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In the last decade, several studies have investigated the application of Fibre Reinforced Polymer (FRP) wraps to masonry piers in order to provide a confinement effect and enhance compressive strength and ductility. Although this technique has proved to be quite effective, various drawbacks arise when organic resins are used to bind fibres. To solve these problems, different techniques have been developed to be used as alternative methods for enhancing the structural performances of weak masonry columns. Among these, the use of Basalt Fibre Reinforced Cementitious Matrix (BFRCM) wrapping, or the application of steel wires at mortar joints. This paper presents the results of an experimental study on the compressive behaviour of clay brick masonry columns reinforced with FRP wraps, Basalt Fibre Reinforced Cementitious Matrix (BFRCM) or with steel wires. Uniaxial compressive tests were performed on twelve retrofitted columns and four control specimens up to failure. Two masonry grades were considered varying the mix used for the mortar. The results are presented and discussed in terms of axial stress-strain curves, failure modes and crack patterns of tested specimens. Comparisons with unreinforced columns show the capabilities of these techniques in increasing the structural efficiency with reduced aesthetical impact.

A large number of masonry buildings have been designed to sustain gravity loads or with reference to obsolete seismic provisions. Columns are among the weakest elements, especially in historical buildings. Many experiments have been carried out over the last few decades to investigate the effectiveness of fiber-reinforced polymer (FRP) jackets for confinement. Owing to the poor chemical compatibility of FRPs with masonry substrates, a new technique based on the replacement of resin with an inorganic matrix [fabric-reinforced cementitious matrix (FRCM)] has been developed. There are very few reports available on tests conducted on FRCM-confined masonry columns, especially with reference to full-scale specimens. To fill this gap, uniaxial pure compression tests were carried out on seven full-scale limestone masonry columns. In particular, the investigation examined the effectiveness of FRCM systems based on the use of alkali-resistant glass-and basalt-fiber grids embedded in lime-based mortar. The use of an internal reinforcement provided by pultruded glass bars or helical stainless steel bars in a dry application is also analyzed.

Many investigations have shown that fibre reinforced polymer (FRP) composites can be effectively used to induce a passive confinement action on masonry columns and improve their axial capacity and ductility. This paper presents the results of an experimental study on the compressive behaviour of clay brick masonry cylinders externally wrapped with basalt fiber reinforced polymer (BFRP) grids. The circular section shape was chosen to assess the pure confinement effect on the masonry material. Fourteen clay brick masonry cylinders, cored from two different masonry assembly types, were confined with one or two layers of BFRP grids. The two assemblies were used to investigate the effect of vertical joints on the response of the cylinders. The cylinders were tested under uniaxial compression load. The test results showed a strength increase between 30% and 38% for cylinders wrapped with one layer and between 69% and 71% for those wrapped with two layers of BFRP grids.

The Fabric Reinforced Cementitious Matrices (FRCMs) are promising strengthening solution for existing masonry since inorganic matrix is considerably compatible with historical substrates. Nevertheless, matrix is responsible of the stress-transfer in composites so, in case of poor-quality mortar, the effectiveness of the strengthening can be limited or even compromised. For this reason, a few studies have been targeted to this aspect in the recent past, while numerical investigation are still limited. The present paper refers to a Finite Element (FE) analysis of masonry columns confined with FRCM composites developed by Abaqus-code and based on the macro-model approach. At this scope, available experimental results were used for the calibration regarding different types of matrix (lime and cement based) for FRCM-confinement. The model was performed by using the Plastic (P) and the Concrete Damage Plasticity (CDP) material constitutive laws. The FRCM-strengthened system was preliminary modeled as a homogenous elastic material until failure. Typical failures of FRCM-systems are detachment of the matrix from the substrate, slippage of the fibers within the embedding matrix, detachment of the composite strip at the fabric-matrix interface and fiber rupture. In this study, perfect bond was considered for the interaction between the masonry column and the external reinforcement according to the experimental observations (calibration specimens). Parametric analysis allowed to evidence the influence of the mechanical and geometrical parameters on the structural performances of the FRCM-system in confining column.

Columns are one of the most usual supporting structures in a large number of cultural heritage buildings. However, it is difficult to obtain accurate information about their inner structure. Non-destructive testing (NDT) methodologies are usually applied, but results depend on the complexity of the column. Non-flat external surfaces and unknown and irregular internal materials complicate the interpretation of data. This work presents the study of one column by using ground-penetrating radar (GPR) combined with seismic tomography, under laboratory conditions, in order to obtain the maximum information about the structure. This column belongs to a “Modernista” building from Barcelona (Spain). These columns are built with irregular and fragmented clay bricks and mortar. The internal irregular and complex structure causes complicated 2D images, evidencing the existence of many different targets. However, 3D images provide valuable information about the presence and the state of an internal tube and show, in addition, that the column is made of uneven and broken bricks. GPR images present high correlation with seismic data and endoscopy observation carried out in situ. In conclusion, the final result of the study provides information and 3D images of damaged areas and inner structures. Comparing the different methods to the real structure of the column, the potential and limitations of GPR were evaluated.

The application of steel fiber reinforced polymer (SRP) as a means of increasing the capacity of masonry columns is investigated in this study. The behavior of 23 solid-brick specimens that are externally wrapped by SRP sheets in low volumetric ratios is presented. The specimens are subjected to axial monotonic load until failure occurs. Two widely used types of masonry columns of differing square cross-sections were tested in compression (square and octagonal cross-sections). It is concluded that SRP-confined masonry behaves very much like fiber reinforced polymers (FRP)-confined masonry. Confinement increases both the load-carrying capacity and the deformability of masonry almost linearly with average confining stress. A comparative analysis between experimental and theoretical values computed in compliance with the Italian Council of Research (CNR) was also developed.

Stability analysis of masonry piers and columns is one of the most frequently treated subjects in the field of structural engineering. This attention is probably due to the challenge to solving the problem including different effects, which play an important role in evaluating the response of eccentrically-loaded columns. In this connection, accurate stability analysis of masonry piers and columns has to take into account the non-linear stress–strain law of masonry in compression, the limited tensile strength, the induced slenderness due to crack formation and geometrical non-linearity. Different theoretical models and numerical approaches were developed in the past to analyze the combined effect of buckling and strength in such structural members. In this paper a numerical method is derived and particularized for the case of clay brick masonry members. After a review of the most widely used analytical models for the compressive behaviour of masonry, the effects of a non-linear constitutive law in compression and cracking were taken into account with suitable moment–curvature curves. The latter were implemented in a simple numerical procedure, and made it possible to calculate the force–displacement curves and safety domains, which account for both strength and stability. The method was finally verified with results derived from non-linear finite element analyses, making it possible to make considerations about the suitability of the method and the related computational effort.

The use of composite materials for retrofitting of masonry structures has received great attention during the last two decades. For masonry buildings there are several advantages in using composite materials. Traditional techniques that were largely used and investigated in the past, may be inadequate in seismic areas where the added mass could increase seismic actions. Moreover, for historical and architectural heritage structures, the compatibility, sustainability and reversibility of the intervention is a key factor for the selection of the most appropriate strengthening system. Many investigations have shown that fibre reinforced polymers (FRP) can be effectively used to induce a passive confinement action on masonry columns and improve the axial capacity and ductility of the structural members. This paper presents the results of an experimental study on the compressive behaviour of clay brick masonry cylinders reinforced with basalt fibre reinforced polymer (BFRP) grids. The main aim of this study is to assess the effectiveness of the BFRP wraps on the strength and ductility of masonry columns. Twelve clay brick masonry cylinders, cored from masonry walls and columns, were reinforced using either one or two layers of BFRP grids. Two different arrangements were used for producing the cylinders in order to investigate the effect of vertical joints on the response of masonry cylinders. The basalt grid had a cell size of 6x6 mm. After a preliminary experimental study aimed at characterizing the mechanical properties of bricks, mortar and basalt grid, the cylinders were tested under uniaxial compression loading. The test results showed a strength increase between 30% and 38% for cylinders wrapped with one layer and between 69% and 71% for those wrapped with two layers of BFRP grids.

L’impiego di materiali compositi per il rinforzo di colonne in muratura è diventato una pratica ampiamente diffusa nel corso degli ultimi decenni. Questa tecnica, che consiste generalmente nell’applicazione di materiali polimerici fibrorinforzati (Fibre Reinforced Polymer-FRP), ha mostrato buone potenzialità, essendo in grado di garantire notevoli incrementi di resistenza e duttilità dell’elemento rinforzato, grazie ad un’azione di confinamento passivo. Tuttavia, l’impiego di compositi a matrice polimerica presenta alcuni limiti legati soprattutto alle prestazioni delle resine epossidiche, che a causa della loro natura sintetica danno luogo a problemi di compatibilità con il supporto murario. Per questo motivo, recenti lavori di ricerca hanno avuto l’obiettivo di sviluppare dei materiali di rinforzo non affetti dai problemi connessi all’adozione delle resine epossidiche, portando allo sviluppo dei compositi FRCM (Fibre Reinforced Cementitious Matrix), in cui la matrice polimerica viene sostituita da una matrice di natura inorganica, come una malta cementizia. Inoltre, la crescente domanda di nuovi materiali prodotti con un dispendio minimo di energia in grado di garantire adeguati livelli di sostenibilità, senza però rinunciare a buone prestazioni meccaniche, ha posto l’attenzione sui materiali compositi facenti uso di fibre di basalto per il rinforzo di strutture in muratura. L’obiettivo della presente tesi è quello di valutare l’efficacia, in termini incrementi di resistenza e duttilità, dell’azione di confinamento fornita da avvolgimenti in FRP o FRCM con fibre di basalto, quando questi sono applicati per il rinforzo di elementi in muratura. Lo studio viene condotto prevalentemente da un punto di vista sperimentale, attraverso la progettazione e realizzazione di una campagna di prove di compressione su cilindri in muratura di mattoni fasciati con FRP o FRCM. Preliminarmente si presentano i dettagli ed i risultati di un’ampia fase di caratterizzazione dei materiali, finalizzata ad indagare le proprietà meccaniche della malta e dei mattoni che costituiscono la muratura, a caratterizzare la malta impiegata nel rinforzo FRCM e a definire il comportamento in trazione della fibra di basalto impiegata nei sistemi di rinforzo studiati. In una fase successiva si analizza il comportamento meccanico del rinforzo in FRCM attraverso prove di trazione su strisce di composito, discutendo i risultati in termini di curve tensione-deformazione ed analizzando l’evoluzione del quadro fessurativo e le modalità di rottura. Viene quindi studiato sperimentalmente il comportamento in compressione dei cilindri in muratura confinati con FRP o FRCM, mostrando l’influenza delle principali variabili coinvolte nel problema, come il numero di giunti verticali di malta nella muratura o la percentuale di tessuto presente nel composito. I risultati ottenuti in termini di incrementi di resistenza a compressione e deformazione ultima permettono di formulare alcune considerazioni sull’efficacia dei sistemi di rinforzo studiati. Tutte le prove condotte sono supportate dalla tecnica della Digital Image Correlation (DIC), che viene impiegata come sistema di misura, integrato talvolta a dispositivi tradizionali, in grado di fornire informazioni sui campi di spostamento e sulla formazione e propagazione delle fessure durante le prove condotte. Infine, sono proposte alcune formulazioni analitiche per la previsione del comportamento in compressione dei cilindri in muratura rinforzarti con FRP o FRCM. Le espressioni adottate si basano su alcune proposte esistenti in letteratura e vengono confrontate con i risultati sperimentali ottenuti, al fine di trarre alcune conclusioni sulla loro applicabilità nelle pratiche applicazioni. The use of composite materials for the confinement of masonry columns having weak mechanical characteristics has become a widespread practice during the last decades. This technique, usually realized through the application of Fibre Reinforced Polymer (FRP) externally bonded jackets, has shown good capabilities, being able to significantly improve the load carrying capacity and the ductility of masonry members, thanks to a passive confinement action. However, FRP composites, when applied on masonry substrates, have shown some shortcomings due to the organic nature of the matrix. For this reason, during the last years growing attention has been paid to Fibre Reinforced Cementitious Matrix (FRCM) composites, in which the polymeric matrix is replaced by an inorganic matrix. Moreover, due to the increasing demand for new materials produced with low energy consumption that offer sustainability and good mechanical properties, composites reinforced with basalt fibres have lately attracted interest as material for strengthening masonry structures. The target of the present thesis is the evaluation of the effectiveness, in terms of strength and deformation capacity, of the confinement action provided by both basalt FRP and FRCM jackets, when the latter are applied on masonry members. In this framework, a detailed experimental investigation is performed by testing FRP and FRCM-confined clay brick masonry cylinders in compression. A preliminary investigation is carried out on the mechanical properties of constituent materials of masonry, namely bricks and mortar. Moreover, the strengthening systems are deeply analyzed through tests on the mortar matrix of the FRCM and an extensive study on the tensile behaviour of the basalt textile grid used as reinforcement. The mechanical behaviour of the FRCM composite is characterized under tension and the results are discussed in terms of stress-strain curves, evolution of cracks and failure modes. Then, the cylinders reinforced with FRP/FRCM jackets are subjected to uniaxial compressive loads, showing the influence of the key parameters involved in the problem, such as the number of vertical mortar joints in the masonry and the number of wrapping layers. The results in terms of compressive strength increases and corresponding strains allow drawing some conclusions on the effectiveness of the investigated strengthening systems. The whole experimental study is carried out employing the Digital Image Correlation (DIC), which is the only monitoring system in some cases and serves as support to traditional systems in other tests, giving information about the displacement fields and the development of cracks during the performed tests. Finally, analytical formulations useful for the prediction of the compressive behaviour of FRP/FRCM-confined masonry are proposed and compared to the experimental results, allowing some conclusions to be drawn on their reliability for practical design/verification purposes.