Abstract

There are locations in Canada where buildings are equally affected by wind and earthquake loads. In these areas, designers may rise questions about the governing lateral load. It is known that buildings are designed to respond in the elastic range under wind load and in the inelastic range when subjected to earthquake load. Besides, there are other elements that influence the building responses under lateral loading, such as: building configuration, height, selected ductility level, structural irregularity types and geotechnical characteristics.
This thesis addresses the effect of wind-induced shear and torsion on 22 low-rise and medium-rise steel buildings located on Site Class C and Site Class B. These buildings were designed as earthquake resistant systems according to the 2015 edition of National Building Code of Canada (NBCC 2015) and Steel Design standard specifications (CSA S16-2014). The study examines the impacts from building configurations by considering different width-to-length ratios and heights on two sets of buildings: i) width-to-length ratio 1:4 and ii) width-to-length ratio 1:2. The 1st set comprises five buildings with heights ranging from 14.8 m (4-storey low-rise building) to 43.6 m (12-storey medium-rise building). The 2nd set comprises only medium-rise buildings with 8, 10, and 12 storeys. In addition, two types of ductility levels were selected for the lateral force resisting systems (LFRS): limited-ductility (LD-CBF) and moderately-ductile concentrically braced frames (MD-CBF). Two types of geotechnical characteristics were considered: Site Class C (firm soil) and Site Class B (rock). All designed buildings are structural regular. The effects from torsion, notional lateral load, and P- effect was also studied.
On the process of computing wind load, several ambiguities have been found in the NBCC 2015 wind load provisions. Consequently, recommendations were made to resolve these issues. In addition, these recommendations were implemented in several low-rise and medium-rise buildings before comparing with the results obtained when the ASCE/SEI 7-10 standard and the wind tunnel test were used. It was found that for low-rise buildings, the American standard and Canadian code yielded similar shear but quite different torsional coefficients. On the other hand, for medium-rise buildings, clear agreement was found, for both shear and torsion coefficients.
The comparisons between earthquake and wind loadings show that depending on building heights, horizontal dimensions, location and ductility level, the dominant loads are different. In taller, larger and more ductile buildings in Montreal, for direction normal to the larger face, wind loads may exceed the earthquake loads in the lower floor levels. In all other cases, earthquake load controls the design. For Montreal buildings taller than 8 storeys, selecting LD-CBF is recommended for the LFRS in order to balance the earthquake/wind design criteria. Caution should be given to buildings taller than 10 storeys when verifying the building deflection under the dynamic effect of wind load.