•Results of compression tests on SRP confined concrete members are presented.•Results are analyzed by varying layers number, tape density and concrete strength.•SRP confinement significantly ...increased strength and ultimate strain of concrete.•A value of the SRP strain efficiency factor is calculated.•Predictive strength and strain models of the SRP confined concrete are developed.
Steel 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.
Several 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 40MPa were considered.
In the field of external strengthening and repairing of existing reinforced concrete structures, steel reinforced polymers (SRP) systems have emerged as a competitive alternative to the use of the ...more common carbon and glass fiber reinforced polymer (FRP) composites. Experimental investigations have frequently shown the potentials of these innovative composite systems in improving the performance of deficient structural members. At the same time, additional studies are needed to expand the existing knowledge and either to provide design recommendations or to develop specific guidelines. The paper fills some of the foregoing knowledge gaps by presenting an analytical investigation on the bond behaviour between SRP and concrete in which closed-form solutions are derived to predict the entire debonding propagation process. In particular, accurate and simplified local shear stress-slip (τ-s) laws are employed in the proposed modelling from which different expressions for the interfacial shear stress distribution, the axial stress profile and the concrete-SRP relative displacement (slip) are developed and commented in the paper; analytical estimates of the SRP effective bonded length are provided as well as relationships for calculating the maximum axial stress (or peak force) at SRP laminate debonding.
The analytical procedure was, firstly, applied to simulate some single-lap shear tests performed in a previous experimental program with the purpose to investigate the influence on the debonding propagation process of the following main parameters: a) concrete strength, b) concrete surface finish and c) steel tape density. Then, the comparisons between the numerical simulations and the experimental results available for some bond tests have allowed for verifying the accuracy of the proposed modelling.
Fabric-reinforced cementitious matrix (FRCM) composites have emerged as a viable solution for the external confinement of masonry members. However, what still discourages the use of these composites ...in the civil engineering field is the lack of analytical models capable of estimating the compressive strength of FRCM confined members with appreciable accuracy.
This paper contributes to filling this knowledge gap by presenting an analytical study on the compressive strength of masonry confined by FRCM systems. The goal is twofold: a) to assess existing formulae published in the literature or in some international guidelines, and b) to provide new and more accurate proposals. To this purpose, a large database including results of compression tests on masonry members wrapped with FRCM systems was compiled from the literature. The database was organized by considering some relevant parameters, such as: type of fiber and geometry of the mesh, number of employed layers, mechanical properties of the inorganic matrix, compressive strength of the masonry. The accuracy of the strength models is examined by both considering all FRCM confined members together and treating natural and artificial masonry separately.
•SRG strips were bonded to concrete blocks by an inorganic matrix.•Shear tests were performed in displacement control.•Two different mortar curing conditions were investigated.•Two different average ...concrete cylindrical strength were considered: 13 and 40 MPa.•SRG systems mainly exhibited a debonding failure at steel fibers-matrix interface.
Composite materials consisting of high tensile strength steel cords embedded in a cementitious matrix (Steel Reinforced Grout, SRG) are becoming an attractive solution for strengthening existing structures thanks to the lower cost than “traditional” FRP systems, the isotropy of the steel and the ability of the mortar to resist fire. With respect to Steel Reinforced polymer (SRP) systems – whose mechanical behavior is predominantly dependent on the strength of the substrate to which the steel fibers are epoxy bonded – the mechanical properties of SRG systems are mainly dependent on the cement-based matrix which is sensitive to curing the installation conditions and methods.
The experimental results presented and discussed in this paper contribute to expanding the existing knowledge on the bond behavior between the SRG and concrete substrate. To this purpose, a number of SRG strips were bonded to concrete blocks by an inorganic matrix and the lap joint was subsequently subjected to direct shear tests performed in displacement control.
Since mortars are very sensitive to environmental conditions and humidity as previously mentioned, two different curing conditions were used. In the first case – termed “curing a” – specimens were cured at room temperature for 28 days and wet cloths were placed on top of the composite surface each day for two weeks. In the second case – termed “curing b” – specimens were just cured at room temperature for 28 days.
In addition to the curing condition, the following study parameters were considered: (a) the concrete surface roughness in the bonded region, (b) the density of the dry steel fabric, (c) the bonded interface length, and (d) the concrete strength. Relatively to the latter parameter, concrete prisms were broadly divided into two strength groups: Normal Strength Concrete (NSC) having an average concrete cylindrical strength between 13 and 25 MPa and High Strength Concrete (HSC) having an average strength equal to 40 MPa.
Experimental evidence underlines that SRG systems mainly exhibited a debonding failure at steel fibers-matrix interface (due to the sliding phenomena) irrespective of the concrete strength and surface finish. Furthermore, like the SRP systems, the low tape density showed better performances with respect to the higher densities considered in this paper, both in terms of the efficiency factor (i.e., the ratio between the tensile stress experienced by SRG in each test and the average tensile ultimate strength of dry steel fabric) and of the maximum force transferred by the system.
► Experimental tests on full scale RC 300×700mm rectangular columns are presented. ► Performances of different strengthening techniques with FRP materials are discussed. ► It is shown that the FRP ...confinement significantly increases the columns ductility. ► The combined use of FRP confinement and steel angles also improves the flexural strength. ► The FRP confinement increases the cumulative dissipated energy of columns.
A limited number of experimental studies have been performed on FRP-confined columns having rectangular cross section with high aspect ratio.
The experimental study presented herein addresses this knowledge gap by investigating performances, under constant axial load and cyclically reversed horizontal force, of full scale rectangular (300×700mm) RC columns externally confined by using Fiber Reinforced Polymers (FRPs) or strengthened with FRP wraps and steel profiles. The study is a part of a wider experimental campaign also including tests on square (300×300mm) columns whose details have been already published elsewhere.
Test results discussed herein aim to evaluate the influence on the column performance of relevant parameters, such as: unconfined concrete strength, longitudinal steel reinforcement (smooth or deformed rebars), strengthening system (FRP confinement with or without steel profiles); axial load level and number of FRP layers. Finally, the effectiveness of the used strengthening techniques is investigated through the comparison with the performances obtained in the case of square members.
Steel Reinforced Polymer (SRP) systems have recently emerged as attractive solutions for external strengthening and repairing of existing structures. Experimental studies have frequently shown the ...potentials of these innovative composite systems in improving the performance of concrete and masonry structures. However, additional studies are needed to expand the existing knowledge and either to provide design recommendations or to develop specific guidelines. The paper fills some of the foregoing knowledge gaps by discussing the experimental results of 130 direct single-lap shear tests performed to investigate the bond behavior between the SRP reinforcement and the concrete substrate; different concrete surface finishes were investigated, i.e., sandblasted, bush hammered and grinded which are among the surface treatments mostly used in practice. Comparisons between the maximum load resisted by the SRP-concrete joints and the theoretical value calculated using some relationships available for similar FRP-concrete assemblages are discussed.
Then, the experimental results relative to SRP-concrete joints with sandblasted finish were used to: a) calibrate the parameters of some bond-slip interface models available in the literature for FRP-concrete interface, and b) compare the obtained relationships with the interface models proposed in a previous study for SRP-concrete joints with bush-hammered and grinded concrete surface finish only. The bond-slip models calibrated for the three considered concrete surfaces were finally used to develop theoretical relationships between the maximum bond stress in the steel strip at debonding and the concrete strength. Comparisons with the experimental data were also performed.
This paper presents a large database including results from compression tests performed on over 450 concrete cylinders externally wrapped with Fiber Reinforced Polymer materials. The collected ...results were first employed to perform a statistical evaluation of the FRP strain efficiency factor; in particular, the influence of the type of fiber and the strength of the unconfined concrete were considered. New relationships for estimating the compression strength of the FRP confined concrete were then developed through best-fit analyses. Finally, a procedure available in the literature was applied by the Authors for the statistical determination of the FRP confined concrete strength to use for design purposes.
Steel Reinforced Polymer (SRP) is an innovative system for the external strengthening of structures, which comprises unidirectional textiles of High Tensile Strength Steel applied with polymeric ...resin. The first applications of SRP in civil engineering date back to 2004, and, since then, a number of studies have been carried out on both mechanical characterization and structural applications. Nevertheless, the existing knowledge has mostly remained a fragmented skillset of the scientific community and specific guidelines for qualification and design have not been developed yet. This paper reviews the experimental works on SRP to establish its advantages and drawbacks and promote a proper knowledge transfer from academia to engineering design practice. With respect to the already well-established Fibre Reinforced Polymers (FRPs) with carbon or glass textiles, SRP exhibits comparable, or even better, tensile and bond behaviour, and, when applied for bending reinforcement or for confinement, provides equivalent or higher improvement of structural performance in terms of load bearing and displacement capacity. Even if long-term durability, shear strengthening of reinforced concrete beams and applications to masonry would still deserve more investigations, the research performed so far has already demonstrated that SRP is an effective and cost efficient solution for the rehabilitation of structures and that it can be reliably designed with the same relationships developed for FRPs.
