This thesis presents the results of an experimental study aimed at evaluating the influence of the multi-directionality of ground motions on the dynamic response of unreinforced masonry buildings. The research was motivated by recent post-earthquake observations of greater structural damage at sites near the fault, where horizontal and vertical ground motions were strong and well synchronised. Vertical accelerations can result in the fluctuation of gravity loads, which, in turn, control the in-plane lateral load capacity of masonry piers, and affect the out-of-plane overturning stability of slender walls. Downward accelerations result in the instant decrease of frictional resistance of masonry walls, which can lead to a potential increase of sliding between the bricks in case of simultaneous horizontal seismic action of considerable intensity. In this study, the damage potential of vertical accelerations to masonry buildings was investigated through a series of multi-directional shake-table tests on masonry structures, under simulated near-fault ground motions of increasing intensity. The experiments included a set of three nominally identical building specimens, subjected to the principal horizontal component only, the horizontal component combined with the vertical one, and to the full three-component ground motion, respectively. The test buildings comprised gable walls, chimneys, and parapets, which appear to be more sensitive to variations in gravity loads. Two different ground-motion records were employed to assess the effects of both tectonic and induced seismicity scenarios. The experiments were carried out at the testing facilities of the EUCENTRE in Pavia, Italy. This thesis describes the key characteristics of the building specimens, including the geometry and construction details. A series of strength tests on small masonry assemblies was performed to characterise the mechanical properties of the materials used for the construction of the buildings. The adopted instrumentation plan, the seismic input motions, and the test protocol are thoroughly detailed. The thesis summarises the observations from the shake-table tests, illustrating the evolution of the structural and non-structural damage, and the global and by-parts hysteretic response of the buildings. The general behaviour of the three structures is discussed, and their seismic performance is assessed by linking engineering demand parameters, performance limits states, and points of the global force-displacement response. The experiments presented in this thesis were part of an extensive experimental campaign that started in 2014 with the aim to assess the seismic vulnerability of unreinforced masonry buildings in the Groningen region of the Netherlands. The area, historically not prone to tectonic ground motions, during the last two decades, has been hit by small-magnitude earthquakes induced by the local natural gas production activities and consequent reservoir depletion.
Esperimenti su tavola vibrante di tre edifici in muratura identici sottoposti ad input sismico multidirezionale. Questa tesi presenta i risultati di uno studio sperimentale volto a valutare l'influenza della multi direzionalità dei moti del terreno sulla risposta dinamica di edifici in muratura semplice. La ricerca è stata motivata dalle recenti osservazioni (post-terremoto) di maggiori danni strutturali in siti vicino alla faglia, dove i movimenti del terreno, orizzontali e verticali, sono stati forti e ben sincronizzati. Le accelerazioni verticali possono provocare la fluttuazione dei carichi di gravità, che a loro volta influiscono sulla capacità di carico laterale nel piano dei maschi in muratura e sulla stabilità al ribaltamento fuori dal piano delle pareti snelle. Le accelerazioni verso il basso si traducono nella riduzione istantanea della resistenza all'attrito delle pareti in muratura, che può portare a un potenziale aumento dello scorrimento tra i mattoni in caso di azione sismica orizzontale simultanea di notevole intensità. In questo studio, è stato valutato il potenziale danno delle accelerazioni verticali sugli edifici in muratura attraverso una serie di prove multidirezionali su tavola vibrante, simulando terremoti di intensità crescente avvenuti in prossimità della faglia. Sono state eseguite prove su tre edifici nominalmente identici ma testati in maniera differente; il primo edificio è stato sottoposto alla sola componente orizzontale principale, il secondo sottoposto ad una componente orizzontale combinata con quella verticale, e il terzo sottoposto a un moto tridimensionale. Negli edifici testati erano presenti un timpano, due camini e tre parapetti, elementi che sembravano essere più sensibili alle variazioni dei carichi gravitazionali. Sono stati impiegati due diversi segnali per valutare gli effetti degli scenari di sismicità sia tettonica che indotta. Gli esperimenti sono stati eseguiti presso i laboratori di EUCENTRE di Pavia, in Italia. Questa tesi descrive le caratteristiche principali degli edifici testati, inclusi la geometria e i dettagli costruttivi. È stata eseguita una serie di prove di resistenza su piccoli elementi in muratura per caratterizzare le proprietà meccaniche dei materiali utilizzati per la costruzione degli edifici. Inoltre, sono stati dettagliatamente descritti: la strumentazione adottata, gli input sismici scelti e il protocollo di test. La tesi sintetizza le osservazioni tratte dalle prove sulla tavola vibrante, illustrando l'evoluzione del danno strutturale e non strutturale e la risposta isteretica globale e secondaria delle costruzioni. Viene discusso il comportamento generale delle tre strutture e la loro prestazione sismica viene valutata considerando i parametri della domanda, gli stati limite e i punti della risposta globale in termini di forza – spostamento. Gli esperimenti presentati in questa tesi fanno parte di una vasta campagna sperimentale iniziata nel 2014 con l'obiettivo di valutare la vulnerabilità sismica degli edifici in muratura semplice nella regione di Groningen, nei Paesi Bassi. L'area, storicamente non soggetta a moti terrestri tettonici, negli ultimi due decenni è stata colpita da terremoti di piccola entità indotti dalle attività locali di estrazione di gas naturale e dal conseguente esaurimento dei giacimenti.
Shake-table experiments on three identical clay-brick masonry structures under multi-directional seismic input
PANATTI, MATTEO
2018/2019
Abstract
This thesis presents the results of an experimental study aimed at evaluating the influence of the multi-directionality of ground motions on the dynamic response of unreinforced masonry buildings. The research was motivated by recent post-earthquake observations of greater structural damage at sites near the fault, where horizontal and vertical ground motions were strong and well synchronised. Vertical accelerations can result in the fluctuation of gravity loads, which, in turn, control the in-plane lateral load capacity of masonry piers, and affect the out-of-plane overturning stability of slender walls. Downward accelerations result in the instant decrease of frictional resistance of masonry walls, which can lead to a potential increase of sliding between the bricks in case of simultaneous horizontal seismic action of considerable intensity. In this study, the damage potential of vertical accelerations to masonry buildings was investigated through a series of multi-directional shake-table tests on masonry structures, under simulated near-fault ground motions of increasing intensity. The experiments included a set of three nominally identical building specimens, subjected to the principal horizontal component only, the horizontal component combined with the vertical one, and to the full three-component ground motion, respectively. The test buildings comprised gable walls, chimneys, and parapets, which appear to be more sensitive to variations in gravity loads. Two different ground-motion records were employed to assess the effects of both tectonic and induced seismicity scenarios. The experiments were carried out at the testing facilities of the EUCENTRE in Pavia, Italy. This thesis describes the key characteristics of the building specimens, including the geometry and construction details. A series of strength tests on small masonry assemblies was performed to characterise the mechanical properties of the materials used for the construction of the buildings. The adopted instrumentation plan, the seismic input motions, and the test protocol are thoroughly detailed. The thesis summarises the observations from the shake-table tests, illustrating the evolution of the structural and non-structural damage, and the global and by-parts hysteretic response of the buildings. The general behaviour of the three structures is discussed, and their seismic performance is assessed by linking engineering demand parameters, performance limits states, and points of the global force-displacement response. The experiments presented in this thesis were part of an extensive experimental campaign that started in 2014 with the aim to assess the seismic vulnerability of unreinforced masonry buildings in the Groningen region of the Netherlands. The area, historically not prone to tectonic ground motions, during the last two decades, has been hit by small-magnitude earthquakes induced by the local natural gas production activities and consequent reservoir depletion.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.
Per maggiori informazioni e per verifiche sull'eventuale disponibilità del file scrivere a: unitesi@unipv.it.
https://hdl.handle.net/20.500.14239/11563