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Single-storey braced steel frame buildings (SSBSFs) are currently the most widely used commercial structures, which include strip malls, power centres, warehouses, small and medium-sized industrial plants. The lateral seismic or wind forces acting on such low-rise structures are usually transferred from a metal roof-deck diaphragm to a system of vertical bracing members. Because these flexible roof diaphragms have a considerable effect on the dynamic response of SSBSFs during an earthquake, they also play an important role in the evaluation of the fundamental vibration period, a key parameter in determining the magnitude of the design seismic forces. It is therefore of utmost importance to reliably predict the fundamental period of SSBSFs. This paper presents the results of a four-year field measurement research project on the dynamic behaviour of SSBSFs. The goal of the project was to create a reliable database for the dynamic characteristics of SSBSFs (periods, mode shapes, and damping) and to find a relationship between them and the geometric parameters (height and plan dimensions). The field tests are described, along with the selected buildings and experimental setup. The measured fundamental periods are then compared to the National building code of Canada (NBCC) empirical equations. A statistical analysis of the data, based on different regression models, yielded new proposed building geometric parameters to be used in simple equations for the prediction of the fundamental period of SSBSFs. [ABSTRACT FROM AUTHOR]