Master of Science
Civil and Environmental Engineering
El Damatty, A.
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. A load reduction factor is chosen by the designer and accordingly a certain ductility capacity needs to be achieved in the structure. Two reasons have triggered the investigation of this ductility-based concept under wind loads. First, 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. Second, the structure always possesses a certain level of ductility that the wind design does not benefit from. The load reduction factor that could be applied in wind design might not be as high as its counterpart in seismic design, and it should be applied only on the resonant component of the wind loading. 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 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 pressure 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 redesigned these walls. Displacement-controlled pushover analysis is carried out to assess the ductility demand of shear walls with reduced cross sections to justify the application of the load reduction factor “R”. Furthermore, a parametric study is conduced to evaluate the effect of ductility level on target performance level reached in each shear wall.
Elezaby, Fouad Y., "A performance based design approach for tall buildings under wind loading" (2017). Electronic Thesis and Dissertation Repository. 5101.
Available for download on Saturday, December 15, 2018