Possibilities and limitations of innovative retrofitting for masonry churches: Advanced computations on three case studies

The use of fiber reinforced polymers (FRP) represents an interesting option to inhibit the formation of partial collapse mechanisms on macro-blocks, which is a typical failure mode shown by masonry churches under seismic actions. Furthermore, FRP strips exhibit a very good performance at failure, low invasiveness and high speed of execution. This study provides an insight into the possible applications of FRP on three masonry churches damaged by the 2012 Emilia seismic sequence. Several different linear and non-linear analyses are carried out, including standard response spectrum analyses, limit analyses with both pre-assigned failure mechanisms and Finite Elements (FE), pushover and non-linear dynamic analyses. A remarkable consistency is found between the real seismic performance of the churches and the results obtained through both limit and advanced non-linear dynamic analyses. In particular, both the damage distributions and the active failure mechanisms derived from the numerical analyses are consistent with those observed on the churches after the seismic event. A seismic upgrading of the churches through the application of FRP is proposed, using a proper design procedure based on comprehensive advanced FE computations, with the aim of obtaining the required seismic performance and limited invasiveness. The interaction between FRP strips and masonry substrate is accounted for assuming the FRP behavior in agreement with Italian Guidelines for strengthening with composite materials (CNR DT200). It is found that through a rational design procedure of the FRP strengthening intervention it is possible to prevent the premature collapse of the macro-elements, considerably increasing their load carrying capacity.