Showing papers in "Journal of Composites for Construction in 2015"

Prediction of Long-Term Performance and Durability of BFRP Bars under the Combined Effect of Sustained Load and Corrosive Solutions

Abstract: Unlike carbon-fiber-reinforced polymer (CFRP) bars and the maturely developed glass FRP (GFRP) bars, the long-term performance of the newly developed basalt-fiber reinforced polymer (BFRP) bars under severe environmental conditions remains unclear This paper evaluates the residual tensile properties of unstressed and stressed BFRP bars exposed to four types of simulated harsh environments: alkaline solution, salt solution, acid solution, and de-ionized water at 25, 40, and 55°C Microstructural analysis using scanning electronic microscopy (SEM) was also conducted to reveal the inherent degradation mechanism of BFRP bars in alkaline environment The residual tensile strength of unstressed BFRP bars exposed to alkaline solution was used for long-term performance prediction based on Arrhenius theory The results showed that the effect on the durability of BFRP bars exposed to acid, salt, and deionized water was less than that for bars exposed to alkaline solution The effects of sustained stress on

Performance of Concrete Beams Reinforced with Basalt FRP for Flexure and Shear

Abstract: The flexural and shear performances are evaluated for concrete beams reinforced with basalt fiber-reinforced polymer (BFRP) rebar and stirrups. Nine 150× 300× 3, 100-mm beams were tested in four-point bending to examine the effect of BFRP flexural reinforcement ratios varying from 0.28 to 1.60 the balanced ratio on the structural performance. The beams were reinforced by either BFRP or steel stirrups, and some had no shear reinforcement. It was shown that ultimate and service loads increased with flexural reinforcement ratio for all shear reinforcement types while the service load levels were not affected by stirrup type. Beams without stirrups and those with BFRP stirrups failed in shear, with the former reaching 55–58% of ultimate flexural capacity and the latter failing by stirrup rupture at 90–96% of flexural capacity. Beams with steel stirrups failed in flexure. Deformability values show that methods that combine strength and curvature digress more from those based on midspan strain energy as...

Concrete Damage Plasticity Model for Modeling FRP-to-Concrete Bond Behavior

Abstract: The technique of externally bonding fiber-reinforced polymer (FRP) composites has become very popular worldwide for retrofitting existing reinforced concrete (RC) structures. Debonding of FRP from the concrete substrate is a typical failure mode in such strengthened structures. The bond behavior between FRP and concrete thus plays a crucial role in these structures. The FRP-to-concrete bond behavior has been extensively investigated experimentally, commonly using a single or double shear test of the FRP-to-concrete bonded joint. Comparatively, much less research has been concerned with numerical simulation, chiefly due to difficulties in the accurate modeling of the complex behavior of concrete. This paper presents a simple but robust finite-element (FE) model for simulating the bond behavior in the entire debonding process for the single shear test. A concrete damage plasticity model is proposed to capture the concrete-to-FRP bond behavior. Numerical results are in close agreement with test data,...

General Stress-Strain Model for Steel- and FRP-Confined Concrete

Abstract: A new and general stress-strain model for concrete confined by steel or fiber reinforced polymer (FRP) is developed in this work. One additional variable and one constant are added to the well-known Popovics model to control the type and the shape of the stress-strain curve. The proposed model has one simple, continuous, and explicit expression and can exhibit either hardening or softening types of responses. This general model provides a unified platform for modeling stress-strain of concrete confined by different materials, such as steel or FRP, and help to overcome inconsistency or complexity. The parameters of the stress-strain model are determined by analytical study and data regression using a large and up-to-date test database. The proposed stress-strain model is validated with experimental results and compared with existing models; it shows good performance and superior flexibility and versatility of the model.

Characterization and Comparative Durability Study of Glass/Vinylester, Basalt/Vinylester, and Basalt/Epoxy FRP Bars

Abstract: This paper presents an experimental study that investigated the physical, mechanical, and durability characteristics of three different types of fiber-reinforced polymer (FRP) bars made of basalt and glass fibers with vinylester and epoxy resins, namely basalt/vinylester (B/V) FRP bars, glass/vinylester (G/V) FRP bars, and basalt/epoxy (B/E) FRP bars. First, their physical and mechanical properties were assessed. Then, a comparative durability study was performed on the three types of FRP bars under alkaline exposure simulating a concrete environment. The alkaline exposure was achieved by immersing the bars in an alkaline solution for up to 5,000 h at 60°C. Thereafter, the properties were assessed and compared with the unconditioned (reference) values. The test parameters were (1) fiber type (basalt or glass); (2) resin type (vinylester or epoxy); and (3) conditioning time (1,000, 3,000, and 5,000 h). The test results reveal that the G/V composite had the best physical and mechanical properties an...

Seismic strengthening of masonry-infilled RC frames with TRM: Experimental study

Abstract: This paper presents a technique for retrofitting nonseismically reinforced concrete (RC) masonry-infilled frames with textile-reinforced mortar (TRM) jacketing. In the present study the application of TRM is examined on nearly full-scale, as-built and retrofitted, three-story frames, subjected to in-plane cyclic loading. The results of testing a 2∶3 scale, as-built frame representing typical structures with nonseismic design and detailing characteristics and of a companion frame retrofitted via TRM jacketing are presented and compared in terms of the efficiency of the proposed technique to enhance the strength and deformation characteristics of substandard infilled frames.

Unified Stress-Strain Model for FRP and Actively Confined Normal-Strength and High-Strength Concrete

Abstract: Accurate modeling of the complete stress-strain relationship of confined and unconfined concrete is of vital importance in predicting the overall flexural behavior of reinforced concrete structures. The analysis-oriented models, which utilize the dilation characteristics of confined concretes for stress-strain relationship prediction, are well recognized for their versatility in such modeling applications. These models assume that at a given lateral strain, the axial compressive stress and strain of fiber-reinforced polymer (FRP)–confined concrete are the same as those of the same concrete when it is actively confined under a confining pressure equal to that supplied by the FRP jacket. However, this assumption has recently been demonstrated experimentally to be inaccurate for high-strength concrete (HSC). It was shown that at a given axial strain, lateral strains of actively confined and FRP-confined concretes of the same concrete strength correspond when they are subjected to the same lateral con...

Experimental Investigation of the Hysteretic Performance of Dual-Tube Self-Centering Buckling-Restrained Braces with Composite Tendons

Abstract: This paper presents the results of experimental testing a novel dual-tube self-centering buckling-restrained brace (SC-BRB) with pretensioned basalt fiber-reinforced polymer (BFRP) composite tendons. Cyclic tensile experiments are first conducted on two sets of BFRP tendons with different diameters. The results confirm that the BFRP tendons have a stable cyclic elastic modulus and sufficient elongation capacity, making them suitable for use as the self-centering tendons in SC-BRBs. Quasi-static experiments are performed using two dual-tube SC-BRB specimens with different core plate areas. Before the failure of the self-centering system, both specimens stably exhibit the expected flag-shaped hysteresis response, with a relatively small residual deformation. The internal forces in the BFRP tendons and the gaps between the tubes and the end plates are measured to validate the performance of the self-centering system. Both specimens meet the requirements for ultimate ductility and cumulative ductility...

Bond performance of basalt fiber-reinforced polymer bars to concrete

Abstract: This paper presents the test results of a study on the bond behavior of basalt fiber-reinforced polymer (BFRP) bars to concrete. Thirty six concrete cylinders reinforced with BFRP bars and twelve cylinders reinforced with glass fiber-reinforced polymer (GFRP) bars were tested in direct pullout conditions. Test parameters included the FRP material (basalt and glass), the bar diameter, and the bar embedment length in concrete. Bond-slip curves of BFRP and GFRP bars revealed similar trends. BFRP bars developed average bond strength 75% of that of GFRP bars. All BFRP specimens failed in a pullout mode of failure along the interfacial surface between the outer layer of the bar and the subsequent core layers. The influence of various parameters on the overall bond performance of BFRP bars is analyzed and discussed. The well-known BPE and modified-BPE analytical models were calibrated to describe the bond-slip relationships of the bars. Test results demonstrate the promise of using the BFRP bars as an alternative to the GFRP bars in reinforcing concrete elements.

Innovative CFRP-Prestressing System for Strengthening Metallic Structures

Abstract: An innovative retrofit system to prestress carbon fiber reinforced polymer (CFRP) plates and attach them to existing metallic beams was developed (patent number CH 706 630 B1) and tested. The system does not require any glue between the CFRP plates and the beams; therefore, surface preparation is not necessary, which reduces the time and cost of retrofitting. The proposed prestressed unbonded reinforcement (PUR) system includes a pair of mechanical clamps that function based on friction. Each clamp can simultaneously hold and attach three CFRP plates to the beam. The design considerations of the clamps, which are the most important elements of the PUR system, were explained. The system has a trapezoidal configuration that offers an easy on-site installation and uninstallation procedures without residual damage on the metallic beam. Three 5-m-long steel beams were statically tested until failure, including one reference unstrengthened beam and two beams that were strengthened with 15% and 31% CFRP prestress levels. A considerable increase in the yielding and ultimate load capacities of the retrofitted beams was achieved. The ultimate load-carrying capacity of the strengthened beams with 15% and 31% CFRP prestress levels increased by more than 23% and 31%, respectively, compared to that of the reference specimen. A finite-element (FE) model was created to simulate the behavior of the retrofitted beams. Next, the FE results were compared with those from the experiments.

Mechanical characterization of basalt FRP rebars and long-term strength predictive model

Abstract: The use of basalt fiber–reinforced polymers (BFRP) in construction applications is relatively new and, although its mechanical performance is expected to be similar to that of glass fiber–reinforced polymer, not many studies have addressed its performance in concrete and mortar environments. This paper examines the degradation of BFRP bars at their product development stage after exposure to accelerated environmental conditions and proposes a methodology to predict their long-term design strength. A total of 132 BFRP specimens comprising two types and seven different diameters were tested in tension after conditioning in pH9 and pH13 solutions at 20, 40, and 60°C for 100; 200; 1,000; and 5,000 h. Based on the results obtained and adopting the durability approach of industry standards for FRP reinforcement in concrete structures, a comprehensive long-term strength predictive model for fiber-reinforced polymer (FRP) bars in multiple environments is proposed and exemplified. The BFRP bars tested as p...

Shear Strength of FRP Reinforced Concrete Members with Stirrups

Abstract: The mechanisms of shear transfer in fiber-reinforced polymer (FRP) reinforced concrete members with shear reinforcement are discussed, and it is explained how these were used to derive the shear design provisions of the Canadian standard for design and construction of building structures with FRPs. Subsequently, the accuracy of these provisions and the validity of their underlying assumptions are assessed by comparing the predicted shear strengths of over three hundred FRP-reinforced beams with their corresponding experimental values. Although the focus of the paper is mainly on beams with FRP shear reinforcement, for completeness beams with and without shear reinforcement are analyzed. It is determined that the mean and standard deviation of the ratio of the test to predicted shear strength of the beams without shear reinforcement are 1.16 and 0.24, respectively, whereas those of beams with shear reinforcement are 1.15 and 0.23. The strengths of these beams are also computed using the recommendat...

Bond Durability of Basalt Fiber–Reinforced Polymer Bars Embedded in Concrete under Direct Pullout Conditions

Abstract: The use of basalt fiber–reinforced polymer (BFRP) bars as a reinforcing material has gained increasing interest worldwide. However, few studies have reported on these bars’ performance in concrete when exposed to harsh environments. This paper investigates the effect of five different accelerated environments, namely (1) tap water, (2) seawater, (3) elevated temperature, (4) elevated temperature followed by tap water, and (5) elevated temperature followed by seawater, on the bond stress-slip response, adhesion to concrete, and bond strength [of two types of BFRP bars and one type of glass fiber–reinforced polymer (GFRP) bar]. The bond-slip responses of all specimens were governed by the surface treatment of each bar and its manufacturing quality, regardless of the fiber type. Sand-coated BFRP bars showed higher bond characteristics than helically grooved bars after conditioning. Moister environments caused enhanced adhesion at the early loading stages for all specimens. Nevertheless, such environm...

Analysis-Oriented Stress-Strain Model for Concrete under Combined FRP-Steel Confinement

Abstract: Extensive research has been conducted on fiber-reinforced polymer (FRP)-confined plain and RC columns, leading to a large number of stress–strain models. Most of these models have been developed for FRP-confined plain concrete and are thus applicable only to concrete in FRP-confined RC columns with a negligible amount of transverse steel reinforcement. The few models that have been developed for concrete under the combined confinement of FRP and transverse steel reinforcement are either inaccurate or too complex for direct use in design. This paper presents an accurate design-oriented stress–strain model for concrete under combined FRP-steel confinement in FRP-confined circular RC columns. The proposed model is formulated on the basis of extensive numerical results generated using an analysis-oriented stress–strain model recently proposed by the authors and properly captures the key characteristics of FRP-steel-confined concrete as revealed by existing test results. The model strikes a good balanc...

Stress-Strain Behavior of FRP-Confined Recycled Aggregate Concrete

Abstract: A large amount of research has been conducted on recycled aggregate concrete (RAC) due to its social, environmental, and economic significance. However, the in situ application of RAC has so far been mainly limited to nonstructural purposes, as the performance of RAC, in both the short and long term, is inferior to its normal concrete counterpart. Existing research has shown that the performance of concrete in compression members can be significantly enhanced through external confinement using steel tubes and fiber-reinforced polymer (FRP) tubes/wraps. Some recent research has examined the behavior of steel tubes filled with RAC, but the research on the behavior of RAC confined with FRP has been rather limited. Research is therefore needed to better understand the stress-strain behavior of and develop a reliable stress-strain model for FRP-confined RAC to facilitate the design of members with FRP-confined RAC. This paper presents the results of the first systematic experimental study on the axial ...

Axial Stress-Strain Model of CFRP-Confined Concrete under Monotonic and Cyclic Loading

Abstract: Experimental results of the axial stress-strain response of eighteen carbon-fiber-reinforced polymer (CFRP) confined circular, square, and rectangular column specimens when subjected to cyclic axial compression are presented and discussed. Guided by these test results and other test data reported in the technical literature, a constitutive axial stress-strain material model of CFRP-confined concrete under generalized loading is developed. The proposed model, which is composed of a monotonic envelope response and a cyclic response, accounts for a wide range of test parameters and assumes a more simplified approach than existing models available in the literature. The model covers all important parameters in a unified manner, and predicts both ascending and descending postpeak responses. In addition to its simplicity in application, despite little discrepancy, the model was able to reproduce the test results generated in the experimental part of this investigation and other test data reported in the...

Axially Loaded Reinforced Concrete Columns with a Square Section Partially Confined by Light GFRP Straps

Abstract: The study presents the experimental behavior of reinforced concrete columns strengthened externally by transverse glass fiber-reinforced polymer (GFRP) sheets. The columns had a square section and very low concrete strength. The internal steel reinforcement comprised sparse stirrups and longitudinal bars with two different qualities, S220 or B500C. The specimens were lightly confined by full wraps or partial GFRP straps. The straps were placed in between the existing steel stirrups. Three different widths of GFRP straps were examined. A series of plain concrete columns with identical GFRP strengthening was designed in order to assess the partial wrapping effects and compare them with reinforced concrete columns. The columns were subjected to axial compressive monotonic load up to failure. The achieved strength and ductility levels of the strengthened columns suggest that partial wrapping can efficiently upgrade the mechanical behavior of columns with a square section. Fully or partially GFRP wrapped columns with S220 slender bars require relatively higher GFRP strengthening than their counterparts with B500C columns to achieve similar ultimate strains.

Optimized FRP Wrapping Schemes for Circular Concrete Columns under Axial Compression

Abstract: This study investigates the behavior and failure modes of fiber-reinforced polymer (FRP) confined concrete wrapped with different FRP schemes, including fully wrapped, partially wrapped, and nonuniformly-wrapped concrete cylinders. By using the same amount of FRP, this study proposes a new wrapping scheme that provides a higher compressive strength and strain for FRP-confined concrete, in comparison with conventional fully wrapping schemes. A total of 33 specimens were cast and tested, with three of these specimens acting as reference specimens and the remaining specimens wrapped with different types of FRP (CFRP and GFRP) by different wrapping schemes. For specimens that belong to the descending branch type, the partially-wrapped specimens had a lower compressive strength but a higher axial strain as compared to the corresponding fully-wrapped specimens. In addition, the nonuniformly-wrapped specimens achieved both a higher compressive strength and axial strain in comparison with the fully-wrapped specimens. Furthermore, the partially-wrapping scheme changes the failure modes of the specimens and the angle of the failure surface. A new equation that can be used to predict the axial strain of concrete cylinders wrapped partially with FRP is proposed.

Behavior of Concrete-Filled FRP Tubes under Cyclic Axial Compression

Abstract: Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) are an attractive form of hybrid compression members incorporating FRP. CFFTs have several advantages over traditional column forms, including their excellent corrosion resistance and ductility. Much research has been conducted on CFFTs over recent years, but no systematic experimental study has been concerned with the cyclic axial compressive behavior of CFFTs with a filament-wound FRP tube; such studies are needed for the development of a cyclic stress-strain model for the concrete in CFFTs. This paper therefore presents an experimental study on the behavior of circular CFFTs under cyclic axial compression. The experimental program included the strength of concrete as a key variable so that it also provides a much needed supplement to the very limited existing research on the cyclic compressive behavior of FRP-confined high-strength concrete (HSC). The test results are compared with a monotonic stress-strain model and a cyclic stress-strain model for FRP-confined concrete, both of which have been based on test databases that are limited to concrete confined with an FRP wrap and include only a small number of tests for HSC. The test results show that the cyclic axial stress-strain behavior of concrete in CFFTs is generally similar to that of concrete confined by an FRP wrap. The test results also show that the monotonic stress-strain model perform reasonably well for HSC in CFFTs, but revisions to the cyclic stress-strain model are needed before it can provide accurate predictions for HSC in cyclically loaded CFFTs.

Compressive Behavior of Prestressed High-Strength Concrete-Filled Aramid FRP Tube Columns: Experimental Observations

Abstract: This paper presents an experimental investigation on the influence of prestressing fiber reinforced polymer (FRP) confining shell on the axial compressive behavior of high-strength concrete (HSC)-filled FRP tube columns. A total of 24 aramid FRP (AFRP)-confined concrete specimens with circular cross-sections were manufactured in the form of concrete-filled FRP tubes (CFFTs). The influence of the amount of prestress was examined by preparing the specimens with three different levels of lateral prestress ranging from 4.1 to 7.3 MPa. In addition to the prestressed specimens, companion specimens with no applied prestress were manufactured and tested to establish reference values. Results of the experimental study indicate that the influence of prestress on compressive strength is significant, with an increase in ultimate strength observed in all prestressed specimens compared to that of nonprestressed specimens. On the other hand, the influence of prestress on axial strain was found to be dependent on...

Monotonic and Cyclic Compression Tests on Concrete Confined with PET-FRP

Abstract: Given developments in the construction material industry, existing knowledge of concrete confined with fiber-reinforced polymer (FRP) must be validated for newly developed FRP-type materials. Polyethylene terephthalate (PET), which has a high ultimate tensile strain, is a relatively new type of fiber. Given the limited number of studies on PET-FRP, the goal of this study is to observe and define the mechanical behavior of PET-FRP-confined concrete specimens subjected to monotonic/cyclic compression loading. In this study, the behavior of concrete confined with PET-FRP is compared with the behavior of concrete confined with other types of FRP. The general form of the compression stress-strain relationship of PET-FRP-confined concrete consists of two parts that are connected with a transition part, which is similar to concrete confined with other FRP types. Additionally, to understand whether available models are able to predict the compressive behavior of PET-FRP-confined concrete, the predictions ...

Compressive Strength of CFRP Composites Used for Strengthening of RC Columns: Comparative Evaluation of EBR and Grooving Methods

Abstract: In the present study, application of carbon-fiber-reinforced polymer (CFRP) composites with fibers aligned along the column’s axis to improve compressive strength of reinforced concrete (RC) columns has been investigated. Global buckling of fiber-reinforce polymer (FRP) composite with fibers along the column’s axis may result in debonding of FRP from the column’s surface, and thus, the compressive load carrying capacity of the strengthened column would not be increased considerably. To limit the global buckling of composite under compression, a newly introduced strengthening method, named as grooving method (GM), was utilized in the present study and compared with externally bonded reinforcement (EBR) method using conventional surface preparation and near surface mounted (NSM) method. For this purpose, 22 circular RC columns with 150-mm diameter and 500-mm height were tested under uniaxial compression. Two techniques of GM named as externally bonded reinforcement on grooves (EBROG, to be pronounce...

Analytical modeling of masonry-infilled RC frames retrofitted with textile-reinforced mortar

Abstract: This paper proposes an analytical approach for modeling the behavior of textile-reinforced mortar (TRM)-strengthened masonry-infilled reinforced-concrete (RC) frames under seismic loading. The model falls into the discrete diagonal-element type and is based on the use of single-strut and single-tie elements to represent the infill panel. It builds on the results of past experimental studies by the writers, in which the application of TRM jacketing was effective for seismic retrofitting of masonry-infilled RC frames. The model is implemented in a nonlinear finite-element code, with the parameters of the diagonal elements being determined from a series of tests on TRM coupons and masonry specimens. The results of the numerical analyses are compared with the experimental data of cyclic tests on 3-story masonry infilled RC frames (as-built and after retrofitting). The model developed in this paper adequately accounts for the TRM-strengthening contribution to the global response of masonry-infilled frames.

Flexural Behavior of Sandwich Panels with Bio-FRP Skins Made of Flax Fibers and Epoxidized Pine-Oil Resin

Abstract: Structural sandwich panels with fiber-reinforced polymer (FRP) skins are becoming an increasingly popular system because of their remarkable light weight, ease and speed of installation, and high thermal insulation capabilities. This paper looks into the potential for replacing conventional glass fiber–reinforced polymer (GFRP) skins with bio-based skins made of unidirectional flax fibers and a resin blend consisting of epoxidized pine oil. A comprehensive material testing program was first carried out on 70 standard tension and compression coupons. Then, 36 sandwich panels of 1,000×150×75 mm were tested under four-point loading. The number of flax fiber–reinforced polymer layers of skin was varied from one to five [in comparison to one layer of GFRP, an epoxidized pine oil resin blend to epoxy, and the wet layup (WL) fabrication method to vacuum bag molding]. Sandwich panels with three layers of flax fibers provided equivalent strength and stiffness, but better deformability, compared to panels ...

Performance of Concrete-Filled FRP Tubes under Field Close-in Blast Loading

Abstract: Blasts, whether deliberate or accidental, are a great concern for a society’s critical infrastructure as well as expeditionary military installations. Improvement to existing construction methods that enhance blast resilience can ultimately save lives and property. Concrete-filled FRP tubes (CFFTs) are known to improve a conventional reinforced concrete member’s resistance to traditional loads by strengthening, protecting, and confining the reinforced concrete core. Glass fibre reinforced polymer (GFRP) tubes are readily available in a variety of sizes suitable for use as a stay-in-place structural formwork for midsized reinforced concrete members, which can simplify and expedite construction. These advantages point to CFFTs’ great potential in resisting blast loads. This study aimed to quantify the advantages of encasing a reinforced concrete member with a GFRP tube subjected to close-in blast loading and to investigate the effects of the presence of the tube, the internal steel reinforcement rat...

Finite Element Modeling of Insulated FRP-Strengthened RC Beams Exposed to Fire

Abstract: This paper presents a finite element (FE) model for the thermo-mechanical analysis of insulated FRP-strengthened reinforced concrete (RC) beams exposed to fire. In the model, the effects of loading, thermal expansion of materials, and degradations in both the mechanical properties of materials and the bond behavior at FRP-to-concrete and steel-to-concrete interfaces due to elevated temperatures are all considered. The validity of the FE model is demonstrated through comparisons of FE predictions with results from existing standard fire tests on insulated FRP-strengthened RC beams.

Influence of Slenderness on Stress-Strain Behavior of Concrete-Filled FRP Tubes: Experimental Study

Abstract: Concrete-filled fiber reinforced polymer (FRP) tubes (CFFTs) have received significant research attention over the last two decades, with recent experimental studies identifying significant benefits of CFFTs filled with high-strength concretes (HSC). However, many test parameters of high-strength CFFTs, such as specimen slenderness, remain experimentally limited. This paper presents an experimental investigation on the axial compressive behavior of 33 monotonically loaded circular normal-strength and high-strength CFFTs (NSCFFTs and HSCFFTs). The influence of specimen slenderness is investigated on test specimens with height-to-diameter ratios (H/D) of 1, 2, 3, and 5. The CFFT specimens were instrumented with numerous lateral strain gauges to examine the development of hoop strains along the specimen height and around specimen perimeter. The experimentally recorded stress-strain relationships are presented graphically and the ultimate axial stresses and strains, and FRP tube hoop strains at rupture are tabulated. The results indicate that specimens with a height-to-diameter ratio (H/D) of 1 outperform specimens with a H/D ratio of 2 to 5, with significantly increased strength and strain enhancements. The influence of slenderness on specimens with a H/D ratio between 2 and 5 was found to be significant in regards to axial strain enhancement, with a decrease observed as specimen slenderness increased. Conversely, the influence of slenderness on axial strength enhancement of specimens with a H/D ratio between 2 and 5 was found to be negligible. The strain results indicate that hoop rupture strains along the height of CFFTs become more uniform for specimens with higher amounts of confinement. On the other hand, the variation of hoop strains around the perimeter of CFFTs was not observed to be significantly influenced by slenderness, concrete strength or amount of confinement.

Experimental and Numerical Investigation of the FRP Shear Mechanism for Concrete Sandwich Panels

Abstract: This paper investigates the composite action of 46 segments representing precast concrete sandwich panels (PCSPs) using a fiber-reinforced polymer [FRP; specifically, a carbon fiber–reinforced polymer (CFRP)] grid/rigid foam as a shear mechanism. The experimental aspect of the research reported in this paper examined the effect of various parameters believed to affect the shear flow strength for this CFRP grid/foam system. The parameters that were considered are the spacing between vertical lines of CFRP grids and the thickness of the rigid foam. Results of the experimental aspect of the research reported in this paper indicated that increasing the spacing between vertical lines of CFRP grid increase the overall shear flow strengths due to the increase of the bonded contact area of the rigid foam to the concrete surface. However, the overall shear stresses were decreased due to the increase of this interface surface area. Test results also indicated that increasing the rigid foam thickness decreas...

New Anchorage Technique for FRP Shear-Strengthened RC T-Beams Using CFRP Rope

Abstract: This study investigates the effectiveness of a new anchorage technique for fiber-reinforced polymer (FRP) shear-strengthened reinforced concrete T-beams using carbon fiber-reinforced polymer (CFRP) ropes. The rope is a bundle of flexible CFRP strands held together using a thin tissue net. In this technique, holes are drilled through the web at the web-flange intersection, where the CFRP ropes are inserted and flared onto the two free ends of the U-wrap scheme. This converts the U-wrap scheme to a full-wrap scheme. The experimental program includes three series based on the number of steel stirrups. No steel stirrups are provided in the first series, whereas the spacing between steel stirrups is 260 and 175 mm in the second and the third series, respectively. Each series includes a control specimen, with no external CFRP for shear strengthening, a specimen strengthened with CFRP sheets, a specimen strengthened with CFRP L-strips, and a specimen strengthened with CFRP L-strips and anchored with CFRP...

Comparative Study on Static and Fatigue Performances of Pultruded GFRP Joints Using Ordinary and Blind Bolts

Abstract: Bolted connections are often used in pultruded glass fiber reinforced polymer (GFRP) structures. Blind bolts, which require installation from one side only, become convenient when access is limited to tighten the ordinary bolts, especially for tubular GFRP sections. This paper presents the results of a comparative study on pultruded GFRP double-lap joints using ordinary bolts and blind bolts. Static experiments were conducted on pultruded GFRP double-lap joints with two columns of bolts, whereas the number of rows varied by one, two, and three. The static behaviors of ordinary bolted and blind bolted joints were compared in terms of load-displacement response, failure modes, and failure load. Then, constant amplitude fatigue tests were carried out on the double-lap joints with two bolts in a row. The maximum fatigue load varied from 30 to 80% of the static failure load of the corresponding joint. The fatigue life of each specimen was recorded and S-N curve was obtained. It was found that the stati...