FRP-wrapped Columns Research Articles

Effect of compression casting method on the axial compressive behavior of FRP-confined seawater sea-sand concrete columns

The application of the novel compression casting method is beneficial to improve the compressive strength and durability of concrete. However, the compressed concrete fails rapidly after the peak load and exhibits stronger brittleness than the normal concrete, which could impair the seismic performance of the columns. As one of the passive confining measures, wrapping fiber-reinforced polymer (FRP) could be a practical technique to improve the ductility of such brittle columns. In this regard, this study experimentally investigated the axial compression behavior of both the partially and fully FRP-confined compression-cast seawater sea-sand concrete (SSC) columns. The test results indicated that the compression casting method enhanced the compressive strength but weakened the axial deformation capacity of the unconfined and FRP-confined SSC specimens. The compressive strength of unconfined concrete was improved by 38.5% due to compression casting. The measured average FRP rupture strain of the FRP-confined compression-cast SSC specimens was 6.3% smaller than that of FRP-confined normal SSC specimens due to the sudden appearance of the main oblique cracks, indicating poorer FRP utilization efficiency. Meanwhile, the average ultimate axial strain enhancement ratio of FRP-confined SSC specimens decreased from 12.04 to 7.83 after compression casting. The FRP hoop strain of the fully FRP-wrapped columns distributed more uniformly compared to the partially FRP-wrapped columns as the mean value of FRP efficiency factor increased from 0.807 to 0.928. With increasing FRP strip spacing, the post-peak segment of the stress–strain curve transferred from strain-hardening to strain-softening regardless of the confining stiffness. Finally, several existing stress–strain models were employed to examine their accuracy in anticipating the ultimate conditions of the FRP-confined compression-cast SSC columns.

Experimental Investigation on the Ecofriendly External Wrapping of Glass Fiber Reinforced Polymer in Concrete Columns

An ecofriendly fiber reinforced polymer (FRP) had been used in the last decade to enhance the short concrete column’s strength and deformation capacity. This study involves the wrapping of FRP sheets with a thickness of 3 mm and 5 mm on a short column, and then the compressive strength is determined. The rectangular columns of size 150 mm × 300 mm are used for this study, and cast under the grades of M20 and M40 are wrapped with GFRP sheets at the thickness of 3 mm and 5 mm. These results are clarified at a specific thickness of the FRP‐wrapped columns. It provides a maximum axial compressive strength, and Young’s modulus gets enhanced rigorously when it is to be compared to the normal concrete. This thesis deals with experimental studies of different parameters associated with wrapped glass fiber reinforced polymer (GFRP). In M20 grade, when the 3 mm wrapped specimen and the 5 mm wrapped specimen are compared, the specimen wrapped with 5 mm increases 5.182% more than the specimen wrapped with 3 mm. In M40 grade, when the 0 mm, 3 mm, and 5 mm wrapped specimens are compared, the specimen wrapped with 5 mm increases 2.47% more than the specimen wrapped with 0 mm. The 5 mm wrapping attains the maximum strength.

Factors Affecting the Structural Behavior of FRP Wrapped Concrete Columns and Applications in Design

In this paper, the FRP wrapped concrete column is investigated. . According to the research results of Shan et al. (2020) [2], Li et al. (2006) [3], and Deb et al. (2010) [4], this paper analyzes the variables that need to be controlled in the design of columns from these three perspectives: the shape of the cross-section, fiber orientation and bonding between the concrete column and FRP confinement. Impact tests and compressive tests are performed on different specimen. The setting of different samples follows the principle of controlling variables. The results indicate that FRP-wrapped columns with a circular cross-section are better than that with square or rectangular columns and basalt FRP is the optimal FRP material for strengthening the concrete column under the impact. Fiber orientation and types of bonding layers have a great impact on the mechanical properties of FRP wrapped concrete columns.

Shear strengthening of corroded reinforced concrete columns using pet fiber based composties

Polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) composites are characterized by a large rupture strain (LRS) (usually larger than 5%) but a low elastic modulus compared to conventional FRP materials made of carbon, glass, and aramid fibers. Previous studies have proved that the use of PET FRP sheets as jacketing materials for plain concrete or reinforced concrete (RC) columns could efficiently enhance their ductility. This paper presents a combined experimental and analytical study on the shear strengthening of corroded RC columns with stirrups having different levels of corrosion before strengthening. The shear resistance contributions from the substrate column and PET FRP sheets at various volume ratios were carefully examined and their interaction mechanisms were discussed. Design equations following a conventional truss analogy were then proposed to predict the shear strength of PET FRP-wrapped columns considering the effect of stirrup corrosion, and the predictions were verified against the test results.

FRP-confined concrete filled PVC tubes: A new design concept for ductile column construction in seismic regions

In their recent work Fakharifar and Chen (2016) [1] have introduced and validated a new ductile design concept of confined concrete-filled polyvinyl-chloride tubular (CCFPT) columns through experimental and analytical studies. Confinement was provided with the use of a polyvinyl-chloride (PVC) tube and fiber-reinforced polymer (FRP) wrappings or FRP with a sandwiched layer of foam to enhance impact energy reduction due to potential FRP rupture and PVC fracture. In the present paper, additional flexural tests on CCFPT columns were undertaken to further investigate the structural behavior of the proposed system for column construction in seismic regions. Axial and flexural behavior of CCFPT columns was investigated with compressive and flexural tests, respectively, and compared with those of their corresponding concrete-filled polyvinyl-chloride tubular (CFPT) and FRP-wrapped (FW) columns. Test results obtained from 152×305mm (6×12in.) stub columns under axial loads and 152×1524mm (6×60in.) flexural beams under four-point loads indicated that the CCFPT columns can significantly enhance strength over the CFPT columns and enhance ductility over the FW columns. The transverse confining pressure from FRP wrapping and the interface property between the FRP and PVC proved critical in CCFPT design. Furthermore, the idea of introducing a cushioning foam layer between FRP layers and PVC to lessen the brittleness of FRP rupture in seismic regions proved effective.

Modeling the Corrosion Rate of Steel Reinforcement in FRP-Wrapped Concrete

AbstractA model to predict the corrosion rate of steel reinforcing bars in fiber-reinforced polymer (FRP) wrapped concrete columns is presented. A model proposed by the author to predict the reinforcement corrosion rate and cracking of the concrete cover due to diffusion of chloride ions and oxygen in concrete members is modified to predict the corrosion rate of reinforcing bars inside FRP-wrapped columns. As corrosion progresses and rust layers build up, oxygen has to diffuse through three different layers to be consumed in the cathodic reaction: the FRP wrap, the concrete cover, and the rust layer. As the rust layer thickness increases, the corrosion rate decreases until it reaches a very slow steady-state descent. The predicted corrosion rate is compared with experimental results reported in the literature. Initially, the model proposed previously by the author was used to predict the corrosion rate of an unwrapped pile to calibrate parameters such as the diffusion coefficient of oxygen with experiment...

Uncertainty Definition on the Constitutive Models for RC Columns Wrapped with FRP

This paper aims to explore the effectiveness of the fiber-reinforced polymer (FRP)-confining mechanism in concrete in which parameters are uncertain. The confinement effect of high stiffness FRP jackets results an increase in the compressive strength of reinforced concrete columns and should be clearly defined. Various constitutive models have been constructed to predict the mechanical behavior of FRP-wrapped columns by considering this effect. However, the mechanical response of confined concrete columns due to FRP jackets under concentric compression has still been a challenging issue, and there are still some uncertainties in mechanical and also geometrical properties in the analysis and design procedure. These uncertainties can be studied with interval analysis (IA) to determine sharp bounds of the mechanical parameters such as effective lateral confining stress, Young’s modulus of concrete and FRP, and geometrical parameters. For this purpose, an IA has been performed using deterministic values of compressive strength for significant number (163) of experimental data being reported by several researchers on FRP-confined square/rectangular columns. The results indicate that uncertainties in material parameters and compressive strengths play an important role in determining the lateral stresses of FRP-confined columns.

FRP rupture strains in the split-disk test

The strengthening of concrete and concrete-filled steel columns by applying externally-bonded fibre-reinforced polymer (FRP) composite jackets has become a popular retrofit technique. Failure of such FRP-wrapped columns is usually governed by rupture of the FRP in the hoop direction. Two common material test methods have been used to obtain the hoop strength and rupture strain of FRP composites used in these applications: tensile tests of flat coupons and split-disk tests. The FRP rupture strain obtained from a split-disk test is usually less than that obtained from a flat coupon test, but there is neither a well-defined relationship between the two nor a comprehensive explanation for why they are different. This paper presents an investigation, using finite element (FE) analysis, into FRP hoop strains in the split-disk test with the aim of explaining possible reasons of the reduction of the FRP rupture strain in the test. The FE results show that the local strains in an FRP ring in a split-disk test are increased by the geometric discontinuities at the ends of the FRP and by circumferential bending of the FRP ring at the gap due to change of curvature there caused by the relative moment of the two half disks. The FRP ruptures once the strain at one of these locations reaches the FRP coupon rupture strain, leading to a lower apparent tensile strength than that obtained from flat coupon tests. The influence of parameters such as adhesive properties, FRP stiffness, geometry of the overlapping zone and FRP-to-split disk friction are examined.

Effect of Geometric Discontinuities on Strains in FRP-Wrapped Columns

Extensive research on fiber-reinforced polymer (FRP) confinement strengthening for concrete columns has led to a good understanding of, and accurate models for, circular columns subjected to axial load. This research is being extended to noncircular and eccentrically loaded columns, steel tubular, and concrete-filled steel tubular columns. A significant gap in our understanding of all these columns, however, is that the apparent FRP strain at failure is significantly lower than the ultimate strain in a flat coupon test. There may be many factors contributing to this complex phenomenon. This paper shows that one of these factors is the geometrical discontinuities at the ends of the FRP wrap. The significance of the effect of discontinuities on the strain concentrations in the FRP wrap and the bonding adhesive is explored through an elastic finite-element analysis.

Investigation of insulated FRP-wrapped reinforced concrete columns in fire

Research has demonstrated that fibre-reinforced polymers (FRPs) can be used efficiently and safely in strengthening and rehabilitation of reinforced concrete structures. However, the use of FRPs in buildings has been limited because relatively little is known about the behaviour in fire of reinforced concrete structural members that have been strengthened with FRP systems. This paper presents the recent results of an ongoing experimental study of the fire performance of FRP-wrapped reinforced concrete circular columns. The results of fire tests on two columns are presented, one of which was tested without supplemental fire protection, and one of which was protected by a supplemental fire protection system applied to the exterior of the FRP-strengthening system. The primary objective of these tests was to compare the fire behaviour of the two FRP-wrapped columns and to investigate the effectiveness of the supplemental insulation system. The thermal and structural behaviour of the two columns are discussed. The results show that, although FRP systems are sensitive to high temperatures, satisfactory fire endurance ratings can be achieved for reinforced concrete columns that are strengthened with FRP systems by providing adequate supplemental fire protection. In particular, the insulated FRP-strengthened column in this study was able to resist elevated temperatures during the fire tests for at least 90 min longer than the equivalent uninsulated FRP-strengthened column.

Experimental investigation of load carrying capacity of the slender reinforced concrete columns wrapped with FRP

Axial compression test was conducted on 6 elliptical modified rectangular slender reinforced concrete columns wrapped with FRP, with a slenderness ratio L/b ranging between 4.5 and 17.5. The test result showed that the effect of the slenderness ratio on the load carrying capacity of FRP-wrapped concrete columns is more significant than that of ordinary reinforced concrete columns. The strengthening effect decreases with increase of the slenderness ratio. When the slenderness ratio is less than 17.5, the load carrying capacity of FRP-wrapped columns is still 20% higher than that of ordinary reinforced concrete column. The columns were then successfully analyzed with the commercial finite element software ANSYS, taking into account of the constitutive relationship of concrete reinforced with FRP, the failure criterion and the initial geometrical imperfections. The effect of the cross-sections, steel ratio and the confinement ratio is investigated and a simplified formula for the stability coefficient to facilitate design of FRP-wrapped columns is derived.

Modeling the Behavior of Fiber Reinforced Polymer-Confined Concrete Columns Exposed to Fire

Very little information is available on the behavior of fiber reinforced polymer (FRP) materials and FRP-strengthened concrete members in fire, and this is a primary factor hindering the widespread implementation of FRP strengthening technologies in the construction industry. This paper presents a numerical model for evaluating the fire behavior of conventionally reinforced circular concrete columns, FRP-wrapped reinforced concrete columns, and insulated FRP-wrapped reinforced concrete columns. The model is validated against data available in the literature from full-scale fire endurance tests on conventionally reinforced concrete columns, and preliminary predictions of the model are presented and discussed. It is demonstrated that the model agrees reasonably well with experimental data obtained from tests on circular reinforced concrete columns, that it is unlikely that the structural effectiveness of FRP materials can be maintained during fire, and that the fire behavior of FRP-wrapped columns can be dramatically improved by providing supplemental insulation for the FRP.

Numerical parametric studies on the fire endurance of fibre-reinforced-polymer-confined concrete columns

Confinement of reinforced concrete columns by circumferential fibre reinforced polymer (FRP) wraps is a promising application of FRP materials for structural strengthening and seismic upgrading of deteriorated or under-strength members. However, if this technique is to be used in buildings, parking garages, and industrial structures, then the ability of FRP materials and FRP-wrapped columns to withstand the effects of fire must be demonstrated and evaluated. This paper presents the results of parametric studies conducted using a previously presented and partially validated numerical fire simulation model to investigate the effects of a number of parameters on the fire behaviour of FRP-wrapped reinforced concrete columns. It is demonstrated that appropriately designed and adequately protected FRP-wrapped reinforced concrete columns are capable of achieving fire endurances equivalent to conventionally reinforced concrete columns. Furthermore, this study also suggests that a holistic approach to the fire design of FRP-wrapped members is required, rather than an approach based on the specific performance of the FRP materials. Design recommendations for the fire-safe design of FRP-wrapped concrete columns are presented and discussed.Key words: reinforced concrete, rehabilitation, strengthening, fibre reinforced polymer, fire endurance, fire insulation, numerical modelling.

Performance Evaluation of Reinforced Concrete Bridge Columns Wrapped with Fiber Reinforced Polymers

This study investigates the performance of new bridge columns wrapped with fiber reinforced polymers (FRP) when exposed to aggressive environmental conditions. This has been accomplished through field monitoring and laboratory tests. As part of the field monitoring, temperature data were collected at various locations of bridge columns. In addition, visual inspection of two bridges was performed periodically for over a period of two years. No evidence of deterioration of the FRP wraps was detected during that period. Laboratory tests were performed to investigate how FRP wraps protect reinforced concrete columns from corrosion, and freeze–thaw laboratory tests were conducted to study the impact of temperature cycles on the mechanical behavior of FRP-wrapped columns. From the corrosion experimental tests, it was found that FRP provides excellent protection against aggressive agents (salty water or moisture) even when a single layer is used. Compression tests were conducted on specimens subjected to freeze–thaw cycles. It was found that minor thermal cycles have no effect on the performance of FRP-wrapped concrete specimens. However, for large thermal cycles, some degradation of ductility in the axial and the hoop directions was observed.