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Mechanical properties and debonding strength of Fabric Reinforced Cementitious Matrix (FRCM) systems for masonry strengthening
Full text linkCalibration of end-debonding strength model for FRP-reinforced masonry
Full text linkThe adherence between Fiber Reinforced Polymers (FRP) reinforcements and masonry is investigated in this paper. Debonding is, in fact, one of the dominant failure modes in the reinforcement of masonry structures by means of FRP materials. Relationships are proposed in design recommendations in order to evaluate the debonding load on the basis of the fracture energy concept. Corrective coefficients are also suggested in order to take into account the effect of bond length and width on the bond strength. In this work experimental double lap push-pull shear tests results are first presented and combined with experimental outcomes from the literature in order to create an enlarged database. An analytical model for the load transfer mechanism between the reinforcement and the substrate is then proposed. Besides, a refined fracture energy based model for the bond strength is suggested taking into account the effect of bond length and width. The experimental outcomes are first used to validate the analytical model for the load transfer mechanism. The enlarged database is then analyzed to achieve a refined statistical calibration of the experimental coefficients of the bond strength model and to highlight the variation of the maximum transmitted force with respect to mechanical properties of the substrate
In-situ experimental tests on masonry panels strengthened with Textile Reinforced Mortar composites
No full textTextile Reinforced Mortar (TRM) composites are a retrofitting techniques used for strengthening masonry structures. The system is composed of dry fibers grids embedded in two layers of inorganic matrix. The paper describes the results of an in-situ experimental campaign on ancient masonry panels reinforced with different TRM systems. The tests were performed in a building located in Finale Emilia (north of Italy) built at the beginning of the last century. Four diagonal compressive tests were performed on unreinforced and reinforced walls.
The walls were strengthened with different configurations: two panels were reinforced with a TRM systems composed of a lime mortar and two different types of glass fiber grids and twist steel bars used as anchors; one panel was reinforced with a layer of TRM on one side and a Near Surface Mounted (NSM) system on the other one.
The results of the tests are described and a complete mechanical characterization of the reinforcement systems and of the masonry was performed to analyze the experimental results and validate simple analytical models
Fabric Reinforced Cementitious Matrix (FRCM) Systems for Strengthening of Masonry Elements Subjected to Out-of-Plane Loads
No full textFabric Reinforced Cementitious Matrix (FRCM) composites are a retrofitting technique used for
strengthening concrete and masonry structures. The system is composed of a dry fabric (fibre grid)
embedded in inorganic matrix. FRCM composites are particularly indicated in the reinforcement of
historical masonry buildings due to various aspects: high compatibility with the substrates,
reversibility, vapour permeability and durability to external agents. In this work the mechanical
properties of two FRCM materials are studied. The first one is realised with a PBO fabric, the second
with a fabric composed by PBO and glass rovings. These systems then are applied on medium-scale
panels realised with clay solid bricks or light hollow bricks in order to investigate the relevant out-ofplane
behaviour. The failure modes have displayed a collapse due to cracks development in the
cementitious matrix and slippage of the fibre grid. Earthquake events can produce in many cases
injuries correlated to the collapse of infill walls. In the literature just few researches on this topic are
available and then the results of this experimental campaign can provide background data for future
design recommendations
Mechanical properties and numerical modeling of Fabric Reinforced Cementitious Matrix (FRCM) systems for strengthening of masonry structures
Full text linkThe behavior of single bricks and small masonry pillars strengthened by means of fabric reinforced cementitious matrix systems made with glass-fiber grids is discussed both from an experimental and numerical standpoint.A standard Push-pull double lap test is performed on three different series of experimental set-ups for reinforced single bricks and on masonry pillars, evaluating the role played by the anchorage length on the overall behavior of the strengthened system.Standard Italian bricks with very good mechanical properties are used, in order to evaluate the ultimate strength of the grid for delamination within the mortar. The masonry pillar is built with 3 bricks spaced out by two thick mortar joints. When dealing with the single bricks, three different anchorage lengths were tested, equal to 5, 10 and 15. cm, in order to evaluate the reduction of the ultimate strength induced by an insufficient anchorage.To suitably interpret experimental results, both a newly developed analytical-numerical approach and a recently presented 3D FEM model were utilized to have an insight into experimental results.In the analytical-numerical approach only the glass-fiber grid was considered and modeled by means of 1D Finite Elements interacting with the surrounding mortar by means of interfaces exhibiting a non-linear stress-slip behavior deduced from experimental data.The 3D model uses 8-noded rigid elements interconnected by inelastic interfaces exhibiting softening. The incremental non-linear problem is solved by means of a robust Sequential Quadratic Programming routine already tested on medium and large scale examples with softening materials. The grid is modeled through non-linear truss elements, interacting with surrounding mortar by means of non-linear interfacial tangential stresses. Stress-slip behavior of the interface between the mortar and the textile is deduced through ad hoc experimentation conducted on a mortar specimen reinforced with a single yarn and subjected to a standard tensile test.Good agreement was found between experimental evidences and numerical simulations, meaning that the combined approach proposed may be considered as reference for design considerations
Numerical modelling of Fabric Reinforced Cementitious Matrix composites (FRCM) in tension
Full text linkExisting masonry structures often need to be strengthened or repaired. In many cases, the intervention is realized using composite materials bonded to the surface of the structural element.
In many masonry structures the use of fabric reinforced cementitious matrices (FRCM) is preferred to the fiber reinforced polymers (FRP).
The typical experimental stress-strain behavior exhibited by a FRCM composite under a direct tensile test is a tri-linear curve with a first phase that increases linearly according to mortar Young's modulus, a second phase where the cracks in the mortar start to grow, and a last phase in which the mortar is fully cracked and the curve assumes the same slope of the stiffness of the fabric. According to a wide experimental campaign conducted on the subject at the Politecnico di Milano, the curves exhibit a relatively wide scatter, especially in the second phase, making the standardization of the direct tensile test a rather difficult task.
With the aim of having an insight into the observed experimental variability, a comprehensive FE numerical analysis was conducted and is presented in this paper. Two different FE codes were utilized. One with less sophisticated material models, the second with the possibility to deal with softening and damage in the post peak range. The use of commercial codes instead of home-made models was voluntary, with the precise final aim of enabling other researchers the reproduction of results with similar models and for analogous experiments. Three different variables that can affect the mechanical behavior in tension were examined (non-planarity of the composite grid, bending of the specimen and pre-existing micro-cracks), leading to three different sets of simulations.
A final objective of the numerical simulation was to study and compare possible constitutive models for the cementitious matrix to simulate the experiments. At this aim, three different material models were used for mortar belonging to FRCM specimens in tension.
The numerical results obtained satisfactory reproduce experimental evidences and provide a justification of the relative large scatter of the data
New Italian guidelines for design of externally bonded Fabric-Reinforced Cementitious Matrix (FRCM) systems for repair and strengthening of masonry and concrete structures
No full textThe paper summarizes the main features of a standardization activity carried out in Italy by the Ministry of Public Works, to which two of the authors have taken part, for the homologation and the acceptance of Fabric-Reinforced Cementitious Matrix (FRCM) composites. During the last years, such composite materials have becoming increseangly popular in the civil engineering field for strengthening existing constructions, even if difficulties can occur in their mechanical characterization that is strongly affected by different and complex failure mechanisms. The American ACI 549.4R-13 is currently the only available guideline for design and construction of these systems. In this framework, the paper describes the Italian proposals for the homologation process of FRCM materials as well as for the design of strengthening interventions with these composites. Comparisons with the American guideline are also reported together with some considerations regarding the different partial safety factors
Analisi dell'aderenza di elementi in muratura rinforzati mediante FRP
No full textIl presente lavoro ha la finalità di definire prove standardizzate da effettuare per il controllo di accettazione di sistemi di rinforzo in FRP per elementi in muratura.
Sono state inizialmente svolte prove di strappo tangenziale su elementi in muratura rinforzati mediante rete in GFRP e malta cementizia o a base calce. La rottura è avvenuta per strappo della rete o scorrimento della rete nel letto di malta.
Sono state inoltre eseguite molte prove su elementi rinforzati con resina epossidica e tessuto in carbonio con differenti lunghezze e larghezze di rinforzo. La rottura è avvenuta per distacco e i valori della forza ultima sono stati confrontati con il documento CNR-DT 200/2004.
Tra le prove sperimentali da effettuare per la caratterizzazione in situ dei rinforzi sono state eseguite prove semidistruttive di tipo pull-off e svolte indagini termografiche per l’individuazione dei difetti di adesion
Fabric-Reinforced-Cementitious-Matrix (FRCM) per la riabilitazione strutturale: aderenza al supporto
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