Earthquake Engineering Applications Research Articles

Editorial: Artificial Intelligence-Powered Methodologies and Applications in Earthquake and Structural Engineering

Editorial: Artificial Intelligence-Powered Methodologies and Applications in Earthquake and Structural Engineering

Bandgaps for flexural waves in infinite beams and plates with a periodic array of resonators

ABSTRACT The subject of seismic metamaterials, inspired from novel ideas in optics and acoustics, has attracted great attention in the last decade for potential applications in earthquake engineering. Simple structure systems, like beams and plates, with periodically attached mechanical resonators provide a simple physical model to interpret the existence of certain frequency bandgap in dispersion relations and to simulate the mechanism of flexural energy attenuation. In this work, we consider simple structure systems of beams and plates with periodically attached resonators. The resonator is composed of a spring, a damper and a mass attached along the beam direction. We utilize the Timoshenko beam model and the Mindlin plate theory to incorporate the shear effect. The plane wave expansion method together with the Bloch theorem is used to expand the governing field into an eigenvalue problem of an infinite complex system, allowing us to characterize the band structures of the dispersion relations. Local resonance and Bragg bandgaps are identified and examined. The effect of thickness ratios, the damping ratio and the shear modulus are exemplified to demonstrate how these factors will affect the formation of bandgaps. This formulation demonstrates a feasibility that a periodic array of mechanical resonators together with suitable material and geometric parameters of beams and plates can be designed to tune with the dispersion behavior in the control of flexure waves. This study may open up new potential in the control of wave propagation in complex continuum systems through the interaction of adequately designed resonators.

Fiber optic jerk sensor.

Jerk is directly related to a physical mutation process of structural damage and human comfort. A fiber optic jerk sensor (FOJS) based on a fiber optic differentiating Mach-Zehnder interferometer is proposed. It can directly measure jerk by demodulating the phase of interference light, which avoids the high-frequency noise interference caused by differentiating the acceleration. The sensing theory and sensor design are given in detail. The experimental and theoretical results agree, demonstrating that the FOJS has a high sensitivity, an ultralow phase noise floor, a wide measuring range, and good linearity. The impact test shows that the FOJS can directly measure jerk and has good consistency with a standard piezoelectric accelerometer. The FOJS has potential applications in earthquake engineering, comfort evaluations, and railway design. This is the first time that directly measuring jerk with an optical sensor is reported.

Multi-source geographically weighted regression for regionalized ground-motion models

This work proposes a novel approach to the calibration of regionalized regression models, with particular reference to ground-motion models (GMMs), which are key for probabilistic seismic hazard analysis and earthquake engineering applications. A novel methodology, named multi-source geographically-weighted regression (MS-GWR), is developed, allowing one to (i) estimate regionalized regression models depending on multiple sources of non-stationarity (such as site- and event-dependent non-stationarities in GMMs), and (ii) make inference on the significance and stationarity of the regression coefficients. Unlike previous approaches to the problem, the proposed framework is non-parametric – in the sense of the distribution of the errors – the inference being based on a permutation scheme. MS-GWR is here used to calibrate a new regionalized ground-motion model for predicting peak ground acceleration in Italy, based on a large scale database of waveforms and metadata made available by the Italian Institute for Geophysics and Vulcanology (INGV).

Parametric influence of magneto elasticity, initial stresses, porosity and thickness ratio on the phase and attenuation traits of SH-waves

The present study is devoted to investigate the traversal of shear horizontal wave (SH-waves) in an initial-stressed fluid saturated porous stratum bounded between an initial-stressed magneto-elastic upper stratum and an initial-stressed elastic substrate. We have obtained the exact solution of the governing equations and explained in detail for various effective parameters. The displacement relation is developed with the help of Maxwell’s fundamental equations and Maxwell’s tensor. The impact of diverse parameters such as initial stress, porosity, magneto-elasticity, thickness ratio of attenuation coefficient and phase velocity of SH-wave has been discussed extensively by means of graphical depictions. Results indicate that such parameters possess a great positive impact on attenuation coefficient. This model contains a huge potential to deal with many commercial and industrial applications in Geo-technical, earthquake engineering and Geophysics.

Phenomenological hysteretic model for superelastic NiTi shape memory alloys accounting for functional degradation

AbstractThis study presents a simple hysteretic model to reproduce the stress–strain relationship of superelastic NiTi shape memory alloys (SMAs). The proposed model explicitly includes the functional degradation of SMAs, which has been ignored in earthquake engineering applications. This effect causes a reduction in the transformation stress and accumulation of residual strain. Because SMA devices are mainly used for seismic retrofit and account for a small portion of the structural system, their numerical model should not increase the computational time needed to perform nonlinear dynamic analyses. Computational efficiency can be achieved by representing their stress–strain response in a phenomenological way. Additionally, practitioners who may not have a professional background in materials science can easily manipulate the proposed model for the appropriate reproduction of model parameters such as transformation stress and residual strain. The ability to properly reproduce the experimental stress–strain response is validated for the test results of 65 NiTi SMA specimens. The amount of forward and reverse transformation stress degradation and the amount of residual strain accumulation per cycle, which are observed in the experimental results, are captured with reasonable accuracy in the proposed model. Additionally, the response of SMA braces in a four‐story steel moment frame is modeled using the proposed model to examine the residual story drift of the SMA braced frame under a set of ground motions. At higher intensity levels, the functional degradation of SMA braces increased the residual story drift up to 60% in comparison to the SMA‐braced model without functional degradation.

Determination of the Mechanical Properties of Shape Memory Alloys

Shape memory alloys are materials which can be deformed by cooling below a certain critical temperature and then regain their original shape after heating above this critical transition temperature.. Shape memory alloys (SMAs) are a class of functional materials that possess unique thermo mechanical properties, such as shape memory effect (SME), super elasticity (SE), damping, and good fatigue and corrosion resistance, which enable them to become ideal materials for applications in earthquake engineering. Numerous studies have shown that the mechanical properties of Superelastic SMAs mainly depend on the wire form or the relationship between the microstructure and thermally induced phase transitions. However, extremely few studies have elucidated the effects of the heat-treatment strategy, size effect of large diameters, and cyclic loading. Here in, the mechanical properties of SMA bars, such as residual strain, energy dissipation, and equivalent damping ratio, were studied with different heat-treatment strategies, cyclic loadings, and strain amplitudes; this was achieved by conducting cyclic tensile tests on SMA bars with four different diameters. In this research work, two types of methods i.e. tensile testing and cantilever deflection method is used to determine the mechanical properties of NiTi alloy. In the first part of the experiment, mechanical properties of two NiTi samples of different composition are determined by tensile test. Both of the wire-shaped samples have the same diameter of 300µm but differ in the transformation temperature Cantilever deflection method (CDM) is used to characterize the shape memory alloy film deposited on the Mo substrate. The sample is placed on the holder which lies close to the thermoelement.

Conditioned Simulation of Ground-Motion Time Series at Uninstrumented Sites Using Gaussian Process Regression

ABSTRACTGround-motion time series are essential input data in seismic analysis and performance assessment of the built environment. Because instruments to record free-field ground motions are generally sparse, methods are needed to estimate motions at locations with no available ground-motion recording instrumentation. In this study, given a set of observed motions, ground-motion time series at target sites are constructed using a Gaussian process regression (GPR) approach, which treats the real and imaginary parts of the Fourier spectrum as random Gaussian variables. Model training, verification, and applicability studies are carried out using the physics-based simulated ground motions of the 1906 Mw 7.9 San Francisco earthquake and Mw 7.0 Hayward fault scenario earthquake in northern California. The method’s performance is further evaluated using the 2019 Mw 7.1 Ridgecrest earthquake ground motions recorded by the Community Seismic Network stations located in southern California. These evaluations indicate that the trained GPR model is able to adequately estimate the ground-motion time series for frequency ranges that are pertinent for most earthquake engineering applications. The trained GPR model exhibits proper performance in predicting the long-period content of the ground motions as well as directivity pulses.

An assessment of the 3 February 2002 Cay (Turkey) earthquake (Mw=6.6): Modeling of ground motions and felt intensity distribution

Estimation of earthquake ground motions is important for several purposes including seismic design, analysis, risk mitigation and disaster management. For regions with insufficient data, simulations become critical, particularly for earthquake engineering applications requiring full ground motion data. In this study, stochastic finite-fault simulation of the 3 February 2002 Cay event is presented at three available stations within epicentral distances less than 200 km. The simulations are initially validated at these stations. Next, simulations of the earthquake at dummy nodes are performed in Afyon region. The simulated ground motion records for the Cay event are evaluated by comparing them against selected ground motion prediction equations. Then, the distributions of the observed intensity and damage are compared against the distribution of simulated intensities. The results reveal that the earthquake is simulated effectively.

Efficient selection of up to three-component ground excitation sets for earthquake engineering applications

Ground motion record selection methodologies are commonly developed to ensure that the input excitation used in response history analyses embodies essential conditions such as spectral compatibility, hazard and intensity measure consistency, seismological and site-specific criteria, always performing in a computationally efficient manner. A methodology utilizing genetic algorithms is revisited here, expanded to select multi-component ground motions and satisfying the typically required selection objectives of earthquake engineering applications, while ensuring increased efficiency. Multi-objective optimization is performed, claimed to be superior in delivering robust results that account for spectral compatibility in first and second order statistics (mean and standard deviation) in a wide range of spectral values, as well as satisfying seismological and site-specific criteria. A unique contribution is the ability to include probability distribution targets in specific ordinates of the spectrum, on top of the mean and standard deviation, allowing for more refined ground motion sets that can be used to reduce the number of records required in response history analyses. Additionally, a novel benchmarking process to assess the efficiency of ground motion record methodologies is introduced here, in terms of providing sets that are globally-optimal solutions to the optimization problem. Through this benchmarking algorithm, the proposed methodology appears to be impeccable in extracting the best possible ground motion sets.

Student Zone

A student training program, Engineering Seismology and Seismic Microzonation for Seismic Site Effects Assessment, was held 18–22 January 2020 in Lalitpur, Nepal. It was created through the collaboration of Thammasat University and Tribhuvan University, with support from Geoscientists Without Borders® (GWB). The goal of the program was to connect students with modern geophysical instrumentation and software through training. It specifically advanced theoretical and hands-on field-based knowledge pertaining to geotechnical earthquake engineering aspects and applications. The training served as part of a broader GWB project, Seismic Site Effects Study in Nepal, encompassing basin geometry, site characteristics, and the study of seismic site effects through microtremor measurements in Kathmandu Valley.

Seismic response of monopiles to vertical excitation in offshore engineering

This paper studies the dynamic response of a large diameter and thin-walled monopile, embedded in a partially saturated porous seabed with saturation degrees larger than 95%, under a seawater layer, subjected to vertically incident P wave excitations. The ground is a semi-infinite homogenous half-space with a horizontal surface. The solution of the coupled water-pile-soil vibration problem is constructed using a rigorous semi-analytical method. By considering the coupled boundary conditions at the pile-soil and water-soil interfaces, the earthquake induced response is reduced to integral equations and solved numerically. Results for the free field soil displacement and kinematic interaction factor are obtained, which are different from the results reported in the literature for onshore earthquake engineering applications as these do not have the effects of the water layer and the vibration induced dynamic water pressures. The existence of a water layer will always decrease the vertical response of the seabed, but may amplify the monopile's displacement near some resonant frequencies, compared to the case of no water. These results are useful in understanding the kinematic interaction of soil and monopile in offshore engineering applications.

Bayesian calibration of hysteretic reduced order structural models for earthquake engineering applications

Seismic risk assessment entails frequently a large number of nonlinear time-history analyses. The use of high-fidelity Finite Element Models (FEMs) in this context, though supports high accuracy predictions, involves a substantial computational burden. This has incentivized researchers to explore the use of calibrated Reduced Order Models (ROMs) to replace the computational expensive FEMs, with the calibration process established so that the ROM can match the desired FEM characteristics. Recent studies have explicitly examined this calibration for hysteretic, multi-degree-of-freedom ROMs utilizing FEM time-history response data. This calibration has been posed as a least-squares optimization problem for the configurable ROM parameters, considering the discrepancy between the ROM and FEM responses for a selected number of excitations, for different output quantities of interest (QoIs). This work extends these efforts to examine a Bayesian calibration framework of ROMs for earthquake engineering applications. The entire posterior distribution of the ROM parameters is identified, instead of solely the point estimate that the current least-squares optimization provides. This facilitates a quantification of the uncertainty in the calibrated ROM parameters. For formulating the likelihood function different assumptions are discussed, impacting, ultimately, how the different earthquake excitations and QoIs are effectively combined. Comparisons to the objective function utilized in the established least-squares approach are drawn. Furthermore, a model class selection is advocated to compare different candidate ROMs in order to choose the most appropriate one given the available data. Finally, a hierarchical Bayesian inference approach is examined, treating independently the ROM calibration for each earthquake excitation, but unifying the ROM parameters under a common prior, updated using data from all excitations. Different challenges are discussed for implementing such a multilevel Bayesian framework for the current application. The illustrative implementation considers two different structures, corresponding to different materials and heights, with the FEMs developed in OpenSees. The different calibration approaches are evaluated by utilizing the calibrated ROMs for seismic risk assessment for different seismicity scenarios.

Investigation of Mechanical Properties of Large Shape Memory Alloy Bars under Different Heat Treatments.

Shape memory alloys (SMAs) are a class of functional materials that possess unique thermomechanical properties, such as shape memory effect (SME), superelasticity (SE), damping, and good fatigue and corrosion resistance, which enable them to become ideal materials for applications in earthquake engineering. Numerous studies have shown that the mechanical properties of superelastic SMAs mainly depend on the wire form, or the relationship between the microstructure and thermally induced phase transitions. However, extremely few studies have elucidated the effects of the heat-treatment strategy, size effect of large diameters, and cyclic loading. Herein, the mechanical properties of SMA bars, such as residual strain, energy dissipation, and equivalent damping ratio, were studied with different heat-treatment strategies, cyclic loadings, and strain amplitudes; this was achieved by conducting cyclic tensile tests on SMA bars with four different diameters. The results indicate that the maximum phase transformation stress was obtained with a 14 mm SMA bar subjected to heat treatment at 400 ℃ for 15 min. The mechanical properties were relatively stable after five loading–unloading cycles, which should be considered in engineering applications. The test results provide a mechanical basis for using large SMA bars in self-centering structures in seismic regions.

Influence of spectral acceleration correlation models on conditional mean spectra and probabilistic seismic hazard analysis

SummaryInnovative engineering applications are proposed to satisfy the current necessities of earthquake engineering, which are well established from a conceptual perspective, and frequently, the development of some missing inputs is only required to employ them, such as the case of the correlations between spectral values at different vibration periods. Accordingly, we computed the correlation between spectral accelerations at two vibration periods using ground motions from interplate and, alternatively, intraslab events, recorded in firm ground of Mexico City. Results show that the spreading of correlation values depends on the rupture mechanism. Then, based on hypothesis test analyses, we used four correlation models available in the literature to predict our correlation values. According to the findings, we proposed a predictive correlation mathematical model for interplate and, separately, for intraslab seismic events. We evaluated the influence of the predictive correlation models on the results corresponding to two earthquake engineering applications. The first refers to compute conditional mean spectra and the second to perform probabilistic seismic hazard analysis (PSHA) using INp and, alternatively, Saavg, intensity measures. We found that while the conditional mean spectra might be affected in the region of short vibration periods, the computations of the PSHA with improved intensity measures are not affected significantly.

Analysis of the performance of strut models to simulate the seismic behaviour of masonry infills in partially infilled RC frames

The proposed study analyses the performance of existing approaches to model the behaviour of partially infilled reinforced concrete (RC) frames for computationally-intense performance-based earthquake engineering applications. The study addresses the use of reduction factors that are applied to the strength and the stiffness of a fully infilled masonry wall to account for the effect of an opening and also the application of a macro-model calibration procedure proposed in previous research to the case of partial infills. Several empirical expressions defining reduction factors are analysed and their performance is compared using real experimental data for different masonry infill typologies. Additionally, new reduction factors exhibiting a better performance are also proposed. Despite the reasonable performance of approaches based on reduction factors, their limitations are discussed and the performance of an alternative macro-model calibration procedure is also analysed. The behaviour of several partially infilled RC frames is simulated using both approaches and the results are compared with the corresponding experimental data. Even though the new reduction factors that are proposed exhibit a reasonable performance, the alternative macro-model calibration procedure showed a more consistent performance and a better agreement with experimental data to simulate the effect of openings in masonry infills.

Experimental testing and analytical modeling of CFS shear walls filled with LPM

Cold-formed steel (CFS) shear walls filled with lightweight polymer material (LPM) is an efficient structural system which can provide high lateral stiffness and strength to resist lateral loads. Despite the significant advantages, the nonlinear behavior of the CFS shear wall filled with LPM is not fully understood. In this study, a total of seven full-scale CFS shear walls filled with LPM were tested under cyclic loads. The test parameters included different LPM types, X-shaped bracing configurations, sheathing types and wall openings. The failure modes hysteresis curves, envelope curves, feature values, ductility ratio, stiffness and energy dissipation of CFS shear wall with and without filling LPM were systematically compared. The experimental data reveled that this type of shear wall showed higher load carrying and energy dissipation capacities than CFS framing wall without LPM. To assist with the design of CFS shear walls filled with LPM, a modified strut-and-tie model was proposed. The modified strut-and-tie model was validated using the experimental data. The result demonstrates that the proposed model can be utilized to accurately estimate the load carrying capacity of CFS shear walls filled with LPM. The presented experimental and analytical results can be used by engineers to design CFS shear walls filled with LPM for earthquake engineering applications.

Vine Copula-Based Dependence Modeling of Multivariate Ground-Motion Intensity Measures and the Impact on Probabilistic Seismic Slope Displacement Hazard Analysis

ABSTRACT Multivariate normality of logarithmic intensity measures (IMs) is conventionally assumed in earthquake engineering applications. This article introduces a vine copula approach as a useful tool for multivariate modeling of IMs. This approach provides a flexible way to decompose a joint distribution into individual marginal distributions and multiple dependences characterized by a cascade of bivariate copulas (pair-copulas), whereas the conventional multivariate normality can be considered as a special case of the vine copula model. Based on the Next Generation Attenuation-West1 database and various combinations of ground-motion prediction equations (GMPEs), the optimal dependence structures among peak ground acceleration, peak ground velocity, and Arias intensity, as well as that for spectral accelerations at four periods, are identified. The joint normality assumption for the two vector sets of logarithmic IMs is examined from the perspective of copula theory. The results illustrate that the normality assumption is generally adequate for bivariate IMs but may not be optimal for multivariate IMs. Using the same set of GMPEs (developed by the same researchers) may improve the joint normality for logarithmic IMs. Furthermore, the impact of dependence structures among IMs on probabilistic seismic slope displacement hazard analysis is explored. The results indicate that using the same Pearson correlation coefficients but different dependence structures for IMs produces different hazard results and this difference is generally enlarged with increasing hazard levels. As hazard difference from different dependence structures is generally not significant, the multivariate normality distribution for logarithmic IMs is judged to be an acceptable assumption in engineering practice. Alternatively, engineers may make a choice between the joint normal distribution and the vine copula tool depending on the specific situation because of the better generality of the latter.

Análisis probabilístico de peligro sísmico y terremoto de diseño para Santiago-República Dominicana

Este artículo presenta los resultados de un Análisis Probabilístico de Peligro Sísmico (APPS) realizado para un sitio ubicado en el centro de la ciudad de Santiago, localizada en la República Dominicana. Para realizar el APPS se utilizaron datos sismológicos recientes de la falla Septentrional (fuente sísmica) con el fin de calibrar un modelo de recurrencia de terremotos, y para calcular las curvas de peligro sísmico de varios parámetros de terremotos, movimiento del suelo y respuesta estructural de interés en aplicaciones de ingeniería sísmica. Los parámetros estudiados incluyen aceleración horizontal pico del suelo y ordenadas del espectro de respuesta de pseudo-aceleración con 5 % de amortiguamiento. El efecto de la incertidumbre de la ubicación de la zona de ruptura en la falla es estudiado usando un análisis de Monte Carlo; con este propósito la ubicación de la ruptura se trata como una variable aleatoria uniforme en la longitud de la falla. Los resultados del APPS son comparados con el espectro de diseño del sitio con 2 % de probabilidad de excedencia en 50 años, especificado en la normativa de diseño de la República Dominicana. Se concluye que hay un 17 % de probabilidad de que el valor actual de las ordenadas espectrales con 2 % de excedencia sea mayor que el valor especificado en el espectro de diseño, debido a incertidumbres relacionadas a la ley de atenuación usada para relacionar la fuente de terremotos y las características del movimiento del suelo en el sitio. Basado en el modelo de atenuación, el espectro de diseño en el sitio es consistente con los espectros generados por terremotos de magnitud (momento) de 7.9, lo cual es cercano al terremoto característico de magnitud de 7.8 estimado en estudios recientes de la falla Septentrional.

RESIF RAP and RLBP Dataset of Earthquake Ground Motion in Mainland France

AbstractThis work presents the implementation of a high standards dataset of earthquake ground motions recorded in Metropolitan France between 1996 and 2016. This dataset is intended to serve the scopes of a large seismological community; however, its primary aims are engineering seismology and earthquake engineering applications. The dataset includes records from broadband and accelerometric sensors provided by permanent and temporary seismic networks operated by French research institutions and partners grouped within the Réseau Sismologique et géodésique Français (RESIF) consortium (see Data and Resources). All the waveforms are first homogenized to acceleration units and underwent a full quality control process including: (1) visual verification and manual phase picking, (2) processing scheme, and (3) consistency check by residual analysis. These make the dataset fully compliant with international standards. Finally, the RESIF dataset includes more than 6500 quality-checked records from 468 earthquakes recorded at 379 stations. Over the 379 stations included in the dataset, 177 are permanent stations (RA and FR networks) and 202 are temporary stations (YP and X7 networks). The dataset is complete down to magnitude ML 3.5 over the whole French territory and less (about ML 2.5) in the eastern part. Magnitudes range from ML 2.4 to 5.6 and from Mw 2.0 to 5.2, whereas distances range from less than 1 to 600 km. The disseminated dataset is constituted of (1) a versioned flatfile containing the metadata and main intensity measures computed on each processed record, (2) time histories, and (3) response spectra for several damping values and Fourier spectra.