Generally, the Load of upper structures is transferred to concrete foundations through columns supporting them. So, the anchor connection system is usually adopted in order to connect the columns and the concrete foundations. To apply this system, the column-foundation connections need to be designed with enough stiffness. This study was experimentally conducted to effectively improve the structural detail of circular CFT column-foundation connections, to which axial and lateral load simultaneously apply. For this study, the test specimen with a general anchor and an anchor frame, and the specimens with the high-tension bolt and inner reinforcement were fabricated. In addition, double base plates were adopted to have the enough stiffness of connections. The behavioral characteristics and the failure mode were investigated and compared, and the improvement of structural detail of circular CFT column-foundation connections was suggested.

In this study, a series of dynamic centrifuge tests were performed for a soil-foundation-structural interaction system in dry sand with various embedded depths and superstructure conditions. Sinusoidal wave, sweep wave and real earthquake were used as input motion with various input acceleration and frequencies. Based on the results, a natural period and an earthquake load for soil-structure interaction system were evaluated by comparing the free-field and foundation accelerations . The natural period of free field is longer than that of the soil-foundation-structure system. In addition, it is confirmed that the earthquake load for soil-foundation-structure system is smaller than that of free-field in short period region. In contrast, the earthquake load for soil-foundation-structure interaction system is larger than that of free-field in long period region. Therefore, the current seismic design method, applying seismic loading of free-field to foundation, could overly underestimate seismic load and cause unsafe design for long period structures, such as high-rise buildings.

이 논문은 반복-수평력을 받는 프리캐스트 기둥-RC 기초 Anchor 접합부의 반복-수평력에 대한 내력 특성을 규명하기 위함이다. 본 연구는 하부 기초에 프리캐스트 콘크리트 기둥과 기초를 Anchor식으로 접합한 콘크리트 구조체가 정확한 응력전달 경로 및 파괴 메커니즘에 있어서 기존의 콘크리트-강재 연결부와 어떠한 차이가 있는지 제시한다. 반복-수평력 작용하의 철근의 인발력 실험결과는 프리캐스트 기둥-RC 기초 Anchor 시공에 필요한 철근의 최소 필요 삽입 깊이를 제시한다. 또한, 실험을 통해 제시된 응력 전달 경로 및 파괴 메커니즘을 제품별 메뉴얼에 제시되어 있는 메커니즘과 비교, 검토함으로서 접합부의 명확한 응력전달 경로 및 파괴 메커니즘을 시공자의 요구 성능에 맞게 제시한다. 그러므로 본 연구를 통해 프리캐스트 콘크리트 기둥의 정확한 주근의 개수, 공칭직경, 정착 길이 등에 대한 최적의 설계 조건을 제시함으로써, 시공 시 이들에 대한 정확한 데이터를 제공한다.

This paper analyzed design bearing capacities of pile foundations strengthened by pre-loading method for vertical expansion. The bearing capacities were investigated for two different pre-loading strategies: (1) after partial removals of structural/non-structural elements (e.g. finish, masonry wall etc.); and (2) after vertical expansions. Based on the numerical studies, more than 60% of the existing piles exceeded the design bearing capacities due to the difference of pre-loading strategies, which should be considered in structural design.