Existing unreinforced masonry buildings frequently suffered damages and collapses due to the activation of local out-of-plane (OOP) mechanisms when subjected to earthquake excitations. The assessment of the out-of-plane response of masonry structures has been largely studied in literature by assuming walls responding as rigid blocks or assemblies of rigid bodies. This thesis describes a single-degree of freedom (SDOF) numerical model for the dynamic simulation of the OOP behaviour of URM walls or portion of walls. It takes into account both the elastic phase and the non-linear rocking response phase of URM walls. A detailed investigation intoon the force-displacement relationship of different parapets typologies has been carried out in order to provide reliable parameters for the simulation of their dynamic behaviour. Particular emphasis is placed on the energy dissipation involved in such mechanisms. Different equivalent viscous damping models based on equivalent viscous damper have been adopted and compared in order to individuate identify the most appropriate one to capture the dependence of the damping phenomenon with the oscillation amplitude and subconsequently to the system frequency. Modelling the energy dissipation involved in such mechanisms is extremely important to capture the dependence of the damping phenomenon with the system frequency. Some studies, recurring to the classical hypothesis of the impulsive dynamics, simulated the energy dissipation by means of the coefficient of restitution assuming as the overall reduction of energy was concentrated at the instant of the impact. In other works, the damping force has been modelled as a velocity dependent acting force. It is proposed a numerical formulation for the direct equivalence of the two damping approaches for simple overturning mechanisms assuming as force-displacement relationship nonlinear elastic bi-linear curves.
Modello numerico per il comportamento dinamico fuori piano di parapetti e camini in muratura. Gli edifici esistenti in muratura non rinforzata hanno spesso subito danni e collassi a causa dell'attivazione di meccanismi locali fuori piano (OOP) quando sottoposti a eccitazioni da terremoto. La valutazione della risposta fuori dal piano delle strutture in muratura è stata ampiamente studiata in letteratura assumendo pareti che rispondono come blocchi rigidi o assemblaggi di corpi rigidi. Questa tesi descrive un modello numerico a singolo grado di libertà (SDOF) per la simulazione dinamica del comportamento OOP delle pareti URM o delle pareti. Prende in considerazione sia la fase elastica che la fase di risposta a dondolo non lineare delle pareti URM. Un'indagine dettagliata sulla relazione forza-spostamento di diverse tipologie di parapetti è stata effettuata al fine di fornire parametri affidabili per la simulazione del loro comportamento dinamico. Particolare enfasi è posta sulla dissipazione di energia coinvolta in tali meccanismi. Sono stati adottati e confrontati diversi modelli di smorzamento viscoso equivalenti per catturare la dipendenza del fenomeno di smorzamento con l'ampiezza dell'oscillazione e in modo subdolo rispetto alla frequenza del sistema. La modellizzazione della dissipazione di energia coinvolta in tali meccanismi è estremamente importante per catturare la risposta del sistema. I modelli di smorzamento confrontati si basano su ipotesi differenti, dove il primo ricorre all'ipotesi classica delle dinamiche impulsive ovvero simulando la dissipazione di energia per mezzo del coefficiente di restituzione assumendo come se la riduzione complessiva di energia fosse concentrata nell'istante dell'impatto. Per gli altri modelli, la forza di smorzamento è stata modellata come forza di azione dipendente dalla velocità. Viene proposta una formulazione numerica per l'equivalenza diretta dei diversi approcci di smorzamento per i meccanismi di ribaltamento semplici che assumono come relazione di spostamento di forza curve bi-lineari elastiche non lineari.
Numerical modelling of the out-of plane dynamic behaviour of masonry parapets and chimneys.
MAZZOTTA, VINCENZO
2016/2017
Abstract
Existing unreinforced masonry buildings frequently suffered damages and collapses due to the activation of local out-of-plane (OOP) mechanisms when subjected to earthquake excitations. The assessment of the out-of-plane response of masonry structures has been largely studied in literature by assuming walls responding as rigid blocks or assemblies of rigid bodies. This thesis describes a single-degree of freedom (SDOF) numerical model for the dynamic simulation of the OOP behaviour of URM walls or portion of walls. It takes into account both the elastic phase and the non-linear rocking response phase of URM walls. A detailed investigation intoon the force-displacement relationship of different parapets typologies has been carried out in order to provide reliable parameters for the simulation of their dynamic behaviour. Particular emphasis is placed on the energy dissipation involved in such mechanisms. Different equivalent viscous damping models based on equivalent viscous damper have been adopted and compared in order to individuate identify the most appropriate one to capture the dependence of the damping phenomenon with the oscillation amplitude and subconsequently to the system frequency. Modelling the energy dissipation involved in such mechanisms is extremely important to capture the dependence of the damping phenomenon with the system frequency. Some studies, recurring to the classical hypothesis of the impulsive dynamics, simulated the energy dissipation by means of the coefficient of restitution assuming as the overall reduction of energy was concentrated at the instant of the impact. In other works, the damping force has been modelled as a velocity dependent acting force. It is proposed a numerical formulation for the direct equivalence of the two damping approaches for simple overturning mechanisms assuming as force-displacement relationship nonlinear elastic bi-linear curves.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/20.500.14239/19467