FRP Type Research Articles

Behavioral trends of shear strengthened reinforced concrete beams with externally bonded fiber-reinforced polymer

Numerous experimental studies have been conducted on reinforced concrete (RC) beams strengthened in shear with externally bonded fiber reinforced polymer (EBFRP). The objectives of this work are to study the behavioral trends of shear strengthened EBFRP RC beams after updating the existing database. The previously published databases have been updated, enriched and cross checked for completeness, redundancy and consistency. The updated database now contains data on 698 EBFRP beams and covers the time span from 1992 to 2018. The collected database then refined applying certain filters and used to investigate and capture better interactions among various influencing parameters affecting the shear strength of EBFRP beams. These parameters include the type and properties of FRP, fiber orientation as well as the strengthening scheme, the shear and the longitudinal steel reinforcement ratios, the shear span ratio, and the geometry of the member. The refined database is used to test the prediction accuracy of the existing design models. Considerable scatters are found in the results of all tested prediction models and in many occasions the predictions are unsafe. To better understand the shear behavior of the EBFRP RC beams and then enhance the prediction models, it was concluded that focused experimental programs should be carried out.

Finite element analysis of seismic behavior of FRP reinforced concrete frame structure

A finite element model of FRP reinforced concrete frame structure is established to analyze the structural performance of FRP reinforced concrete frame. The load displacement hysteretic curve, skeleton curve and ductility of the AFRP reinforcement, CFRP bar and GFRP reinforced concrete frame model are analyzed. The results show that the bearing capacity of the CFRP reinforced concrete frame is the highest, and the AFRP coagulation is used for the concrete frame. The GFRP reinforced concrete frame is the smallest, and the reinforced concrete frame model with AFRP reinforcement is the best in the three types of FRP reinforced concrete frame models.

Seismic Behaviors of Concrete Beams Reinforced with Steel-FRP Composite Bars under Quasi-Static Loading

Steel-fiber reinforced polymer (FRP) composite bar (SFCB) is a new composite material with good corrosion resistance and designable post-yield stiffness. Substitution of steel bar with SFCB can greatly increase the durability and ultimate capacity associated with seismic performance. First, the method and main results of the experiment are briefly introduced, then a simplified constitutive model of composite bar material was applied to simulate the seismic behaviors of the concrete beams reinforced with SFCBs by fiber element modeling. The simulation results were found to be in good agreement with test results, indicating that the finite element model is reasonable and accurate in simulating the seismic behaviors of beams reinforced with SFCB. Based on the numerical simulation method, a parametric study was then conducted. The main variable parameters were the FRP type in composite bars (i.e., basalt, carbon FRP and E-glass FRP), the concrete strength, basalt FRP (BFRP) content in SFCBs and shear span ratio. Seismic behaviors such as load-displacement pushover curves, seismic ultimate capacity and its corresponding drift ratio of the SFCBs reinforced concrete beams were also evaluated. The results showed that (1) the fiber type of the composite bar had a great impact on the mechanical properties of the beam, among which the beam reinforced with BFRP composite bar has higher seismic ultimate capacity and better ductility. With the increase of the fiber bundle in the composite bar, the post-yield stiffness and ultimate capacity of the component increase and the ductility is better; (2) at the pre-yield stage, concrete strength has little influence on the seismic performance of concrete beams while after yielding, the seismic ultimate capacity and post-yielding stiffness of specimens increased slowly with the increase in concrete strength, however, the ductility was reduced accordingly; (3) as the shear span ratio of beams increased from 3.5 to 5.5, the seismic ultimate capacity decreased gradually while the ultimate drift ratio increased by more than 50%. Through judicious setting of the fiber content and shear span ratio of the composite bar reinforced concrete beam, concrete beams reinforced with composite bars can have good ductility while maintaining high seismic ultimate capacity.

Durability performance and long-term prediction models of sand-coated basalt FRP bars

Basalt-fiber-reinforced polymer (BFRP) bars are expected to provide benefits that are comparable or superior to other types of FRP while being significantly cost-effective. However, extensive investigations are needed to evaluate the long-term characteristics and durability performance of these bars. This article presents an experimental study that investigated the physical, mechanical, microstructural, and durability characteristics of newly developed basalt-fiber-reinforced polymer (BFRP) bars. The physical, mechanical properties and microstructural characteristics were evaluated first on the unconditioned BFRP bars. The durability performance of the BFRP bars was then assessed by conducting the mechanical tests, such as transverse-shear test, flexural test, and interlaminar-shear test, on the specimens after different exposure periods (1000; 3000; and 5000 h) at 60 °C. Thereafter, the BFRP bar properties were assessed and compared with the values obtained on the unconditioned specimens. The test parameter was conditioning time (1000; 3000; and 5000 h). The test results revealed that the unconditioned BFRP bars had the best physical properties. On the other hand, the long-term durability performance revealed that the transverse shear-strength, flexural-strength, and interlaminar shear-strength retention were decreased by 12%, 19%, and 21%, respectively.

Numerical evaluation of blast resistance of RC slab strengthened with AFRP

In this study, in order to precisely evaluated the retrofitting effectiveness of the Aramid Fiber Reinforced Plastic (AFRP) sheet on the blast response of reinforced concrete (RC) slab, a refined non-linear finite element model is proposed for simulating of the structural response of RC slab strengthened with AFRP under blast loads. The complicated material models are applied in the simulation considering the high strain rate effects of the materials as well as the dynamic interfacial behavior between AFRP and concrete. Also, a appropriate erosion criterion technique is specially applied to capture the fracture and material separation process during the detonation of the explosive. At first, the numerical model of an actual laboratory sample of a conventional RC slab subjected to blast loads was simulated and verified using available experimental results. Then with the calibrated model, numerical simulations of RC slabs strengthened with AFRP to blast loadings are carried out. The numerical results of strengthened and non-strengthened RC slab (i.e., conventional slab) are compared to investigate the retrofitting effectiveness of AFRP on blast-resistant performance of RC slabs. In addition, a comprehensive investigation on the blast responses of FRP-strengthened RC slabs affected by these parameters, i.e. different AFRP layer, FRP type, strengthening mode, FRP bond strength and TNT mass, are also reported.

Bond characteristics of SFRP composites containing FRP core/anchors coated on geopolymer mortar

The present study investigates the bending bond characteristics of novel hybrid sprayed fiber-reinforced polymer (SFRP) composites containing fiber core/anchors. Carbon or basalt fiber cores were embedded in SFRP composites as core reinforcements, and of which their ends were inserted into the beams to act as anchors. Four-point bending bond tests were conducted to characterize the bonding behavior of these hybrid SFRP composites in terms of enhancement of the ultimate bond strength (τu). The effects of the type and number of FRP core/anchors on τu of SFRP-coated geopolymer mortar were investigated. Furthermore, geopolymer mortar was reinforced with 0.5 and 1.5 wt% of short steel fibers to study the effects of fibers on τu, and their results were compared with the efficiency of hybrid SFRP composites. The test results revealed that the hybrid SFRP composites had significant effects on the bond strength, and their bonding performance was relatively better than the fiber-reinforcement in geopolymer mortar. About 46% and 37% increments were observed in τu through the use of hybrid SFRP composites and steel fiber-reinforcement, respectively. The effective bond length (Le) of hybrid SFRP composites was approximately 39 mm.

Durability of bonded FRP-to-steel joints: Effects of moisture, de-icing salt solution, temperature and FRP type

This paper investigates the effects of environmental ageing on the mechanical response of adhesively bonded double-lap shear joints made of steel and CFRP or GFRP adherents. One hundred and ninety-two specimens, 84 joints and 108 material coupons, were aged for up to three years in various environments including (i) immersion in distilled water at 20 °C and 45 °C, (ii) immersion in de-icing salt solution at 20 °C and 45 °C and (iii) exposure to 95% relative humidity at 45 °C. In general, immersion at 45 °C resulted in noticeably greater strength reductions at both material and joint level. While the strength and stiffness of the joints made of GFRP material underwent significant reductions, the CFRP/steel joints were affected to a considerably smaller degree. FE simulations showed the impact of the permeability of FRP adherents and moisture distribution at the FRP/adhesive interface on the integrity and strength of the joints. The joint-level results are compared with the most relevant durability data in the literature.

New model for post-fatigue behaviour of CFRP to concrete bond interface in single shear

In this paper, a finite element model using ABAQUS 6.10-1 is developed to simulate the CFRP-to-concrete bonded joint behaviour in single shear pull-out tests. The model adopts the cohesive surface approach and the simulation results are checked against the authors’ test results (monotonic and post-fatigue) in order to demonstrate the accuracy of the model. Parametric studies using the validated model were carried out to investigate the effects of varying the bond length, the thickness of FRP, the type of FRP, the concrete strength, and the bond width ratio. The results were then used to assess the various existing design code approaches for predicting the FRP-concrete bond behaviour. The post-fatigue numerical results indicate that the existing design code methods all have significant discrepancies. Based on the work conducted a simple and potentially more accurate model for predicting the debonding strain of CFRP plate in single shear is then presented.

Bio-based resins for flexural strengthening of reinforced concrete beams with FRP sheets

Two types of bio-based resins; an epoxidized pine oil resin blend (EP) and a furfural alcohol resin (FA) derived from corn cobs and sugar cane were explored for strengthening reinforced concrete beams using externally bonded carbon and glass fiber reinforced polymer (CFRP and GFRP) sheets. Twenty one small scale bond tests using notched concrete beams, and nine full scale beams were tested. The EP resin resulted in a comparable bond strength to conventional epoxy when used in wet layup, with a 7% higher strength for CFRP, reaching 4.2MPa, and 17% lower strength for GFRP, reaching 2.8MPa. FA resin, on the other hand, resulted in a very weak bond, likely due to concrete alkalinity affecting curing. However, when FA resin was used to produce prefabricated cured CFRP plates which are then bonded to concrete using conventional epoxy paste, it showed excellent results as a 5MPa bond strength was achieved. Full scale beams achieved 18–54% increase in peak load and 9–46% increase in yielding load, depending on number of FRP layers and type of fibers and resin. Increasing the number of FRP layers from one to two resulted in only 13–21% increase in ultimate load. While FA resin is successfully used to produce prefabricated FRP plates that can be bonded to concrete using epoxy paste, further studies on curing and surface treatments are required if FA resin is to be used in FRP-concrete wet layup.

Flexural Behavior of Concrete Beams Reinforced with Ribbed Basalt-FRP Bars under Static Loads

AbstractRecently, basalt fiber–reinforced polymer (BFRP) reinforcement emerged as a new FRP type. Research is needed, however, to understand the behavior of BFRP bars in concrete members. This paper presents an experimental study aimed at investigating the flexural behavior and serviceability performance of concrete beams reinforced with ribbed BFRP bars. A total of eight concrete beams measuring 3,100 mm in length×200 mm in width×300 mm in depth were constructed and tested up to failure. Six beams were reinforced with 8-, 12-, and 16-mm BFRP bars with ribbed surfaces and two reference beams were reinforced with 10M and 15M steel bars. The beam specimens were designed in accordance with Canadian standards, and tested under four-point bending over a clear span of 2,700 mm until failure. The test results are presented and discussed in terms of cracking behavior, deflection, and failure modes. The test results yielded an average bond-dependent coefficient (kb) of 0.83, which is lower than 1.0 recommended b...

Efficiency of near surface mounted technique using fiber reinforced polymers for the flexural strengthening of RC beams

This paper presents the test results of an experimental study that investigates the behavior of reinforced concrete (RC) beams strengthened in flexure with near surface mounted (NSM) technique using glass and carbon fiber reinforced polymers (GFRP & CFRP). A total of 10 full scale reinforced concrete beams were constructed and strengthened in flexure with FRPs. This study included four parameters; technique used (NSM or Hybrid), type of FRP used (carbon or glass), amount of FRP used, and steel reinforcement ratio. All beams were tested under four point bending set-up. The test results included ultimate capacity, deflection, cracking, strains and mode of failure. All strengthened beams showed an increase in the capacity ranging between 31 and 133% compared with the reference beams. The NSM-CFRP strengthened beams showed greater ultimate capacities than the NSM-GFRP beams but they showed less ductile behavior. The NSM-GFRP strengthened beam, however, showed good ductile behavior with high deflection values at ultimate load. This gave ample warning before failure and can be considered as an advantage of strengthening RC beams with NSM-GFRP system. The measured ultimate capacities of all strengthened beams were compared with the design provisions provided by ACI440-2R guidelines, which showed very reasonable and conservative predictions for all strengthened beams.

Compressive behavior of FRP-confined concrete-filled PVC tubular columns

This paper presents a new composite confinement system of FRP wrap and PVC tube with and without an impact absorption medium (compressible foam) in between. The compressive behavior of the proposed FRP-confined concrete filled PVC tube (CCFPT) was investigated and compared with those of the concrete filled PVC tube (CFPT) and FRP-wrapped (FW) concrete cylinder. The effect of compressible foam on the post-peak behavior of the CCFPT specimen was explored. The applicability of seven existing FRP-confined stress–strain relationships to predict the ultimate strength and ductility enhancement of FW and CCFPT specimens was evaluated. A total of 14 FW, 5 CFPT, and 17 CCFPT specimens with 152mm in diameter and 305mm in height were tested under monotonically increasing axial loads in compression. The key parameters examined included the type and thickness of FRP wraps, the presence and thickness of compressible foam, and loading area. Test results indicated that, without compressible foam, the CCFPT cylinders resembled the FW cylinders in stress–strain relationships with brittle failures upon FRP rupture and immediately-followed PVC fracture due to sudden transfer in confining pressure. With compressible foam, the CCFPT cylinders can combine the strength of the FW cylinders and the ductility of the CFPT cylinders.

Behavior of recycled aggregate concrete-filled basalt and carbon FRP tubes

This paper presents the results of an experimental study on the axial compressive behavior of concrete-filled FRP tubes (CFFTs), prepared using different amounts of recycled concrete aggregate (RCA). Thirty-six CFFTs were tested under axial compression. The effects of the RCA replacement ratio, specimen cross-sectional shape, FRP type, and concrete strength were studied. The results suggest that the axial stress–strain behavior of CFFTs is affected by the amount of RCA, which particularly affects the ultimate axial strain and FRP hoop rupture strain. For a given in-place concrete strength, an increase in RCA content leads to a decrease in compressive strength and an increase in ultimate axial strain of FRP-confined concrete. The results also indicate that the increased RCA content leads to a decrease in the hoop rupture strain of CFFTs. CFFTs manufactured with carbon FRP tubes instead of basalt FRP tubes and CFFTs with circular cross-sections instead of square cross-sections develop a higher compressive strength and lower ultimate axial strain. The effects of specimen cross-sectional shape and FRP type on the axial compressive behavior of CFFTs vary with RCA content.

INFLUENCE OF NEAR-SURFACE MOUNTED FRP WITH CEMENTITIOUS MATERIAL ON OUT-OF-PLANE BEHAVIOR OF REINFORCED MASONRY WALLS

Eight medium scale reinforced masonry walls were built as a part of this study. These reinforced walls were strengthened using carbon fiber reinforced polymer [FRP] (bars and tapes) and glass FRP (bars) using a near surface mounted technique (NSM) with cementitious material; constant mild steel reinforcement ratio (ρ) was used. These strengthened walls were supported as a simply supported wall under an out-of-plane cyclic load applied along two line loads. This study presented the effect of different parameters, these parameters related to FRP (type and amount), bond pattern (stack and running), and existing of FRP in compression face of the walls. This paper reveals the relation between these factors and the out-of-plane capacity of the reinforced wall strengthened with FRP. Different modes of failure occurred in the strengthened reinforced walls, including a punching shear failure through the concrete block, crushing of concrete block and debonding of FRP reinforcement from the masonry substrate.

Behavior of Concrete Cylinder Confined with Helical Composites Strips

This paper presents theexperimental investigations on the behavior of a short concrete cylinder confined with helical FRP strip under axial compressive load,the results show that the compressive strength increases with increase in the width of the FRP and the decrease in pitch of the helix that follows the FRP on the side surface of the concrete cylinder. The numerical analysis conducted to describe the behavior of confined cylinders confirmed the experimental stress-strain curves and the numerical ones are recorded. A new method for predicting the ultimate compressive strength is also presented. The model is quite simple and can be adapted to the concrete cylinders confined with other types of FRP, for different widths and different values of the pitch of the helix, and for different values of the compressive strength of reference concrete. The mathematical optimization, of the function that describes the ultimate strength of confined cylinder is adjustable. It allows predicting the optimal values of various parameters: the confinement strength, the width of the FRP, the pitch of the helix, and the compressive strength of concrete, for different expected strength gain rates and for different intervals containing the studied variables.

Preparation Parametric Comparison and Performance Evaluation of FRP and HDPE Type Biogas Digesters

Preparation Parametric Comparison and Performance Evaluation of FRP and HDPE Type Biogas Digesters

Peak strength and ultimate strain prediction for FRP confined square and circular concrete sections

It is widely accepted that axially loaded FRP confined concrete presents significant strength and ductility increase with reference to the unconfined case. Adequate FRP confinement provides bilinear – like and hardening stress–strain behavior to concrete up to failure. Therefore, to model the mechanical behavior of adequately confined concrete two quantities are necessary: peak strength and ultimate strain. Many studies have been published regarding confinement of circular section elements; fewer studies analyze the case of square and rectangular section. Numerous predictive expressions of peak strength and ultimate strain, suitable for circular section elements, are available. Only in recent years, complete equations have been proposed to cover both circular and square sections. The aim of this work is the assessment of the performances of significant predictive expressions published in literature. Four groups of predictive expressions have been considered; they differ by the type of the predictive quantity (peak strength or ultimate strain) and by their applicability (only circular sections or both circular and square sections). For this reason a wide database has been assembled; it collects results of more than 655 compressive tests, performed on square and circular specimens confined with FRP. This comparison has been diversified as a function of cross section shape and FRP type (CFRP, GFRP, AFRP).

Confinement model for FRP confined normal- and high-strength concrete circular columns

This study establishes a confinement model for FRP confined normal- and high-strength concrete circular columns. A new column parameter was suggested for estimating the compressive strength of FRP confined concrete. The proposed model is able to predict the ultimate condition of FRP confined concrete columns that have similar unconfined concrete strength and confining pressure but significant differences in the jacket stiffness. The proposed model was then verified using a database of 574 FRP confined concrete circular columns with different types of FRP. This database covers unconfined concrete strength between 15MPa and 170MPa and specimens with a diameter ranging from 51mm to 406mm. Furthermore, this database includes specimens with a variety of FRP types: carbon FRP (CFRP), glass FRP, high-modulus carbon FRP, aramid FRP (AFRP), CFRP tube, ultra-high-modulus CFRP tube, and AFRP tube. Finally, the model’s prediction fits the experimental results very well by verifying the proposed model with the extensive database.

Constitutive Relationship of FRP Reinforced Column Plastic Hinge Zone Based on Pushover Analysis

The formation and development of plastic hinge is the basis of the whole process of FRP reinforced concrete eccentricity compression and flexural member nonlinear analysis. The moment-rotation relationship of FRP reinforced rectangular column plastic hinge zone was studied. Its yield and ultimate moment formulas were proposed. The specific values of the moment and rotation were discussed in different modes of failure, retrofitting methods as well as FRP types. A constitutive relationship of FRP reinforced rectangular column plastic hinge zone was established. Based on the constitutive relationship, a pushover analysis of the numerical model is conducted, and the feasibility of its application in Etabs software through cases is verified.

Composite Cutting with Abrasive Water Jet

Abrasive Water Jet (AWJ) technology has demonstrated to be an interesting manufacturing process for space, aircraft, boat and automotive sectors due to its specific advantages when machining composite materials. However, AWJ cutting of composite laminates possesses several challenges. It is necessary to develop a methodology to adapt the process parameters for each type of FRP & CFRP material which will allow AWJ trimming operations to be easily carried out on composite materials, since machine manufacturers still do not provide good databases for composite cutting. The presented work aims at studying the behaviour of a machinability model in composite materials. The machinability index for various composite materials with different thicknesses was found experimentally, which showed very different results for different materials. A study of the effect of the abrasive waterjet process parameters on the quality of cut (taper and surface roughness) was carried out.