1,721,010 research outputs found
Advanced and Simplified Modeling Approaches for the Study of the Bond Behavior of FRP Systems on Curved Masonry Substrates
No full textCurved masonry structures externally strengthened by Fiber Reinforced Polymer (FRP) systems exhibits failure mechanisms which emphasize a local bond behavior particularly influenced by the curved geometry of the substrate and the position of the strengthening (i.e. at the intrados or extrados). Indeed, together with tangential stresses, normal stresses in tension or compression also arise by leading to a combined mode I–mode II behavior of strengthening system at the reinforcement/masonry interface level. In recent studies the Authors proposed different modeling approaches for FRPs applied to curved masonry structures. In particular, both micro-modeling detailed approaches and simplified approaches were generally proposed. The present paper critically analyzes these models by underlining the main differences among them, the assumptions and their ability to reproduce specific phenomena experimentally observed
Innovative Fiber Optic Sensor monitoring of delamination phenomenon for FRCM reinforced curved masonry pillars
No full textInorganic-based strengthening materials are deemed to be a viable alternative for strengthening of existing structures. Unlike FRP composites, TRM or FRCM strengthening solutions are based on inorganic matrices to ensure correct stress transfer between the support, strengthening and reinforcement fabric. Therefore, the bond between these three components plays a crucial role and is influenced by multiple aspects including the mechanical properties of the matrix. The improvement in the quality of the adhesion directly shifts the failure mode of such composites to textile tensile failures, which implicitly guarantees a better exploitation of the mechanical properties of the composite. Several experimental investigations have focused on the study of the bond quality by implicitly considering the global response of coupons or isolated elements strengthened with TRM/FRCM composites. As far as the authors are aware, despite the amount of experimental and numerical investigations produced in recent decades on these composites, several open questions still require further investigations possibly helped by the adoption of the latest technologies. An important advance in this sense is represented by the development of Fiber Optic (FO) sensors that can be easily incorporated into inorganic-based matrices or glued onto different surfaces. The adoption of FO strain sensors is particularly suitable for studying the quality of adhesion in highly heterogeneous materials where the transfer of stresses between the components is influenced by many aspects and a clear understanding using traditional sensors is not possible. This article discusses the experimental results obtained from a pilot experimental campaign comprising masonry pillars tested in single-lap shear tests having flat and curved geometries strengthened with TRM/FRCM composites on which FO distributed strain sensors have been installed on the central textile bundle. The results shed light on the mechanism of stress transfer along the effective bond length and provided valuable data for the calibration of interfacial stress-the slip laws
Curved masonry supports strengthened with TRM materials: Advanced Fe modelling
No full textThe article compares two numerical approaches with different levels of details used to simulate curved masonry supports subjected to single lap shear tests. The masonry pillars were strengthened on the extrados and on the intrados with TRM materials comprising a 100 mm wide PBO textile embedded into 10 mm thick mortar layer. The numerical analyses were carried out using two approaches: a heterogeneous micro modelling FE approach and a spring model approach. The first modelling strategy was developed using the commercial software Abaqus and it involved the separate modelling of the constituent materials (i.e., bricks and mortar joints) as well as the simulation of the PBO textile and mortar matrix. The second approach was specifically developed to analyze curved supports and it comprised the adoption of equivalent normal and shear springs used to model the components of specimens (support, matrix and reinforcement) and, moreover, the interface between reinforcement and matrix. It is worth mentioning that this numerical investigation is part of an ongoing experimental and numerical work focused on analyzing the effect of curved brittle supports on the adherence properties of innovative strengthening materials (i.e., FRPs) and herein extended to the adoption of TRM composites. In absence of a comprehensive experimental characterization of the TRM constituent materials, the mechanical properties of the textile and mortar matrix were deduced from available data provided by the manufacturer. The numerical results are herein presented and critically compared in terms of global force-displacement curves and damage maps obtained at the end of the simulations
FRCM-to-masonry bonding behaviour in the case of curved surfaces: Experimental investigation
Full text linkFabric-reinforced cementitious matrix (FRCM) are composite materials more and more used for the reinforcement of masonry structures. The combination of high tensile strength fabrics (or meshes) with cementitious matrices, having good thixotropic capabilities and vapour permeability, makes such composites suitable for reinforcing a large number of masonry structures, including the one belonging to the historic heritage. FRCMs are bonded to the outer surfaces of structural masonry elements and, thanks to their adhesive capacity, bear much of the tensile stresses that unreinforced masonry cannot withstand. The effectiveness of such reinforcements, which is highly dependent on their ability to adhere to the masonry substrate, is generally investigated throughout specific experimental investigations (shear tests). Almost all the papers in the literature devoted to bond-slip analysis refer to the case of flat bonding surfaces, although these reinforcements are also widely used on curved structural elements such as arches and vaults. Therefore, this paper reports and examines the results of an extensive experimental program concerning the behavior of FRCM systems applied on curved masonry specimens. The results point out the influence of both curvature and reinforcement position (intrados or extrados) on the response of specimens in terms of bearing capacity, failure mode and post-peak response
Experimental characterization of the textile-to-mortar bond through distributed optical sensors
Full text linkTRM (Textile Reinforced Mortar) and FRCM (Fiber Reinforced Cementitious Mortar) strengthening materials are highly heterogeneous composites involving domains that have dramatically different mechanical properties (i.e., inorganic matrix and fabric textile). Maximizing their exploitation ratio involves achieving a better bond between textile and inorganic matrix which shifts the failure mode from textile sliding to textile rupture or cohesive failure modes. So far, the local bond behaviour between fiber bundles and inorganic matrix has been analysed indirectly through the evaluation of the global performance of TRM/FRCM materials subjected to tensile tests or single lap shear tests. In this article, the authors adopted distributed fiber optic sensors directly installed to textile bundles to track the strain evolutions of PBO-TRM strengthening materials. The strain evolutions were used, for the first time, (i) to understand the behaviour of TRM coupons subjected to tensile tests and (ii) to experimentally calibrate the interfacial tangential bond-slip law in flat masonry pillars strengthened with TRMs. The results allowed a better insight of the response of TRM materials not possible with traditional sensors and an accurate characterization of their bond performance. The interfacial tangential stress-slip law was then adopted in analytical models to predict the global performance of TRM materials providing satisfactory results compared with experimental outcomes
Some considerations about the effects of the bonding length on the effectiveness of spike anchors in cfrp reinforcements of masonry
No full textThe main results of an experimental program concerning masonry pillars reinforced by CFRP strips (also provided by spike anchors) subjected to single lap shear tests are described in this paper. The experimental results, also compared with a previous experimental program, allowed to analyze the increment of bearing capacity produced by spike anchors to CFRP sheets having different bonding length
Mechanical model based on a BVP for FRPs applied on flat and curved masonry pillars with anchor spikes
Full text linkThe use of fiber reinforced polymer (FRP) materials for strengthening interventions of existing constructions is a consolidated and widespread technique. In this context, although strengthening interventions generally involve curved masonry elements (arches, vaults, domes, etc.), only a few studies specifically concern the influence of the geometry curvature, or the effect of mechanical anchors (widely used in current practice for preventing premature failures), on the bond behavior of FRPs. The present paper proposes an interface exponential model for simulating the bond behavior of curved masonry pillars reinforced with FRP strips applied at the intrados or extrados by both epoxy adhesive and anchor spikes. The proposed model is based on a relatively simple boundary value problem (BVP) obtained by assuming for the spike a constitutive behavior under shear forces quantitatively deduced by post-processing the numerical data from a finite element micro-modeling approach previously proposed by the authors. The application of the proposed model to experimental cases carried out by the authors underlines the stability of solution and the reliability of the proposed approach to account for the effect of both the curvature of the substrate and the presence of the spike anchor on the bond behavior of FRPs
An experimental study on the effectiveness of cfrp reinforcements applied to curved masonry pillars
No full textThe paper synthetizes the main results of an experimental program devoted to the analysis of the structural behavior of both flat and curved masonry pillars reinforced with anchored and not anchored Carbon Fiber Reinforced Polymer (CFRP) sheets. A single lap shear test scheme has been selected: the specimens were constrained at the upper and lower faces and were loaded by a force tangent to an end of the reinforcement. The experimental outcomes allowed to analyze the effects of the position (intrados/extrados), of the curvature and of the anchor on the performance of the reinforcement
The Bond Behaviour of FRP and FRCM Strengthening Sheets Externally Bonded to Masonry Pillars: An Experimental Based Comparison
No full textFibre reinforced composite materials have been increasingly used in recent decades as reinforcement systems for masonry structures. Initially, externally bonded fibre reinforced polymer (FRP) sheets were mainly used in in structural applications. Subsequently, the use of composite materials with inorganic matrix (mainly, fiber reinforced cementitious matrix – FRCM) became widespread. Both systems present advantages and disadvantages that make them suitable in particular conditions and for specific practical applications. In any case, the structural effectiveness of such externally bonded reinforcements strongly depends on the composite-to-substrate adhesive capacity. The experimental behaviour of two different reinforcing systems (the first with organic matrix and the second having inorganic matrix) externally bonded to masonry pillars is compared in this paper
Numerical analysis of the bond behavior of frp applied to masonry curved substrates with anchor spikes
No full textThe paper presents two different modeling strategies for the study of the debonding of anchored Fiber Reinforced Polymers (FRP) externally applied to curved masonry substrates. The first one is based on a fast and computationally effective simple 1D-schematization of specimens based on the use of linear and nonlinear spring elements schematizing the support, the FRP strengthening and the masonry/FRP interface. The second one consists of a tri-dimensional micro-modelling FE approach comprising a damaging behavior of the constituent materials and elastic zero-thickness cohesive masonry-to-FRP interfaces. Both the approaches are presented in detail in the paper and they are validated by considering experimental tests performed by the authors
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