Masonry Quality in Seismic Performance of Historic Buildings

The seismic events of the last few decades have highlighted the vulnerability of historic buildings with large hall spaces, like churches and palaces. Post-earthquake site surveys reveal that, depending on the building characteristics, the damage is very different for the same seismic action. Historically, masonry was made using the materials found on the sites where the buildings were constructed. Combining stones, bricks, and binders (like mortar or mud) in different ways gives rise to the wall structure. Each composition has its own mechanical characteristics that depend on the base materials and process used. In churches and palaces, the seismic performance is mainly defined by the dynamic behaviour of their walls, usually not connected by rigid diaphragms. When referring to the effects of an earthquake orthogonal to the middle plane of a wall, the current dynamic reference model is the free-standing rigid block subjected to rocking. This reference model would seem to indicate that all masonry can exhibit the same dynamic behavior regardless of the materials and the way in which it was built. In reality, the displacement capacity of the wall is greatly conditioned by its characteristics. Using an energetic approach proposed in the early ’60s, studying the rocking of blocks, it is possible to quantify the out-of-plane performances of different wall types. The displacement capacity of different historical walls is analyzed, and a theoretical approach is used to verify that it can be greater than that of a single rigid block. An equilibrium configuration that allows a greater displacement capacity of a multi-block wall is compared to a monolithic wall. The “potential energy capacity” is used as a parameter to define the outof- plane seismic quality of different types of historic masonry. An unexpected connection was revealed when comparing past construction methods used in high-risk seismic areas, such as Turkey, Italy, and Nepal, with the present knowledge of the rocking dynamics. By documenting real situations in the past where solutions were used to increase the seismic resistance of the masonry when subjected to out-of-plane actions, the rules used to build walls in ancient buildings have been re-evaluated.

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