In the United States, seismic design standards are crucial in classifying buildings into Risk Categories I to IV. These categories are based on the buildings' occupancy type and the potential risk they pose to public safety, the protection of human life, and the socioeconomic consequences of structural collapse in the event of an earthquake. As the risk category increases, a higher seismic importance factor and more stringent drift limits are imposed on the respective building. This results in enhanced lateral strength and stiffness of the seismic force-resisting system. This study, which compares the seismic demands of special moment frame buildings assigned to high-risk categories, focusing on static system overstrength, ductility, and collapse risk, provides practical insights for structural engineers and architects. For this purpose, nonlinear static and dynamic analyses are performed to quantify the seismic demands of 18 steel frame buildings assigned to Risk Categories II, III, and IV. The findings indicate that buildings in Risk Category II do not meet the target collapse risk of 1% in 50 years, as specified in ASCE/SEI 7. For buildings in higher risk categories, the equivalent lateral force method for estimating seismic base shear is deemed more effective in ensuring adequate seismic performance.

The 3T irregular shape structure is used for designing wind loads in high-rise buildings. Among them, the Tapered shape is a shape with a cross-section that changes throughout the entire floor. Recently, various advanced Tapered shapes have been applied, such as having a cross-section that varies only in part of the height or combining different shapes. In this study, an analysis model was selected by applying three types of Tapered part locations(Bottom, Middle, Top) and angles as design variables. Equivalent static seismic loads and historical earthquake records were applied to compare and analyze the seismic response of the Tapered models with regular-shaped models. As a result of the analysis, positioning the partial taper in the middle shows the lowest seismic response. Additionally, a larger taper angle decreased the story drift ratio, top-story displacement, shear wall shear force, and column bending moment, while increasing absolute acceleration and column axial force.

최근 지구온난화로 인한 피해가 심각해짐에 따라 화석연료 사용을 줄이고자 친환경 수소 에너지의 활용이 증가하고 있다. 이에 따라 수소의 저장 및 운송을 위한 수소 저장 용기의 수요가 확대되고 있으나, 현재 널리 사용되고 있는 강재 기반 저장 용기는 부식과 같은 내구성 저하 현상에 취약하다. 따라서 선행 연구는 지지부 부식에 따른 내진 성능 저하 문제를 해결하기 위해 부식 저항성 이 뛰어난 CFRP를 지지부 기둥을 적용하여 설계 하중에서 적용성을 검토하였다. 이때 본 연구는 CFRP의 강도-중량비가 높음을 고려 하여 기존 강재 구조물 지지부 ㄱ 단면 대비 높은 강성을 가진 H 단면과 ㅁ 단면을 지지부 기둥에 적용하여 연구를 수행하였다. 이때 실제와 가까운 해석 결과를 도출하기 위해 고유진동수 추출해석을 진행하여 감쇠 계수를 적용 시켰고, AC 156 인공 지진을 설계 하중 으로 적용한 결과, ㅁ 단면을 적용한 강재 기둥의 접합부 응력은 222.34 MPa로 기존 ㄱ 형강 대비 78.93%로 설계 하중에 만족함을 보였다. ㅁ 단면 적용 CFRP 기둥은 파손 지수(DI)를 통해 평가하였고, 이때 최대 DI는 수지 인장에서 발생하였으며, 그 값은 0.708로 파괴 기준 대비 29.2% 낮아 설계 하중에 만족함을 보였다. 또한, 기초 슬래브에서 쪼갬 인장 응력과 휨 인장 응력을 통한 평가를 진행 하였고, 현장 실험 결과와 마찬가지로 설계 하중에 휨 인장 파괴가 발생하는 것으로 확인하였다. 하지만 파단 시점은 CFRP에서 1.54배 오래 설계 하중에 견디는 것을 확인하여, 그 적용성을 확인하였다. 결론적으로 지진의 발생 빈도가 높아짐에 따라 수소 저장 용기의 안전성 확보가 시급하다. 따라서 기존 강재 대상 구조물의 부식으로 인한 강성 저하 문제를 해결하기 위해, 높은 내구성 및 부식 저항성 재료의 적용은 필수적이다. 동시에 기초 슬래브의 안전성 확보에 대한 연구가 추가적으로 수행되어야 한다.

Existing reinforced concrete buildings with seismically deficient columns experience reduced structural capacity and lateral resistance due to increased axial loads from green remodeling or vertical extensions aimed at reducing CO2 emissions. Traditional performance assessment methods face limitations due to their complexity. This study aims to develop a machine learning-based model for rapidly assessing seismic performance in reinforced concrete buildings using simplified structural details and seismic data. For this purpose, simple structural details, gravity loads, failure modes, and construction years were utilized as input variables for a specific reinforced concrete moment frame building. These inputs were applied to a computational model, and through nonlinear time history analysis under seismic load data with a 2% probability of exceedance in 50 years, the seismic performance evaluation results based on dynamic responses were used as output data. Using the input-output dataset constructed through this process, performance measurements for classifiers developed using various machine learning methodologies were compared, and the best-fit model (Ensemble) was proposed to predict seismic performance.

Reinforced concrete (RC) piloti buildings are vulnerable in the event of earthquake because the stiffness in the 1st story columns is weak to compare with the members in upper stories. In this study, seismic performances of RC piloti structures were evaluated considering with different types of floor plane layouts according to core eccentricity. With four types of floor plane layouts, five stories plioti structures were evaluated by two approaches, a nonlinear pushover analysis and a nonlinear time-history analysis. In order to improve seismic performances by satisfying the collapse prevention (CP) level, two ductile reinforcing methods by carbon fiber sheets and steel jackets were applied. Due to eccentricities in stiffness and mass with directions of plane and vertical stories, piloti structures were greatly influenced by higher order modes, so the seismic performances by the time-history analysis were significantly different from by the static pushover analysis.

과거 지진 발생 시 구조요소에 비해 비구조요소에서 더 많은 피해가 발생하였다. 비구조요소의 손상은 건물 및 시설의 기능에 영향을 줄 뿐만 아니라 인명피해를 유발할 수 있다. 건축물 내진설계 기준에서는 피난경로상의 비구조요소는 내진설계 또는 검토가 필요하다. 국내에서는 경주지진 이후 피난경로에 위치할 수 있는 천장 시스템의 내진성능 검증이 활발히 진행되고 있다. 그러나 옥외 계단, 문 등에 설치되는 캐노피 시스템의 내진설계 및 검증은 미흡한 실정이다. 지진으로 인해 캐노피가 위치유지를 하지 못하여 탈락 하거나 손상될 경우, 피난경로가 차단되어 인명피해로 이어질 수 있으므로 내진설계 및 내진성능을 평가할 필요가 있다. 따라서 본 연구에서는 모듈형 캐노피 시스템을 개발하고, 주요 요소에 대한 구조실험을 수행하였으며, 기존의 캐노피 시스템과 그 성능을 비교분 석 하였다.

Piloti-type buildings are widely constructed in urban areas of South Korea. Due to stiffness irregularities, piloti-type buildings are vulnerable to lateral loads such as earthquakes. Although seismic retrofitting is necessary for piloti-type buildings, many of these structures are privately owned, and the extensive number of buildings creates significant challenges in terms of cost and time for regional seismic performance evaluation. This study proposes a methodology for determining the seismic performance of multiple piloti-type buildings within a region by utilizing structural parameters. Information on piloti-type buildings is classified into public building data and exterior building data, which are integrated to define structural parameters for estimating the first natural period of the buildings. Linear regression analysis was performed to develop a regression equation correlating structural parameters with the natural period. Additionally, the natural period and structural parameters are used to perform another linear regression analysis to estimate the yield and ultimate points of the capacity curve. The capacity curves derived from the regression equations facilitate seismic performance evaluation based on structural parameters.

The seismic performance of lead-rubber bearings (LRBs) is significantly affected by both the axial force and loading rate they experience. Accurate assessment of LRBs’ seismic performance, therefore, requires realistic simulation of these forces and rates, as well as of the response of the isolated structure during seismic events. This study conducted a series of real-time hybrid simulations (RTHS) to evaluate the seismic behavior of LRBs in such conditions. The simulations focused on a two-span continuous bridge isolated by LRBs atop the central pier, exposed to horizontal and vertical ground motions. In the RTHS framework, the LRBs were physically tested in the laboratory, while the remainder of the bridge was numerically modeled. Findings from these simulations indicated that the vertical ground motion had a minimal effect on the lateral response of the bridge when isolated by LRBs.

Structures compromised by a seismic event may be susceptible to aftershocks or subsequent occurrences within a particular duration. Considering that the shape ratios of sections, such as column shape ratio (CSR) and wall shape ratio (WSR), significantly influence the behavior of reinforced concrete (RC) piloti structures, it is essential to determine the best appropriate methodology for these structures. The seismic evaluation of piloti structures was conducted to measure seismic performance based on section shape ratios and inter-story drift ratio (IDR) standards. The diverse machine-learning models were trained and evaluated using the dataset, and the optimal model was chosen based on the performance of each model. The optimal model was employed to predict seismic performance by adjusting section shape ratios and output parameters, and a recommended approach for section shape ratios was presented. The optimal section shape ratios for the CSR range from 1.0 to 1.5, while the WSR spans from 1.5 to 3.33, regardless of the inter-story drift ratios.

The primary purpose of this study is to develop system modules of school buildings and the seismic loss function of the system modules for regional loss assessment of school buildings. System modules of school buildings were developed through statistical analysis of school facilities in Korea. The structural system of school buildings with non-seismic details is defined as reinforced concrete with partially masonry walls (RCPM), and 27 system modules of RCPM were developed considering the number of stories, spans, and the age of the building. System modules were designed to assess the structural behavior by applying the shear spring model and the shear failure of the columns of the school building. Probabilistic seismic demand models for each component of system modules were derived through nonlinear dynamic analysis to determine the relationship between seismic intensity, drift ratio, and peak floor acceleration of system modules. The seismic loss function was defined as the total damage ratio, which is the ratio of replacement cost to repair cost to evaluate the seismic loss quantitatively. The system module-based seismic loss well predicted the observed data. It will be possible to help many stakeholders make risk-informed decisions for a region through the regional loss assessment of school buildings in Korea.

In densely populated urban areas, reinforced concrete residential buildings with an open first floor and closed upper floors are preferred to meet user demands, resulting in significant vertical stiffness irregularities. These vertical stiffness irregularities promote the development of a soft-story mechanism, leading to concentrated damage on the first floor during seismic events. To mitigate seismic damage caused by the soft-story mechanism, stiffness-based retrofit strategies are favored, and it is crucial to determine an economically optimal level of retrofitting. This study aims to establish optimal seismic retrofit strategies by evaluating the seismic losses of buildings before and after stiffness-based retrofitting. An equivalent single-degree-of-freedom model is established to describe the seismic response of a multi-degree-of-freedom model, allowing for seismic demand analysis. By convolving the seismic loss function with the hazard curve, the annual expected loss (EAL) of the building is calculated to assess the economic losses. The results show that stiffness-based retrofitting increases first-story lateral stiffness by 20-40%, enhancing structural seismic performance, but also results in a rise in EAL compared to the as-built state, indicating lower cost-effectiveness from an economic perspective. The research concludes that retrofit options that increase first-story lateral stiffness by at least 60% are more appropriate for reducing financial losses.

There are now many seismic observatory stations, excluding the acceleration monitoring network for infrastructures, of more than 300 operated by several public and governmental organizations across South Korea. The features of the site and properties of the stations were not investigated, and they have been assumed or guessed to estimate the site-specific seismic responses during the 2016 Gyeongju and 2017 Pohang earthquake events. For these reasons, various and intensive geotechnical and geophysical investigations have been conducted to quantify the site characteristics at 15 seismic stations selected in southeastern Korea. The VS profiles were, at first, obtained by performing only a downhole seismic test (DHT) at 7 stations, and were compared with those from a surface wave method. Then, the shear wave velocity (VS) profiles were deduced by combining three types of in situ seismic methods composed of a cross-hole seismic test, DHTs, and full-waveform sonic loggings at the 8 other stations, especially to complement the application limits of DHT and reduce the depth-dependent uncertainty in VS profile. The representative site characteristic profiles for each station regarding VS and VP with borehole stratigraphy and density were determined based on robust investigations. Various site parameters related to seismic responses at the seismic stations of interest were obtained for the site-specific geotechnical information, which would be useful to earthquake engineering practices.

This study presents a seismic fragility assessment methodology incorporating the cumulative damage effects of repeated seismic loading on structures. Conventional seismic fragility assessment methods typically focus on single earthquakes across multiple structures; however, seismic events often occur in sequences, with each event adding cumulative damage that can amplify the overall damage. Ignoring the effects of repeated earthquakes in fragility assessments may lead to underestimating seismic risk. This study proposes a simplified but efficient fragility assessment method that accounts for repeated earthquake effects using probabilistic combinations of each damage state. This procedure applied the capacity spectrum method to consider capacity degradation from displacement caused by prior earthquakes. Applying various earthquake scenarios, this study analyzes the effects of damage accumulation from earthquake occurrence sequences, structural behavior types, and seismic design levels on the fragility of structures under repeated earthquake events.

Reinforced concrete (RC) moment frames are widely used to resist lateral loads associated with wind and earthquakes. However, most older RC moment frames performed poorly against past earthquakes. In moment frames, beam-column connections play a crucial role in system performance. Among the connections, corner connections are more vulnerable because they are restrained by only two beams and are affected most strongly by bidirectional loading. High-performance fiber-reinforced cementitious composites (HPFRCC) were used in previous studies to improve the seismic performance of older beam-column connections. This study aims to evaluate the level of improvement of seismic behavior of older beam-column connections under bidirectional loading after retrofitted with HPFRCC by comparing the seismic behavior of the HPFRCC connections to beam-column connections used in intermediate (IMF) and special moment frames (SMF). Test results revealed that the seismic behavior of the HPFRCC connections was almost close to that of SMF connections.

저층 건축물의 횡-비틀림 거동은 고차모드 효과를 증폭시킬 수 있으며, 내진성능평가 시 관련 기준은 고차모드 지배 구조물에 대해 비선형정적해석과 함께 선형동적해석을 추가로 수행하도록 규정하고 있다. 선형동적절차에는 상당한 안전계수가 적용되므로, 이는 과도한 내진보강설계로 이어질 수 있다. 이를 방지하기 위해 엔지니어들은 내진보강 시 고차모드 효과를 줄이기 위해 시행착오법을 사용해 왔다. 그러나 시행착오법에는 많은 시간과 노력이 소요되며, 결정된 보강안이 최적인지 확인하기 어렵다. 본 연구는 저층 건 축물의 수학적 모델을 수립하고 응답스펙트럼해석을 통해 고차모드 효과에 비틀림이 독립적으로 미치는 영향을 파악하였다. 이를 바탕으로 효율적인 내진보강 설계를 위해 활용될 수 있는 도표와 절차를 제시하였다. 제시된 절차를 통해 최소한의 내진보강으로 횡- 비틀림 거동하는 저층 건축물의 고차모드 효과를 효율적으로 감소시킬 수 있음을 확인하였다.

The dome structure is suitable as a roof for large spatial structures because it can maintain the shape without installing columns in the internal space. However, the structure characteristics of the lower and upper structures of the dome structure are different, and damage may occur when an earthquake occurs. Therefore, in this study, mid-story isolation system was applied to the ribbed dome and geodesic dome structures to analyze the seismic response of the lower and upper structures according to the dome shape. As a result of the analysis, the displacement of the ribbed dome increased, but the deformation of the ribbed dome and the response of the lower structure decreased, and the seismic response of the geodesic dome decreased overall. From this result, the effect of the isolator according to the shape of the dome structure was confirmed, and the mid-story isolation is considered effective in reducing the seismic response of the upper and lower structures.

Performance-Based Seismic Design (PBSD) is an approach that evaluates how structures will perform under different levels of seismic activity. It focuses on ensuring that buildings not only withstand earthquakes but also meet specific performance objectives, such as minimizing damage or maintaining functionality after the event. Unlike traditional methods, PBSD allows for more tailored, cost-effective designs by considering varying degrees of acceptable damage based on the structure's importance and use. PBSD was introduced in Korea in 2016 to replace elastic design, which is inevitable to over-design to cope with all variables such as earthquakes and winds. When PBSD is applied to the structural design new building, One of the challenges of PBSD is the complexity involved in creating accurate inelastic analysis models. The process requires significant time and effort to analyze the results, as it involves detailed simulations of how structures will behave under seismic stress. Additionally, organizing and interpreting the analysis data to meet performance objectives can be labor-intensive and technically demanding. In order to solve this problem, a post-processor program was developed in this study. A post-processor was developed based on Excel program using Visual Basic for Applications(VBA). Because analysis outputs of Perform-3D, that is a commercial software for structural analysis and design, are very complicated, generation of tables and graphs for report is significant time and effort consuming task. When the developed post-processor is used to make the seismic design report, the required task time is significantly reduced.