Fiber-reinforced Polymer Stirrups Research Articles

Experimental and Theoretical Studies on the Shear Performance of Concrete Beams Reinforced with Fiber-Reinforced Polymer Stirrups.

In this paper, the shear behavior of concrete beams reinforced with FRP stirrups is studied. The shear performances of six concrete beams with a size of 150 mm × 300 mm × 3000 mm under four-point loading up to failure were experimentally analyzed. The critical parameters included the shear span to depth ratio (λ) and stirrup spacing (S). The test results revealed that as λ increased from 1 to 2, 3, and 4, the ultimate shear capacity of the beam decreases by 50.5%, 67.7%, and 69.2%, respectively. Meanwhile, as S increased from 100 mm to 150 mm and 200 mm, the ultimate shear capacity decreased by 16.1% and 44.6%, respectively. A new shear capacity calculation model of concrete beam reinforced with FRP stirrups was also proposed, which further considered the shear capacity of the FRP stirrups on the basis of the shear capacity of an RC beam without stirrups using the strut-and-tie model. Finally, the experiment and calculation results of 56 beam specimens reinforced with FRP stirrups extracted from this paper and previous studies were compared using the calculation models proposed in this paper, in order to evaluate the accuracy of these calculation models.

Shear Strength Prediction of Concrete Beams Reinforced with FRP Bars and Stirrups Using Gene Expression Programming

Existing reinforced concrete (RC) structures in humid regions suffer from deterioration due to the corrosion of ordinary reinforcement bars damaging the whole system. The deterioration of the transverse reinforcement leads to shear failure, which is one of the most dangerous failure modes. Therefore, researchers suggested using fiber-reinforced polymer (FRP) bars as a replacement for reinforcement bars in humid regions to integrate sustainability and improve their serviceability and durability. A simple model that can accurately estimate the shear strength of concrete beams designed with FRP longitudinal bars and stirrups is lacking. This research proposed a simplified Gene expression programming (GEP) based model to estimate the shear strength of FRP concrete beams. Seven parameters that principally dominate the shear behavior of FRP beams were utilized to create the GEP model. The parameters are the beam width, beam depth, concrete compressive strength, FRP tensile longitudinal reinforcement ratio, area of stirrups, spacing between the stirrups, and the ultimate FRP strength of stirrups. A comparison was made between the GEP and ACI-440 models; the R2 values of the total database were 92% and 54% for the GEP and ACI models, respectively. The R2 of the GEP model is considerably higher than that measured for the ACI model, and the errors of the GEP model are low, which affirms that the GEP is superior to the ACI model in estimating the shear strength of FRP beams. The trends of the GEP and ACI-440 models and the empirical results are similar, confirming the GEP model’s consistency. Using the GEP model to estimate the shear strength of concrete beams designed with FRP longitudinal bars and stirrups is recommended.

Compressive behavior degradation of FRP-confined RC columns exposed to a chlorine environment

Fiber-reinforced polymer (FRP) has been recognized as a promising method for strengthening reinforced concrete (RC) structures under a chlorine environment; however, it cannot prevent steel reinforcements from chloride-induced corrosion. Thus, the main objectives of this study were to (1) investigate the corrosion-induced performance degradation in FRP-confined RC columns under axial compression; (2) quantity the reduction of FRP rupture strain in FRP-confined RC columns subjected to a chlorine environment; and (3) propose a formula to estimate the load carrying capacity of FRP-confined RC columns considering the corrosion ratio. Twenty-eight columns with different FRP types (carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP)) and different layers of FRP (0, 1, 2, and 3) were conditioned under an accelerated corrosion process to obtain various corrosion ratios (0%, 5%, 10%, and 20%) and then tested under axial compression. The results showed that steel corrosion degraded the compressive response of FRP-confined RC columns, especially their deformation capacity. GFRP-confined RC columns generally had a better deformation capacity and were less vulnerable to steel corrosion than were CFRP-confined RC columns. Based on these test results, predictive equations for estimating the rupture strain of FRP were proposed as a function of corrosion ratio, which was introduced to modify an existing strength model of concrete confined with both FRP and steel stirrups. Finally, the ultimate load of FRP-confined RC columns with or without corrosion was predicted based on the modified concrete strength model.

Shear behavior of concrete beams reinforced with closed-type winding glass fiber-reinforced polymer stirrups

Conventional pultruded fiber-reinforced polymer (FRP) rod stirrups are susceptible to premature bent corner rupture and bond slip failure of overlapping legs. This research proposed a new type FRP shear reinforcement, closed-type winding GFRP (CW-GFRP) stirrups, featuring a fully closed rectangular cross-section. CW-GFRP stirrups completely avoided slip and significantly improved the strength of bent portion of stirrups. To investigate the feasibility of using CW-GFRP stirrups as shear reinforcement, shear test of 8 concrete beams reinforced with conventional pultruded stirrups and CW-GFRP stirrups was conducted. The beams were 300 mm deep and 150 mm wide, and their shear span ratio were 2.07. The effect of the material of stirrups, the spacing of stirrups, and the width of CW-GFRP stirrups were investigated. The test results showed that pultruded stirrups exhibited bond slip failure, in contrast, CW-GFRP stirrups reinforced beams prevented this failure and showed enhanced stiffness, narrower shear crack width and 1.09–1.12 times higher shear capacity. The splitting failure typical of CW-GFRP stirrups was reported, and a smaller stirrups width is expected to avoid splitting and generate greater strain at ultimate. It can be concluded that the new type of CW-GFRP stirrups is an optimized form of FRP shear reinforcement to supersede conventional pultruded stirrups. Strut-and-tie models based on ACI 318-19 and CSA S806-14 were used to predict the shear strength and produced a safe but relatively accurate prediction.

Steel-FRP Reinforced Concrete Moment-Resisting Frames under Lateral Loads: Numerical Investigation

This paper suggests using a combination of steel and fiber-reinforced polymer (FRP) reinforcements to introduce sustainable reinforced concrete moment-resisting frames (RC-MRFs) characterized by damage-controlled seismic performance, cost-effectiveness, and postearthquake recoverability. The aim of this study is twofold. First, according to a predefined seismic performance of RC-MRFs, this study introduces the optimum replacement ratio of the longitudinal FRP reinforcement of FRP RC-MRFs with steel bars. Second, this study investigates the application of FRP-steel reinforcement details to alleviate damage in the plastic-hinge zones of the beams. A detailed three-dimensional finite-element model (3D-FEM) of an RC-MRF is developed and validated against the experimental results of a large-scale, two-bay, two and half story MRF entirely reinforced with FRP rebars and stirrups. Results indicate that compared with FRP RC-MRFs, for a replacement ratio of FRP reinforcement ≤42%, the serviceability state of the proposed steel–FRP RC-MRFs is characterized by a controlled deformability, and the ultimate state is characterized by an acceptable residual lateral strength ensuring safe exit of the structure from its functionality. Furthermore, when steel reinforcements are only provided at the ends of the beams, the frame lateral deformability is based on the development of two sequential plastic hinges at each end of the beams, leading to higher deformability and lower damage levels.

Shear Behavior of Concrete Beams Reinforced With A New Type of Glass Fiber Reinforced Polymer Reinforcement: Experimental Study.

The article presents experimental tests of a new type of composite bar that has been used as shear reinforcement for concrete beams. In the case of shearing concrete beams reinforced with steel stirrups, according to the theory of plasticity, the plastic deformation of stirrups and stress redistribution in stirrups cut by a diagonal crack are permitted. Tensile composite reinforcement is characterized by linear-elastic behavior throughout the entire strength range. The most popular type of shear reinforcement is closed frame stirrups, and this type of Fiber Reinforced Polymer (FRP) shear reinforcement was the subject of research by other authors. In the case of FRP stirrups, rupture occurs rapidly without the shear reinforcement being able to redistribute stress. An attempt was made to introduce a quasi-plastic character into the mechanisms transferring shear by appropriately shaping the shear reinforcement. Experimental material tests covered the determination of the strength and deformability of straight Glass Fiber Reinforced Polymer (GFRP) bars and GFRP headed bars. Experimental studies of shear reinforced beams with GFRP stirrups and GFRP headed bars were carried out. This allowed a direct comparison of the shear behavior of beams reinforced with standard GFRP stirrups and a new type of shear reinforcement: GFRP headed bars. Experimental studies demonstrated that GFRP headed bars could be used as shear reinforcement in concrete beams. Unlike GFRP stirrups, these bars allow stress redistribution in bars cut by a diagonal crack.

Effectiveness of Glass Fiber-Reinforced Polymer Stirrups as Shear Reinforcement in Glass Fiber-Reinforced Polymer Reinforced Concrete Edge Slab-Column Connections

Effectiveness of Glass Fiber-Reinforced Polymer Stirrups as Shear Reinforcement in Glass Fiber-Reinforced Polymer Reinforced Concrete Edge Slab-Column Connections

SHEAR STRENGTHENING OF R/C BEAMS USING AFRP STIRRUPS WITH ANCHORED ENDS

Many studies have been conducted on the behaviour of reinforced concrete (R/C) beams shear-strengthened with fiber reinforced polymer (FRP) sheets. The studies show that FRP materials can produce good performance when used to carry some portions of shear force in the shear-strengthened beam. However, the performance of the FRP sheets used for shear strengthening is found limited by bond capacity between the FRP sheets and concrete surface. To improve the bond performance, an anchorage system can be introduced to the FRP strengthening scheme. This paper presents experimental and analytical studies conducted to evaluate the contribution and behaviour of aramid fiber reinforced polymer (AFRP) sheets with anchored ends in carrying the shear force in reinforced concrete beams. In the study, nine reinforced concrete beam specimens were fabricated and tested. Test parameters of the study include thickness of AFRP sheet used, type of wraps applied, type of anchors and diameter of anchor head used. Two types of anchorage system were proposed in the study, i.e. insert anchor system and C-embedded anchor system. The results from this study showed that the proposed anchorage system can improve the contribution of the FRP sheets in carrying the shear force in beams. In addition, the C-embedded anchor system exhibits better performance than the insert anchor system. Lastly, the behaviour of beams strengthened using FRP stirrups with anchored ends can be closely predicted by the ACI 440 design equations applicable for full-wrap scheme.

Behavior of Reinforced Concrete T-Beams Strengthened in Shear Using Closed Carbon Fiber-Reinforced Polymer Stirrups Made of Laminates and Ropes

Behavior of Reinforced Concrete T-Beams Strengthened in Shear Using Closed Carbon Fiber-Reinforced Polymer Stirrups Made of Laminates and Ropes

Shear Capacity of RC Beams with Carbon Fiber-Reinforced Polymer Stirrups with Rectangular Section

AbstractExperimental observations were made for the shear capacity of reinforced concrete beams with carbon fiber-reinforced polymer rectangular stirrups (CFRPRS). In total, 12 concrete beams were tested under three-point loading. Each beam measured 1,400 mm long, 150 mm wide, and 250 mm deep. For comparative studies, different parameters were considered: different sectional shapes (circular and rectangular CFRP stirrups), material types (steel and CFRP), and reinforcement ratios of stirrups (0.0038 and 0.0096). All beams were subjected to three-point loading. Test results indicated that concrete beams reinforced with CFRPRS stirrups could maintain shear behavior comparable to that of the concrete beam reinforced with steel stirrups. Compared with the beams with conventional CFRP stirrups with circular sections, superior shear behavior was observed for the beams reinforced with CFRPRS stirrups in terms of shear strength and crack width.

Optimized shear design equation for slender concrete beams reinforced with FRP bars and stirrups using Genetic Algorithm and reliability analysis

A lack of confidence in the shear design of concrete beams reinforced with Fiber Reinforced Polymer (FRP) bars may lead to excessive reinforcement and thus increase the overall cost of construction. In order to improve the accuracy of the current guidelines, two databases of slender (shear span to depth ratio>2.5) FRP reinforced concrete (RC) beams were developed from literature. The first set of data contains slender beams of 116 tests with only FRP rebar as longitudinal reinforcements whereas the second set contains 46 test beams reinforced with FRP as both longitudinal reinforcements and stirrups. The second database was used to evaluate the confinement effect of FRP rebar as stirrups. Thereafter a Genetic Algorithm was implemented to optimize the shear equations proposed in FRP design guidelines of ACI 440.1R-06, CSA S806-02, CSA S6-09, and Reineck’s tooth model. The optimized shear equations showed less scatter than the original equations as they could achieve an average Vtest/Vcalc close to 1.0 with a significant improvement in coefficient of variation (CoV) with the validation database compared to the original equations. It was observed that the concrete shear equation prediction could be improved if the concrete strength could be taken to a power value less than what is currently recommended in the guidelines. In the case of transverse shear equations, the inclusion of concrete strength improved the results of the optimized equations. The optimized shear equations were further calibrated by performing reliability analysis in order to use them for design purposes. The resistance factors for the shear design equations were calculated at a target reliability index, βT of 3.5 in order to achieve an acceptable level of structural safety.

Innovative hybrid reinforcement constituting conventional longitudinal steel and FRP stirrups for improved seismic strength and ductility of RC structures

The use of fiber reinforced polymer (FRP) reinforcement is becoming increasingly attractive in construction of new structures. However, the inherent linear elastic behavior of FRP materials up to rupture is considered as a major drawback under seismic attacks when significant material inelasticity is required to dissipate the input energy through hysteretic cycles. Besides, cost considerations, including FRP material and construction of pre-fabricated FRP configurations, especially for stirrups, and probable damage to epoxy coated fibers when transported to the field are noticeable issues. The current research has proposed a novel economical hybrid reinforcement scheme for the next generation of infrastructures implementing on-site fabricated FRP stirrups comprised of FRP sheets. The hybrid reinforcement consists of conventional longitudinal steel reinforcement and FRP stirrups. The key feature of the proposed hybrid reinforcement is the enhanced strength and ductility owing to the considerable confining pressure provided by the FRP stirrups to the longitudinal steel reinforcement and core concrete. Reinforced concrete beam specimens and beamcolumn joint specimens were tested implementing the proposed hybrid reinforcement. The proposed hybrid reinforcement, when compared with conventional steel stirrups, is found to have higher strength, stiffness, and energy dissipation. Design methods, structural behavior, and applicability of the proposed hybrid reinforcement are discussed in detail in this paper.

Torsional Behavior of Rectangular and Flanged Concrete Beams with FRP Reinforcements

AbstractThe demand for sustainable future infrastructures calls for new and innovative alternatives to avoid the problems associated with the conventional methods of construction. Fiber-reinforced polymer (FRP) bars have superior properties over conventional steel, mainly being noncorrosive. The objective of this study is to propose a model for predicting the full torsional behavior of concrete beams with the following: (1) carbon (C) or glass (G) FRP reinforcements, (2) different cross section shapes, and (3) adhesively bonded FRP stirrups or bent FRP stirrups. A brief recount of the findings from previous works is presented. Two previous models were adapted, and several new features were added to them, including but not limited to (1) recommending appropriate constitutive models for both the FRP and the concrete and (2) proposing failure criteria based on the experimentally observed failure modes. In addition, the first model was extended from an original strength model to a full behavior model (modifie...

Punching-shear design equation for two-way concrete slabs reinforced with FRP bars and stirrups

Recently, the Canadian Standard Association (CSA) provided its first punching-shear equation in the CSA S806-12, which represented a step forward in designing two-way concrete slabs reinforced with fiber-reinforced-polymer (FRP) bars. Yet neither the new CSA S806-12 equation nor any other design guide addresses the contribution of FRP stirrups as shear reinforcement for such elements due to the very limited research work. This study proposes a preliminary design equation to predict the punching-shear resistance of two-way concrete slabs reinforced with FRP bars and stirrups. The proposed equation is based on adopting the concrete contribution equation from the CSA S806-12 and modifying the stirrup contribution equation of the CSA A23.3-04 to reflect using FRP materials instead of steel. The proposed modification was verified against the test results of an extensive experimental work conducted at the University of Sherbrooke on full-scale two-way specimens measuring 2500mm×2500mm×200mm or 350mm. The accuracy of the predictions was compared to the test results. The results of this study supported the strain limit of 4000microstrains in the FRP stirrups for calculating the contribution of the FRP stirrups to the punching-shear capacity, as provided by ACI 440 Committee and CSA S6S1-10. In addition, the proposed punching-shear design equation shows good yet conservative predictions with a tested-to-predicted punching-shear ratio (Vtest/Vpred) of 1.17±0.21.

Bend Strength of Complete Closed-Type Carbon Fiber-Reinforced Polymer Stirrups with Rectangular Section

AbstractComplete closed-type carbon fiber-reinforced polymer stirrups with a rectangular section (CFRPRS) were developed and tested in the research reported in this paper. The use of a CFRPRS is intended to relieve stress concentrations and reduce the number of kinked fibers at the bent portion. A total of 16 B.5 specimens were tested with consideration of the bend strength of the CFRPRS as well as carbon fiber-reinforced polymer (CFRP) stirrups with circular sections. Observations were made regarding the bend strength and failure modes. Three different types of CFRPRS were tested with different width-thickness ratios (34.4 for a sectional area of 27.9 mm2 and 4.5 or 8.0 for 72 mm2) and three different ratios of the bend radius to the area-equivalent bar diameter (1.5, 3.0, and 4.5). The test results indicated that CFRPRSs exhibited improved bend strength as compared to its counterpart, the conventional CFRP stirrups with circular sections. CFRPRSs possessing a larger stirrup width-thickness ratio provi...

Seismic Behavior of Beam-Column Joints Reinforced with GFRP Bars and Stirrups

Reinforced concrete beam-column joints are commonly used in structures such as parking garages and road overpasses, which might be exposed to extreme weathering conditions and the application of deicing salts. The use of the noncorrodible fiber-reinforced polymer (FRP) reinforcing bars in such structures is beneficial to overcome the steel-corrosion problems. However, FRP materials exhibit linear-elastic stress-strain characteristics up to failure, which raises concerns on their performance in beam-column joints in which energy dissipation, through plastic behavior, is required. The objective of this research project is to assess the seismic behavior of concrete beam-column joints reinforced with glass (G) FRP bars and stirrups. Five full-scale exterior T-shaped beam-column joint prototypes were constructed and tested under simulated seismic load conditions. The longitudinal and transversal reinforcement types and ratios are the main investigated parameters in this study. The experimental results showed that the GFRP-reinforced joints can successfully sustain a 4.0% drift ratio without any significant residual deformation. This indicates the feasibility of using GFRP bars and stirrups as reinforcement in the beam-column joints subjected to seismic-type loading. It was also concluded that, increasing the beam reinforcement ratio, while satisfying the strong column-weak beam concept, can enhance the ability of the joint to dissipate seismic energy.

Fibre-reinforced polymer composite shear reinforcement: performance evaluation in concrete beams and code prediction

This paper evaluates the performance of carbon and glass fibre-reinforced polymer (FRP) stirrups and the accuracy of the shear design provisions incorporated in the currently available design codes and guidelines. A total of seven large-scale T-beams were constructed and tested: three reinforced with carbon fibre-reinforced polymer (CFRP) stirrups, three reinforced with glass fibre-reinforced polymer (GFRP) stirrups, and one reinforced with a steel stirrup for comparison, when applicable. The test results revealed that the design strength of the tested beams is not affected by the reduced strength of FRP stirrups at bend locations. Also, the recent CAN/CSA-S6 update is capable of adequately predicting the shear strength of the beam specimens reinforced with FRP stirrups. The software, Response-2000, which is based on the modified compression field theory (MCFT), predicted well the shear strength and the average strain in the stirrups of the tested beams; however, it overestimated the shear crack width.

Shear Strength of Large Concrete Members with FRP Reinforcement

Increasing interest in the use of fiber-reinforced polymer (FRP) reinforcement for reinforced concrete structures has made it clear that insufficient information about the shear performance of such members is currently available to practicing engineers. This paper summarizes the results of 11 large shear tests of reinforced concrete beams with glass FRP (GFRP) longitudinal reinforcement and with or without GFRP stirrups. Test variables were the member depth, the member flexural reinforcement ratio, and the amount of shear reinforcement provided. Results showed that the equations of the Canadian CSA shear provisions provide conservative estimates of the shear strength of FRP-reinforced members. Recommendations are given along with a worked example on how to apply these provisions including to members with FRP stirrups. It was found that members with multiple layers of longitudinal bars appear to perform better than those with a single layer of longitudinal reinforcing bars. Overall, it was concluded that the fundamental shear behavior of FRP-reinforced beams is similar to that of steel-reinforced beams despite the brittle nature of the reinforcement.

Behavior of RC Beams Shear Strengthened with Bonded or Unbonded FRP Wraps

Reinforced concrete (RC) beams shear-strengthened with fiber-reinforced polymer (FRP) fully wrapped around the member usually fail due to rupture of FRP, commonly preceded by gradual debonding of the FRP from the beam sides. To gain a better understanding of the shear resistance mechanism of such beams, particularly the interaction between the FRP, concrete, and internal steel stirrups, nine beams were tested in the present study: three as control specimens, three with bonded FRP full wraps, and three with FRP full wraps left unbonded to the beam sides. The use of unbonded wraps was aimed at a reliable estimation of the FRP contribution to shear resistance of the beam and how bonding affects this contribution. The test results show that the unbonded FRP wraps have a slightly higher shear strength contribution than the bonded FRP wraps, and that for both types of FRP wraps, the strain distributions along the critical shear crack are close to parabolic at the ultimate state. FRP rupture of the strengthened ...

Evaluation of the new Canadian highway bridge design code shear provisions for concrete beams with fiber-reinforced polymer reinforcement

The Canadian highway bridge design code (CHBDC) contains provisions for designing concrete members with fiber-reinforced polymer (FRP) reinforcement. In the second edition of the code, new shear design procedures for FRP-reinforced sections are provided. These procedures are consistent with those for steel-reinforced members in the code, in consideration of some modifications that account for the substantial differences between FRP and steel reinforcement. The shear approach adopted in the CHBDC follows the traditional approach of Vc + Vs for shear design. This paper presents an evaluation of this approach by comparing it with experimental shear strengths of available test data on beams longitudinally reinforced with FRP bars and with or without FRP stirrups. In addition, the CHBDC approach was compared with the FRP shear design provisions currently in effect in North America using the available test results. The comparison shows that the CHBDC method significantly underestimates the shear strength of FRP-reinforced concrete beams. A proposed modification to this method is presented and verified against available test results.