Seismic Fragility Curves Research Articles

Failure modes-based seismic fragility analysis of concrete gravity dams considering concrete heterogeneity

The heterogeneity of mass concrete often leads to the initiation of micro-cracks in gravity dams, while the accumulation of damage of concrete on the meso-scale leads to the cracking behaviour on the macro-scale. To improve the seismic safety of the dam, a comprehensive study on the effect of heterogeneous properties is crucial in seismic fragility analysis. A novel methodology considering concrete heterogeneity for seismic fragility analysis was developed by combining damage element model for seismic failure analysis, a five-level standard for failure modes-based seismic damage state and a method to generate seismic fragility curves. Then, seismic failure analysis of the Koyna gravity dam was taken as an example to verify the correctness of the damage element model, the damage process of dam from micro-cracks to macro-cracks were simulated. Finally, the seismic fragility of a practical dam in China was studied to verify the effectiveness of the proposed methodology. The results showed that simulated failure modes-based fragility curves were suitable for the target dam and more capable of considering the uncertainty of concrete material parameters. The obtained fragility curve proved valuable in optimizing seismic design, reinforcement and maintenance measures and improve seismic capability of the dam.

Seismic fragility analysis of subway station structure subjected to sequence-type ground motions

As a critical urban infrastructure, the subway station damaged in an earthquake not only leads to interruption of underground transportation, but may also result in serious casualties and economic losses. The current seismic design of underground structures only considers the mainshock effects but ignores the potential hazards of aftershocks. However, most mainshocks are often followed by aftershocks in a short period of time. In the past earthquakes, it was reported that the mainshock-damaged engineering structures suffered more serious structural damage and even complete collapse when subjected to aftershocks before restoration. This paper proposes a framework for the development of seismic fragility curves of underground structures subjected to sequence-type ground motions. Finite element models of a two-story, three-span subway station considering nonlinear dynamic soil-structure interaction (SSI) was established in this study. A comprehensive assessment of the seismic performance of the subway station structure under the sequence-type ground motions was conducted on the SSI model. Both the mainshock-aftershock fragility analysis of the intact structure and the aftershock fragility analysis of the mainshock-damaged structures were performed by combining the traditional seismic probability demand model and the back-to-back mainshock-aftershock probability demand model. The numerical results indicated that the impact of aftershocks on the seismic performance of subway station structures cannot be ignored. The aftershock fragility of the structure is highly dependent on the mainshock-damaged state. The failure probability of a severely mainshock-damaged subway station structure is much higher in the aftershocks than structures in other damage states. Besides, the probability of the mainshock-damaged structure transferring to a more severe level of damage state increases with the increase of the intensity of aftershock motions. For the subway station under sequence-type ground motions, the transition probability of one severer level of damage state is greater than 40 % for the 1.0 g peak ground acceleration of aftershocks and the transition probability of more than two severer level of damage state is less than 10 %.

Horizontal bearing characteristic and seismic fragility analysis of CFRP composite pipe piles subject to chloride corrosion

This paper studies the time-dependent horizontal bearing characteristic and seismic fragility analysis of carbon fiber reinforced polymers (CFRP) composite pipe piles under chloride corrosion. A diffusion model of chloride ions in CFRP composite pipe piles is established based on Fick's second law, allowing for the prediction of corrosion initiation time of CFRP composite pipe piles. The flexural stiffness of composite pipe piles for different CFRP replacement ratios is calculated, and the time-dependent horizontal bearing capacity of CFRP composite pipe pile is calculated using the finite difference method. Considering the uncertainties of structural modeling and earthquake waves, an analysis is conducted to study the effect of earthquakes on piles with different CFRP replacement ratios at various service times. The seismic fragility curves are then derived. The research results show that with the increase of service time, the flexural stiffness of CFRP composite pipe piles decreases. Moreover, higher CFRP replacement ratios result in reduced loss of pile bending stiffness and greater stability of the flexural bearing capacity. As the service time increases, the failure probability of composite pipe piles under seismic action exhibits a smaller increase, particularly for higher CFRP replacement ratios, thereby resulting in a lower loss of seismic performance.

Effects of Deck-Abutment Pounding on the Seismic Fragility Curves of Box-Girder Highway Bridges

ABSTRACT Earthquake-induced pounding in bridges is a complex contact phenomenon in which the dynamic responses of structures, including collisions between deck and abutments, are strongly related to structural properties and earthquake excitation. The goal of this study is to develop and compare the seismic fragility curves of overall system and individual components of regular and irregular box-girder highway bridges in two cases: with pounding and without pounding. For this purpose, four levels of altitudinal irregularity, ranging from regular to highly irregular, are considered. To extend the results for all bridges in the same class, different sources of uncertainties related to earthquakes, structural geometries, and material properties are taken into account. The analytical fragility curves have been developed based on nonlinear time history analyses in OpenSees finite element software for the cases with and without pounding effects. The process has been repeated for each two-, three-, and four-span classes at four irregularity levels. The fragility function parameters for the two cases with and without pounding have been compared for all classes considered in this study. Using fragility functions, this paper clarifies the interactive roles of irregularity and pounding between deck and abutments for seismic vulnerability of multi-span box-birder highway bridges. The results indicate that collisions often show an adverse effect on all structural components. It has also been observed that the detrimental effect of pounding on seismic fragility is more apparent in irregular bridges when compared with regular ones. In addition, the study introduces a conversion coefficient to clarify the effects of pounding on the fragility of bridge components and the overall system. This coefficient can be applied in both conventional analytical methods like static or simplified analysis and technical earthquake models like HAZUS, adjusting fragility values for pounding and irregularity effects.

Optimizing net present values of risk avoidance for mountain railway alignments with seismic performance evaluation

AbstractRailway alignment optimization in earthquake‐prone mountainous (EPM) regions should quantify and trade off construction investments and seismic risks. Unfortunately, slight attention has been previously devoted to this trade‐off. To this end, based on the FEMA‐P58 methodology, a net present value (NPV) model of risk avoidance is presented and solved. In the model, alignment alternatives are first segmented into structural groups with different probabilistic seismic fragility curves, which are then used to generate structural repair cost and repair time curves. Afterward, a probabilistic seismic hazard curve is introduced to estimate the expected annual repair cost and time for computing railway direct and indirect seismic losses. Hence, the railway total annual loss caused by seismic activity can be obtained. Next, a benefit–cost analysis is performed to combine construction cost and seismic loss as the risk‐cost NPV. To optimize this objective function, a particle swarm algorithm is used as the basic approach. For implementing the probabilistic seismic performance analysis, a Monte Carlo simulation (MCS) is employed as the risk assessment module. Furthermore, due to the computationally intensive nature of MCS, a CPU‐based parallelization is embedded into the algorithm to expedite the search. Finally, the proposed model and method are applied to a representative real‐world railway case in an EPM region. Their effectiveness is discussed and verified in five experiments, including algorithm convergence analysis, alignment solution comparison, seismic risk interpretation, computational efficiency test, and a specific sensitivity analysis.

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.

Seismic Fragility Curves of Combined Multiple Tunnel Complexes in Soft Soils

Seismic fragility assessment is the probability of damage exceeding a certain design limit. The dynamic performance of a combined multiple tunnel complex is less explored and requires thorough study. This research is based on the numerical approach to evaluate the damage caused to the two new types of tunnel complexes, i.e. twin and triple tunnel complexes in a soft soil profile. A two-dimensional (2D) finite element analysis is performed to determine the induced bending moments for each of the tunnel complexes and develop the seismic fragility curves. A set of full acceleration-time histories are applied to the soil–tunnel complex system by varying embedment depths in different soft soil profiles. From the results, it is concluded that increasing the embedment ratio results in an increased probability of tunnel damage. The developed fragility curves are also inter-compared for both the tunnel complexes to evaluate the better performer during a seismic event. This study serves as an initial step toward the guidelines to determine the percentage of incurred damage and design the combined multiple tunnel complex in a seismic-prone area.

Seismic fragility analysis of water supply pipelines retrofitted with corrosion-protection liner buried in non-uniform site

The corrosion-protection liner (CPL) technology consists of installing flexible plastic liners with anchoring studs inside existing pipelines and subsequently filling cement mortar to the gap between the waterproof liner and the pipeline. With the excellent chemical resistance, impermeability and fast construction speed, CPL provides an economical and environmentally friendly alternative for pipeline rehabilitation without large-scale excavation. However, the seismic performance of water supply pipelines after being retrofitted with CPL has not been well studied yet. In this study, a series of full-scale quasi-static experiments were firstly conducted on ductile-iron push-on joints before and after reinforcement with CPL to investigate the nonlinear behavior of the joints under longitudinal load and transverse bending. Simplified numerical models of straight pipelines with joints before and after retrofitting in the non-uniform site were then developed in the OpenSees platform, and incremental dynamic analysis (IDA) were performed with consideration of nonlinear soil-pipeline interaction. Twenty-eight pairs of ground motions with the peak ground velocities (PGV) collectively scaled from 200 mm/s to 3000 mm/s were used as inputs. Seismic fragility curves of the pipelines before and after retrofitting were developed with respect to the optimum intensity measure, PGV. It can be seen from the experimental results that the longitudinal load and bending moment capacity of the push-on joint increased about 400% and 20% after CPL reinforcement, respectively, and the joint opening and rotation decreased about 20% and 18% after retrofitting. Numerical results show that the CPL reinforced pipelines exhibit better seismic performance and CPL effectively reduces the failure probability of segmented pipelines under earthquake ground excitations.

Seismic fragility functions for earthquake-induced landslide risk assessment using identified optimal earthquake intensity measures

Seismic fragility analysis can relate the probability of unsatisfactory performance of slopes with increasing intensity of ground motions, which is the basic component of landslide hazard risk assessment. Determination of the optimal earthquake intensity measure (IM) is one of important prerequisite for seismic fragility analysis. Although a small number of studies have already performed seismic fragility analysis of slopes, the optimal IM for seismic fragility analysis of slopes have not been discussed and researched. In the present study, 15 IMs and two different engineering demand parameters (EDPs), including factor of safety (FOS) and Newmark permanent displacement (NPD), are selected for probabilistic seismic demand and seismic fragility analysis of slopes. The metrics of correlation, practicality, efficiency, and proficiency are adopted to identify the optimal earthquake IMs among the studied 15 IMs for two EDPs in seismic fragility analysis of slopes respectively. The results have found that the optimal IM is different for slope fragility analysis when different EDPs are selected. Acceleration spectrum intensity is the most optimal IM among the examined 15 IMs for seismic fragility analysis of slopes when FOS is adopted as the EDP. When NPD is selected as the EDP, root mean square of acceleration and velocity spectrum intensity are in general more appropriate than other IMs. In the last, the seismic fragility curves with regard to two EDPs and corresponding optimal IMs are derived for interpreting more properly slope seismic performance and earthquake-induced landslide risk.

The effect of the ground motion frequency content on seismic performance and fragility curve of special concentric braced frames

Several articles have investigated the effect of various seismic parameters on the response of the structure. However, there has been limited discussion on the impact of seismic frequency content on the brace failure modes and the collapse mechanism of this system. This study investigated the effect of this parameter, considering three special concentric bracing frames of 2, 4, and 6 stories. For the frame dynamic analysis, the open system for earthquake engineering simulation software (OpenSees) is used. To evaluate the effect of frequency content, 60 earthquake records with high, medium and low frequency content are selected from the pacific earthquake engineering research center ground motion database, considering the peak ground acceleration divided by the peak ground velocity ratio. Incremental dynamic analysis is conducted to draw fragility curves and examine the response of structures.The results indicated that the collapse capacity of structures decreased as the frequency content was reduced. The percentage of reduction in collapse capacity under earthquakes with high to the low frequency content in 2, 4 and 6 story structures were 68, 67 and 71, respectively. In fact, reducing the frequency content increased the probability of occurrence of low cycle fatigue mode in the brace.

Quantification of variability in simulated seismic performance of RC wall buildings

This paper quantifies the variability in the seismic performance of slender reinforced concrete (RC) wall buildings simulated using different fiber based nonlinear models. The models use the same material constitutive relationships and other analysis inputs (e.g., damping) so that the quantified variability in the building performance is caused by the numerical modeling approach rather than user-selected parameters. These models were first validated against the measured shake-table test behavior of a 7-story RC wall building. Then, nonlinear dynamic analyses of the 7-story wall test specimen and three RC wall archetype buildings of 4-, 8-, and 12-stories were conducted to quantify the variability in the resulting seismic performance assessment parameters and damage fragility curves. The variability in the numerical model responses was evaluated using ground motion suites corresponding to three hazard levels with 50%, 10%, and 2% probability of exceedance in 50 years, while the damage fragility curves were obtained following the FEMA P695 methodology. The variability was quantified based on global response parameters (interstory drift ratio and roof drift ratio) and local response parameters (plastic hinge rotation and curvature at the critical length), since these parameters are commonly used in seismic performance assessment of RC buildings. Based on the results, it is strongly recommended that the performance assessment of slender RC wall buildings be done using global response parameters rather than local response parameters, since the variability of the predicted response among the nonlinear models was significantly smaller for global response parameters.

On efficient seismic fragility assessment using sequential Bayesian inference and truncation scheme: A case study of shear wall structure

The seismic performance of shear walls in nuclear power plants is critical because a failure of such structures can cause severe accidents. Thus, research on the seismic fragility of shear walls in nuclear power plants has been attempted. However, conventional seismic fragility analysis requires high computational costs. In this context, several researchers proposed an efficient seismic fragility method by reducing required numerical analyses. But, this method still demands quite an amount of numerical cost. To overcome this issue, this paper presents an enhanced method for more efficiently assessing the seismic fragility of shear walls through sequential Bayesian inference and truncation strategy. The core idea of the proposed method introduces a binary analysis result chain and combines such a chain with sequential Bayesian inference. The sub-strategy of the method employs the truncation strategy for reducing the number of analyses. Also, an approach to evaluate a convergence index of a seismic fragility curve for each step is embedded into the sequential Bayesian inference for minimizing additional analysis cost. As a result, the proposed method of this paper reduces the computational cost even though it provides similar accuracy results compared to the existing seismic fragility methods.

A Comprehensive Approach to Earthquake-Resilient Infrastructure: Integrating Maintenance with Seismic Fragility Curves

A severe seismic event can cause significant damage to infrastructure systems, resulting in severe direct and indirect consequences. A comprehensive risk-management approach is required for earthquake-resilient infrastructure. This study presents an innovative approach to seismic risk assessment and aims to integrate maintenance considerations with seismic fragility curves. The proposed methodology uniquely quantifies the impact of maintenance conditions on seismic risk, presenting a dynamic perspective of risk changes attributable to maintenance and deterioration. The methodology hinges on the hypothesis that the maintenance condition of the infrastructure and the level of deterioration impacts the seismic resilience of the infrastructure. The methodology synergizes the Building Performance Index (BPI) and the deterioration over time to evaluate their cumulative effect on fragility curves to estimate the infrastructure’s total risk over the lifecycle (TRLC). This proposed methodology is demonstrated through a case study of a low-voltage substation in Bik’at HaYarden, Israel. A Monte Carlo simulation was carried out for the specific conditions of the analyzed substation. A comprehensive sensitivity analysis was performed to understand better the effect of maintenance conditions over time on the TRLC. Key insights reveal a statistically significant correlation between infrastructure performance and maintenance and their consequential impact on the TRLC. Notably, declining maintenance conditions intensify seismic risk uncertainties. The research proposes to researchers, stakeholders, and decision-makers a novel comprehensive perspective on the indispensability of maintenance for seismic risk management and mitigation.

Seismic performance of RC bridge piers reinforced through FRCM confinement

AbstractCorrosion of reinforced concrete (RC) structures is one of the main issues concerning existing buildings and especially of infrastructures. Corrosion phenomena, that is induced mainly by carbonatation and by high chlorides concentration, can significantly affect the performance of existing structures. In particular, the seismic performance can be significantly affected. Loss of transversal reinforcement in RC elements can reduce the concrete ductility while corrosion affecting bending reinforcement reduces the lateral load‐bearing capacity of RC elements. To enhance the performance of corroded elements and extend service life of deteriorated structures confinement is one of the most effective and commonly used techniques. This paper investigates the deterioration of the seismic performance of a RC bridge affected by corrosion and retrofitted through FRCM confinement. Different deterioration and retrofitting scenarios are combined and seismic fragility curves are computed for each case. Finally, time‐variant seismic reliability profiles are used to evaluate the best retrofitting scenario and intervention time to maximize reliability gains.

Comparative Study on Seismic Fragility Curve Derivation Methods of Buried Pipeline Using Finite Element Analysis

Comparative Study on Seismic Fragility Curve Derivation Methods of Buried Pipeline Using Finite Element Analysis

Mechanical modeling, seismic fragility, and correlation issues for groups of spherical pressure vessels

A roadmap is outlined for determining comprehensive seismic fragility curves for (single or groups of) spherical pressure vessel structures commonly found in oil refineries. The developed modeling techniques aim to strike a balance between accuracy and computational efficiency, with a focus on capturing the most pertinent failure modes relevant to these structural types. First, a set of “partial” fragilities is determined based on each vessel’s fill ratio, as the response varies substantially depending on the amount of liquid content. Considering that a seismic assessment process invariably involves simultaneous consideration of such partial fragilities, a Monte Carlo-based approach is employed for their combination. The results naturally depend on the level of correlation employed, but can be almost perfectly matched by simpler analytical methods in the edge cases of full and zero correlation.

A mechanical-based seismic vulnerability assessment method with an application to masonry structures in Cosenza (Italy)

AbstractThe paper presents a mechanical-based framework for the evaluation of local-scale seismic fragility curves. The approach is oriented to a seismic vulnerability assessment of unreinforced masonry buildings and makes use of basic exposure data easily obtained from survey or available in existing database. An efficient finite element model and static nonlinear analyses are employed to assess the structural behaviour. The mechanical-based fragility curves are evaluated using Monte Carlo simulations that allow to account for the uncertainties propagation. The proposed approach is tested on a case-study regarding the city centre of Cosenza, in southern Italy, using exposure information available from CARTIS database.

Seismic vulnerability of shield tunnels in interbedded soil deposits: Case study of submarine tunnel in Shantou Bay

This paper presents a numerical approach for deriving seismic fragility curves for a submarine shield tunnel subjected to transverse ground shaking in interbedded soil deposits. To simulate the nonlinear behavior of soils, PM4Sand and HS-small constitutive models were adopted. In contrast, the closed-form elastic design method or elastic–plastic design method was used for modeling the shield tunnel lining considering the effect of joints on the seismic performance of structures. Fully coupled numerical analyses provided a satisfactory interpretation of the seismic responses of soil–structure systems considering the effects of groundwater level and soil–tunnel interaction. Subsequently, free-field peak ground acceleration was selected as the intensity measure. The ratio of maximum bending moment to capacity bending moment or permanent joint rotation of the tunnel lining was selected as the damage measure, combined with incremental dynamic analysis, a series of fragility curves were generated. In this study, one-dimensional equivalent-linear earthquake site response analysis was implemented to validate the nonlinear dynamic analysis under weak earthquakes. However, the analysis overestimates the amplitude periodic vibrations in interbedded soil deposits under strong earthquakes. Additionally, numerical results show that the examined tunnel is prone to slight or moderate damage under ground shaking, and its joints are more vulnerable to damage than its segments. The fragility curves constructed were compared with existing fragility curves, highlighting the significant effects of local soil profiles, groundwater conditions, soil–tunnel interaction, and segmental joints on the seismic vulnerability of shield tunnels in a submarine environment. The developed fragility functions contribute to the prediction of seismic damage to submarine shield tunnels of similar characteristics, enabling the rapid and efficient response of structures to disasters in ocean engineering.

Evaluation of performance and storey drift ratio limits of high-rise structural systems with separated gravity and lateral load resisting systems using time history analysis and incremental dynamic analysis

To increase the efficiency of prefabricated construction of high-rise structure, a composite structural system with separated gravity and lateral load resisting systems (referred to as a ‘new separable system’) is proposed. Efficient numerical models of the composite frames, reinforced-concrete (RC) shear walls, RC coupling beams, and braces in the new separable system were developed using the finite-element program MSC.Marc. The fragility curves of these components were developed through parametric analysis and a literature review of previous research and database documents. Through time history analysis, the responses of roof displacement, storey drift, and residual drift were analysed and compared with those of the traditional composite frame–shear wall system. An incremental dynamic analysis (IDA) was performed to obtain the IDA curves of the new separable system and the traditional system, and the seismic fragility curves of the two systems were built. The seismic performance of the new separable system was compared with that of the traditional system in terms of the collapse probability, dynamic safety factor, and risk of seismic damage. The results indicated that for high-rise composite structural systems with separated gravity and lateral resisting systems under frequently occurring earthquakes, the reasonable range of the storey drift ratio limit in design is 1/800 to 1/1000, and a limit value of 1/1000 is recommended conservatively.

EFFECT OF EPISTEMIC UNCERTAINTY ON SEISMIC FRAGILITY OF BASE-ISOLATED RC-BUILDING FRAME USING INCREMENTAL DYNAMIC ANALYSIS

The quantification and impact of epistemic uncertainty in the RC frame building can analyze due to recent advancements in processing power and the availability of reliable seismic vulnerability assessment techniques. In the present study, a base-isolated 10-story RC building frame is designed and analyzed per the latest Indian standards, with lead rubber bearing as the base isolation system. The selected base-isolated RC frame building was analyzed using probabilistic and deterministic approaches. As the fundamental epistemic uncertainty parameter, the mechanical strength of concrete and steel is considered. The Monte-Carlo method is determined the unpredictability of the RC frames' structures. The incremental dynamic analysis is conducted per the FEMA P695 guidelines to evaluate the wide range of 32 far-field ground motions on the base-isolated RC frame structure. Maximum roof drift ratio responses are utilized to generate the seismic fragility curve by adopting the several threshold values of damage index, such as, slight, moderate, severe, and complete. The traditional linear regression method is implemented to derive the seismic fragility curves of various damage thresholds. The study results reveal that the deterministic strategy is more likely to predict damage by 10 to 25 percent less than the probabilistic approach. The probabilistic analysis approach shows that epistemic uncertainty significantly affects the prediction of the seismic damage probability