Confinement Of Masonry Columns Research Articles

Confinement of masonry columns with FRCM: A new confined strength formulation and experimental validation

In this work, a wide experimental dataset about the axial behavior of masonry columns confined with Fabric Reinforced Cementitious Matrix (FRCM) jackets (also refered to as TRM - Textile Reinforced Mortar or TRCC - Textile Reinforced Cementitious Composites), that contains the results from 226 confined specimens, was collected. Data were critically analyzed with the aim of identifying the influence of the most important parameters considered within the dataset (i.e., fibers type and number of layers, masonry type and unconfined strength, mortar type and mechanical strength, the effective lateral pressure, etc.). Further, a review of the main models proposed in different Codes and in literature was carried out, which were then applied to the dataset, highlighting some discrepancies in their predictions. Thus, a new formulation for the confined strength of masonry columns was proposed, aiming to consider also some other influencing variables such as the compressive strength of the masonry blocks and that of the mortar joint. Lastly, the validity of the proposal was verified on a new set of experimental results, which were obtained by the authors testing three unconfined and confined clay brick masonry columns. Specimens were subject to monotonic axial loading under displacement control until failure, and stress and strains were monitored continuously during the test. The jacketing system was realized with one layer of glass-based FRCM (GFRCM).

Confinement of masonry columns through SRG: experimental results and analytical prediction

Steel Reinforced Grout (SRG) composites represent, nowadays, a very compatible, reversible, and profitable strengthening solution for existing masonry buildings in earthquake prone regions. They can be employed to enhance the in-plane and out-of-plane behavior of masonry panels or to confine masonry columns. When these materials are applied to columns, different layouts can be adopted, mainly differing in the number of reinforcing layers.The objective of the present research is to evaluate the effectiveness of the use of SRG for the confinement of masonry columns. In more detail, clay brick masonry columns are realized and strengthened with 1 to 3 SRG layers. Uniaxial compression tests are then performed to evaluate the benefit provided by the composite material. Comparisons between the unreinforced and the strengthened samples are carried out in terms of load bearing capacity, deformability, and failure mode. In general, an increase in terms of strength and deformability was obtained by increasing the number of SRG layers applied.An analytical approach, derived by adapting the Spoelstra-Monti approach – formulated for FRP-strengthened concrete columns – to the case of SRG-strengthened masonry columns, is also adopted to predict the compressive behavior of the confined samples. The comparison between analytical and experimental results shows a good agreement, confirming the accuracy of the analytical prediction.

Numerical Strategy for Column Strengthened with FRCM/SRG System

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.

Analytical model for CFRP confined masonry columns subjected to monotonic and cyclic compression

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.

A Design-Oriented Stress-Strain Constitutive Model for Clay-Brick Masonry Columns Confined by FRP

Experimental tests proved that the external confinement of masonry columns through Fiber-Reinforced Polymers (FRP) induces increment of axial strength and ductility. Contrary to FRP-confined concrete, for which reliable unified theoretical stress-strain models are available in literature or included in the codes, to develop easy-to-use constitutive models valid for whatever type masonry represents a difficult challenge. In fact, several parameters influence the axial stress-strain response of confined masonry, such as the relative mortar-to-stones strength, masonry texture, deformation capacity of materials, type of reinforcement ad its arrangement. In this paper, a design-oriented stress-strain model devoted to describe the compressive behavior of FRP-confined clay-brick masonry columns is presented. The main scope of the research consists of providing an easy-to-use predictive model, applicable both in the research field and design practice. The stress-strain response of the confined masonry has been idealized in a parabola-rectangular behavior described by Lam and Teng’s equations - originally developed for FRP-confined concrete - adapted to masonry elements. The equations are ruled by the mechanical properties of confined and unconfined masonry, those of composite material and by a parameter that takes into account the dispersion of the experimental data (i.e., variability of materials properties, different stone arrangements and masonry textures). The entire stress-strain behavior has been calibrated by means of the least-squares optimization criterion, based on a sufficient number of experimental results available in the literature. Comparisons between experimental and theoretical stress-strain curves show good accordance of the results. The design-oriented model is able to capture the experimental response of the confined masonry, in terms of initial elastic stiffness, ductility ad maximum confinement pressure.

Confinement of Masonry Columns with Natural Lime-Based Mortar Composite: An Experimental Investigation

The paper presents the results of an experimental campaign on the confinement of masonry square columns with fiber-reinforced lime mortar (FRLM) composites made of a natural lime-based matrix. The experimental results show the effectiveness of such a composite for increasing both strength and ductility performances of strengthened columns. Predictive formulas from the literature and from the Italian guidelines CNR-DT 215/2018 do not perfectly fit the experimental outcomes and do not confirm the strength increase of the confined columns. The reason can be attributed to the very low mechanical properties of the natural matrix used to form such a composite. Therefore, considering that the use of a natural and sustainable matrix fully compatible with the masonry substrate is a fundamental requirement for strengthening masonry columns of buildings belonging to architectural heritage, an additional future effort should be made by researchers involved in this field. In particular, for a reliable prediction of the strength of masonry columns confined with composites made of natural matrices, wider experimental campaigns are necessary to refine available formulas with respect to different substrates and component materials.

Monotonic and cyclic compression characteristics of CFRP confined masonry columns

The lateral confinement of masonry columns using composites have shown to improve their strength and ductility. Although, several research studies were focused on investigating the monotonic compression behaviour of confined masonry columns in the past, their cyclic compression characteristics, which are necessary for seismic and dynamic analyses, are not well investigated. Thus, an attempt has been made to experimentally characterise the confined masonry columns under monotonic and cyclic axial compression in this research. In total, 36 masonry columns were built and tested under monotonic and cyclic compression. Out of 36 columns, twelve columns were unconfined and tested under monotonic compression, while the rest of the columns were confined with Carbon Fibre Reinforced Polymer (CFRP) laminates and tested under monotonic and cyclic compression. The experimental results are presented in terms of observed failure modes, compressive strengths and stress–strain curves. Cyclic loading protocol was displayed to marginally reduce the compressive strength of CFRP confined masonry columns by 6% to 13% compared to the compressive strengths obtained through monotonic compression testing. The analytical models available to predict the monotonic stress–strain curves were used to predict the cyclic envelop stress–strain relationship of confined masonry columns. Finally, the best fit analytical model to predict the cyclic envelop compression behaviour of CFRP confined masonry columns has been proposed.

Confinement of Masonry Columns with the FRCM-System: Theoretical and Experimental Investigation

Fabric Reinforced Cementitious Matrix (FRCM) systems are promising solutions for the confinement of masonry columns because they demonstrate strengthening effectiveness and, at the same time, compatibility with historical substrates. Nevertheless, the matrix is responsible for the stress-transfer from the structural element to the fabric-reinforcement. Therefore, in the case of poor-quality mortar, the effectiveness of the strengthening can be limited or even compromised. On the other hand, the low content of fibers utilized for FRCM systems generally involves the need to apply more layers in order to accomplish design requirements and a continuous configuration of the reinforcement is more often addressed. Few experimental and theoretical investigations have been targeted to the before mentioned aspects in the recent past, namely the influence of the kind of mortar, the number of layers, and the strengthening configuration (continuous, discontinuous) on the effectiveness of confinement. The present paper refers to the results of an experimental investigation on FRCM confined clay brick masonry. A series of small-scale masonry columns were tested under monotonic centered load until collapse. The varied parameters were the number of confining layers (i.e., 1, 2, and 3) and the confinement configuration (i.e., continuous and discontinuous). The performed research aims to contribute in strengthening to the knowledge in the field of FRCM-confinement, mainly focusing on some of the mentioned unexplored aspects (number of layers, strengthening configuration) that could be considered for validation/improvement of analytical design-oriented formulas. In particular, some analytical models, available in the technical literature, were adopted for predicting the herein reported experimental results. Even if based on few experimental results, the outcomes showed that the number of FRCM-layers and the confinement configuration were crucial parameters affecting the confining effectiveness. The compressive strength was satisfactorily predicted in all cases by the two available utilized models. On the other hand, an improvement in the utilized AOM model is suggested in order to include the stress–strain curves of the hardening type.

Axial Stress–Strain Model for FRCM Confinement of Masonry Columns

Abstract Masonry columns often exhibit a lack of load-carrying capacity that is due to overloads and do not provide any ductility or dissipation capacity under seismic forces. Column confinement ha...

Confinement of masonry columns with textile-reinforced mortar jackets

This paper presents an experimental investigation on the confinement of masonry columns with textile-reinforced mortar (TRM) jackets as a means of enhancing their axial load-carrying capacity and axial deformability. The experimental program included the construction and testing of twenty-six masonry prisms, which were subjected to monotonic concentric compression. The specimens were equally divided in two testing Series based on their cross-section geometry; square and rectangular with 2:1 aspect ratio. One specimen from each Series was tested unconfined and served as reference specimen, whereas the rest twelve specimens were tested after receiving TRM jacketing. Apart from the cross-section geometry, the investigated parameters included the textile material (two types of carbon-fibre textiles, one glass and one basalt-fibre textile), and the amount of the textile reinforcement (no. of layers). Overall, TRM confinement of masonry columns increased both their compressive strength and ultimate axial strain, with effectiveness factors varying between 1.02 and 1.61 for the strength and from 1.05 to 4.11 for the strain. The effect of the investigated parameters is carefully examined and discussed in the paper, in terms of both the compressive strength and the ultimate axial strain enhancement. Modelling of masonry confined with TRM jackets is presented by adopting a widely accepted confinement model, properly calibrated with the test results to account for the behaviour of the TRM confined masonry. From the results obtained in this study, it is believed that TRM jacketing is a promising solution for the confinement of masonry columns.

Masonry columns confined with glass textile-reinforced high ductile concrete (TRHDC) jacket

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.

Discontinuous FRP-Confinement of Masonry Columns

Recent seismic events, all over the world, demonstrated that masonry constructions are prone to brittle collapses when shear or compression capacity is reached. It is clear that, in many real cases, masonry columns need to be strengthened for enhancing their load-carrying capacity and to develop a more ductile response. The Fiber Reinforced Polymers (FRPs) confinement of masonry columns is a well-known technique that may produce these advantages. Unfortunately, full-wrapping insulates the column from the environment; so interstitial humidity can easily occur and cause the acceleration of the masonry’s decay. In order to prevent it, partial-confinement is commonly assessed instead of total-jacketing. For this reason, a research was led, consisting of an experimental and theoretical study focused on the discontinuous FRP-confinement. Thus, two different series of masonry columns were confined with Glass-FRP (GFRP) and Carbon-FRP (CFRP) strips bonded to the column with an epoxy resin. Different schemes of FRP-wrapping were investigated by means of uniaxial compression tests. Moreover, an analytical method for the prediction of the experimental results was also provided. The proposed model was based on the relationship between the different lateral deformations of the confined and unconfined regions (experimentally recorded by using strain gauges). The new iterative procedure was found able to provide theoretical stress vs strain curves; which demonstrated to accurately match the experimental recordings. The proposed model was also validated by parametric analyses, presented in the paper.

Confinement of Masonry Columns with PBO and Basalt FRCM Composites

A new generation of composite materials in the form of Fiber Reinforced Cementitious Matrix (FRCM) was recently used to strengthen the masonry structures. Six small scale masonry columns were tested under monotonic concentric load until collapse; three columns were confined with PBO (short of polyparafenilenbenzobisoxazole)-FRCM jackets, two with basalt–FRCM jackets while an unconfined column was used as a control specimen. The masonry columns investigated have a rectangular cross section 250x250 mm among the overall length equal to 770 mm, and the corners were rounded to a radius of 20 mm. The analysis was conducted varying the confinement ratio i.e. the number of fabric layers for each FRCM system. Obtained results allow evidencing the effectiveness of the confinement and the effect n-layer on the structural response of the masonry columns.

Experimental study on carbon fiber textile reinforced mortar system as a means for confinement of masonry columns

Abstract The present paper demonstrates the results of an experimental and analytical research programme on masonry structures confined with Textile Reinforced Mortars (TRMs). A total of 39 small scale masonry columns were subjected to uniaxial compression tests after being strengthened with TRM layers. The variables studied during the experiments were, the number of TRM layers, the cross-section aspect ratio and the corner radii. The purpose of this experimental investigation was to examine the influence of the aforementioned parameters on the performance of confined masonry. In general, the TRM jackets increased substantially both the strength and the ductility of the confined specimens. The results obtained from the current experimental study allowed the development of a simple set of equations, using a linear and a non-linear approach, for the prediction of the strength and the ultimate strain of TRM-confined masonry. The non-linear approach gives a better approximation for the prediction of the compressive strength, and the relevant strain. Further experimental investigation is needed in the future to include more types of fibers, textiles, mortars, and masonry materials.

Confinement of Masonry Columns with Steel and Basalt FRCM Composites

The rehabilitation of existing masonry elements by means of jacketing of columns using composite materials is becoming a remarkable technique in several applications that aim to increase the strength of existing masonry buildings. Fiber reinforced cementitious matrix (FRCM) composites are a newly developed strengthening system that consist of high-strength fibers embedded in a cementitious grout and externally bonded to the substrate. High resistance to fire and high temperatures, ease of handling during application, and vapor permeability with the substrate are some of the characteristics that make FRCMs a promising alternative to traditional organic composites such as fiber reinforced polymer (FRP) composites. This work presents the results of an experimental study carried out to understand the behavior of masonry columns with a square cross-section confined by steel and basalt fiber sheets embedded in a mortar matrix subjected to monotonic concentric compressive load. The effectiveness of the confinement is studied in terms of load-bearing capacity with respect to unconfined columns. The effect of corner radius for columns confined with basalt fibers is investigated.

Unified model for hollow columns externally confined by FRP

Nowadays, the employment of Fibre Reinforced Polymer (FRP) composites in civil engineering field has been successfully experienced. Different potential applications of solid concrete-filled FRP tubes are exploitable in marine piles, overhead sign structures, poles and posts, bridge columns and piers, girders, large pipes and tunnels (mainly circular cross-section). This technique is also used for the confinement of masonry columns, typically encountered in monuments and historical buildings (both rectangular and circular cross-section); hence the need of providing formulas for the design of an appropriate strengthening. Several analytical models are available in the scientific literature for assessing the increase of strength and ductility of concrete or stone solid elements externally confined with FRP or for hollow columns internally steal enclosed and externally FRP-confined but, there is still a lack of research about hollow columns only externally confined. The presence of an empty core implies a different stress state in the inner cylindrical surface with respect to the outer one. Inwards deformations are more significant and this behaviour is not taken into account by available models.The present study aims to illustrate a detailed summary of the existing analytical models and to provide a unified procedure for concrete and masonry hollow columns valid for both circular and square cross-sections. An iterative method that updates the geometrical parameters according to step-by-step uniaxial compressed column is shown in order to capture the real deforming behaviour of the compressed solid. This analytical approach has two important implications: the first is the ability of calculating the stress state of the column and of the external FRP reinforcement at each step; the second is that of theorizing a procedure, which is independent on the type of material used for the column. The outputs of the proposed method are then compared with experimental results currently available in the scientific literature. A good matching is obtained between the available experimental results and the analytical predictions in term of axial stress–strain curves.

Confinement of Masonry Columns with PBO FRCM Composites

The overarching goal of this work is to provide a fundamental understanding of the behavior of solid brick masonry columns confined with fiber reinforced cementitious matrix (FRCM) composites. FRCM is a newly-developed type of composite material comprised of a cementitious inorganic matrix (binder) and embedded fibers that are usually bundled to improve the bond between the matrix and the fibers. Compression tests were carried out to investigate the influence of the FRCM confinement and the brick patterns on the load-carrying capacity of the confined columns. Compression tests were conducted on brick masonry columns with different brick configurations. Digital image correlation measurements on the surface of the composite and on the surface of the brick for the control specimens were attempted in order to understand the role of the mortar joints and the arch effect across the section of the columns due to the confinement. The experimental results indicate that FRCM composites can effectively increase the load-carrying capacity of brick masonry columns and the failure mode could be different from the one observed for masonry columns confined with fiber-reinforced polymer (FRP) composites.

Masonry columns confined by composite materials: Design formulae

The present paper is aimed at assessing analytical formulations and calibrating an accurate and reliable design formula for FRP-confined masonry columns. After a short introduction about the key issues regarding the confinement of masonry columns by means of composite wrapping, a wide experimental database is assembled in a second section of the paper. Such a database has been obtained by merging the test results presented by the authors in a companion paper with other ones available in the scientific literature. The content of the database, the nature of the specimens and the range of variation of the relevant parameters are reported in the paper. The most well-established analytical formulae for FRP-confined concrete members are summarised in the third section of the paper; their effectiveness when applied to confined masonry elements is investigated on the basis of the collected database. The very limited number of models currently available for masonry members are also reported and discussed; they generally result in inaccurate and non-conservative predictions, as they have been commonly calibrated on experimental results carried out on specific types of masonry. Finally, a general expression for a design-oriented formula is calibrated with respect to the above-mentioned experimental database. As a matter of principle, different levels of accuracy can be achieved in calibrating such an expression, depending on the number of parameters considered in its calibration: the higher the number of such parameters, the lower the expected residual error of the resulting formula. Thus, three different proposals of design formulae for FRP-confined masonry columns are reported and commented with the aim of describing their accuracy in terms of scatter, average error and distribution of the experimental-to-theoretical ratios.

FRP Confinement of Tuff and Clay Brick Columns: Experimental Study and Assessment of Analytical Models

In recent years, fiber-reinforced polymer (FRP) wrapping effectiveness has been clearly confirmed especially with reference to concrete structures. Despite evident advantages of FRP based confinement on members subjected to compressive overloads due to static or seismic actions, the use of such technique in the field of masonry has not been fully explored. Thus, to assess the potential of confinement of masonry columns, the present paper shows the results of an experimental program dealing with 18 square cross sections (listed faced tuff or clay brick) masonry scaled columns subjected to uniaxial compression load. In particular, three different confinement solutions have been experimentally analyzed in order to evaluate and compare the effectiveness of uniaxial glass FRP, carbon FRP, and basalt FRP laminates wrapping. The main experimental outcomes are presented and discussed in the paper considering mechanical behavior of specimens, axial stress-axial strain relationships, and effective strains at failur...

Strengthening masonry columns: steel strands versus FRP

Masonry structures are prone to brittle failure due to seismic forces or compressive overloads. A novel retrofitting technique is presented for the confinement of masonry columns subjected to compressive loads. The use of steel strands immersed in a cementitious matrix is described in terms of the mechanical properties of steel-confined columns. The structural behaviour of steel-confined columns was also compared with that of fibre-reinforced plastic (FRP)-confined columns. Experimental results showed the effectiveness of the proposed technique in terms of structural efficiency and installation procedure. The mechanical behaviour of steel-confined masonry and FRP-confined masonry was found to be very similar. The advantages of the proposed techniques with respect to confinement with FRP consist of the use of a cementitious matrix that does not require specialised labour and dry surface, allows moisture migration through the masonry surface of the column, is not prone to premature degradation or debonding under fire events, and is easily removable with mechanical tools without damaging the masonry core.