Out-of-plane rocking response of unreinforced masonry churches after the 2011 Canterbury (New Zealand) and 2016 Central Italy earthquakes

Abstract

Churches are an essential part of the historical and architectural heritage of a country and various earthquakes around the world have highlighted the significant seismic vulnerability of ancient religious buildings. Recently, the 2010-2011 Canterbury (New Zealand) earthquake sequence caused extreme damage, being particularly extensive in Christchurch unreinforced masonry churches. Similarly, the 2016 Central Italy earthquake strongly affected the religious buildings of the stricken area, where churches showed systematic collapses, causing uncountable losses to the Italian ecclesiastic heritage. Historical unreinforced masonry buildings are known to suffer from local collapses during strong earthquakes, and this observation is even more evident for churches, because of their open plan, large wall height-to-thickness and length-to-thickness ratios, and the presence of thrusting horizontal structural elements for vaults and roofs. A sample of approximately 80 affected buildings was directly surveyed after each seismic sequence, with the aim of identifying the activated collapse mechanisms, highlighted by cracks and deformations. Although geographically on opposite sides of the world, several churches in the two stricken regions exhibited out-of-plane response of their façades, and the corresponding mechanism is herein analysed for a church for each country using rigid-body non-linear dynamic models. The models, which account for the real geometry of the structural element, are excited by recorded accelerograms. The outcomes of such analyses are in good agreement with observed damages.