Average 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.

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.

Next-generation non-linear and collapse prediction models for short- to long-period systems via machine learning methods

Since the 1960 s, a cornerstone of earthquake engineering has been estimating the non-linear response of structures based just on lateral strength, modal properties, and the anticipated seismic demand. Over the years, several studies have quantified this empirical relationship and integrated it within seismic design and assessment methodologies. These have been widely accepted for practical application and adopted in building codes worldwide. While these models work reasonably well, there are still areas in which improvements can be made, especially concerning their robust quantification of uncertainty. This is mainly due to the amount of data used to quantify these empirical relationships, the choice of functional forms during the fitting, the model fitting and testing process, and how the ground motion shaking intensity is characterised. This study tackles these issues via the non-linear analysis of single-degree-of-freedom oscillators to train several machine learning (ML) models. This was to examine the accuracy and applicability of such models within a seismic engineering context and explore potential gains in quantifying the non-linear response of structures via next-generation intensity measures, namely average spectral acceleration, Saavg. The results show that the Decision Tree and XGBoost models worked well across a broad range of periods, accurately predicting collapse and non-collapse responses. Appraising these with existing models showed a notable improvement all around. It indicates that the models based on data-driven ML approaches represent a positive step and can be seamlessly integrated with seismic analysis methodologies utilised worldwide. Subsequently, a Python-based library of these XGBoost ML models was developed and made available online to foster practical application.

An advanced assessment framework for seismic resilience of railway continuous girder bridge with multiple spans considering 72h golden rescue requirements

Given the common sense that people in danger could survive with high probability in the golden rescue time of 72 h after earthquakes, railway bridges that are important transportation hubs and the lifelines for earthquake relief have been required to satisfy the necessities of safe passage and fast traffic for emergency response personnel in this critical period. To ensure the post-earthquake temporary functionality of the railway bridges to a sufficient safety level in golden rescue scenario, an advanced resilience assessment framework, including seismic resilience determinations for individual bridge components based on residual responses with respect to the plastic capacities originated from performance limit state definitions, definitions of three recovery levels considering repair efficiency for different recovery phases, and the series-parallel and parallel-serial system resilience models developed in temporal and spatial domains, was established. A commonly constructed irregular railway multi-span continuous girder bridge was chosen to verify the practicability of the aforementioned framework. The finite-element model of the illustrative bridge was developed taking abutment-girder interaction effects and nonlinear seismic behaviors of girder into account. Average spectral acceleration was taken as the intensity measure (IM) to consider the response variations originated from higher modes and natural period extension during earthquakes, and the site-matched and IM-based scaled ground records were adopted in the multiple stripe analysis to obtain instantaneous peak and residual seismic responses. Based on the framework, post-event resilience characteristics of bridge components were discussed, four recovery strategies were proposed for bridge system, and the seismic resilience of the illustrated bridge was assessed at system level. The research shows that the response contribution of fundamental dominant mode is only 64.37 %, indicating the dynamic response contributions from higher modes are considerable and the case bridge can show a strong irregularity during seismic events. Obvious nonlinear seismic behaviors occur to the superstructure where material strain in girder critical sections can increase to 0.00422 during earthquakes, which illustrates the inaccuracy of girder modeling only taking elastic behavior into consideration. Also, the prestress loss after earthquakes can reach 31.14 % and attention should be paid to the prestress recovery in subsequent repair works. Most components can satisfy the easy recovery resilience level, and the resilience is closely related to ground intensities and repair-waiting time; earthquake-induced functionality reduction can be 46.57 %, and resilience can increase by 25.35 % if the waiting time is shortened by 5 h. System resilience is influenced by the similar factors with component and varies in cases of different repair sequences due to the accumulation effect of repair-waiting time for various subsystems.

A risk-targeted approach for the seismic design of bridge piers

Designing a structure to resist earthquakes by targeting an explicit failure risk has been a key research topic over the past two decades. In this article, a risk-targeted design approach is developed for circular reinforced concrete bridge piers, based on a probabilistic optimization procedure aimed at minimising the design resisting moment at the pier base. In order to reduce the computational effort, a surrogate model is developed to describe the influence of two key design parameter (i.e., the pier diameter and the longitudinal reinforcement ratio) on the structural behaviour and performance. The proposed approach is applied in a case study for Italy for target mean annual frequencies of failure selected according to European codes using a probabilistic seismic hazard assessment for average spectral acceleration across a wide range of structural periods. The variation in the design parameters across Italy is considerable because of the large variation in seismic hazard. It is found that in areas of low seismic hazard the level of seismic design required is near the minimum allowed by Eurocode 8 in terms of reinforcement ratio. In areas of the highest seismic hazard much higher reinforcement ratios and pier diameters are required to meet the risk targets. If both pier diameter and longitudinal reinforcement ratios are considered as design parameters then the optimisation procedure may mean adjacent sites have significant different pairs of these parameters as the target can be reached in multiple ways. This problem can be solved by fixing one parameter and optimising the other.

Evaluation of typology‐specific fragility curves used for risk‐targeted seismic demand maps in regions of low seismicity: A German case‐study

AbstractInvestigations of risk targeted peak ground acceleration (PGA) maps for European countries typically adopt a single generic fragility curve definition. The aim of this study is to investigate the use of typology‐specific fragility curves in the derivation of risk‐targeted PGA maps in low seismicity regions. This study differs from previous works in that it derives expressions for the relationship between design PGA and the median collapse capacity for several different structural typologies designed according to European standards, namely, reinforced concrete (RC) moment‐resisting frames (MRFs), reinforced concrete wall and dual systems, and steel MRFs. The expressions were determined from the regression analysis of a database of fragility curve parameters collected from the literature. The influence of the different typology‐specific fragility functions on the derivation of risk‐targeted seismic maps in regions of low seismicity, using Germany as a case‐study, is discussed. The key findings of this study are as follows: the fragility curves derived using the database possess significant inherent lateral capacity; the consideration of this inherent lateral capacity implies the reduction of the regions where seismic design is compulsory; and that fragility curves adapted from fragility analyses from structures in the US may not be representative of European structures. Recommendations for the direction of future research include focusing primarily on improving the definition of the typology‐specific fragility curves; developing fragility curves for modern IMs such as average spectral acceleration; and investigating the use of typology‐specific curves in regions of high seismicity.

Intensity measures as interfacing variables versus response proxies: The case of rigid rocking blocks

AbstractA comparative study of alternative Intensity Measures (IMs) for structures of rocking response is presented, focusing on the salient characteristics that define the selection of an optimal IM for the problem at hand. An IM may play the role of an interfacing variable, linking hazard with fragility/vulnerability for the risk assessment of structures, or it may only be employed as a proxy for predicting structural response under a given ground motion. In the first case, low conditional variability (high efficiency) and low conditional dependence on seismological parameters (high sufficiency) are needed. For response proxy usage, one may place more importance on the predictive capability of the IM within a simple regression model, favoring high correlation and low fitting errors over an extended range of response. The results showcased that (i) the peak ground acceleration and peak ground velocity, tend to be highly efficient and sufficient in specific regions of rocking response, that is, onset of rocking and overturning, respectively, but not necessarily everywhere; (ii) the average spectral acceleration shows a more consistent performance at the cost of requiring the definition of a proper period range; (iii) magnitude sufficiency is generally more difficult to achieve, compared to the distance from the rupture, and (iv) IMs that may be unsuitable for risk and vulnerability assessment, can still be highly effective as response predictors in statistical models.

A far-field ground motion prediction model for interface earthquakes at the hill zone of Mexico City

This study presents an updated attenuation model to predict the peak ground acceleration (PGA), peak ground velocity (PGV), 5% damped pseudo-spectral acceleration (SA), and the average spectral acceleration (AvgSA) at the hill zone of Mexico City for interface earthquakes. The strong-motion dataset comprises 33 earthquakes recorded at CU station, covering a moment magnitude (Mw) range from 6.0 to 8.1 and a source-to-site distance (Rrup) range from 240 to 490 km. Given the small number of available observations, a Bayesian regression scheme is used to obtain the coefficients of the ground-motion prediction model (GMPM). In addition, the epistemic uncertainty in the estimation of the regression coefficients is evaluated, showing its impact on the framework of a probabilistic seismic hazard analysis (PSHA). The results are compared with models previously developed for the CU station, discussing the differences observed between the median predictions and their standard deviations. Likewise, seismic hazard curves are computed and compared with empirical curves obtained by counting the number of times per year that a given value of ground-motion intensity is exceeded. The results show that the dispersion of the GMPM proposed is lower than the previous models for PGA and SA, which means better predictability and more reliable estimates of the seismic hazard at the site.

Unbiased simplified seismic fragility estimation of non-ductile infilled RC structures

Infilled reinforced concrete (RC) buildings represent a prevalent taxonomy class in the Mediterranean region. Many were constructed before proper seismic provisions and detailing were enforced meaning they typically possess non-ductile failure mechanisms. Therefore, their simple but adequate seismic fragility estimation remains a challenge for the research community and practitioners. Moreover, their performance quantification can typically require characterisation via detailed numerical models that capture salient behaviour features, which involves extensive non-linear dynamic analyses with large computational burden. In this regard, an unbiased seismic fragility estimation methodology for the simplified assessment of infilled RC frame structures is described for both collapsing and non-collapsing scenarios. Its development is using extensive cloud analyses carried out with a large set of oscillators representative of the infilled RC frame's structural behaviour to permit the well-established pushover-based methods to be adopted in practice. The result is a novel set of empirical relationships relating the seismic behaviour of these typologies to their pushover curve parameters to allow practitioners to perform an accurate risk assessment and verification in an expedited manner. The choice of average spectral acceleration as the intensity measure used to characterise the fragility parameters for these relationships is shown to present notable advantages in reducing bias compared with other existing approaches. The results are validated via comparison with a detailed hazard-consistent assessment of case studies from a database of three-dimensional archetype building models. These were also developed here to capture the temporal evolution of building codes and architectural features of the building class in Italy.

Effectiveness of Instantaneous Power in predicting the collapse responses of structures under pulse-like ground motions by Esra ZENGİN

This study investigates the performance of the Instantaneous Power (IP(T1)) intensity measure (IM) for predicting the structural collapse of structures under near-fault pulse-like ground motions. The efficiency and sufficiency of vector IM consisting of elastic spectral acceleration at the fundamental period of the structure (Sa(T1)) and IP(T1) are compared with those obtained using Sa(T1), average spectral acceleration (Saavg), and spectral shape-based vector IMs. A proportional reduction in error, which quantifies to what extent the other ground-motion parameter eliminates the error in the collapse capacity prediction relative to IM of interest, is used to assess the sufficiency. Our findings reveal that [Sa(T1), IP(T1)] yields better collapse capacity prediction compared to all IMs considered and is found to be sufficient with respect to most of the seismological parameters, duration-related IMs, pulse period, and scale factor.

A seismic fragility model accounting for torsional irregularity in low‐rise non‐ductile RC moment‐resisting frames

AbstractBuildings characterized by torsional irregularity are notorious for their vulnerability to earthquakes. However, most fragility/vulnerability models used for regional seismic risk assessment fail to distinguish between buildings with torsionally balanced and unbalanced configurations. The present study aims to develop a seismic fragility model sensitive to torsional irregularity for low‐rise non‐ductile RC moment frame buildings. To this end, a numerical investigation centred on 13 three‐storied plan‐asymmetric models, each characterized by a distinct combination of normalized stiffness eccentricity, torsional radius to mass radius of gyration ratio and normalized strength eccentricity, is presented. Using high‐dimensional model representation (HDMR), a metamodel for the maximum inter‐storey drift under bi‐directional seismic action is calibrated, considering average spectral acceleration and the above trio of torsional irregularity descriptors (TIDs) as the predictor variables. Carrying out numerical simulations on limit state functions formulated using the above demand model and appropriate capacity thresholds, the seismic fragility is estimated. The parameters of a lognormal fragility function compatible with the above estimates are determined using the method of maximum likelihood. A strong correlation is observed between the TIDs and the fragility function parameters. This reinforces the importance of accounting for all three TIDs while rating the seismic fragility of a building. Using least‐square error minimization technique, a functional relationship is established between the fragility model parameters and the TIDs. The framework described herein provides a simple, yet rational means to develop the next generation of seismic fragility models accounting for one of the most critical factors governing seismic behaviour––‘torsional irregularity’.

Seismic acceleration demand and fragility assessment of storage tanks installed in industrial steel moment-resisting frame structures

Recent seismic events highlighted the importance of non-structural elements in seismic assessment and performance-based earthquake engineering. When referring to industrial facilities, storage tanks represent one of the most critical components for the continuous functionality of industrial and building plants after seismic events. At the same time, the dispersion of dangerous or inflammable materials, due to their collapse, could become a safety issue in terms of both human life and environmental impact. This study focuses on the seismic performance assessment of a liquid-storage tank installed in an industrial steel moment-resisting frame building. The performance is assessed in terms of fragility curves, that are provided for the meaningful limit states that affect the liquid-storage tank and considering several intensity measures. The results related to the structural performance are also discussed in detail in terms of fragility functions and floor response. The assessment is performed through nonlinear dynamic analyses using two different modelling approaches to evaluate the structural and non-structural performance. The first modelling approach explicitly accounts for the tank-structure interaction, while in the second one the tank is only modelled considering its seismic mass. The results show the importance of the modelling assumptions to accurately estimate the seismic demand on liquid-storage tanks and corresponding fragility, which is calculated in terms of different intensity measures (IM): average ground spectral acceleration, peak floor acceleration, and floor spectral accelerations. Peak floor acceleration, drift profiles, and absolute acceleration and relative displacement floor response spectra are instead scrutinised for what concerns demand. The comparison with the code formulations available in the literature for estimating the seismic demand to non-structural elements pointed out their inaccuracy for the analysed liquid-storage tank and the need for further efforts to develop more accurate procedures. Furthermore, the outcomes indicate that the IM adopted for secondary components, i.e. peak floor acceleration, may not always be the optimal one hence additional attention should also be paid to the definition of updated fragility curves for non-structural elements, identifying and adopting more suitable IMs.

Evaluation of intensity measure performance in regional seismic risk assessment of reinforced concrete bridge inventories

Seismic risk assessment requires fragility functions derived using non-linear time-history analysis with earthquake records compatible with the site hazard and characterised via a suitable intensity measure (IM), which poses a challenge given the wide variety of structural characteristics found in bridge inventories. Given the lack of consensus on a suitable IM, regional studies often use peak ground acceleration (PGA), which despite being recognized as a poor indicator of structural performance, has persisted in earthquake response characterisation. Average spectral acceleration (AvgSa) has recently gained popularity since it describes earthquake intensity over a range of pertinent periods of vibration; however, its suitability as an IM has not been demonstrated on real bridge inventories with a wide variety of structural characteristics. In this study, hazard-consistent records selected for both PGA and AvgSa are used to evaluate the response of a large inventory of existing bridges with varying structural characteristics, from the Italian roadway network. The results indicate that AvgSa is a more accurate IM compared to PGA when applied to the regional assessment of RC bridges.

Ground Motion Intensity Measures for Seismic Vulnerability Assessment of Steel Storage Tanks With Unanchored Support Conditions

Abstract This paper aims to comprehensively evaluate the performance of a series of ground motion intensity measures (IMs) used in the seismic vulnerability assessment of steel storage tanks with unanchored support conditions. Sixteen well-known IMs are thus selected, which are classified into amplitude-, frequency-, and time-based categories. A comparative study is then performed on four different unanchored steel storage tanks subjected to a suite of 140 ground motion records that is comprised of seven different bins of records with different hazard levels. In this regard, the tanks are appropriately modeled based on a simplified approach, whose uplift and sliding nonlinear behaviors are properly implemented based on a three-dimensional nonlinear pushover analysis of the tanks. Four characteristics of the examined IMs including efficiency, practicality, proficiency, and sufficiency are evaluated based on a probabilistic seismic demand model of two critical failure modes of the tanks, i.e., plastic rotation of the shell-to-bottom connection and elephant's foot buckling of the shell plate. According to the comparative study, frequency-based IMs demonstrate their superior performance for all criteria compared with other groups; in particular, the average spectral acceleration gains the highest ranking. Finally, an appropriate range of the upper period considered in the average spectral acceleration IM is then proposed to optimize the efficiency of this IM for the examined tanks.

Seismic intensity measures for risk assessment of bridges

In performance-based seismic assessment, structural response is characterised using fragility functions based on a seismic intensity measure (IM). IMs are typically related to the characteristics of ground shaking and structural dynamic properties, with the spectral acceleration at the first and dominant mode of vibration, Sa(T1), being a popular choice for buildings. In bridge structures, where no single dominant mode typically exists for bridges with some degree of irregularity, the use of Sa(T1) may be inefficient (i.e. large dispersion) due to multi-modal transverse response. To avoid having to choose a single bridge mode when using Sa(T1) and to appease the needs of bridge portfolio assessment, peak ground acceleration (PGA) can often be the IM used for bridge fragility functions in some countries. This study examines the efficient assessment of simple bridge structures characteristic of the European context by exploring different IMs based on Sa(T), peak ground velocity (PGV) or a recent candidate average spectral acceleration, AvgSa. Several case study bridges are evaluated via multiple stripe analysis with hazard-consistent ground motion records. The results indicate that PGA and PGV are indeed inefficient IMs compared to other IMs of similar complexity, especially at serviceability limit states, for the bridge structures examined. Also, a relatively casual record selection strategy is seen to not be suitable for risk assessment of bridges and can result in notable differences in risk. In contrast, AvgSa, which is an IM based on a simple combination of Sa(T) values across a range of periods, showed very good predictive power and robustness in terms of its risk estimates across all ranges of structural response. This was observed for the structure-specific IMs in addition to the group IMs used for assessing multiple structures with the same ground motion records. This study has thus shown these AvgSa-based IMs to be an appealing choice to consider for further examination in future fragility function and risk model development for bridge structures.

Updated probabilistic seismic performance assessment framework for ordinary standard bridges in California

AbstractWith the recent advent of performance‐based earthquake engineering (PBEE) in seismic design practice of buildings serving as an impetus for this work, initial steps toward a fully probabilistic performance‐based seismic design (PBSD) method for bridges, a less trodden area in terms of PBEE applications, are taken herein by assembling an updated probabilistic seismic performance assessment framework for ordinary standard bridges (OSBs) in California. The framework stems from the comprehensive PBEE methodology developed under the auspices of the Pacific Earthquake Engineering Research (PEER) Center. With performance measures defined as the risk associated with the exceedance of a set of damage/limit‐states (LSs), improvements from the state‐of‐the‐art literature on the PEER PBEE methodology are incorporated, including (1) introduction of an improved intensity measure ‐ average spectral acceleration over a period range, (2) conditional mean spectrum‐based hazard‐consistent and site‐specific ground motion selection, (3) introduction of material strain‐based engineering demand parameters, (4) use of practical LSs pertinent to seismic damage evaluation of bridges, and (5) development of strain‐based normalized fragility functions for the considered LSs. The updated framework, assembled herein using a specific testbed California OSB as a case in point, is general within its scope and is applicable to the gamut of design situations representative of the population of OSBs in California. With the PEER PBEE framework implemented for OSBs in an updated and rigorous form, the groundwork for utilizing this framework in the context of PBSD of such bridges is laid.

FOSID: a fractional order spectrum intensity for probabilistic seismic demand modeling of extended pile-shaft-supported highway bridges under liquefaction and transverse spreading

An appropriate seismic intensity measure (IM) for response prediction is central to reliable probabilistic seismic demand modeling of structures and subsequently, risk and resilience quantification. Bridges in liquefiable and laterally spreading ground may undergo nonlinear responses with large uncertainties when subjected to earthquakes. These issues often lead to low-confidence demand models based on traditional IMs. Fractional order IMs have shown the potential to yield improved demand models in recent studies. To further increase confidence in demand models, this study proposes Fractional Order Spectrum intensity considering Integral period and Damping ratio (named FOSID). The viability of FOSID for use in probabilistic seismic demand modeling of structures is evaluated in the context of extended pile-shaft-supported bridges against liquefaction-induced lateral spreading. The performance of FOSID is systematically assessed by comparisons to an existing fractional order spectrum intensity (SIr,α), Housner intensity (HI)—an optimal traditional IM for these structures, and the average spectral acceleration (Saavg)—a state-of-the-art non-fractional-order IM. Multiple metrics for characterizing an optimal IM are adopted, including practicality, efficiency, proficiency, sufficiency, and relative sufficiency. Optimal variables of integral period, damping ratio, and fractional order for FOSID are identified for different demand parameters such as peak and residual column-drift-ratios. Results show that FOSID is generally more practical, efficient, proficient and sufficient than SIr,α, HI and Saavg. In particular, FOSID significantly outperforms HI by improving the proficiency by nearly 40% and 20% for the peak and residual column-drift-ratios, respectively. With respect to SIr,α, FOSID improves the proficiency by 20% and 15% on average. When compared with Saavg, such improvements are as large as 13% and 24% on average for the peak and residual column-drift-ratios, respectively.

Limitations of Sa(T1) as an intensity measure when assessing non-ductile infilled RC frame structures

An important decision in seismic risk assessment involves a good choice of intensity measure (IM) used to describe ground motion intensity. Depending on the structural typology and type of analysis, the choice of an optimal IM may differ. Ideally, it should have accurate response predictions and not be biased by parameters like scaling factors or other ground motion characteristics. This article investigates this topic in the context of non-ductile reinforced concrete (RC) frames with masonry infills. It examines several case study structures with IMs like peak ground acceleration (PGA), peak ground velocity (PGV), first mode spectral acceleration, Sa(T1), and average spectral acceleration, AvgSa. It reveals PGA and PGV to possess undesirable traits relating to inefficiency, sensitivity to scaling and dependence on other ground motion parameters. Sa(T1) is shown to be an optimal IM at lower intensities, but runs into difficulty once the infill panels collapse and a non-ductile mechanism forms in the structure. Further investigation shows that the response is strongly biased by the velocity-based characteristics of the record upon infill panel collapse when using Sa(T1). On the other hand, AvgSa is seen to possess many of the same benefits regarding efficient response prediction for both intensity-based assessment and fragility function development but is not biased by the ground motion velocity-based characteristics. In light of this, this study presents a case for the traditional IM Sa(T1) to be set aside and for a more promising alternative in AvgSa to be adopted when analysing existing infilled RC frames.

Micro-seismic hazard assessment of Ahmedabad city, Gujarat (Western India) through near-surface characterization/soil modeling

The micro-seismic hazard estimation including quantification of the ground motion amplification has been conducted at Ahmedabad city based on near-surface characterization/soil modeling. The city has experienced substantial damage in the course of the 2001 Bhuj earthquake. A total of 20 boreholes were drilled in the city up to the depths of 40–80 m. A five-fold methodology is adopted: (1) Assessment of the seismic perspective of the area under study, (2) demarcation of the engineering bed layer (EBL) through geophysical (seismic) surveys and the soil properties, (3) soil modeling using geotechnical and the geophysical parameters, (4) assessment of the strong ground motion at EBL through simulation considering far-field earthquake scenarios and near-field earthquakes scenario and (5) surface strong-motion estimation by ground response analysis based on equivalent-linear approach. The near-surface soil models were prepared from the borehole logs, shear-wave velocity estimated from the seismic survey and the soil properties like soil classification and density. The strong motion at EBL is computed by simulating seismotectonically justified scenario earthquakes through the stochastic finite-fault source modeling technique using the region-specific input parameters. The surface-strong motion is estimated by performing ground response analysis (with SHAKE) at every borehole using EBL-strong motion and prepared soil models. The EBL was found varying from 28 to 54 m in depth in Ahmedabad city. The effect of far-field and near-field earthquake sources was considered for assessing the hazard. To compensate for the uncertainty, a total of 108 and 81 input parametric combinations for near-field earthquake scenarios, and far-field earthquake scenarios, respectively have been considered for estimating the strong motion at EBL. The peak ground acceleration (PGA) of 52–111 cm/s2 and 108 cm/s2 are estimated at EBL due to near-field earthquake scenarios and far-field earthquake scenarios, respectively. The PGA through ground response analysis at surface level is found to be varying from 101 to 279 cm/s2 for near-field earthquake scenarios and, 118–161 cm/s2 for the far-field earthquake scenarios. The spectral acceleration (SA) (at surface level) has also been calculated for damping of 5%. The average SA distribution maps for 0.2 s (1–2 story), 0.55 s (4–5 story), 1 s (high rise) and 1.25 s period (large structures) have been prepared for both types of scenario earthquakes. The strong motion amplification is computed to be in the range of 1.6–3.3 for near-field earthquake scenarios and 2.2–3.0 for near-field earthquake scenarios.

Multi‐criteria decision making for seismic intensity measure selection considering uncertainty

SummarySeismic intensity measure (IM) selection is associated with consideration of multiple criteria, and there are uncertainties within the selection process. In this paper, a novel multi‐criteria decision making (MCDM) approach by incorporating stochastic multi‐criteria acceptability analysis (SMAA) with technique for order preference by similarity to ideal solution (TOPSIS) is proposed to solve the stochastic decision making problem of IM selection. TOPSIS provides an alternative rank function, and the SMAA is used to address the uncertainties within the IM selection. The performance criteria (e.g., efficiency, proficiency, practicality, sufficiency, and correlation) are evaluated for the investigated structural components, and the decision matrix is formulated based on the criteria of each IM alternative. Furthermore, the importance of the component to system reliability is quantified in a probabilistic manner using nonlinear time history analysis and serves as the weighting factors in MCDM stage. The holistic acceptability indices indicating the overall acceptability levels of IM alternatives are computed by the proposed approach. Additionally, the effects of different IMs (e.g., average spectral acceleration, peak ground velocity, and spectral acceleration) on probabilistic seismic loss and resilience are investigated to further support the IM selection. The proposed approach is illustrated on a highway bridge, and the results are presented.