Seismic assessment of single-block rocking elements in masonry structures

This paper summarizes the main results achieved as a result of a PhD research project into the seismic assessment of single-block rocking elements in masonry structures (such as parapet walls, pinnacles, spires, etc…). In particular, this work refers to those elements located in the upper levels of structures. As demonstrated by past earthquakes, these elements are all significantly vulnerable to seismic events, due to their high slenderness and narrowness. Furthermore, due to their elevated position the seismic effect at their base is usually amplified by the dynamic response of the main building. Seismic assessment compares the structural capacity of an element with the seismic demand (loading) in order to check if the element is able to fulfil its design function, with an appropriate safety level. To this aim, two methods of analysis can be adopted: nonlinear dynamic analysis, which is complex and demanding, or the Displacement-Based Approach (DBA), which is based on an incremental static analysis. DBA requires three fundamental steps: i) the definition of the capacity model, which is an equivalent single-degree-of-freedom system; ii) the definition of the seismic input in terms of a floor acceleration-displacement spectrum; iii) a computational procedure which enables the displacement demand, to be compared with the capacity. The final goal of this research was to prove the applicability of the DBA approach to the seismic assessment of elevated single-block rocking elements in masonry structures, in order to provide practise-oriented tools. Original contributions have been achieved in all the three fundamental steps of the procedure.