Peak Ground Acceleration Range Research Articles

Double friction pendulum-based isolation optimization for transformer-bushing systems

Transformers and their bushings are critical equipment pieces in power substations, which are often exposed to significantly high seismic risk. To enhance the seismic performance of the transformer-bushing system, isolation through double friction pendulum (DFP) bearings has been considered. However, the selection of appropriate isolation parameters lacks theoretical guidance and efficient analysis methods. A theoretical model for the transformer-bushing system isolated with DFP bearings has been proposed. Based on this model, isolation parameters that ensure acceptable displacement response while achieving optimal acceleration isolation efficiency can be determined. Taking a high-voltage transformer isolated by DFP bearings as an example, a set of isolation parameters is optimized and used to design a shaking table test. The results demonstrate that the proposed model exhibits reliable calculation accuracy for the seismic response of the transformer-bushing system, regardless of whether it is isolated or not, within the range of peak ground acceleration(PGA) of 0.1–0.6 g. Moreover, at 0.4 g, the experimental results indicate that the isolation efficiency remains consistent with the parameter optimization, approaching 50 %. This research contributes to the understanding of seismic resistance and isolation strategies for transformer-bushing systems, providing valuable insights for the selection and optimization of isolation parameters in practice.

The “Glass Beads” Coupling Solution for Borehole and Posthole Accelerometers: Shaking Table Tests and Field Retrievability

AbstractBorehole accelerometers are designed to record strong ground movements at depth. They have become an important complement to surface accelerometers for seismic and earthquake engineering applications. Borehole accelerometers present several implementation challenges, including their coupling with the geological environment. One possible coupling solution is the use of small glass beads, which are placed inside the borehole casing with the purpose of filling in any empty space between the sensor and the casing walls. We carried out a test on a shaking table, over a wide range of peak ground accelerations (PGA from 0.17 to 1.64g), allowing the comparison of the signals between a surface accelerometer and a borehole accelerometer coupled through the glass beads. These tests show that there is almost no difference between the surface and borehole accelerometer signals between 0.5 and 25 Hz, and only very small differences outside this band (0.2–0.5 Hz and 25–80 Hz). Furthermore, experience from multiple vertical accelerometric arrays show that an installation using glass beads is “reversible”, that is, 30 yr after the initial installation it can still be possible to easily extract the accelerometers for repair or replacement, without any problems or damage to the sensors.

Seismic risk to beam end corner in railway bridges

The beam end of the railway bridge is the crucial part of the whole bridge, and the earthquake will cause damage to the beam end. In order to ensure the safety of the bridge and track system. To investigate the risk of seismic deformations at the beam end in railway bridges, a three-span continuous rigid frame bridge was taken as a case study and a three-dimensional finite element model of the whole bridge was established in ABAQUS. The deformation angle of the beam end was selected as the damage index, and the seismic vulnerability and risk curves of the beam end were calculated by the incremental dynamic analysis (IDA) method using 22 scaled ground motion time histories. The results show that in the same range of peak ground accelerations (PGAs), the influence of cross-bridge ground motion on the corner deformations of the beam end was much greater than that of the along-bridge ground motion. Under the along-bridge seismic excitation, the damage probabilities for the rotation angles in X, Y and Z-directions did not exceed 50 %. In different damage states, increasing in PGA correlated positively with the beam end damage probability. The vulnerability curves for PGA can be used for the seismic risk assessment of the beam end and can also provide decision support for prioritizing the seismic reinforcement of bridges.

Hybrid simulation modeling framework for evaluation of Thermal Power Plants seismic resilience in terms of power generation

This study puts forward a comprehensive hybrid simulation modeling framework for assessing the resilience of Thermal Power Plants (TPPs) in terms of Nominal Power Generation Capacity (NPGC) following various earthquake Intensity Measures (IMs). The proposed framework utilizes a combination of agent-based and system dynamics simulation approaches to simulate disaggregated and aggregated aspects of thermal power plant systems with higher compatibility to investigate various earthquake physical damage scenarios and the system restoration process. A case study involving a large Gas Turbine Combined Cycle Power Plant (GTCC-PP) is examined to demonstrate the applicability of the proposed model and framework. The results of the analysis provide an estimate of the Power Plant (PP) ‘s mean NPGC vs. time and across a wide range of Peak Ground Accelerations (PGAs), with current condition (in operational status) and after employing anchoring equipment and increasing the number of repair crews as two main resilience enhancement strategies. Finally, the impact of the investigated strategies on improving seismic resilience and the seismic resilience trends in the PP under the conditions mentioned above are compared. The proposed framework provides a tool for the TPPs administrators and decision-making to plan for emergency response and evaluate the seismic resilience of TPPs and understand how to develop it efficiently.

Sensitivity analysis of input ground motion on surface motion parameters in high seismic regions: a case of Bhutan Himalaya

Abstract. Historical earthquakes demonstrate that strong motion characteristics and local soil condition, when coupled, significantly influence seismic site response. Interestingly, most of the Himalayan earthquakes depicted anomalous behavior per the site conditions historically. Being one of the most active seismic regions on earth, the eastern fringe of the Himalaya has observed many devastating earthquakes together with non-uniform damage scenarios. To quantify such anomalies, we evaluate surface motion parameters for a soft soil deposit located in the city of Phuentsholing in western Bhutan. Using one-dimensional site response analysis, the sensitivity of ground motion variation is estimated. This study accounts for the earthquakes of moment magnitudes 6.6 to 7.5 with a wide variation in peak ground acceleration (PGA). To dissect the characteristics of six inputted ground motions on eight local ground conditions, a sensitivity analysis is performed statistically. The statistical correlation of the response datasets and the linear regression model of the bedrock outcrop and the surface motion spectral acceleration along the stratified depth are examined to quantify the variation in surface motion parameters. The results highlight that the strong motions with PGA greater than 0.34 g demonstrate greater sensitivity, leading to some anomalies in response parameters, especially amplification. Similar results were obtained for the low PGA range (<0.1 g).

A new modified stochastic linearization technique to analyze structures with nonlinear fluid viscous dampers

Nonlinear viscous dampers can efficiently improve the seismic performance of structures by dissipating large amounts of earthquake-induced energy. In common practice, the spectral analysis of structures with nonlinear viscous dampers is generally conducted based on an estimated equivalent damping ratio. To this end, the stochastic linearization technique can be used as an effective probabilistic approach to take into account the evolutionary characteristics of the input earthquake excitation. This study aims to present optimal non-Gaussian probability density functions to improve the accuracy of the stochastic linearization technique for nonlinear viscous dampers in both firm and soft soil-based structures. It is shown that by using the optimum probability density functions, the computational error of the stochastic linearization technique for a single-degree-of-freedom structure under simulated ground motions, with a range of peak ground accelerations between 0.1 and 0.6 g, is reduced by up to 70%. The efficiency of the proposed probability density functions is then demonstrated for multi-degree-of-freedom structures, by estimating the roof displacements of a six-story steel frame with nonlinear viscous dampers under a set of natural ground motions using different linearization methods. The comparison of the stochastic linearization technique estimated responses with the exact values confirms that using the proposed probability density functions leads to considerably lower errors in both firm and soft soil-based structures compared with the other linearization techniques.

A three-dimensional investigation on performance of batter pile groups in laterally spreading ground

The performance of batter pile groups in laterally spreading ground has rarely been investigated. The present study evaluates the performance of 2 × 1 batter pile groups with four different configurations subjected to lateral spreading displacement through three-dimensional, fully coupled numerical investigations. Pressure dependent multi-yield model for the soil medium complemented with variation in permeability of liquefiable soil for excess pore pressure generation is considered. The nonlinear behaviour of the reinforced concrete pile is also incorporated. The behaviour of batter pile groups is evaluated for various earthquake time histories. The study indicates that the bending moment developed in the pile sections of both upstream and downstream sides of the ground displacement is observed to reduce under combined (kinematic + inertial) loading conditions for batter pile group configurations considered. However, shear and axial forces show increasing trends for batter pile groups, especially with higher batter angles for both kinematic and combined loading conditions. It is also observed that the presence of batter piles reduces both pile cap and superstructure displacements. However, significant pile cap rotations are recorded for pile groups with higher batter angles. The performances of the pile groups are confirmed for earthquake motions with a wide range of peak ground accelerations.

Characterization of Ground Response and Liquefaction for Kathmandu City Based on 2015 Earthquake Using Total Stress and Effective Stress Approach

This chapter presents the seismic vulnerability of Kathmandu City (Nepal), based on Nepal 2015 earthquake, in terms of the ground response and liquefaction potential. The spatially well-distributed 10-boreholes and ground motions of Mw 7.8 Nepal 2015 earthquake recorded at five different stations were adopted for the analysis. The range of peak ground acceleration and peak spectral acceleration were in the order of 0.21g-0.42g and 0.74g-1.50g, respectively. Liquefaction potential of the sites were computed using both semi-empirical approach and liquefaction potential index (LPI). LPI shows that the 6 sites out of 10 sites are at high risk of liquefaction.

Relationship between earthquake-induced excess pore water pressure and strong ground motion observed in a monitored fill slope

The generation of excess pore water pressures during ground shaking can be an important earthquake-induced landslide trigger. We measured pore water pressures and seismic ground motion in filled slopes and examined their relationships obtained from 29 observed earthquakes. We characterized pore water pressure and seismic waveforms by calculating several parameters that described their magnitudes and durations. We demonstrate that whilst the instantaneous magnitude of strong ground motion is responsible for the generation of excess pore water pressure, the magnitude of excess pore water pressure generated is related to the peak ground acceleration (PGA) and Arias Intensity (AI) in the observed PGA range of 0.12–1.9 m/s2. The magnitude of peak ground velocity (PGV) also produced a strong correlation although a few exceptional events where long period component (>1 s) of seismic waves is dominant were observed. Lastly, the time-span over which excess pore water pressure continues to rise is affected by the duration of seismic ground motion. Our study shows how excess pore water pressures can be generated in fill-slopes during seismic events. This new knowledge could be used to improve future earthquake-induced landslide hazard assessment.

Quantifying the out-of-plane response of unreinforced masonry walls subjected to relative support motion

TThe supports of out-of-plane loaded unreinforced masonry walls in buildings are subjected to a motion that is filtered and amplified by the building structure and, in some cases, can be significantly different from the ground motion. Moreover, because these walls span one or several storeys, their top and bottom supports are subjected to motions that differ in phase and amplitude. In state-of-the-art assessment procedures for the out-of-plane stability of masonry walls any effect of a relative support motion is neglected. The objective of this paper is to study the effect of the relative support motion on the response of out-of-plane loaded vertically-spanning unreinforced masonry walls. The acceleration capacity of the walls is investigated by means of a discrete element model representative of different wall configurations. A set of ground motions covering a wide range of peak ground acceleration and peak ground displacement is used as input to the simulations. The relative motion between the wall supports is included in the model in a systematic way: firstly, through a motion that is non-synchronous but of equal amplitude; secondly, through a motion that is synchronous but of different amplitude. The effect of the relative support motion is studied on different wall configurations where the elastic modulus of masonry, the wall height-to-thickness ratio, the wall effective thickness and the overburden at the top wall are varied. The study shows that, because of the relative support motion, the acceleration capacity of the walls can drop by 20% and, in the cases where the overburden is high, by more than 50%.

Effect of mechanical degradation of laminated elastomeric bearings and shear keys upon seismic behaviors of small-to-medium-span highway bridges in transverse direction

Laminated elastomeric bearings have been widely used for small-to-medium-span highway bridges in China, in which concrete shear keys are set transversely to prohibit large girder displacement. To evaluate bridge seismic responses more accurately, proper analytical models of bearings and shear keys should be developed. Based on a series of cyclic loading experiments and analyses, rational analytical models of laminated elastomeric bearings and shear keys, which can consider mechanical degradation, were developed. The effect of the mechanical degradation was investigated by examining the seismic response of a small-to-medium-span bridge in the transverse direction under a wide range of peak ground accelerations (PGA). The damage mechanism for small-to-medium-span highway bridges was determined, which can explain the seismic damage investigation during earthquakes in recent years. The experimental results show that the mechanical properties of laminated elastomeric bearings will degrade due to friction sliding, but the degree of decrease is dependent upon the influencing parameters. It can be concluded that the mechanical degradation of laminated elastomeric bearings and shear keys play an important role in the seismic response of bridges. The degradation of mechanical properties of laminated elastomeric bearings and shear keys should be included to evaluate more precise bridge seismic performance.

Effects of Spatial Variability on Liquefaction-Induced Settlement and Lateral Spreading

AbstractNonlinear dynamic numerical simulations of infinite slopes are used to examine the effects of spatial variability in penetration resistances on liquefaction-induced settlement and lateral spreading for gently sloping ground and to develop guidance on selecting representative properties for uniform models. Simulation results for models having uniform properties (uniform models) are compared to results for models having spatially correlated Gaussian random field property distributions (stochastic models). Results are presented for sets of stochastic model realizations and a set of ground motions scaled to a range of peak ground accelerations. Computed responses and ground deformations (settlements and lateral displacements) for these uniform and stochastic models are used to identify representative properties (as a percentile of the stochastic distributions) for which the uniform models produce reasonable agreement with the median of the stochastic model responses. The effects of the scales of fluct...

Behavior of rigid blocks with geometrical defects under seismic motion: an experimental and numerical study

SummaryThe present work investigates the influence of small geometrical defects on the behavior of slender rigid blocks. A comprehensive experimental campaign was carried out on one of the shake tables of CEA/Saclay in France. The tested model was a massive steel block with standard manufacturing quality. Release, free oscillations tests as well as shake table tests revealed a non‐negligible out‐of‐plane motion even in the case of apparently plane initial conditions or excitations. This motion exhibits a highly reproducible part for a short duration that was used to calibrate a numerical geometrically asymmetrical model. The stability of this model when subjected to 2000 artificial seismic horizontal bidirectional signals was compared with the stability of a symmetrical one. This study showed that the geometrical imperfections slightly increase the rocking and overturning probabilities for earthquake signals in a narrow range of peak ground acceleration. Copyright © 2016 John Wiley & Sons, Ltd.

Seismic Vulnerability Assessment Form for Free-Standing Columns Based on a Simplified Numerical Analysis

ABSTRACTThis article describes the creation of a seismic vulnerability assessment form for free-standing columns, based on Discrete Element Method simulations. A broad range of column configurations, selected after archaeological research, was analyzed. Each soil-column configuration was tested with 56 artificial accelerograms in the range of peak ground acceleration between 0.2 and 0.8 g. Fragility curves were created for each configuration and used to quantify the effects of soil, and the slenderness, height, and number of drums of each column. The influence factors of all parameters were used in the assessment form to categorize the columns into vulnerability classes, according to their probability of collapsing when subjected to a certain level of seismic excitation. The proposed tool can be used for rapid, preliminary, seismic vulnerability assessment, without the need for further sophisticated calculations. Four ancient columns, which have survived earthquakes of known acceleration amplitude, were used to apply, test and validate the proposed assessment form.

Ground Motions at the Outermost Limits of Seismically Triggered Landslides

Abstract Over the last few decades, we and our colleagues have conducted field investigations in which we mapped the outermost limits of triggered landslides in four earthquakes: 1987 Whittier Narrows, California ( M 5.9), 1987 Superstition Hills, California ( M 6.5), 1994 Northridge, California ( M 6.7), and 2011 Mineral, Virginia ( M 5.8). In an additional two earthquakes, 1976 Guatemala ( M 7.5) and 1983 Coalinga, California ( M 6.5), we determined limits using high‐resolution aerial‐photographic interpretation in conjunction with more limited ground investigation. Limits in these earthquakes were defined by the locations of the very smallest failures ( 3 ) from the most susceptible slopes that can be identified positively as having been triggered by earthquake shaking. Because we and our colleagues conducted all of these investigations, consistent methodology and criteria were used in determining limits. In the six earthquakes examined, we correlated the outermost landslide limits with peak ground accelerations (PGAs) from ShakeMap models of each earthquake. For the four earthquakes studied by field investigation, the minimum PGA values associated with farthest landslide limits ranged from 0.02 g to 0.08 g . The range for the two earthquakes investigated using aerial‐photographic interpretations was 0.05–0.11 g . Although PGA values at landslide limits depend on several factors, including material strength, topographic amplification, and hydrologic conditions, these values provide an empirically useful lower limiting range of PGA needed to trigger the smallest failures on very susceptible slopes. In a well‐recorded earthquake, this PGA range can be used to identify an outer boundary within which we might expect to find landsliding; in earthquakes that are not well recorded, mapping the outermost landslide limits provides a useful clue about ground‐motion levels at the mapped limits.

Seismic hazard assessment for Yanbu metropolitan area, western Saudi Arabia

The stochastic method is used to predict ground motions for Yanbu metropolitan area which has been affected byseveral earthquakeswiththe maximum magnitudeof6.8in 1121 AD. The stochastic method has been used for simulating the time domain history for the peak ground acceleration (PGA), peak ground velocity (PGV), and peak ground dis- placement (PGD) at Yanbu metropolitan area. In addition, the response spectra at 3, 5, and 10 % of the damped pseudo-spectral acceleration (PSA) have been calculated at Al-Majd Sporting Club, Al-Maktabah, and Al-Shate Secondary School sites within the Yanbu metropolitan area. The results show that the values of PGA range from 137 to 388 cm/s 2 , PGV values vary from 8.96to 25.5 cm/s, and PGD values range from 6.7 to 20.9 cm. The values of pseudo- spectral acceleration and predominant period are 974.53 cm/ s 2 (with 5 % damping) at 0.14 s for Al-Majd Sporting Club, 487.06cm/s 2 at 0.19s for Al-Maktabah site, and 700.83cm/s 2 at 0.14 s for Al-Shate Secondary School. It is cleared that the values of ground motion parameters are amplified due to the presence of thick sections of very soft to soft sediments to more than six times those of the hard rocks. Furthermore, the estimated predominant periods from this study are corre- lated well with that of multichannel analysis of surface wave (MASW) approach. These results should be taken into account during design and construction of civil engineering structures within the Yanbu metropolitan area.

Experimental and numerical response of rigid slender blocks with geometrical defects under seismic excitation

The present work investigates on the influence of small geometrical defects on the behavior of slender rigid blocks. A comprehensive experimental campaign was carried out on one of the shake tables of CEA/Saclay in France. The tested model was a massive steel block with standard manufacturing quality. Release, free oscillations tests as well as shake table tests revealed a non-negligible out-of-plane motion even in the case of apparently plane initial conditions or excitations. This motion exhibits a highly reproducible part for a short duration that was used to calibrate a numerical geometrically asymmetrical model. The stability of this model when subjected to 2 000 artificial seismic horizontal bidirectional signals was compared to the stability of a symmetrical one. This study showed that the geometrical imperfections slightly increase the rocking and overturning probabilities under bidirectional seismic excitations in a narrow range of peak ground acceleration.

Impact of earthquake on mining slopes—a numerical approach

Earthquake that occurs in the vicinity of open-pit slopes produces ground vibrations and may trigger instability. The impact of earthquake on open-pit slopes, where the slopes are non-homogenous and having different depths and slope angle, needs elaborate studies. To analyse the impact of earthquake on open-pit slopes, numerical modelling is performed in this study using SLOPE/W and FLAC3D. The failure mechanism, surface non-homogeneity, geometry, material properties and earthquake loading are defined for the numerical simulations. Different open-pit slopes of various rock mass types are simulated against a range of peak ground accelerations (PGA). The results obtained are presented as failure surface and factor of safety. The outcomes of the finite difference modelling are analysed in static and dynamic stages using Mohr–Coulomb elasto-plastic material model. To analyse the impact of earthquake on slope angle, different slope angles were considered for design and simulated against a range of PGA both in SLOPE/W and FLAC3D. It is interesting to note the earthquake impact on various slope angles.

Seismic Ground Response Analysis of Some Typical Sites of Guwahati City

In this study, one dimensional equivalent–linear ground response analyses were performed for some typical sites in the Guwahati city, India. Six bore locations covering about 250 km2 area of the city were considered for the analyses. As the strong motion significantly influences the ground response, seven different recorded ground motions, varying in magnitude (6.1 to 8.1) and other ground motion parameters, were adopted. Seismic site analyses were carried out for all layers of borelogs using all the seven earthquakes. Results are presented in terms of surface acceleration histories, strain and shear stress ratio variation, response spectrum, Fourier amplitude ratio versus frequency. The results indicate that accelerations were amplified the most at the surface level. The range of peak ground acceleration (PGA) values obtained at the ground surface is about 0.2 g to 0.79 for a range of PGA considered at bedrock level (rigid half space at bottom of borelog) of 0.1 g to 0.34 g. The Fourier amplifications of ground motion at surface are in the range of 4.14 – 8.99 for a frequency band of 1.75 Hz to 3.13 Hz. The maximum spectral acceleration at six locations varies in the range of 1.0 g – 4.71 g for all the seven earthquakes. The study clearly demonstrated the role for site effect and the type of ground motion on the ground response. For a given earthquake motion, amplification factors at surface level change by almost about 20% to 70% depending on local site conditions.

Constraining regional paleo peak ground acceleration from back analysis of prehistoric landslides: Example from Sea of Galilee, Dead Sea transform

Accurate estimation of expected peak ground acceleration (PGA) in seismically active regions is a challenging task. The best way to estimate, quantitatively, expected PGA is by investigating instrumental data of past strong earthquakes in a given area. In some regions of the world however recorded data are scarce, and if they exist, they are typically available only since the late 19th century. As such they are hardly representative of the true seismicity in the studied region. We propose here an analytical approach to constrain the lower threshold of paleoseismic PGA on the basis of back analysis of old landslides. To perform the analysis we need a mapped landslide with geomorphic features that have been preserved in the field, the slip surface, a good reconstruction of the slope geometry and ground water level prior to failure, and the mechanical properties of the sheared material. We perform static and pseudo-static limit equilibrium analyses using standard solution procedures to obtain lower bounds of paleoseismic PGA. Back analyses of three different landslides around the Sea of Galilee (SOG) return similar results that range between 0.15 and 0.5 g, thus constraining the threshold paleoseismic PGA range for this region. The analytically inferred regional PGA is supported by results of an independent numerical analysis of toppled columns in a nearby Byzantine church. Using results from a recent paleoseismic trenching study performed on one of the studied landslides and a modified attenuation relationship for the study area we localize the loci of moment magnitude M w = 7.0 earthquakes that can explain the studied failures along the boundaries of the SOG, and find that they coincide with traces of the Eastern and Western Margin faults of the Dead Sea transform. The temporal relationships between the observed failures are discussed on the basis of dated colluvial sediments, geomorphologic constraints, and archeological evidence.