Spectral Acceleration Research Articles

Review Paper on Seismic Analysis of Multi-Storied Reinforced Concrete Building with Fluid Viscous Dampers

Abstract: Frequent earthquakes around the world and the large number of buildings at risk have made it essential to focus on controlling how structures respond to these events. This demand has driven the increased use of structural response control methods globally. This study investigates the seismic performance of multi-storied Reinforced Concrete (RC) Buildings, distinguishing between Regular and Irregular Plan , with a focus on the role of Fluid Viscous Dampers (FVDs). The study aims to quantify the improvements in seismic resilience provided by these damping devices in mitigating the adverse effects of seismic events. Buildings having Regular and Irregular Plans are analyzed, with and without FVD using ETABS2018. The story responses in terms of Pseudo Spectral Accelerations, Maximum Displacement, Story Drift and Story Shear have been compared. The results of the Time History Analysis represent the effectiveness of dampers in improving the structural response and the damping demand on structural systems

Correlation models for next-generation amplitude and cumulative intensity measures using artificial neural networks

Various next-generation intensity measures (IMs) have emerged in recent years. For instance, filtered incremental velocity, FIV3, was shown to be efficient in predicting the collapse of structures, or average spectral acceleration, Saavg, shown to be well-correlated with a wide range of response, from initiation of structural damage yielding to structural collapse. Different ground motion models (GMMs) are available to predict the probabilistic distribution of these IMs, given a set of seismological parameters. Nonetheless, a few key correlation models are still missing in the literature, which are elemental for a more holistic approach to ground motion record selection. These models are vital when performing seismic hazard analysis and ground motion record selection using state-of-the-art approaches like the conditional spectrum or generalized conditional intensity measure (GCIM) methods. This study uses a single machine-learning-based generalized ground motion model (GGMM) to estimate all the IMs. The model is based on the Next-Generation Attenuation (NGA)-West2 database and was utilized to quantify the correlations between the residuals. Correlations were calculated for intra- and inter-event residuals, but only those for total residuals are presented here, given their utility. Since the calculation of residuals comes from the same GMM and the same database of ground motions, this produces more consistent correlation coefficients between all IMs. To facilitate the usage of these correlation coefficients, predictive models of the empirical data were developed using machine-learning-based techniques, namely artificial neural networks (ANNs). It was found that FIV3 is strongly correlated with Sa(~1 s) and itself across all periods and has a weak negative correlation with duration at short periods and near-zero correlation for longer periods. Also, a stronger negative correlation between Sa and significant duration was found, compared with other prominent existing models. Direct correlation models between Sa and Saavg are also proposed.

Directionality of average spectral acceleration, SaAvg, in the 2023 Kahramanmaras, Türkiye earthquake sequence

Directionality of average spectral acceleration, SaAvg, in the 2023 Kahramanmaras, Türkiye earthquake sequence

K-means for earthquakes: disaggregation analyses of small events by considering wave components and soil types

In this paper, k-means algorithm has been used to disaggregate seismic parameters to evaluate their inter-correlations. A goal is to quantify in a disaggregated way the weights and effects of each parameter with respect to other ones. From the database, about 4900.0 data, divided into 22.0 categories, have been collected. The main divisions regard the wave components in horizontal and vertical axis and the soil characteristics. The studied seismic zone is the “Norpirenaica oriental,” placed in the Pyrenees area between Spain and France, classified as a very high seismic hazard. Numerical and analytical analyses have been carried out to implement the algorithm. Preliminary analyses and results would quantify the role of the sand horizontal stratigraphy, the non-linear effects, the elasticity of the soil, and the energy damping phenomenon. Curves are plotted in stochastic distributions and elastic spectra accelerations. Results show good prediction for vertical spectral accelerations and for far and relative strong events. Rigorously, results are valid only for the studied seismogenic zone under predefined constrictions and ranges.

The role of underground archaeological remains on the seismic response of a historic tower

The Italian territory features plenty of historic masonry buildings, many of which have undergone reconstruction, often atop ancient ruins. The presence of archaeological remains in the shallow layers of the ground is always disregarded in the seismic assessment of masonry buildings. To address this gap, the paper delves into the influence of underground masonry ruins on the seismic response of a bell tower built above a historic soil deposit. A comprehensive 3D finite-element model encompassing the tower, foundation, soil, and underground remains was developed. A parametric analysis was conducted, involving modifications to the geometry, mechanical properties, and location of the buried ruins. From the parametric study it emerged that the buried walls could alter the seismic signal at the base of the structure. The most critical scenario occurs when the buried archaeological ruins have a grid spacing comparable to the characteristic size of the foundation, especially in soft soils. Analysis of displacements, accelerations, and spectral accelerations at different elevations along the tower height revealed that the presence of archaeological ruins could modify the seismic response of the structure built above them.

Impact of Vertical Vibration on Group Piles During Earthquake Loading: Experimental Findings

This study presents novel research on the impact of vertical vibration on the dynamic response of pile groups embedded in stratified soil under seismic loading conditions. An experimental setup was employed wherein the piled machine foundation was subjected to vertical vibrations at three operating frequencies (10, 20, and 30 Hz) and subsequently exposed to four levels of seismic acceleration (0.1 g, 0.34 g, 0.77 g, and 0.82 g). Piles with a length-to-diameter ratio of 25 were embedded in a stratified soil profile, with an upper loose layer (30% relative density) and a lower dense layer (80% relative density) acting as end-bearing. Measurements and analyses of horizontal and vertical accelerations, and amplification factors were conducted using the Fast Fourier Transform (FFT), spectral acceleration (Sa), and variation of acceleration with depth. The results demonstrated a significant reduction in horizontal acceleration, with a peak ground acceleration (PGA) reduction of up to 64% in average, particularly at higher frequencies such as 30 Hz. The mitigation efficiency at 30Hz improved with increasing PGA, showing reductions of 42, 68, 75, and 63% for seismic accelerations of 0.1 g, 0.34 g, 0.77 g, and 0.82 g, respectively. The analysis further revealed harmonic resonance and higher mode effects at lower frequencies, with nonlinear soil behavior affecting the resonance and amplification patterns. Additionally, the results demonstrate that the far-field accelerations exceeded the near-field accelerations within the pile group, particularly in the surface layer. The results indicated that the initial vibration amplitudes exceeded the safe operating limits outlined in ACI 351.3R-18 under seismic loading, particularly at higher seismic acceleration levels and lower frequencies. Additional modified charts were presented to account for these conditions. The results presented promising evidence for using vertical vibrations as an earthquake-mitigation strategy. However, avoiding operating at frequencies less than 10 Hz is recommended because of the potential resonance and interaction with horizontal accelerations during earthquakes. Doi: 10.28991/CEJ-SP2024-010-010 Full Text: PDF

Seismic Wave Amplification Characteristics in Slope Sections of Various Inclined Model Grounds

The collapse of slopes caused by earthquakes can lead to landslides, resulting in significant damage to both lives and structures. Seismic reinforcement of these slopes can protect social systems during an earthquake. In South Korea, where more than 70% of the land is mountainous, the stability of slopes is of paramount importance compared to other countries. While many seismic designs are based on peak ground acceleration (PGA), there is relatively little consideration given to the extent of PGA’s influence, and few studies have been done. This study aims to assess the seismic amplification of slopes with multilayers using a 1 g shaking table and verify the results through numerical analysis after confirming the impact of PGA at specific points. Typically, slope model experiments are conducted on single-layered ground models. However, actual ground conditions consist of multiple layers rather than a single layer, so a multi-layered model was created with different properties for the upper and lower layers. Two multi-layered ground models consisting of two layers were created, one with a flat ground surface and the other with a sloped surface. The properties of the two layers in each model were configured as a single layer to create the slope models. The peak ground acceleration (PGA) of the four ground models was compared, revealing that seismic wave amplification increases as it moves upward, and the amplification is even greater when transitioning from the lower to the upper ground layers, leading to different dynamic behavior of the slope. Through the contour lines, the influence of PGA was further confirmed, and it was found that approximately 60% of the PGA impact occurs at the topmost part of the slope on average. Analysis of the earthquake waves showed that the top of the slope experienced an average amplification of about 31.75% compared to the input motion, while the lower part experienced an average amplification of about 27.85%. Numerical analysis was performed using the ABAQUS program, and the results were compared with the 1 g shaking table experiments through spectral acceleration (SA), showing good agreement with the experimental results.

Seismic response of deep soft soil sites with varying shear wave velocities

The variations in seismic response between deep soft soil sites with different shear wave velocities were not fully understood. This study focuses on the seismic response of deep soft soil sites in the lower reaches of the Yangtze River, China. A nonlinear dynamic finite element model was developed for two representative deep soft soil sites with borehole profiles and the shear wave velocity tested by the single borehole method. Two nonlinear cyclic constitutive models are used and thus compared through the site seismic response. To accurately calibrate the nonlinear cyclic model parameters, resonant column tests were conducted on 21 soil samples collected from the two boreholes. The results show that the peak ground acceleration (PGA) under low-frequency (Liuan) input motion was higher for soft soil sites compared to that under medium- and high-frequency (Kobe and Nahanni) input motions. The PGA amplification factor for deep soft soil sites under different input motions can be approximated by an exponential function. The peak ground acceleration tends to be lower as the equivalent shear wave velocity (Vse) decreases. The shapes of the spectral acceleration were similar for the two sites, despite a substantial difference in the Vse between them. Additionally, a crossover point was observed in the spectral acceleration for the two sites. The period corresponding to this crossover point increased with increasing intensity of input motions, indicating that the sites became softer with higher intensity and thus generally exhibited a longer characteristic period of the spectral acceleration. This paper also highlights the significance of selecting nonlinear constitutive models and the precise calibration of model parameters in the seismic response analysis of deep soft soil sites, providing a scientific basis for future similar site analyses.

Evaluation of directionality in physics-based ground motion simulations of strike-slip earthquakes

Recent advances in engineering seismology and computing power have led to the development of realistic physics-based ground motion simulations. The use of these simulations for engineering applications requires that the ground motions exhibit characteristics consistent with those of recorded ground motions. While several studies have evaluated the intensity, frequency content, duration, and other characteristics of ground motion simulations for their possible use in engineering applications, few have focused on directionality. This article evaluates directionality in the response of single-degree-of-freedom oscillators when subjected to CyberShake Study 15.12 simulated ground motions from strike-slip earthquakes, by carefully comparing it to the directionality in recorded ground motions having the same style of faulting. Physics-based ground motion simulations at 334 stations from 5 different rupture variations in two large-magnitude earthquake scenarios on the Elsinore fault are evaluated. The orientation of maximum oscillator response and its spatial distribution are studied for each rupture. The orientation of maximum oscillator response is found to occur systematically close to the epicentral transverse orientation at all rupture distances, consistent with recent findings for ground motions recorded during strike-slip earthquakes. In addition, the orientation-specific spectral accelerations, when computed as a function of angular distance from the epicentral transverse orientation, are found to exhibit a variation consistent with the overall trend observed in records from the next-generation attenuation (NGA)-West2 database. However, the level of polarization at short periods in the simulated hybrid broadband waveforms used in this study is larger than that in recorded ground motions.

A Framework for High-Fidelity and Efficient Collapse Fragility Estimation of Structures Using Cluster Analysis

ABSTRACT A clustering-based framework that can select a smaller number of ground motions from the entire ground motion set for collapse fragility estimation of structures while preserving the accuracy is proposed in this study. The bisecting k-means clustering algorithm is applied to the feature space that we construct. The construction is done by using spectral acceleration over a certain period interval to obtain a small number of ground motions until the fragility curve converges. The efficiency and applicability of the proposed framework is successfully demonstrated through a generic set of single-degree-of-freedom systems and six moment-resisting frame buildings having from 1 to 20 stories. The results indicate that collapse fragilities estimated by a smaller number of ground motions selected by using the proposed framework converge to a near optimal value.

Generative Adversarial Networks-Based Ground-Motion Model for Crustal Earthquakes in Japan Considering Detailed Site Conditions

ABSTRACT We develop a ground-motion model (GMM) for crustal earthquakes in Japan that can directly model the probability distribution of ground-motion acceleration time histories based on generative adversarial networks (GANs). The proposed model can generate ground motions conditioned on moment magnitude, rupture distance, and detailed site conditions defined by the average shear-wave velocity in the top 5, 10, and 20 m (VS5, VS10, and VS20) and the depth to shear-wave velocities of 1.0 km/s and 1.4 km/s (Z1.0 and Z1.4). We construct the neural networks based on styleGAN2 and introduce a novel neural network architecture to generate ground motions considering the effect of source, path, and such detailed site conditions. The resulting 5% damped spectral acceleration from the proposed GMM is consistent with empirical GMMs in terms of magnitude and distance scaling. The proposed GMM can also generate ground motions accounting for the shear-wave velocity profiles of surface soil with different magnitudes and distances and represent characteristics that are not explained solely byVS30.

Comparative analysis of seismic response and vulnerability of laminated bamboo frame structure under near-field and far-field earthquake actions

The study offers an evaluation of seismic response and vulnerability for a five-story laminated bamboo frame structure, assessing the effectiveness of seismic intensity measures across various damage thresholds and the modeling uncertainties involved. A structural finite element model was developed in OpenSees software, utilizing the Pinching4 model to accurately represent the non-linear characteristics of T-shaped steel connections in beam-column joints. Two collections of earthquake records, one consisting of pulse-like near-field and the other of far-field events, were utilized to examine the structure's nonlinear behavior. Additionally, vulnerability curves for various damage states were generated using the multiple stripe analysis technique, applied to both ground motion datasets. The applicability of 24 seismic intensity measures was also analyzed across various damage limit states. The modeling uncertainty under different seismic actions was further estimated using a first-order second-moment method. Ultimately, the annual collapse probability of the structure are elucidated. Research indicates that due to the influence of joint stiffness, the overall structure demonstrates dynamic characteristics that are predominantly of the first mode shape. The spectral acceleration associated with the fundamental period achieves a reduced logarithmic standard deviation in the vulnerability analysis across various limit states. Other IMs considering higher mode effects or softening period actions no longer predominate. In most cases, the modeling uncertainty under far-field seismic action is higher than that under near-field, especially at the severe damage limit states by using an efficient intensity measure. The laminated bamboo frame structure faces a much higher collapse risk in near-field than in far-field conditions.

Spatial correlation assessment of multiple earthquake intensity measures using physics-based simulated ground motions

Predictive models for spatial correlation play an effective role in the assessment of seismic risk associated with distributed infrastructure and building portfolios. However, existing models often rely on simplified approaches, assuming isotropy and stationarity. This paper verifies these assumptions by presenting a comprehensive study using a database of 3D physics-based simulated broadband ground motions for Istanbul, generated by the SPEED software. The results reveal significant event-to-event variability and nonstationary and anisotropic characteristics of spatial correlation influenced by source, path, and site effects. The development of nonstationary correlation models requires exploring influential metrics beyond spatial proximity and gaining a deep understanding of their impact, which is the focus of this study. Analysis of the spatial correlations of peak ground displacement, peak ground velocity, peak ground acceleration, and response spectral accelerations at different periods, employing both stationary and nonstationary correlation modelling methods and considering the finite fault model, indicates that the slip distribution pattern, direction and distance of station pairs relative to earthquake rupture, soil softness, and homogeneity of soil properties significantly influence the spatial correlations of near-field earthquake ground motions. Implementation of the introduced parameters in predictive spatial correlation models enhances the precision of regional seismic hazard assessments.

A vector‐valued ground motion intensity measure for base‐isolated buildings in far‐field regions

AbstractIn this study, the effects of the spectral acceleration at the superstructure first‐mode period on the isolator displacement are investigated for far‐field ground motions. For this purpose, two different base‐isolated models are subjected to 165 far‐field ground motions. It is demonstrated that considering the spectral acceleration at the superstructure first‐mode period, besides that at the effective period, improves the estimation accuracy of isolator displacement. ASCE 7‐22 modifies the scaling period range to consider the superstructure first mode period and proposes the new period range from the superstructure first‐mode period to the 1.25 times effective period. In the ASCE 7‐22, the same weight factor is used for the whole period range. However, the present study shows that adding the superstructure first‐mode related period range with appropriate weight factor to the effective period‐based scaling range decreases the dispersion of isolator displacement in the nonlinear response history analyses (NRH). Then, to overcome the spectral shape effects on the fragility curves, a vector‐valued intensity measure parameter is obtained by combining spectral acceleration at the effective period and reduced spectral acceleration at the superstructure first‐mode period. The optimum contribution factor for the spectral acceleration at the superstructure first‐mode period is defined as the ratio of the superstructure first‐mode period to the effective period. The article shows that the proposed parameter is efficient and sufficient to be used as an intensity measure for far‐field ground motions. Furthermore, regression analysis results indicate that this vector‐valued intensity measure parameter correlates well with the isolator displacement. Further, the article shows that using the proposed IM parameter in the fragility curves makes the collapse margin ratio of these curves less sensitive to the spectral shape of the selected ground motions.

Modified fragility functions for offshore wind turbines considering soil-structure interaction subjected to wind, wave, and seismic loads

Investment allocation for offshore wind turbines (OWT) as an important class of structures is typically carried out through supporting decision-making approaches utilizing some fragility functions. This study attempts to deliver fragility functions for OWTs on monopile foundations accounting for soil-structure interaction (SSI) effects. Simultaneous wind, wave, and earthquake loads were considered probabilistically by adjusting their occurrence hazard levels for predefined damage states in diverse performance levels. The designated damage states in this study are defined based on collapse probability and some targeted performance levels which could be very straightforward to distinguish. The damage state detection is based on rotation in the connection section of the tower’s transition part to the foundation, which perceptibly reveals the effects of SSI on fragility functions. The expected results comprise modified fragility functions accounting for SSI effects contributing to less median spectral acceleration, more evidently rotational demands, further dispersions, and a subsequent dominant increase in the probability of exceeding performance limit states. Considering operational performance level, the most applied design performance level for turbines as an important class of structures, not considering the SSI effects could noticeably underestimate the demands and lead to high-risk decisions.

A boosted deep learning-based approach for near real-time response estimation of structures under ground motion excitations

This article presents an improved Convolutional Neural Network (CNN)-based approach to predict the vibration response of structures under seismic events without installing sensors at different stories. To do so, three different benchmark buildings, including a Single Degree of Freedom (SDOF) system, a two-dimensional three-story steel moment-framed structure, and a three-dimensional three-story steel structure, were used to validate the proposed framework. A suite of 111 ground motion records, which was originally developed by the SAC project and FEMA P695 instruction, was used to generate a generalized dataset. These records were uniformly scaled to 18 different peak ground accelerations, from 0.05 g to 1.7 g, to ensure the generalization of the dataset in terms of seismic intensity. A strengthened CNN was introduced to provide a prediction model capable of estimating the acceleration, velocity, and displacement histories of the buildings under earthquake records. This network receives not only the ground motion records as the input attribute but also catches additional features such as spectral accelerations at 0.2s and 1.0s as RGB values of colourful images. Results indicate that the proposed algorithm is reliable in estimating the response histories of the buildings under linear and nonlinear conditions.

Development of data-driven models to predict seismic drift response of RC wall structures: An application of deep neural networks

This research aimed to develop data-driven models using deep neural networks (DNNs) that can rapidly predict the seismic drift responses of reinforced concrete (RC) wall structures in building frame systems, aiming to overcome the challenges of costly seismic performance evaluation of building structures. A total of 46 RC wall structures ranging from four to 40 stories were analyzed and subjected to 1,000 ground motions including far-field, near-field-pulse, and near-field-no-pulse types. Two input sets were investigated initially. The first input set comprises peak ground acceleration (PGA), spectral accelerations at 1 s–6 s with 1-s intervals, and the first five natural periods of the wall structure. The second input set contains PGA and spectral accelerations at the first five natural periods of the wall structure. The DNN model developed based on the first input set demonstrated superior accuracy achieving an R2 value of 0.880, and slightly outperformed other reputable machine learning models. To enhance the applicability of the developed model, the ground motion type was incorporated as an additional variable to the first input set, which led to an R2 value of 0.869. Ultimately, two DNN models, one based on the first input set and the other considering the ground motion type, were proposed in this study. Finally, the two models were applied to quickly predict seismic drift responses of a new 24-story RC wall structure, and the predicted results were then utilized to efficiently construct the fragility function. The findings highlight the potential of DNNs as an efficient solution to address complex and costly challenges in the earthquake engineering domain.

Unsymmetricity effects on seismic performance of multi-story buildings

The unsymmetrical configurations in buildings lead to non-uniform distributions in their strength, mass, and stiffness, and they are consequently prone to damage during seismic hazards. In this study, the seismic performance of multi-story buildings with 5, 8, 10, and 12 stories of square, ‘L’, ‘T’, and ‘U’-shaped buildings have been investigated. The research deals with the variation of the natural time periods and how it affects the seismic performance of unsymmetrical multi-story buildings. The coupled and uncoupled equations of motion, based on the symmetricity of the buildings about both axes, were solved to obtain natural time periods that influence the spectral acceleration of the ground accelerations. Six important ground accelerations were considered. Nonlinear static analysis, such as pushover analysis, was also carried out on all the buildings. Comparisons were made on the seismic behavior of both the symmetrical and unsymmetrical structures. The results revealed that the spectral acceleration influences dynamic responses, such as base shear, base moment, base torsion, roof displacement, roof rotation, and story drifts of the buildings. Moreover, it was found that even though the ‘L’-shaped buildings are unsymmetrical about both axes, they are less vulnerable than the ‘T’ and ‘U’-shaped buildings, which are unsymmetrical about one axis.

Serviceability fragility assessment of non-seismically designed railway viaducts in Turkey under near-field and far-field earthquakes

While many railway viaducts still in use in Turkish railway networks are located on active fault zones that produced historical destructive earthquakes, they are not seismically designed in accordance to current standards. This study aims to provide a better understanding about the serviceability fragility of such systems by conducting detailed probability-based seismic assessments under near-field and far-field earthquakes. To achieve this, firstly, 3D finite element models of a range of selected viaducts in Turkey were generated based on their original design drawings. The developed FE models were validated by comparing the analytical modal frequencies with the results of in-situ dynamic tests involving a series of acceleration measurements. Nonlinear time history analyses were then carried out under 25 near-field and 25 far-field real three-component ground motion recordings to obtain the seismic response of each selected viaduct. Subsequently, probabilistic seismic demand models were defined using linear regression analysis to determine relationships between engineering demand parameters (EDPs) and ground motion intensity measures (IMs). Peak ground acceleration (PGA), peak ground velocity (PGV) and spectral acceleration at 1.0 s (Sa (1.0)) were used as the IM parameter, while the maximum lateral displacement of the bridge spans for different service velocities defined in the Eurocode was considered as the EDP at serviceability damage state. Finally, analytical fragility curves for all the selected railway viaducts were developed considering maximum damage probability for the IM levels. The results, in general, demonstrate the seismic vulnerability of the existing viaducts in Turkey. It is shown that while at low speed limits the viaducts exposed to far-field ground motions were more vulnerable than those under near-field ground motions, at high speed limits the viaducts subjected to near-field ground motions were more vulnerable. Also, it is seen that reinforced concrete and masonry viaducts are generally more vulnerable to earthquakes than the steel viaducts. The outcomes of this study should prove useful for the seismic risk assessment, loss estimation and rehabilitation of the railway transportation networks in future studies.

SITE-SPECIFIC DISAGGREGATION ANALYSIS OF RECENT EARTHQUAKE ON THE AMBON COAST

Seismic activity in the eastern region of Indonesia, particularly in Ambon, has been a matter of great concern because of its high tectonic activity. The devastating magnitude 6.5 earthquake in September 2019, which resulted in fatalities and significant damage, highlighted the region’s vulnerability and emphasized the importance of understanding the area’s seismic hazards. Although previous studies have been conducted, this study aims to fill critical gaps in the literature by using the latest seismic data until 2022 and updated attenuation equations. Disaggregation analysis is employed to identify ground motion characteristics, that are crucial for calculating synthetic ground motion acceleration. Under risk-targeted maximum considered earthquake (MCER) conditions, the study results show a peak ground acceleration of 0.444 g, with spectral acceleration at 0.2 s reaching 1.093 g, which decreases to 0.350 g at 1.0 s. Notably, background earthquake sources play a dominant role in contributing to the region’s high seismic hazard potential. The results of this study highlight the urgency of updating Indonesia’s national seismic hazard map. The study also recommends future studies to explore additional parameters of newly discovered faults to enhance understanding of fault movements and their impacts in the study area.