SIMPLIFIED ANALYTICAL METHODOLOGIES FOR SEISMIC FRAGILITY ASSESSMENT OF RC BUILDINGS WITH INFILLS

The development of analytical methodologies for seismic vulnerability assessment and damage prediction, used in the evaluation of seismic damage scenarios and risk assessment of building portfolios, is necessarily based on a reasonable compromise between accuracy and simplicity, because of the detail level – often very low – of the available input data on buildings’ characteristics, and the need for a limitation of the computational demand. Then, it can be useful to develop analytical methodologies with different levels of simplification (and, thereby, of approximation). In this study, a spectral analytical procedure – based on the simplified definition of capacity curves representative of the nonlinear static response of Reinforced Concrete (RC) buildings and of the corresponding damage displacement thresholds at different Damage States, and the consequent assessment of seismic capacity, up to the definition of fragility curves, within a statistical framework – is calibrated on the basis of another, less simplified, spectral analytical procedure, named POST (PushOver on Shear-Type buildings), which is based on the definition of capacity curves and corresponding damage displacement thresholds of RC buildings through a simulated design process and the definition of a simplified nonlinear structural model based on the assumption of Shear-Type behaviour. Both of the procedures account for the presence of infill panels, both in the definition of the seismic response and of the damage displacement thresholds. The advantages of the first, more simplified, procedure lie in the extreme ease and quickness of implementation and use. The second, less simplified, procedure is, of course, more robust, and has recently been validated through comparisons with post-earthquake observed damage scenarios, but requires a relatively higher computational demand and difficulty in the implementation. In this study, the results of the second procedure, mainly in terms of capacity curves and displacement thresholds at different Damage States – evaluated for a set of RC buildings with different characteristics in terms of number of storeys, age of construction and type of design, are used as a reference in order to calibrate simplified formulations providing, with higher accuracy but still with very high simplicity, the parameters defining the nonlinear static response of buildings (or building classes) used in the first procedure. Finally, the “numeric-to-numeric” calibration carried out through this approach is validated by means of a comparison with post-earthquake observed damage scenarios, in order to observe the predictive capacity of the calibrated methodology and discuss possible further refinements and developments.