Current seismic fragility functions for buildings were developed by defining damage state threshold based on story drift concerning foreign references and using the capacity spectrum method based on spectral displacement. In this study, insufficient details and dependence on the core location of piloti-type buildings were not reflected in the fragility function because it was developed before the Pohang earthquake. In order to develop an improved one for piloti-type buildings, several types of core were selected, damage state threshold was determined based on the capacity of structural members, and three-dimensional analyses were utilized. As a result, seismic fragility functions based on spectral acceleration were developed for various core locations and different shear strengths of the column stirrup. The fragility of piloti-type buildings significantly varied according to core location, an additional single wall, and whether the contribution of column stirrup was included or not. To estimate fragility more reasonably, it is necessary to prepare the parameters to reflect actual state well.

가속도로부터 변위를 계산 방법 중 상대적으로 사용이 간단한 변위재구성기법이 Lee et al.(2010)과 Hong et al.(2010)에 의해 제안되었다. 목표주파수는 변위재구성기법을 사용할 때 사용자가 결정해야 할 중요한 변수 중 하나로 이것을 결정하기 위해선 주파수영역 분석에 대한 경험이 필요하다. 이 논문은 지진하중을 받는 사장교에 한정된 변위재구성기법의 목표주파수 결정 방법을 제시한다. 사장교가 지진에 의해 가진될 경우 목표주파수는 유효한 모드의 고유주파수 중 가장 낮은 주파수로 결정된다. 여기서 유효한 모드라 함은 가속도의 자유도에 유의미한 영향을 주는 모드형상을 가진 모드를 의미한다. 제안된 목표주파수 결정방법의 타당성을 검증하기 위해 포항지진 발생 당시 측정된 3개 실 교량의 주경간 중앙에서 측정된 가속도와 변위 시간이력을 분석했다. 또한 제안된 방법을 포항지진 발생 당시 측정된 실교량의 주탑 상단 가속도에 적용해 계산된 변위를 분석했다.

In 2017 Pohang Earthquake, a number of residential buildings with pilotis at their first level were severely damaged. In this study, the results of an analytical investigation on the seismic performance and structural damage of two bearing wall buildings with pilotis are presented. The vibration mode and lateral force-resisting mechanism of the buildings with vertical and plan irregularity were investigated through elastic analysis. Then, based on the investigations, methods of nonlinear modeling for walls and columns at the piloti level were proposed. By performing nonlinear static and dynamic analyses, structural damages of the walls and columns at the piloti level under 2017 Pohang Earthquake were predicted. The results show that the area and arrangement of walls in the piloti level significantly affected the seismic safety of the buildings. Initially, the lateral resistance of the piloti story was dominated mainly by the walls resisting in-plane shear. After shear cracking and yielding of the walls, the columns showing double-curvature flexural behavior contributed significantly to the residual strength and ductility.

The The purpose of this study is to investigate the actual liquefaction occurrence site in Pohang area and to analyze the ground characteristics of Pohang area using the data of the National Geotechnical Information DB Center and to calculate the liquefaction potential index. Based on the results, the distribution of soil classification in Pohang area and the risk of liquefaction under various earthquake accelerations were prepared. As a result of the study, soils in Pohang has the soil characteristics that can cause the site amplification phenomenon. In the analysis through liquefaction hazard maps under earthquake scenarios, it is found that the liquefaction occurred in the area of Heunghae town is more likely to be liquefied than other areas in Pohang. From these results, it is expected that the study on the preparation of liquefaction hazard maps will contribute to the preparation of countermeasures against liquefaction by predicting the possibility in the future.

The Pohang earthquake with a magnitude of 5.4 occurred on November 15, 2018. The epicenter of this earthquake located in south-east region of the Korean peninsula. Since instrumental recording for earthquake ground motions started in Korea, this earthquake caused the largest economic and life losses among past earthquakes. Korea is located in low-to moderate seismic region, so that strong motion records are very limited. Therefore, ground motions recorded during the Pohang earthquake could have valuable geological and seismological information, which are important inputs for seismic design. In this study, ground motions associated by the 2018 Pohang earthquake are generated using the point source model considering domestic geological parameters (magnitude, hypocentral distance, distancefrequency dependent decay parameter, stress drop) and site amplification calculated from ground motion data at each stations. A contour map for peak ground acceleration is constructed for ground motions generated by the Pohang earthquake using the proposed model.

This study aims to create a disaster management system after an earthquake. Japan’s earthquake disaster management system, including the Disaster Countermeasures Basic Act, addresses all of the disaster phases of prevention, mitigation, preparedness and emergency response as well as recovery and reconstruction with roles and responsibilities among the national and local governments clearly defined. Korea’s earthquake disaster management system are including the Disaster Countermeasures Basic, but when the 9.12 earthquake occurred, problems such as insufficient early response, study on the earthquake lack were revealed. This study conducted a field survey and analyzed coping process after Po Hang earthquake. Therefore, this study have found that Disaster Management Headquarters are operated rapidly. They are coped with urgent safety inspection for damage facilities and soil liquefaction with advanced equipment. And The headquarters interviewed with victims. So they found out What the victims needed. However, when carrying out relief activities, Research of temporary housing and allocation of donations was not rapid. Further, this study have found that earthquake specialists were lack and disaster information transfer was not working. This study will be utilized as fundamental data in planning disaster management system after an earthquake.

A total of 594 reservoirs (17%), which are managed by KRC, equipped with earthquake-resistant facilities whereas remaining ones did not. In addition, reservoirs were placed without the effect of geological structures (i.e., fault and lineament). Therefore, development on technique for alleviating the potential hazards by natural disasters along faults and lineaments has required. In addition, an effective reinforcement guideline related to the geological vulnerabilities around reservoirs has required. The final goal of this study is to suggest the effective maintenance for the safety of earth fill dams. A radius 2 km, based on the center of the reservoir in the study area was set as the range of vulnerability impacts of each reservoir. Seismic design, precise safety diagnosis, seismic influence and geological structure were analyzed for the influence range of each reservoir. To classify the vulnerability of geological disasters according to the fault distribution around the reservoir, evaluation index of seismic performance, precise safety diagnosis, seismic influence and geological structure were also developed for each reservoir, which were a component of the vulnerability assessment of geological disasters. As a result, the reservoir with the highest vulnerability to geological disasters in the pilot district was analyzed as Kidong reservoir with an evaluation index of 0.364. Within the radius of 100km from the epicenter of the Pohang earthquake, the number of agricultural infrastructure facilities subject to urgent inspections were 1,180 including reservoirs, pumping stations and intakes. Four reservoirs were directly damaged by earthquake among 724 agricultural reservoirs. As a result of the precise inspection and electrical resistivity survey of the reservoir after the earthquake, it was reported that cracks on the crest of reservoirs were not a cause of concern. However, we are constantly monitoring the safety of agricultural facilities by Pohang aftershocks.

Pohang earthquake occurred on November 15, 2017, with a magnitude of 5.4. The damage of the structure caused by the Pohang earthquake was the most significant in 4-story piloti-type buildings, where the damage patterns were different according to the location of columns and walls at the first story. One　building with a staircase at a corner shows shear failure at columns, and Another building with a staircase in the middle shows no failure or shear failure at staircase walls. Therefore, two different piloti-type buildings were selected; one has a staircase at a corner and another has in the middle, and the seismic behavior of the buildings were examined by nonlinear dynamic analysis applying a ground motion measured at Pohang. Analytical model well simulated the actual behavior of the piloti-type buildings during the earthquake. Analysis results showed that walls have an insufficient shear strength wherever the location of the staircase is and columns with insufficient transverse reinforcement could be failed when the staircase is located at a corner. Conclusively, structural engineers should design columns and walls in piloti-type buildings to possess sufficient capacity according to the location of staircase.

On November 15, 2017, Pohang earthquake occurred. Its local magnitude was announced to be ML=5.4 by Korea Meteorological Administration (KMA). Ground motion data recorded at KMA stations were obtained from their data bases. From the data, horizontal and vertical response spectra, and V/H ratio were calculated. The horizontal spectra were defined as GMRotI50 spectra. From the statistical analysis of the GMRotI50 spectra, a mean plus one standard deviation spectrum in lognormal distribution is obtained. Regression analysis is performed on this curve to determine the shape of spectrum including transition periods. Applying the same procedure, the shape and transition periods of vertical spectrum were obtained. These results were compared with the Korean standard design spectra, which were developed from domestic and overseas intra-plate earthquake records, and Gyeongju earthquake response spectra. The response spectra of Pohang earthquake were found to be almost identical with the newly proposed design spectra. Even the V/H ratios showed good agreement. These results confirmed that the method adopted when developing the standard design spectra were valid and the developed design spectra were reliable.

Severe earthquakes can cause damage to society both socially and economically. An appropriate initial response can alleviate damage from severe earthquakes. In order to formulate an appropriate initial response, it is necessary to identify damage situations in societies; however, it is difficult to grasp this information immediately after an earthquake event. In this study, an earthquake damage assessment methodology for buildings is proposed for estimating damage situations immediately after severe earthquakes. A response spectrum database is constructed to provide response spectra at arbitrary locations from earthquake measurements immediately after the event. The fragility curves are used to estimate the damage of the buildings. Earthquake damage assessment is performed from the response spectrum database at the building scale to provide enhanced damage condition information. Earthquake damage assessment for Gyeongju city and Pohang city were conducted using the proposed methodology, when an earthquake occurred on September 12, 2016, and November 15, 2017. Results confirm that the proposed earthquake damage assessment effectively represented the earthquake damage situation in the city to decide on an appropriate initial response by providing detailed information at the building scale.

The probabilistic seismic safety assessment is one of the methodology to evaluate the seismic safety of the nuclear power plants. The site characteristics of the nuclear power plant should be reflected when evaluating the seismic safety of the nuclear power plant. The Korea seismic characteristics are strong in high frequency region and may be different from NRC Regulatory Guide 1.60, which is the design spectrum of nuclear power plants. In this study, seismic response of a nuclear power plant structure by Pohang earthquake (2017.11.15. (KST)) is investigated. The Pohang earthquake measured at the Cheongsong seismic observation station (CHS) is scaled to the peak ground acceleration (PGA) of 0.2 g and the seismic acceleration time history curve corresponding to the design spectrum is created. A nuclear power plant of the containment building and the auxiliary buildings are modeled using OPENSEES to analyze the seismic response of the Pohang earthquake. The seismic behavior of the nuclear power plant due to the Pohang earthquake is investigated. And the seismic performances of the equipment of a nuclear power plant are evaluated by the HCLPF. As a result, the seismic safety evaluation of nuclear power plants should be evaluated based on site-specific characteristics of nuclear power plants.

This study examines the seismic failure of RC low-rise building structures having irregularities at the ground story during the 15 November 2017 Pohang, Korea, earthquake, Mw = 5.4, which is the second strongest since the government began monitoring them in 1978 in South Korea. Some 2,000 private houses were damaged or destroyed in this earthquake. Particularly, serious damage to the piloti story of RC low-rise residential building structures of fewer than five stories was observed within 3 km of the epicenter with brittle shear failure of columns and walls due to severe torsional behavior. Buildings below six stories constructed before 2005 did not have to comply with seismic design requirements, so confinement detailing of columns and walls also led to inadequate performance. However, some buildings constructed after 2005 were damaged at the flexible side of the piloti story due to the high torsional irregularity. Based on these results, this study focuses on the problems of the seismic torsion design approach in current building codes.

2017년 11월 15일 Mw 5.4의 포항지진은 흥해지역 지하 약 4 km의 진원 깊이에서 발생하여 포항시에 막대한 피해를 끼쳤다. 포항분지의 중부에 해당하는 흥해지역은 백악기 경상누층군과 백악기 말~고신생기 초 불국사 화성암류를 기반암으로 하여 포항분지 충전물인 신신생기 연일층군이 분포한다. 이 논문에서는 포항 분지에서 지각변형물(습곡, 단층, 절리)과 포항지진 동시성 지표변형물(모래화산, 지표균열, 팝업구조)에 대한 구조지질학적 연구를 수행하여 포항분지의 변형작용사와 포항지진 동시성 지표변형의 특성을 고찰해 보았다. 연구지역의 지각변형물은 제4기 단층운동 이전까지 적어도 5회의 변형단계를 거쳐 형성되었다: (북)북동 주향에 고각 경사하는 정이동(곡강단층) 단층 형성단계, 연일층군에 광역적으로 인지되는 동-서 방향의 고각 절리와 이에 (준)평행한 단층 형성단계, 동-서 주향에 중각 내지 저각 경사하는 공액상 정이동 단층(흥해단층과 형산 단층)과 이에 수반된 동-서 계열의 습곡 형성단계, (역이동성) 좌수향 주향이동의 (북)북서 방향 단층조와 우 수향 주향이동의 동-서(북동) 방향 단층조가 고각으로 경사하는 공액상 주향이동 단층 형성단계, 북북동과 북 북서 주향에 중각 경사하는 공액상 역이동 단층과 이에 수반된 남-북 계열의 습곡 형성단계. 포항지진 동시성 지 표변형물에서 모래화산은 종종 지표균열과 (준)평행한 선상배열을 보인다. 남-북 내지 (북)북동 방향의 팝업구 조와 지표균열, 동-서 내지 서북서 방향의 지표균열 등은 포항지진 발생 응력원의 최대수평응력에 의한 지진원 단층의 역이동성 운동과 이에 수반된 상반지괴의 좌굴습곡작용에 의해 형성되었다. 이러한 구조적 활동은 지 진원 단층의 상반지괴에 해당하는 포항시 흥해읍 중심으로 광범위하게 발생하여 이곳에 막대한 재산 피해를 끼쳤다.

After Po-Hang earthquake(Magnitude 5.4, Nov.15. 2017), total 55 cut slopes along the expressway within 25km from earthquake source were examined if there were any signs of instabilities such as rockfalls, surface failure, cracks and wood tumbles. Examination revealed that no cut slope showed any abnomality. This result raise an issue if design of slope against seismic activity is necessary. In this paper, necessity and seismic analysis method are discussed.