Empirical Fragility Curves Research Articles

Empirical fragility curves for houses in Chile using damage data from two earthquakes

Empirical fragility curves for houses in Chile using damage data from two earthquakes

Development of seismic fragility curves for hospital buildings using empirical damage observations

Fragility curves are widely recognized as an essential tool for assessing and projecting asset damage, vulnerability, and seismic risk. The technical literature provides different fragility curves for residential buildings that exhibit unique characteristics for different categories of buildings, however, comparatively fewer curves are available for hospital buildings. The specific design criteria for hospital buildings necessitate specialized fragility curves for them. In the current study, a set of empirical fragility curves for hospitals have been developed utilizing the data of 341 damaged hospital buildings in previous earthquakes. The peak ground acceleration of the occurred earthquake events in the location of the considered hospitals is utilized as earthquake intensity measure. Fragility curves are developed for the three categories of low-rise concrete moment frame, medium-rise concrete moment frame, and masonry hospital buildings. Due to the lack of appropriate available data, the fragility curves of masonry hospitals are developed by merging the collected data with the fragility curves acquired from the existing literature. The creation of fragility curves for non-structural components of hospitals is another contribution of this study. Finally, a comparison of the fragility curves derived in the current study with those documented in existing research papers is provided.

Monte Carlo analysis of masonry structures under tsunami action: Reliability of lognormal fragility curves and overall uncertainty prediction

Tsunami vulnerability of coastal buildings has gained more and more interest in recent years, in the consciousness of what losses may be caused. The improvement of the available approaches for the quantitative estimation of the probability of building damage and for defining possible strategies for risk mitigation is an actual goal. In this framework, several authors have provided empirical fragility curves based on field surveys after tsunamis. Nevertheless, a predictive approach based on analytical fragility curves, which can be extended to many classes of buildings, is essential for the scopes of civil protection and risk mitigation. In this paper, an approach for the construction of fragility curves, proposed for masonry structures under tsunami waves, is discussed and refined in the part regarding the assignment of the uncertainties. Further, an assessment of the reliability of the lognormal fragility distribution is carried out based on a Monte Carlo simulation applied to 4 classes of buildings. Here, it is shown that Monte Carlo analysis allows a direct evaluation of the uncertainties without the need to resort to ambiguous regression analyses and rules of combination of the uncertainties of demand and capacity based on the regression analysis results or other uncertainty estimation approaches.

Seismic Resilience Scenario of Algerian Buildings’ Context: Blida City Case Study

Several studies have been carried out to assess the building’s seismic vulnerability, to mitigate the seismic risk in urban areas, which is one of the most devastating natural hazards causing considerable economic and human losses. These studies must be incorporated to improve the planning of urban areas to have resistant and resilient cities in case of disasters. The seismic feedback has shown that the build-back-better concept has a direct impact on the city’s economic growth. In this paper, the existing buildings’ resilience is assessed, in order to highlight the capacity of these last to keep the functionality when an earthquake occurs. This building’s resilience has been determined for three types of structures: masonry, reinforced concrete and steel, according to the reconstruction time, the reconstruction cost and the damage state. This last has been assessed from empirical fragility curves developed using the log normal distribution for five structures typologies (Unreinforced masonry; reinforced masonry; RC frame; RC shear walls/Mixed RC frame-RC shear walls and steel structures). A seismic resilience scenario was performed using a geographic information system (GIS) and applied for the Blida city (Algeria) classified as a high seismic zone according to Algerian seismic regulations. According to the results found, the old districts of the Blida city, built mainly during the so-called pre-code period, will not be resilient in case of disaster. The other districts built later in the low-code and high-code periods will have, respectively, medium and good functionality.

Empirical Fragility Analysis of Haitian Reinforced Concrete and Masonry Buildings

This study develops empirical fragility curves for concrete and masonry buildings in Haiti, utilizing data from the 2021 earthquake. A dataset of 3527 buildings from the StEER database, encompassing a diverse range of building types, is used. These buildings types include reinforced concrete structures with masonry infills, confined masonry buildings, reinforced masonry bearing walls, and unreinforced masonry bearing walls. Shakemaps from the USGS are utilized to assess the earthquake’s intensity at each building, with the peak ground acceleration (PGA) as the intensity measure. Damage is classified into five distinct states: no damage, minor, moderate, severe, and partial or total collapse. For each of these states, the corresponding probabilities of exceedance are calculated, and log-normal cumulative distribution functions were fitted to those data to produce empirical fragility curves. The results show a notable similarity in performance among the four types, each having high probability of failure even under low-intensity earthquakes. Total fragility curves (including all four building types) are developed subsequently and they are convolved to the probabilistic seismic hazard map of Haiti to assess the seismic risk. This includes estimating the annual probability of partial/total collapse and the probability of partial/total collapse in the event of 475-year and 2475-year earthquakes. The results indicate a significant risk, with up to 64% probability of collapse in certain areas for the 2475-year earthquake and a probability of collapse of 15% for a 475-year earthquake. These findings underscore the critical vulnerability of Haiti’s buildings to seismic events and the urgent need for their retrofit.

Research on seismic fragility of subway station based on incremental dynamic analysis method

Seismic intensity measure is an significant parameter that affects the accuracy of structural seismic risk assessment, and plays an important role in the performance-based earthquake engineering research framework. Taking a two story, three span, and shallow buried subway station as the research object, a two-dimensional finite element analysis model of soil structure underground in a typical engineering site was established using ANSYS. Ten earthquake records were selected from PEER as input, and the structural seismic fragility analysis method based on incremental dynamic analysis (IDA) method was introduced into the subway station structure. The maximum story drift angle was used as the structural damage index, and three typical seismic intensity measures were selected, the exploration is conducted on the seismic intensity measures applicable to shallow buried subway stations and the variation pattern of seismic response of subway stations with increasing seismic amplitude. The seismic fragility curve of shallow buried subway station structures is established to obtain the failure probability of the structure at different seismic intensity levels. The analysis results indicate that for shallow buried subway stations, PGA is the most suitable seismic intensity measure, and the comparison with existing empirical fragility curves shows that the vulnerability analysis method is feasible and can quantitatively provide the failure probability of structures at different performance levels, providing reference for seismic design of underground structures.

Empirical fragility curves for masonry churches and their macro-elements using a large database: Proposal of a new likelihood function

Several earthquakes have highlighted over time the high vulnerability of masonry churches to horizontal actions, so that more and more research is being devoted to the assessment of their seismic response and to the design of strengthening interventions to guarantee their preservation.This paper analyses in detail the damage suffered by a large sample of 2870 masonry churches hit by the 2016–17 Central Italy seismic sequence, using the damage data extracted from the DaDO Web GIS. Fragility curves based on the empirical/observational approach are elaborated starting from the damage probability matrices (DPMs) in terms of global damage, both for the whole database and for some subsets of churches with homogeneous characteristics, in order to analyze the influence of some typological features. In particular, it is highlighted that the subset of small churches with rectangular plan and single nave show a generally lower vulnerability compared with those of the whole database.Moreover, the damage observed in the most common macro-elements detectable in masonry churches is examined by defining specific damage indices for macro-elements. The fragility curves for the macro-elements are, then, compared with those referring to the global damage, evidencing some interesting aspects useful both in the survey phase and for planning specific interventions. One of the main outcomes is that the seismic responses of the ‘Façade’ and ‘Principal nave’ macro-elements may closely approximate the global response of the church.Finally, the paper presents a new fitting procedure of the observational damage data aimed to build fragility curves for subsets of churches characterized by a reduced number of data falling in some PGA ranges. A ‘weighting’ procedure is, indeed, proposed in order to give less relevance to small groups of churches falling in the less populated PGA ranges.

Empirical fragility and ROC curves for masonry buildings subjected to settlements

In the Netherlands, the potential damage to the building stock due to subsidence phenomena has recently received increased awareness. However, evaluating and predicting damage to buildings in subsiding areas is a complex task that requires associating the vulnerability of exposed structures with the intensity of the subsidence hazard. Considering the widespread presence of subsidence-related damage to the built heritage, the focus of this study is to provide empirical-based insights to assess and forecast subsidence damage to masonry buildings. A rich dataset with manual levelling measurements was collected comprising 386 surveyed masonry buildings, mainly low-rise (terraced) houses built before 1950. Of the total set of buildings, 122 cases rest on shallow foundations and 264 on piled foundations. For each building, the recorded damage is related to the settlement, calculated from the bed-joint levelling measurements, using four different intensity parameters, namely differential settlement, rotation, relative rotation and deflection ratio. These four parameters are appraised in their capacity to effectively predict the intensity of the damage. The Receiver Operating Characteristic (ROC) method is used to evaluate the relative efficacy of the selected hazard parameters. The rotation, the relative rotation (angular distortion) and the deflection ratio are observed as the most accurate when predicting the intensity of damage, while the differential settlement appears less accurate.Additionally, the dataset was used to generate empirical fragility curves where the probability of damage is described as a function of the aforementioned parameters. Thresholds were set to distinguish between the light damage and the functional and structural damage state. At a relative rotation of 1/500 masonry buildings on shallow foundations were observed to reach or exceed light damage with a probability of 13%, and functional and structural damage with 5%. The availability of the bed joint levelling measurements made it possible to classify eight recurrent settlement profiles, including both symmetric and asymmetric profiles, associated with both the overall deformation and the rigid rotations of the surveyed buildings.

Empirical fragility curves for masonry buildings struck by the 2016 Central Italy earthquake

The prevention of seismic risk at urban scale can be pursued through the estimate of the probability to reach or exceed a certain damage grade given the seismic input. In this framework, seismic fragility curves are nowadays of large interest as they express this probability in a synthetic way, also extended to large-scale applications. Real damage data are crucial in making more reliable predictions of damage occurrence, although they can be influenced by a proper definition of the structural types and the completeness of observations. The paper shows the empirical fragility curves obtained for a sample of 2263 masonry buildings located within 19 historical centers struck by the 2016 Central Italy earthquake. The damage grade was evaluated according to the European Macroseismic Scale (EMS-98), also considering undamaged buildings, at the end of the sequence that spanned between August and October. The buildings largely underwent several repairs and strengthening actions with reinforced concrete elements starting from the 1980s. The systematization of the structural features led to a taxonomy for strengthened and original buildings, which, based on the observed damage patterns, was matched to the EMS-98 vulnerability classification. The sample ranges from class A (worst behavior) to D (best behavior). Class A was typically assigned to original buildings (without interventions) or ill-advisedly tampered ones, i.e., those in which interventions had an unfavorable contribution to their seismic behavior. Class D described buildings with properly designed strengthening interventions, classes B and C intermediate situations. Fragility curves were obtained per each vulnerability class, as a function of the highest peak ground acceleration (PGA) observed in the sequence from ShakeMaps. The results were then compared to other empirical fragility models.

Empirical fragility curves for macro-elements and single mechanisms of churches damaged during the 2016-2017 Central Italy seismic sequence

The churches represent the most widespread building typology within the monumental masonry heritage present in the Italian territory. A special attention needs to be paid to the assessment of the vulnerability of these structures because of the particular architectural features (slender walls with large openings, wide halls and huge vaults, large façades, etc…). This paper presents several statistical analyses carried out on a wide database that collects damage information and structural characteristics of a large sample of masonry churches (2884) inspected after the 2016-2017 Central Italy seismic sequence. The collected information is used for developing empirical fragility curves starting from the damage probability matrices (DPMs) for discrete intervals of PGA (peak ground acceleration), with reference to the following three damage estimates: i) the global damage referred to the whole church, ii) the damage referred to single macro-elements, and iii) the damage referred to single mechanisms. The fragility functions are determined via the maximum likelihood estimation method and adopt a lognormal cumulative function to define the exceedance probabilities for the five damage levels provided by the European macro-seismic (EMS) scale. The fragility curves related to the three damage estimates are compared to each other to identify the weight of specific macro-elements and mechanisms in determining the global damage level and eventually to point out proper and specific interventions to reduce the vulnerability of the whole church.

Validation of physics-based ground shaking scenarios for empirical fragility studies: the case of the 2009 L’Aquila earthquake

This paper explores and validates the use of ground shaking scenarios generated via 3D physics-based numerical simulations (PBS) for seismic fragility studies. The 2009 L’Aquila seismic event is selected as case-study application, given the availability of a comprehensive post-earthquake database, gathering observed seismic damages detected on several building typologies representative of the Italian built environment, and of a validated numerical model for the PBS of ground shaking scenarios. Empirical fragility curves are derived as a function of different seismic intensity measures, by taking advantage of an improved statistical technique, overcoming possible uncertainties in the resulting estimates entailed by data aggregation. PBS-based fragility functions are compared to the corresponding sets of curves relying on updated ShakeMaps. The predictive capability of the adopted simulation strategies is then verified in terms of seismic damage scenarios, by respectively coupling PBS- and ShakeMap-based fragility models with the corresponding ground shaking scenarios. Comparison of observed and predicted damage distributions highlights the suitability of PBS for region-specific seismic vulnerability and risk applications.

Building retrofit with reduced web (RWS) and beam (RBS) section limited-ductility connections

Softening of beams near the moment connection can be regarded as one of the most convenient methods for retrofitting non-seismically designed buildings. This can be done by drilling the beam web near the connection (aka RWS–Reduced Web Section) or cutting the beam flanges (aka RBS–Reduced Beam Section). Thus, becoming a cost-effective option for retrofitting and erection of new buildings, while optimising use of steel; making the most of this high environmental impactful material. This study presents a comprehensive investigation of the effects of using extended end-plate bolted RWS and RBS connections in building behaviour when subjected to strong ground motion. For that purpose, incremental dynamic analyses (IDA) were performed in a low height building fitted with RWS and RBS connections capable of limited ductility. This was done with the aim of characterising the seismic behaviour of buildings with deficient earthquake design after being subjected to seismic upgrade. It is observed that empirical fragility curves show that probabilities of exceeding 1%, 2% and 4% inter-story drifts are significantly lower (more than 25%) for the building that is designed with RWS connections instead of RBS connections; while the probability of collapse is reduced by at least one third. This indicates that deployment or RWS connections can reduce the risk of both; severe structural damage and, large economical loss due to damage of non-structural elements when seismic demands are moderate.

Urban seismic scenario-based risk analysis using empirical fragility curves for Kerend-e-gharb after Mw 7.3, 2017 Iran earthquake

Urban seismic scenario-based risk analysis using empirical fragility curves for Kerend-e-gharb after Mw 7.3, 2017 Iran earthquake

Masonry structures: A proposal of analytical generation of fragility functions for tsunami impact – Application to the Mediterranean coasts

Evaluation of tsunami vulnerability of coastal buildings is gaining high interest in recent years in the areas with high tsunami hazard. Fragility evaluation is a fundamental step to obtain a quantitative estimation of the probability of building damage and in order to define possible strategies for risk mitigation. Several empirical fragility curves are available for masonry structures. However, an empirical fragility curve is generally based on field surveys after tsunami events, not always available. Conversely, analytical fragility curves are based on prediction approaches. In this paper, a proposal for the evaluation of analytical fragility curves for masonry structures typical of the Mediterranean coasts based on simplified structural analyses and damage indexes is presented. The proposal considers the uncertainties in both the structural demand and capacity probabilistically. Several Monte Carlo simulations on some masonry structure types have been carried out to evaluate the fragility related to each fixed damage state assuming the inundation depth as intensity measure. Finally, the validity of the results is discussed by comparisons with empirical fragility curves available in the literature.

Empirical fragility curves of engineered steel and RC residential buildings after Mw 7.3 2017 Sarpol-e-zahab earthquake

This study investigates the damage data after November 12, 2017, Iran earthquake (Mw 7.3), collected on 440 steel and reinforced concrete residential buildings. Structures have low-to-medium height and are located in Sarpol-e-zahab city, as well as in the west and northwest parts of Kermanshah province, Iran. The peak ground acceleration demands are determined according to data of the micro-shakemap of Sarpol-e-zahab city and the shakemap of Kermanshah province, while the mean values of intensities are determined from the existing empirical relationship between PGA and intensity. The investigated buildings are engineered steel and RC structures nominally erected according to the second and third editions of the Iranian code for earthquake-resistant buildings, but mostly under careless supervision and with low-quality materials. Damage probability matrix, vulnerability index and empirical fragility curves are presented for three subgroups of steel and RC structures on the basis of (i) structural materials and seismic resistant systems (i.e. braced, moment and combination of braced and moment steel frames, as well as moment and combination of moment and shear wall RC frames), without considering the height of structures; (ii) structural materials and height of structures, without considering the seismic resistant systems (i.e. low and medium-height steel and RC structures); (iii) structural materials, without considering the seismic resistant systems and height of structures (i.e. total data for steel and RC frames). The proposed fragility curves are compared with other fragility curves for steel and RC buildings from previous studies. Finally, since this earthquake was the first seismic event in Iran affecting a considerable number of steel and RC engineered buildings, the proposed empirical fragility curves are definitely unique and crucial for realistic damage and vulnerability assessment of similar buildings in future earthquake scenarios, as well as for developing rapid seismic loss assessment after damaging earthquakes.

Subsidence in Como historic centre (northern Italy): Assessment of building vulnerability combining hydrogeological and stratigraphic features, Cosmo-SkyMed InSAR and damage data

Como historic centre, located at the SW branch of Lake Como (northern Italy), is prone to subside because of a thick sequence of late Pleistocene to Holocene glacio-lacustrine, palustrine and alluvial sediments in the subsoil. After the 1950s, the combination of natural causes and anthropogenic activities amplified subsidence-induced differential settlements at building foundation depths, resulting in damage on the superstructures.This work presents the first subsidence vulnerability analysis of the historic buildings in Como city centre by combining hydrogeological and stratigraphic features, in situ damage investigations, and remote sensing Synthetic Aperture Radar (SAR) data acquired by Cosmo-SkyMed mission. First, the relationships between local hydrogeological features and vertical displacements retrieved by SAR Interferometry (InSAR) analysis were qualitatively assessed. This highlighted that cumulative vertical InSAR-derived settlements have a stronger linear correlation with the groundwater level rather than the thickness of compressible soil units at the city scale. The largest vertical displacements are located in the NW sector of the city centre and along the shore of Lake Como, where they remark the pre-Roman shoreline. Then, the cause-effect relationships between building damage severity and Subsidence-Related Intensity (SRI) parameters were investigated using a probabilistic approach based on empirical fragility curves. To this aim, two InSAR-derived SRI parameters were tested for both masonry and reinforced concrete buildings: differential settlements and relative rotations. The former resulted to relate better to distinct damage levels in Como historic centre. The analyses performed can contribute to the management of the inestimable architectural and cultural heritage of Como historic centre.

Seismic Scenario of Algiers City: Case Study of Strengthened Masonry Buildings

Strengthened masonry buildings are one of the most common types of old structure usually located in the ancient Algerian urban nuclei. The present study focused on common strengthened masonry buildings. Feedback from seismic experiments has shown that their dynamic behavior is generally nonlinear and highly vulnerable to earthquakes. Also, in order to predict the rate of damage that could occur to this type of structure in the event of earthquakes, empirical fragility curves based on a probabilistic method have been developed. In this study, seismic fragility analysis has been performed using the vulnerability index and the average damage rate. The vulnerability index will belong to one of three vulnerability classes determined by nonlinear dynamic analysis. The average damage is obtained using a deterministic method taking into account the vulnerability index and the seismic intensity. The fragility curves, which give the probability of achieving or exceeding a certain damage level for the three classes of vulnerability considered, have been compared to different studies that developed similar analyses. A seismic scenario was performed using a geographic information system and applied to strengthened masonry buildings located in Algiers city, which was built before the first Algerian seismic regulations of 1981.

Seismic Retrofitting Solutions for Precast RC Industrial Buildings Struck by the 2012 Earthquakes in Northern Italy

In 2012, the North of Italy was hit by a seismic sequence characterized by two main events occurred on May 20 and 29 with MW = 6.1 and 6.0, respectively. Those earthquakes were particularly severe toward precast Reinforced Concrete (RC) structures not designed for seismic resistance. In the past years, the authors implemented a database collecting damage data and typological information on the industrial buildings struck by the Emilia earthquakes. That database was used to develop empirical fragility curves, which highlighted the considerable vulnerability of precast buildings conceived in accordance with pre-seismic code provisions. More recently, the interventions of seismic retrofitting on the same buildings, funded by the Emilia-Romagna region and designed by engineers which were directly hired by the companies, were examined in detail and critically revisited. A selection of these interventions is presented in this paper, which analyzes the effectiveness of the various retrofitting solutions, with a specific attention to the force transfer mechanisms between existing structures and strengthening systems. The interventions are divided between column strengthening (based, for example, on RC or steel jacketing) and interventions aimed at providing the building with a suitable earthquake resistant system (based, for example, on either the use of the existing cladding panels or the implementation of new bracing systems). Graphical representations of the analyzed solutions with the relevant construction details are provided.

Empirical fragility curves for Italian residential RC buildings

In this paper, empirical fragility curves for reinforced concrete buildings are derived, based on post-earthquake damage data collected in the aftermath of earthquakes occurred in Italy in the period 1976–2012. These data, made available through an online platform called Da.D.O., provide information on building position, building characteristics and damage detected on different structural components. A critical review of this huge amount of data is carried out to guarantee the consistency among all the considered databases. Then, an in-depth analysis of the degree of completeness of the survey campaign is made, aiming at the identification of the Municipalities subjected to a partial survey campaign, which are discarded from fragility analysis. At the end of this stage, only the Irpinia 1980 and L’Aquila 2009 databases are considered for further elaborations, as fully complying with these criteria. The resulting database is then integrated with non-inspected buildings sited in less affected areas (assumed undamaged), to account for the negative evidence of damage. The PGA evaluated from the shakemaps of the Italian National Institute of Geophysics and Volcanology (INGV) and a metric based on six damage levels according to EMS-98 are used for fragility analysis. The damage levels are obtained from observed damage collected during post-earthquake inspections through existing conversion rules, considering damage to vertical structures and infills/partitions. The maximum damage level observed on vertical structures and infills/partitions is then associated to the whole building. Fragility curves for two vulnerability classes, C2 and D, further subdivided into three classes of building height, are obtained from those derived for specific structural typologies (identified based on building height and type of design), using their frequency of occurrence at national level as weights.

Empirical fragility assessment using conditional GMPE-based ground shaking fields: application to damage data for 2016 Amatrice Earthquake

Recent earthquakes have exposed the vulnerability of existing buildings; this is demonstrated by damage incurred after moderate-to-high magnitude earthquakes. This stresses the need to exploit available data from different sources to develop reliable seismic risk components. As far as it regards empirical fragility assessment, accurate estimation of ground-shaking at the location of buildings of interest is as crucial as the accurate evaluation of observed damage for these buildings. This implies that explicit consideration of the uncertainties in the prediction of ground shaking leads to more robust empirical fragility curves. In such context, the simulation-based methods can be employed to provide fragility estimates that integrate over the space of plausible ground-shaking fields. These ground-shaking fields are generated according to the joint probability distribution of ground-shaking at the location of the buildings of interest considering the spatial correlation structure in the ground motion prediction residuals and updated based on the registered ground shaking data and observed damage. As an alternative to the embedded coefficients in the ground motion prediction equations accounting for subsoil categories, stratigraphic coefficients can be applied directly to the ground motion fields at the engineering bedrock level. Empirical fragility curves obtained using the observed damage in the aftermath of Amatrice Earthquake for residential masonry buildings show that explicit consideration of the uncertainty in the prediction of ground-shaking significantly affects the results.