Effects of non-traditional isolator placement for Seismic retrofit

Seismic isolation delivers improved performance by means of a flexible layer at which lateral deformation is concentrated. However, for seismic retrofit applications base isolation systems can be of considerable expense, in significant part because of major alterations required at the base of the structure. The cost of introducing an additional diaphragm, constructing a seismic gap, and modifying the foundation causes the initial cost of isolation to be significantly higher than traditional non-isolation retrofit methods. To minimize initial costs, isolators may be placed directly at the top of the column level, without an additional diaphragm, instead of at the base of the building. To investigate the effects of this placement and the limits of applicability, experiments were conducted at McMaster University of a column-bearing subassembly. These experiments tested bearings on increasing flexible steel columns, investigating the effect of allowing end rotations on the bearing behaviour and the effect of large displacements on the overall stability of the beam-column system. This research looks at developing clear strength and stiffness requirements for the sub-isolation system with the aim of increasing the number of existing buildings that are candidates for retrofit with isolation.