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The use of composite materials, in particular Carbon Fibre Composite Materials (CFRP), as reinforcement of both concrete and masonry structures is more and more widespread in the structural rehabilitation and retrofitting of existing buildings, thanks to their excellent mechanical performance combined with lightness and simplicity of application. Since the bond capacity of CFRP-to-masonry bonded joints, with respect to in-plane loads, is generally lower than the composite tensile strength, several methods have been proposed in the literature to increase their structural performance. Among these, CFRP spike anchors showed to be able to effectively increase strength and dissipative capability of CFRP reinforcement sheets. Nevertheless, their use in technical practice is discouraged by the lack of specific rules that adequately support designers. The development of predictive formulas, appearing necessary to bridge this gap, requires an extensive experimental database that highlights the peculiar characteristics of these reinforcements. As a contribution in this field, this paper presents an experimental program concerning the analysis of the mechanical behavior of this type of reinforcements applied to masonry structural elements loaded by out-of-plane actions. The experimental results showed that the effectiveness of such anchors strongly depends on the shape ratio of the specimens. [ABSTRACT FROM AUTHOR]

Fiber reinforced composite materials are widely used for structural rehabilitation and retrofitting of existing buildings; recent studies, devoted to Carbon Fiber Reinforced Polymers (CFRP) reinforcements of concrete structural elements [1–5], demonstrated that spike anchors are able to effectively increase the load carrying capacity and the ductility of CFRP bonded joints. However, application to masonry structures is disregarded by research since few experimental results are available. One of these, described in Refs. [6,7], compares the efficiency of a CFRP strengthening system provided with one or more CFRP spike anchors, also in dependence of some geometrical parameters; reinforcement sheets and spike anchors were applied only on the brick surface in order to evaluate the effects due to anchors only. In this paper the authors investigate the influence of mortar joints on the efficiency of anchored CFRP reinforcements on brick masonry. For this reason, an experimental campaign was planned on masonry pillars built with the same materials employed in Refs. [6,7], subjected to Near End Supported Single Shear Tests. Masonry pillars were built according to two different patterns, in order to detect the influence of both bed and perpend joints. The results are compared with results obtained from previous experimental campaign. [ABSTRACT FROM AUTHOR]

Abstract: Fiber reinforced composite materials are widely used for structural rehabilitation and retrofitting of existing buildings. Failure of not anchored CFRP reinforcements, applied to both concrete and masonry, mainly occurs in the substrate or at the bonding surface, for load values lower than the tensile strength of the composite. Mechanical anchors can effectively increase the maximum load of this type of reinforcements. Particular attention should be paid to the design and sizing of mechanical anchors so that these can produce adequate increments of both strength and ductility of the reinforcement. At the moment there are no specific rules or reliable predictive formulas that adequately support designers in the design choices and sizing of anchors. Of course, these can be defined only after collection of an extensive experimental database that highlights the peculiar characteristics of these reinforcements also with reference to the substrate material. In this context, the present work describes the results of an experimental campaign carried out on brick specimens reinforced with CFRP strips, anchored to the substrate by CFRP spike anchors. Almost all research in the literature about this topic refers to the use of this reinforcement technique for concrete structural elements. Studies concerning masonry are limited: this work contributes to bridge part of this gap. Plane CFRP reinforcement strips generally exhibit brittle failure mode. The experimental campaign reported in this paper shows that properly designed mechanical anchors increase both the failure load and the ductility of the reinforcement. [Copyright &y& Elsevier]

• Experimental investigation on strengthened and unstrengthened rammed earth arches. • Assessment of the efficiency of an eco-friendly strengthening system. • Calibration of uniaxial compressive parameters using experimental data. • Sensitivity analysis with respect to fracture energy and tensile strength. • Numerical simulations of strengthened and unstrengthened rammed earth arches. This paper shows experimental and numerical analyses on rammed earth arches asymmetrically loaded and successively strengthened with a natural composite. The aim is to evaluate the capability of finite element codes to faithfully describe the mechanical response, including the post peak branch and post elastic deformations. The mechanical properties of rammed earth were determined through specific experimental tests and used to calibrate uniaxial compressive parameters of the constitutive models implemented in three numerical software (ANSYS, Abaqus, ADINA). The mechanical parameters of the jute fabric are reported here together with the description of the calibration of the constitutive models. According to the experimental results, the strengthening system proposed was capable to increase the load bearing capacity and ductility of the structures, preserving their integrity for higher load levels and consequently postponing failure without adding significant mass to the system. The numerical models were able to describe the failure process in good agreement with the experimental results for both strengthened and unstrengthened arches; the effects of uncertainties on the tensile behaviour parameters of rammed earth, due to the scarce amount of data available in literature and to the difficulty in performing reliable tests for their determination, were numerically evaluated through sensitivity analysis. [ABSTRACT FROM AUTHOR]

Synthetic and artificial fiber fabrics are commonly used as masonry structures reinforcement, both for seismic retrofitting of historical buildings and for realization of new constructions in seismic areas. Correspondingly, natural fiber fabrics are appropriate to earth buildings reinforcement, being compatible from the point of view of environmental sustainability. In this paper the results of tensile tests on jute yarns are reported, organized and statistically analyzed in order to interpret the basic laws of size effects involved. The great variability of yarns behavior and the difficulties in controlling the boundary conditions induced to perform numerical tensile tests on statistical samples of jute fabric, generated in compliance with the statistical distribution of yarns mechanical properties. The comparison between laboratory and numerical tests permits to make some considerations on the difficulties involved in the experimental analysis, in order to define a reliable experimental technique to determine the properties necessary to the successive design. [ABSTRACT FROM AUTHOR]

This paper describes the development of a micro-mechanical Finite Element model apt to reproduce the behavior of masonry walls reinforced with Carbon Fiber Reinforced Polymer (CFRP) sheets, monotonically loaded by out of plane actions. According to the results of previous experimental programs carried out by the Authors, in the case of CFRP sheets bonded parallel to the bed joints, such walls behave like un-connected masonry portions (similar to strengthened masonry beams). For this reason, only such effective part was considered in both the experimental program (already published by the Authors) and the numerical simulations. Both simply bonded and anchored CFRP reinforcements have been considered in the paper. Particular attention was paid to the definition of the constitutive parameters, calibrated on the basis of several experimental campaigns previously performed by the Authors. Since fracture energy of bulk materials and adhesive tangential strength of the reinforcement are generally thought of as difficult to experimentally determine and can be affected by uncertainties, a sensitivity analysis concerning such parameters is described in the paper. The numerical predictions have been compared to the experimental outcomes in terms of load displacement diagrams, stress distribution and damage evolution; the proposed numerical model seems to well reproduce the general experimental behavior. [ABSTRACT FROM AUTHOR]

Fibre-reinforced composite materials have gained an increasing success, mostly for strengthening, retrofitting, and repairing existing structures. However some problems may arise with the use of traditional FRP (Fiber Reinforced Polymer), particularly when the compatibility with the substrate and the reversibility of the intervention are required, as in case of cultural heritage buildings, or specific exposition conditions may compromise the long term effectiveness of the reinforcement, as in presence of high temperature and humidity. Starting from these considerations new composite materials are emerging as a more effective solution in certain fields of application and under specific service conditions; in this context, mortar-based composite systems, consisting of one or more layers of uni- or bi-directional fibre nets embedded in cement/lime-based matrix layers, can be used as reinforcement of both concrete and masonry structures. However, the research work dealing with these emerging materials and their performances when used as a strengthening system for existing structures is still limited. Both experimental and theoretical investigations are needed in order to deliver reliable design methodologies. In this work, a Round Robin Test aimed to the characterization of both bond with the existing substrate and tensile performance of glass fabric (in the form of grids) coupled with inorganic mortar matrices is presented. The investigation was conducted at fifteen laboratories involved in the RILEM Technical Committee 250-CSM (Composites for the Sustainable Strengthening of Masonry). With the aim of studying the bond behaviour between Fabric Reinforced Cementitious Matrix (FRCM) composites and masonry substrate, single and double lap shear tests were carried out on brick-masonry prisms. Results provide useful informations about the mechanical properties, the bond capacity and the failure mechanisms of different commercially available glass FRCM systems. Finally, critical aspects are underlined to address the progress of the research work. [ABSTRACT FROM AUTHOR]

• RRT activity on the bond behavior of FRCM composites. • Evaluation of the influence of different set-up parameters. • Estimation of the expected experimental scattering. • Recommendations for set-up standardization. • Contribution to the improvement of test procedures included in current guidelines. Fabric Reinforced Cementitious Matrix (FRCM) composites represent an innovative and effective retrofitting solution for masonry structures. The use of FRCMs as an external retrofitting technique requires an insight knowledge of their mechanical behavior, failure modes and masonry-to-FRCM bond properties. A Round Robin Test (RRT) programme was launched by twelve Italian Universities, aimed at evaluating the effect of the shear test set-up parameters and at assessing the test variability. The experimental tests were performed on systems made of glass and steel fibers/cords applied onto masonry substrates. The results were carefully analyzed discussing failure modes, bond capacity, and slip statistical dispersion. Differences in the set-up, including the clamping method, textile impregnation, and instrumentation used for measuring the slip during the tests, were discussed in detail providing useful considerations and suggestions for reducing experimental scattering and obtaining reliable results. [ABSTRACT FROM AUTHOR]

This paper reports the results of an experimental campaign that aims at evaluating the capability of a composite made of jute fabric and stabilized earth matrix to act as a reinforcement of earth structures, and the analytical models able to interpret the results. Preliminary studies carried out in order to test adequate reinforcement systems for earthen structures, demonstrated that jute fabric applied with a stabilized earth plaster, among other natural fibers or systems, is able to develop exceptional adhesion and adequate stiffness. However, the collapse mechanisms observed seems to favor the rupture of reinforcement rather than the crisis of adhesion usually observed when dealing with artificial FRC reinforcements. It was necessary to step back to the theories of adhesion to plan the experimental analysis of the jute reinforcement for rammed earth structures. The poor material, the fact that adhesive and support are almost the same material (differing only for grain size, density and a small amount of gypsum), the difficulty in measuring fabric properties, strength and, most of all, local deformation and fracture energy in earthen materials, induced to define a specific procedure. The uncertainties connected to the determination of mechanical parameters were overcome both using statistical approach and numerical analysis of data, and reducing the number of parameters necessary to the analysis, that is turning to simple adhesion models. [ABSTRACT FROM AUTHOR]