Seismic Retrofitting of a Reinforced Concrete Building with Unidirectional Frames and Low Strength Concrete

The displacement capacity of an existing Reinforced Concrete (RC) school building, representative of medium-high vulnerability structures, does not meet the requirements of the current Italian Building Code. The building structure is made by unidirectional frames and shear walls. The modal analysis reveals that the building has low torsional stiffness, with translation in the direction of the frames coupled with torsional motion. For seismic retrofitting, a minimally invasive solution involving external steel braced frames, placed adjacent to the building façades, is proposed. These frames aim to enhance the building’s torsional stiffness and reduce the ductility demands on the RC structural elements. The proposed intervention is deemed adequate, with its effectiveness evaluated through nonlinear dynamic analysis. To comply with the Code requirements, local strengthening interventions are also proposed.