An Innovative Seismic Force Resisting System for Damage-Free Self-centring Elastic Response of Low-Rise Steel Building Structures

An innovative braced frame system is proposed to develop nonlinear elastic self-centring response for low-rise steel building structures for which enhanced seismic performance is required. The system comprises an inverted-V-bracing with brace-to-beam connections at the first level that are detailed to transmit compression loads by direct bearing and open under tension load. Energy is dissipated by friction upon gap opening and closing in the connections. This behaviour intentionally reduces the stiffness of the first storey that acts similar to a base isolation system for the building. V-braces connected to the floor beams are also provided in the first storey to develop sufficient effective stiffness upon activation of the inverted-V-braced frame nonlinear response. This new system is first described, together with the equations that can be used to calculate the first-storey effective period and equivalent viscous damping properties that are needed to control the building lateral displacements. The system is then used for two- and three-storey buildings located in Montreal, QC, and Vancouver, BC. Nonlinear response history analyses are then performed to examine its seismic response under design level ground motions. The results show that the system can exhibit enhanced seismic performance in terms of peak lateral displacements and peak horizontal floor and roof accelerations, with no structural damage nor residual deformation. This exploratory study also shows that peak lateral displacements can be reliably predicted using the simple single-mode method for base isolation systems.