The linear seismic analysis approaches based on the behaviour factor q theory, as Lateral Force Method (LFM) or the Modal Response Spectrum Analysis (MRSA) that are widely used in the seismic design of Moment-Resisting (MR) Steel Frames, do not lead to an always accurate prediction of the seismic response and of the structural damage either in the design phase or in the post-earthquake condition. Nowadays, non-linear analysis methods as Pushover Analysis (PSV) and the most sophisticated Non-Linear Time History (NLTH) are admitted by the design codes. These methods provide a more precise assessment of the seismic performance but designers rarely use them due to their complexity. In the first part of this PhD research, the differences in terms of design quantities obtained by applying all the methods admitted by the European Seismic Design Code (EC8) are investigated considering a set of MR steel frames. Then, a numerical approach based on the integration between Non-Linear Time History, Low Cycle Fatigue (LCF) theory and Non-Linear Static Analysis is discussed and applied for the assessment of the residual properties of a MR steel frame damaged by one and more earthquakes. The proposed numerical procedure is also applied in a parametric form via Incremental Dynamic Analysis (IDA) considering an extended earthquake set. Four moment-resisting frames differing in beam-to-column connections are considered. The damage level is statistically evaluated at each seismic intensity with the following three damage intensity measures (DMs): i) the maximum residual inter-story drift, ii) the maximum LCF local damage index and iii) the residual load carrying capacity. The results underline the utility of the proposed approach, that provides further information with respect to the standard IDA application, which considers only the maximum transient inter-story drift as damage intensity measure.
Gli approcci di analisi sismica lineare basati sulla teoria del fattore di struttura q, come l’analisi statica equivalente (LFM) e l'analisi modale a spettro di risposta (MRSA), vengono ampiamente utilizzati nella progettazione sismica dei telai in acciaio resistenti a momento (MR), sebbene non sempre portino ad una previsione accurata della risposta sismica e del danno strutturale sia in fase di progettazione che in fase di post-terremoto. Al giorno d’oggi i codici di progettazione ammettono i metodi di analisi non lineare come l’analisi Pushover (PSV) e la più sofisticata analisi dinamica non lineare (NLTH). Questi metodi forniscono una valutazione più precisa delle prestazioni sismiche. Tuttavia, a causa della loro complessità, vengono raramente impiegati dai progettisti. Nella prima parte di questa ricerca di dottorato vengono individuate le differenze in termini di quantità progettuali ottenute applicando tutti i metodi ammessi dalla normativa sismica Europea (EC8) considerando un set di telai in acciaio MR. Viene poi introdotto un approccio numerico basato sull'integrazione tra l’analisi dinamica non lineare, la teoria della fatica oligociclica (LCF) e l'analisi statica non lineare, al fine di valutare le proprietà residue di un telaio in acciaio MR danneggiato da uno e più terremoti. La procedura numerica proposta viene anche applicata in forma parametrica tramite analisi dinamica incrementale (IDA) considerando un set esteso di terremoti. Vengono dunque presi in considerazione quattro telai in acciaio che differiscono tra di loro per le connessioni trave-colonna. Il livello di danno viene valutato statisticamente a ciascuna intensità sismica mediante i seguenti valori di intensità di danno (DM): i) lo spostamento d’interpiano residuo, ii) il massimo indice di danno locale LCF e iii) la capacità portante residua. I risultati forniscono ulteriori informazioni rispetto all'applicazione standard delle IDA, che considera invece solo il massimo spostamento d’interpiano transiente come misura dell'intensità del danno.
Earthquake damage assessment in moment-resisting steel frames
RODIGARI, DAVIDE
Abstract
The linear seismic analysis approaches based on the behaviour factor q theory, as Lateral Force Method (LFM) or the Modal Response Spectrum Analysis (MRSA) that are widely used in the seismic design of Moment-Resisting (MR) Steel Frames, do not lead to an always accurate prediction of the seismic response and of the structural damage either in the design phase or in the post-earthquake condition. Nowadays, non-linear analysis methods as Pushover Analysis (PSV) and the most sophisticated Non-Linear Time History (NLTH) are admitted by the design codes. These methods provide a more precise assessment of the seismic performance but designers rarely use them due to their complexity. In the first part of this PhD research, the differences in terms of design quantities obtained by applying all the methods admitted by the European Seismic Design Code (EC8) are investigated considering a set of MR steel frames. Then, a numerical approach based on the integration between Non-Linear Time History, Low Cycle Fatigue (LCF) theory and Non-Linear Static Analysis is discussed and applied for the assessment of the residual properties of a MR steel frame damaged by one and more earthquakes. The proposed numerical procedure is also applied in a parametric form via Incremental Dynamic Analysis (IDA) considering an extended earthquake set. Four moment-resisting frames differing in beam-to-column connections are considered. The damage level is statistically evaluated at each seismic intensity with the following three damage intensity measures (DMs): i) the maximum residual inter-story drift, ii) the maximum LCF local damage index and iii) the residual load carrying capacity. The results underline the utility of the proposed approach, that provides further information with respect to the standard IDA application, which considers only the maximum transient inter-story drift as damage intensity measure.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/153289