Seismic assessment of four inclined masonry towers located in the neighborhood of the area stricken by the May 2012 Emilia Romagna (Italy) earthquake

The paper presents some FE results on four masonry towers located in Emilia Romagna Region, Italy, classified as a moderate seismic area, but recently stricken by a destructive earthquake sequence occurred in 2012 (20th-29th May), with peak events of 5.8 and 5.9 magnitude. These existing construcions are from 400 to 900 years old, well representative of their cities and have in common a meaningful inclination cumulated over years. Whilst the seismic sequence determined secondary damages on the structures under investigation, the paper is aimed at providing an insight on the role played by inclination in increasing the seismic vulnerability. The examples under study deliberately exhibit very different slenderness, so that the seismic vulnerability reduction can be estimated in a large range of geometrical cases. In order to secure the towers against collapse for dead loads, some interventions were recently carried out, introducing tendons and hooping systems, to favor a box behavior under possible seismic events and preclude the diffusion of dangerous cracks due to the insufficient compressive strength of the masonry material. A number of analyses are carried out in absence and presence of tendons, to check the capacity of the structures and to conceive further retrofitting interventions. The computations consist of advanced nonlinear analyses, carried out with the commercial FE code SAP2000. As expected, the conducted pushover analyses show that the masonry towers are very vulnerable. Comparing the results for the inclined real case and the hypothetical vertical case, it can be observed that the inclination may considerably reduce the load carrying capacity. The role played by reinforcement is found to be marginal in the global non-linear analyses. Further considerations are presented dealing with possible intervention techniques implementable to a vulnerability reduction.