Seismic Performance of Concentrically Braced Steel Frames of the Conventional Construction Category

The main objective of this research project was to study the seismic behaviour of regular conventional construction (CC Type) concentrically braced steel frames (CBFs). More specifically, this objective was achieved through the following objectives: -Evaluate the deformation capacity of typical brace connections used in these structures; and -Evaluate the suitability of the 15 m height limit imposed by the 2005 NBCC. This limit should also be studied to determine whether it can be made a function of several building parameters, such as the type of connections used (ductile versus non-ductile), the building location (eastern versus western Canada), the site class (C versus E), and the number of storeys, among others. Two experimental phases were carried out in order to assess the ductility capacity of typical vertical bracing connections. For both phases, the specimens consisted of back-to-back angles bolted to a gusset plate. This configuration is representative of typical connections used in practice. The first phase consisted of testing five different connection failure modes: failure of welds parallel to loads, bolt bearing failure on the gusset plate, net area rupture of the angles, bolt shear rupture, and shear and tension block failure of the angles. All specimens were tested under monotonic tensile loadings. It was found that bolt bearing failures offered the best potential for being used as a ductile connection failure mode in CC Type buildings. The second phase consisted of performing further tests on bolt bearing failures in order to optimize their deformation capacities. Different connection parameters were studied: bolt end distance and bolt spacing, and types of holes (drilled and punched holes, standard and short-slotted holes). All specimens used 8 mm thick gusset plates, except for one sub-group of specimens where 13 mm plates were used to ensure bearing failures can take place in thicker plates.