RISK ANALYSIS OF A MEDIEVAL TOWER BEFORE AND AFTER STRENGTHENING

The objective of this analysis has been the evaluation of the probabil ity of failure under gravity load (P-f) of the Fraccaro tower in Pavia before and after a recent strengthening intervention. Both P-f, and i ts sensitivity to the parameters of the distributions of the random qu antities controlling the system response have been evaluated. A probab ilistic model of the spatial variability and of the uncertainties of t he material properties typical of ancient conglomerate masonry constru ctions has been proposed. It accounts for both the continuous variabil ity of material parameters and the drastic strength reductions due to localized areas of degraded material and construction defects. A 3-D n onlinear finite element model allowing for local crushing and fracturi ng of the masonry has been adopted for the numerical analyses. An exte nded version of the Response Surface (RS) method, coupled with a SORM algorithm, allowed for an efficient treatment of the several thousands of random variables of the model. The control variables of the RS hav e been reduced to a few major sources of uncertainty while the effects of all other variables, grouped in appropriate subsets, have been con sidered in a cumulative manner with a statistical treatment of the res ults of suitably planned numerical experiments. Copyright (C) 1996 Els evier Science Ltd.