• Wind and Structures
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• 제31권2호
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• pp.143-152
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• 2020

The wind design of buildings is typically based on strength provisions under ultimate loads. This is unlike the ductility-based approach used in seismic design, which allows inelastic actions to take place in the structure under extreme seismic events. This research investigates the application of a similar concept in wind engineering. In seismic design, the elastic forces resulting from an extreme event of high return period are reduced by a load reduction factor chosen by the designer and accordingly a certain ductility capacity needs to be achieved by the structure. Two reasons have triggered the investigation of this ductility-based concept under wind loads. Firstly, there is a trend in the design codes to increase the return period used in wind design approaching the large return period used in seismic design. Secondly, the structure always possesses a certain level of ductility that the wind design does not benefit from. Many technical issues arise when applying a ductility-based approach under wind loads. The use of reduced design loads will lead to the design of a more flexible structure with larger natural periods. While this might be beneficial for seismic response, it is not necessarily the case for the wind response, where increasing the flexibility is expected to increase the fluctuating response. This particular issue is examined by considering a case study of a sixty-five-story high-rise building previously tested at the Boundary Layer Wind Tunnel Laboratory at the University of Western Ontario using a pressure model. A three-dimensional finite element model is developed for the building. The wind pressures from the tested rigid model are applied to the finite element model and a time history dynamic analysis is conducted. The time history variation of the straining actions on various structure elements of the building are evaluated and decomposed into mean, background and fluctuating components. A reduction factor is applied to the fluctuating components and a modified time history response of the straining actions is calculated. The building components are redesigned under this set of reduced straining actions and its fundamental period is then evaluated. A new set of loads is calculated based on the modified period and is compared to the set of loads associated with the original structure. This is followed by non-linear static pushover analysis conducted individually on each shear wall module after redesigning these walls. The ductility demand of shear walls with reduced cross sections is assessed to justify the application of the load reduction factor "R".

• 한국지반공학회논문집
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• 제33권8호
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• pp.5-16
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• 2017

근입깊이가 직경에 비하여 상대적으로 작은 말뚝은 편심이 큰 횡방향 하중을 받는 경우 전도되어 파괴된다. 지금까지 횡방향하중을 받는 짧은말뚝의 지지거동에 대해서는 주로 모형실험을 적용한 연구가 수행되었지만, 전주, 표지판, 가로등 기초와 같이 매우 큰 모멘트를 받는 짧은말뚝의 지지거동은 아직까지 명확히 규명된 바 없다. 본 연구에서는 직경 750mm의 실물크기 말뚝에 대한 재하시험을 수행하였다. 실제 하중조건을 모사하기 위하여 기초로 부터 8m 이격된 지점에 횡방향 하중을 가하여 매우 큰 모멘트를 유발하였으며, 말뚝의 근입깊이를 2.0m, 2.5m, 3.0m로 변화시킨 3회의 시험을 수행하였다. 시험결과 큰 모멘트를 받는 짧은말뚝은 파괴 직전까지 변위나 회전각이 거의 발생하지 않다가 전도로 인해 급격한 변위가 발생하는 취성형태로 파괴 되었다. 이러한 거동은 기존의 횡방향 위주의 하중을 받는 짧은말뚝에서 나타난 연성파괴 거동과는 대조적이다. 기존에 제안된 세 종류의 지지력 예측식으로 부터 구한 짧은말뚝의 극한 횡방향지지력을 시험결과와 비교하였으며, 말뚝 근입깊이가 상대적으로 작은 경우는 말뚝선단 중심의 회전을 가정한 제안식이 적절하지만, 근입깊이가 커지면서 회전점을 중심으로 응력방향이 반전되는 토압분포를 가정한 제안식이 보다 적절한 것으로 평가되었다.