This study proposes a methodology for the regional seismic risk assessment of structural damage to buildings in Korea based on evaluating individual buildings, considering inconsistency between the administrative district border and grid lines to define seismic hazard. The accuracy of seismic hazards was enhanced by subdividing the current 2km-sized grids into ones with a smaller size. Considering the enhancement of the Korean seismic design code in 2005, existing seismic fragility functions for seismically designed buildings are revised by modifying the capacity spectrum according to the changes in seismic design load. A seismic risk index in building damage is defined using the total damaged floor area considering building size differences. The proposed seismic risk index was calculated for buildings in 29 administrative districts in 'A' city in Korea to validate the proposed assessment algorithm and risk index. In the validation procedure, sensitivity analysis was performed on the grid size, quantitative building damage measure, and seismic fragility function update.

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.

The paper presents the damage estimation of bridge structures in Daegu city based on the scenario-based earthquakes. Since the fragility curves for domestic bridge strucures are limited, the Hazus methodology is employed to derive the fragility curves and estimate the damage. A total of four earthuquake scenarios near Daegu city are assumed and structure damage is investigated for 81 bridge structures. The seismic fragility function and damage level of each bridge had adopted from the analytical method in HAZUS and then, the damage probability using seismic fragility function for each bridge was evaluated. It was concluded that the seismic damage to bridges was higher when the magnitude of the earthquake was large or nearer to the epicenter.

Post-earthquake risk assessment technique in Korea is developed in 2013 by National Disaster Management Research Institute, at the same time, related manual and standard regulation is distributed to every local government by National Emergency Management Agency. The objectives of this research are to investigate and evaluate the post-earthquake risk assessment of 9.12 Earthquake (M5.8, Gyeongju City, 2016) and 11.15 Earthquake (M5.4, Pohang City, 2017). To suggest and improve the assessment process of post-earthquake risk, first post-earthquake risk assessment method of advanced foreign countries including US, New Zealand and Japan are compared, and post-earthquake evaluation activities in 9.12 Earthquake and 11.15 Earthquake are analyzed. From the results, it is needed to expand the adapted building and structure types and strengthen the earthquake disaster response capacity of local government.

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.

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.

In this study, the seismic performance of concrete-steel composite moment frame structures equipped with seismic retrofitting systems such as seismic reinforcement, base isolators, and bracing members, which are typical earthquake damage mitigation systems, is evaluated through nonlinear dynamic analyses. A total of five frame models were designed and each frame model was developed for numerical analyses. A total of 80 ground acceleration data were used to perform the nonlinear dynamic analysis to measure ground shear force and roof displacement, and to evaluate the behavioral performance of each frame model by measuring inter-story drift ratios. The analysis results indicate that the retrofitting device of the base isolator make a significant contribution to generating relatively larger absolute displacement than other devices due to flexibility provided to interface between ground and column base. However, the occurrence of the inter-story drift ratio, which is a relative displacement that can detect the damage of the structure, is relatively small compared with other models. On the other hand, the seismic reinforced frame model enhanced with the steel plate at the lower part of the column was found to be the least efficient.

After the Gyeong-ju 9.12 earthquake, we found the necessity of seismic design of nonstructural element is important to reduce damages in view of properties and economic losses. This study focused on the investigation of damages including both properties and human beings. It was found that most of the damages are leaking of water pipe line, rupture of glasses, spalling of roof finishing, cracks of building, and falling from roof. It was also found that the seismic design force of nonstructural elements is taking account into the natural periods, amplification factors, response modification factors to forsee inelastic behaviors. From this studies, it is recommended that more studies are necessary on the seismic design force of nonstructural element.

For earthquake loss estimation of building structures in Gangnam-Gu district in Seoul, three scenario earthquakes were selected by comparison of the response spectra of these scenario earthquakes with the design spectrum in Korean Building Code (KBC 2009), and then direct losses of the building structures in the Gangnam-Gu district under each scenario earthquake are estimated. The following conclusions are drawn from the results of damage and loss in the second scenario earthquake, which has a magnitude = 6.5 and epicentral distance =15 km: (1) The ratio of building stocks undergoing the extensive and complete damage level is 40.0% of the total. (2) The amount of direct economic losses appears approximately 19 trillion won, which is 1.2% of the national GDP of Korea. (3) About 25% of high-rise (over 10-story) RC building wall structures, were inflicted with the damage exceeding moderate level, when compared to 60% of low-rise building structures. (4) From the economical view point, the main loss, approximately 50%, was caused by the damage in the high-rise RC wall building structures.

서울을 비롯한 수도권 일대는 우리나라 인구의 약 40%가 집중되어 갑작스럽게 닥치는 지진재해에 매우 취약한 곳이다. 역사문헌 분석에 의하면 과거 2000여 년간 서울 지역에서 발생한 피해 지진의 최대 크기는 MMI 진도 VIII-IX로 평가되며, 이들 지진으로 건물의 큰 흔들림, 담장과 성첩의 붕괴, 민가 붕괴, 다수의 사상자가 발생하였다. 서울 지역에서 MM 진도 VIII 이상의 피해지진은 1세기(A.D. 27년, 89년)에 2회 발생하였으며, 약 1430여년의 긴 휴지기 후 16-17세기(1518년, 1613년, 1692년)에 다시 3회 발생하였고, 그 후 현재 까지 휴지기 상태이다. 1518년 서울 지진(진도 VIII-IX)시에는 약 19일에 걸쳐 24회 이상의 여진이 발생하였으며, 서울 인접 지역과 황해도 지역에도 20여 일간에 걸쳐 많은 유발지진을 발생시켰다. 역사문헌에 근거한 서울 지역의 발생 가능한 최대 피해 지진은 진도 VIII-IX 이며 이러한 지진의 발생은 약 1400-1500여년의 긴 간격을 보인다.

지반가속도의 초당 최대값은 최근 제정된 지진재해대책법에 따라 지진기록계로부터 통신망을 통해 방재청으로 실시간 제공되어야 한다. 본 연구에서는 현재 PGA를 기반으로 한 신속한 지진피해통보 용도로만 고려되고 있는 지반가속도의 초당 최대값의추가적인 활용성을 검토하고자, 국내외 강진자료 및 중소규모 지진자료에 대한 초당 100 샘플링된 지반가속도 자료의 1초 구간내 최대절대값을 30초 동안 적산한 결과(BSPGAk)를 CAV(Cumulative Absolute Velocity) 및 진도 등과 비교하였다. CAV는 진도와의 높은상관성으로 지진발생시 원자력발전소의 운전초과기준으로 사용되고 있으나, 계산시 초당 100 샘플링 이상의 많은 양의 지진파형 디지털자료를 필요로 하는 단점이 있다. 비교 결과 BSPGAk는 지진규모에 따른 지진동 수준과 상관없이 CAV와 전 범위에서 높은 상관성을나타내었으며, 다수의 관측소가 연계된 지진관측망 운영시 유용하게 활용될 수 있는 신속 지진피해평가 지진동 파라미터로 확인되었다.국내 중소규모 유감지진자료에 대한 지진진도 자료와의 비교결과, BSPGAk-진도 상관식을 이용한 진도추정 오차는 CAV-진도 상관식의진도추정 오차와 유사하였으며, PGA-진도 상관식보다 진도를 신뢰성 있게 추정하였다.

본 연구에서는 항만 구역의 지진피해예측 평가체계를 구축하기 위해 필요한 지진피해예측 관련 시스템 및 내진설계 현황 및 항만구조물의 지진피해 사례를 조사하였으며, 더불어 주요 항만 구역의 구조물의 현황 및 특성을 조사, 분석하였다. 이를 토대로 지반 정보와 항만 구조물의 지진 취약도를 고려한 항만 구역(구조물)의 지진피해예측 간이 평가방안을 개발하였다.

본 연구에서는 도로교의 지진피해평가체계를 구축하기 위해 필요한 정보항목들을 정의하고 우리나라 실정에 맞는 데이터 베이스 구축방법을 제시하였다. 도로교 지진피해평가를 위한 정보요소는 크게 구조물 관련 정보와 위치관련 정보로 구분하였다. 구조물 관련정보는 도로망에 위치한 교량의 지진피해를 예측하는데 필요한 도로교의 취약도 곡선 정보항목으로 구성하였다. 위치관련 정보항목인 도로망의 데이터구조는 상세한 교차로 모델링이 가능하도록 기존의 GIS 데이터구조를 보다 세분화하여 정의하였다. 고속도로망에 위치한 110개의 교량을 대상으로 시범 시스템을 개발하였으며, 제시된 데이터베이스 구축 방법은 도로망의 신속한 피해복구를 위한 의사결정 지원체계 구축에 효과적으로 활용이 가능함을 보였다.

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.

본 연구는 캘리포니아 내 고속도로망을 대상으로 지진발생 후 교통흐름의 변화를 평가하는 기법에 대하여 이루어졌으며, 고속도로망 상에 위치한 교량의 손상정도가 평가기법의 가장 기본적인 요소로 사용되었다. 본 연구에 사용된 교량의 지진취약도는 PGA 또는 PGV의 함수로 나타내어졌고, 1994년 Northridge 지진과 일련의 시나리오 지진에 대하여 교통망 손상 평가를 수행하였다. 또한 교량 보수 및 보강 후 교통망에 대한 피해정도를 정량화하기 위해 확률모델을 개발하였으며, 그 피해정도는 시간(Drivers Delay)으로 나타내었다. 본 연구가 캘리포니아를 대상으로 이루어져 국내적용 및 활용가능성에 대해서는 후속 연구가 뒤따라야 할 것으로 사료된다.

The structure which was designed until then had no resistance to earthquake, since enforcement ordinance for seismic design was established in 1988. Most of mid or low story building have no resistance to earthquake, though it is the structure which was designed since then. Prior to this experiment, the experiment, which was repair and retrofit method for seismic performance progress of the reinforcement structure which was not designed to be protected from an earthquake, had been performed and obtained good results. The aim of study is that repair the structure and evaluate seismic performance of the repaired structure in the case of the structure damaged by earthquake.