The present thesis stems from the desire to give a contribution to research in the field of structural reinforcement for masonry. It should be remembered that masonry is a quasi brittle material which works very well under compressive stresses but tends to crack under tensile stresses. For this reason, masonry structures can withstand vertical loads in the plane very well, but they show all their weakness in the case of out-of-plane bending and horizontal actions. Reduced tensile strength leads to fragile fractures that result in sudden loss of strength and may lead to the unexpected collapse of masonry structures; it is therefore easy to understand where the necessity of using FRP for reinforcement comes from. In particular, reference is made to carbon fibre reinforcement systems. In view of the large architectural heritage in our country, the theme of the recovery and reinforcement of masonry structures is very relevant. The technology explored in this thesis allows both the recovery of damaged structures and the consolidation of existing ones in order to improve their mechanical performance, for example in view of seismic activity. In the first part of this work, the state of the art in relation to this technology was outlined through an in-depth bibliographic research. The main contributions made by scientific research and the guidelines set out in various international standards have been highlighted, pointing out the most frequently addressed aspects. As mentioned, many studies have been carried out on the subject, but many aspects are still obscure. The behaviour of composites is in fact extremely variable; it is strongly influenced by the constituent materials and by the constraint and loading conditions imposed. It is easy to understand how the variability of the structural response is very large and therefore not totally investigated yet. The aim of the work presented here is to provide a contribution to research by studying the shear behaviour of reinforced and unreinforced masonry triplets. In order to do this, an experimental campaign was organised, which naturally involved the study of the triplets themselves but also of the mortar with which they were made. A considerable amount of data was collected through the experimental tests. First of all, the numerical data that in quantitative terms describe the mechanical characteristics of the tested specimens. The values obtained are useful both for obtaining practical information on the effectiveness of the reinforcement systems and for calibrating numerical simulation models. During the experimental investigations, it was also possible to monitor the behaviour of the test specimens using optical systems. In this way, it is possible to trace the macroscopic behaviour of the test specimens when stressed to failure. It is also worth noting that the photographic data and reports collected in this thesis are a kind of guide to the fabrication of reinforced triplet specimens. In fact, the experimental campaign was an opportunity to experience the operational problems associated with laboratory testing, to find solutions and thus create a useful background of knowledge for future research. From a computational point of view, this thesis provides a useful numerical tool that can be used with the ABAQUS software. The 'Plastic-damage model for cyclic loading of concrete structures' by Jeeho Lee and Gregory L. Fenves has been implemented here in a user subroutine (VUMAT), creating a fully controllable calculation tool able to deal with the problem of quasi brittle materials such as masonry. The model has been extensively tested and validated, providing good results in terms of computational speed. The Lubliner functions have also been exploited to create an algorithm that requires few input parameters, unlike the Concrete damage plasticity model implemented in the ABAQUS software. With just a few experimental data, it is therefore possible to reliably define the behaviour of the material. The implemented constitutive law was then used to perform some finite element simulations. The triplet tests and the three-point bending test on the mortar specimen conducted in the laboratory were simulated. The thesis therefore also provides some examples of finite element modelling, highlighting the advantages and disadvantages of the numerical simulations in relation to the experimental reality.
La presente tesi nasce dalla volontà di dare un contributo alla ricerca nel campo dei rinforzi strutturali per murature. É bene ricordare infatti che le murature sono materiali quasi fragili che lavorano molto bene se sottoposti a sforzi di compressione ma che tendono a fessurarsi in condizioni di trazione. Per questa ragione le strutture murarie sopportano molto bene i carichi verticali nel piano ma mostrano tutta la loro debolezza nei confronti delle flessioni fuori piano e delle azioni orizzontali. La ridotta resistenza a trazione infatti conduce a fratture di tipo fragile, che hanno come conseguenza repentine perdite di resistenza e possono condurre al collasso improvviso delle strutture murarie; è facile quindi capire da dove nasce la necessità dell'impiego di FRP per il rinforzo. In particolare si fa riferimento ai sistemi di rinforzo con fibre di carbonio. Alla luce del vasto patrimonio architettonico presente nel nostro paese il tema del recupero e del rinforzo di strutture in muratura è attualissimo; la tecnologia approfondita in questa tesi permette infatti sia il recupero di strutture danneggiate sia il consolidamento di quelle esistenti al fine di migliorarne le prestazioni meccaniche, per esempio in ottica sismica. Nella prima parte di questo lavoro, tramite un’approfondita ricerca bibliografica, è stato delineato lo stato dell’arte in relazione a questa tecnologia. Sono stati evidenziati i principali contributi forniti dalla ricerca scientifica e le linee guida presenti in varie normative internazionali mettendo in luce gli aspetti maggiormente trattati. Come detto molti studi sono stati svolti sul tema ma ancora molti aspetti sono oscuri. Il comportamento dei compositi è infatti molto vario; questo è influenzato fortemente dai materiali costituenti ,dalle condizioni di vincolo e carico imposte. È facile capire come la variabilità della risposta strutturale sia molto ampia e di conseguenza non ancora totalmente indagata. Lo scopo del lavoro qui presentato è quello di dare un contributo alla ricerca studiando il comportamento a taglio di triplette in muratura rinforzate e non. Per fare questo è stata organizzata una campagna sperimentale che ha coinvolto naturalmente lo studio delle triplette stesse ma anche della malta con cui sono state realizzate. Tramite le prove sperimentali è stato possibile raccogliere una considerevole mole di dati. Primi fra tutti dati numerici che in termini quantitativi descrivono le caratteristiche meccaniche dei provini testati. I valori ottenuti risultano essere utili sia per avere informazioni concrete riguardo l’efficacia dei sistemi di rinforzo sia per poter tarare modelli di simulazione numerica. Durante le prove sperimentali è stato possibile anche monitorare il comportamento dei provini tramiti sistemi ottici. Si ha quindi a disposizione una traccia del comportamento macroscopico che questi manifestano se sollecitati fino a rottura. Vale la pena notare inoltre come i dati fotografici e i resoconti raccolti in questa tesi siano una sorta di guida alla realizzazione di provini di triplette rinforzate. La campagna sperimentale è stata infatti un’occasione per poter toccare con mano i problemi operativi legati alle prove di laboratorio, trovare soluzioni e creare quindi un utile background di conoscenze per future ricerche. Da un punto di vista computazionale questa tesi fornisce un utile strumento di calcolo utilizzabile tramite il software ABAQUS. Il modello 'Plastic-damage model for cyclic loading of concrete structures' di Jeeho Lee e Gregory L. Fenves è stato qui implementato in una user subroutine (VUMAT), creando uno strumento di calcolo totalmente controllabile in grado di trattare il problema dei materiali quasi fragili, quali sono le murature in esame. Il modello è stato ampiamente testato e validato, fornendo buoni risultati in termini di velocità computazionale. Lo sfruttamento delle funzioni di Lubliner inoltre ha permesso di realizzare un algoritmo che richiede pochi parametri in ingresso diversamente da quanto accade per il modello Concrete damage plasticity implementato nel software ABAQUS. Tramite pochi dati sperimentali è quindi possibile definire in modo affidabile il comportamento del materiale. Il legame costitutivo implementato è stato quindi usato per realizzare alcune simulazioni ad elementi finiti. Sono state simulate le prove su triplette e la prova di flessione a tre punti sul provino di malta condotte in laboratorio. La tesi fornisce quindi anche alcuni esempi di modellazioni ad elementi finiti mettendo in luce pregi e difetti delle simulazioni numeriche in relazione alla realtà sperimentale.
Shear tests on FRP reinforced masonry triplets and their FE simulations
Barcellini, Roberto
2020/2021
Abstract
The present thesis stems from the desire to give a contribution to research in the field of structural reinforcement for masonry. It should be remembered that masonry is a quasi brittle material which works very well under compressive stresses but tends to crack under tensile stresses. For this reason, masonry structures can withstand vertical loads in the plane very well, but they show all their weakness in the case of out-of-plane bending and horizontal actions. Reduced tensile strength leads to fragile fractures that result in sudden loss of strength and may lead to the unexpected collapse of masonry structures; it is therefore easy to understand where the necessity of using FRP for reinforcement comes from. In particular, reference is made to carbon fibre reinforcement systems. In view of the large architectural heritage in our country, the theme of the recovery and reinforcement of masonry structures is very relevant. The technology explored in this thesis allows both the recovery of damaged structures and the consolidation of existing ones in order to improve their mechanical performance, for example in view of seismic activity. In the first part of this work, the state of the art in relation to this technology was outlined through an in-depth bibliographic research. The main contributions made by scientific research and the guidelines set out in various international standards have been highlighted, pointing out the most frequently addressed aspects. As mentioned, many studies have been carried out on the subject, but many aspects are still obscure. The behaviour of composites is in fact extremely variable; it is strongly influenced by the constituent materials and by the constraint and loading conditions imposed. It is easy to understand how the variability of the structural response is very large and therefore not totally investigated yet. The aim of the work presented here is to provide a contribution to research by studying the shear behaviour of reinforced and unreinforced masonry triplets. In order to do this, an experimental campaign was organised, which naturally involved the study of the triplets themselves but also of the mortar with which they were made. A considerable amount of data was collected through the experimental tests. First of all, the numerical data that in quantitative terms describe the mechanical characteristics of the tested specimens. The values obtained are useful both for obtaining practical information on the effectiveness of the reinforcement systems and for calibrating numerical simulation models. During the experimental investigations, it was also possible to monitor the behaviour of the test specimens using optical systems. In this way, it is possible to trace the macroscopic behaviour of the test specimens when stressed to failure. It is also worth noting that the photographic data and reports collected in this thesis are a kind of guide to the fabrication of reinforced triplet specimens. In fact, the experimental campaign was an opportunity to experience the operational problems associated with laboratory testing, to find solutions and thus create a useful background of knowledge for future research. From a computational point of view, this thesis provides a useful numerical tool that can be used with the ABAQUS software. The 'Plastic-damage model for cyclic loading of concrete structures' by Jeeho Lee and Gregory L. Fenves has been implemented here in a user subroutine (VUMAT), creating a fully controllable calculation tool able to deal with the problem of quasi brittle materials such as masonry. The model has been extensively tested and validated, providing good results in terms of computational speed. The Lubliner functions have also been exploited to create an algorithm that requires few input parameters, unlike the Concrete damage plasticity model implemented in the ABAQUS software. With just a few experimental data, it is therefore possible to reliably define the behaviour of the material. The implemented constitutive law was then used to perform some finite element simulations. The triplet tests and the three-point bending test on the mortar specimen conducted in the laboratory were simulated. The thesis therefore also provides some examples of finite element modelling, highlighting the advantages and disadvantages of the numerical simulations in relation to the experimental reality.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/179100