Planning proper lifeline management policies is a key task to satisfy the primary needs of communities not only under operational conditions, but also in a state of emergency. Resilience is becoming a driving concept for new generations of Building Codes and Standards, informing innovative trends and practical policies for design, assessment, monitoring, and maintenance of strategic structures and infrastructure facilities. In civil engineering, resilience represents the ability of infrastructure systems and lifelines to withstand the effects of extreme events and to recover promptly and efficiently the pre-event performance and functionality. In this context, road infrastructure networks play a key role in the emergency response to seismic events and related hazards to ensure both a quick deployment of emergency aids and resources to distressed communities and a prompt repair of the surrounding lifelines and buildings. Resilience of structures and infrastructure systems is generally investigated considering damage and disruptions caused by sudden extreme hazards, such as earthquakes. Nevertheless, key vulnerable components in the infrastructure systems may be exposed to an aggressive environment and damage can also arise continuously in time due to the effects of aging and structural deterioration. Consequently, seismic resilience of deteriorating structures and infrastructure systems depends on the time of occurrence of the seismic event. The thesis focuses on the definition of a life-cycle probabilistic framework for resilience assessment of bridges and road networks considering the uncertainties involved in seismic and environmental hazards, in the vulnerability of spatially distributed aging bridges and in the recovery process of damage network components. The initial damage induced by seismic events and its recovery process through structural repair is related to traffic restrictions to different road users. The time-variant seismic fragilities of deteriorating bridges are assessed via nonlinear time-history analysis and Monte Carlo simulation for several limit states, from damage limitation up to collapse. A novel computationally efficient approach for the evaluation of time-variant fragility curves is also proposed. This procedure exploits Importance Sampling and data reduction techniques based on clustering to account for the time-variant modeling uncertainties typical of life-cycle structural reliability analysis by efficiently selecting a set of sample structural systems to be analyzed. Traffic flow distribution analyses are carried out over the road network to assess the post-event system functionality and the corresponding seismic resilience under prescribed post-event recovery scenarios. The role of different factors related to bridge capacity and network layout are investigated considering highway networks with detours and re-entry links characterized by spatially distributed reinforced concrete bridges exposed to chloride-corrosion. The beneficial effects of infrastructure investments such as the upgrade of existing road networks with the construction of a new highway branch, as well as the detrimental impact of climate change scenarios on exacerbating the lifetime bridge vulnerability and road network resilience, are also investigated. The results of the applications show the effectiveness of the proposed framework and the importance of a life-cycle-oriented approach to probabilistic assessment of seismic resilience of aging bridges and infrastructure systems.
Definire opportune politiche per la gestione ottimale delle infrastrutture critiche è indispensabile per garantire i bisogni primari delle comunità, non solo in condizioni stazionarie, ma anche in caso di emergenza. Il concetto di resilienza sta assumendo un ruolo centrale nelle nuove generazioni di normative e linee guida per le costruzioni, ispirando la buona pratica in fase di progettazione, analisi, monitoraggio e manutenzione di strutture e infrastrutture di rilevanza strategica. Nell'ambito dell'ingegneria civile, la resilienza rappresenta la capacità di un sistema infrastrutturale di sostenere l'impatto di eventi catastrofici e di recuperare in maniera rapida ed efficace la funzionalità pre-evento. In questo contesto, le reti infrastrutturali viarie ricoprono un ruolo fondamentale nel permettere un immediato dislocamento delle risorse necessarie per assistere le comunità colpite e per la riparazione di edifici ed infrastrutture danneggiate. Le linee di ricerca principali riguardo la valutazione della resilienza di strutture e infrastrutture è in genere analizzata in riferimento al danno ed alle interruzioni del servizio causati da eventi estremi improvvisi, quali i terremoti. Tuttavia, gli elementi più vulnerabili all'interno dei sistemi infrastrutturali possono essere esposti ad ambienti aggressivi che determinano un loro progressivo deterioramento nel corso del tempo. Di conseguenza, la resilienza sismica a ciclo di vita di strutture ed infrastrutture è funzione dell'istante temporale di occorrenza dell'evento sismico. La tesi si focalizza sulla definizione di un modello analitico probabilistico per la valutazione della resilienza a ciclo di vita di ponti ed infrastrutture stradali. Il modello recepisce le incertezze relative alla pericolosità sismica, alla aggressività ambientale, alla vulnerabilità variabile temporalmente di reti di ponti spazialmente distribuiti ed al processo di recupero di componenti infrastrutturali danneggiate. Nel modello proposto, la perdita di capacità portante causata dall'evento sismico viene messa in relazione ad opportune restrizioni di traffico nei confronti di diversi utenti della strada, progressivamente rilassate in seguito al ripristino dell'integrità strutturale mediante attività di riparazione. La fragilità sismica a ciclo di vita dei ponti all'interno della rete stradale viene valutata mediante analisi dinamica nel dominio del tempo e simulazione di Monte Carlo considerando diversi stati limiti, a partire dalla limitazione del danno fino al collasso strutturale. Con riferimento alla valutazione di curve di fragilità sismica, la tesi propone un approccio computazionale efficiente mediante "Importance Sampling" e tecniche di clusterizzazione. Le procedure proposte permettono di valutare le incertezze di modello e la loro variabilità nel tempo tipiche dell'analisi di affidabilità strutturale a ciclo di vita analizzando un insieme ridotto di campioni del sistema strutturale opportunamente selezionato. La valutazione della distribuzione dei flussi di traffico all'interno della rete permette di valutare la funzionalità della rete stessa e la relativa resilienza sismica sulla base di scenari prestabiliti di recupero. Le applicazioni della tesi consentono di mettere in evidenza gli aspetti caratteristici dell'approccio proposto e l'importanza della definizione di approcci probabilistici a ciclo di vita per la valutazione della resilienza sismica di ponti e sistemi infrastrutturali. Vengono proposti diversi casi studio per valutare l'impatto di diversi fattori relativi alla capacità strutturale dei ponti in calcestruzzo armato spazialmente distribuiti e soggetti a degrado da cloruri e alla topologia di sistemi viari composti da strade principali e secondarie. Inoltre, le applicazioni proposte permettono di quantificare l'effetto di investimenti infrastrutturali, quali la costruzione di un nuovo ramo della rete, e l'impatto dei cambiamenti climatici sulla vulnerabilità a ciclo di vita di singoli ponti e la resilienza dell’intero sistema infrastrutturale.
Life-cycle seismic resilience of aging bridges and infrastructure networks
CAPACCI, LUCA
Abstract
Planning proper lifeline management policies is a key task to satisfy the primary needs of communities not only under operational conditions, but also in a state of emergency. Resilience is becoming a driving concept for new generations of Building Codes and Standards, informing innovative trends and practical policies for design, assessment, monitoring, and maintenance of strategic structures and infrastructure facilities. In civil engineering, resilience represents the ability of infrastructure systems and lifelines to withstand the effects of extreme events and to recover promptly and efficiently the pre-event performance and functionality. In this context, road infrastructure networks play a key role in the emergency response to seismic events and related hazards to ensure both a quick deployment of emergency aids and resources to distressed communities and a prompt repair of the surrounding lifelines and buildings. Resilience of structures and infrastructure systems is generally investigated considering damage and disruptions caused by sudden extreme hazards, such as earthquakes. Nevertheless, key vulnerable components in the infrastructure systems may be exposed to an aggressive environment and damage can also arise continuously in time due to the effects of aging and structural deterioration. Consequently, seismic resilience of deteriorating structures and infrastructure systems depends on the time of occurrence of the seismic event. The thesis focuses on the definition of a life-cycle probabilistic framework for resilience assessment of bridges and road networks considering the uncertainties involved in seismic and environmental hazards, in the vulnerability of spatially distributed aging bridges and in the recovery process of damage network components. The initial damage induced by seismic events and its recovery process through structural repair is related to traffic restrictions to different road users. The time-variant seismic fragilities of deteriorating bridges are assessed via nonlinear time-history analysis and Monte Carlo simulation for several limit states, from damage limitation up to collapse. A novel computationally efficient approach for the evaluation of time-variant fragility curves is also proposed. This procedure exploits Importance Sampling and data reduction techniques based on clustering to account for the time-variant modeling uncertainties typical of life-cycle structural reliability analysis by efficiently selecting a set of sample structural systems to be analyzed. Traffic flow distribution analyses are carried out over the road network to assess the post-event system functionality and the corresponding seismic resilience under prescribed post-event recovery scenarios. The role of different factors related to bridge capacity and network layout are investigated considering highway networks with detours and re-entry links characterized by spatially distributed reinforced concrete bridges exposed to chloride-corrosion. The beneficial effects of infrastructure investments such as the upgrade of existing road networks with the construction of a new highway branch, as well as the detrimental impact of climate change scenarios on exacerbating the lifetime bridge vulnerability and road network resilience, are also investigated. The results of the applications show the effectiveness of the proposed framework and the importance of a life-cycle-oriented approach to probabilistic assessment of seismic resilience of aging bridges and infrastructure systems.File | Dimensione | Formato | |
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2020_03_PhD_Capacci_depositata.pdf
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https://hdl.handle.net/10589/166644