• 한국지진공학회논문집
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• 제17권3호
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• pp.133-141
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• 2013

This paper presents the seismic evaluation and prediction of a damaged piloti-type Reinforced Concrete (RC) building before and after post-retrofitting under successive earthquakes. For considering realistic successive earthquakes, the past records measured at the same station were combined. In this study, the damaged RC building due to the first earthquake was retrofitted with a buckling-restrained brace (BRB) before the second earthquake occurred. Nonlinear Time History Analysis (NTHA) was performed under the scaled intensity of the successive ground motions. Based on the extensive structural response data obtained form from the NTHA, the fragility relationships between the ground shaking intensity and the probability of reaching a pre-determined limit state was were derived. In addition, The the fragility curves of the pre-damaged building without and with the BRBs were employed to evaluate the effect of the successive earthquakes and the post-retrofit effect. Through the seismic assessment subjected to the successive records, it was observed that the seismic performance of the pre-damaged building was significantly affected by the severity of the damage from the first earthquake damages and the hysteresis behavior of the retrofit element.

• 한국구조물진단유지관리공학회 논문집
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• 제13권5호통권57호
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• pp.149-159
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• 2009

본 연구에서는 1980년대 표준설계도면에 의해서 건설된 국내 학교건물을 대상으로 일본 내진진단 기준, 비선형 정적 및 동적해석을 수행하여 내진안전성을 평가하였다. 내진진단 결과, 구조내진지표($I_S$)는 0.2~0.4로 평가 되었으며, 이 결과는 150gal정도의 지진 규모에서 중규모 이상의 지진피해를 받을 가능성이 있다고 판단된다. 비선형 정적해석결과, 장변방향은 부재각 R=1/150rad., 단변방향은 1/100rad.에서 각각 항복하였으며, 비선형 동적해석결과, Hachinohe. EW(200gal)입력지진동에서 대상건물 1층 장변방향 19.85cm 및 단변방향 23.3cm의 최대 지진응답변위를 각각 나타내었다. 지진피해도 판정법을 이용하여 1980년대 국내 학교건물의 내진안전성을 최종적으로 평가한 결과에 의하면 150gal이상의 지진에서 중규모 지진피해가 발생할 가능성이 예측되며, 내진보강 등 실제적인 지진대책이 시급하다고 판단된다.

• 대한건축학회논문집:구조계
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• 제35권2호
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• pp.3-11
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• 2019

The recent earthquake of Pohang (M5.4) and the Gyeongju earthquake (M5.8) suggested the possibility of a strong earthquake in Korea and reminded us that the Korea is no longer an earthquake-safe zone. In the disaster recovery stage in a disaster like an earthquake, the investigation of the damage situation and the safety assessment of the building serve to provide important information for the initial action such as establishment of the recovery strategy and rescue of the survivor. However, the research that depends on manpower can not cope with the difficulty of processing a large number of doses in a short time, and the expertise of the manpower must be taken into consideration, which may result in delayed initial action. In this study, we propose an rapid safety evaluation technique of building using unmanned aerial vehicle which evaluates the performance and safety of buildings by integrating conventional safety inspection method with unmanned aerial vehicle technology and developed evaluation method of each evaluation factor. In order to verify this, the buildings damaged by the earthquake in Pohang were checked and compared using this system. The results are consistent with the results of the existing emergency earthquake risk assessment. As a result, the possibility of checking the emergency safety using the unmanned aerial vehicle for the damaged structures in case of a large-scale disaster such as an earthquake was confirmed.

• 한국구조물진단유지관리공학회 논문집
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• 제15권3호
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• pp.106-115
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• 2011

본 연구에서는 비선형 지진응답해석을 이용하여 유도된 전단 및 휨파괴형 부재가 혼합된 저층 철근콘크리트(RC) 건물의 비선형 요구내력스펙트럼을 수식화하여, 특정 연성률 별로 지진입력수준과 내진성능잔존률을 산정하여, 건물의 지진손상정도를 정량적으로 평가 가능한 새로운 내진성능 평가법을 제안하였다. 또한 저층 RC 건물을 대상으로 본 연구의 내진성능 평가법을 적용하여 평가한 결과와 보다 정밀한 부재수준의 비선형 동적해석을 실시하여 그 결과를 각각 비교 검토함과 동시에, 내진진단기준에서 입력지진동 0.2g 수준에 대해서 구조체에 대규모이상의 지진피해를 막기 위한 임계값으로 설정한 내진성능판정지표값 (Es=0.6)과의 상관관계를 분석하여 본 연구에서 제안한 내진성능 평가법의 타당성 및 그 적용가능성을 검증하였다. 본 평가법은 비선형해석 또는 능력스펙트럼법 등의 상세 내진성능 평가법을 수행하지 않고도 대상건물에 대한 연성률 단계별의 입력지진 수준, 지진손상도를 정량적으로 평가할 수 있다. 향후 전단 및 휨파괴형 부재가 혼합된 저층 RC 건물의 내진성능을 효과적으로 평가하기 위한 자료로서 활용이 가능하다고 판단된다.

• Earthquakes and Structures
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• 제24권2호
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• pp.81-90
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• 2023

The maximum drifts are important to the seismic evaluation of steel buildings and connections, but the information can hardly be obtained from the post-earthquake field investigation. This research studies the feasibility of using the loss rate of bolt pretension as an earthquake damage predictor. Full-scale tests were made on four steel connections using bolted-web-welded-flange details. One connection was unreinforced (UN), another was reinforced with double shear plates (DS), and the other two used reduced beam sections (RBS). The preinstalled strain gauges were used to control the pretensions and monitor the losses of the high-strength bolts. The results showed that the loss rate of bolt pretension was highly related to the damage of the connections. The pretensions lost up to 10% in all the connections at the yield drifts of 0.5% to 1%. After yielding of the connections, the pretensions lost significantly until fracture occurred. The UN and DS connections failed with a maximum drift of 4 %, and the two RBS connections showed better ductility and failed with a maximum drift of 6%. Under the far-field-type loading protocol, the loss rate grew to 60%. On the contrary, the rate for the specimen under near-fault-type loading protocol was about 40%. The loss rate of bolt pretension is therefore recommended to use as an earthquake damage predictor. Additionally, the 10% and 40% loss rates are recommended to predict the limit states of connection yielding and maximum strength, respectively, and to define the performance levels of serviceability and life-safety for the buildings.

• 한국지진공학회논문집
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• 제7권4호
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• pp.89-95
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• 2003

본 논문에서는 시간영역에서의 응답을 이용하여 복잡한 트러스의 구조물에서 발생할 수 있는 손상의 위치와 크기를 추정할 수 있는 알고리즘을 제안하였다. 일정한 시간동안 획득한 응답데이터를 각 부재별 평균 변형에너지를 구하기 위하여 공간적으로 확장하였다. 이렇게 확장된 평균 변형에너지는 다시 손상 지표를 구축하는데 사용하였으며, 손상 지표는 손상 전과 손상 후의 구조물의 강성의 비이다. 본 논문에서 제안한 방법론의 타당성은 유한요소 모델로 손상을 모의하고 이로부터 얻은 응답데이터를 적용하여 입증하였다. 또한 응답데이터에 노이즈를 추가하여 노이즈가 제안한 알고리즘에 미치는 영향도 분석하였다.

• Structural Engineering and Mechanics
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• 제86권5호
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• pp.589-605
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• 2023

This paper investigates the ductility demands of steel frames equipped with self-centring fuses under near-fault earthquake motions considering multiple yielding stages. The study is commenced by verifying a trilinear self-centring hysteretic model accounting for multiple yielding stages of steel frames equipped with self-centring fuses. Then, the seismic response of single-degree-of-freedom (SDOF) systems following the validated trilinear self-centring hysteretic law is examined by a parametric study using a near-fault earthquake ground motion database composed of 200 earthquake records as input excitations. Based on a statistical investigation of more than fifty-two (52) million inelastic spectral analyses, the effect of the post-yield stiffness ratios, energy dissipation coefficient and yielding displacement ratio on the mean ductility demand of the system is examined in detail. The analysis results indicate that the increase of post-yield stiffness ratios, energy dissipation coefficient and yielding displacement ratio reduces the ductility demands of the self-centring oscillators responding in multiple yielding stages. A set of empirical expressions for quantifying the ductility demands of trilinear self-centring hysteretic oscillators are developed using nonlinear regression analysis of the analysis result database. The proposed regression model may offer a practical tool for designers to estimate the ductility demand of a low-to-medium rise self-centring steel frame equipped with self-centring fuses progressing in the ultimate stage under near-fault earthquake motions in design and evaluation.

• Earthquakes and Structures
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• 제8권1호
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• pp.37-56
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• 2015

The Emilia, May-July 2012, earthquake has dramatically highlighted the only the hazards facing the people in insufficiently secured workplaces, but also the socio-economic consequences of interruption of production activities. After the event, in order to guarantee suitable safety levels, the Italian government asked for a generalized seismic retrofit of buildingsaffected by the earthquake under consideration. Considering that Emilia is one of the most industrialized Italian region, the number of the industrial buildings to be verified could however lead to not acceptable resumption of production time. So, with the aim to speed up the recovery, were leaved out from this request the buildings which had undergone a strong enoughshaking without any damage. In practice, the earthquakes were being used as a "test" to evaluate the seismic structural strength. Besides, the Italian government provision specifies also the zones, within which buildings that escaped evident damage are exempt from obligatory checks, and termed "exclusion zones", shall be individuated using the data provided by the Italian National Institute of Geophysics and Volcanology in the form of so-called "shakemaps". Obviously, the precision of such data greatly influences the determination of the exclusions zones and so all the economic issues related to them. Starting from these considerations, the present paper describes an evaluation of the reliability of the procedure of shakemap generation with specific regard to the seismic events that struck the Emilia region on May 20 and 29, 2012.

• Earthquakes and Structures
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• 제9권2호
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• pp.339-352
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• 2015

Ancient masonry towers constitute a relevant part of the cultural heritage of humanity. Their earthquake protection is a topic of great concern among researchers due to the strong damage suffered by these brittle and massive structures through the history. The identification of the seismic behavior and failure of towers under seismic loading is complex. This strongly depends on many factors such as soil characteristics, geometry, mechanical properties of masonry and heavy mass, as well as the earthquake frequency content. A deep understanding of these aspects is the key for the correct seismic vulnerability evaluation of towers and to design the most suitable retrofitting measure. Recent tendencies on the seismic retrofitting of historical structures by means of prestressing are related to the use of smart materials. The most famous cases of application of prestressing in towers were discussed. Compared to horizontal prestressing, vertical post-tensioning is aimed at improving the seismic behavior of towers by reducing damage with the application of an overall distribution of compressive stresses at key locations.

• Structural Monitoring and Maintenance
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• 제3권1호
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• pp.51-69
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• 2016

Monitoring the performance and estimating the remaining useful life of aging civil infrastructure in the United States has been identified as a major objective in the civil engineering community. Structural health monitoring has emerged as a central tool to fulfill this objective. This paper presents a review of the major structural monitoring programs that have been recently implemented in the United States, focusing on the integrity and performance assessment of large-scale structural systems. Applications where response data from a monitoring program have been used to detect and correct structural deficiencies are highlighted. These applications include (but are not limited to): i) Post-earthquake damage assessment of buildings and bridges; ii) Monitoring of cables vibration in cable-stayed bridges; iii) Evaluation of the effectiveness of technologies for retrofit and seismic protection, such as base isolation systems; and iv) Structural damage assessment of bridges after impact loads resulting from ship collisions. These and many other applications show that a structural health monitoring program is a powerful tool for structural damage and condition assessment, that can be used as part of a comprehensive decision-making process about possible actions that can be undertaken in a large-scale civil infrastructure system after potentially damaging events.