Seismic Risk Assessment of Existing RC Frame-Buildings with Shear Walls

In Italy, Reinforced Concrete (RC) core structural systems, formed by RC walls and frames, represent a common solution for existing multi-story buildings designed only for gravity loads. However, the most of the available studies on seismic assessment of existing RC buildings are focused on framed structures, and engineering demand parameters (EDPs) for the construction of fragility curves are in turn calibrated for RC frames. The presence of the core significantly modifies the global behaviour of the building, producing torsional effects and structural irregularities. For these reasons, the EDPs commonly adopted for framed structures (such as the inter-story drift) and the corresponding damage threshold levels could be not appropriate for core structural systems and possible alternative solutions should be explored. The problem is treated in this work by considering a reference case study, represented by an existing six-story RC framed building with a stairwell core, whose position is asymmetric in plan. The structural behaviour of the building is studied by performing pushover analyses on a finite element model including both geometric and mechanical non-linearity. Different EDPs are considered for the construction of fragility curves and the obtained results are compared to verify their suitability to the case of core structural systems.