Seismic response of two-storey buildings with concentrically braced steel frames

The seismic performance of two-storey steel buildings with concentrically braced frames as the lateral load resisting system is evaluated. The buildings are designed in accordance with the National Building Code of Canada (1995) and CSA Standard S16.1-94 for live seismic zones in western Canada. Only frames designed with a force modification factor of 1.5 are considered. Analytical models of the buildings are developed, which consider the nonlinear seismic behaviour of the concentrically braced frame, the shear strength of the roof diaphragm, and the stiffness and strength contributions of the nonstructural partitions. The seismic response is estimated with nonlinear static and dynamic time history analyses. Roof diaphragm flexibility does not influence the dynamic behaviour significantly. The distribution of lateral forces from response spectrum analysis agrees well with that specified. Current design procedures provide reasonable estimates of the lateral drift in low and moderate seismic zones. Brace ductility demands are reasonable and may be limited due to the contributions of nonstructural partitions. However, in moderate and high seismic zones, the connections, beams, columns, and roof diaphragm are overloaded. The capacity design procedure is recommended to provide adequate resistance to the overloaded components.