FRP Type Research Articles

BP-ANN based bond strength prediction for FRP reinforced concrete at high temperature

In view of the difficulty in establishing a mathematical model to characterize the interfacial performance of FRP reinforced concrete at high temperature, the back-propagation neural network (BP-ANN) paradigm is used as a computational tool for capturing the bond behavior in this paper. Through taking temperature, FRP type, surface form, FRP bar diameter, anchorage length, failure mode, concrete compressive strength and normalized concrete cover thickness as input variables and the interface bond strength as output objective, the BP-ANN model has been established, well-trained and tested by using 151 sets of pull-out experimental data of FRP reinforced concrete at different temperatures in the literatures. The prediction accuracy of BP-ANN model has been evaluated by comparing the training and testing values with experimental results. The more advantages in universality of BP-ANN model than the currently available mathematical models are demonstrated by comparing their applicable scopes and computational errors.

Axial compressive behavior of seawater sea-sand coral aggregate concrete-filled circular FRP-steel composite tube columns

To better directly apply undisturbed seawater, sea sand and coral aggregates to ocean engineering, a new type of circular concrete-filled FRP-steel composite tube structure was designed. The core concrete is composed of sea sand as a fine aggregate, coral as a coarse aggregate and seawater as the mixing water. The FRP-steel composite tube is formed by wrapping FRP on the inner and outer walls of the steel tube. Thirty-six new circular seawater sea sand coral aggregate concrete (SSCC)-filled FRP-steel composite tube columns (SCCFCTs) were subjected to monotonic axial compression tests. The main test variables were the steel tube diameter-thickness ratio, FRP layers and FRP type. According to the different diameter-thickness ratios, the final failure mode of the specimen was divided into shear failure and extrusion expansion failure. The increase in the number of FRP layers and the decrease in the diameter-thickness ratio of the steel tube led to a significant improvement in the ultimate stress and strain of the specimens. When the other test parameters were kept the same, the CFRP-confined specimens had a higher ultimate strength and the BFRP-confined specimens had a slightly higher ultimate deformation capacity. Finally, the versatility of the existing model for the test data was evaluated and the complete stress–strain curve of the SCCFCTs under compression was simulated. The calculated results were satisfactory.

Tensile behavior of FRP bar butt joints built with new FRP sleeves

This paper reports a comprehensive investigation on the tensile behavior of FRP bar butt joints built with new FRP sleeves. The simplified bond-slip constitutive relationship between FRP bars and bonding medium was firstly established by using the existing research results. Based on five proposed assumptions, the stress–strain analysis of the FRP bar butt joint was performed on the FRP bar, bonding medium and sleeve under tensile load. The bond-slip behavior and the shear force between FRP bars and bonding medium were discussed in detail. According to the stress–strain analysis, the key design parameters of the FRP sleeve and the anchor length of FRP bars were determined, which is also verified by comparing test data. According to the design parameter and anchor length, two types of FRP sleeves with two different internal structures and lengths were designed, and then these FRP sleeves were made of GFRP by professional manufacturers. In addition, the axial tensile tests were conducted on a total of 10 BFRP bar butt joints, GFRP bar butt joints and CFRP bar butt joints which are connected by the proposed GFRP sleeves. Based on the test results, the failure modes of various FRP bar butt joints built with GFRP sleeves were observed, and the corresponding tensile load–displacement curves, maximum tensile load and strain were analyzed. Finally, it is found that all fractures occur on the connected FRP bars instead of the GFRP sleeves, which indicates that various FRP bars can be effectively connected by the two types of GFRP sleeves. The load–displacement curves of the GFRP sleeves exhibit a small linear elastic deformation before the FRP bars rupture. The maximum elongated length of the GFRP sleeves is only 13% of the maximum tensile displacement of FRP bar butt joints uner tensile load, while the maximum circumferential strain of GFRP sleeves is about 41.72% of their corresponding longitudinal strain.

Fiber Reinforced Polymer as Wood Roof-to-Wall Connections to Withstand Hurricane Wind Loads

Light wood roof-to-wall connections are vulnerable when subjected to high-speed winds. In lieu of traditional metal connections, the present finite element analysis (FEA) study focuses on the use of epoxy and easy-to-apply, noncorrosive FRP ties to connect the roof and the walls in wood frames. The FEA models of the wood roof-to-wall GFRP connection were validated with an experimental study in the literature. Subsequently parametric study was performed on the validated FEA models. Parameters considered were the addition of anchorages to secure the GFRP ties for FEA models of shear and uplift tests, and various FRP types. Wood roof-to-wall connection uplift model was subjected to monotonic cyclic loading to simulate the effect of wind load. In addition, carbon and basalt FRP ties were also examined under monotonic cyclic loading. To evaluate the efficiency of GFRP ties with and without anchorages, the shear and uplift design loads specified in ASCE 7-16 were calculated. Finally, a formula was proposed to approximate the shear strength of GFRP connection in comparison with double shear bolted metal plate connections. The FEA models and experimental results were in good agreement. The finite element results revealed that anchorage increased the uplift load capacity by 15% but the increase in shear capacity was insignificant. Comparing glass, carbon, and basalt FRP ties, BFRP was superior in deformation capacity and CFRP provided more stiffness on uplift test simulation. GFRP ties were found to be approximately nine times stronger in shear and two times stronger in uplift resistance than hurricane clips. Finally, the proposed formula could predict the shear strength of GFRP tie connection which in turns contributes to the design and future research.

Compressive performance of high-strength seawater and sea sand concrete-filled circular FRP-steel composite tube columns

A new high-strength seawater and sea sand concrete (HSSC)-filled circular FRP-steel composite tube (HFSCT) structure, consisting of an internal FRP, carbon steel tube and external FRP, was investigated in this study. Thirty-six specimens were tested to investigate the axial behaviour of HFSCTs. FRPs and steel tubes were used as the test parameters. The results indicate that the specimen failure modes change from shear failure to waist drum failure based on the steel tube thickness (4.5–7.0 mm). An increase in the FRP and steel tube significantly affect the axial compressive behaviour of HFSCTs. The ultimate stress of specimens confined by CFRPs is better than those confined by BFRPs; however, specimens confined by BFRPs show excellent ultimate deformation ability. Additionally, 155 axial compressive data samples of concrete-filled circular FRP-steel composite tube columns were collected to establish the test database. The calculation formulas for the ultimate stress, ultimate strain, peak stress and peak strain were developed by considering the efficiency of different FRP types in lateral confinement, which possess a more accurate applicability for concrete-filled circular FRP-steel composite tube columns. Last, a complete calculation model was recommended to predict the full nominal stress–strain curve and accurately reflect the stress–strain behaviour.

Experimental study on the flexural behavior of RC beams strengthened with prestressed BFRP laminates

In this study, the flexural behavior of RC beams strengthened with prestressed basalt FRP (BFRP) laminates was investigated. Compared with the conventional carbon FRP (CFRP) laminate, BFRP exhibits a larger failure strain but lower modulus, in addition to its high strength and prominent creep rupture behavior; this makes BFRP a suitable option for cost-effective strengthening of existing beams. Nine specimens were prepared to investigate the effects of the FRP type, laminate thickness, strengthening method, reinforcement ratio, prestressing level, and adhesive on the flexural behavior of RC beams. The differences in the failure mode, L-D curve, cracking behavior, and strain development of concrete, steel, and FRP laminate were analyzed. The results demonstrated that specimen strengthened with BFRP laminate could achieve 85% of the loading capacity of the specimen strengthened with CFRP laminate under the same laminate section and but ensured a superior crack control effect and ductility. Meanwhile, a higher prestressing level led to a higher material utilization of BFRP, and the prestressing method lowered the reinforcement ratio effectively. Moreover, the bonded system had a better crack control effect and higher laminate strength utilization ratio than the unbonded system did.

Guidelines for flexural design of FRP reinforced concrete beams

This paper investigates the effects of different parameters on the live load carrying capacity of concrete beams reinforced with FRP bars. The author performed a parametric study utilizing an innovative numerical approach to inspect the effects of multiple variables such as reinforcement ratio, concrete compressive strength, span to depth ratio, FRP type, and bar diameter on load carrying capacity of FRP reinforced concrete beams. This study concluded that unless the span to height ratio is smaller than 8, tension-controlled sections are impractical as they do not meet code requirements for serviceability. In addition, it is recommended to use higher reinforcement ratios when using larger span to depth ratios and/or when using CFRP reinforcing bars. Moreover, larger number of bars with small diameter is more practical than fewer large diameter bars. Furthermore, this research suggests that increasing the concrete compressive strength is associated with a significant increase in the ultimate flexural capacity of FRP reinforced beams.

Behaviors of Large-Rupture-Strain Fiber-Reinforced Polymer Strengthened Reinforced Concrete Beams Under Static and Impact Loads

Reinforced concrete (RC) structures may be damaged seriously when subjected to impact loading, and it is necessary to strengthen existing structures to improve their impact resistance. Large-rupture-strain FRP (LRS-FRP) is a promising material to strengthen RC structures under impact because of its good deformation capacity. The paper conducted experimental studies on performances of LRS-FRP strengthened RC beams under static and impact loads. The influences of FRP types, impact weight and velocity, and whether applying end anchorages on the strengthening efficiency were investigated. The end anchorage LRS-FRP strengthening system reduced the maximum deflection and damage of strengthened beam significantly. However, the end anchorage was more susceptible to damage and failure under impact. Therefore, the end anchorage and the EA-FRP connection should be designed with caution for impact condition.

Effect of Different Bond Parameters on the Mechanical Properties of FRP and Concrete Interface.

This paper presents double shear tests performed to investigate factors influencing the bond behavior between basalt fiber-reinforced polymer (BFRP), glass fiber-reinforced polymer (GFRP) laminate, and concrete blocks. In detail, thirty-six twin concrete blocks strengthened with the aforementioned FRP types were tested to evaluate the influence of FRP length, width, and thickness, and their bonding behavior. The 2D-DIC (digital image correlation) technique and several strain gauges bonded along the laminate were used to measure the strain distributions of the FRP-to-concrete interface. The failure mode, ultimate load, load–slip, strain distribution, and bond–slip relationships between the laminates and concrete were analyzed. Furthermore, bond–slip curves were compared with some other existing literature models. The results from the experiment showed that the ultimate load, peak bond stress, and slip increased with the increase in the BFRP and GFRP laminates length, width, and thickness. The values of peak shear stress and the corresponding maximum shear slip were significantly different because of the above-mentioned factors’ influence on them. The bond interface that contributes to the bearing of the shear load may grow to an extent and later shift from the loaded end when debonding progresses. Finally, the fractured surfaces of the failed FRP laminates were examined using scanning electron microscope (SEM), revealing that FRP rupture, debonding in concrete, and debonding in an adhesive–concrete interface were the main failure types.

Investigation on bond performance between different types of FRP -reinforcedrebars and concrete

In this paper the test results of a study on the bond behaviour of FRP bars to finegrained concrete are presented. Five series of concrete cylinders reinforced with basalt-reinforced polymer (BFRP) and glass fiber-reinforced polymer (GFRP) bars are tested in direct pullout conditions. As well as two series with steel bars are tested for comparison. For each specimen, the bond failure mode, the average bond strength, the initial bond stiffness, and the load–strain relationship curves and bar relative extension were analysed. Test results demonstrate the promise of using the FRP bars as an alternative to the steel bars in reinforcing concrete elements.

A novel seawater and sea sand concrete filled FRP-carbon steel composite tube column: Concept and behaviour

A novel type of seawater and sea sand concrete (SSC)-filled FRP-carbon steel composite tube (SFSCT) column composed of FRP-carbon steel composite tubes and core-filled SSC is proposed. The FRP carbon steel composite tube is made by wrapping FRP sheets around the inner and outer walls of steel tubes to isolate the transport of chloride ions from the external corrosive environment and the internal SSC, respectively. A total of 36 SFSCT columns were tested under axial compression to investigate the axial compressive performance. The test parameters include the FRP thickness, FRP type and steel tube thickness. The test results show that internal FRPs and external FRPs can work together and effectively improve the bearing and deformation capacities of the structure under axial compression. Compared with concrete-filled steel tube (CFST) columns, with different numbers of FRP wrapping layers, the strength of the SFSCT columns can be increased by 11.7–66.5%. The confinement effect of CFRP is better than that of BFRP. Compared with the steel tube thickness, the FRP type and FRP thickness have a more significant influence on the stress-strain behaviour of SFSCT columns.

Mechanical, Thermal and Morphological Characterization of Basalt Fibre Composite- A Review

In fibre reinforced polymers as well as fibre reinforced mortar, basalt fibre has been made an important replacement to glass, polymeric fibre and steel after its exploration. Now a day’s BF (Basalt Fibre) has shown a rise in its attention as a replacement for glass and CF (Carbon Fibre). Basalt is a type of rock mainly dark coloured volcanic rock, which is formed after cooling lava from the volcano. In the production of fibre, basalt rocks having SiO2 (Silicon Dioxide) content of 46% is mainly used. Although basalt rock is found having various proportion of materials, only particular type of basalt rocks is used. The recently develop BFRP (Basalt Fibre Reinforced Polymer) manufactured from naturally occurring volcanic rooks shows tremendous advantages for example its recyclable, eco-friendly or does not harm the eco-system, consumes less energy in productions and as compared other types of FRP, has high performance to cost ratio. Therefore, pertaining to these advantages basalt fibre reinforced fibre has become a more reliable material to use in civil works or buildings various infrastructure. As steel material comes in contact to the corrosion, BFRP is preferred over steel as it has resistance to chemical corrosion as well as it is light weight also.

FE modeling of concrete beams and columns reinforced with FRP composites

Compression and flexure members such as columns and beams are critical in a structure as its failure could lead to the collapse of the structure. In the present work, numerical analysis of square and circle short columns, and reinforced concrete (RC) beams reinforced with fiber reinforced polymer composites are carried out. This work is divided into two parts. In the first part, numerical study of axial behavior of square and circular concrete columns reinforced with Glass Fiber Reinforced Polymer (GFRP) and Basalt Fiber Reinforced Polymer (BFRP)bars and spiral, and Carbon Fiber Reinforced Polymer (CFRP) wraps is conducted. The results of the first part showed that the axial capacity of the circular RC columns reinforced with GFRP increases with the increase of the longitudinal reinforcement ratio. In addition, the results of the numerical analysis showed good correlation with the experimental ones. An interaction diagram for BFRP RC columns is also developed with considering various eccentricities. The results of numerical modeling of RC columns strengthened with CFRP wraps revealed that the number and the spacing between the CFRP wraps provide different levels of ductility enhancement to the column. For the cases considered in this study, column with two middle closely spaced CFRP wraps demonstrated the best performance. In the second part of this research, flexural behavior of RC beams reinforced with BFRP, GFRP and CFRP bars is investigated along with validation of the numerical model with the experimental tests. The results resembled the experimental observations that indicate significant effect of the FRP bar diameter and type ont he flexural capacity of the RC beams. It was also shown that Increasing the number of bars while keeping the same reinforcement ratio enhanced the stiffness of the RC beam.

Distortional analysis of laminated composite box girder: A review

With increase of maintenance and durability issues in bridge industry have motivated researchers to explore laminated composite FRP box girders in bridges. Box beams have good eccentric load distribution and better stability characteristics due to their high torsional stiffness. The combination of box-girder with FRP is perfect for light weight long span bridges. The potential for application of FRP box section has been particularly high in deployable bridges used in defense, temporary bridges, emergency replacement bridges, FOB and short span light loaded vehicular bridges etc. The objective of this paper is to provide highlights of the most important references related to the development of current guide specifications for laminated composite FRP box girder/beam and to understand distortional behavior of thin walled box girder. In this study, an attempt is made to study the significance of the laminated composite FRP box girder & type, distortion effect on thin walled box girder, methods used for distortional analysis of box girder. There are very limited studies in the field of laminated composite FRP box girder. Most of the studies are on distortional behavior of steel box girder. There is not detailed study available on distortional behavior of laminated composite FRP box girder. Thus, there appears to be a dearth of information on the distortional behavior of laminated composite FRP box girder. The present state of art has motivated the interest to contribute towards a better understanding of distortional behavior of laminated composite FRP box girders.

Finite element modeling of creep behavior of FRP-externally strengthened reinforced concrete beams

In this study, a nonlinear numerical analysis is carried out to predict the creep response of reinforced concrete (RC) beams externally strengthened using carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP) laminates. The beams are tested under static four-point bending; the level of sustained service load is equal to 59% of the ultimate capacities of the un-strengthened beams. The Burger rheological model is used to evaluate the flexural creep response (compressive and tensile creep) and then to validate the findings with experimental results. It is shown that the Burger model effectively predicts the creep of CFRP-bonded RC. Furthermore, parametric studies are performed to investigate the effects of: three fiber orientations of CFRP composites (0°, 45° and 90°), the CFRP thickness, and the type of FRP (CFRP and GFRP) on the flexural creep of FRP-externally retrofitted RC beams based on the Burger rheological model. According to the numerical results, a major reduction in creep strain is obtained with the 45° orientation of CFRP. An increase in CFRP-thickness significantly lowers the creep strain. Moreover, the CFRP laminates prove to be more effective than GFRP in improving the creep response.

Effects of CFRP/GFRP flexural retrofitting on reducing seismic damage of reinforced concrete frames: a comparative study

Flexural retrofitting of structures using glass/carbon fibre reinforced polymer (GFRP/CFRP) has been widely investigated. However, comparison on the effects of GFRP/CFRP flexural retrofitting at plastic hinges on reducing the potential seismic damage of reinforced concrete (RC) structures is hardly found in the literature and is thus aimed by this study. Toward this aim, two-, four- and eight-storey RC frames were chosen to represent different building structures. These frames were then retrofitted by CFRP/GFRP bonded sheets to increase flexural capacities of beams and columns at plastic hinge regions. The original, CFRP and GFRP retrofitted frames were modelled using nonlinear hysteresis elements. After verification, nonlinear time-history analyses of those frames under various seismic intensities were carried out, followed by cumulative damage analyses. Damage states of original, CFRP and GFRP retrofitted frames were compared with one another. The obtained comparison results reaffirmed the effectiveness of CFRP and GFRP flexural retrofitting. More importantly, obtained results indicated that CFRP is more effective than GFRP on reducing seismic damage of RC structures when they are employed for flexural retrofitting. These outcomes can help in deciding on the FRP type to be used for flexural retrofitting of RC structures.

Bond-slip behaviour between FRP tubes and seawater sea sand concrete

In the present study the bond-slip behavior between FRP tubes and seawater sea sand concrete is studied using push-out tests. Pultruded and filament winding FRP tubes with different fibre orientations and diameter-to-thickness ratios (D/t) were constructed to investigate the effect of confinement pressure on the bond behaviour. Moreover, to study the effect of fibre type, three types of FRP (i.e.; GFRP, CFRP and BFRP) were used. In addition, the mechanical and chemical bond strength of concrete filled FRP tubes were quantified and compared. CFRP and BFRP tubes showed the highest and the lowest bond strengths, respectively. Furthermore, it was concluded that the real confinement pressure of the tubes has a significant effect on the bond strength: the greater the real confinement pressure, the larger the bond strength (i.e. the tubes with smaller D/t ratio and fibres orientated in 89° showed greater bond strength compared to the tubes with larger D/t and different fibres orientations). Repeating the push-out test for four times, for each sample, showed that the slip starts earlier by increasing the number of repetition, while the bond strength remained almost the same. This shows that the bond strength of tubes is mostly governed by the friction (confinement pressure) rather than the adhesion (chemical bond).

Effectiveness of Various Techniques Using FRP for the Strengthening of R. C. Beams with Tension Lap Splices

This paper presents an experimental program conducted to investigate the flexural performance of RC beams with tension reinforcement lap splice strengthened using externally bonded FRP different techniques in splice region. The specimens were reinforced on the tension side with four deformed bars spliced at mid span. The tested beams are of 3200 mm total length and 250*120 mm cross section, tested in positive bending. The considered parameters were splice length, type of FRP (glass or carbon), strengthening techniques in splice region (externally confine strips around cross section, Near Surface Mounted technique "NSM" stirrups, externally bonded sheets or bars on the tension face, number of GFRP strips layers (one layer, two layers, and three layers), and shape of NSM stirrups (Box or U shape). No additional anchorage mechanism or bonding methodology was applied for the FRP strips on the concrete except the epoxy adhesive. The effect of these factors on the failure of modes, the ultimate load, the bond strength and that the ductility were investigated. The results indicated that all applied strengthening techniques were efficient in improving the bond strength of the lap splices, the ductility, and the load-deflection behavior of the tested beams, especially when strips were installed over the splice region. This study approved that NSM technique gave more prominent simplicity of employ.

Comparison of CFRP and GFRP Wraps on Reducing Seismic Damage of Deficient Reinforced Concrete Structures

The effectiveness of glass/carbon fibre reinforced polymer (GFRP/CFRP) wraps at plastic hinges has been confirmed; however, their respective effectiveness on reducing seismic damage of deficient reinforced concrete structures has hardly been compared. The current study aims at this comparison, providing some useful information to realise the better FRP for confinement retrofitting of reinforced concrete structures poorly confined due to deficient transverse reinforcement. Four- and eight-storey poorly confined reinforced concrete frames were selected to represent low- and mid-rise building structures, respectively. These deficient frames were then strengthened by CFRP/GFRP wraps via external confinement. Inelastic time history and cumulative damage analyses of the original, CFRP- and GFRP-retrofitted frames were performed. The damages of CFRP- and GFRP-retrofitted frames were compared with each other and with the damage of the original frame. The comparison results show that CFRP and GFRP wraps at plastic hinges substantially reduce damage. More importantly, GFRP wraps are more effective than CFRP wraps by reducing a higher amount of the cumulative damage index. The conclusions can help in deciding on the type of FRP to be used for confinement retrofitting of RC structures poorly confined due to deficient transverse reinforcement.

Seismic Assessment and Retrofitting of a Heritage Brick Masonry Building Using FRP

Uttarakhand in the foothills of Himalayas is considered to be one of the most tectonically active regions of northern India as it had experienced several destructive earthquakes such as Pithoragarh (1980), Uttarkashi (1991), Chamoli (1999) and Gopeshwar (2005). The state of Uttar Pradesh (now Uttarakhand) being the center of activity during British regime is having numerous historical brick masonry structures such as churches, missionaries, hospitals, administrative building and educational institutions required to be safeguarded against catastrophic future earthquakes. One such building: Forest Research Institute Dehradun which suffered extensive damages during the Uttarkashi earthquake has been considered for seismic vulnerability assessment and achieving a generalized retrofitting strategy for the region which can be extrapolated globally. Structural assessment by non-linear static analysis has been carried out for FRP retrofitted and an un-retrofitted building using FEM. Different types of FRP has been modeled numerically as wrapped around the piers of huge brick masonry structure and analyzed under site specific earthquake loading which reported in an improved performance of strengthened structure.