Journal of Composites for Construction

This paper presents an experimental study that investigates the behavior of reinforced masonry (RM) columns strengthened using carbon fiber-reinforced polymer (CFRP) wraps under eccentric axial loading. Nine half-scale square RM columns with reinforced concrete (RC) end blocks were tested under three different eccentricity-to-section height ($e/h$) ratios (0.15, 0.25, and 0.50). For each load eccentricity, the columns were tested unwrapped, wrapped with one layer of CFRP, and wrapped with two layers. The effect of partially grouted masonry cells on column capacity was also evaluated. Existing analytical procedures for RC column sections were applied to the fully grouted RM columns. The experimental tests showed that CFRP wrapping increased the column’s axial capacity by up to 41% at a nominal $e/h$ ratio of 0.25, while an enhancement of 45% was achieved at a nominal $e/h$ ratio of 0.50. The analytical procedures were able to predict the failure mode and axial capacity of the tested columns. The columns’ axial capacities were estimated with a maximum error of 11%, which indicates the validity of the analytical procedures for eccentrically loaded RM columns.

This study investigated carbon fiber–reinforced polymer (CFRP) spike anchor parameters that govern their effectiveness in developing the full strength of CFRP strips, including any size effects that may exist in anchored CFRP systems. Twelve tests were conducted on concrete beams reinforced in flexure with anchored CFRP strips up to 25.4 cm (10 in.) wide. The primary parameters investigated were width of CFRP strip, number of layers of fabric in CFRP strip, number of anchors per strip width, ratio of anchor to strip cross section, anchor fan overlap length, and chamfer radius of the anchor hole. The full distribution of strains at the surface of the anchored CFRP strips was monitored using an optical measurement system. These measurements helped evaluate the effectiveness of various anchor details in distributing strains across strips. The experimental program confirmed size effects in anchored CFRP systems. The larger the CFRP strip area developed per anchor, the lower was the stress at fracture of that strip. In addition, the anchor-hole chamfer radius was found to influence both anchor strength and the strain distribution in CFRP strips.

Shear walls, diaphragms, and shear web structures are generally subjected to in-plane shear loading. Only a small number of test data regarding the in-plane shear behavior of glass fiber–reinforced polymer (GFRP) sandwich structures are currently available. Using ASTM’s picture frame shear test, this work reports a systematic experimental approach coupled with both two-dimensional (2D) and three-dimensional (3D) digital image correlation (DIC) methods to characterize the failure modes of sandwich structures. Constituent materials such as plain foams, GFRP laminates, and GFRP-foam sandwich panels featuring different polyvinyl chloride (PVC) foam core densities and face sheet thicknesses were tested. The principal strain ratio measurement presented in this work was able to outline the interaction of failure modes. A simplified analytical model to assess the core in-plane shear load contribution was developed and validated. The core contribution was clear and should be taken into account for high-density foam materials and web-reinforced core designs. This research produced new in-plane shear data and a simplified design equation that will assist engineers in confidently sizing, designing, and predicting the in-plane shear capacity of sandwich structural members.

This paper presents an investigation, both experimental and analytical, on RC beams that are strengthened in flexure using externally bonded steel-reinforced grout (SRG) composites. An experimental investigation was conducted on four reinforced concrete beams: one unstrengthened and three strengthened with SRG. The study parameter was the presence or absence of mechanical anchors. Test results emphasize the efficiency of the SRG system in terms of strength and ductility and evidence that the use of the anchors is useful only in reducing the strains of the strengthening system. A numerical model founded on a finite-element procedure, developed through Abaqus CAE version 6.14, is proposed. The SRG-to-concrete interface was reproduced by a cohesive model and a bilinear local bond-slip law was adopted. The implemented numerical model was verified by a comparison between its predictions and test results in terms of ultimate loads and load-deflection diagrams. Finally, through a parametric analysis, run by the numerical model, the influence of the main parameters on the structural performances of an SRG-strengthened RC beam was investigated and a predictive relationship for the fiber strain at debonding is proposed.

The use of mechanical anchorage systems can delay or prevent premature failure of RC structures with externally bonded fiber-reinforced polymer (EB-FRP) laminates. This work reports the results of an experimental program aimed at studying the bond behavior of a metallic anchorage plate, typically used for prestressed EB-FRP systems. The overall experimental program comprised 17 concrete prisms with carbon fiber–reinforced polymer (CFRP) laminates externally bonded to the concrete with mechanical anchorage at the end and to which different levels of normal stress were applied. Direct shear tests were carried out using two configurations: (1) steady-state tests, in which the laminate was pulled out from the block with increasing force and at constant temperature (20°C, 60°C, and 80°C); and (2) transient tests, in which the laminate was pulled out with constant force (0.36%, 0.45% and 0.54% of strain) and the temperature was gradually increased. Experimental results showed that the ultimate capacity of the mechanical anchorage can decrease by 44%–59% depending on the temperature and level of normal stress.

In this study, a new type of composite comprised of steel cords embedded in a mortar matrix—referred to as steel-reinforced grout (SRG)—is explored for use in the confinement of masonry columns. This paper presents the results of an experimental study carried out to understand the behavior of solid clay brick masonry columns confined by single-layer SRG jackets. Thirty-one confined and three unconfined columns with a square cross-section were tested to failure under a monotonic concentric compressive load. Test parameters considered were the SRG matrix type, column corner condition, and steel cord sheet density (i.e., steel cord spacing) in the SRG jacket. SRG confinement improved the compressive strength, ultimate strain, and energy absorption of masonry columns relative to the unconfined condition. Models from the literature for FRP-confined masonry were examined for their applicability to predict the strength increase from the SRG jacket, with certain models predicting the confined compressive strength within 9% of the test values.

Unreinforced masonry (URM) buildings, largely found in Euroasian regions, are particularly vulnerable to in-plane shear failures during seismic events due to the poor shear capacity of masonry walls. In the case of historical masonry buildings, the use of strengthening solutions with polymeric and polymer-modified matrices composites is not recommended since the breathability of the masonry could be reduced, leading to a fast and undesired degradation. In this paper, an innovative fiber-reinforced cementitious mortar (i.e., FRCM) system was used to improve the shear capacity of old-type solid clay brick masonry walls. An experimental program on 24 masonry panels subjected to diagonal compression tests was carried out. The innovative FRCM system consisted of a basalt grid embedded in an improved inorganic matrix, made of lime-based mortar reinforced with short glass fibers (i.e., Fiber-reinforced mortar, FRM). Two sets of specimens were tested, single-leaf masonry panels and double-leaf masonry panels, to investigate the typical configurations of load-bearing walls and partition walls. The effectiveness of the innovative FRCM system was investigated for both a conventional symmetric strengthening configuration and an asymmetric strengthening configuration with anchors, a solution often adopted in the case of internal/external interventions only. Furthermore, the response of masonry panels strengthened with only symmetric FRM with a slightly greater amount of short glass fibers embedded in the matrix was also investigated. The experimental outcomes outlined that panels reinforced with symmetric FRM achieved similar effectiveness in the shear strength increase to panels reinforced with symmetrical FRCM. Conversely, a reduced deformability was observed in FRM panels with respect to those strengthened with FRCM. The experimental results also allowed the quantification of the effectiveness of FRCMs in the case of asymmetric strengthening configurations. Finally, a comparison between experimental results and American Code provisions for FRCM-strengthened systems was reported.

This paper presents the experimental and numerical results of an ongoing investigation aimed at developing high-strength, high-deformability fiber-reinforced polymer (FRP) confined rubberized concrete (CRuC) suitable for structural applications. The rubberized concrete (RuC) utilizes recycled rubber particles as a replacement for both fine and coarse aggregates. Rubber aggregates reduce the compressive strength and stiffness of RuC, thus limiting its application for structural purposes. Confining RuC with FRP jackets recovers strength and enables the development of high deformability, ductility, and energy dissipation capacity. Recent research mainly focuses on the axial performance of RuC and CRuC, but little work exists on the shear behavior of this flexible concretes. This paper adopts a nonlinear numerical approach for the practical implementation of the smeared, fixed-angle crack approach in finite element analysis to predict the shear response of RuC and CRuC. Constitutive models are proposed on the basis of fundamental test results. The model is validated through a simulation of a series of shear tests on RuC and CRuC with different shear span-to-depth ratios ($a/d$). The model predictions are then compared against the experimental results, and good agreement is found.

This paper presents experimental and numerical investigations of the bending performance of innovative splice connections developed for tubular section FRP members. Each of the splice connections consists of a steel bolted flange joint between two tubular steel-FRP bonded sleeve joints. Three connection specimens with different bolt configurations or bond lengths are prepared and tested under four-point bending. Finite element (FE) models are developed featuring a mixed-mode bilinear traction-separation relation for the adhesive bond, the Tsai-Wu failure criterion for the FRP, and yielding of the steel components. The contact behavior and bolt pretensioning are also modeled in detail. All of the connection specimens exhibit excellent ductility through yielding of the steel flange-plate before ultimate failure. The FE modeling, validated by the experimental failure mode, moment-rotation behavior, and strain response, provides insight into the adhesive stress distribution and the yielding mechanism of the steel flange-plates. According to Eurocode 3 for steel structures, the connection specimens are all classified as semirigid and partial-strength connections. The results also show that under flexural loading, the splice connections, which have ductility indices between 5.7 and 8.4, are able to impart ductility to a structure made of brittle FRP members.

The transverse static performance and low-velocity impact response of individual carbon fiber–reinforced polymer (CFRP) wires were investigated experimentally in this study. First, the axial tensile properties of CFRP wires with a nominal diameter of 4.17 mm were obtained through axial tensile tests. Then transverse static tests and low-velocity impact tests were conducted on 15 and 12 preloaded wire specimens, respectively, using a custom-designed device and a drop-weight impact test system. The results show that the maximum wire tension, maximum contact force, and transverse deflection at fracture of the specimens in the impact tests were 89%, 72%, and 82%, respectively, of those in the transverse static tests. In a pretension ratio range of 0 to 0.34, the average transverse static load resistance and average impact resistance of the wire were approximately 4.65 and 3.38 kN, respectively, and were slightly affected by the pretension ratio. Because of the shear effect and contact damage, a wire subjected to a transverse static load and impact load absorbed a total energy of 17.8 and 12.4 J, respectively, which is lower than the absorbed energy under an axial tensile load. Based on the experimental results, the dynamic reduction factor for CFRP wires under impact was determined to be 0.85. Combined with an analytical model, the prediction formulas for transverse static load resistance and corresponding impact resistance of CFRP wires were proposed. Compared with an individual CFRP wire, the axial tensile properties and transverse impact resistance of a twisted seven-wire CFRP strand were only 86% and 70%, respectively, of those of a single wire.

The response of a shear critical substandard reinforced concrete beam and the structural repair of the predamaged beam by carbon-fiber-reinforced polymer sheets (CFRPs) were investigated by advanced numerical modeling method. First, the specimen was tested up to failure under monotonic loading in a four-point bending test. Owing to spatial variability of the concrete mechanical properties over a specific region, the damage was concentrated on one side of the beam. The severe shear cracks on the damaged side were then successfully repaired by externally bonded CFRP sheets. The former load-carrying capacity of the repaired beam was recovered, and the crack formation was transferred to the other side of the specimen, which had not been repaired. After repairing the unrepaired side of the beam using the same process, the failure mode was characterized by concrete crushing when the limiting strain of the concrete was reached under compression. The unsymmetrical crack pattern in the as-built specimen due to the uneven distribution of the concrete mechanical properties was reproduced by a random fields approach that combines the nonlinear finite-element method with stochastic sampling. In addition, the nonlinear response of the repair processes on the predamaged beam was adequately reproduced in the finite-element environment. The crack patterns and capacities obtained in the numerical solutions matched well the experimentally observed responses of the as-built and twice-repaired specimens.