Vulnerability Curves Research Articles

Field test and probabilistic vulnerability assessment of a reinforced concrete bridge pier subjected to blast loads

Bridge piers have a high risk of being attacked in wartime, which has the potential to trigger progressive bridge collapse. This study aims to predict the failure probability of reinforced concrete (RC) piers exposed to military attack scenarios. Field explosion test and axial compression test were conducted to investigate the damage and post-blast performance of the RC pier first. Then, the uncertainties sourcing from the weapon accuracy were investigated. A performance-based (PB) vulnerability probabilistic assessment framework is developed which combines the Monte Carlo simulation (MCS) with a full-scale finite element (FE) model which was verified with test results. A probabilistic vulnerability assessment of a typical RC pier subjected to stochastic blast loading is conducted, and the vulnerability curve corresponding to three performance levels is developed. In addition, the damage modes and post-blast performance of the RC pier under blast loading are analyzed. Results show that the blast-induced damage to an RC pier had a significant influence on the axial bearing capacity, and the pier presents different damage modes at different scaled distances, which has a critical value of 0.65 m/kg1/3 between local and global damage modes. The failure probability of the pier corresponding to different performance levels increased with an increase in the TNT charge. The pier’s probability of collapse is less than 20 % when the TNT charge weight does not exceed 500 kg.

Seismic vulnerability analysis of reinforced concrete frame with infill wall considering in-plane and out-of-plane interactions

The seismic performance of a building hinges on the seismic capacity and damage features of the reinforced concrete (RC) frame with masonry infill walls. To reasonably evaluate the seismic performance and seismic economic loss of masonry infill walls, it is necessary to consider the in-plane (IP) and out-of-plane (OOP) interactions of these walls under seismic actions, and to model the vulnerability of the infill walls and the frame. Based on the test data on masonry infill walls, this paper designs a performance indicator for infill wall in the light of IP-OOP interactions, and determines the response threshold of each damage state. With the aid of OpenSees, the authors developed and verified a reasonable modeling method for RC frames with infill walls. As per the current code in China, a 5-storey RC frame with infill walls was designed, and two three-dimensional (3D) space models were established for the structure by the proposed modeling method. One of them considers IP-OOP interactions, and the other does not. Then, the structure was subjected to incremental dynamic analyses (IDA), and different damage indicators were determined to examine the damage of the infill walls and the overall structure, producing a set of vulnerability curves. The results show that the consideration of IP-OOP interactions significantly increases the probability of seismic damages on the infill walls and the overall structure. The most prominent increase was observed in the medium to serious damage stages.

Vulnerability Assessment of School Buildings: Generic Versus Building-Specific Fragility Curves

ABSTRACT The aim of this paper is to investigate whether existing generic fragility curves for various residential building typologies can be safely applied for the vulnerability assessment of school buildings. We select three representative typologies of actual reinforced concrete (RC) school buildings in Thessaloniki, Greece and we conduct a detailed fragility analysis combining field inspection and structural monitoring data to advanced numerical modeling. Building-specific fragility and vulnerability curves are derived for the three school buildings based on 3D incremental dynamic analysis (IDA) of the calibrated numerical models. The comparisons of the developed curves with generic ones showed their significant differences.

A Method for Assessing Flood Vulnerability Based on Vulnerability Curves and Online Data of Residential Buildings—A Case Study of Shanghai

Flood vulnerability is the key to understanding and assessing flood risk. However, analyzing flood vulnerability requires sophisticated data, which is usually not available in reality. With the widespread use of big data in cities today, it is possible to quickly obtain building parameters in cities on a large scale, thus offering the possibility to study the risk flooding poses to urban buildings. To fill this research gap, taking Shanghai as an example, this study developed a new research framework to assess urban vulnerability based on vulnerability curves and online data of residential buildings. First, detailed information about residential buildings was prepared via web crawlers. Second, the cleaned residential building information fed a support vector machine (SVM) algorithm to classify the buildings into four flood vulnerability levels that represented the vulnerability curves of the four building types. Third, the buildings of different levels were given vulnerability scores by accumulating the depth–damage ratios across the possible range of flood depth. Further, combined with the unit price of houses, flood risk was assessed for residential buildings. The results showed that the F1-score for the classification of buildings was about 80%. The flood vulnerability scores were higher in both the urban center and the surrounding areas and lower between them. Since 1990, the majority of residential buildings in Shanghai have switched from masonry–concrete structures to steel–concrete structures, greatly reducing the vulnerability to floods. The risk assessment showed decreasing risk trend from the center outward, with the highest risk at the junction of the Huangpu, Jing’an and Xuhui districts. Therefore, this framework can not only identify the flood vulnerability patterns but also provide a clue for revealing the flood risk of residential buildings. With real estate data becoming increasingly accessible, this method can be widely applied to other cities to facilitate flood vulnerability and risk assessment.

Prediction of fragility deterioration of earthquake-damaged RC structure based on damaged section analysis

Evaluating quantitatively the performance of earthquake-damaged structures is significant for facilitating post-earthquake reconstruction. However, it is difficult to quantitatively assess the effect of earthquake-induced damage on structural performance. In this paper, a new method to establish the earthquake-damaged structure model (EDSM) based on the damaged section analysis (DSA) procedure is proposed. DSA can consider the effect of the seismic damage on material properties and sectional dimensions, which are the primary difference between DSA and classical moment-curvature analysis. Furthermore, the DSA is verified on two RC columns by the comparison of hysteretic curve between damaged column models and test columns under cyclic loadings. The EDSM is established by replacing the plastic hinge regions of the damaged components with “Hysteretic” material. This method is applied to a RC frame structure and is verified for different ground motions with various intensities. Moreover, by the comparison of vulnerability curves between undamaged structure model (UDSM) and EDSM, the vulnerability of EDSM regarding the moderate limit state is more fragile than the vulnerability of UDSM regarding the slight limit state. A reduction index is proposed to quantitatively evaluate the deterioration of seismic performance of EDSM. It can be identified that the reduction in vulnerability decreases gradually as the limit state increases, which shows the earthquake-induced damage has a more significant effect on the elastic properties of structure.

Damage assessment in single-nave churches and analysis of the most recurring mechanisms after the 2016–2017 central Italy earthquakes

AbstractAssessment of churches based on empirical data at a territorial scale is a suitable tool to have an overview of the seismic behaviour of this peculiar structural typology and to evaluate their current state of vulnerability. Fragility and vulnerability curves are also aimed to perform the analysis of different seismic scenarios. The paper presents a detailed typological analysis of 633 single-nave churches, as a selected subset of the database previously examined by the authors, with the aim of evaluating more in detail the influence of some parameters, such as masonry typology, church dimensions and presence of the bell tower, on the vulnerability of the overall church. Then, specific analyses are carried out to assess the influence played by single mechanisms on the definition of the overall damage index, with the focus of providing qualitative evaluations and explicit vulnerability and fragility curves related to the most recurring and significant collapse mechanisms. This is an original contribution of the paper in the field of the vulnerability assessment of churches, since nowadays little information is available in the literature about the damage levels related to specific mechanisms, while most attention is still focused on global damage.

Seismic vulnerability assessment of reinforced concrete buildings having nonlinear fluid viscous dampers

Seismic resilience is the residual capacity of a damaged system for recovering and sustaining an acceptable level of performance as a consequence of a seismic event. Firstly, this paper summarizes the current calculation framework of seismic resilience using fragility analyses. After that, a new metric based on vulnerability analyses is developed to calculate seismic resilience. Finally, a typical hospital building is adopted as a single building and then retrofitted with supplemental Energy Dissipation Systems (EDS) to show the applicability of the new metric and compare it with the current calculation model of the seismic resilience. The considered supplemental EDS is the Nonlinear Fluid Viscous Damper (NFVD) located as the diagonal damper-brace system. The seismic performance of the supplemental EDSs is to enhance structural performance by reducing induced lateral displacements and as a result the level of physical damages and losses. To this end, Incremental Dynamic Analysis (IDA) is implemented to achieve the damage fragility and vulnerability curves. A comparison of the fragility, vulnerability, and functionality curves indicates that NFVDs are potentially useful for attenuating seismic damages to structural and non-structural components.

Seasonal adjustment of leaf embolism resistance and its importance for hydraulic safety in deciduous trees.

Embolism resistance is often viewed as seasonally stable. Here we examined the seasonality in the leaf xylem vulnerability curve (VC) and turgor loss point (ΨTLP ) of nine deciduous species that originated from Mediterranean, temperate, tropical, or sub-tropical habitats and were growing on the Volcani campus, Israel. All four Mediterranean/temperate species exhibited a shift of their VC to lower xylem pressures (Ψx ) along the dry season, in addition to two of the five tropical/sub-tropical species. In three of the species that exhibited VC seasonality, it was critical for avoiding embolism in the leaf. In total, seven out of the nine species avoided embolism. The seasonal VC adjustment was over two times higher as compared with the seasonal adjustment of ΨTLP , resulting in improved hydraulic safety as the season progressed. The results suggest that seasonality in the leaf xylem vulnerability is common in species that originate from Mediterranean or temperate habitats that have large seasonal environmental changes. This seasonality is advantageous because it enables a gradual seasonal reduction in the Ψx without increasing the danger of embolism. The results also highlight that measuring the minimal Ψx and the VC at different times can lead to erroneous estimations of the hydraulic safety margins. Changing the current hydraulic dogma into a seasonal dynamic in the vulnerability of the xylem itself should enable physiologists to understand plants' responses to their environment better.

A unit pipe pneumatic model to simulate gas kinetics during measurements of embolism in excised angiosperm xylem.

The pneumatic method has been introduced to quantify embolism resistance in plant xylem of various organs by applying a partial vacuum to cut-open xylem. Despite the similarity in vulnerability curves between the pneumatic and other methods, a modeling approach is needed to investigate if changes in xylem embolism during dehydration can be accurately quantified based on gas diffusion kinetics. Therefore, a unit pipe pneumatic (UPPn) model was developed to estimate gas extraction from intact conduits, which were axially interconnected by inter-conduit pit membranes to cut-open conduits. The physical laws used included Fick's law for diffusion, Henry's law for gas concentration partitioning between liquid and gas phases at equilibrium and the ideal gas law. The UPPn model showed that 91% of the extracted gas came from the first five series of embolized, intact conduits and only 9% from the aqueous phase after 15s of simulation. Considering alternative gas sources, embolism resistance measured with a pneumatron device was systematically overestimated by 2-17%, which corresponded to a typical measuring error of 0.11MPa for P50 (the water potential equivalent to 50% of the maximum amount of gas extracted). It is concluded that pneumatic vulnerability curves directly measure embolism of intact conduits due to the fast movement of gas across interconduit pit membranes, while gas extraction from sap and diffusion across hydrated cell walls is about 100 times slower. We expect that the UPPn model will also contribute to the understanding of embolism propagation based on temporal gas dynamics.

Safety-efficiency tradeoffs? Correlations of photosynthesis, leaf hydraulics, and dehydration tolerance across species.

The tradeoffs between carbon assimilation and hydraulic efficiencies and drought-tolerance traits on different scales are considered a central tenet in plant ecophysiology; however, no clear tradeoff between these traits has emerged in previous studies using woody angiosperms or grasses by investigating several hydraulic tolerance and gas exchange efficiency and/or water transport efficiency traits. In this study, we measured numerous efficiency, resistance, and leaf anatomical traits, including light-saturated gas exchange, leaf hydraulic vulnerability curves, pressure-volume curves, and leaf anatomical traits, in seven species with diverse drought tolerance. A substantial variation in photosynthetic rate, stomatal conductance, mesophyll conductance, maximum leaf hydraulic conductance (Kmax), mesophyll anatomical traits, and leaf vein density across species was observed. Both mesophyll conductance and Kmax were related to leaf anatomical traits, but other gas exchange traits were decoupled from Kmax. Although the efficiency and tolerance traits varied widely across estimated species, no clear trade-off between safety traits and efficiency traits was observed. These findings suggested that postulated leaf-level drought tolerance-carbon assimilation and hydraulic efficiency tradeoff does not exist among distant species and that the fact that different leaf anatomical traits determine efficiency and tolerance capacity might contribute to the lack of such tradeoffs.

Analysis of an empirical seismic fragility prediction model of wooden roof truss buildings

To explore the vulnerability of wood roof truss buildings (WRTBs) under earthquake action, the empirical damage typical characteristics of 12,343.4 × 104 m2 and 21,490 buildings of this type of building that suffered different degrees of loss in 22 typical destructive earthquakes in China from 1993 to 2013 were observed and analysed. Based on the analysis methods of the nonlinear vulnerability model, probability statistics, and prediction model, a novel fragility probability matrix, plane, surface, nonlinear regression curve, and function model of different intensity zones under the latest Chinese macrointensity standard (GB/T 17742–2020, CMS-20) assessment were established, and vulnerability curve models were employed based on the damage ratio (DR) and actual cumulative damage probability (ACDP) parameters. According to 1993–1999, 2000–2010, and after 2011, the time-varying fragility specimen data were classified and censusly analysed. The fragility prediction curve models of DR and ACDP were performed using the probabilistic demand modal analysis method. Combined with the matrix probability and confidence interval calculation model, a novel regional mean fragility index domain model for typical structural (WRTB) vulnerability assessment was developed.

Influence of spiral anchor composite foundation on seismic vulnerability of raw soil structure

A typical single-layer raw soil structure in villages and towns in China is taken as the research object. In the probabilistic seismic demand analysis, the seismic demand model is obtained by the incremental dynamic time history analysis method. The seismic vulnerability analysis is carried out for the raw soil structure of non-foundation, strip foundation, and spiral anchor composite foundation, respectively. The spiral anchor composite foundation can reduce the seismic response and failure state of raw soil structure, and the performance level of the structure is significantly improved. Structural requirements sample data with the same ground motion intensity are analyzed by linear regression statistics. Compared with the probabilistic seismic demand model under various working conditions, the seismic demand increases gradually with the increase of intensity. The seismic vulnerability curve is summarized for comparative analysis. With the gradual deepening of the limit state, the reduction effect of spiral anchor composite foundation on the exceedance probability becomes more and more obvious, which can reduce the probability of structural failure to a certain extent.

Seismic vulnerability analysis for shallow-buried underground frame structure considering 18 existing subway stations

The variability of structural engineering parameters is not accounted for in available literature on seismic vulnerability of underground frame structures. This study investigates the seismic vulnerability of 18 existing subway stations with different site condition, structural stiffness, reinforcement ratio and buried depth employing two-dimensional (2D) finite element analysis considering soil-structure interaction. The peaks of structure inter-story drift ratio under different earthquake intensity of different ground motion records are obtained from non-linear dynamic time-history analysis. Taking the inter-story drift ratio as the damage measure (DM) and the peak ground acceleration (PGA) as the ground motion intensity measure (IM), the seismic vulnerability curves of 18 subway stations are constructed. The comparison of seismic fragility curves of different subway stations demonstrates that site conditions are critical to the post-earthquake structure probability of failure. Furthermore, representative seismic fragility curves are established based on the data collected form the computed results of 18 subway stations, which can aid in evaluating the seismic performance of existing urban underground frame structures in China. The results of this study can provide reference for the performance-based seismic design of urban underground frame structures.

System Vulnerability Analysis Simulation Model for Substation Subjected to Earthquakes

To evaluate the earthquake-resistance capability of an entire substation, which is a complex multi-input-multi-output system (MIMOS) composed of many various types of electrical equipment interconnected by conductors, a flow-based analysis model integrating the merit of the flow block diagram and state tree method was introduced. Two performance indicators of a substation were defined from different stakeholders, one is the expected total power transmission capacity and the other is the power accessibility to the targeted users from the substation. And directed graph logic system analysis models were developed on the Simulink platform based on the original internal logic relationship among distributed components and the power delivery path in the substation with different function types. Afterward, the defined reliability indicators associated with the overall system under a certain seismic intensity level can be obtained by combining the seismic vulnerability curve at the equipment level through the Monte Carlo simulation method. The feasibility and accuracy of the proposed system vulnerability analysis model were verified by comparison with the analytical solution through the illustrative simple MIMOS. Then A case study on a practical 220/110 kV substation was conducted, the analysis results can assist decision-makers in seismic optimization of different retrofitting measures and distribution plans for substations.

Seismic Damage Scenarios Induced by Site Effects on Masonry Clustered Buildings: A Case Study in South Italy

ABSTRACT The present research aims to explore the influence of site effects on the seismic vulnerability of the historical centre of Baranello, a little town in the Molise Region of Italy. Structural and typological classification of the investigated urban area has been done according to the EMS-98 scale. The vulnerability assessment of the inspected historical buildings has been carried out through an appropriate survey form to identify the buildings most susceptible to seismic damage. Consequently, using the Post-Earthquake Damage and Safety Assessment (AeDES) form implemented by the Italian Civil Protection Department (DPC), the typological vulnerability curves of the built-up area have been derived based on the damages recorded after the 2002 Molise earthquake. Finally, a local amplification factor, which increases the severity of the seismic damage to the structures, has been taken into account based on the time-domain method. Results reveal that the local amplification effects significantly increase the expected damage, which should lead to the collapse of almost all the investigated buildings for epicentre distance of 5.0 km and magnitude of 6.0. This means that the proposed simplified approach can represent a useful tool to more appropriately foresee the seismic risk of urban centres.

Assessment of fuzzy global seismic vulnerability for RC structures

This paper proposed a fuzzy global seismic vulnerability analysis framework to investigate the effect of stochastic uncertainty and epistemic uncertainty for RC structures simulated by Monte Carlo simulation (MCS) and OpenSeesPy. The classical probability model was used to describe the stochastic uncertainty in fuzzy-random variables (model design parameters). The epistemic uncertainties in the probability model parameters and performance level threshold values were portrayed by incorporating triangle fuzzy numbers. Meanwhile, the vine copula-based global vulnerability curves were obtained by R-Packages to reflect that the dependence configuration between each component-level seismic response. The results showed that the global vulnerability can be accurately simulated by the selected d-vine structure and situated between the upper and lower bounds. The third floor can be regarded as the least fragile component under all performance levels in the case of perfectly independence, and the pair-copula model C34 consisted of the third and fourth floors showed a sensitive seismic response. Moreover, epistemic uncertainties showed different effects on the global vulnerability for RC structures under four limit states. The vulnerability curves considering fuzzy performance level and distribution parameters included a wider interval. The framework provided a practical approach for engineers and researchers to be informed of how stochastic, epistemic uncertainties, and dependence configuration affect global seismic vulnerability, facilitating the structure design, decision-making, and post-earthquake rehabilitation.

Potential vulnerability of black bullheads to multiple predators in small impoundments: implications for biological control

Overabundant species can alter a fish community and negatively influence recreationally important species. Introducing new or more predators into a system to control such nuisance fish has been met with limited success and may involve some risk. Understanding to what degree consumption of nuisance species occurs by existing predators and whether an existing predator community is physically capable of consuming the nuisance species can help to determine whether biological control may be possible without new introductions of predators. The objectives of this study were to: (1) document consumption of black bullheads Ameiurus melas by three predators; and (2) determine the relative vulnerability and potential ingestion of bullheads by these predators. We used gastric lavage monthly from May through September to collect stomach contents of channel catfish Ictalurus punctatus, largemouth bass Micropterus salmoides, and walleye Sander vitreus in four reservoirs to calculate the percent occurrence of black bullheads in predator stomachs. We also collected various sizes of juvenile black bullheads to measure body width and depth, with and without the pectoral and dorsal spines extended, respectively. This information was coupled with measured gape widths from the predators to calculate relative vulnerability curves and probabilities of ingestion based on predator size. Black bullheads were rarely consumed by the three predators, and stomach contents generally contained a single black bullhead when consumption did occur. Relative vulnerability based on body depth was similar for all three predators. Potential ingestion was similar among all three predators but was higher for channel catfish compared to the other two predators when black bullhead depths were measured with the dorsal spines extended. This study provides new information about the potential for biological control of black bullheads by an existing predator community.

Seismic vulnerability analysis of vertical pile-supported wharf structure

In order to study the seismic vulnerability of pile-supported wharf structure, taking a vertical pile-supported wharf as the research object and considering the influence of the site, seismic spectrum characteristics and the uncertainty of ground motion intensity, we establish a dynamic nonlinear numerical model of structure-foundation soil coupling of vertical pile-supported wharf by using the geotechnical finite element software of Midas GTS NX. Selecting the maximum strain of pile foundation in soil as the damage index, we obtain the seismic vulnerability curves and the corresponding damage state probability based on the the incremental dynamic analysis method. The analysis results show that when peak ground acceleration is less than 0.80<italic>g</italic>, the wharf structure is mainly in mild damage state or moderate damage state, otherwise the probability of serious damage basically exceeds 50% and the structure will lose operational capacity. Based on the vulnerability analysis of pile foundation damage in foundation soil, the influence of earthquake on the vertical pile-supported wharf is described from macroscopic and quantitative point of view, which can provide reference for seismic design and disaster prevention prediction of vertical pile-supported wharf.

Seismic vulnerability assessment and fragility analysis of pre-code masonry buildings in Portugal

Despite the fact that in recent years Portugal has not seen the occurrence of high-magnitude earthquakes, it remains threatened by these events due to its geographic location. Since the 1960s, reinforced concrete has been the most used material for new constructions; however, the historic urban centers are dominated by old unreinforced masonry (URM) buildings, which techniques and construction materials have evolved since the Great Lisbon earthquake that occurred in 1755 (Mw = 8.5). Given the presence of these buildings in areas of significant seismicity, extensive research is needed to assess the seismic risk and define mitigation policies. This kind of studies is often supported by empirical methods and based on expert judgment due to the high variability of the building stock and lack of information. The main purpose of this work is: (i) to provide analytical fragility curves, supported by nonlinear static analysis, for the entire population of old masonry buildings, built before the introduction of the first design code for building safety against earthquakes (RSSCS) in 1958; (ii) define vulnerability curves to be used by the technical community for seismic assessment of pre code URM buildings. The characterization of the building stock geometry and material properties is based on information previously collected, which was essential to define representative archetypes and typologies.

Fragility curves for light damage of clay masonry walls subjected to seismic vibrations

The probability of light damage to unprepared, unreinforced masonry structures exposed to induced seismicity due to gas extraction in the north of the Netherlands is still under investigation. Repeated light seismic excitations caused by frequent, light and nearby earthquakes have been linked to economical losses and societal unrest in particular, with extensive damage claims. Moreover, the damaging potential of the seismic events has been related to the condition of the structure, especially if damage corresponding to settlement causes is already present. A comprehensive testing campaign oriented towards the initiation and progression of light damage of replicated clay brick masonry has been conducted at Delft University of Technology. Based on these tests, calibrated finite element models have been produced. This article uses the calibrated non-linear time-history models to simulate the effect of earthquake ground motion on a variety of initial conditions, wall geometry, material properties, and number, type and intensity of earthquakes. The results are then used to regress a relationship between damage and these parameters. This is subsequently employed to run a MonteCarlo simulation and produce fragility curves where the probability of exceeding specific damage values for various initial damage levels is presented against the seismic hazard. The vulnerability or fragility curves show that visible damage, with cracks wider than 0.1 mm, appears, with a 10% exceedance probability, at 13 mm/s of peak ground velocity; but, if the masonry had already undergone some light, yet imperceptible damage, a PGV of 6 mm/s was sufficient to aggravate it into visible cracks. To attain a 1% probability of exceeding light damage however, for which the masonry would need more invasive repair, it was observed that PGVs larger than 15 mm/s were required. These fragility curves were finally compared to graphs from other authors and found to capture well the variability in the range assigned to light damage.