Assessment of Seismic Risk and Reliability of Road Network

Abstract

Essential services for road users as well as for every kind of human activity are strongly dependent from road network that is considered a “lifeline” as one of the essential linear infrastructures for human life. When a catastrophic event strikes a wide area, it is necessary that the infrastructure system is designed with a high redundancy and/or low risk of failure to maintain network function to give access for the rescue service. In the case of damage produced by seismic events, the effects of an interruption to the road network and the consequent reduction of what remains available profoundly affect the overall performance of the system (increasing travelling time, distance and costs). The road network must be reliable, that is, it must (Wakabayashi, Idia, 1992) “.... provide a safe and not fluctuating service for the traffic and offer the users alternative routes, even when some parts of the system are not available due to road accidents, maintenance or natural disasters”. If network Reliability is able to measure the ability of the system to maintain its performance due to the vulnerability to suffer damages of some of its components, Risk assessment is able to consider other aspects in addition to the overall functionality of the network system such as the consequences in terms of victims that can derive from the reduction of its functionality. In the chapter a comprehensive methodology framework for the evaluation of the seismic risk and reliability of rural road networks will be presented. These original methodologies make it possible to identify beforehand critical parts of the road network as regards to possible structural damage and the importance of the connection related to the number of inhabitants that could suffer a delay in the emergency services. The analyses were carried out considering bridges as the “weak” element of the road infrastructure in case of seismic events, but the procedure could also be applied to different types of element (trenches, embankments, culverts, etc). The methodology has been designed for applications based on Geographic Information System (GIS). With reference to different seismic emergency scenarios (road network, seismic intensity, O/D routes), case studies are presented to highlight the possibility of a preventive estimation of towns and links that present different levels of Risk. 15