Spectral Acceleration Research Articles

Seismic fragility analysis of RC frame structures based on IDA analysis and machine learning

This study introduces a machine learning-based methodology designed to rapidly predict the seismic responses of reinforced concrete (RC) frame structures. The research focuses on three types of RC frame structures: low-rise, multi-story, and small high-rise buildings. Ground shaking records are selected according to the conditional mean spectrum (CMS). A sample database, constructed via Incremental Dynamic Analysis (IDA), facilitates the prediction of structural responses using ground shaking intensity and structural details as inputs. Concurrently, the study performs a feature importance analysis of the model. Machine learning algorithms, including integrated learning and neural networks, are utilized to predict the seismic responses of the RC frame structures. This methodology also assists in evaluating the seismic fragility of these structures. The results show that the discrepancy between the neural network-based seismic fragility assessments and the IDA results is minimal, indicating a high degree of accuracy in the proposed methodology. Among the characteristic parameters, Average Spectral Acceleration (AvgSa) is identified as the most significant. This methodology serves as a valuable tool for the rapid prediction of seismic responses in RC frame structures, demonstrating substantial practical value.

Response spectrum and modal dynamic analyses of gravity dams using ground motion accelerations modified to account for hydrodynamic effects

This research proposes simplified methods for response spectrum and modal dynamic analyses of gravity dams using time-history and spectral seismic accelerations modified to directly account for hydrodynamic effects. The developed methods waive the need for specialized fluid-structure interaction software. They also lead to more accurate assessment of coupled structural flexibility and hydrodynamic effects due to each vibration mode than the static correction method commonly used in traditional simplified methods. The methodology utilizes analytical formulations of hydrodynamic pressure or simplified added masses to obtain the contributions of the selected vibration modes to the total seismic response. A hydrodynamic modification factor characterizing the amplification/de-amplification of acceleration seismic demands due to earthquake-induced hydrodynamic effects is also introduced. The application of the proposed methods is illustrated numerically through examples of two typical gravity dam-reservoir systems subjected to four earthquakes. The obtained results are in excellent agreement with the classical reference solutions. Time-history and spectral seismic acceleration demands modified by hydrodynamic effects as well as selected key response indicators, such as relative displacements and stresses within the studied gravity dams, are discussed.

Ground-motion models for earthquakes occurring in the United Kingdom

This article presents models to predict median horizontal elastic response spectral accelerations for 5% damping from earthquakes with moment magnitudes ranging from 3.5 to 7.25 occurring in the United Kingdom. This model was derived using the hybrid stochastic-empirical method based on an existing ground-motion model for California and a stochastic model for the UK that was developed specifically for this purpose. The model is presented in two consistent formats, both for two distance metrics, with different target end-users. Firstly, we provide a complete logic tree with 162 branches, and associated weights, capturing epistemic uncertainties in the depth to the top of rupture, geometric spreading, anelastic path attenuation, site attenuation and stress drop, which is more likely to be used for research. The weights for these branches were derived using Bayesian updating of a priori weights from expert judgment. Secondly, we provide a backbone model with three and five branches corresponding to different percentiles, with corresponding weights, capturing the overall epistemic uncertainty, which is tailored for engineering applications. The derived models are compared with ground-motion observations, both instrumental and macroseismic, from the UK and surrounding region (northern France, Belgium, the Netherlands, western Germany and western Scandinavia). These comparisons show that the model is well-centred (low overall bias and no obvious trends with magnitude or distance) and that the branches capture the body and range of the technically defensible interpretations. In addition, comparisons with ground-motion models that have been previously used within seismic hazard assessments for the UK show that ground-motion predictions from the proposed model match those from previous models quite closely for most magnitudes and distances. The models are available as computer subroutines for ease of use.

Seismic fragility analysis of human perception in high‐rise buildings subjected to far‐field long‐period earthquake ground motions: A case study for Shanghai tower

AbstractHuman perception in high‐rise buildings during far‐field long‐period earthquake ground motions often induces psychological discomfort, including fear and anxiety. A comprehensive understanding on human perception of seismic events is vital for city planning and emergency management, facilitating effective evacuation plans and minimizing stampede risks. This study addresses a gap by employing the seismic fragility analysis method to delineate how human perception in high‐rise buildings is affected during far‐field long‐period ground motions. The methodology involves several key steps. First, the far‐field long‐period earthquake ground motion was identified by detecting the later‐arriving surface waves, and a series of records were selected from the next generation attenuation (NGA) West‐2 ground motion database of the Pacific Earthquake Engineering Research center. Then, a high‐rise building in Shanghai, China was modeled using ETABS 20. Through the linear‐elastic time history analysis, the structural seismic response at each floor was computed. Furthermore, human perception thresholds to vibration were introduced to assess the degree of human perception at each floor, illustrating the difference of human perception to seismic tremor at different floors. Finally, a novel earthquake intensity measure (IM), namely average response spectrum intensity (ARSI) within the vibration period ranging from 0.1 s to 10 s was introduced to generate seismic fragility curves for human perception. According to the investigation, it was found that the corner frequency and the associated energy ratio are useful indicators to identify the far‐field long‐period earthquake ground motions. The ARSI is an effective parameter to assess human perception to seismic tremor compared to the spectral acceleration at a given fundamental period. The generated seismic fragility analysis can provide a complete and thorough understanding on the probability of people that should be evacuated under different earthquake intensity levels. The probability of human perception at different floors varies along the building height, demonstrating the difficulty to make crowd evacuation plan in practice. This insight is vital for understanding and mitigating seismic concerns in high‐rise buildings, particularly in low‐to‐moderate seismicity regions.

Use of spatial autocorrelation of microtremor using L- and triangle- arrays for estimations of S-wave velocity model and soil response at ITS Surabaya

Abstract Institut Teknologi Sepuluh Nopember (ITS) Surabaya is geologically vulnerable to earthquake hazards. Therefore, preparedness is necessary to address emergencies and risks caused by earthquake at ITS Surabaya. In this study, dispersion curve were obtained through the analysis of microtremor data using the Spatial Autocorrelation (SPAC) method. Microtremor data acquisition was performed at the PLN ITS Futsal Field using L- and triangle-arrays. We successfully got dispersion curves from both arrays. The shear wave velocity (Vs) profile and the best model of Vs profile for each array were obtained by inverting the dispersion curves. By using a two-layer model, the first layer produces identical velocities with a depth of 5.44 meters for an L-array and 5.02 meters for a triangle array. In the second layer, the resulting velocities for each array have quite a difference. The best model of Vs profile for both arrays were used to analyse 1D soil response with a linear approach in the frequency domain. Parameters including Peak Ground Acceleration (PGA), 5% damped Pseudo Spectral Acceleration (PSA), and Fourier Amplitude Ratio (FAR) were obtained from the linear approach analysis that could describe the ground’s response to seismic waves. Vs influences the soil response, the higher the difference in Vs values of a layer with the layer below it (half-space), the higher the increase in PGA, PSA, and FAR.

Evaluation of vertical-to-horizontal spectral acceleration ratio for the 2023 Turkey-Syria seismic sequences

This paper aims to evaluate the vertical-to-horizontal, V/H, spectral acceleration ratios from the earthquake ground motions recorded during the February 6, 2023 Turkey-Syria seismic events, which include doublet events with moment magnitudes of Mw7.7 and Mw7.6 that struck the city of Kahramanmaraş and a considerable aftershock with Mw6.7 that mainly struck the city of Nurdağı. Statistics of the observed V/H spectral ratios computed from records that have peak ground acceleration larger than 0.1g showed that most records of the three earthquakes yielded spectral V/H ratios higher than 2/3, which is a typical value recommended by several seismic codes. Additionally, comparison of the observed V/H spectra with respect to the Ground Motion Predictive Models, GMPMs, for V/H ratios introduced by Bozorgnia and Campbell (2016), BC model, and Bommer et al. (2011), BAK model, revealed that both GMPMs mostly underestimate the V/H ratios at long spectral periods. Residual analysis showed that the capability of the BAK model for large source-to-site distances is more than that for small distances for which the ratios may be underestimated specially at long periods, while the estimations of the BC model do not significantly depend on the distance. Additionally, comparison of the observed V/H ratios with those computed based on the current 2018 edition of the Turkish seismic code indicated that the three considered earthquakes mostly yielded V/H ratios considerably higher than the code-based values in the long period range that could have higher damaging potential than those ratios in short period range.

Magnitude estimation and site characterization in southwestern British Columbia: application to earthquake early warning

In this study, we took a close look at the Ocean Networks Canada’s earthquake early warning system in southwestern British Columbia through analysis of the magnitude estimates by this system and characterization of site conditions for both onshore and offshore stations. Using magnitude values estimated at each station, over hundreds of notifications, we provided station terms to correct the magnitudes for stations that systematically generate high or low magnitude values. Moreover, by compiling a rich ground motion amplitude dataset and applying the horizontal-to-vertical spectral ratio method from Fourier amplitude of acceleration and response spectral acceleration, we investigated site characterization through evaluation of non-linear site response behavior and estimation of the site dominant frequency (fpeak) and its peak amplitude (Apeak) for each station. In general, no strong evidence of non-linearity is observed at any stations considering the magnitude-distance distribution of ground motions in this study. Offshore sites show fpeak and Apeak in the range of approximately 1.7–6 Hz and 0.4–1.2 (in base-10 log unit), respectively, whereas onshore sites show approximately 1–6 Hz for fpeak and 0.3–0.7 (in base-10 log unit) for Apeak.

Lessons learned from four recent Turkish earthquakes: Sivrice-Elazığ, Aegean Sea, and Dual Kahramanmaraş

Türkiye is located in an earthquake-prone region where almost all of its population resides in risky areas. In the past 100 years, there has been a strong earthquake every two years and a major one every 3 years. This study investigates the impact of four recent earthquakes, that occurred between 2020 and 2023, on reinforced concrete (RC) buildings. The first, Sivrice-Elazığ, struck the eastern part of Türkiye on January 24, 2020, with a moment magnitude of Mw = 6.8. The second, the Aegean Sea, hit the western part of the country on October 30, 2020, with an Mw of 6.6. The third and fourth are the February 6, 2023 dual Kahramanmaraş earthquakes with Mws of 7.7 and 7.6, which struck the eastern part of Türkiye approximately 9 h apart. Immediately following these earthquakes, a technical team investigated each of the damaged areas. This study summarizes their findings on RC buildings. It was discovered that the majority of the collapsed or severely damaged RC buildings were constructed before 2000. The main reasons for this included technological limitations, specifically on producing high-quality concrete, as well as a lack of public policies and enforced laws in the construction sector to maintain an acceptable international standard. Furthermore, the damage patterns of buildings from these four earthquakes indicated poor workmanship, low material quality, improper structural framing, a common appearance of soft and weak stories, the inadequate use of shear walls, and defective reinforcement configuration. The significance of soil studies and the enforcement of building inspections are also discussed, along with the earthquake codes. The study concludes that the maximum peak ground accelerations from the dual Kahramanmaraş earthquakes were almost triple the code-prescribed values. Therefore, it is recommended that the current mapped spectral acceleration values be revised and that buildings constructed before 2000 should be prioritized while determining their structural performances.

Site-specific probabilistic seismic hazard analysis in Nuweiba, Gulf of Aqaba, Egypt: Combining area source model and active faults

Gulf of Aqaba in Eastern Egypt is characterized by significant seismic activity and high deformation rate, making it a major source of destructive earthquakes in the region. While previous studies have produced probabilistic seismic hazard analysis (PSHA) maps for the region, they have not adequately accounted for active faults or site response in their calculations. This study introduces a newly developed seismic source model for the Gulf of Aqaba, considering area source, active fault source, and a combination of both models to improve seismic hazard assessment for the region. The study incorporates the previously measured average shear-wave velocity for the upper 30 m (Vs30), fundamental frequency (F0), and amplification factor (A0) at some selected sites in Nuweiba city. Accordingly, site-specific PSHA is carried out for the bedrock condition (Vs30 = 800 m/s, according to the Egyptian Building Code) and for the surface of soft sediments using F0, A0, and Vs30. Uncertainties in slip rate, maximum magnitude, and recurrence model are accounted during PSHA computation. Ground motion parameters such as peak ground acceleration (PGA) and spectral acceleration (SA) for various probabilities of exceedance in 50-year lifetime are calculated for both rock site conditions and soft sediments. The maximum calculated PGA and SA are 0.65 g and 1.25 g, respectively, for a 10% probability of exceedance over 50 years at bedrock conditions.

Development of Seismic Fragility Functions for Reinforced Concrete Buildings Using Damage-Sensitive Features Based on Wavelet Theory

In this study, wavelet-based damage-sensitive features are employed to derive the seismic fragility functions/curves for reinforced concrete moment-resisting frames. Two different wavelet transform functions, namely, Bior3.3 and Morlet mother wavelet families, were applied to absolute acceleration time histories of building frames to extract the wavelet-based and refined wavelet-based damage-sensitive features (i.e., DSF and rDSF). The accuracy of seismic assessments and certainty in predicting structural behavior strongly depend on the specific optimal intensity measures selected, reliability of wavelet-based damage-sensitive features, and some such intensity measures as PGA, PGV, PGD, Sa, and Sdi as the conventionally utilized measures to detect the damage state of a structure. These measures were examined against their statistical properties of efficiency, practicality, proficiency, coefficient of determination, and sufficiency to select the appropriate optimal intensity measures, which were then used to drive the fragility curves disclosing the failure or other damage states of interest. For the purposes of this study, three different concrete moment-resisting frames with four-, eight-, and twelve-story building frames were adopted for implementing the proposed approach. The findings demonstrate that the wavelet-based damage-sensitive features (DSFs/rDSF) simultaneously satisfy all the statistical properties cited above. This is evidenced by the low variance and dispersions observed in the frame damage state predictions by the fragility functions derived from the wavelet-based DSF when compared with those derived from the classical fragility analyses such as spectral acceleration at the first mode period of the structure. A final aspect of the study concerns the superior performance and efficiency of the fragility curves derived by the Bior3.3 wavelet-based DSF over those derived from Morlet wavelet-based DSF.

Impact of Randomized Soil Properties and Rock Motion Intensities on Ground Motion

Seismic site response is inevitably influenced by natural variability of soil properties and anticipated earthquake intensity. This study presents the influence of variability in shear wave velocity (Vs) and amplitude of input rock motion on seismic site response analysis. Monte Carlo simulations were employed to randomize the Vs profile for different scenarios. A series of 1-D equivalent linear (EQL) seismic site response analyses were conducted by combining the randomized Vs profile with different levels of rock motion intensities. The results of the analyses are presented in terms of surface spectral acceleration, amplification factors (AFs), and peak ground acceleration (PGA). The mean and standard deviation of these parameters are thoroughly discussed for a wide range of randomized Vs profile, number of Vs randomizations, and intensities of input rock motions. The results demonstrate that both the median PGA and its standard deviations across different number of Vs profile realization exhibit a slight variation. As few as twenty Vs profile realizations are sufficient to compute reliable response parameters. Both rock motion intensity and standard deviation of Vs variability cause significant variation in computed surface parameters. However, the variability in the number of records used to conduct site response has no significant impact on ground response if the records closely match the target spectrum. Incorporating the multiple sources of variabilities can reduce uncertainty when conducting ground response simulations.

Applicability of 1D site response analysis to shallow sedimentary basins: A critical evaluation through physics‐based 3D ground motion simulations

AbstractOne‐dimensional site response analysis (1D SRA) remains the standard practice in considering the effect of local soil deposits and predicting site‐specific ground motions, although its range of applicability to realistic seismic wavefields is still in question. In this 1D approach, horizontal and vertical ground shaking are assumed to be induced by vertically propagating shear and compressional waves, respectively. A recent study based on analytical two‐dimensional (2D) plane waves and simple point source earthquake simulations has shown two mechanistic limitations in this 1D modelling technique for general inclined seismic waves, that is, systematic over‐prediction of the vertical motion and wave trapping in the 1D soil column. In this article, we evaluate in detail the applicability of this 1D modelling approach to realistic three‐dimensional (3D) simulated seismic wavefields in shallow sedimentary basins. Linear‐viscoelastic 1D SRA predictions using two types of input motions that are commonly used in practice—rock outcrop and in‐column motions, are compared with the reference true site response results from 3D earthquake simulations in terms of various measures in the frequency and time domain. It is shown that the horizontal motion in the 3D seismic wavefield exhibits dominant shear wave propagation phenomenon, while the vertical motion is a combined effect of compressional and shear waves and can be over‐predicted by the 1D approach when the incident seismic waves are inclined. Direct evidence of the wave refraction process that leads to the vertical motion over‐prediction is provided. 1D SRA with in‐column inputs can yield motions that have significantly longer duration compared to the true 3D site response solution due to trapped waves, casting in doubt the frequent need for increased soil damping in existing site studies to compensate for wave attenuation due to scattering alone. Sensitivity investigation on the increase of soil profile damping by a multiplier Dmul shows Dmul values compatible with those found in the literature for both horizontal and vertical motions. It is shown that the level of Dmul optimized for a best match of the spectral acceleration is dependent on the characteristic of the input motion and a larger Dmul is typically required for the vertical component. In contrast, 1D SRA with outcrop motions predicts motions with shorter significant duration due to its inability to capture the basin‐edge generated surface waves. A suite of ground motion simulations was performed to assess the sensitivity of the observations to the basin geologic structure including the velocity gradient, rock‐basin impedance contrast and basin depth. The analysis results show that the accuracy of the simplified 1D procedure is dependent on the wavefield composition of both the input motions and the true 3D site response solution. While the horizontal motions in shallow sedimentary basins can, to the first order, be reasonably captured by the simplified 1D approach, 1D SRA for the vertical component is in general not reliable and contributions from inclined shear waves should be accounted for in site‐specific evaluation of the vertical design ground motion.

Empirical models for Fourier amplitude spectrum of ground-motion calibrated on data from the Iranian plateau

Ground-motion models (GMMs) are frequently used in engineering seismology to estimate ground motion intensities. The majority of GMMs predict the response spectral ordinates (such as spectral acceleration) of a single-degree-of-freedom oscillator because of their common application in engineering design practices. Response spectra show how an idealized structure reacts to applied ground motion; however, they do not necessarily represent the physics of ground motion. The functional forms of the response spectra GMMs are built around ideas taken from the Fourier spectral concept. Assuming the validity of Fourier spectral concepts in the response spectral domain could cause physically inexplainable effects. In this study, using a mixed-effects regression technique, we introduce four models capable of predicting the Fourier amplitude spectrum that investigates the impact of incorporating random-effect event and station terms and variations in using a mixed-effects regression technique in one or two steps using truncated dataset or all data (nontruncated dataset). All data consists of 2581 three-component strong ground motion data resulting from 424 events with magnitude ranging from 4.0 up to 7.4, from 1976 to 2020, and 706 stations. The truncated dataset’s records, events, and stations are reduced to 2071, 408, and 636, respectively. As part of this study, we develop GMMs to predict the Fourier amplitude spectrum for the Iranian plateau within the frequency range of 0.3–30 Hz. We adopted simple, functional forms for four models, and we included a limited number of predictors, namely Mw (moment magnitude), Rjb (Joyner–Boore distance), and VS30 (time-averaged shear-wave velocity in the top 30 m). Due to statistical analyses, the style-of-faulting term was excluded from the final functional forms. The robustness of the derived models is indicated by unbiased residual variation with predictor variables.

Seismic Risk Assessment of Built Environment in the Himalayan Foothill City of Dehradun, Uttarakhand

Himalayan foothill city of Dehradun in Uttarakhand state is located in a tectonically active region and is prone to earthquakes. The growth of Dehradun city is analysed using high resolution remote sensing datasets in the current study, with a focus on its vulnerability to seismic risks for single and double storey structures as the city is predominantly made up of low-rise structures. Analysis shows that 10% of urban expansion has occurred in spectral acceleration zones that are vulnerable to double-storey buildings, while 38% of urban expansion has happened in spectral acceleration zones that are vulnerable to single-storey buildings. The proposed land use as per Dehradun Masterplan 2041 is examined with reference to National Earthquake Hazards Reduction Program (NEHRP) for seismic regulating provisions. It is emphasized that the intended land use is incongruous in areas with higher spectral acceleration zones since it comprises structures with higher occupancy and the amenities required during post-earthquake rehabilitation. On the other hand, the open spaces are more appropriate in these locations, which will lessen susceptibility as the influence of seismic forces can be sufficiently attenuated. The present study, thus highlights the significance of including seismic risk information in urban planning processes in order to ensure resilient cities.

Average spectral acceleration (AvgSa) for high-confidence probabilistic seismic demand modeling of urban highway bridge portfolios: What period range and damping ratio shall we use?

The average spectral acceleration (AvgSa), i.e., the geometric mean of spectral accelerations over a period range, has attracted widespread recognition as one of the most promising intensity measures (IMs) for probabilistic seismic demand modeling of structures. As AvgSa is a structure-related spectral IM, a pivotal step in calculating AvgSa is to determine an appropriate period range and damping ratio. Whilst optimal AvgSa has been well documented for buildings, consensus on the period range and damping ratio of AvgSa for urban highway bridges is yet to be reached. To this end, a pool of AvgSa candidates with different combinations of lower and upper period bounds and damping ratios are assessed to identify the optimum combination(s) for straight and curved urban highway bridge portfolios against bidirectional seismic excitations, in terms of peak pier drift ratio, peak bearing displacement, and residual pier drift ratio. Results indicate that for the peak demand parameters, optimal AvgSa is characterized by a damping ratio of 0.2 and a period range of [Tf, 1.5Tf], where Tf is the structural fundamental period, for bridges with relatively short piers; and the optimal period range becomes [Tf, 2Tf] for medium to tall-pier bridges. Besides, the optimal period range for the conventional 5%-damped AvgSa is also detected, where [0.5Tf, 1.5Tf] is the optimal range for bridges with relatively short piers, while [0.5Tf, 2Tf] is recommended for medium to tall-pier bridges. Regarding the residual pier drift ratio, averaging spectral accelerations over any examined period ranges does not outperform traditional spectral accelerations at specific periods.

Evaluation of the response of historical structures fitted with seismic-isolation

The paper highlights the performance of the seismic isolation devices installed on retrofitted buildings in reducing the seismic response when subjected to earthquakes. Two buildings from the beginning of the XXth century in Bucharest are chosen from many more, monitored over the city area. We discuss the response of these base-seismic isolated structures, relying on good quality data acquired from the recent strong earthquake (3 November 2022, MW = 5.0). Elastic response spectra computed from recordings at two levels of each structure are used, placed under and right above the isolating layer. At one building, the existence of previous recordings and the particularity of the sensors allow a comparison with the other two relatively recent medium-intensity earthquakes. The assessment is carried out in terms of maximum acceleration amax, measured at certain levels in each structure, spectral acceleration amplitude SAmax, and spectral-peak corresponding period. We find that the base-isolation methodology is effective in reducing the response of the building right above the isolating layer, an observation valid for both structures, all components of the recordings, and spectral acceleration values. Moreover, the outcomes from the modal evaluation performed prior to rehabilitation and the seismic isolation process are presented by pointing out a higher newly acquired fundamental period of the isolated structures.

Exploring the Use of Orientation-Independent Inelastic Spectral Displacements in the Seismic Assessment of Bridges

ABSTRACT Seismic intensity measures (IMs) provide a link between the seismic hazard and the dynamic response of structures subjected to earthquake shaking. The spectral acceleration at the first and usually dominant vibration mode, Sa(T 1), is a popular choice for building structures. Meanwhile, the IM selection for bridges is non-trivial since they do not typically possess a single dominant mode. Even for ordinary bridges with a dominant mode, the behavior can change significantly in each principal direction through the activation, or yielding, of its different components. This study examines the performance of a novel IM that incorporates ground motion directionality and structure non-linearity in this context: the nn th percentile of all rotation angles of the inelastic spectral displacement, Sd i,RotDnn. This evaluation is carried out within the context of an ordinary bridge structure and is compared with other conventional IMs used in regional risk assessment of bridges. The case study bridge utilized is a highway overcrossing located in California with two spans and a continuous prestressed reinforced concrete box girder deck section. A large ground motion set was selected from the NGA-West2 database, and incremental dynamic analysis was carried out on the structure to assess the IM performance to characterize collapse. The results indicate that Sd i,RotDnn performs very well compared to other IMs for the bridge structure and could be a prudent choice to characterize inelastic response of bridges with several possible mechanisms in different principal directions. Also, using the RotD50 definition, typically used in ground motion models, showed a 17.3% increase in efficiency compared to RotD100 definition typically used in engineering practice.

Partially non-ergodic ground motion model for the Bucaramanga seismic nest in Northern South America (NoSAm Nest GMM)

The Bucaramanga seismic nest has the highest concentration in volume of intermediate depth seismic events with light and moderate magnitudes (Mb > 4.8) worldwide. Despite the nest depth (Zhypo ≥ 100 km), these events play a crucial role in the seismic hazard assessment for several cities in northern South America (NoSAm), particularly those situated close to their epicenters. Moreover, these earthquakes are widely felt across the country, even hundreds of kilometers away from the nest. This paper assesses the performance of commonly used subduction intraslab Ground Motion Models (GMMs) in predicting the updated nest database gathered and processed by the Colombian Geological Survey. This analysis confirms the necessity of a partially non-ergodic ground motion model for estimating the spectral accelerations produced by Bucaramanga nest earthquakes in northern South America. The GMM presented herein is the first model developed specifically for seismic nests in the region and is conceived as a regionalization of the recent NGA-Sub Abrahamson and Gülerce (Earthq Spectra 38(4):2638−2681, 2022) GMM. Additionally, we provide estimates of the variance components at both the earthquake and station levels and compare the developed GMM with the spectral accelerations recorded for typical earthquakes, for the highest magnitude earthquake in the database, and for a recent Bucaramanga nest earthquake having a moment magnitude over 5.

A new simple masing-type soil nonlinear model considering modified damping and its application on KiK-net site response

In this paper, a series of simple Masing rules is first proposed for best fitting the shear modulus reduction and the damping ratio curves of soil based on the extended Masing rules and hysteretic damping formulation. A new masing-type nonlinear model is established and implemented in ABAQUS software based on the Matasovic back-bone curve and the new proposed Masing rules. To validate the practical applicability of the new model, the 1-Directional 3-Component nonlinear site response analysis for station KSRH10 (in Hamanaka, Hokkaido, Japan) is conducted. The numerically predicted results of the proposed nonlinear model are in excellent agreement with the recordings. The surface peak ground acceleration obtained by ABAQUS agrees well with the recording, which has a little difference of about 8.3% on average. The comparison between the proposed nonlinear model and the DEEPSOIL model indicate that the results of the former match better with recording to some extent, in term of acceleration time histories, spectral acceleration (SA) curves, and peak ground acceleration (PGA). The mean square error of acceleration time histories and SA curves obtained by the proposed model is smaller than the model in DEEPSOIL. The agreement with recording is improved by 10.8% compared with the DEEPSOIL model.

Prediction of the fundamental period of infilled RC framed structures considering the maximum inter-story drift at different design limit states

The fundamental period of vibration is a key parameter for the spectral approach to seismic design of structures, as it significantly affects the evaluation of the response spectra values. Even though infill elements can significantly increase a building's lateral stiffness, they are not always considered in the structural design process. This is particularly significant at the damage limitation states considered by the European (Eurocode 8) and Italian (NTC2018) seismic codes, where mostly elastic behaviour is expected. Non-structural elements, in fact, can influence the natural elastic period of buildings, determining spectral accelerations different from those evaluated by the simplified formulas provided by the seismic standards and related guidelines. This research aims to develop novel simplified period-height relationships to estimate the fundamental period of vibration of infilled Reinforced Concrete (RC) framed buildings more accurately at various limit states, as a function of inter-story drift value. To collect information about the fundamental period of structures in different damage conditions, several experimental campaigns involving more than 330 RC framed structures have been considered. Nonlinear numerical analyses have also been performed to integrate the database, especially for the Ultimate Limit State (ULS), considering different number of floors, infill distributions, and geometries. Collected data have been parametrized as a function of the damage level suffered by the considered structures, and different empirical period-height formulations have been defined for each limit state. The proposed relationships have been compared with those found in international, European, and national seismic codes, as well as with simplified formulations in previous literature studies. In particular, the results strongly suggested that the fundamental periods estimated according to the EC8 formulation, overestimates the experimental data, resulting in a potential underestimation of the seismic forces and therefore of damage to non-structural elements. To quantify the differences in spectral acceleration and spectral displacement at all design limit states, some examples have been proposed, considering different Italian seismic zones.