Seismic Rehabilitation of a Soft Story Structure with Hysteretic Dampers

Soft stories are a common reason for building collapses during severe earthquakes. This paper investigates a solution for seismic rehabilitation with hysteretic dampers for a building in Spain affected by the Lorca earthquake in 2011. The building had reinforced concrete frames, stronger beams than columns, a soft first story, and masonry walls. The dimensions of hysteretic dampers are presented in terms of their mechanical properties as stiffness, strength, and yield deformation. The energy-based method provides the stiffness, strength, and energy dissipation capacity required by hysteretic dampers to get the entire structure to endure the design earthquake without exceeding the maximum imposed drift on the first story. The seismic performance of the upgraded structure is evaluated by nonlinear dynamic analyses, considering the energy that contributes to structural damage expressed in terms of equivalent velocity based on the Seismic Standard NCSE-02, the accelerograms of the Lorca earthquake, and 23 historic earthquakes scaled to the energy input. In conclusion, the solution improves seismic performance. Hysteretic dampers increase the stiffness of the soft story and take it to similar levels to the upper stories. The modes of vibration are translational, the drift of the first story decreases by 50%, and drifts of the upper stories are kept low. The damage is concentrated on the hysteretic dampers instead of the main structure, and plastic joints are concentrated on the base of the first-story columns, which is an acceptable mechanism to dissipate energy to avoid the main structure collapse.