Cumulative damage to masonry structures due to repeated earthquakes and effectiveness of strengthening provisions
The quantification of the response of buildings to consecutive shaking from strong motions occurring at the same site in relatively rapid succession, and before repairs can be implemented, is not a recent problem. Examples are documented from at least the late 1990’s. However, after major swarms of earthquakes at the beginning of this decade, the Maule Chile earthquake, 2010, Christchurch, New Zealand earthquake, 2011, and the Tohoku, Japan earthquake, 2011, the scientific and technical community has been paying more attention to this issue with a significant number of studies devoted to this problem with the intent of providing design guidance for structures exposed to repeated shaking.
Such studies rely on:
- more accurate documentation and reliable records of seismic sequences, thanks to denser and more sensitive arrays of sensors;
- better understanding and modelling of fault ruptures and relationship among consecutive strong motions;
- more detailed post elastic modelling of structures, with improved characterization of degrading capacity phenomena.
Designing for multiple earthquakes is a logical extension of the performance-based design, responding to the necessity of minimizing damage, so as to reduce recovery times and costs, improve resilience and render the building stock more sustainable.
The paper summarizes key developments in this field within the framework of probabilistic risk assessment and illustrates the fundamental elements of such analyses with reference to the case of the 2016 Central Italy earthquake sequence, with particular attention to masonry structures.
Using accurate data collected in situ for building affected by the earthquake in Norcia and in Amatrice, the mechanics approach coded in FaMIVE is used to determine initial and residual capacities of a large number of buildings under repeated shaking. Cloud of performance points are generated for each event to be used to determine fragility curves, representative of the percentage of buildings undergoing certain damage levels under the specific seismic scenario. A discussion on the obtained results and the capability of the method to represent the observed damage extents concludes the paper.
Dina D’Ayala is the Professor of Structural Engineering at University College London, within the Department of Civil, Environmental and Geomatic Engineering. She is head of Civil Engineering and Co-Director of the Earthquake and People Interaction Centre, EPICentre. She is a director of the International Association of Earthquake Engineers and Fellow of the ICE. Her specialism is Structural Resilience Engineering with particular emphasis on the assessment, strengthening, preservation and resilience of existing buildings, structures, transport infrastructure and cultural heritage. Her current research focusses on resilience of structures and infrastructure to natural hazards, supported through research grants from EU FP7, INFRARISK, and the UK RC, PARNASSUS, STORMLAMP, SCOSSO, PRISMH. She has 25 years’ experience working with international agencies, the World Bank, ODA, UNDP, British Council, in countries such as Nepal, Jordan, Turkey, Iraq, Philippines etc., and leading interdisciplinary projects on enhancing resilience against natural hazards. She has produced Guidelines for DfID on assessment and strengthening of hospitals and reconstruction efforts in Nepal. She is the chief scientist for the World Bank on the Global Programme for Safe Schools (GPSS) and leads the development of the World Bank GLoSI project. She is a member of the Management Board of the International Centre for Collaborative Research on Disaster Risk Reduction (ICCR-DRR) at Beijing Normal University.