Partially grouted reinforced masonry (PG-RM) shear walls have a vast presence in many countries, even in seismic-prone regions. These walls have had acceptable seismic performance in strong earthquakes, although in-plane shear failures have been reported. Although past studies have addressed some of the detected issues, experimental information is still limited, a situation even more notorious when focusing on bed-joint reinforced (BJR) PG-RM shear walls. Besides, most numerical approaches proposed for analyzing masonry elements are aimed at reproducing unreinforced masonry elements. Additionally, recent studies have demonstrated the inaccuracy of some design codes and some existent expressions when estimating the shear strength of PG-RM shear walls. Therefore, it is necessary to gather further experimental data on PG-RM shear walls, improve or adapt numerical approaches to study them, and also propose suitable formulas to estimate their in-plane shear resistance. In response to the identified necessities, 18 full-scale PG-RM shear walls were tested under constant axial load and incremental in-plane lateral cyclic loading. Nine walls were built with multi-perforated clay bricks (MPCBLs), and nine with hollow concrete blocks (HCBs). Different design properties were varied, such as the walls’ geometrical properties, reinforcement ratios, reinforcement layout, and material properties. All tested walls failed in a diagonal tension failure mode. In general, the studied variables affected the walls’ response. For instance, using lower aspect ratio or joint thickness; and higher axial load ratio, horizontal or vertical reinforcement ratio, or mortar compression strength produced a higher shear strength in the BJR-MPCLB walls. In BJR-HCBs walls, using a higher vertical or horizontal reinforcement ratio increased the shear strength and providing edge elements generated a more stable post-peak behavior. Additionally, in HCB walls, providing a combination of horizontal reinforcement embedded in mortar bed-joints and bond-beams resulted in better hysteretic behavior, energy dissipation capacity, and ductility compared to the walls provided with only one horizontal reinforcement type. Also, a numerical study on the implementation of detailed micro-models (DMMs) of PG-RM shear walls was performed. Good accuracy was obtained when reproducing the experimental behavior of the MPCLB walls tested in this study, being more accurate than the selected shear expressions. It is highlighted the importance of choosing an appropriate numerical solution strategy to avoid misleading results considering the strong non-linear response of these models. Then, DMMs were used to perform a parametric study on the influence of selected design variables on the shear response of PG-RM shear walls of MPCLBs. The results were also employed to corroborate a combined effect of the axial stress and aspect ratio on the walls’ shear strength. Besides, implementation details of simplified micro-models (SMM) of PG-RM shear walls of HCBs are given. Two identical BJR-PG-RM shear walls of HCB were reproduced with this approach, obtaining an appropriate accuracy. Finally, design expressions for estimating the resistance of bed-joint reinforced PG-RM shear walls of MPCLBs and HCBs were fitted to databases composed of experimental and numerical results. The obtained expressions are more accurate than the studied code expressions in terms of the error average and range.
Le pareti a taglio in muratura parzialmente rinforzata con iniezioni (in inglese, partially grouted reinforced masonry, PG-RM) sono diffuse in molti paesi, incluse regioni classificate come zone sismiche. Questi elementi hanno presentato prestazioni sismiche accettabili anche in caso di terremoti di elevata intensità, tuttavia sono stati comunque osservati meccanismi di collasso nel piano. Nonostante studi passati avessero già evidenziato alcune delle problematiche rilevate, i dati sperimentali sono ancora limitati. Questa mancanza è ancora più marcata nel caso delle pareti PG-RM rinforzate sui giunti orizzontali (bed-joint reinforced, BJR PG-RM). Oltretutto, la maggior parte degli approcci numerici proposti per lo studio degli elementi strutturali in muratura trattano muratura non rinforzata. Inoltre, studi recenti hanno dimostrato l'inesattezza di alcune norme di progettazione ed alcune formule di calcolo esistenti circa la stima della resistenza al taglio delle pareti PG-RM. Pertanto, è necessario raccogliere ulteriori dati sperimentali riguardo le pareti a taglio PG-RM, migliorare e adeguare gli approcci numerici per questi elementi, ed infine proporre adeguate formulazioni per stimarne correttamente la resistenza al taglio nel piano. In risposta alle necessità evidenziate, sono state testate 18 pareti a taglio PG-RM in scala reale mediante una configurazione di carico che prevede precompressione assiale costante e carico ciclico laterale incrementale nel piano. Nove pareti sono state costruite con blocchi forati in argilla (multi-perforated clay bricks, MPCBL), le altre nove con blocchi forati in calcestruzzo (hollow concrete blocks, HCB). Nel corso dei test sono state variate diverse caratteristiche progettuali, quali la geometria delle pareti, i rapporti di rinforzo, la disposizione del rinforzo e le proprietà dei materiali. In tutti i muri testati il collasso è avvenuto per fessurazione diagonale. In generale, tutte le variazioni studiate hanno influenzato la risposta delle pareti. Ad esempio, nelle pareti BJR-MPCLB si è osservato un aumento di resistenza al taglio nei seguenti casi: minore rapporto di forma o spessore dei giunti; oppure maggiore rapporto di carico assiale, rapporto di rinforzo orizzontale o verticale, resistenza alla compressione della malta. Nelle pareti BJR-HCB, un maggiore rapporto di rinforzo orizzontale o verticale ha incrementato la resistenza a taglio mentre l’aggiunta di elementi di bordo ha generato un più stabile comportamento post-picco. In aggiunta, nelle pareti HCB la presenza di rinforzo orizzontale incorporato nei giunti di malta combinata con l’applicazione di travi di collegamento è stata associata ad un migliore comportamento isteretico, capacità dissipativa e duttilità rispetto alle pareti dotate di solo rinforzo orizzontale. Inoltre, è stato condotto uno studio numerico basato su una micro-modellazione dettagliata (detailed micro-modeling, DMM) di pareti a taglio PG-RM. Questo studio ha permesso di riprodurre con buona precisione il comportamento sperimentale delle pareti MPCLB, risultando più accurato delle formule di calcolo del taglio fornite dalle norme. Si è sottolineata l’importanza di adottare un’appropriata strategia di soluzione numerica al fine di evitare risultanti fuorvianti, data la forte non-linearità nella risposta strutturale di questi modelli. Successivamente, tramite i DMM sono state eseguite analisi parametriche sull'influenza delle selezionate variabili di progetto sulla risposta a taglio delle PG-RM con MPCLB. I risultati hanno anche permesso di confermare l’effetto combinato di carico assiale e rapporto di forma sulla resistenza a taglio della parete. Inoltre, vengono presentati alcuni dettagli su un approccio di micro-modellazione semplificata (simplified micro-models, SMM) per le pareti PG-RM con HCB. Tramite questo approccio sono state riprodotte due pareti identiche BJR-PG-RM con HCB, ottenendo un’adeguata accuratezza. Infine, alcune formule di calcolo per la stima della resistenza di BJR PG RM con MPCLB e HCB sono state adattate ai risultati sia numerici che sperimentali presenti nei database. Le nuove formulazioni ottenute risultano più accurate rispetto alle precedenti in termini sia di errore medio sia di campo di variazione.
Experimental and numerical study of partially grouted reinforced masonry shear walls subject to in-plane loading
CALDERÓN DÍAZ, SEBASTIÁN ANDRÉS
2020/2021
Abstract
Partially grouted reinforced masonry (PG-RM) shear walls have a vast presence in many countries, even in seismic-prone regions. These walls have had acceptable seismic performance in strong earthquakes, although in-plane shear failures have been reported. Although past studies have addressed some of the detected issues, experimental information is still limited, a situation even more notorious when focusing on bed-joint reinforced (BJR) PG-RM shear walls. Besides, most numerical approaches proposed for analyzing masonry elements are aimed at reproducing unreinforced masonry elements. Additionally, recent studies have demonstrated the inaccuracy of some design codes and some existent expressions when estimating the shear strength of PG-RM shear walls. Therefore, it is necessary to gather further experimental data on PG-RM shear walls, improve or adapt numerical approaches to study them, and also propose suitable formulas to estimate their in-plane shear resistance. In response to the identified necessities, 18 full-scale PG-RM shear walls were tested under constant axial load and incremental in-plane lateral cyclic loading. Nine walls were built with multi-perforated clay bricks (MPCBLs), and nine with hollow concrete blocks (HCBs). Different design properties were varied, such as the walls’ geometrical properties, reinforcement ratios, reinforcement layout, and material properties. All tested walls failed in a diagonal tension failure mode. In general, the studied variables affected the walls’ response. For instance, using lower aspect ratio or joint thickness; and higher axial load ratio, horizontal or vertical reinforcement ratio, or mortar compression strength produced a higher shear strength in the BJR-MPCLB walls. In BJR-HCBs walls, using a higher vertical or horizontal reinforcement ratio increased the shear strength and providing edge elements generated a more stable post-peak behavior. Additionally, in HCB walls, providing a combination of horizontal reinforcement embedded in mortar bed-joints and bond-beams resulted in better hysteretic behavior, energy dissipation capacity, and ductility compared to the walls provided with only one horizontal reinforcement type. Also, a numerical study on the implementation of detailed micro-models (DMMs) of PG-RM shear walls was performed. Good accuracy was obtained when reproducing the experimental behavior of the MPCLB walls tested in this study, being more accurate than the selected shear expressions. It is highlighted the importance of choosing an appropriate numerical solution strategy to avoid misleading results considering the strong non-linear response of these models. Then, DMMs were used to perform a parametric study on the influence of selected design variables on the shear response of PG-RM shear walls of MPCLBs. The results were also employed to corroborate a combined effect of the axial stress and aspect ratio on the walls’ shear strength. Besides, implementation details of simplified micro-models (SMM) of PG-RM shear walls of HCBs are given. Two identical BJR-PG-RM shear walls of HCB were reproduced with this approach, obtaining an appropriate accuracy. Finally, design expressions for estimating the resistance of bed-joint reinforced PG-RM shear walls of MPCLBs and HCBs were fitted to databases composed of experimental and numerical results. The obtained expressions are more accurate than the studied code expressions in terms of the error average and range.| File | Dimensione | Formato | |
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CALDERON - 2021 - EXPERIMENTAL AND NUMERICAL STUDY OF PARTIALLY GROUTED REINFORCED MASONRY SHEART WALLS SUBJECTED TO IN-PLANE LOADING.pdf
Open Access dal 29/05/2022
Descrizione: Phd thesis
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https://hdl.handle.net/10589/179695