Fragility analysis of structures with controlled rocking beamcolumn connections and viscous dampers

Controlled rocking system has been proposed as an alternative design method to improve the structural performance of buildings. The rocking systems allow vertical and horizontal components to rotate freely at boundaries. When integrated in a frame system, rocking columns may reduce the yielding strength of the entire system. The acceleration response of yielding structure is proportional to its own weight, but it is limited by the yield strength. Thus using a rocking system, a limited acceleration response can be achieved. However, the displacements of a structure may become undesirably large due to lower strength, but they can be controlled adding damping. A simplified model of the rocking column was developed and verified through experimental tests conducted at the University at Buffalo. As a case study in this paper, the response of an analytical model of a scaled reinforced concrete frame structure is considered. Synthetic ground motions developed using the Barrier model are used as seismic input of the nonlinear dynamic analysis. Fragility analyses are performed to show the seismic performance of the original structures and the retrofitted structure with the rocking beam-column connections and viscous dampers. The analysis shows that the story accelerations can be limited by using rocking columns, while the story displacements can be controlled by using viscous dampers.