Behavior Of FRP-confined Concrete Research Articles

Experimental investigation on the compressive behaviour of FRP-confined rectangular concrete columns

This paper presents a comprehensive experimental study on the behaviour of FRP-confined concrete in square and rectangular columns and focuses on some issues that might be addressed with a view to improving the predictive models. For this purpose, 31 prismatic concrete specimens with a height of 600 mm and low- and medium-strength concrete (20–35 MPa) were tested under centred compression. The parameters studied were the aspect ratio between the sides of the section (1, 1.5 and 2), the radius of curvature of the corners (20, 25 and 30 mm) and the number of carbon FRP layers applied. The experimental results included stress–strain curves of specimens and detailed information about the confined concrete strength and the axial and lateral strain achieved on the FRP jacket during the tests. The stress–strain response and ultimate condition are analysed, showing that FRP jacketing is an efficient technique for increasing the strength and strain capacity, but that confinement efficiency decreases as the aspect ratio of the section increases. In spite of such decrease, significant strength improvement was achieved for low-strength concrete in rectangular sections with aspect ratios of 1.5 (strength gain up to 81%), and even 2 (up to 36%). The axial strength of the tests was compared with the design criteria of four international guidelines, resulting in predictions that did not properly fit for rectangular sections. A predictive equation is proposed to assess the axial compressive strength of the FRP-confined concrete, which includes a better adjustment for the strain efficiency factor and the shape factor for rectangular columns.

Experimental Study on the Confinement of Concrete Cylinders with Large Rupture-Strain FRP Composites

Large rupture strain (LRS) fiber-reinforced polymer (FRP) composites, typically formed from polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) fibers, generally exhibit ultimate rupture strains >5%. Such fibers are particularly suited to the confinement of concrete columns on account of their LRS and sufficient elastic modulus. There are currently a limited number of studies on LRS FRP-confined concrete, particularly with high- and ultrahigh-strength concrete, so their behavior across a range of variables is still unknown. To improve this understanding, this paper systematically investigates the influence of fiber type, fiber thickness, and concrete strength on the behavior of FRP-confined concrete. To achieve this objective, the current investigation presents the results of 66 circular FRP-confined cylinders that are loaded concentrically. Three main parameters are investigated, namely, fiber type (i.e., PEN, PET, carbon, glass, and aramid), concrete strength (i.e., normal, high, and ultrahigh strength), and fiber thickness. The results show that regardless of fiber type, the stress–strain response is bilinear when the concrete is sufficiently confined. However, when there is insufficient confinement provided to the concrete core, the stress–strain response becomes trilinear. This trilinear response is more pronounced for LRS FRP-confined specimens because the confinement stiffness of the LRS FRP jacket is lower than that of a traditional FRP-confined specimen with an equivalent confinement ratio. Increasing the confining hoop stiffness (i.e., increasing FRP layers) reduces the magnitude of strength reduction after initial concrete cracking. It is also evident that as the unconfined concrete strength increases, the minimum confinement stiffness ratio necessary to prevent strength reduction after initial concrete cracking increases.

Fiber reinforced polymer-confined concrete under high strain rate compression: Behavior and a unified dynamic strength model

The behavior of FRP-confined concrete (FCC) under quasi-static compressive loadings is well understood, while the research on dynamic compressive behavior of FCC has hitherto been rarely reported. An experimental program consisting of Split Hopkinson Pressure Bar (SHPB) impact tests and quasi-static compression tests on FCC is conducted and the results are presented in this paper. The strain rate effect on the axial compressive behavior of FCC is studied. Additionally, a new unified dynamic strength model for FCC is proposed and the test results from the current study and the literature are compared with the predictions from the proposed model. Results presented in this research demonstrate that the strain rate effect on impact behavior of FCC is significant and the proposed model can well predict the mechanical properties of the FCC.

Monotonic and cyclic response of CFRP-wrapped concrete under uniaxial compression

ABSTRACTStrengthening and retrofitting of reinforced concrete elements using FRP (fibre reinforced polymer) is currently gaining acceptance because of its merits over available conventional practices. FRP confinement enhances the load-carrying capacity of the column by increasing the ultimate strain and ductility. Study of the stress-strain behaviour of FRP-confined concrete is of prime importance to be studied for safe, economical and reliable design. In this paper, authors have attempted to study the stress-strain behaviour of carbon fibre reinforced polymer (CFRP)-confined concrete under both monotonic as well as repeated cyclic loading using analytical as well as numerical models. For numerical analysis, FE software ABAQUS is used. Stress-strain studies on FRP-confined concrete were carried out experimentally on low-strength concrete and the results were validated using existing analytical models by Lam and Teng, and Shao and the proposed analytical and numerical models are compared.

Effect of Load Path on Behavior of FRP-Confined Concrete

AbstractThis paper presents an experimental study on concrete cylinders confined by fiber-reinforced polymer (FRP) and loaded under constant axial load and increasing bending moment. A total of 55 ...

Dynamic Compressive Behavior of FRP-Confined Concrete under Impact and a New Design-Oriented Strength Model

The dynamic mechanical properties of fiber-reinforced polymer (FRP) confined concrete were experimentally and theoretically studied using a 100-mm-diameter split Hopkinson pressure bar (SHPB) apparatus. As test results turned out, the dynamic strength of FRP-confined concrete was improved significantly. Within the mean strain rate range of 50–130 s−1, the dynamic strength increased with the rise in strain rate. With same strain rate, the strengthening effect was influenced by confining ratio. The optimal confining ratio of AFRP-confined concrete is 0.264, once beyond this limit, the failure pattern will be changed, and the dynamic strength will be decreased. In addition, a modified model was proposed for dynamic strength of FRP-confined concrete, which agrees with the test results well.

Influence of Concrete Age on Compressive Behavior of FRP-Confined Concrete

This paper presents the results of an experimental study on the influence of concrete age on the compressive behavior of fiber reinforced polymer (FRP)-confined normal-strength (NSC) and high-strength concrete (HSC). The first part of the paper presents the results of 18 FRP-confined and 18 unconfined concrete specimens tested at 7 and 28 days. To extend the investigation with specimens with concrete ages up to 900 days, existing test results of FRP-confined concrete was assembled from the literature. Based on observations from both short-and long-term influences of concrete age on compressive behavior of FRP-confined concrete, a number of important findings were drawn and are presented in the second part of the paper. It was observed that, at a same level of FRP confinement and unconfined concrete strength, the stress-strain behavior of FRP-confined concrete changes with concrete age. This difference is particularly pronounced at the transition zone of the stress-strain curves. It is found that, in the short-term, the ultimate condition of FRP-confined concrete is not significantly affected by the age of concrete. However, in the long-term, slight decreases in the compressive strength and the ultimate axial strain are observed with an increase in concrete age.

The Effect of Confinement Method and Specimen End Condition on Behavior of FRP-Confined Concrete under Concentric Compression

This paper presents an experimental investigation on the influence of confinement method and specimen end condition on axial compressive behavior of fiber reinforced polymer (FRP)-confined concrete. A total of 12 aramid FRP (AFRP)-confined concrete specimens with circular cross-sections were tested. Half of these specimens were manufactured as concrete-filled FRP tubes (CFFTs) and the remaining half were FRP-wrapped concrete cylinders. The effect of specimen end condition was examined on both CFFTs and FRP-wrapped specimens. This parameter was selected to study the influence of loading the FRP jacket on the axial compressive behavior. In this paper the experimentally recorded stress-strain relationships are presented graphically and key experimental outcomes discussed. The results indicate that the performance of FRP-wrapped specimens is similar to that of CFFT specimens and the influence of specimen end condition is negligible.

State-of-the-Art for Experimental Studies on the Mechanical Behavior of FRP-Confined Concrete

Numerous experimental studies have proven that the confinement with FRP-wrap or tube encasement could enhance the strength, ductility and durability of concrete columns. The variation of each distinct experimental test result to its actual mean value is the general cause of modeling inaccuracy, and this appears to be a lack of consensus among the research community. This paper critically reviewed the current experimental studies with the emphasis on the revelation of the mechanical behavior of FRP-confined concrete and analytical study of its behavior.

Behavior of FRP-confined concrete after high temperature exposure

This paper presents the results of an experimental program to investigate the effect of high temperature on the performance of concrete externally confined with FRP sheets. For this purpose, a two-phase experimental program was conducted. In the first phase, 42 standard 100 × 200 mm concrete cylinders were prepared. Out of these specimens, 14 cylinders were left unwrapped; 14 specimens were wrapped with one layer of CFRP sheet; and the remaining 14 specimens were wrapped with one layer of GFRP sheet. Some of the unconfined and FRP-confined specimens were exposed to room temperature; whereas, other cylinders were exposed to heating regime of 100 °C and 200 °C for a period of 1, 2 or 3 h. After high temperature exposure, specimens were tested under uniaxial compression till failure. The test results demonstrated that at a temperature of 100 °C (a little more than the glass transition temperature ( T g ) of the epoxy resin), both CFRP- and GFRP-wrapped specimens experienced small loss in strength resulting from melting of epoxy. This loss of strength was more pronounced when the temperature reached 200 °C. In the second phase of the experimental program, three 100 × 100 × 650 mm concrete prisms were prepared and then overlaid by one layer of CFRP and GFRP laminates for conducting pull-off strength tests as per ASTM D4541 – 09. The objective of this testing was to evaluate the degradation in bond strength between FRP and concrete substrate when exposed to elevated temperature environments. One prism was exposed to room temperature whereas the other two specimens were exposed to heating regime of 100 °C and 200 °C for a period of 3 h. It was concluded that a significant degradation in the bond strength occurred at a temperature of 200 °C especially for CFRP-overlaid specimens.