The present work of thesis focuses on the improvements seismic isolation provides to the RC frames structural performance when subjected to earthquake action; the new conceptual seismic design (CSD) approach is used inside the framework of performance-based earthquake engineering (PBEE) in order to validated the choice of seismic isolation, showing how it is a recommended and feasible design solution, rather than the fixed-base one, if some designers-defined performance objectives need to be respected. A case study model, represented by a bi-dimensional reinforced concrete moment resisting frames is considered and performance objectives are now defined in terms of expected loss ratios, at three different limit states, and target expected annual loss (EAL). CSD approach is used in order to define the most suitable structural solution able to respect them, through a feasible initial period range definition, proving how, for a fixed-base configuration this does not exist while for a base-isolated one, using friction pendulum isolators (FPB), among all the other possible devices, it does. Two different solutions of isolation are evaluated: (i) medium friction and (ii) low friction FPB. The model is then designed in both cases, fixed base and base isolated, with respect to the corresponding NTC18 requirements, assessing their seismic performance in order to validate the conclusion driven by the CSD approach. Static pushover analysis (SPO) and non-linear response history analysis (NRHA) using 11 set of 40 ground motion records each, corresponding to 11 different levels of intensity measure, are performed. In order to estimate the seismic induced losses, maximum inter-story drift ratios (IDR) and peak floor accelerations (PFA) are selected as engineering demand parameters (EDP) and their floor median value, assuming a lognormal distribution over the survived records (which do not cause structural collapse), is considered as representative of structural response and used to derive the floor median expected loss, from available story-specific EDP-DV functions that consider, at each level, the presence of three damageable components: (i) structural drift sensitive, (ii) non-structural drift sensitive and (iii) non-structural acceleration sensitive. Seismic performance is so evaluated through the comparison of the above defined EDP envelopes and definition of vulnerability and loss curves between fixed base case and base isolated one. Moreover, medium to low friction FPB isolators variability is examined to see the impact that friction coefficient has on the structural response. Expected annual loss is computed as the governing performance index to demonstrate how using a base isolated structural solution lead to the fulfilment of the above defined performance objectives, having an EAL below the imposed target, while the fixed base does not, validating what was anticipated by the CSD approach.
Progetto sismico per strutture a base isolata e valutazione delle perdite con metodo ingegneristico basato sulla performance e risposta strutturale. Il presente lavoro di tesi si concentra sui miglioramenti che l'isolamento sismico fornisce alle prestazioni strutturali di telai in ca quando sottoposti ad azione sismica; il nuovo approccio di progettazione sismica concettuale (CSD) viene utilizzato all'interno del quadro dell'ingegneria sismica basata sulle prestazioni (PBEE) al fine di convalidare la scelta dell'isolamento sismico, mostrando come sia una soluzione progettuale consigliata e fattibile, piuttosto che quella a base fissa, se alcuni obiettivi prestazionali, definiti dai progettisti, devono essere rispettati. Viene considerato un modello di caso studio, rappresentato da un telaio resistente al momento in cemento armato bidimensionale e gli obiettivi di prestazione sono ora definiti in termini di rapporti di perdita attesa, a tre diversi stati limite e perdita annuale prevista (EAL). L'approccio concettuale viene utilizzato al fine di definire la soluzione strutturale più idonea in grado di rispettarli, attraverso una possibile definizione di intervallo di periodo iniziale, dimostrando come, per una configurazione a base fissa questa non esista mentre per una base isolata, utilizzando il pendolo di attrito isolatori (FPB), tra tutti gli altri possibili dispositivi, esista. Vengono valutate due diverse soluzioni di isolamento: (i) attrito medio e (ii) e basso attrito. Il modello viene quindi progettato in entrambi i casi, base fissa e base isolata, rispetto ai corrispondenti requisiti NTC18, valutandone le prestazioni sismiche al fine di validare la conclusione trovata con l’approccio concettuale. Vengono eseguite analisi statiche pushover (SPO) e analisi dinamiche non lineari (NRHA) utilizzando 11 set di 40 storie temporali del suolo ciascuno, corrispondenti a 11 diversi livelli di intensità. Al fine di stimare le perdite sismiche indotte, i drift interpiano massimi (IDR) e le accelerazioni massime di piano (PFA) sono selezionati come parametri (EDP) e il loro valore medio di piano, assumendo una distribuzione lognormale sui record sopravvissuti (che non causare collasso strutturale), è considerato rappresentativo della risposta strutturale e utilizzato per derivare la perdita attesa media, dalle funzioni EDP-DV disponibili che considerano, ad ogni livello, la presenza di tre componenti danneggiabili: (i) struttrali sensibili al drift, (ii) non strutturali sensibili al drift e (iii) non strutturali sensibili all’accelerazione. Le prestazioni sismiche vengono così valutate attraverso il confronto degli inviluppi dei parametri strutturali sopra definiti e la definizione delle curve di vulnerabilità e di perdita tra il caso a base fissa e quello a base isolata. Inoltre, viene esaminata la variabilità fra gli isolatori ad attrito medio e basso per vedere l'impatto che il coefficiente di attrito ha sulla risposta strutturale. La perdita annuale attesa viene calcolata come indice di prestazione principale per dimostrare come l'utilizzo di una soluzione strutturale isolata porti al raggiungimento degli obiettivi di prestazione definiti sopra, avendo un EAL inferiore all'obiettivo imposto, mentre la base fissa no, convalidando quanto previsto da l'approccio concettuale.
Seismic design and loss assessment of base-isolated structures using Performance Based Earthquake Engineering (PBEE)
DAMIANI, FEDERICO
2019/2020
Abstract
The present work of thesis focuses on the improvements seismic isolation provides to the RC frames structural performance when subjected to earthquake action; the new conceptual seismic design (CSD) approach is used inside the framework of performance-based earthquake engineering (PBEE) in order to validated the choice of seismic isolation, showing how it is a recommended and feasible design solution, rather than the fixed-base one, if some designers-defined performance objectives need to be respected. A case study model, represented by a bi-dimensional reinforced concrete moment resisting frames is considered and performance objectives are now defined in terms of expected loss ratios, at three different limit states, and target expected annual loss (EAL). CSD approach is used in order to define the most suitable structural solution able to respect them, through a feasible initial period range definition, proving how, for a fixed-base configuration this does not exist while for a base-isolated one, using friction pendulum isolators (FPB), among all the other possible devices, it does. Two different solutions of isolation are evaluated: (i) medium friction and (ii) low friction FPB. The model is then designed in both cases, fixed base and base isolated, with respect to the corresponding NTC18 requirements, assessing their seismic performance in order to validate the conclusion driven by the CSD approach. Static pushover analysis (SPO) and non-linear response history analysis (NRHA) using 11 set of 40 ground motion records each, corresponding to 11 different levels of intensity measure, are performed. In order to estimate the seismic induced losses, maximum inter-story drift ratios (IDR) and peak floor accelerations (PFA) are selected as engineering demand parameters (EDP) and their floor median value, assuming a lognormal distribution over the survived records (which do not cause structural collapse), is considered as representative of structural response and used to derive the floor median expected loss, from available story-specific EDP-DV functions that consider, at each level, the presence of three damageable components: (i) structural drift sensitive, (ii) non-structural drift sensitive and (iii) non-structural acceleration sensitive. Seismic performance is so evaluated through the comparison of the above defined EDP envelopes and definition of vulnerability and loss curves between fixed base case and base isolated one. Moreover, medium to low friction FPB isolators variability is examined to see the impact that friction coefficient has on the structural response. Expected annual loss is computed as the governing performance index to demonstrate how using a base isolated structural solution lead to the fulfilment of the above defined performance objectives, having an EAL below the imposed target, while the fixed base does not, validating what was anticipated by the CSD approach.È consentito all'utente scaricare e condividere i documenti disponibili a testo pieno in UNITESI UNIPV nel rispetto della licenza Creative Commons del tipo CC BY NC ND.
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https://hdl.handle.net/20.500.14239/12441