Multi-hazard lifecycle methods for aging structures and infrastructure systems

Extreme hazards such as earthquakes, floods, and hurricanes can significantly affect the performance and serviceability of structures and infrastructure systems during their lifetime. Recent prominent examples include the 2017 earthquake in the vicinity of Iran-Iraq border and the 2017 earthquake in Mexico that led to hundreds of fatalities. Hurricane Matthew (2016), Harvey (2017), Irma (2017), and Jose (2017) caused significant damage to critical infrastructure systems in a number of south-eastern states in the U.S. Such hazards can occur multiple times during the lifetime of infrastructure systems. Each event is accompanied by a set of adverse consequences including, among others, human casualties, physical damage, and downtime due to the repair of damage and restoration of the functionality of the system. In addition, as infrastructure assets are exposed to environmental stressors and service loads, they undergo gradual aging and deterioration over their lifetime. The subsequent degradations in the capacity of the systems increase their vulnerability against hazards over time. These compounding effects, among others, pose a tremendous challenge for evaluating the performance of structures and infrastructure systems, and managing their performance. In the light of such challenges and budget limitations, it is important to evaluate the lifecycle cost of infrastructure systems in order to minimize the potential losses over their service lifetime. For structures or infrastructure systems that are exposed to multiple hazards during their lifetimes, damage accumulation is a critical issue. As supported by historical records, the accumulation of damage from prior events can considerably increase the vulnerability of these systems to future hazards. However, this phenomenon is either disregarded or addressed inadequately in existing risk management frameworks. Additionally, these frameworks do not incorporate effects of gradual deterioration on the reduced capacity of infrastructure systems against hazards, or they make significant simplifications in doing so. This limitation may lead to unrealistic assessments of the lifecycle performance of these critical assets, and subsequently, ineffective retrofit or repair decisions. This doctoral research proposes probabilistic lifecycle cost and resilience analysis methods that properly incorporate the foregoing effects to arrive at optimal design or retrofit decisions among a list of pre-specified alternatives for individual structures and infrastructure systems. In the developed methods, design or retrofit alternatives are considered to be applied at the current time for a specified lifetime, where the state of the system is known perfectly at the current time. In addition, hazards of the same or different types are considered to be independently occurring. The new contributions of the proposed frameworks in this research include: - Probabilistic consideration of the impact of damages induced by prior hazards on the increased vulnerability of systems against future potential hazards for lifecycle cost and resilience assessments when hazards are of the same type. - Incorporation of the dependencies between different types of damages that are induced by multiple types of hazards in the lifecycle cost analysis. - Integration of the impact of gradual deterioration on the reduced capacity of the system over time in lifecycle cost analysis with multiple types and occurrences of hazards.