Design of Steel Exoskeleton Equipped with BRBs for Seismic Upgrading of RC Frames

The main part of the Italian building stock was mainly erected between ‘70s and ‘80s of the previous century. Hence, existing RC buildings present structural deficiencies because were designed according to old standards and often only considering gravity loads. The goal is to evaluate the seismic performance of these structures and compare it to the minimum standards required by current legislation. To achieve this goal, first, a building with RC framed structure has been designed according to the codes and the practice in force at the time of construction. From this building two case study frames have been derived considering different mechanical properties of the concrete. Then, the addition to the existing RC building of a steel exoskeleton equipped with BRBs is proposed for seismic upgrading of these structures and the effects of this intervention on the seismic performance of the frames are investigated. A design method of seismic upgrading interventions by exoskeleton and BRBs is developed and applied to the two case study frames. The design method is calibrated determining the seismic response of the upgraded frames by means of non-linear dynamic analyses. The parametric analysis allowed the identification of the combinations of the parameters that lead to the achievement of the performance objectives at Near Collapse and Significative Damage limit states. Both the frames designed according to this combination of design parameters show suitable seismic performance for both considered limit states. Finally, the combination of the parameters ruling the design method is determined as the most economical among those that allow the fulfilment of the requirements at NC and SD limit state.