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The near-surface mounted (NSM) has proven to be a highly effective retrofitting technique for strengthening existing masonry structures without compromising their dead load, cross-section, or aesthetics. This investigation conducted a series of experiments on masonry columns strengthened with NSM steel and glass fiber reinforced polymers (GFRP) reinforcements. In total, 22 masonry columns were tested, of which 2 served as control specimens. A total of ten different combinations were considered to examine the NSM technique's effectiveness. The two identical specimens were constructed for each retrofitting combination. The strengthened specimens were confined vertically by steel or GFRP reinforcements and horizontally by stirrups (50 turns of small-diameter steel bars). The specimens underwent uniaxial compression testing, and results were observed in the specimens' failure mode, stress-strain curves, energy absorption capacity, and displacement-ductility index responses. This study concluded that utilizing NSM reinforcements (steel and GFRP) enhances the overall stress-strain behavior of masonry columns, especially in the post-peak regions. However, no significant improvement was observed in the pre-peak response of the retrofitted specimens. The GFRP bars' performance was superior to steel bars in improving the peak and post-peak performance of the retrofitted specimens. The maximum improvement in GFRP bar specimens was recorded as 34 % and 118 % for compressive strength at peak loading and 1.5 % strain, 60 % for energy absorption, and 93 % for displacement ductility index. Based on the experimental results, an analytical model is proposed that accurately predicts the complete stress-strain curve of NSM-retrofitted specimens. • Brick masonry columns were strengthened by NSM steel or GFRP bars. • The NSM retrofitting improved the post-peak stress-strain response. • GFRP bars' performance was superior to steel bars. • Analytical modeling was proposed to predict the complete stress-strain response. [ABSTRACT FROM AUTHOR]

The use of fabric-reinforced cementitious mortar (FRCM) or steel-reinforced grout (SRG) is now recognized to be effective in enhancing the axial capacity of masonry columns when confinement is achieved. Numerous experimental tests demonstrated the symbiotic role of the fabric and the inorganic matrix. An open issue is still related to the numerical simulation. In fact, if the compressive behavior by the numerical simulation of the unreinforced and reinforced masonry columns confined by a FRCM/SRG jacket may follow different approaches. The inorganic matrix transfers the stresses from the substrate to the fabric differently, depending on the presence or absence of cracks. The fabric consists of an open grid whose yard could be differently stressed after the matrix damage because of the occurrence of a possible slippage at the fabric–matrix interface. Definitely, these aspects are difficult to numerically predict. The paper herein is devoted to the assessment of different numerical approaches for the FRCM/SRG confinement of masonry columns by considering data from the literature and varying the parameters related to the matrix, the fabric, and the masonry itself. The goal is to best fit the experimental outcomes (from different available sources) with different strategies based on a finite element (FE) modeling. The results show good matching between the experimental and theoretical curves for the different FRCM/SRG systems. The results evidenced that the accuracy of the experimental versus the numerical curves match is met for the different FRCM/SRG systems. [ABSTRACT FROM AUTHOR]

A mechanistic model is presented for the strength prediction of squared columns made of masonry with a periodic arrangement and strengthened with a fibre–polymer composite jacketing. The formulation is based on an incremental plasticity theory that relies on equilibrium, compatibility, and kinematic equations. The strength domain of brick units and mortar joints is bounded by a multi-surface yield criterion: a Mohr–Coulomb strength domain with a linear cap in compression and a Rankine cut-off in tension. An elasto-plastic response with limited ductility is assumed for both masonry components. Differently, the FRP response is assumed elastic with a brittle failure governed by a limited tensile strain. Phenomenological-based assumptions are undertaken and justified. Details are also provided for the computational implementation of the procedure. The model accuracy is validated against experimental data on masonry squared columns and compared with existing standard-based formulas. Results demonstrate it provides real-time and accurate compressive strength solutions for squared masonry columns with or without a polymer-based wrapping and yet requiring few input parameters for the masonry constituents and reinforcement. [ABSTRACT FROM AUTHOR]

Fiber Reinforced Polymer (FRP) and Engineered Cementitious Composites (ECC) have been widely used to strengthen masonry columns due to their superior mechanical performance. Compression tests of masonry columns strengthened with ECC-jacket, FRP-strips, and ECC-jacket-FRP-strips were conducted in this study. The influence of the ultimate tensile strain of ECC and the number of FRP strip layers was investigated. The failure modes, load-displacement curves, strength, deformation, lateral strain, and energy absorption were analyzed and discussed. The results indicate that, compared with unconfined columns, the load-bearing capacity of columns strengthened by ECC jacket and two layers of FRP strips was significantly improved; 119% and 90.2% increases were achieved, respectively. There was a 242.4% and 119.4% increase in the corresponding ultimate deformation, respectively. In addition, the columns combine strengthened with ECC jacket and two layers of FRP strips exhibited excellent compression behavior, and their compressive strength was 274.5% higher than that of unconfined columns. The compressive strengths predicted by the available analytical models were adopted to evaluate the predictive ability of different models. The prediction model of the code CNR-DT 200/2013 exhibited better agreement with the experimental results in this study. • Compression performance of ECC-jacket-FRP-strips combined strengthened masonry columns. • The effects of ECC elongation and FRP sheet distribution on the load-bearing capacity of columns. • Strength, deformation, and energy absorption capacity of strengthened masonry columns were revealed. • A recalibrated analytical model was proposed to predict the compressive strength. [ABSTRACT FROM AUTHOR]

This paper investigates the in-plane seismic behaviour of hinged steel frames that are enhanced with masonry columns and/or infilled walls. First, eight half-scaled hinged steel frame specimens were constructed according to the realistic structural system of Bund 18, which is a historical building in Shanghai, China. Then, cyclic loads were exerted on these frames. The test results indicated that the seismic behaviours of the hinged steel frames can be significantly improved with the use of masonry columns and/or infilled masonry walls as well as with proper strengthening due to carbon fibre-reinforced polymer (CFRP) sheets. A simplified model was developed to simulate the seismic behaviours of these frames. In this model, infilled walls and CFRP sheets were replaced by diagonal struts, and the steel members and their surrounding elements were treated as composite members. Finally, this model was verified by experimental results. [ABSTRACT FROM AUTHOR]

• Confined masonry columns were subjected to monotonic and cyclic compression. • Axial behaviour of continuously and discontinuously confined masonry are different. • Cyclic stress–strain characteristics of confined masonry columns were verified. • Formulations to describe the stress–strain model under cyclic loading are suggested. Confinement of masonry columns using fibre reinforced polymer (FRP) composites have displayed to enhance the axial capacity and ductility. Although, mechanisms of FRP confined masonry column (CMC) subjected to monotonic compression loading with various configurations have been investigated and rational design rules were developed, the response of FRP-CMC under cyclic compression is not widely researched. Therefore, this paper presents an analytical stress–strain model for FRP-CMC subjected to cyclic compression based on the experimental data generated through a testing program. The experimental program has been executed in this research by testing twelve masonry columns confined with discontinuous FRP sheets subjected to monotonic and cyclic compression. The masonry columns were assembled with two varieties of masonry bricks and mortars. The data from the testing of discontinuously CMCs and previous experimental program involving twenty-four continuously CMCs were employed to analytically predict the cyclic compression characteristics. The testing results of discontinuously CMCs subjected to axial monotonic and cyclic compression have shown that they are quite different in terms of their strength and deformability compared to continuously CMCs. The discontinuous FRP strengthening columns resulted in strength and ductility increments in the range of 100–150% and 60–80%, respectively. For the analytical model, the envelop curve, plastic strain, stress deteriorations in cycles, unloading and reloading segments of the proposed stress–strain model have been verified against the experimental data. It has been shown that the suggested analytical model is capable of describing the cyclic axial stress–strain characteristics of FRP-CMCs. [ABSTRACT FROM AUTHOR]

Strengthening masonry columns by spraying them with glass fibre reinforced polymer (GFRP) was investigated experimentally. The study was aimed at assessing the strength and strain increases imparted by the technique under both concentric and eccentric axial loading. Plain and steel-reinforced columns were tested. Twenty-four columns were constructed from Type S mortar and straight and bullnose clay masonry units. The columns were 1 m high and either 290 mm × 290 mm or 390 mm × 390 mm in cross section. Two thicknesses of sprayed GFRP (SGFRP) were attempted, but it was found to be difficult to maintain uniform thickness. Nevertheless, with only minor increases in strength, large increases in strain capacity were achieved with both the plain and reinforced columns under concentric axial compression. Eccentric loading reduced the effect of the SGFRP laminate on the strength of masonry columns. Failure of SGFRP included both mode I and mode III fractures. [ABSTRACT FROM AUTHOR]

• TRC optimized with short fibers, is used in the masonry confinement. • Eighteen masonry piers are tested under concentric axial loading. • TRHDC confinement can improve strength, ductility and energy absorption. • Applicability of models from literature are evaluated to predict the masonry strength. Textile-reinforced high ductile concrete (TRHDC) (Li et al., 2020) is an optimized textile reinforced concrete (TRC) by using short polyvinyl alcohol (PVA) fibers. This work presented an experimental study on the compressive behavior of masonry piers confined with TRHDC jacket. The considered parameters were textile types, number of textile layers, together with a group of fiber reinforced polymer (FRP) confined columns as a reference set. Although the strength was greatly improved by the FRP wraps, the brittle failure and rather weak post-peak behavior were observed in the FRP strengthened columns. By contrast, TRHDC composites changed failure mode of columns with multiple thin cracks opening on the jacket. The compressive strength, ultimate strain and energy absorption capacity were improved by the TRHDC confinement. Analytical models from the literature were evaluated for their applicability to estimate the compressive strength of masonry piers confined with FRP or TRHDC jacket. Predictions were in good agreement with experimental data, which can be adopted in the engineering application. [ABSTRACT FROM AUTHOR]

• Masonry columns confined with three different techniques were reviewed. • Strength and deformation characteristics of the confined masonry columns were evaluated. • Analytical models to predict the confined masonry compressive strengths were appraised. • The compressive stress–strain behaviour of confined masonries was assessed. The confinement technique has been effectively used to enhance the strength and ductility of structural elements. Since masonry possesses relatively limited ductility and tensile strength, the confinement has been shown to improve the performance of masonry elements, particularly the columns. Primarily three different techniques are implemented to confine the masonry columns (1) fibre reinforced polymer (FRP) wrapping (2) fabric reinforced cementitious matrix (FRCM) application and (3) confinement of mortar joints by steel grinds or wire hooping. Although the above mentioned techniques have shown to provide confinement and improve the performance of masonry columns, each has its own advantages and disadvantages in terms of applicability, compatibility, strength enhancement, ductility gain and reversibility. Therefore in this paper, an attempt has been made to critically review the performance of masonry columns confined with above mentioned techniques to appraise their performances in relation to various parameters. For these purposes, three sets of experimental databases have been developed for the above stated techniques from the past research studies. Further several analytical models have been independently developed to predict the confined compressive strength and axial stress–strain behaviour of the masonry columns; subsequently the predictabilities of those analytical models were verified by comparing against with the experimental database. The analyses revealed, that the analytical models given in the Italian guidelines CNR DT 200/215 conservatively predict the confined strength of masonry columns. Therefore it can be recommended to use deliberately across different confinement techniques investigated. [ABSTRACT FROM AUTHOR]

• A study on the mechanical behavior of eccentrically loaded BTRC confined masonry. • BTRC confinement can significantly improve the ultimate compressive strength of masonry columns. • Strain gradient effect existed on the strains of BTRC jackets. • A nonlinear iterative procedure was proposed to evaluate the second order effect. The mechanical behavior of masonry columns confined with basalt textile reinforced concrete (BTRC) under eccentric compression was investigated. The main objects of this research include: i) the effects of load eccentricity and confinement ratio on the failure modes of masonry columns; ii) the confinement effectiveness of BTRC on columns involving increases in peak load and ductility; iii) confinement mechanism of BTRC jackets under eccentric loading, i.e. , how the confinement was activated; iv) the theoretical predictions of mechanical behavior of masonry columns through an analytical procedure. A total of 20 masonry columns with or without confinement of BTRC jackets were eccentrically loaded and two parameters were varied, i.e. , confinement ratio, ρ f , and eccentricity-to-section height ratio, e/h. The experimental results were discussed and analyzed in terms of failure modes, load-axial deformation response, load-lateral deflection response and load-strains curves of BTRC jackets. A nonlinear second order iterative procedure was developed to predict mechanical behavior of eccentrically loaded masonry columns, in which the variation of eccentricity along the entire height induced by lateral deformations could be considered. Finally, the theoretical predictions were compared with experimental results to evaluate the findings herein. [ABSTRACT FROM AUTHOR]

• TRC confinement effectively improved the compressive performance of masonry columns. • The prediction model of compressive strength was proposed with a better generality. • Some available data in other literature were considered in the analytical models. Masonry structures strengthened with textile-reinforced concrete (TRC) have been extensively studied, and many results have confirmed the TRC-strengthened effectiveness. The present paper demonstrated the experimental investigation on the compressive performance of TRC-confined masonry columns in terms of failure mode, carrying capacity, deformability and energy dissipation. The prediction formulas of the compressive strength and ultimate strain were also proposed based on the test results in this paper and available data in other literature. The results indicated that the brittle failure feature of unconfined masonry columns was relieved after TRC confinement. The specimens confined with the carbon-glass TRC showed a better ductile behavior compared with that of the basalt-glass TRC because a relatively poor ability to disperse cracks was observed for basalt-glass TRC-confined specimens in this test. The carrying capacity, deformability and energy dissipation of the specimens after TRC confinement all gained the different degrees of increase, and the increased effectiveness of the carbon-glass TRC-confined specimens was more prominent compared with that of basalt-glass TRC. The compressive strength of TRC-confined masonry columns can be well predicted by the formula obtained in this paper with a better generality, while the prediction formula of the ultimate strain for TRC-confined masonry columns has a lower accuracy, and needs to be further researched. [ABSTRACT FROM AUTHOR]

In this study, a new type of composite comprised of glass textiles embedded in the short fiber reinforced cementitious composite, referred to as textile-reinforced high ductile concrete (TRHDC), is explored for use in the confinement of masonry columns. This paper presents the results of an experimental study on the effect of TRHDC jacket on the compressive behavior of clay brick masonry columns. Six unconfined and twelve confined columns with a rectangular cross-section are tested under monotonic concentric and eccentric loads. Test parameters are binding mortar grade and loading eccentricity. The data in terms of failure mode, peak load, stress-strain and moment-curvature response are analyzed and discussed. The test results indicate that TRHDC confinement can clearly improve both the load carrying capacity and the deformability of masonry columns relative to the unconfined condition. However, a noticeable reduction in peak load is observed under strain gradient condition with the increase of eccentricity level. Analytical models available in the literatures are used to predict the strength increase from the TRHDC jacket, with certain models predicting the confined compressive strength accurately. For the eccentrically-loaded masonry columns confined with TRHDC jacket, the confined compressive strength is reduced depending on the eccentricity ratio (e / h) to evaluate the axial load carrying capacity. The predicted values are in agreement with test results but should need further experimental investigations in the future to verify the reliability of expressions rather than those used in this paper. [ABSTRACT FROM AUTHOR]

• ·The effectiveness of HDC system used to confine masonry was studied. • ·The HDC as binding mortar clearly improved the deformability rather than strength. • ·The HDC jacket could increase both the strength and deformability. • ·Analytical model was proposed for predicting strength of confined masonry. This work presents the results of an experimental investigation on the compressive behavior of clay brick masonry columns confined with highly ductile fiber reinforced concrete (HDC). The study aims to prove the effectiveness of the proposed confinement technique and detect the efficiency of different confinement forms of HDC, including internally-placed HDC which was used as binding mortar in the joints (i.e. internal HDC mortar) and external HDC jacket. Furthermore, the effect of confinement materials is examined. Analysis of the failure mode, axial load–displacement curves, peak load and ductility reveals that internal HDC mortar could considerably improve the deformability of masonry columns. Although the external HDC jacket could increase the load carrying capacity and deformability, the detachment between the external layer and masonry substrate is observed at the post-peak stage. Contribution of cement-based mortar jacket to the masonry columns is merely enhancing the load carrying capacity rather than deformability, which was caused by its quite low tensile strength. Moreover, based on the theories of mesh-reinforced brick masonry and steel tube confined concrete, analytical models available in the literatures are adopted to predict the compressive strength of HDC systems confined masonry columns. The calculation model gives a better approximation to predict the compressive strength of confined masonry columns but should need further experimental data in the future other than those adopted in this paper to verify the accuracy and reliability. [ABSTRACT FROM AUTHOR]

• The effectiveness of HDC system as a means for reinforcement of masonry was studied. • The BMHDC jacket improved both load bearing capacity and deformability. • The BMHDC jacket can be used to strengthen the large eccentric columns. • Theoretical prediction is proposed for strengthened masonry columns. This work presents the results of an experimental study on the compressive performance of clay brick masonry columns strengthened with bar mesh highly ductile fiber reinforced concrete (BMHDC) jacket. The test parameters consist of strengthening method and loading eccentricity. The analysis in terms of failure mode, peak load, axial load-displacement curves and ductility proves that BMHDC jacket is an effective reinforcing technique which can significantly improve the load carrying capacity and deformability of masonry columns. Although the maximum load of masonry column is decreased with the increase of loading eccentricity, the effectiveness of using BMHDC jacket is not weakened by the initial eccentricity. Moreover, for the convenience of strengthening design in the practical applications, a theoretical prediction of load carrying capacity for strengthened masonry columns tested under concentric and eccentric loads is proposed on the basis of the plane cross-section assumption and modified biaxial strength criterion of bricks. Predicted results are accurate and consistent with experimental results. [ABSTRACT FROM AUTHOR]

The behavior of FRCM (Fabric Reinforced Cementitious Mortar) confined clay brick masonry columns is analyzed in this paper. The results of an experimental investigation conducted on small-scale columns made by clay brick masonry confined with steel-FRCM (or Steel Reinforced Grout, SRG), PBO (poly-paraphenylene-benzo-bisoxazole) FRCM and basalt-FRCM, tested under monotonic compressive load, are described and discussed. Tests were conducted on thirteen prismatic columns; eleven columns (two unconfined and nine confined) were tested under concentric load while an eccentric load was applied on two confined columns. For each confinement system, the parameters investigated were the 'confinement ratio', the 'load eccentricity' and the 'overlap configuration of the fiber fabrics'. FRCM confinement improved the structural response of masonry columns in terms of ultimate strength, ultimate strain and ductility. Some models from the literature were also examined to evaluate their applicability in predicting the axial capacity of confined columns. [ABSTRACT FROM AUTHOR]

Retrofitting of damaged and/or ancient masonry structures is of significant importance to increase their structural safety. In this study, a retrofitting technique of basalt-textile-reinforced concrete (BTRC) was used to repair partially damaged rectangle masonry columns, and the repairing efficiency was assessed by different parameters. Compression tests with different eccentricities were conducted to explore the mechanical behaviors of initial and BTRC retrofitted masonry columns. The data in terms of crack patterns, load-displacement curves, peak load, ductility and longitudinal strains were analyzed and discussed in depth. Results show that BTRC retrofits can substantially improve the load carrying capacity and ductility of the partially damaged masonry columns under different eccentric loads that display different damage characteristics. The uniaxial constitutive (NTR-PP, NTR-PB and Sargin) models of masonry predict a relatively safe bearing capacity of BTRC-confined columns under eccentric loadings. This BTRC retrofitting technique with the features of cheap, easy-to-construct, long durability and environmental friendliness shows promising potentials in engineering applications. The findings of this study provide an effective way for repairing ancient and/or damaged masonry structures with BTRC. [ABSTRACT FROM AUTHOR]