1,721,088 research outputs found
RC Columns Strengthened with FRP systems: Experimental Test Results and Analytical Modeling
No full textCONFINEMENT OF MASONRY WITH FRCM COMPOSITES: STRENGTH PREDICTIVE MODELS
Full text linkFabric reinforced cementitious matrix (FRCM) composites have emerged as an appealing alternative to fiber reinforced polymer (FRP) for the external confinement of masonry members; nevertheless, their use in practice is limited due to the lack of reliable formulas to estimate the compressive strength and ultimate strain of confined members. By following a recently published study, new formulas for the prediction of the compressive strength of the FRCM confined masonry are proposed here, which were obtained by considering an updated experimental database compiled from the literature. These formulas were developed by applying error minimization techniques to the collected experimental results; test data were treated in different ways, such as: (a) separating the members made of natural stones from those built with artificial blocks, and (b) treating separately the fiber types (basalt, carbon, glass, PBO and steel) of the FRCM system, or (c) considering the experimental data all together. Finally, to evaluate the reliability of the developed relationships, the strength predictions provided by the new proposals were compared with those obtained using the expressions reported in some international guidelines
Compressive Behavior of Masonry Columns Confined with FRCM Systems: Research Overview and Analytical Proposals
No full textFabric–reinforced cementitious matrix (FRCM) composites have emerged as a viable solution for the external confinement of deficient masonry members. They represent an appealing alternative to fiber–reinforced polymer (FRP) systems since the use of epoxy matrixes raises some unsolved issues, such as the poor composite–substrate compatibility, low permeability of the strengthened surface, and the difficulties in removing the FRP sheets without damaging the substrate. To investigate the efficacy of FRCM confinement, a number of experimental investigations have been published in the literature, and a wide overview will be reported in this paper. However, to date there is a lack of relevant analytical studies that propose sound models to estimate the compressive strength of FRCM confined masonry; difficulties are related to the high complexity and heterogeneity of the masonry and to the uncertainties that are derived from FRCM confinement, whose performance is affected by many variables, which include the quality of the inorganic matrix and geometry of the fabric mesh. Most of the collected studies focus on investigating the applicability of the existing formulations that are suitable for FRP systems to examples of FRCMs, a few others provide promising proposals although they were validated using a limited amount of experimental data.
This paper will present an analytical study on the confinement of masonry columns with FRCM composites with two aims: (a) propose new models to estimate the compressive strength; and (b) assess the existing formulas.
A wide database that includes the results of compression tests on 211 masonry members that are externally wrapped with FRCM systems will be assembled from the literature.
The collected data will be organized into a systematic framework and will be analyzed based on some relevant parameters, such as the type of fiber [e.g., basalt (B), carbon (C), glass (G), steel (S), and poliparafenilenbenzobisoxazole (PBO)], the geometry of the mesh, number of layers employed, mechanical properties of the inorganic matrix, and compressive strength of the unconfined masonry (fmc).
Strength models for FRCM confined masonry will be developed by best-fit analyses, and comparisons with formulations that are available in the literature and some international guidelines will be performed
COMPORTAMENTO DEL CALCESTRUZZO CONFINATO CON TESSUTI IN FIBRA DI ACCIAIO: RISULTATI SPERIMENTALI
No full textCompressive behavior of concrete confined by SRP wraps
No full textSteel Reinforced Polymer (SRP) materials have recently emerged as a viable and cost-effective solution for the external confinement of concrete members. So far, a few studies have been performed to investigate the compressive behavior of concrete confined by SRP wraps, as well as specific guidelines have not been published yet. In this paper, the experimental results of a large number of compression tests performed on SRP confined concrete cylinders are presented and discussed. Test results have allowed for examining the SRP effectiveness in increasing the strength and ultimate strain of concrete by mainly varying the confining stiffness of the steel jacket and the unconfined concrete strength.Preliminary predictive models for the strength and ultimate strain of concrete confined by SRP were also developed and compared with some formulations suitable for glass or carbon FRP composites, today mostly used for the external confinement of concrete members
Compressive strength of concrete confined with fabric reinforced cementitious matrix (FRCM): Analytical models
No full textComposite materials employing cement-based mortars, usually known as fabric-reinforced cementitious matrix (FRCM) composites, have recently emerged as an attractive solution for the repairing and strengthening of re- inforced concrete or masonry members. They represent a promising alternative to the use of Fiber Reinforced Polymer (FRP) composites when there is a need to overcome some of the drawbacks related to the epoxy resin, such as moderate matrix heat and fire resistance, difficulty of application at low temperatures, impossibility of application on wet surfaces, and lack of vapor permeability. This paper presents an analytical study on the con- finement of concrete columns with FRCM composites with the twofold objective to: (a) propose new models for the estimate of the compressive strength, and (b) assess existing models available in the literature and in some international guidelines. To this purpose, a wide database including results of compression tests performed on over 290 concrete cylinders externally wrapped with FRCM was assembled from the literature. The collected results were employed to perform an overall analysis of the efficiency of the FRCM confinement by varying some of the relevant parameters, such as: type of fiber (glass, carbon, steel, PBO or basalt) and geometry of the mesh, number of employed layers, mechanical properties of the inorganic matrix and compressive strength of the unconfined concrete. Relationships for estimating the compression strength of the FRCM confined concrete were then developed through best-fit analyses, and comparisons with some formulations available in the literature and in some international guidelines were performed
Reinforced concrete beams strengthened with SRP/SRG systems: Experimental investigation
Full text linkSteel reinforced polymer (SRP) and steel reinforced grout (SRG) have emerged as promising and cost-effective technologies for the external strengthening of RC structures.
Although the first studies date back to 2004, so far the literature related to the flexural strengthening of RC slabs/beams with steel tapes is rather limited. As a result, the application of such materials on a real structural member may be discouraged and, conversely, the use of carbon/glass FRP alternative systems may be preferred.
The study presented in this paper contributes to filling this knowledge gap by presenting the results of 10 four-point bending tests performed on RC slabs strengthened with SRG/SRP systems. Test results have provided valuable information in terms of maximum forces, deformability and failure modes by varying number of layers and density of the steel tape. In particular, it has been shown that, disregarding the nature of the matrix (inorganic or polymeric), the presence of the external strengthening significantly increased the flexural strength of slabs, with percentage increases over the control (unstrengthened) member ranging from a minimum value of 27%, when using a single layer of low density tape, to a maximum of 106% in the case of SRP system with one layer of high density sheet.
Preliminary analytical studies were also performed in order to investigate the possibility of extending to the SRP/SRG systems the applicability of formulations currently reported in some national and international guidelines for the flexural strengthening of RC members with FRP sheets
Predictive Models for the Compressive Strength and Ultimate Strain of FRCM Confined Masonry
No full textSo far, the use of fabric reinforced cementitious matrix (FRCM) composites for the external confinement of masonry is still limited due to the lack of accurate formulas for estimating the compressive strength and the ultimate strain of confined members. With the aim to contribute to partially filling this knowledge gap, the authors have been carrying out studies on the FRCM confined masonry for some time and, in a recent study, they proposed some formulations for the prediction of the compressive strength which are also reported in this paper. In continuity to that work, analytical formulas for the prediction of the ultimate strain are proposed here, which were derived by considering a wide experimental database compiled from the technical literature. This database includes results of compression tests on FRCM confined masonry columns with square, rectangular and circular cross-sections; most of the collected members consist of artificial blocks and only a limited number of specimens is made of natural stones (tuff units or limestone). The mentioned formulas were developed by applying error minimization techniques to the collected experimental results which were either treated all together or treated separately based on the FRCM systems. The suitability of the found relationships was examined based on a comparison in terms of reliability with the few formulas published in
the literature or reported in international guidelines. To this purpose, it is worth highlighting that the current Italian Guidelines CNR-DT 215/2018 do not provide indications about the estimate of the ultimate strain of the FRCM confined masonry, and the study proposed here represents a first attempt to provide a contribute to the document
Confining concrete members with FRP systems: Predictive vs design strain models
No full textSeveral analytical models are available in the literature to predict the compressive strength and the ultimate strain of the FRP confined concrete. The reliability of such models is often affected by an inaccurate definition of the “effective” confining pressure exerted by the FRP jacket and/or by an incorrect evaluation of the reduced confinement effectiveness in the case of square and rectangular cross sections. In this paper, following a previous study on the compression strength, an investigation on the ultimate strain of the FRP confined concrete is presented. To this aim, a large database including results from compression tests performed on over 450 FRP confined concrete cylinders was considered, and some of the most accredited predictive strain models were recalibrated through best-fit analyses of the experimental data. Finally, a probabilistic procedure was applied in order to define design models; for this purpose only data sets for which the unconfined concrete strength was below 40 MPa were considered
Cyclic behavior of RC columns strengthened by FRP and steel devices
No full textThis paper presents several results of a wide experimental program undertaken to evaluate the seismic performance of RC columns, externally confined with fiber-reinforced polymers (FRPs). Specimens consisted of full scale square columns, 300 mm on each side, reinforced by using both smooth and deformed steel rebars and subjected to a constant axial load and monotonic or cyclic flexure; in particular, two levels of the axial load were considered. Tests were conducted, in displacement control, on both FRP confined and unconfined RC columns: the confinement system was obtained by partially wrapping two or four unidirectional carbon (CFRP) or glass (GFRP) fiber layers around the member; additionally, some tests were performed on members strengthened by using both the external CFRP wrapping and longitudinal steel angles. Experimental results allowed evaluating depending on the level of applied axial load and on the type of steel rebars adopted for reinforcing each column-the benefits introduced by the considered strengthening systems in terms of strength, ductility, and energy dissipation capacity
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