Effect of dampers on the seismic performance of masonry walls assessed through fragility and demand hazard curves

In a damage avoidance design perspective, seismic rocking of rigid-like blocks, such as masonry walls, precast r.c./timber panels, art objects, etc., can be controlled through viscous elastic dampers. This paper discusses how to perform a seismic risk assessment of masonry walls undamped and damped by viscous-elastic dampers installed at the top of them. Firstly, a preliminary fragility analysis allows understanding the role of the damper, whose coupling with a recentering component attenuates the motion, increases the rotation frequency and, in some cases, impedes overturning as compared to to the undamped case. Secondly, the risk assessment is made by developing a multiple stripe analysis to compute univariate fragility curves combining uplift, overturning probability and probability of exceedance. Thirdly, seismic demand hazard curves are obtained for two walls representative of buildings and monumental structures in an Italian site of high seismicity. The PSHA results show the remarkable risk reduction of the ultimate limit states, for which the annual exceedance rate is respectively one and two orders of magnitude lower than the undamped case.