Behaviour Factor Assessment of Ancient Masonry Towers Through an Innovative Simplified Pushover Method

Abstract

The seismic vulnerability of masonry towers is a critical research field and it has an important role in the preservation of worldwide conservation of such kind of masonry building. Indeed, masonry towers have a very high seismic vulnerability and are often located in high seismic hazard zones. Researches about this topic have become even more frequent in the last decades. However, the results about the seismic behaviour of the masonry towers are still limited and further researches are needed. This paper aims to study the value of the behaviour factor (usually called q-factor or R-factor) of ancient masonry tower-like structures. This parameter provides quantitative information about the ductility of the tower and it can be computed by the capacity curve of the structure. In particular, the pushover curve can be bilinearized, and the q-factor can be computed according to the equal dis-placement or equal energy rule. The bilinearization of the capacity curve implies the knowledge of the ultimate displacement, whose computation is not a trivial task for this kind of structures because the capacity curves usually computed for such structures are apparently infinite ductility curves and the ultimate displacement cannot be directly computed. Therefore, an innovative pushover method (called "manual" pushover) has been formulated and implemented in a Matlab® code to achieve the q-factor computation goal. The tower is modelled by a vertical cantilever beam with lumped plasticity and it is loaded by self-weight and a user-defined horizontal distributed load profile. The non-linearities are modelled by the Moment-Curvature diagram of the cross-section where the plasticity is lumped. These cross-sections are positioned along the height of the tower splitting it into parts as uniform as possible in material and geometry characteristics. It allows considering the influence of openings and irregularities. The capacity curve is built by curvature control; it is similar to a displacement control and it allows to