Jungwhee Lee

This study proposes a simplified modeling technique for use in combination with the perfectly matched layer (PML) element, aiming to improve computational efficiency and reliability in soil-structure interaction (SSI) analysis. The simplified model was validated against a detailed model with differences in stiffness and natural frequencies within 1%, confirming its accuracy in simulating static and dynamic responses. The SSI analysis was performed using semi-infinite and PML applied soil models. With the use of the PML element, the size of the soil domain was reduced to 1/5 of the semi-infinite model, which significantly reduced the analysis time to approximately 7% while maintaining identical natural frequencies. These results demonstrate the effectiveness of combining the simplified modeling technique and the PML element for efficient and reliable SSI analysis. Future work should explore its application to various structures and soil conditions.

This study investigates how structural dynamic characteristics affect the response to high-frequency dominant seismic excitations, using a 3D numerical analysis considering soil–structure interaction (SSI). For this purpose, an SSI analysis was conducted using the finite element analysis software LS-DYNA, incorporating four representative Korean geotechnical characteristics and the 2016 Gyeongju earthquake, characterized by dominant high-frequency components. A comparison was conducted between a fixed-end model without considering SSI and an embedded model with SSI for a high-rise structure (40 stories) with low natural frequencies, and a low-rise structure (5 stories) with high natural frequencies. The analysis focused on key dynamic responses, including the natural frequency, frequency of maximum response, and maximum relative displacement of the structures, to identify differences in the SSI effect based on the structures’ dynamic characteristics and the soil types. The analysis generally revealed that the SSI effect lowers the natural frequencies of structures and increases the damping effect. It was also found that depending on the match between the dominant frequency range of the seismic excitations and the range of the structure’s natural frequencies, larger dynamic responses were calculated when SSI was considered, suggesting that it may be necessary to consider SSI for conservative design results.

한국전산구조공학회 논문집 제37권 제6호(2024.12) 361 1. 서 론 원자력발전소 구조물에 항공기 충돌이 발생하는 경우, 항 공기 전체의 충격에 의한 전반거동과 항공기 엔진 속 회전축 (Shaft)에 의한 국부손상이 함께 발생하는 것이 일반적이다. 국 부손상은 항공기 엔진 속 회전축(Shaft)과 같은 강성 충돌체에 의한 구조물의 국부적인 손상을 의미하며 다음과 같은 세 가 지 단계로 진행된다. 1) 미사일의 타겟 관입, 2) 타겟의 전면 박 리 및 후면 박리, 3) 관입이 진행됨에 따른 미사일의 타겟 완전 관통. 여기서 후면박리란 미사일과 타겟의 충돌 반대면에서 타겟의 일부가 떨어져 파편화 되는 것을 의미하며, 이를 배면 파쇄(Scabbing)라고도 한다(NEI07-13, 2011). 배면파쇄가 발생하면 원전 벽체 내부의 시스템 및 사용자의 피해를 초래할 수 있기 때문에 배면파쇄의 발생 유무 및 범위 를 파악하는 것은 중요하다. 설계 시 배면파쇄가 발생하지 않 는 원전 벽체의 두께는 일반적으로 실험을 통해 예측된 산정 식을 사용하여 결정한다. 하지만 대부분의 국부손상 산정식은 콘크리트의 강도, 벽체 두께, 발사체의 충돌속도 및 직경 등의 영향만을 고려하여 평가하고, 철근 및 강재라이너의 영향은 포함되어 있지 않다.

As the demand and construction of cable-stayed bridges have increased, research on the safety of cable-stayed bridges in the event of natural disasters such as fires and explosions is actively being conducted. If a cable-stayed bridge is damaged by an unexpected natural disaster or accident, it can cause serious traffic congestion and huge economic losses. This study evaluates the usability of the cable-stayed bridge in the event of cable damage. Additionally, seismic performance and the impact of the damage are evaluated by numerical analysis. To achieve this goal, the cable-stayed bridge is modeled using 3D BEAM elements and two-node cable elements. Then, the impact of the damage was evaluated by gradually damaging the cable. The deflection, axial force of the girder, and cable stress changes under far-field ground motion (El-Centro earthquake) were reviewed. A representative dynamic analysis program LS-DYNA was utilized for the numerical analyses. The results show that the loss of a small number of cables does not affect the usability of the bridge. However, if five or more cables are continuously lost, or if an earthquake occurs when cables are already lost, excessive deflections and changes in the girders’ axial forces can cause usability problems.

Piloti‐type structure is a popular architectural style consisting of only columns or minimum number of shear‐resisting walls on the first floor. The large difference in lateral stiffness between the first and the upper floors makes the structure very vulnerable to earthquakes. Through the recent earthquakes in Gyeongju (2016) and Pohang (2017), due to such structural disadvantages, many damage cases have been reported, especially in low‐rise piloti‐type buildings with five stories or less. In this study, seismic soil‐structure interaction (SSI) analysis is conducted on low‐rise piloti‐type buildings considering Korean geotechnical characteristics, and the effect is analytically evaluated. To achieve this goal, seismic SSI analysis applying the measured Gyeongju earthquake and design response spectrum (DRM) based on the architectural design codes are conducted by constructing three‐dimensional structural analysis models with a five‐story piloti‐type building and four different soil properties: fill (FI), alluvial soil (AS), weathered soil (WS), and weathered rock (WR). From the analysis results, it is found that WS soil is largely affected by the seismic SSI, and the influence of the seismic SSI is different for each soil type regardless of the type of earthquake. Through the parameter study, simple and reasonable estimates are proposed to consider the SSI effect on the base shear in low‐rise piloti‐type buildings.

Cable-stayed bridges are infrastructure facilities of a highly public nature; therefore, it is essential to ensure operational safety and prompt response in the event of a collapse or damage, which are caused by natural and social disasters. Among social disasters, blast accidents can occur in cable-stayed bridges as a result of explosions produced by vehicle collisions or terrorist attacks; this can lead to the degradation in their structural performances and subsequent collapse. In this research, a procedure to assess structural blast-resistance performance is suggested based on a numerical analysis approach, and the feasibility of the procedure is demonstrated by performing an example assessment. The suggested procedure includes (1) selection of major structural components that severely affect the global structural behavior, (2) set-up blast hazard scenarios consisting of various blast levels and locations, and (3) assessment of the components using numerical blast simulation. By performing an example assessment, the critical blast level for each component could be determined and the blast location that affects the considering components the most severely could be found as well. The scenario-based assessment process employed in this study is expected to facilitate the evaluation of bridge structures under blasts in both existing bridges and future designs.