison to the Chinese seismic design code for buildings, it is proposed that the probability level for the strength level earthquake and ductility level earthquake have a return period of 200 and 1000–2500 years, respectively. The validity of these proposed values is discussed. Finally, the PGAs corresponding to these two probability levels are calculated for different sub-regions of the Bohai Sea.

Discussion by Abbas Moustafa of ‘A new approach of selecting real input ground motions for seismic design: The most unfavorable real seismic design ground motions’, Earthquake Engineering and Structural Dynamics, 2007; 36(8):1009–1027

Discussion by Abbas Moustafa of ‘A new approach of selecting real input ground motions for seismic design: The most unfavorable real seismic design ground motions’, <i>Earthquake Engineering and Structural Dynamics</i>, 2007; <b>36</b>(8):1009–1027

Discussion of ‘A new approach of selecting real input ground motions for seismic design: The most unfavourable real seismic design ground motions’ by C‐H Zhai and L‐L Xie

AbstractThis discussion consists of two parts. The first part raises a few comments and questions on the method presented in the above paper. The second part proposes a measure for identifying resonant accelerograms in a set of earthquake records without the need for pre‐processing of the records or inclusion of the structure dynamic analysis. Copyright © 2008 John Wiley &amp; Sons, Ltd.

A Simple Uniform Hazard Design Spectral Shape for Rock Sites

Performance-based earthquake engineering (PBEE) concepts dictate that the return period of the seismic design ground motions be known. While the NEHRP (2001) seismic design spectrum is constructed using two spectral accelerations that have a 2,475-year return period, the overall spectral shape is not representative of a uniform hazard spectrum. Consequently, other than the two spectral accelerations used to construct the NEHRP spectrum, the return periods of the spectral accelera tions defined by the NEHRP spectrum are unknown and may vary significantly. An alternative spectrum is proposed for firm rock sites. The proposed parabolic spectrum is constructed using three spectral accelerations ( i.e., pga, S S , and S 1 ) and a calibration parameter T pga . Parabolic spectra were computed for approximately 500 cities across the conterminous 48 states using the pga, S S , and S 1 having 2,475-year return period, as determined by the U.S. Geological Survey National Seismic Hazard Mapping Project. The correlation coefficients ( r 2 ) of the parabolic spectra to spectral accelerations for several oscil lator periods having uniform probabilities of exceedance were computed for the cities. The results confirm that the spectral accelerations defined by the parabolic spectra have approxi mately constant return periods.

A new approach of selecting real input ground motions for seismic design: The most unfavourable real seismic design ground motions

AbstractThis paper presents a new way of selecting real input ground motions for seismic design and analysis of structures based on a comprehensive method for estimating the damage potential of ground motions, which takes into consideration of various ground motion parameters and structural seismic damage criteria in terms of strength, deformation, hysteretic energy and dual damage of Park &amp; Ang damage index. The proposed comprehensive method fully involves the effects of the intensity, frequency content and duration of ground motions and the dynamic characteristics of structures. Then, the concept of the most unfavourable real seismic design ground motion is introduced. Based on the concept, the most unfavourable real seismic design ground motions for rock, stiff soil, medium soil and soft soil site conditions are selected in terms of three typical period ranges of structures. The selected real strong motion records are suitable for seismic analysis of important structures whose failure or collapse will be avoided at a higher level of confidence during the strong earthquake, as they can cause the greatest damage to structures and thereby result in the highest damage potential from an extended real ground motion database for a given site. In addition, this paper also presents the real input design ground motions with medium damage potential, which can be used for the seismic analysis of structures located at the area with low and moderate seismicity. The most unfavourable real seismic design ground motions are verified by analysing the seismic response of structures. It is concluded that the most unfavourable real seismic design ground motion approach can select the real ground motions that can result in the highest damage potential for a given structure and site condition, and the real ground motions can be mainly used for structures whose failure or collapse will be avoided at a higher level of confidence during the strong earthquake. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Variation of earthquake ground motion with depth

The variation of ground motion with depth is investigated in this paper, which is essential in determining the seismic design ground motion for embedded structures and pipelines. Firstly the earthquake ground motion on surface and in subsoil recorded by Hosokura Mine array of Japan and six California Strong Motion Instrumentation Program geotechnical arrays of the United States from about fifty moderate and strong earthquakes are described. Then the arrays were classified into three different categories according to their site conditions. Finally the variation law of ground and sub-ground motion with depth is established as a result of a nonlinear regression analysis of the above-mentioned data. Through comparing the features in different sites, it is concluded that, in general, the amplitude (acceleration, velocity and displacement) of ground motion are decreasing with depth and the attenuation rate is higher in the shallow strata than that in deeper ones.

Study on the severest real ground motion for seismic design and analysis

How to select the adequate real strong earthquake ground motion for seismic analysis and design of structures is an essential problem in earthquake engineering research and practice. In the paper the concept of the severest design ground motion is proposed and a method is developed for comparing the severity of the recorded strong ground motions. By using this method the severest earthquake ground motions are selected out as seismic inputs to the structures to be designed from a database that consists of more than five thousand significant strong ground motion records collected over the world. The selected severest ground motions are very likely to be able to drive the structures to their critical response and thereby result in the highest damage potential. It is noted that for different structures with different predominant natural periods and at different sites where structures are located the severest design ground motions are usually different. Finally, two examples are illustrated to demonstrate the rationality of the concept and the reliability of the selected design motion.

Research on performance-based seismic design criteria

The seismic design criterion adopted in the existing seismic design codes is reviewed. It is pointed out that the presently used seismic design criterion is not satisfied with the requirements of nowadays social and economic development. A new performance-based seismic design criterion that is composed of three components is presented in this paper. It can not only effectively control the economic losses and casualty, but also ensure the building’s function in proper operation during earthquakes. The three components are: classification of seismic design for buildings, determination of seismic design intensity and/or seismic design ground motion for controlling seismic economic losses and casualties, and determination of the importance factors in terms of service periods of buildings. For controlling the seismic human losses, the idea of socially acceptable casualty level is presented and the ‘Optimal Economic Decision Model’ and ‘Optimal Safe Decision Model’ are established. Finally, a new method is recommended for calculating the importance factors of structures by adjusting structures service period on the base of more important structure with longer service period than the conventional ones. Therefore, the more important structure with longer service periods will be designed for higher seismic loads, in case the exceedance probability of seismic hazard in different service period is same.