Seismic retrofitting of a reinforced concrete building with strongly different stiffness in the main directions

The displacement capacity of the existing reinforced concrete building under study does not satisfy the seismic Italian Code requirements. The modal analysis highlights that the structure has strongly different stiffnesses along its main directions and, in the stiffer one, translation is coupled with torsion. To improve the seismic behavior of the building, it is proposed to install an external steel frame with stiff braces along the side of the structure which is the most deformable due to torsional effect. Conversely, in the orthogonal direction, where the ductility demand is much higher, external steel frames with dissipative braces are used. The effectiveness of the proposed solution is checked by push-over analysis.