• Earthquakes and Structures
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• 제9권1호
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• pp.1-27
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• 2015

In this paper Fragility Curves (FCs) relevant to existing RC framed building types representative of the Italian building population designed only to vertical load and regular in-plan have been derived from an extensive campaign of non-linear dynamic analyses. In the generation of the FCs, damage states according to the EMS98 scale have been considered while the intensity measure has been defined by adopting an integral parameter, such as the Housner intensity. FCs have been generated by varying different parameters, including building age, number of storeys, presence and position of infill panels, plan dimensions, external beams stiffness and concrete strength. In order to verify the effectiveness of the damage prediction, comparisons were made between the results obtained from the proposed FCs with those deriving from both prominent fragility studies available in the technical literature and damage distributions observed in past earthquakes. Results show that damage grades obtained by adopting the proposed FCs are generally lower than those provided by the other approaches considered. A comparison with real damage data, shows that the proposed FCs generally estimate more severe damage distributions than those observed in past earthquakes, although they give lower differences with respect to the other approaches.

• Earthquakes and Structures
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• 제1권2호
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• pp.197-214
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• 2010

The paper presents a methodology for developing earthquake damage and loss scenarios for urban areas, as well as its application to two cities located in Mediterranean countries, Grevena (in Greece) and D$\ddot{u}$zce (in Turkey), that were struck by strong earthquakes in the recent past. After compiling the building inventory in each city, fragility curves were derived using a hybrid approach previously developed by the authors, and a series of seismic scenarios were derived based on microzonation studies that were specifically conducted for each city (see companion paper by Pitilakis et al.). The results obtained in terms of damage estimates, required restoration times and the associated costs are presented in a GIS environment. It is deemed that both the results obtained, and the overall methodology and tools developed, contribute towards the enhancement of seismic safety in the Mediterranean area (as well as other earthquake-prone regions), while they constitute a useful pre-earthquake decision-making tool for local authorities.

• Structural Engineering and Mechanics
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• 제76권6호
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• pp.751-763
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• 2020

Available records of recent earthquakes show that near-field earthquakes have different characteristics than far-field earthquakes. In general, most of these unique characteristics of near-fault records can be attributed to their forward directivity. This phenomenon causes the records of ground motion normal to the fault to entail pulses with long periods in the velocity time history. The energy of the earthquake is almost accumulated in these pulses causing large displacements and, accordingly, severe damages in the building. Damage to structures caused by past earthquakes raises the need to assess the chance of future earthquake damage. There are a variety of methods to evaluate building seismic vulnerabilities with different computational cost and accuracy. In the meantime, fragility curves, which defines the possibility of structural damage as a function of ground motion characteristics and design parameters, are more common. These curves express the percentage of probability that the structural response will exceed the allowable performance limit at different seismic intensities. This study aims to obtain the fragility curve for low- and mid-rise structures of reinforced concrete moment frames by incremental dynamic analysis (IDA). These frames were exposed to an ensemble of 18 ground motions (nine records near-faults and nine records far-faults). Finally, after the analysis, their fragility curves are obtained using the limit states provided by HAZUS-MH 2.1. The result shows the near-fault earthquakes can drastically influence the fragility curves of the 6-story building while it has a minimal impact on those of the 3-story building.

• Advances in concrete construction
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• 제9권4호
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• pp.337-343
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• 2020

In the present study, by employing fragility analysis, the seismic vulnerability of a concrete girder bridge, one of the most common existing structural bridge systems, has been performed. To this end, drift demand model as a fundamental ingredient of any probabilistic decision-making analyses is initially developed in terms of the two most common intensity measures, i.e., PGA and Sa (T₁). Developing a probabilistic demand model requires a reliable database that is established in this paper by performing incremental dynamic analysis (IDA) under a set of 20 ground motion records. Next, by employing Bayesian statistical inference drift demand models are developed based on pre-collapse data obtained from IDA. Then, the accuracy and reasonability of the developed models are investigated by plotting diagnosis graphs. This graphical analysis demonstrates probabilistic demand model developed in terms of PGA is more reliable. Afterward, fragility curves according to PGA based-demand model are developed.

• Structural Engineering and Mechanics
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• 제82권3호
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• pp.385-400
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• 2022

Sky-bridges between adjacent buildings can enhance lateral stiffness and limit the impact of lateral forces. This study analysed the structural capabilities and dynamic performances of sky-bridge-coupled buildings under various sets of ground motions. Finite Element (FE) analyses were carried out with the link being iteratively repositioned along the full height of the structures. Incremental dynamic analysis (IDA) and probabilistic damage distribution were also applied. The results indicated that the establishment of sky-bridges caused a slight change in the natural frequency and mode shapes. The sky-bridge system was shown to be efficient in controlling displacement and Inter-Storey Drift Ratio (%ISDR) and reducing the probability of damage in the higher floors. The most efficient location of the sky-bridge, for improving its rigidity, was found to be at 88% of the building height. Finally, the effects of two types of materials (steel and concrete) and end conditions (hinged and fixed) were studied. The outcomes showed that coupled buildings with a sky-bridge made of steel with hinged connection could withstand ground motions longer than those made of concrete with fixed connection.

• Structural Engineering and Mechanics
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• 제88권4호
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• pp.311-322
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• 2023

Riverine flood is one of the critical natural threats to river-crossing bridges. As floods are the most-occurred natural hazard worldwide, survival probability of bridges due to floods must be assessed in a speedy but precise manner. In this regard, the paper presents a reliability-based approach for a rapid assessment of failure probability of vulnerable bridge components under floods. This robust method is generic in nature and can be applied to both concrete and steel girder bridges. The developed methodology essentially utilizes limit state performance functions, expressed in terms of capacity and flood demand, for probable failure modes of various vulnerable components of bridges. Advanced First Order Reliability Method (AFORM), Monte Carlo Simulation (MCS), and Latin Hypercube Simulation (LHS) techniques are applied for the purpose of reliability assessment and developing flood fragility curves of bridges in which flow velocity and water height are taken as flood intensity measures. Upon validating the proposed method, it is applied to a case study bridge that experiences the flood scenario of a river in Gujarat, India. Research outcome portrays how effectively and efficiently the proposed reliability-based method can be applied for a quick assessment of flood vulnerability of bridges in any flood-prone region of interest.

• 한국지진공학회논문집
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• 제20권7_spc호
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• pp.435-441
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• 2016

The Korean peninsula has known as a minor-to-moderate seismic region. However, some recent studies had shown that the maximum possible earthquake magnitude in the region is approximately 6.3-6.5. Therefore, a seismic vulnerability assessment of the existing infrastructures considering ground motions in Korea is necessary. In this study, we developed seismic fragility curves for a continuous steel box girder bridge and two typical transmission towers, in which a set of seven artificial and natural ground motions recorded in South Korea is used. A finite element simulation framework, OpenSees, is utilized to perform nonlinear time history analyses of the bridge and a commercial software, SAP2000, is used to perform time history analyses of the transmission towers. The fragility curves based on Korean ground motions were then compared with the fragility curves generated using worldwide ground motions to evaluate the effect of the two ground motion groups on the seismic fragility curves of the structures. The results show that both non-isolated and base-isolated bridges are less vulnerable to the Korean ground motions than to worldwide earthquakes. Similarly to the bridge case, the transmission towers are safer during Korean motions than that under worldwide earthquakes in terms of fragility functions.

• 한국지진공학회논문집
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• 제27권5호
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• pp.213-220
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• 2023

Seismic fragility curves play a crucial role in assessing potential seismic losses and predicting structural damage caused by earthquakes. This study compares non-sampling-based methods of seismic fragility curve derivation, particularly the probabilistic seismic demand model (PSDM) and finite element reliability analysis (FERA), both of which require employing sophisticated finite element analysis to evaluate and predict structural damage caused by earthquakes. In this study, a three-dimensional finite element model of API 5L X65, a buried gas pipeline widely used in Korea, is constructed to derive seismic fragility curves. Its seismic vulnerability is assessed using nonlinear time-history analysis. PSDM and a FERA are employed to derive seismic fragility curves for comparison purposes, and the results are verified through a comparison with those from the Monte Carlo Simulation (MCS). It is observed that the fragility curves obtained from PSDM are relatively conservative, which is attributed to the assumption introduced to consider the uncertainty factors. In addition, this study provides a comprehensive comparison of seismic fragility curve derivation methods based on sophisticated finite element analysis, which may contribute to developing more accurate and efficient seismic fragility analysis.

• 한국구조물진단유지관리공학회 논문집
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• 제10권4호
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• pp.135-144
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• 2006

지진에 대한 구조물의 특성, 지반과의 상호작용, 현장 조건 등의 예측에 다수의 불확실성이 존재하는 경우 그 취약성 또는 손상도를 평가하는 방법이 필요하다. 본 연구에서는 범용구조해석 프로그램과 일반적인 확률밀도함수를 사용하여 면진 콘크리트 교량의 손상도 곡선을 구하는 방법을 제시하였으며, 제시된 방법을 교량에 적용하여 교량의 손상도를 평가하였다. 손상도 곡선을 작성하는 데에는 2변수를 갖는 대수정규분포를 사용하였으며, 지진의 여러 특성인 최대지반가속도(PGA), 최대지반속도(PGV), 스펙트럼가속도(SA), 스펙트럼속도(SV), 스펙트럼강도(SI) 등에 대해 납 면진받침(LRB)이 설치된 면진교량의 손상도 곡선을 구하였다. 또한 손상도 곡선의 합성 방법을 사용하여 합성된 면진교량의 손상도 곡선을 유도하였다.

• 국제강구조저널
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• 제18권4호
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• pp.1325-1335
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• 2018

This study dealt with investigating the seismic performance of the smart and shape memory alloy (SMA) and magnets plus rubber-spring (MRS) dampers and their effects on the seismic resistance of multiple-span simply supported bridges. The rubber springs in the MRS dampers were pre-compressed. For this aim, a set of experimental works was performed together with developing nonlinear analytical models to investigate dynamic responses of the bridges subjected to earthquakes. Fragility analysis and probabilistic assessment were conducted to assess the seismic performance for the overall bridge system. Fragility curves were then generated for each model and were compared with those of as-built. Results showed dampers could increase the seismic capacity of bridges. Furthermore, from system fragility curves, use of damper models reduced the seismic vulnerability in comparison to the as-built bridge model. Although the SMA damper showed the best seismic performance, the MRS damper was the most appropriate one for the bridge in that the combination of magnetic friction and pre-compressed rubber springs was cheaper than the shape memory alloy, and had the similar capability of the damper.