Journal of Composites for Construction

This paper presents a study on the behavior and modeling of the stress-strain behavior of confined high-strength concrete (HSC) without silica fume. The behavior of actively confined HSC is first examined, and a unified active-confinement model applicable to both HSC and normal-strength concrete (NSC) is then proposed based on a large test database assembled from the existing literature. An experimental study on fiber-reinforced polymer (FRP)-confined HSC is next presented and interpreted to examine its behavior, forming the basis for the subsequent modeling work. It is eventually shown that a recent analysis-oriented model developed by the writers’ group for NSC also provides close predictions for FRP-confined HSC. While the work is primarily concerned with HSC without silica fume, the effect of incorporating silica fume into HSC on the behavior of confined HSC is also given appropriate attention. The presence of silica fume in HSC is shown to reduce the effectiveness of confinement in term of strain capacity.

The principal motivation of this study is to obtain a clear understanding of size effects for fiber-reinforced polymer (FRP) shear-strengthened beams. The experimental program consists of seven beams of various sizes grouped in three test series. One beam of each series is used as a benchmark and its behavior is compared with a beam strengthened with a U-shaped carbon FRP (CFRP) jacket. The third test series includes an additional beam strengthened with completely wrapped external CFRP sheets. The experimental results show that the effective axial strains of the CFRP sheets are higher in the smaller specimens. Moreover, with a larger beam size, one can expect less strain in the FRPs. A nonlinear finite-element numerical analysis is developed to model the behavior of the CFRP shear-strengthened beams. The numerical model is able to simulate the characteristics of the shear-strengthened beams, including the interfacial behavior between the concrete and the CFRP sheets. Three prediction models available in current design guidelines for computing the CFRP effective strain and shear contribution to the shear capacity of the CFRP shear-strengthened beams are compared with the experimental results.

The goal of this paper is to present work that demonstrates the application of probabilistic modeling to evaluate the long-term performance of fiber-reinforced polymer (FRP) rehabilitated piping components. The time-dependent reliability index is evaluated for a fully deteriorated piping component rehabilitated with FRP considering the demands of internal fluid pressure, external soil pressure, and traffic loading. Carbon FRP (CFRP) and glass FRP (GFRP) composites are compared and the influence of material deterioration, fiber volume fraction (FVF), and variation in thickness of the composite are assessed using a first order reliability method and compared to a steel pipe under similar loading. A CFRP rehabilitation scheme having a FVF greater than 40% would be needed to exceed the as-built reliability index of a steel pipe under time-dependent composite deterioration, while no practical GFRP FVF can achieve the performance of steel pipe in the presence of time-dependent composite deterioration. Variations in the coefficient of variation (COV) can adversely affect the safety of both FRP rehabilitation schemes where an increase in COV from 10 to 30% result in decreases in the reliability index by 39.4% for CFRP (40% FVF) and 39.7% for GFRP (40% FVF).

External bonding of circumferential fiber-reinforced polymer (FRP) wraps is a widely accepted technique to strengthen circular RC columns. To date, most of the tests performed on FRP strengthened columns have considered short, unreinforced, small-scale concrete cylinders, with height-to-diameter ratios of less than three, tested under concentric, monotonic, and axial load. In practice, most RC columns have height-to-diameter ratios considerably larger than three and are subjected to loads with at least minimal eccentricity. Results of an experimental program performed to study the effects of slenderness on carbon FRP (CFRP) wrapped circular RC columns under eccentric axial loads are presented. It is shown that CFRP wraps increase the strength and deformation capacity of slender columns, although the beneficial confining effects are proportionally greater for short columns, and that theoretical axial-flexural interaction diagrams developed using conventional sectional analysis (but incorporating a simple FRP confined concrete stress-strain model) provide conservative predictions for nonslender CFRP wrapped columns under eccentric loads. The use of longitudinal CFRP wraps to reduce lateral deflections and allow slender columns to achieve higher strengths, similar to otherwise identical nonslender columns, is also demonstrated.

Torsion failure is an undesirable brittle form of failure. Although previous experimental studies have shown that using fiber-reinforced polymer (FRP) sheets for torsion strengthening of reinforced concrete (RC) beams is an effective solution in many situations, very few analytical models are available for predicting the section capacity. None of these models predicted the full behavior of RC beams wrapped with FRP, account for the fact that the FRP is not bonded to all beam faces, or predicted the ultimate FRP strain using equations developed based on testing FRP strengthened beams in torsion. In this paper, an analytical model was developed for the case of the RC beams strengthened in torsion. The model is based on the basics of the modified compression field theory, the hollow tube analogy, and the compatibility at the corner of the cross section. Several modifications were implemented to be able to take into account the effect of various parameters including various strengthening schemes where the FRP is not bonded to all beam faces, FRP contribution, and different failure modes. The model showed good agreement with the experimental results. The model predicted the strength more accurately than a previous model, which will be discussed later. The model predicted the FRP strain and the failure mode.

In several cases of loading and geometrical configurations, flexure beams, and girders are subjected to combined shear and torsion. Failure of a structural element under combined shear and torsion is brittle in nature. Externally bonded fiber-reinforced polymer (FRP) fabrics are currently being studied and used for the rehabilitation, repair, and retrofit of concrete structure. The objective of this study is to investigate the strengthening techniques for T-beams subjected to combined shear and torsion. Six half-scale beams—two control specimen and four strengthened beams—were constructed and tested using a specially designed test setup that subjects the beam to combined shear and torsion with different ratios. Four strengthening techniques using carbon FRPs were tested. The experimental results were reported and analyzed to assess the effectiveness of the proposed strengthening techniques. An innovative strengthening technique namely the extended U-jacket showed promising results in terms of strength and ductility while being quite feasible for strengthening. Future areas of research are being outlined.

This paper deals with the experimental behavior of solid clay brick masonry arches strengthened with glass fiber-reinforced polymer composites. Twelve half-scaled segmental masonry arches subjected to a load applied at the quarter span were tested under displacement control up to failure. The arches were built using handmade low strength bricks and a commercial lime-based mortar, trying to mimic ancient structures. Besides reference unreinforced arches, five different strengthening arrangements, including the use of spike anchors, were studied. The experimental results provide significant information for validation of advanced numerical models and analytical tools and for code drafting. The experimental results also show that (1) only continuous strengthening strategies are able to prevent typical local failure mechanisms of unreinforced arches; (2) strengthening at the intrados is the most effective option to increase strength; and (3) strengthening applied at the extrados provides the higher deformation capacity prior to failure, endowing arches with considerable ductility behavior.

This paper presents experimental and analytical results of a study conducted to investigate the use of carbon fiber-reinforced polymer (CFRP) laminates to rehabilitate shear-span and full-span corrosion-damaged RC beams. Fifteen RC beams were fabricated and were divided into three groups: control, shear-span, and full-span corrosions. The control beam was kept uncorroded and unstrengthened while the remaining 14 beams were corroded. One-half of the corroded beams were repaired with CFRP laminates, while the other one-half was tested without repair. Corrosion was induced in the tension steel reinforcement at a theoretical mass loss of 5, 10, and 15% using an accelerated technique. Test results showed that shear-span corrosion had a negligible influence on the flexural capacity, while full-span corrosion caused significant reductions up to 23% and 12% in the yield and ultimate capacity, respectively. The ductility of all corroded beams increased in comparison to the uncorroded unstrengthened beam (control). Repairing the corroded RC beams with CFRP laminates increased the flexural yield load and ultimate capacity by 19 and 50%, respectively, compared to the control beam. An analytical model based on section analysis, including the effect of steel reinforcement corrosion, was developed and compares well with the experimental results.

This paper highlights the failure mechanism of beams composed of carbon fiber-reinforced polymer (CFRP) box with and without infill concrete, and subjected to four point bending and axial load. In an experimental study performed with 20 small scale beams from five types of CFRP laminates, the beams failed near a loading plate. This study employs finite-element analysis to investigate the failure mechanism. Concrete is modeled as an isotropic material capable of cracking in tension and crushing in compression. CFRP is modeled as an orthotropic material with linear constitutive relation, and Tsai-Wu failure criterion is employed for CFRP. The analysis reproduces the observed beam failure. Local bending of top flange governs the failure of empty beams. CFRP failure near loading plate governs the failure of filled beams. Failure of CFRP occurs with more than 60% contribution by longitudinal compressive stress and the rest by in-plane shear stress. The contribution of the longitudinal compression increases with an increase in axial load. Moreover, the beams with more fibers in the transverse direction fail by longitudinal compression.

An experimental investigation on square high-strength concrete short columns confined with aramid fiber-reinforced polymer (AFRP) sheets is carried out in this study. Nine plain concrete specimens and 54 wrapped concrete specimens were tested under monotonic axial compressive loading. The specimens were grouped by three different grades of concrete strength. In each grade, some specimens were partially wrapped and others were fully wrapped, and the amount of wrapping AFRP sheets was varied also. Based on the experimental results, the regression formulas for strength and strain are obtained. The experimental results demonstrate that two types of axial stress-strain curves were observed depending on the form of AFRP wrapping, and the strength and ductility of the columns were increased when fully wrapped AFRP sheets, while only the strength was increased when partially wrapped AFRP sheets.