Field investigations after recent large earthquakes have confirmed that several structures were severely damaged and collapsed not only by the earthquake, but also by the subsequent tsunami, landslide, or fault displacement. Effect of material degradation due to chloride attack on structural performance should be considered when structures are located in a harsh environment. In addition, climate change has produced typhoons and hurricanes with extreme intensity in recent years. Sea-level rise could cause severe storm surges and tsunamis, and global warming is accelerating the deterioration of structures. When structures are exposed to these different types of hazards, it can be difficult to ensure their safety and additional performance indicators such as risk and resilience are needed. Several lessons were learned about the importance of investigating individual structures from the perspective of ensuring network functionality. A probabilistic life-cycle framework for quantifying the loss of functionality of road networks including bridges is needed. A risk-based decision-making approach at the network level is required to identify the dominant hazard and the vulnerable structures that require strengthening and retrofitting. After a catastrophic event, the functionality of transportation networks can be significantly degraded, resulting in catastrophic economic impacts. To quantify the promptness of recovery, it has become common to use the concept of resilience. In addition, the economic, environmental, and social impacts of disaster waste management systems need to be examined in terms of sustainability. Consequences related to resilience and sustainability need to be investigated and implemented in the risk assessment of road networks under multiple hazards. Life-cycle design and assessment methodologies can incorporate risk, resilience, sustainability and multiple hazards, learning from the lessons of past disasters. This keynote paper provides an overview of measures to ensure the functionality of individual and spatially distributed structures under multiple hazards from the perspectives of reliability, risk, resilience and sustainability.
