Performance-based assessment of r.c. buildings strengthened with frp

In recent years, the use of fibre-reinforced plastic (FRP) composites to repair and strengthen existing reinforced concrete (r.c.) structures has been widely used. In this paper the performance-based assessment of r.c. framed buildings strengthened with FRP is carried out. A fiber element uniaxial model for concrete confined with FRP is used. The model accounts for the interaction between the lateral strain of concrete and the confining pressure, through the incremental-iterative approach proposed by Spoelstra and Monti [1]. The reduced effect of confinement in r.c. columns with rectangular cross section is considered through a coefficient that reduces the lateral confining pressure. This coefficient is characterized from experimental results as a function of the shape of the cross section of the columns. The performance of the building during various loading scenarios is evaluated resorting to non-linear static analysis. In particular, a method based on the Capacity Spectrum Method and the Inelastic Demand Response Spectra is used to compare the structural strength and deformation demands and the available capacities at desired performance levels. Seismic damage to the building is not only caused by the maximum response quantities like force or lateral displacement, but also by the duration-related damage that is a function of the energy absorbed in the structure. To account for the energy dissipation a procedure based on the dynamic analysis of an equivalent SDOF system is used to characterize the hysteretic energy dissipation under seismic loading starting from the monotonic energy dissipation. The Park & Ang [2] damage index and the interstory drift damage index are used as control parameters to check the attainment of the different levels of performance of the building for a given earthquake: Full Operational Level, Operational Level, Life Safety Level, Collapse Prevention Level.