Types Of Fiber Reinforced Polymer Research Articles

Responsibility of NSM FRP Bars in Shear Fortifying of Strengthened R.C. Beams

Several R.C. (reinforced concrete) beams research have been surveyed in the shear area using fiber-reinforced polymer (FRP) composites and ended in collapse in the shear due to the separation of the FRP. The NSM method utilizing fiber fortified polymer (FRP) bars is currently an entrenched method for the reinforced concrete strengthening structures. The main proposal of this search is to look into experimentally for strengthening shear behavior with RC NSM carbon fiber reinforced polymer (CFRP) bars and exhibit the numerical outcomes for strengthened beams in shear with various FRP types; carbon fiber bar (CFRP), aramid fiber bar (AFRP), and glass fiber bar (GFRP) in shear. Three-dimensional beam models using finite element method are formed with software ANSYS-2013 to study the behavior of FRP in strengthening. Finally, a simply proposed equation is produced to estimate the shear strengthening capacity. The proposed equation affirms the exactness and viability of the experimental numerical result.

Shear capacity of unbonded post-tensioned concrete T-beams strengthened with CFRP and GFRP U-wraps

Existing codes and design guidelines have not mentioned a procedure to calculate the shear resistance of unbonded post-tensioned concrete beams strengthened with fiber reinforced polymer (FRP) sheets. Up to date, the number of studies about the shear behaviour of post-tensioned concrete beams strengthened with FRP sheets in shear is very limited, particularly for unbonded post-tensioned beams. The effect of many factors on the shear resistance of such the beams has not been well investigated, for example, fiber factors (the type of fiber, the strengthening scheme, and the number of layers), the concrete strength, and the ratio of the shear span to effective depth. The study deals with the shear behaviour of unbonded post-tensioned beams strengthened with FRP U-wraps. The experiment consists of twenty-two post-tensioned beams with T section and unbonded tendons. The variables include concrete strength, number of FRP layers, FRP U-wraps scheme (continuous and spaced), types of FRP, and varied shear span to effective depth. The experimental results have shown that the FRP shear strengthening is more effective with higher concrete strength. The number of FRP layers, strengthening scheme, and type of FRP have a slight influence on the shear resistance of the beams but they significantly affect the ultimate deformation of the FRP sheets. The efficiency of FRP U-wraps considerably reduces with a reduction of the shear span to effective depth. As a result, the existing design guides may not yield reliable predictions since they have not considered this ratio. Moreover, a semi-empirical model is proposed to predict the shear resistance of unbonded post-tensioned beams strengthened with FRP U-wraps. The predictions from the proposed model fit well with the experimental results from other studies.

Progressive failure prediction of FRP tubes by modified damage model

ABSTRACTAn accurate material model plays a significant role in predicting the progressive damage of fibre-reinforced polymer (FRP) structures. A modified bilinear constitutive model is proposed to describe the stiffness degradation caused by the progressive intra-lamina damage, and has been embedded into the commercial software ABAQUS through the subroutine VUMAT. All coefficients, corresponding to various damage mechanisms, could be identified by specimen tests under typical loading conditions. As a case study, the compression test of a FRP composite tube is carried out and compared with the simulation results obtained by this model to verify the accuracy and versatility in predicting impact energy absorption and peak force as well as failure modes. Compared with other published simulation methods, the proposed model has better versatility, in which the progressive damage control coefficients are stable and insensitive to different types of FRPs.

Performance and dynamic behaviour of FRP strengthened CFST members subjected to lateral impact

Due to the increasing popularity of concrete-filled steel tubular (CFST) members, there will be more chances of vehicles/vessels or terrorist attacks on these structures in near future. Fibre-reinforced polymer (FRP) strengthening can be an effective option to reduce impact damage or failure of CFST members. However, existing knowledge is very limited in understanding the behaviour of FRP strengthened CFST structures under lateral impact loading. This paper outlines drop hammer impact test results of a series of experimental programs of bare and FRP strengthened CFST specimens. A total of sixteen CFST specimens were prepared and tested under lateral impact at their mid-span. The results indicate that permanent lateral displacement of CFST members can be reduced up to 18.2% by externally bonded FRP sheets. The effects of FRP type, FRP wrapping direction, carbon fibre-reinforced polymer (CFRP) wrapping layers, wrapping length, and impact velocity were investigated to understand the influences of these parameters on the behaviour of strengthened CFST specimens. CFRP laminates were found to be weak under impact loading when wrapped in only longitudinal direction. However, a combination of longitudinal and hoop layers of CFRP laminates, or only GFRP wrapping, can remarkably minimise the severity of damage and failure of FRP in CFST specimens under lateral impact. A comparison of current test results with recent works has been presented to understand the effect of impact energy on the lateral displacement control ability of FRP strengthened CFST members.

Flexural performance of bamboo scrimber beams strengthened with fiber-reinforced polymer

This study presents a new type of bamboo scrimber beams that are strengthened by fiber-reinforced polymer (FRP) composite sheets embedded in the internal tensile region with an additional bamboo plate. To investigate the flexural performance of the bamboo scrimber beams, four-point bending tests were conducted to determine the failure modes, the load-displacement relationship, the load carrying capacity and the flexural rigidity of reinforced bamboo scrimber beams. The main parameters in the tests were the number of FRP layers and the type of FRP. The results indicated that the failure of the strengthened beams started with tensile fractures on the bottom bamboo plates, and no slipping was observed between the strengthening materials and the original bamboo beams prior to the rupturing of the bamboo plates. The flexural load-carrying capacity and the flexural rigidity of the strengthened beams effectively increased due to the FRP composite sheets and an additional bamboo plate. The strengthening method has a beneficial effect on promoting the compression behavior in the compression zone of the cross-sections of bamboo beams. Based on a simple stress-strain model of bamboo scrimber, a theoretical method for predicting the flexural load carrying capacity was developed. The predicted results are consistent with the test results.

Experimental Study on FRP-Strengthened Steel Tubular Members under Lateral Impact

The hollow structural members are highly vulnerable structural components subjected to transverse impact loads. These tubular members have been used widely in both onshore and offshore structures where lateral impact force can be expected from moving vehicles/vessels or terrorist attacks. Thus, strengthening of steel hollow tubular members is required to safely carry both service static and imposed dynamic impact loads. This paper presents the results from a series of tests on bare and fibre reinforced polymer (FRP) strengthened circular hollow section (CHS) steel members subjected to transverse impact loading at mid span. A total of fourteen (two bare and twelve strengthened) medium scale specimens were tested to investigate the effect of FRP wrapping on the global and local deformation capacity of strengthened members under drop hammer impact. Both carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP) sheets were used as strengthening materials. The results indicate that the FRP strengthening of the tubes enhances their impact resistance capacity by reducing lateral displacements up to 29% compared to bare steel CHS specimen. The influence of FRP type, CFRP orientation, CFRP thickness and effective bond length on the structural response and failure behaviour of wrapped members were investigated. The results showed that the application of FRP in the longitudinal direction was effective to control the global deformations whereas the hoop layers were effective in reducing local inward deformations of CHS members.

Shear strength of FRP reinforced deep beams without web reinforcement

Deep beams are common elements in concrete structures such as bridges, water tanks and parking garages, which are usually susceptible to harsh environmental conditions. To mitigate corrosion induced damage in those structures, steel reinforcement is being increasingly replaced by Fiber Reinforced Polymers (FRPs). Yet Eurocode doesn’t provide any guidance regarding the design of FRP reinforced concrete structures in general and deep beams in particular. This study proposes a Eurocode based Strut and Tie Model (STM) to assess the shear strength of FRP reinforced deep beams without web reinforcement. The proposed STM as well as those adopted by other codes were evaluated using a data base of 52 deep beams reinforced with different types of FRPs. The proposed STM has proven to be not only accurate but also conservative with a mean predicted to experimental value of 0.96 and a standard deviation of 0.13. While the STMs adopted by other codes have either overestimated or underestimated the shear strength.

Flexural behaviour of fibre-reinforced polymer–aluminium sandwich curtain walls

A new type of fibre-reinforced polymer–aluminium sandwich curtain wall panel, which consists of layers of aluminium plate, fibre-reinforced polymer plate, foam core and gypsum board, was proposed to achieve high strength and stiffness, efficient energy saving and good fire resistance for the modern curtain wall systems in buildings. An experimental study was conducted to investigate the flexural behaviour of the fibre-reinforced polymer–aluminium composite curtain wall panels. Three groups of large-scale specimens with different thickness of foam core with and without a phase change material layer were tested under uniformly distributed loads. The test results showed that due to the asymmetric arrangement of sandwich layers, the loading directions had a significant effect on the flexural behaviour of the panels with and without a phase change material layer. It was also shown that with the increase of the foam core thickness, the flexural behaviour of panels was significantly improved. In addition, the phase change material layer had little effect on the flexural behaviour of the sandwich panels under and beyond the serviceability conditions, but significantly reduced the serviceability strength.

Serviceability and Shear Response of RC Beams Prestressed with a Various Types of FRP Bars

The present study focuses on crack width prediction and shear response analysis of prestressed concrete (PC) beams with certain type of fiber-reinforced polymers (FRP) to be used. Recommendations are introduced taking into account the degree of bond between FRP bar and concrete interface considering a new type of FRP such as basalt FRP as well as glass FRP bars. Experimental program is presented in order to verify regulation formulae addressed for traditional steel applications. Further, a certain shear design model is proposed for PC beams consuming longitudinal basalt or carbon FRP concluding with a very accurate results.

Numerical investigation of the uplift performance of prestressed fiber-reinforced polymer floating piles

ABSTRACTFinite element analyses of prestressed fiber-reinforced polymer floating piles subjected to uplift force have been conducted in this paper. First, parameters of the modified BPE model (bond–slip model at the fiber-reinforced polymer–concrete interface) were calibrated using existing pullout testing data on fiber-reinforced polymer rebars embedded in concrete. Nonlinear spring elements were used in numerical modeling to characterize the bond–slip behavior at the fiber-reinforced polymer–concrete interface. A parametric study was performed to assess the influence of rebar diameter, fiber-reinforced polymer material, embedment length, and concrete strength on the mobilized bond stress. Upon the successful modeling of the pullout performance of fiber-reinforced polymer rebars in concrete, numerical models were developed to investigate the dependence of the uplift performance of floating piles on the prestress level, uplift force, fiber-reinforced polymer type, and compressive strength of concrete.

FRP-Confined Recycled Coarse Aggregate Concrete: Experimental Investigation and Model Comparison.

The in situ application of recycled aggregate concrete (RAC) is of great significance in environmental protection and construction resources sustainability. However, it has been limited to nonstructural purposes due to its poor mechanical performance. External confinement using steel tubes and fiber-reinforced polymer (FRP) can significantly improve the mechanical performance of RAC and thus the first-ever study on the axial compressive behavior of glass FRP (GFRP)-confined RAC was recently reported. To have a full understanding of FRP-confined RAC, this paper has extended the type of FRP and presents a systematic experimental study on the axial compressive performance of carbon FRP (CFRP)-confined RAC. The mechanical properties of CFRP-confined RAC from the perspective of the failure mode, ultimate strength and strain, and stress–strain relationship responses were analyzed. Integrated with existing experimental data of FRP-confined RAC, the paper compiles a database for the mechanical properties of FRP-confined RAC. Based on the database, the effects of FRP type (i.e., GFRP and CFRP) and the replacement ratio of recycled coarse aggregate were investigated. The results indicated that the stress–stain behavior of FRP-confined RAC depended heavily on the unconfined concrete strength and the FRP confining pressure instead of the replacement ratio. Therefore, this study adopted eleven high-performance ultimate strength and strain models developed for FRP-confined normal aggregate concrete (NAC) to predict the mechanical properties of FRP-confined RAC. All the predictions had good agreement with the test results, which further confirmed similar roles played by FRP confinement in improving the mechanical properties of RAC and improving those of NAC. On this basis, this paper finally recommended a stress–strain relationship model for FRP-confined RAC.

Behavior of glass and carbon FRP tube encased recycled aggregate concrete with recycled clay brick aggregate

In literature, there are few studies which investigated compressive behavior of fibre reinforced polymer (FRP) tube confined recycled aggregate concrete (RAC) where the recycled aggregates (RAs) mainly came from demolished old concrete components. Study which considered FRP tube confined RAC using recycled clay brick aggregates (RCBA) originating from demolished brick masonry components is rare. Thus, this paper reports a systematic study on axial compressive behavior of FRP tube encased RAC containing RCBA (termed as FRP-confined RAC-RCBA). The experimental variables considered are, i.e., replacement ratio of RCBA (r=0, 50, 70 and 100%), FRP tube thickness (nf=2, 4 and 6 layers) and type of fibre material (GFRP and CFRP). This study shows that both GFRP and CFRP tubes enhanced strength and deformation of the confined RAC-RCBA specimens remarkably. The ultimate compressive stress of the confined specimens decreased with an increase of RCBA replacement ratio but their axial deformation kept approximately constant. Failure mode and the compressive stress-strain behavior of G/CFRP-confined RAC-RCBA were similar to these tube confined normal aggregate concrete (NAC) and the ultimate compressive strength of G/CFRP tube confined RAC-RCBA specimens enhanced with an increase in FRP tube thickness. The CFRP-confined specimens showed higher ultimate strength but lower ultimate axial strain than those of GFRP-confined specimens. The applicability of eight widely used confinement models, i.e., 5 design-oriented and 2 analysis-oriented models, for FRP-confined NAC to FRP-confined RAC-RCBA was also evaluated.

Structural Damage Assessment of FRP Strengthened Reinforced Concrete Beams under Cyclic Loads

Worldwide, the need for structural retrofit is on the rise and the use of Fibre Reinforced Polymer (FRP) composite material systems is becoming an accepted method for repairs, rehabilitations, and strengthening of deficient structures. The great qualities of the FRP materials, certified in the laboratories and confirmed in the fields have all contributed to propel the material as a very promising one, though more works need to be done to certify the fatigue resistance and durability criteria. This research looked at the experimental investigations of Reinforced Concrete (RC) beams strengthened flexurally with externally-epoxy bonded FRP laminates under four point cyclic loads. Dynamic tests are used to assess damages in the FRP-strengthened RC beams under cyclic loads. 6 RC beams of 150 x 200 mm cross-section and length of 2.20m and were reinforced with four 12mm ribbed longitudinal steel bars. Three types of FRP laminates made of high modulus carbon fibre, high strength carbon fibre and glass fibre were adopted. The results confirm that dynamic-based method is an efficient way of assessing damage evolution in RC beams strengthened with FRP laminates under cyclic loads. The results offered a criterion that can be adopted for quick assessment of the efficiency of FRP composite systems before applying them to civil applications.

Compression behavior of FRP strengthened bridge timber piles subjected to accelerated aging

The use of fiber reinforced polymer (FRP) composites has been identified an effective way to strengthen and protect timber piles in many different applications. This experimental study focuses on examining the performance of glass-FRP (GFRP) strengthened bridge timber piles under uniaxial compression after exposure to long-term degradation. Field extracted red oak pile specimens with different degrees of initial deterioration are used in the study. The initial condition of the timber is assessed through stress wave timing. In order to simulate natural degradation in unretrofitted and retrofitted timber piles due to environmental exposure in a short period of time an accelerated aging procedure is used. In total, 24 timber pile specimens are tested in uniaxial compression. The number of FRP layers and type of resin used (polyester, standard epoxy, and moisture tolerant epoxy) are varied. Results show that accelerated aging induces significant deterioration in unretrofitted timber piles but the effects are relatively minor in the FRP wrapped specimens. It is also proven that FRP composite is able to significantly improve the performance of timber piles in terms of peak stress and ductility even after being subjected to extreme degradation.

Experimental study and modelling of CFRP-confined damaged and undamaged square RC columns under cyclic loading

While the cyclic behaviour of fiber-reinforced polymer (FRP)-confined columns is studied rather extensively, the cyclic response especially the energy dissipation of FRP-confined damaged and undamaged square RC columns is not yet fully understood. In this paper, an experimental and numerical investigation was conducted to study the cyclic behavior of two different types of Carbon FRP (CFRP)-confined square RC columns: strengthened and repaired. The main variables investigated are initial damage, confinement of CFRP, longitudinal steel reinforcement ratio. The experimental results show that lower initial damage, added confinement with CFRP and longitudinal reinforcement enhance the ductility, energy dissipation capacity and strength of the columns, decrease the stiffness and strength degradation rates of all CFRP-confined square RC columns. Two hysteretic constitutive models were developed for confined damaged and undamaged concrete and cast into the non-linear beam-column fiber-based models in the software Open System for Earthquake Engineering Simulation (OpenSees) to analyze the cyclic behavior of CFRP-confined damaged and undamaged columns. The results of the numerical models are in good agreement with the experiments.

Inelastic Local Buckling and Rotation Capacity of Steel I-Beams Strengthened with Bonded FRP Sheets

AbstractThis paper presents an analytical investigation of the inelastic local buckling of steel I-section beams strengthened with bonded fiber-reinforced polymer (FRP) sheets. Attention is focused on the ability of the FRP sheets to increase the beam rotations before onset of local buckling takes place. An inelastic stability analysis technique is presented that models the beam as a group of connected plates. The behavior of the steel beyond the elastic limit was modeled using the deformation theory of plasticity. The model results were verified through comparison with the results of a finite-element model and some reported experimental data. The developed model was used to conduct a parametric study to investigate the effect of each of the parameters of the problem focusing on FRP type and strengthening configurations. The study results showed that FRP materials with high longitudinal elastic modulus do not necessarily result in higher increases in the inelastic local buckling capacity. The FRP in-plane...

Rational Approach for Evaluating Fire Resistance of FRP-Strengthened Concrete Beams

AbstractThis paper presents a rational approach for evaluating the fire resistance of reinforced concrete (RC) beams strengthened with different types of fiber-reinforced polymers (FRP). This approach is based on conventional fire design principles for RC beams, but incorporates the contribution of FRP and fire insulation in fire resistance calculations. Simplified equations are proposed for evaluating cross-sectional temperatures in fire-exposed FRP-strengthened RC beams with and without fire insulation. These temperatures are used to determine the loss of strength in steel, FRP, and concrete using temperature-dependent strength properties. Employing the strength in different materials, the moment capacity of FRP-strengthened beams is calculated, at any given fire exposure time, by applying force equilibrium and strain compatibility principles. At each time step, the limit state is applied to define the failure of an FRP-strengthened RC beam, and the time to failure is taken as the fire resistance of the...

Shake Table Tests on FRP Retrofitted Masonry Building Models

AbstractThe current study is devised to evaluate the seismic performance of fiber-reinforced polymer (FRP) retrofitted buildings with openings at different FRP reinforcement levels. Required objectives are achieved by performing five shake table tests on 1/4-scale models of single-story boxlike masonry buildings. Out of five building models, one was an unreinforced masonry (URM) building model whereas the other four were retrofitted with different quantities and layouts of FRP reinforcement. FRP reinforcement is reduced by decreasing FRP strip widths and strip spacing and applying FRP strips on either the inside or outer faces of walls. Each building model was subjected to the same series of input ground motions with gradually increasing amplitudes. A series of diagonal compression tests was also conducted to decide the appropriate type of FRP and trial FRP reinforcement ratios for the masonry building models. Descriptions of the tested models are provided, including the structural response in terms of ba...

Structural performance of notch damaged steel beams repaired with composite materials

An experimental program and an analytical model using ANSYS program were employed to estimate the structural performance of repaired damaged steel beams using fiber reinforced polymer (FRP) composite materials. The beams were artificially notched in the tension flanges at mid-spans and retrofitted by FRP flexible sheets on the tension flanges and the sheets were extended to cover parts of the beams webs with different heights. Eleven box steel beams, including one intact beam, one notch damaged beam and nine notches damaged beam and retrofitted with composite materials, were tested in two-point loading up to failure. The parameters considered were the FRP type (GFRP and CFRP) and number of layers. The results indicated that bonding CFRP sheets to both of the tension steel flange and part of the webs, instead of the tension flange only, enhances the ultimate load of the retrofitted beams, avoids the occurrence of the debonding and increases the beam ductility. Also the numerical models give acceptable results in comparison with the experimental results.

In-Plane Shear Performance of Masonry Walls after Strengthening by Two Different FRPs

This experimental study was aimed to investigate the in-plane shear performance of externally strengthened masonry walls using two types of fiber-reinforced polymer (FRP) sheets, namely, carbon FRP (CFRP) and polyethylene terephthalate-FRP (PET-FRP) sheets. Among these two, PET-FRP has a low tensile strength but possess a higher fracturing strain than CFRP. Twelve masonry walls made from clay brick were tested for static lateral loading under constant compression, after bonding CFRP and PET-FRP sheets onto their surfaces in three different configurations. The ultimate shear strength and deformation at peak load were the two important observations. The mechanisms by which load was carried were observed, varying from the initial uncracked state to the final, fully cracked state. The results demonstrate that a significant increase in the in-plane shear capacity of masonry can be achieved by bonding these two FRPs to the surface of the walls but ductility is compromised when CFRP is used. Walls retrofitting with PET-FRP in a crossdiagonal fashion show a good ductile behavior in both prepeak and postpeak regimes. The experimental data were used to assess the effectiveness of the strengthening of one FRP over the other. PET-FRP in diagonal configuration was found to be the most effective way of strengthening without compromising the two most essential aspects of masonry, that is, strength and ductility.