Acceleration Response Spectra Research Articles

Effects of the Geotechnical Knowledge Levels on the Definition of the Design Seismic Input for a School in Catania (Italy)

This paper deals with the seismic response of the soil underneath a school in Catania (Italy), characterized by a high seismic hazard. Studies of the seismic soil response by 1D analyses are carried out according two different levels of knowledge proposed for the soil: i) a limited level (LC1) acquired by initial design information; ii) an adequate level (LC2) acquired by recent geotechnical investigations. Each knowledge level is characterized by a proposed geotechnical confidence factor. Italian Regulations propose knowledge levels and confidence factors for structures, but ignore theme for soil and foundations. Seven different accelerograms, scaled at the same PHA with reference to the estimated seismicity of Catania, are applied at the bedrock. Soil nonlinearity is taken into account according to Eurocode 8. The dynamic response of the system is analysed in the time and frequency domains. The main goal of the paper is to stress the importance of the different geotechnical knowledge levels in the evaluation of the design/retrofitting seismic inputs in terms of acceleration time histories, amplification factors, response spectra and amplification function. The application of the proposed procedure is a useful methodological example for the designers.

Acceleration response spectra for Tbilisi city with site effects

The utilization of time histories of earthquake ground motion has grown considerably in the field of earthquake engineering. It is very unlikely, however, that recordings of earthquake ground motion will be available for all sites and conditions of interest. Hence, there is a need for efficient methods for the simulation of strong ground motion for a given region. Due to lack of the real strong ground motion records the objective of this research is to develop a methodology for rapid generation of horizontal and vertical components of earthquake ground motion at any site for Tbilisi city. The model developed in this study provides simulation of ground motion over a wide range of magnitudes and distances at 8 earthquake sources zones of Tbilisi region (within 50 km). The research includes three main topics: (i) the stochastic simulation of earthquake ground motion at a given site of the city of Tbilisi; (ii) the estimation of acceleration time histories at a given site using the direct method of engineering seismology considering soil conditions based on the theory of the reflected waves and (iii) calculation of horizontal and vertical acceleration elastic response spectra for main sites of Tbilisi territory. The simulation procedure typically consists of multiplying deterministic modulating function with a stationary process of known power spectral density. The obtained results in the terms of normalized elastic response spectra can be widely applied in the practice of earthquake engineering in Georgia.

The Beni Haoua, Algeria, Mw 4.9 earthquake: source parameters, engineering, and seismotectonic implications

A moderate Mw 4.9 earthquake struck the Beni Haoua (Algeria) coastal area on April 25, 2012. The mainshock was largely recorded by the accelerograph network of the Centre National de Recherche Appliquee en Genie Parasismique (CGS). The same day the earthquake occurred, eight mobile short period stations were deployed through the epicentral area. In this study, we use accelerogram and seismogram data recorded by these two networks. We combined the focal mechanism built from the first motion of P waves and from waveform inversion, and the distribution of aftershocks to well constrain the source parameters. The mainshock is located with a shallow focal depth, ∼9 km, and the focal mechanism shows a nearly pure left lateral strike slip motion, with total seismic moment of 2.8 × 1016 N.m (Mw = 4.9). The aftershocks mainly cluster on a narrow NS strip, starting at the coast up to 3–4 km inland. This cluster, almost vertical, is concentrated between 6 and 10 km depth. The second part of this work concerns the damage distribution and estimated intensity in the epicentral area. The damage distribution is discussed in connection with the observed maximum strong motion. The acceleration response spectrum with 5 % damping of the mainshock and aftershocks give the maximum amplitude in high frequency which directly affects the performance of the high-frequency structures. Finally, we tie this earthquake with the seismotectonic of the region, leading to conclude that it occurred on a N–S transform zone between two major compressional fault zones oriented NE–SW.

Inelastic Displacement Spectra for Bridges Using the Substitute-Structure Method

AbstractThe design of bridge structures for seismic loading by displacement-based procedures has become preferred over force-based procedures in modern specifications. One key step in displacement-based design (DBD) is the estimation of inelastic displacement. Current AASHTO specifications rely on a linear response spectrum analysis with an amplification factor, Rd, for conventionally designed bridges and on the substitute structure method (SSM) for analysis of isolated bridges to estimate inelastic displacements. Both methods are used in this study for a selected site and target acceleration response spectrum. The procedures for both are outlined in detail. Displacement spectra from nonlinear response history analyses (NLRHA) are generated for seven ground-motion sets and compared to results from the two simplified methods. The SSM is shown to produce inelastic displacement estimates that more closely match NLRHA results than do results from the AASHTO Rd method over a wide range of periods for the speci...

Evaluating nonlinear effective stress site response analyses using records from the Canterbury earthquake sequence

A widely used one-dimensional nonlinear effective stress site response analysis program is used to model the response of potentially liquefiable soils during strong shaking. Ground motion records from six events of the 2010–2011 Canterbury earthquake sequence and the extensive site investigation data that have been obtained for the Christchurch area provide the basis for the analyses. The results of the analyses depend significantly on the input motions and soil profile characterization, so these important aspects are examined. Deconvolved Riccarton Gravel input motions were generated, because recorded rock or firm layer motions were not available. Nonlinear effective stress seismic site response analyses are shown to capture key aspects of the observed soil response through the comparison of acceleration response spectra of calculated surface motions to those of recorded surface motions; however, equivalent-linear and total stress nonlinear analyses capture these aspects as well. Biases in the computed motions compared to recorded motions were realized for some cases but they can be attributed primarily to the uncertainty in the development of the input motions used in the analyses.

A stochastic based approach for a new site classification method: application to the Algerian seismic code

Building codes have widely considered the shear wave velocity to make a reliable subsoil seismic classification, based on the knowledge of the mechanical properties of material deposits down to bedrock. This approach has limitations because geophysical data are often very expensive to obtain. Recently, other alternatives have been proposed based on measurements of background noise and estimation of the H/V amplification curve. However, the use of this technique needs a regulatory framework before it can become a realistic site classification procedure. This paper proposes a new formulation for characterizing design sites in accordance with the Algerian seismic building code (RPA99/ver.2003), through transfer functions, by following a stochastic approach combined to a statistical study. For each soil type, the deterministic calculation of the average transfer function is performed over a wide sample of 1-D soil profiles, where the average shear wave (S-W) velocity, Vs, in soil layers is simulated using random field theory. Average transfer functions are also used to calculate average site factors and normalized acceleration response spectra to highlight the amplification potential of each site type, since frequency content of the transfer function is significantly similar to that of the H/V amplification curve. Comparison is done with the RPA99/ver.2003 and Eurocode8 (EC8) design response spectra, respectively. In the absence of geophysical data, the proposed classification approach together with micro-tremor measures can be used toward a better soil classification.

Response Spectra at Liquefaction Sites during Shallow Crustal Earthquakes

Site amplification studies and building code provisions recognize that soil liquefaction can alter the characteristics of ground shaking at a site. However, guidance as to how the amplitudes of spectral accelerations are modified is lacking. In this paper, available recorded ground motions from shallow crustal earthquakes at sites that exhibited evidence of liquefaction are investigated. Analysis of residuals computed relative to Next Generation Attenuation (NGA) estimates reveal positive bias at longer periods, slight negative bias at intermediate periods, and slight positive bias at short periods. Trends with V S30, NGA-estimated peak ground acceleration (PGA), and moment magnitude are also observed. A model is developed that removes the initially observed residual bias and reduces uncertainty. The proposed model can be used to adjust NGA-estimated acceleration response spectra to account for the effects of liquefaction on ground shaking.

On the Torsional–Translational Response of Wind Turbine Structures

In the present paper, the torsional–translational response of a prototype wind turbine tower considered as an irregular structure is studied. As a matter of fact, a plethora of wind turbine towers has collapsed during the last decades due to torsional dynamic actions. An effective numerical model of the prototype irregular wind turbine tower is herein developed which has been verified by the application of the continuous model method considering both a fully fixed and a partially fixed foundation. As known, the higher eigenmodes of the tower strongly affect the structural response and may become critical in the case that the tower is subjected to strong dynamic loading, as is, e.g., wind loading, when simultaneously excited by a strong seismic motion. In order to estimate the role of the fundamental torsional modes of the above-mentioned structure in its overall structural response, three pairs of appropriately selected artificial seismic accelerograms having response acceleration spectra (for equivalent viscous damping ratio 0.03) equivalent to the Eurocode elastic acceleration spectra are used and then, applying a type of backwards analysis, an equivalent dynamic or static torsion loading is defined.

A Comparative Study on Ground Motion Attenuation in the 2012 Varzaghan-Ahar Doublet Event, Northwest of Iran

Predictive capabilities of the four updated NGA ground-motion models (NGA-WEST2) are evaluated in this study for acceleration response spectra using observed ground motions for August 11, 2012 Varzaghan-Ahar events in Iran. The predicted results were compared with those of regional attenuation equations and NGA08 models as well. The results of analyses revealed that the models of NGA-WEST2 improve prediction performance of NGA08 models for the two studied moderate events. All of models underestimate the recorded spectra of the second event for regionally significant period of 0.2 s at source distances below 50 km. For this distance range, almost all of the models underestimate the recorded spectra for periods larger than 1 s.

A Probabilistic Methodology to Determine Elastic Acceleration Response Spectra for Pulse-Type Records through Multi-Resolution Analyses

This article focuses on the characterizations of pulse-type ground motions which are mainly caused by rupture directivity. Multi-resolution analysis is employed to decompose 53 typical pulse-type records which are selected from 12 large earthquakes into a series of ground motion components. A methodology for deriving design spectra, which could incorporate the special effects caused by pulse-type records is proposed based on the bi-normalized response spectra of ground motion components, and is named as Near-Fault Response Spectrum (NFRS). Analysis results indicate that NFRS might be a reliable candidate for the code-based design spectrum especially for structures constructed close to active fault.

이차원 지반 유한요소 모델링을 통한 사면상부 지진지반운동의 지표면 지형효과 분석

지진지반운동 증폭을 야기하는 부지효과는 지하 토사 조건과 구조뿐만 아니라 지표 지형에 의해 지대한 영향을 받는다. 그럼에도 불구하고 국내에서는 최근 수십 년에 걸쳐 주로 지질 및 토사 조건과 관련된 부지고유 지진응답 연구들이 대부분을 차지해 왔으며, 이러한 국부 지질 효과는 잘 정립되어 현행 국내 내진설계기준들에 반영되고 있다. 이 연구에서는 현행 국내 내진설계기준에서는 고려되고 있지 않은 지표 지형효과 평가의 일환으로, 세 가지 다른 경사각 조건의 유한요소 지반 모델링을 통한 이차원 지진 부지응답 해석을 수행하였다. 이차원 유한요소 해석 결과인 최대 지반가속도와 가속도 응답스펙트럼을 추가적으로 수행한 일차원 유한요소 해석 결과와 비교하였다. 최대 지반가속도와 스펙트럴가속도는 대부분의 사면상부 영역에서 지형효과로 인해 이차원이 일차원 해석에 비해 크게 나타났다. Site effects resulting in the amplification of earthquake ground motion are strongly influenced not only by the subsurface soil conditions and structure, but also by the surface topography. Yet, over the last several decades, most studies of site-specific seismic responses in Korea have focused primarily on the seismic amplification associated with geologic and soil conditions. For example, the effects of local geology are now well established and have been incorporated into current Korean seismic design codes, whereas topographic effects have not been considered. To help address this shortcoming, two-dimensional (2D) seismic site response analyses, using finite element (FE) ground modeling with three different slope angles, were performed in order to assess the site effects of surface topography. We then compared our results, specifically peak ground acceleration (PGA) and acceleration response spectrum, to those of one-dimensional (1D) FE model analyses conducted alongside our study. Throughout much of the upper slope region, PGAs and spectral accelerations are larger in the 2D analyses than in the 1D analyses as a result of the topographic effect.

Estimation of Damping Correction Factors Using Duration Defined by the Standard Deviation of Phase Difference

The damping correction factors (DCFs) to convert the 5% damping acceleration response spectra to those for other damping levels are computed for the records of 13 Japanese earthquakes. Their correlation with the standard deviation of phase difference ( σ) is also investigated in ten frequency bands. The σ-DCF relations obtained are found to be very similar across the different types of earthquakes. Further, regression analysis suggests that for damping ratios of 1% and 2%, with the increase in σ, the DCFs increase in low-frequency bands (up to 4–5 Hz), whereas they decrease in higher frequency bands. On the other hand, for damping ratios of more than 5%, with the increase in σ, the DCFs decrease in low-frequency bands (up to 1 Hz), whereas the opposite tendency is observed in higher frequency ranges. This research also discusses the applicability of the σ-DCF relations to design ground motion simulation.

Estimation of the maximum credible hazard in Kuala Lumpur and Singapore due to gigantic Sumatran megathrust earthquakes: based on a comparative study on attenuation laws

This paper has classified nine attenuation laws derived for subduction interface earthquakes through a comparative study based on the peak ground accelerations (PGAs) recorded in Peninsular Malaysia and Singapore. The goal of classification was to identify the attenuation laws that were the most compatible with the region. The PGAs predicted by the relations provided by Nabilah and Balendra (Earthq Eng 16:1076–1094, 2012) and Zhao et al. (Bull Seismol Soc Am 96:898–913, 2006) were found to correlate well with the recorded PGAs. The maximum credible hazard in Kuala Lumpur and Singapore was obtained by calculating the acceleration response spectra caused by three great Sumatran megathrust earthquakes (the worst possible earthquake scenarios) using Zhao et al. spectral attenuation law. Current building code in the region requires that buildings should be capable of resisting a notional ultimate lateral design load equals to 1.5 % of the characteristic dead weight, simultaneously applied at each floor (i.e., the minimum design level of buildings equals to ~0.15 m/s2). The results show that the risk level for structures of the two cities with natural period Tn = 1–1.5 s corresponding to 10- and 15-story buildings located on hard soil sites [National Earthquake Hazards Reduction Program (NEHRP) site class C] is high as the demand spectrum due to a worst possible earthquake scenario with moment magnitude (MW) 9.5 and an epicentral distance (Repi) of 600 km from Singapore was noticeably higher than their design level. The results of the present study are applicable in seismic hazard assessment projects in Peninsular Malaysia and Singapore. The most interesting conclusion from the earthquake engineering perspective, however, is that the design spectral shapes specified in IBC 2012 and Eurocode 8 (type 2) codes may not be particularly appropriate for sites that could be affected by large-magnitude, distant earthquakes.

Seismic hazard assessment for two cities in Eastern Iran

Iran as one of the countries located on the Alpine-Himalayan seismic belt has recently experienced a few number of catastrophic earthquakes. A well-known index of how buildings are affected by earthquakes is through assessment of probable Peak Ground Acceleration (PGA) and structures' response spectra. In this research, active faults around Kerman and Birjand, two major cities in eastern parts of Iran, have been considered. Seismic catalogues are gathered to categorize effects of surrounding faults on seismicity of the region. These catalogues were further refined with respect to time and space based on Knopoff-Gardner algorithm in order to increase statistical independency of events. Probabilistic Seismic Hazard Analysis (PSHA) has been estimated for each of cities regarding 50, 100, 200 and 500 years of structures' effective life-span. These results subsequently have been compared with Deterministic Seismic Hazard Analysis (DSHA). It has been observed that DSHA not necessarily suggests upper bound of PSHA results. Furthermore, based on spectral Ground Motion Prediction Equations (GMPEs), Uniform Hazard Spectra (UHS) and spectral acceleration were provided for 2% and 10% levels of probability of exceedance. The results show that increasing source-to-site distance leads to spectral acceleration reduction regarding each fault. In addition, the spectral acceleration rate of variation would increase if the source-to-site distance decreases.

Reinforced Concrete Frame Structure Dynamic Analysis Based on SAP2000

Structure under long-term load, environmental erosion, material aging, especially under the seismic action can cause damage accumulation and bearing capacity decrease. In order to make sure its safety and reliable, avoid extreme cases of catastrophic accident, it is necessary to carry out the engineering structural health diagnosis. Using SAP2000 software, seismic response analysis for a two layer reinforced concrete frame structure is carried out. The laws of the acceleration response time history and spectrum under different seismic action were found out by discussing structure in no damage and different damages. The results showed that no matter where the damage located, the top node response increment is bigger than the middle node, the peak of acceleration response spectrum changes little with the beam damage degrees changing. Selecting the acceleration response peak of the top node as a structural damage index is feasible in the damage detection and identification of engineering structures, but analyzing the response spectrum for damage detection is unpractical.

An Improved Stochastic Finite-Fault Method Based on Energy

Owing to the simulated ground motion energy distribution by stochastic finite-fault method is not reasonable, near-field bedrock strong ground motion acceleration time histories are used to study. Fourier transform is adapted to analysis the variation of the energy accumulation curve with frequency. The results show that the record energy accumulation curve is a steep rise curve, 80% of total energy of the vertical ground motion is concentrated on the 2.5-15Hz, while the horizontal is mainly concentrated on the 2-11Hz. An improved stochastic finite-fault method is proposed by multiplying an amplification factor in some frequency. The results show that multiplying an amplification factor, the simulated acceleration energy accumulation curve matches to the record acceleration energy accumulation curve, and the peak of simulated acceleration response spectrum tends to the record acceleration value.

Rocking Soil-Structure Systems Subjected to Near-Fault Pulses

Seismic performance of rocking soil-structure systems subjected to near-fault pulses is investigated considering foundation uplifting and soil plasticity. An extensive parametric study is conducted including medium-to-high-rise buildings with different aspect ratios based on shallow raft foundation at stiff-to-rock sites. Mathematical directivity and fling pulses are used as input ground motion. The superstructure is assumed to have three different boundary conditions: (a) fixed-base, (b) linear soil-structure interaction (SSI), and (c) nonlinear SSI. Evidently, the prevailing pulse period Tp is a key parameter governing nonlinear SSI effects. The normalized acceleration response spectra reveal that despite beneficial effects of foundation uplifting and soil yielding in most cases, there are some minor regions in which the response accelerations are amplified. In addition, more slender buildings significantly benefit from uplifting and soil yielding when subjected to short- and medium-period directivity pulses compared to squat structures. However, response amplifications with respect to fixed-base structures are considerable in case of slender structures subjected to medium- or long-period directivity pulses. So that neglecting the SSI effects on seismic performance of rocking structures with shallow foundations, as mostly assumed in common practice, may give rise to inaccurate estimations of force demands against near-fault pulselike ground motions. Furthermore, the envelope of residual foundation tilting θr is limited to 0.015 rad, in case of directivity pulses.

Seismic Monitoring of a Slope to Investigate Topographic Amplification

Some earthquakes with a magnitude lower than Ms 7.0, such as Ludian earthquake in Yunnan in 2013, have triggered strong secondary geo-hazards in the form of slope failures. Topographic amplification is generally considered to be the main causal factor for these slope failures. However, until recently, this idea is not supported by appropriate seismic monitoring data. The Kangding Ms 6.3 earthquake on November 22 nd , 2014 was monitored in Lengzhuguan, Sichuan Province, located 56 km from the earthquake epicenter. Six monitoring instruments have recorded this earthquake. The horizontal and vertical component Peak Ground Acceleration (PGA), the site response directivity, the directional variation of the Arias intensity, and the acceleration response spectrum were determined from the data obtained. Conclusions could be drawn that the topographic amplification effect of the isolated ridge on the right bank was stronger than that of nearly linear slope on the left bank and the topographic amplification effect at a slope break was stronger than on a linear slope.

核级应急柴油发电机组抗震试验研究

本文中，我们采用试验方法对核级应急柴油发电机组进行抗震鉴定。使用连续白噪声方法，测得机组在三正交轴上的固有频率和阻尼比。根据业主提供的楼板反应谱，生成人工地震波，对机组三正交轴向同时输入模拟地震加速度时程进行激振，分别进行了5次OBE (运行基准地震)和1次SSE (安全停堆地震)地震模拟振动台试验，试验表明机组各项性能指标在抗震试验前后无明显变化，抗震性能满足要求。 In this paper, we do the seismic identification of nuclear emergency diesel generator by test method. Dynamic characteristics including orthogonal tri-axial fundamental frequencies and equivalent damping ratios were measured by using the white noise scanning method. Artificial seismic waves were generated according to the floor acceleration response spectrum provided by the owners. Furthermore, five OBE and one SSE shaking table tests for emergency diesel generator were done by using the artificial seismic waves as seismic inputs along the orthogonal tri-axial simultaneity. The results show that the emergency diesel generator satisfies the seismic requirements and there is no obvious change of its performances before and after the earthquake test.

성능설계 및 진동제어구조시스템 설계에 대비한 설계용 스펙트럼의 제안

In the seismic design, the design spectrum considering the responses of the acceleration, velocity, displacement and energy for the natural vibration period of structure is used. The acceleration response spectrum is the most frequently applied for the seismic design of structure in worldwide. In the case of using peak ground acceleration, the response characteristics of structure are reflected by using the acceleration response value because there is large uncertainties of the ground acceleration itself and it is difficult to consider the response characteristics of structure. The acceleration response spectrum is based on the linear elastic analysis on the single-degree of freedom system, however, practical structures are composed of the multi-degree of freedom system and allow for the plastic deformation, so that it makes a large difference between the both. In this study, the spectra such as the acceleration response and the energy equivalent velocity response are analyzed according to the structural behavior, the distribution of the force, stiffness and mass on each story of structure and the hysteresis characteristics. And the stability of the spectra is verified, so the propriety for the design spectrum is evaluated. Thus, the effective information is sorted for improving the accuracy of the seismic design.