• 한국지진공학회논문집
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• 제26권6호
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• pp.255-265
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• 2022

In order to determine fragility curves, the limit state of piers for each damage level is suggested in this paper based on the previous test results in Korea, including our test results. In previous studies, the quantitative measures for damage levels of piers have been represented by curvature ductility, lateral drift ratio, or displacement ductility. These measures are transformed to lateral drift ratios of piers for consistency, and the transformed values are compared and verified with our push-over test results for flexural RC piers with a circular cross-section. The test specimens are categorized concerning the number of lap-splices in the plastic hinge region and whether seismic design codes are satisfied or not. Based on the collected test results in Korea, including ours, the lateral drift ratio for each pier damage level is suggested.

• Structural Engineering and Mechanics
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• 제51권3호
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• pp.447-470
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• 2014

Numerical simulation of the non-linear behavior of (RC) structural walls subjected to severe earthquake ground motions requires a reliable modeling approach that includes important material characteristics and behavioral response features. The objective of this paper is to optimize a simplified method for the assessment of the seismic response and damage development analyses of an RC structural wall building using macro-element model. The first stage of this study investigates effectiveness and ability of the macro-element model in predicting the flexural nonlinear response of the specimen based on previous experimental test results conducted in UCLA. The sensitivity of the predicted wall responses to changes in model parameters is also assessed. The macro-element model is next used to examine the dynamic behavior of the structural wall building-all the way from elastic behavior to global instability, by applying an approximate Incremental Dynamic Analysis (IDA), based on Uncoupled Modal Response History Analysis (UMRHA), setting up nonlinear single degree of freedom systems. Finally, the identification of the global stiffness decrease as a function of a damage variable is carried out by means of this simplified methodology. Responses are compared at various locations on the structural wall by conducting static and dynamic pushover analyses for accurate estimation of seismic performance of the structure using macro-element model. Results obtained with the numerical model for rectangular wall cross sections compare favorably with experimental responses for flexural capacity, stiffness, and deformability. Overall, the model is qualified for safety assessment and design of earthquake resistant structures with structural walls.

• Structural Monitoring and Maintenance
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• 제9권2호
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• pp.107-127
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• 2022

Structural health monitoring (SHM) has been related to damage identification with either operational loads or other environmental loading playing a significant complimentary role in terms of structural safety. In this study, a non-parametric method of time frequency analysis on the measurement is used to address the time-frequency representation for modal parameter estimation and system damage identification of structure. The method employs the wavelet decomposition of dynamic data by using the modified complex Morlet wavelet with variable central frequency (MCMW+VCF). Through detail discussion on the selection of model parameter in wavelet analysis, the method is applied to study the dynamic response of both steel structure and reinforced concrete frame under white noise excitation as well as earthquake excitation from shaking table test. Application of the method to building earthquake response measurement is also examined. It is shown that by using the spectrogram generated from MCMW+VCF method, with suitable selected model parameter, one can clearly identify the time-varying modal frequency of the reinforced concrete structure under earthquake excitation. Discussions on the advantages and disadvantages of the method through field experiments are also presented.

• Earthquakes and Structures
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• 제8권5호
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• pp.1113-1126
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• 2015

A damage localization algorithm based on Operational Deformed Shapes and known as Interpolation Damage Detection Method, is herein applied to the finite element model of a cable stayed bridge for detecting and localizing damages in the stays and the supporting steel beams under the bridge deck. Frequency Response Functions have been calculated basing on the responses of the bridge model to low intensity seismic excitations and used to recover the Operational Deformed Shapes both in the transversal and in the vertical direction. The analyses have been carried in the undamaged configuration and repeated in several different damaged configurations. Results show that the method is able to detect the damage and its correct location, provided an accurate estimation of the Operational Deformed Shapes is available. Furthermore, the damage detection algorithm results effective also when damages coexist at the same time at several location of the cable-stayed bridge members.

• Geomechanics and Engineering
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• 제12권1호
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• pp.161-183
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• 2017

This paper investigates the damage identification of the concrete pile element through axial wave propagation technique using computational and experimental studies. Now-a-days, concrete pile foundations are often common in all engineering structures and their safety is significant for preventing the failure. Damage detection and estimation in a sub-structure is challenging as the visual picture of the sub-structure and its condition is not well known and the state of the structure or foundation can be inferred only through its static and dynamic response. The concept of wave propagation involves dynamic impedance and whenever a wave encounters a changing impedance (due to loss of stiffness), a reflecting wave is generated with the total strain energy forked as reflected as well as refracted portions. Among many frequency domain methods, the Spectral Finite Element method (SFEM) has been found suitable for analysis of wave propagation in real engineering structures as the formulation is based on dynamic equilibrium under harmonic steady state excitation. The feasibility of the axial wave propagation technique is studied through numerical simulations using Elementary rod theory and higher order Love rod theory under SFEM and ABAQUS dynamic explicit analysis with experimental validation exercise. Towards simulating the damage scenario in a pile element, dis-continuity (impedance mismatch) is induced by varying its cross-sectional area along its length. Both experimental and computational investigations are performed under pulse-echo and pitch-catch configuration methods. Analytical and experimental results are in good agreement.

• 한국지진공학회논문집
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• 제9권6호
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• pp.41-52
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• 2005

서울시 모델 구역의 건축물을 대상으로 가상 시나리오 지진에 의한 피해를 추정하였다. 다양한 주거 및 구조 특성을 대표할 수 있고 지반 증폭 효과를 고려할 수 있는 지역을 모델 구역으로 선정하였다. 모델 구역 내 건축물은 구조 형식에 따라 11 종류로 분류하였으며 HAZUS에서 제시한 값을 사용하여 역량 곡선(capacity curve)과 취약도 곡선(fragility curve)을 생성하였다. 가상 시나리오 지진의 지반 운동은 인공 지진 운동 생성 방법을 사용하여 생성하였으며 모델 구역을 표토층 두께에 따라 3개의 구역으로 나누고 지반응답해석을 수행하였다. 건축물의 피해 확률은 역량 스펙트럼 방법과 취약도 곡선을 사용하여 계산하였다. 최종적으로 GIS 데이터베이스를 활용하여 모델 구역 내 건축물의 전반적 피해 정도를 추정하였다.

• 터널과지하공간
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• 제16권1호
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• pp.50-57
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• 2006

도로 확충으로 인한 도로 사면 및 터널 시공의 증가, 핵폐기물, 원유, LPG 저장을 위한 지하 저장 비축기지 개발, 지하 발전소의 개발 등이 갈수록 증가하고 있다. 이들 구조물 개발의 증가와 함께 구조물 주위를 구성하고 있는 암반의 상태를 적절하게 판단할 수 있는 방법도 필요하게 되었다. 이러한 목적에 기인하여 작고 가벼우면서 사용이 간편한 탄성파 검층 시스템을 개발하였다. 탄성파 검층법은 다양한 형태의 암반 상태를 평가하기 위하여 사용될 수 있는 검층법 중의 하나로써 원위치에서 비교적 간편하게 정밀한 자료를 수집할 수 있다. 또한 탄성파 검층법은 지보재가 설치되기 전후 구조물의 거동을 평가하는데도 유용하게 사용될 수 있다. 본 연구를 통하여 얻은 결과에 의하면 첫째, 탄성파 검층법을 이용하여 화약발파로 인한 암반사면 내의 손상 정도를 정량적으로 평가하는 것이 가능하였으며, 암반사면 내의 손상대 범위도 합리적으로 결정할 수 있었다. 둘째, 탄성파 검층의 조사 결과를 이용하면 지보재의 설치 심도를 보다 효과적이고 경제적으로 결정할 수 있을 것으로 기대된다. 마지막으로, 탄성파 검층법은 지보재의 설치 전후에 대한 구조물의 안전 관리에도 적용될 수 있을 것으로 사료된다.

• Structural Monitoring and Maintenance
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• 제7권4호
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• pp.319-344
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• 2020

Inverse analysis of non-linear reinforced concrete bridge pier using recursive Gaussian filtering for in-situ condition assessment is the main theme of this work. For this purpose, minimum variance unbiased estimation using unscented sigma points is adopted here. The uniqueness of this inverse analysis lies in its approach for strain based updating of engineering demand parameters, where appropriate bound and constrained conditions are introduced to ensure numerical stability and convergence. In this analysis, seismic input is also identified, which is an added advantage for the structures having no dedicated sensors for earthquake measurement. First, the proposed strategy is tested with a simulated example whose hysteretic properties are obtained from the slow-cyclic test of a frame to investigate its efficiency and accuracy. Finally, the experimental test data of a full-scale bridge pier is used to study its in-situ condition in terms of Park & Ang damage index. Overall the study shows the ability of the augmented minimum variance unbiased estimation based recursive time-marching algorithm for non-linear system identification with the aim to estimate the engineering damage parameters that are the fundamental information necessary for any future decision making for retrofitting/rehabilitation.

• 한국해안·해양공학회논문집
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• 제25권6호
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• pp.412-421
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• 2013

최근 서해안 등지에서 중소규모 지진이 빈번하게 발생하고 있다. 이러한 지진에 의한 항만 구조물의 손상 및 파괴는 국가 경제에 큰 피해를 유발할 수 있다. 따라서 이러한 지진에 대비하기 위한 내진 설계 및 지진 경보시스템 개발이 필요한 실정이다. 본 연구에서는 항만 지진 피해 예측 시스템에 입력치 제공을 위한 부산 및 인천항의 안벽 구조물의 지진 취약도 해석을 수행하였다. 해석 대상은 부산 및 인천항의 잔교식, Caisson식, 부벽식, 블록식 안벽을 각각 4가지 Case를 해석하였으며 기능수행수준 및 붕괴방지수준에 대하여 변위기반 지진취약도 해석을 수행하였고 해석결과를 다른 항만의 안벽에도 적용할 수 있도록 회귀분석하였다.

• Earthquakes and Structures
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• 제17권6호
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• pp.599-609
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• 2019

After an earthquake, a quick seismic assessment of a structure can facilitate the recovery of operations, and consequently, improve structural resilience. Especially for facilities that play a key role in rescue or refuge efforts (e.g., hospitals and power facilities), or even economically important facilities (e.g., high-tech factories and financial centers), immediately resuming operations after disruptions resulting from an earthquake is critical. Therefore, this study proposes a prompt post-earthquake seismic evaluation method that uses displacement and acceleration measurements taken from real structural responses that resulted during an earthquake. With a prepared pre-earthquake capacity curve of a structure, the residual seismic capacity can be estimated using the residual roof drift ratio and stiffness. The proposed method was verified using a 6-story steel frame structure on a shaking table. The structure was damaged during a moderate earthquake, after which it collapsed completely during a severe earthquake. According to the experimental results, a reasonable estimation of the residual seismic capacity of structures can be performed using the proposed post-earthquake seismic evaluation method.