Strong Motion Duration Research Articles

Basin boundary seismic effects in Mexico City southern region

AbstractRapid changes in geotechnical and geological ground conditions lead to significant ground motion variability. This condition mainly occurs at the so-called basin edges, where there is an abrupt transition between soft highly compressible soils and stiffer materials. This problem becomes more relevant in areas where ground subsidence drastically changes the dynamic response of high plasticity clay deposits, such as those found in Mexico City, due to fundamental site period evolution with time. This paper presents site response analyses at an abrupt transition area in the southeast Mexico City region, along the edges of the Xochimilco-Chalco lakes. Considerable damage associated with three-dimensional wave propagation effects was observed in this zone during the September 2017 Puebla-Mexico earthquake. A series of three-dimensional finite difference numerical models of the basin edge were developed to evaluate ground motion variability, considering topographic effects and soil non-linearities. Good agreement between the computed response and the observed damage during the 2017 Puebla-Mexico earthquake reconnaissance was found. In addition, several normal and subduction events with a return period of 250 years were considered to evaluate the effect that frequency content, and strong ground motion duration have on the soil response variability. From the results gathered here, it was established the relevance of accounting for three-dimensional wave propagation fields to assess site effects at basin-edge zones properly and to be able to implement proper risk mitigation measurements at these zones.

Effect of site specific soil characteristics on the nonlinear ground response analysis and comparison of the results with equivalent linear analysis

Damages occurring during earthquakes may vary depending on the ground conditions in which the earthquake waves pass, the magnitude of the earthquake, the focal depth of the shaking and as well as the structural characteristics. Regional seismicity, ground movement and behavior of local soil conditions are important in earthquake-resistant building designs. Local site conditions consist of the layering, bedrock depth, and dynamic and topographic characteristics of soil that alter the bedrock waves through the soil profile during an earthquake. The change occurs in terms of amplitude, frequency and the time when the peak happens during the wave propagation. This initiates a big difference between the surface and bedrock motion. The behavior of the soil under cyclic loads resulting from seismic action is non-linear. This study aims to demonstrate the effects of strong ground motion by taking into account the nonlinear behavior of the soil layers. In addition, the results obtained from the equivalent linear and non-linear methods were compared. The results of the study showed that the characteristics of soil layers and strong ground motion (frequency content and duration) significantly affect the field response analysis and generally larger spectral parameters (about %20) have been obtained with the equivalent linear method compared to the nonlinear behavior. Finally, empirical models to estimate the soil amplification reflect different compared to the site specific analysis.

An ameliorative duration of pulse-like ground motion records for nonlinear structural analysis

The near-field pulse-like ground motion contains obvious long-period and large pulse characteristic, which makes the nonlinear response of the structure exceed the general prediction of seismic response results. In order to reserve the obvious pulse component while selecting the strong ground motion duration part of the near-field pulse-like ground motion record without causing a large loss of spectral characteristics, the paper proposes an ameliorative truncated strong ground motion duration—useful duration. It is proposed based on the elastic acceleration response spectrum. Its principle is to make the acceleration response spectrum corresponding to useful duration and that corresponding to the original ground motion record as close and consistent as possible. The research results show that from the perspective of elastic response spectrum matching, the response spectrum matching error corresponding to useful duration is smaller than that of significant duration. In addition, the five types of periods corresponding to useful duration are closer to the period of original ground motion. Ulteriorly, from the displacement ratio spectrum of the elasto-plastic single-degree-of-freedom system, it is found that the average value of the elasto-plastic displacement ratio spectrum of useful duration and the original ground motion record is 0.98, which is very close to 1.00. It shows that the truncated ground motion can be used to replace the original ground motion to fully predict the nonlinear response of typical structures. Additionally, the effectiveness is further verified in the nonlinear response of three reinforced concrete frame structures, and the nonlinear response results of the structures are calculated using the time-history of useful duration, with less discreteness.

Ideal-Pulse-Based Strong-Motion Duration for Multi-Pulse Near-Fault Records

ABSTRACT Serious damage to near-fault structures is caused mainly by velocity pulses in a ground motion, hence, the necessity to develop a pulse-related definition of strong-motion duration to adequately describe the intensity of near-fault ground motion. For a multipulse record, an ideal-pulse-based strong-motion duration, which is defined as the time interval between the beginning of the first pulse and the end of the last pulse in an ideal-pulse signal, is proposed. This strong-motion duration corresponds with the time interval of the occurrence of strong vibrations and energy accumulations in the original record. For near-fault records, pulselike characteristics can be completely presented within this duration. Meanwhile, the ideal-pulse-based strong-motion duration shows good performance in the estimation of structural responses. The elastic and inelastic displacement spectra of the original records agree well with those of the records shortened according to the proposed duration. The validity of applying the proposed duration to structural analysis is further verified by the nonlinear time history analyses of 3-, 9-, and 20-story steel moment-resisting frame structures. The proposed strong-motion duration accurately estimates nonlinear structural responses. It is proven that the ideal-pulse-based strong-motion duration can adequately describe the intensity of near-fault ground motions, both from the perspective of the energy accumulation process in a ground-motion record and that of the structural analyses subjected to these ground motions.

Energy‐compatible modulating functions for the stochastic generation of fully non‐stationary artificial accelerograms and their effects on seismic site response analysis

AbstractThe reliability of non‐linear dynamic analysis aimed to predict the seismic performance of structural and geotechnical systems, as well as their dynamic interaction, is significantly affected by the selection of suitable input motions. Several procedures for selecting actual earthquake records compatible with the seismic hazard at the site of interest and for evaluating synthetic accelerograms consistent with a seismological framework are available in the literature. However, the degree of uncertainty affecting these approaches might lead to unreliable performance predictions especially for strongly non‐linear problems, such as those involving the response of soils to cyclic and dynamic loading. In this vein, the paper presents a procedure for generating fully non‐stationary ground motions ensuring energy compatibility with a target motion. Two different approaches have been introduced: i) the time window method based on the central finite difference approach and ii) the simplified intensity‐compatible approach in which a closed form expression is provided to evaluate a modulating function that depends on the Arias intensity and on the strong motion duration of a target motion. To highlight the reliability and the accuracy of the proposed procedure, several sets of spectrum‐compatible artificial accelerograms, generated starting from a rock outcropping motion, were used as input motions in a series of one‐dimensional site response analyses. The analysis results are presented and discussed in the paper highlighting the influence of the main features of the proposed generation procedure on the variability of the computed site response.

Evaluation of random-vibration procedures to estimate response spectral ordinates on soft soil sites from fourier amplitude spectra

This study evaluates Random-Vibration Procedures (RVP) to estimate 5% damped response spectra of ground motions recorded on soft soil sites from Fourier Amplitude Spectra (FAS). The study makes use of 136 ground motions recorded in the soft soil Mexico City region during two recent large magnitude earthquakes. Seven different RVP are considered in this investigation consisting of four peak factor models, three strong ground motion duration models, and four non-stationary empirical correction factors. Spectral ordinates computed through conventional time integration were compared to approximate spectral ordinates computed using the FAS of the recorded acceleration time series in combination with RVP. A statistical error analysis was then conducted to determine how effective the various RVP were at estimating the exact pseudo-acceleration response spectra computed with response history analyses. It is found that most RVP commonly used today produce significant systematic overestimations of spectral ordinates at the fundamental mode of the soil deposit. Modifications to durations are proposed to be used in conjunction with various peak factors to reduce overestimations at the site period.

A statistical study of inelastic displacement ratio spectrum for existing structures

AbstractDisplacement‐based design has gained importance due to the emergence of the performance‐based engineering, and it has now become desirable to estimate maximum (inelastic) displacements of structures for different levels of seismic hazard. Being closely related to damage, displacement (or drift) has become an important parameter necessary to meet various performance goals. It is considered convenient to estimate the inelastic displacement demand in a structure by multiplying the elastic displacement demand of the structure with a ratio called the inelastic displacement ratio. A comprehensive study is conducted for the parametric dependence of the inelastic displacement ratio in single‐degree‐of‐freedom (SDOF) systems with known relative lateral strengths, on strong motion duration, earthquake magnitude, epicentral distance, and geological site conditions. This study is different from the earlier studies of similar types in that other governing parameters are kept fixed while the effects of variations in any particular parameter are studied. This study is based on the generation of ensembles of synthetic accelerograms from a database of 1274 accelerograms recorded in western USA for the pseudospectral acceleration (PSA) spectra of given source and site parameters. It is found that strong motion duration may influence the inelastic displacement ratios, depending on the hysteretic properties of the oscillator, in the case of durations not much longer than 10 s. Earthquake magnitude has a significant influence on these ratios for the SDOF systems of most periods, while site geology appears to be important for the stiff oscillators. A scaling model is also proposed in this study for estimating the inelastic displacement ratio spectrum from a normalized relative velocity spectrum of the ground motion. The proposed model indirectly includes the effects of various governing parameters and is shown to preserve the trends available from the direct study.

A novel strong ground motion duration to reduce computation time of structural time history analysis

As a widely used dynamic computation method for seismic response analysis of structures, time history analysis (THA) can be a time-consuming procedure in some situations. In order to reduce the calculation time, this study proposed a novel strong ground motion duration which can truncate the head and tail weak signals of records before THA. The initial point of proposed duration refers to the concept of bracketed duration, while the termination point is determined by the maximum displacement responses of equivalent single-degree-of-freedom (SDOF) systems of the structure. The relationship between the fundamental period and period-lengthening level of structure is counted from previous research and fitted with a formula which is used to compute the period range of equivalent SDOF systems. After comparing the structural responses and time-saved percentage of truncated records by proposed duration with those by other definition of durations, results prove that the proposed duration has significant time-saving procedure and reliable computation results on THA.

Tunnel-soil-bridge seismic interaction on soft clay

Seismic tunnel-soil-bridge interaction in high plasticity soft clays can lead to significant ground motion variability, affecting on-ground structures located next to or above underground facilities. This technical note presents a numerical study aiming at establishing tunnel-bridge seismic interaction effects on soft clays. Initially, we revised this interaction considering the impact that frequency content, intensity, and strong ground motion duration have on the interplay between incoming seismic waves reflected in the tunnel and the energy feeding back from the bridge swinging back and forth during a large earthquake. Series of three-dimensional finite difference models were developed. Seismic analyses considered both normal and subduction events with a return period of 250 years. From the results gathered in these analyses, the ground motion modification in the surrounding soil occurs in both the transverse and longitudinal components due to tunnel-bridge interaction. The tunnel underneath the bridge establishes detrimental soil-structure interaction effects for normal and subduction events.

Effect of Multi-Components Strong Motion Duration on Seismic Performance of High CFRDs Based on Fragility Analysis

ABSTRACT This paper investigates the influence of multi-components strong motion duration on seismic performance of high concrete-faced rockfill dams (CFRDs) by fragility analysis based on the method of incremental dynamic analysis (IDA). The contributions of all compositions of earthquake excitations are considered by the definition of integrated duration based on the concept of significant duration. The nonlinear finite element model of a 2D 200-m-high CFRD is established as a case study and the vertical and horizontal displacements are selected as damage measures. Fragility curves and probabilities of two sets of 23 and 25 spectrally equivalent as-recorded bi-directional long-duration and short-duration motions are determined under different failure grades and intensities. The results show that the duration of vertical component has a certain effect on correction between strong motion duration and deformation of the dam and fragility analysis indicates that the ground motions with long duration can make more risk of failure of high CFRDs than short duration motions. Therefore, the seismic performance of high CFRDs will be reformed by taking the effect of ground motion duration into seismic design and risk assessment consideration.

Influence of site-specific strong-motion duration on structural performance

Influence of site-specific strong-motion duration on structural performance

Combining Discrete Wavelet Transform and Strong Ground Motion Duration to Reduce Computational Costs in Dynamic Analysis of Structures

The dynamic time history analysis is the most accurate method for calculating the structure response relative to the vibrating load. The use of this method is time-consuming due to the long-duration earthquakes and is generally less commonly used. Wavelet trans-forms are one of the new methods for filtering waves. The duration of a strong ground motion is actually a concept that can be used to turn an earthquake with a long time into an earthquake with a shorter time. In this paper, two concepts of filtration using wavelet transform and the use of a duration of strong ground motion are used for the time history analysis of structures. For this purpose, the acceleration of the earthquake in 5 states was filtered by wavelet transform. In each stage, the high and low frequencies are separated, and the number of earthquake acceleration points is half-past. Then the beginning and the end of the main earthquake and the approximate waves obtained from the wavelet transform are removed using the concept of the duration of the strong ground motion. Finally, two two-dimensional and three-dimensional structures are analyzed using the main earthquake and the waves obtained by combining the two concepts of wavelet transform and the duration of strong ground motion. The results show that by reducing the number of acceleration points of the main earthquake record to more than 95%, the dynamic response error is less than 8%.

Use of Artificial Neural Networks to predict strong ground motion duration of interplate and inslab mexican Earthquakes for soft and firm soils

Artificial neural network models are developed to predict strong ground motion duration of sub- duction events for soft and firm soils. To train the artificial neural network a database with a total of 3153 seismic records with two horizontal components for interplate and inslab earthquakes is employed. The principal component method is used to carry out a dimensionality reduction of the input parameters to develop the artificial neural network models. The predicted values of the strong ground motion duration trained by the artificial neural network models are compared with those estimated with empirical expressions. In general, the strong ground motion duration predicted with the artificial neural networks follows the same tendency of that calculated with the empirical equa- tions, although in some cases, the strong ground motion duration predicted by using the artificial neural network models presents sudden changes in its behavior. For this reason, it is recommended to carry out several verifications of the trained artificial neural network models before using them for further engineering applications, for example the simulation of synthetic records or the evaluation of seismic damage indices.

A SEISMIC ANALYSIS OF SEGMENTAL TUNNEL LINING USING ARTIFICIAL ACCELERATION

This paper aims to generate a set of artificial accelerations by using PG02 program, based on Yamamoto’s regression equations and response spectrum of Vietnamese National Standard TCVN 9386-2012 condition. Taking the obtained ground motion as input data to calculate the tunnel structure of the project Metro line No.3 (Nhon - Hanoi Railway Station) by program Plaxis2D. The connections among the tunnel segments are replaced by semi-rigid joint under Jassen's assumption. The results show that the peak ground acceleration value can be considered as one of the important factors affecting on the internal force of tunnel besides a number of other acceleration factors (peak ground velocity, root mean square acceleration, intesity of Arias, time duration of strong motion).

Strong Motion Models for Duration and Arias Intensity for Strong Motion Records in Chile

Chile presents a high seismicity and very particular characteristics due to its subductive environment and high convergence rate of the interacting plates. In this paper, ground motion models (GMM) for Arias Intensity and strong ground motion duration are developed based on recently compiled Chilean earthquakes records. The Chilean derived GMM are later compared with global and subduction models. For the duration case, two definitions are considered: significant duration and bracketed duration. Care is taken to consider newly define rupture areas for the major earthquake in the catalog, which allows to redefine the distances to be used in the analysis. The strong motion records are processed using robust techniques and standardized procedures. The model parameters are selected using a Bayesian updating method. This allows to estimate the parameters as well as their corresponding uncertainties recognizing the variability of the coefficients and of the selected model. The derived ground motion predictive model associated is validated through a residual analysis and probability distributions, obtained from the adjustment method. Additionally, for the bracketed duration analysis, a classification method based on Support Vector Machine (SVM) is used, with the aim to incorporate the records with duration of zero seconds. The comparison of the resultant model with the existing ones allows to confirm the differences that the tectonic Chilean environment produces, characterized mainly by a high relative convergence rate between plates and interplate thrust earthquakes with high magnitudes.

Records of Local Earthquakes as a Basis for the Correct Estimation of Strong Ground Motion (the Area of the Second Severomuisk Tunnel)

Abstract ––To obtain realistic and correct estimates of strong ground motion in the area of construction of the second Severomuisk tunnel, the records of local earthquakes obtained by the Severomuisk seismic station (SVKR) in 2005–2010 are studied (magnitudes Mb of ~4.2–5.5, hypocentral distances r of ~15–220 km). Stochastic-simulation methods are used to estimate the regional parameters of radiation and propagation of seismic waves in northeastern Buryatia: the stress parameter Δσ, shapes of source spectra, wave attenuation at high frequencies (k), parameters defining the shape and duration of the acceleration time history, etc. Beforehand, the duration of strong motion as a function of the hypocentral distance was evaluated from the records; the local site amplification A(f) was estimated based on the velocity structure of the region; and the envelope method was applied to estimate the quality function Q(f). The following data were obtained: Δσ ≈ 100 bars; k ≈ 0.012 s; Q(f) as ~60 f1.05 for r of ~15–30 km, ~80 f1.0 for r of ~40–60 km, ~90 f0.9 for r of ~100–110 km, and ~150 f0.7 for r of ~160–220 km; geometris spreading as 1/r for r <50 km, 1/50 for 50 < r <150 km, and 1/r0.5 for r >150 km; and duration as 0 for 0 < r < 5 km, 0.222r for 5 < r < 50 km, and 10 + 0.015r for r > 50 km. These estimates can be used to predict ground motion parameters during future strong earthquakes in the region.

The role of site effects on elevated seismic demands and corollary structural damage during the October 30, 2020, M7.0 Samos Island (Aegean Sea) Earthquake

On October 30, 2020 14:51 (UTC), a moment magnitude (M) 7.0 (USGS, EMSC) earthquake occurred in the Aegean Sea. This paper presents the reconnaissance findings regarding the site effects on recorded strong ground motion intensities and duration, along with the resulting induced-structural damage in Izmir Bay and Samos Island, respectively. In all rock records, relatively high intensity long period rock spectral accelerations were observed in the mid to long period range of 0.5–1.5 s, which are attributed to the source, more specifically, to the slower rupture-mechanism of the event. These rich spectral intensities were further amplified by soil site effects and soil-superstructure resonance, leading to two to six times amplified overall responses and prolonged seismic shaking durations, more pronounced in Bayrakli and other Izmir Bay sites in Turkey. However, these amplified and prolonged excitations are still below design basis earthquake levels, which addresses the lack of proper structural design and construction deficiencies, as the underlying causes for the collapse to heavy damage performance of 795 buildings. On the other hand, although located only about 10 km from the rupture (22 km from the epicenter) and within the near fault zone, the town of Vathy on Samos Island (Greece) was rather lightly affected by the earthquake, with relatively few collapsed or heavily damaged buildings, partially attributed to the low height/low weight of structures in the area. However, a concentration of damage in low-rise buildings in Ano Vathy hill is considered indicative of a combination of coupled valley and topography effects on the strong motion. This event once again addressed the need to develop region-specific zonation and provisions, when more general code practices are proven to be inadequate to assess these extreme site effects.

Effect of intensity measures on the response of a 3D-structure under different ground motion duration

In seismic performance assessment of structures, the features of ground motion (GM) duration on the response of building structures remain vague and have inconclusive results. Also, intensity measures (IMs) link the ground motion hazard with the structural response; hence, using a suitable IM plays a significant role in the prediction of structural response. In this research, the effect of strong ground motion duration and the correlation coefficient of different intensity measures on the residual inter-story drift (RIDR) of a three-dimensional steel structure were investigated. Using nonlinear dynamic analyses and a total number of 34 earthquake records, the relationship between short- and long-duration seismic parameters including amplitude, energy, and frequency content parameters were investigated. The correlation between the 14 selected scalar intensity measures and the RIDR of the structure was also investigated. The results showed the highest correlation between the seismic parameters, such as Peak ground acceleration (PGA), Housner Intensity (HI), and Velocity spectrum intensity (VSI), with other seismic parameters in both short- and long-duration strong ground motions. Based on the maximum residual inter-story drift index, Mehanny and Cordova index (IMC), Bojórquez and Iervolino index (INP), and the geometric mean of Sa (Saave) intensity measures represented the least dispersion versus long-duration records. On the other hand, INP, Spectra acceleration at the period of T1 Sa(T1), and Saave intensity measures showed the least dispersion versus short-duration records.

A probabilistic strong floor motion duration model for seismic performance assessment of non‐structural building elements

AbstractNon‐structural elements (NSEs) are not designed to be part of the structural load‐bearing system of a building but are subjected to the same dynamic environment as the supporting structure during an earthquake. Non‐structural damage and ensuing losses have exceeded structural damage and losses in many buildings during recent earthquakes that have occurred in urban regions around the world. Damage to NSEs is strongly influenced by the amplitude, the frequency content and the duration of floor motions. Although the effects of amplitude and frequency content of floor motions are well captured by floor response spectra, little attention has been given on the characterisation of floor motion duration and how it can impact damage to NSEs, particularly for those responding in the inelastic range. To contribute to a better understanding of these issues, this paper develops a probabilistic strong floor motion duration model through multiple stripes non‐linear time‐history analyses of a population of 100 code‐compliant reinforced concrete frame building models designed for a medium‐to‐high seismicity site in Italy. The resulting probabilistic model can be used when selecting historical or generating synthetic floor motions for the seismic response assessment of NSEs or when generating shake‐table test records for the seismic qualification of NSEs.

Foundation enhancement for reducing tunnel-building seismic interaction on soft clay

Seismic tunnel-soil-building interaction in high plasticity soft clays can led to important ground motion variability that affect medium to low rise buildings located adjacent to the underground structure. This paper presents a numerical study aiming at establishing the performance of an enhanced foundation system to be used as a mean to reduce detrimental interaction and enhanced the seismic performance of mid to low buildings located nearby tunnels. Initially, interaction effects are revised considering the effect that frequency content, intensity, and strong ground motion duration have on the interplay between incoming seismic waves reflected in the tunnel, and the energy feeding back from the building swinging back and forth during a large earthquake. Series of three-dimensional finite difference models were developed. Seismic analyses considered both normal and subduction events with a return period of 250 years were carried out. Finally, the seismic performance of the enhanced foundation system was established. From the results gathered in here, it was clearly established the effectiveness of the proposed system to reduce both foundation ground motions and building seismic demand.