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Infrastructure Resilience Conference 2018

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Civil Infrastructure System Resilience Quantification Using the Re-CoDeS Framework

Past earthquakes have shown that both, the demand of a community for the services of civil infrastructure systems (CISs) and the supply of the CISs are influenced by the consequences of a disaster. While the supply of the system is usually expected to drop, for example due to damage to its components, the community demand might as well rise after a disastrous event. The post-disaster evolution of the demand can, therefore, have a large impact on the resilience of a CIS. This is especially true for hospitals and cellular communication systems, which are expected to be faced with a considerable increase in demand after disasters, due to injured people and a high number of emergency calls.

The Re-CoDeS (Resilience Compositional Demand Supply) framework is a recently developed resilience quantification framework allowing to account directly for the evolution of the community demand for a service provided by a CIS in a resilience assessment. The evolution of the demand is compared to the evolution of the supply of the CIS in order to determine and quantify a potential Lack of Resilience at a component or system level. A Lack of Resilience is observed if, at a given node of the CIS, the demand exceeds the available supply. The Re-CoDeS framework permits, thus, to identify different demand/supply configurations and to identify their impact on the CIS resilience. This allows to move from a resilience assessment accounting only for the vulnerability and the recovery of the supply system to a resilience assessment allowing to engineer and optimize the resilience of systems by considering new post-disaster demand requirements.

The application of the Re-CoDeS framework is shown for the resilience quantification of different CISs in Nepal after the 2015 Mw 7.8 Gorkha earthquake, namely the Nepalese electric power supply system, and the water distribution and cellular communication system in the Kathmandu Valley. The electric power supply and the water distribution system showed already before the earthquake a large supply deficit. The supply was intermittent and available to the population only during some hours a day. However, not only the supply capacity of these two CISs dropped after the earthquake, but as well the community demand for their services. This drop of the demand allowed to compensate for a part of the drop of the supply due to earthquake damage. In fact, damage to the building stock leads often to a decrease of the functionality of buildings: possible access restrictions can, for example, prevent the use of electric appliances in the building, leading consequently to a decrease in the demand for electric power. Contrary, the cellular communication system provided a sufficient supply with a low blocking probability before the occurrence of the 2015 Gorkha earthquake. While the supply capacity of the system dropped as well due to earthquake damage, the high increase in demand (up to more than 10 times the pre-disaster demand), especially for emergency calls, led to a high blocking probability and contributed the major share of the observed Lack of Resilience.

Challenges in the use of the Re-CoDeS framework include especially the modelling of the evolution of the post-disaster demand. While a large collection of literature is available on the modelling of the vulnerability and the recovery of the components of a CIS, and thus of the supply layer, this is not the case for the vulnerability and the recovery of the community demand. Models for demand, based on the observations after the 2015 Gorkha earthquake have been proposed, but they need to be verified with data to collect from other earthquakes and community settings. Combining these demand models with the existing supply models should, then, allow to assess the resilience of CISs during future earthquakes and to make systems more resilient using the proposed demand/supply approach.

Max Didier
ETH Zürich
Switzerland

Bozidar Stojadinovic
ETH Zürich
Switzerland

Marco Broccardo
ETH Zurich
Switzerland

Simona Esposito
Swiss Re Management Ltd
Switzerland

 

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