Seismic Risk Analysis of R.C. Building Classes

Seismic risk assessment at urban scale may be defined as estimation of number of buildings ex-pected to reach a given limit state in the region and time period of interest. It is related to the failure probabili-ty of a homogeneous class of buildings and its characterization. This definition introduces new issues in re-spect of reliability analysis for single structures which, under some conditions, has been already addressed in close form. Mechanical approach may be suitable in respect of the requirements of such territorial evaluation,thus appropriate limit state functions have to be developed to get the failure probability of classes belonging to the building stock. Non-linear seismic capacity, in terms of base shear and/or displacement, has to be ex-pressed as function of those structural parameters which identify single structures within the class. The lattermay be carried out by multiple regression analysis. Distributions of random variables affecting capacity are estimated by sampling the territorial population. In a force-based approach inelastic seismic demand may re-fer to probabilistic seismic hazard analysis at the site and strength reduction factors. All these issues are dis-cussed in the paper; moreover, an explanatory application to R.C. structure classes is presented.