Seismic Risk Assessment Study Research Articles

Capacity curves for monitored existing buildings and within- and between-building variability of secant stiffness

In this study, accelerometric data from seven Japanese buildings under long-term monitoring were analysed to explore the variability of the buildings’ co-seismic response over time and its within- and between-building components, using co-seismic capacity curves developed in acceleration-displacement-response-spectrum format. The data include the 2011 Tohoku Mw9.1 earthquake, which caused building damage of different levels of severity, and the time-varying actual capacity curves were analysed considering earthquakes before and after 2011. Result showed that the initial slope of the capacity curves reflects the amount of damage. The between-building and within-building components of the variability are discussed by comparing a single building and several buildings in the same class for several earthquakes. Finally, the epistemic uncertainty of seismic risk assessment studies is discussed in relation to the selection of a generic capacity model for all buildings in a single class.

Reference prior for Bayesian estimation of seismic fragility curves

One of the key elements of probabilistic seismic risk assessment studies is the fragility curve, which represents the conditional probability of failure of a mechanical structure for a given scalar measure derived from seismic ground motion. For many structures of interest, estimating these curves is a daunting task because of the limited amount of data available; data which is only binary in our framework, i.e., only describing the structure as being in a failure or non-failure state. A large number of methods described in the literature tackle this challenging framework through parametric log-normal models. Bayesian approaches, on the other hand, allow model parameters to be learned more efficiently. However, the impact of the choice of the prior distribution on the posterior distribution cannot be readily neglected and, consequently, neither can its impact on any resulting estimation. This paper proposes a comprehensive study of this parametric Bayesian estimation problem for limited and binary data. Using the reference prior theory as a cornerstone, this study develops an objective approach to choosing the prior. This approach leads to the Jeffreys prior, which is derived for this problem for the first time. The posterior distribution is proven to be proper (i.e., it integrates to unity) with the Jeffreys prior but improper with some traditional priors found in the literature. With the Jeffreys prior, the posterior distribution is also shown to vanish at the boundaries of the parameters’ domain, which means that sampling the posterior distribution of the parameters does not result in anomalously small or large values. Therefore, the use of the Jeffreys prior does not result in degenerate fragility curves such as unit-step functions, and leads to more robust credibility intervals. The numerical results obtained from two different case studies—including an industrial example—illustrate the theoretical predictions.

Spatial correlation models of VS30 values: A case study of the Tehran region

The average shear wave velocity of the top 30 m of soil profile (VS30) is considered as an indicator of local-site effects in seismic hazard assessment (SHA) studies. Previous research works have demonstrated that in addition to actual VS30 values, their spatial correlation characteristics have considerable effects on the estimated values of earthquake intensity measurements, particularly when the seismic risk assessment of spatially distributed assets and infrastructure networks is of interest. Tehran city, in addition to its proximity to several faults, is situated on a variety of sedimentary textures and encompasses a large number of residential buildings and infrastructure networks. The current study utilizes advanced spatial statistics methods and investigates the spatial correlation characteristics of the random field of VS30 values in Tehran. Moreover, by employing a more comprehensive database of VS30 values measured using geoseismic approaches and using eight spatial interpolation methods, a new estimated VS30 map of Tehran city is provided. The geological formations of the study area are also investigated considering the distribution of sample points with different VS30 values. The findings of the current research can be utilized in spatially correlated SHA studies in the Tehran region and can be viewed as a step towards filling the data gap required for seismic risk assessment studies in this region. Moreover, by identifying the local variations in site classes, the findings of the current study can be used for further detailing of geological formations.

Adaptive knowledge-based seismic risk assessment of existing reinforced concrete buildings using the SLaMA method

This paper presents and discusses the ongoing developments towards the definition of a multi-knowledge level seismic assessment procedure for large-scale seismic risk applications. The procedure involves the analytical-mechanical SLaMA (Simple Lateral Mechanism Analysis) method and allows for an adaptive and updatable assessment of the seismic performance of buildings accounting for different data acquisition (knowledge) levels. By coupling this approach with vulnerability assessment survey forms, a range/domain of expected capacity curves of a structure can be obtained and used to evaluate the seismic safety and the expected economic losses according to the state-of-the-art procedures in literature. Moreover, the results of the analytical assessment method can be used to develop fragility curves through simplified spectrum-based procedures. Combining the results of the fragility analysis with the hazard analysis, the seismic risk of a structure can be assessed in terms of Mean Annual Frequency (MAF) of collapse, as well as in terms of Expected Annual Losses (EAL). The proposed SLaMA-based approach is illustrated for an existing reinforced concrete building. Results confirm the effectiveness of the methodology for seismic-risk assessment studies at large scale, thus overcoming the issue related to limited building information, yet allowing for a continuous update of the “digital twin” model as further data/information becomes available.

Seismic Risk Assessment of Nagpur City using the Geographic Information System

Earthquakes are the major threat to mankind accounting for almost half of the fatalities brought about by all of the natural hazards and desert their traces in societies for years. It is well known that seismic risk cannot be eliminated but minimized. Risk studies lay down the roadmap to prepare and minimize the aftermath of any disastrous event. Geographic Information System (GIS) has been proved as an effectual tool for seismic risk assessment study. This study presents the seismic risk assessment of Nagpur city using the GIS framework. Albeit per Indian Standard (IS) 1893-2016 [1] seismic zonation of Nagpur city comes under zone II (relatively low seismic hazard zone), the seismic risk being a combination of hazard, elements at risk and, vulnerability cannot be denied. Similar to other Indian cities the city of Nagpur had a heterogeneous development pattern. Even though Nagpur city is municipalized in well distributed wards, many intra wards distributions show housing clusters of different socioeconomic status. Therefore, using the satellite imagery different socioeconomic housing clusters were identified and mapped in the ArcGIS platform. Six socioeconomic clusters were identified using satellite imagery for Nagpur. From the field survey of randomly selected typical clusters, 14 prevailing Model Building Types (MBTs) were identified. Census data were used to find the population density and its distribution throughout the city. Seismic hazard has been estimated from IS 1893-2016 [1] as well as using the probabilistic hazard map of NDMA [2]. Selected MBTs were assessed for their seismic vulnerability, seismic risk in terms of casualties and damage is calculated. Finally, thematic maps showing damages arrived from the various approach are shown and discussed.

Seismic fragility assessment of high-rise stacks in oil refineries

The seismic fragility is assessed for typical high-rise stacks encountered in oil refineries, namely process towers, chimneys, and flares. Models of varying complexity were developed for the structures of interest, attempting to balance computational complexity and accuracy regarding the structural dynamic and strength properties. The models were utilized along with a set of hazard-consistent ground motions for evaluating the seismic demands through incremental dynamic analysis. Demand/capacity-related uncertainties were explicitly accounted for in the proposed framework. Damage states were defined for each of the examined structure considering characteristic serviceability and ultimate limit states. Τhe proposed resource-efficient roadmap for the analytical seismic fragility assessment of typical high-rise stacks, as well as the findings of the presented research work are available to be exploited in seismic risk assessment studies of oil refineries.

Development of hybrid earthquake vulnerability functions for typical residential buildings in Iran

Residential building stock in Iran, with its diverse types, is exposed to different earthquake events each year that necessities the implementation of disaster risk reduction measures. Conducting seismic risk assessment studies, on the other hand, is crucial as one of the main perquisites of any earthquake disaster risk reduction efforts. Seismic risk assessment is an approach that requires dependable fragility or vulnerability functions, and the more valid these models are, the more realistic the risk assessment results would be. The main objective of the current study is to provide new hybrid seismic vulnerability models for typical residential buildings in Iran. In this regard, existing peer-reviewed fragility or vulnerability models are utilized as basic models besides the damage records of recent earthquake events in Iran. The logic tree approach is used to combine the basic models, and 26 seismic vulnerability models are developed based on three main attributes of material type, construction quality, and building height. The developed models are functions of PGA and are in the form of the cumulative lognormal distribution function. Additionally, the most recent national census data (2016) are utilized to combine vulnerability models via the logic tree approach and develop quality-independent vulnerability models that can be used in circumstances when precise information about the construction quality of buildings is not available. Developed models are finally validated using the real building damage data collected from the records of recent significant earthquake events in Iran.

Development of analytical seismic fragility functions for the common buildings in Iran

One of the main components for developing regional seismic risk models is the fragility functions of common building types. Due to the differences between the national design codes, construction practices, and construction materials, it is necessary to develop specific fragility functions for the common building types which are constructed in each region. For this reason, the present study is devoted to filling this essential gap for Iran. Therefore, in the first step, the existing building types in the country are classified into 31 categories regarding material, lateral-load-resisting system, height, and code level. Also, by conducting comprehensive studies on all previously performed research in the country, structural and dynamic parameters have been collected for buildings in each class. This information was used to compute a large set of backbone curves for Iranian buildings taxonomy. Then nearly three hundred appropriate fragility functions were generated using non-linear time-history analyses on the generic backbone curves and a large set of ground motion records. Based on the existing empirical data from past earthquakes in the country, the validation of the resulting fragility functions was carried out. The resulted fragility functions can be utilized in seismic risk assessment studies in the country.

Seismic Fragility Functions for Non-Seismically Designed RC Structures Considering Pounding Effects

The proposed study develops fragility functions for non-seismically designed reinforced concrete structures considering different pounding configurations. The study addresses an existing research gap, since large-scale seismic risk assessment studies involving the seismic performance assessment of building portfolios usually do not involve fragility functions accounting for the possibility of pounding. The selected structures include configurations involving different separation distance values and exhibiting floor-to-floor pounding, floor-to-column pounding, pounding between structures with a significant height difference, and pounding between structures with a significant mass difference. The behaviour of these pounding configurations was analysed using incremental dynamic analysis and compared with that of the corresponding control cases (i.e., individual structures with no interaction with other structures). The results indicate the type of failure mechanism that contributes to the global collapse of the different configurations and the influence of the separation distance. Results highlight the main differences between the expected performance of different pounding configurations with respect to the occurrence of the failure mechanism that governs their collapse. Finally, results indicate that large-scale seismic risk assessment studies should consider fragility functions accounting for different pounding configurations when the possibility of pounding is not negligible, except in cases involving floor-to-floor pounding.

Seismic Vulnerability Assessment of Portuguese Adobe Buildings

Adobe construction represents 5.3% of the total Portuguese building stock according to the latest National Housing Census. The distribution of these adobe buildings is scattered across the country, with higher density in the central region and in Algarve in the south, where the seismic hazard is highest. A large proportion of these buildings are still in use for residential and commercial purposes and are of historical significance, contributing to the cultural heritage of the country. Adobe buildings are known to exhibit low seismic resistance due to their brittle behavior, thus making them vulnerable to ground shaking and more prone to structural damage that can potentially cause human fatalities. Three buildings with one-story, two-stories, and two-stories plus an attic were numerically modeled using solid and contact elements. Calibration and validation of material properties were carried out following experimental results. A set of 30 ground motion records with bi-directional components were selected, and non-linear time-history analyses were performed until complete collapse occurred. Two novel engineering demand parameters (EDPs) were used, and damage thresholds were proposed. Finally, fragility and fatality vulnerability functions were derived. These functions can be used directly in seismic risk assessment studies.

Seismic risk and loss estimation for the building stock in Isfahan. Part I: exposure and vulnerability

This paper focuses on the exposure and fragility/vulnerability of the residential, mixed residential/commercial, and public building stock of the city of Isfahan, in Central Iran, and constitutes the first part of a seismic risk assessment study for that city. To determine the assets at risk, we first summarize the details of the building stock and population from the available georeferenced 2011 Census data. From this dataset and from a local survey of the city, we categorize the building taxonomy in 27 construction classes characterized by age, height, and material/lateral-load-resisting system. A building exposure model is then assembled by first dividing Isfahan in city blocks and then by assigning the appropriate statistical properties to the buildings, such as construction class, built area, and replacement cost. The population of each city block is also estimated and accounted for. To assess the fragility and vulnerability to earthquake ground motion, for each building class we performed nonlinear dynamic analysis of multiple equivalent single-degree-of-freedom systems. This process generated a set of class- and region-specific fragility and vulnerability functions that considered both record-to-record and building-to-building response variability. In the companion paper we used the exposure model and the fragility and vulnerability curves generated for all these asset classes to probabilistically assess the seismic risk of Isfahan.

Seismic risk and loss estimation for the building stock in Isfahan: part II—hazard analysis and risk assessment

The second part of a seismic risk assessment study for the Iranian city of Isfahan is presented, focusing on the description of the hazard, the risk analysis, and the discussion of the results. This study utilizes the building exposure model, the fragility and the vulnerability curves illustrated in the companion paper. The earthquake occurrence source model adopted is based on the EMME14 hazard study. The site effects accounting for the soil nonlinear behavior are modeled by means of a Vs30 map derived from the topographical slope. The validity of this map is tested based on the local surface geology and geotechnical reports. The probabilistic seismic hazard maps for different return periods that account for site effects are generated and compared with the design spectra mandated by the Iranian national seismic design code. In addition, direct seismic monetary and human losses are estimated for two earthquake scenarios and also for 100- and 475-year return periods. We show loss maps and loss curves, offering insights on the most vulnerable building classes and the spatial distribution of the estimated losses. The results provide a basis for pre- and post-disaster emergency planning, for global and local urban planning, as well as for conceiving adequate risk mitigation strategies including devising fair earthquake insurance policies. This study may also serve as a blueprint for carrying out similar work in other urban areas of the Middle East.

A computational workflow for rupture‐to‐structural‐response simulation and its application to Istanbul

AbstractScenario‐based earthquake simulations at regional scales hold the promise in advancing the state‐of‐the‐art in seismic risk assessment studies. In this study, a computational workflow is presented that combines (i) a broadband Green's function‐based fault‐rupture and ground motion simulation—herein carried out using the “UCSB (University of California at Santa Barbara) method”, (ii) a three‐dimensional physics‐based regional‐scale wave propagation simulation that is resolved at Hz, and (iii) a local soil‐foundation‐structure finite element analysis model. These models are interfaced with each other using the domain reduction method. The innermost local model—implemented in ABAQUS—is additionally enveloped with perfectly matched layer boundaries that absorb outbound waves scattered by the structures contained within it. The intermediate wave propagation simulation is carried out using Hercules, which is an explicit time‐stepping finite element code that is developed and licensed by the CMU‐QUAKE group. The devised workflow is applied to a km region on the European side of Istanbul, which was modeled using detailed soil stratigraphy data and realistic fault rupture properties, which are available from prior microzonation surveys and earthquake scenario studies. The innermost local model comprises a chevron‐braced steel frame building supported by a shallow foundation slab, which, in turn, rests atop a three‐dimensional soil domain. To demonstrate the utility of the workflow, results obtained using various simplified soil‐structure interaction analysis techniques are compared with those from the detailed direct model. While the aforementioned demonstration has a limited scope, the devised workflow can be used in a multitude of ways, for example, to examine the effects of shallow‐layer soil nonlinearities and surface topography, to devise site‐ and structure‐specific seismic fragilities, and for calibrating regional loss models, to name a few.

Correlation of earthquake intensity measures and spectral displacement demands in building type structures

Seismic damage and its correlation with the earthquake intensity measures (IMs) are important for both record selection and probabilistic seismic risk assessment studies. A lot of studies considering the various structural properties were performed to investigate the correlations of mainly PGA and PGV under different strength reduction (R) and ductility factors (μ). In this study, correlation of many scalar IMs named as PGA, PGV, arms, vrms, drms, Ia, CAV, ASI, SI are studied. Building represented by single degree of freedom (SDOF) models were classified according to lateral strength ratios (Vt/W), ratio of strength capacity at yield (Vt) to seismic weight (W), varying from 10% to 50%. Effects of post yield stiffness capacities, hysteretic behavior type and the soil properties on deformation demand of SDOF models are also taken into account. Post yield stiffness ratios of 0%, 5% and 10% considered and assigned to building models. Elastic-perfectly plastic and modified Clough hysteretic models were used in the non-linear dynamic analyses. Strong motion records obtained from firm and soft soil sites were classified according to Vs30 and inelastic deformation demands obtained from both soil conditions are calculated and compared. Variation of correlation coefficients of different IMs indicates that SI is the best earthquake parameter especially along the period range of 0.5–2 s which can be thought to represent building type structures. Furthermore, it was observed that sensitivity of SI parameter to post yield stiffness, hysteretic behavior type and the soil properties is very limited with respect to considered IMs. Correlation coefficients obtained from SDOF models are compared to that of multi-story buildings and the compatibility of both SDOF and MDOF models are presented.

An improved model for seismic risk assessment in Portugal

PurposePortugal experienced very destructive earthquakes in the past, such as the well-known “Lisbon earthquake” in 1755. With such in mind, accurate estimates of human and economic losses can play a significant role in providing various societal key players with objective information for response strategies. This paper aims to present the contribution of the most recent study in Portugal (PRISE) concerning comprehensive seismic risk assessment, which can be used as good practice and reproduced in different contexts.Design/methodology/approachPRISE (earthquake loss assessment of the Portuguese building stock) covered three main lines of research, corresponding to the three components typically considered in any seismic risk assessment study: the characterization of the seismic hazard, the identification of the exposure to earthquakes and loss potential and the vulnerability of the exposed assets. Each of these components has been fully characterized through the collection of census and local data (exposure), used to carry out nonlinear analysis (hazard and fragility).FindingsBy involving different research institutions and partners with extensive knowledge and expertise in the earthquake domains, the developed model is capable of producing economic and human earthquake loss estimates in real time (through an innovative Web-based platform) or for specific event scenarios, considering exposed population, residential and industrial buildings. The platform uses open-source tools and hence, it can be reproduced in other countries or contexts.Research limitations/implicationsResearch wise, the hazard, vulnerability and exposure models can still be significantly improved, e.g. by adding critical infrastructure (hospitals, school buildings and bridges) or updating the nonlinear models, for more accurate loss predictions.Practical implicationsThe findings and loss estimates for different earthquake scenarios show that planned interventions are required. Decision-makers and other relevant stakeholders (Civil Protection) can make use of the developed platform to produce specific estimates, to test the effect of different retrofitting interventions or to plan for emergency scenarios.Originality/valueA real-time Web-based framework to estimate building damage and economic/human losses because of seismic events has been developed, aiming to provide the Portuguese Civil Protection and other playmakers with a unique platform for planning and preparing for emergency scenarios.

Seismic risk assessment at urban scale from 3D physics-based numerical modeling: the case of Thessaloniki

The main aim of this work is to present a prototype of seismic risk assessment study at urban scale which incorporates next generation tools for hazard assessment, with application to the city of Thessaloniki, Northern Greece. The key ingredient of the proposed approach is the characterization of earthquake ground motion by means of three-dimensional broadband physics-based numerical simulations, which explicitly account for the fault rupture, the propagation path in heterogeneous media and complex geological conditions. The seismic damage of contemporary reinforced concrete building stock of the city of Thessaloniki has been evaluated using the capacity spectrum method, for a scenario corresponding to the destructive historical earthquake of June 20th 1978 (MW 6.5). Although the vulnerability model considered in these analyses reflects the contemporary building stock and, hence, differs from the situation at the time of the earthquake, the soundness of our damage estimates has been successfully verified through the comparison with the post-1978 earthquake damage observations. Results of this study demonstrate that 3D physics-based simulations can provide a more accurate and detailed characterization of earthquake ground motion and of its spatial variability, as compared to standard empirical approaches, and can be effectively used to improve seismic risk studies for strategic urban areas.

Analytical fragility curves for non-skewed highway bridges in Chile

Recent earthquakes in Chile and worldwide have caused significant economic losses due to the damage on the road bridge network. To conduct seismic risk assessment studies and to improve resilience of bridges, seismic vulnerability studies are required. The main objective of this study is to construct fragility curves of typical non-skewed highway bridges in Chile. The fragility curves are obtained from an incremental dynamic analysis of a two-dimensional model of the bent cap of a two-span simply supported underpass. As most bridges are constructed with seismic tie-down bars, their constitutive behavior was obtained experimentally. A total of five seismic bar specimens were tested to characterize their cyclic behavior in bridges with and without transverse diaphragms. The incremental dynamic analysis was performed with the two horizontal components of seven seismic records obtained from the Mw 8.8, 2010 Chile earthquake. Additionally, a parametric study is conducted to assess the seismic behavior of bridges with different configurations of seismic bars, with lateral stoppers, and with varying length of the transverse seat width. Results from this study reveal that seismic bars have a limited contribution to the seismic performance of the studied bridge, especially when lateral stoppers are incorporated. Additionally, the transverse seat width is found to be critical to reduce the collapse probability of the superstructure. The provided fragility curves may be used for seismic risk assessment and to evaluate possible improvements in seismic bridge design codes.

Ambient noise H/V spectral ratio in site effects estimation in Fateh jang area, Pakistan

Local geology or local site effect is a crucial component while conducting seismic risk assessment studies. Investigations made by utilization of ambient noise are an effective tool for local site estimation. The present study is conducted to perform site response analysis at 13 different sites within urban settlements of Fateh jang area (Pakistan). The aim of this study was achieved by utilizing Nakamura method or H/V spectral ratio method. Some important local site parameters, e.g., the fundamental frequencies f 0 of soft sediments, amplitudes A 0 of corresponding H/V spectral ratios, and alluvium thicknesses over 13 sites within the study area, were measured and analyzed. The results show that the study area reflects low fundamental frequency f 0. The fundamental frequencies of the sediments are highly variable and lie in a range of 0.6–13.0 Hz. Similarly, amplification factors at these sites are in the range of 2.0–4.0.

From regional- to local-scale seismic hazard assessment: examples from Southern Spain

An approach that relates results from a regional seismic hazard assessment study with local-scale site-effect characterizations in an area of low-to-moderate seismic activity such as Andalusia (southern Spain), is presented. Results of a previous probabilistic seismic hazard analysis of Andalusia on rock conditions are disaggregated to infer hazard controlling earthquakes for different target motions. A collection of controlling magnitude-distance pairs and the corresponding site-specific response spectra at main capital cities of the region are obtained. These spectra are first-order approximations to expected seismic actions required in local earthquake risk assessments. In addition, results of independent, local-scale studies developed in Almeria City (SE Andalusia) are used to derive an updated seismic zonation of the city. These include predominant soil period estimates and shear-wave velocity profiles at different locations. If a local seismic risk assessment study or an earthquake-resistant structural design is to be developed, it may be recommended the use of different seismic actions on sites characterized by distinct response to seismic shaking (as derived from the seismic zonation). The seismic action related to worst-case scenarios may be modeled through a hazard-consistent response spectrum, obtained by hazard disaggregation at the spectral acceleration with period matching the prevailing resonant period of the target site or structure.

Regional seismic risk in British Columbia — damage and loss distribution in Victoria and Vancouver

This paper presents the results of regional seismic risk assessment studies that were carried out for two cities in southwestern British Columbia, Vancouver and Victoria. Ground shaking intensity in the area was obtained using the seismic source zones delineated by the Geological Survey of Canada for a probability level of 10% chance of exceedance in 50 years. Building inventories were compiled by aggregating data from sidewalk surveys as well as municipal databases. Modified Mercalli intensity-based damage matrices that relate the level of ground shaking to the amount of damage expected in different types of structures were used to estimate damage to structural and non-structural components of buildings. Estimated damage and loss distributions were mapped on a block-by-block basis. The historic sections of the cities were estimated to have damage levels between 10% and 30% of the replacement cost, while in the rest of the cities the estimated damage was generally in the 5% to 10% range. The results show the estimated economic loss distribution is considerably different from the damage distribution. Although the older neighbourhoods of the cities are expected to suffer highest amount of damage, the highest amount of economic loss is estimated to occur in areas with concentration of concrete high-rise buildings.Key words: seismic hazard, seismic risk, vulnerability, earthquake, damage, loss, probability, modified Mercalli intensity.