Fiber Reinforced Polymer Beams Research Articles

Electric current distribution of carbon fiber reinforced polymer beam: analysis and experimental measurements

The authors have previously proposed an effective method for analyzing the electric current density of carbon fiber-reinforced polymer (CFRP) composites using an anisotropic electric potential function. The method is based on the assumption that CFRP laminates are homogeneous orthotropic materials. Actual CFRP laminates are, however, heterogeneous materials, having resin-rich layers and carbon fiber layers. In the present study, the electric conductance is calculated on the assumption that CFRP laminates are homogeneous using electrical resistance data measured by a four-probe method, and used for electric current analysis. A new specimen design is proposed to allow the electric current distribution of CFRP laminates to be investigated experimentally. The results obtained confirm that our analysis method is accurate for determining the electric current density of actual CFRP laminates. Thus, the assumption that CFRP laminates may be considered homogeneous orthotropic materials for electric current analysis is experimentally verified.

COMPARATIVE STUDY OF EXPERIMENTAL AND ANALYTICAL RESULTS OF FRP STRENGTHENED BEAMS IN FLEXURE

This paper presents the nonlinear Finite Element Analysis (FEA) that has been carried out to simulate the behaviour of failure modes of Reinforced Concrete (RC) beams strengthened in flexure by Fibre Reinforced Polymer (FRP) laminates. Two beams were modeled in FEM software using ANSYS. In those two beams, one beam is control beam without FRP and other beam is Glass Fibre Reinforced Polymer (GFRP) strengthened beams. From the analyses the load deflection relationships, crack pattern, first crack load and Ultimate load was obtained and compared with the experimental results available in Literature. The load deflection plots obtained from numerical studies show good agreement with the experimental plots. There was a difference in behaviour between the RC beams strengthened with and without GFRP layers. Therefore, modeling of experimental beams can be adoptable in ANSYS. Validation of experimental results can also be done using ANSYS.

Interfacial Slip Calculation of RC Beams Strengthened with FRP Plate under Mid-Span Concentrated Loads

The collaborative work between fiber reinforced polymer (FRP) and concrete is achieved through the binder, so the interface of them is the weak links. The interfacial slip between FRP and concrete beam is one of the key factors to affect the behaviors of RC beams strengthened with FRP plate. According to elasticity theory, this study analyzes the theoretical analysis of interfacial slip of RC beams strengthened with FRP plate under mid-span concentrated loads. The analytical model is established, and the differential equation of interfacial slip of RC beams strengthened with FRP plate is established. Using the boundary conditions, the calculated formula of interfacial slip is deduced under mid-span concentrated loads.

Web Buckling in Pultruded Fiber-Reinforced Polymer Deep Beams Subjected to Concentrated Loads

Five 609.5-mm deep fiber-reinforced polymer (FRP) beams with a span-to-depth ratio of 4∶1 were tested in three-point bending with the beam ends constrained to prevent global failure. A concentrated load was applied at midspan either directly to the top flange or through a 101.6 mm wide by 12.7-mm thick FRP bearing plate resting on the top flange. VIC-3D Digital Image Correlation Measurement Software from Correlated Solutions captured out-of-plane displacement of the webs, and Southwell plots were generated to determine buckling loads. Each specimen experienced a stability failure of the web before undergoing material failure in the upper web-flange junction. On average, web buckling occurred at 90% of the ultimate load. The introduction of a bearing plate did not significantly affect the buckling load or ultimate capacity of the specimens. One specimen was tested into the postbuckling range, unloaded, and reloaded to material failure and experienced no loss of strength or stiffness. Another specimen with significant damage to the unloaded web-flange junction was tested and compared with a virgin sample. The damaged sample experienced no significant loss of strength or stiffness. Comparisons of experimental data with three theoretical equations for web-buckling capacity of FRP beams are provided.

Influence of boundary conditions and geometric imperfections on lateral–torsional buckling resistance of a pultruded FRP I-beam by FEA

Presented are results from geometric non-linear finite element analyses to examine the Lateral Torsional Buckling (LTB) resistance of a Pultruded Fibre Reinforced Polymer (FRP) I-beam when initial geometric imperfections associated with the LTB mode shape are introduced. A data reduction method is proposed to define the limiting buckling load and the method is used to present strength results for a range of beam slendernesses and geometric imperfections. Prior to reporting on these non-linear analyses, Eigenvalue FE analyses are used to establish the influence on resistance of changing load height or displacement boundary conditions. By comparing predictions for the beam with either FRP or steel elastic constants it is found that the former has a relatively larger effect on buckling strength with changes in load height and end warping fixity. The developed finite element modelling methodology will enable parametric studies to be performed for the development of closed form formulae that will be reliable for the design of FRP beams against LTB failure.

Fiber-Reinforced Polymer-Strengthened/Reinforced Concrete Structures Exposed to Fire: A Review

Fire resistance of concrete members reinforced or strengthened with fiber-reinforced polymer (FRP) materials is an extremely crucial area that needs to be investigated before implementing FRP composites in buildings and other structures vulnerable to fire. A review on the fire performance of FRP materials and FRP-strengthened/reinforced concrete members is presented. The review includes the mechanical properties of various types of FRP materials at elevated temperatures (based on experimental results). The behavior of bond adhesive epoxies and the bond of FRP reinforcement are investigated under elevated temperature effects. Experimental (fire test) results and numerical studies for unprotected concrete members strengthened or reinforced with FRPs (beams, columns and slabs), including failure patterns, as well as respective results for insulated concrete members, together with the type of insulation materials are also presented. The measured evolution of temperature at distinct locations within the cross section of the tested element and the role of insulation are discussed. Factors that significantly influence the fire resistance of FRP-strengthened or FRP-reinforced systems are investigated and preliminary guidelines for the efficient design of such systems in a fire environment are provided.

Closed-Form Equations for Flange Force and Maximum Deflection of Box-Beams of Fiber Reinforced Polymer with Partial Shear Interaction between Webs and Flanges

Presented in the paper is the formulation of a governing second-order differential equation for the moment distribution along the length of a beam having two interfaces with partial shear interaction where two flange and two web components join to form the box shaped section. For practical applications such a closed-section beam of Fiber Reinforced Polymer (FRP) can be assembled from individual pultruded profiles using mechanical fasteners. This assembly approach can be used to construct deeper section sizes than can be achieved with a single pultrusion, and which can be transported in flat-pack units. In developing the governing equation for flexural response account is made of the finite connection stiffness at the web/flange interfaces by applying conventional elastic beam theory. The differential equation for the partial interaction problem is solved to formulate closed form equations for the flange force and the maximum deflection of a simply supported beam under four-point bending. A numerical parametric study is presented to show changes in beam performance indicators with the degree of shear interaction between the upper and lower bounds of full- and non-interaction. Results from a series of load tests using a three-layered prototype FRP beam are shown to be in good agreement. The theoretical predictions for maximum deflection are however found to be directly linked to the appropriateness of the measured connection stiffness entered into the closed-form equation.

Study of Crack Width of the Fiber Reinforced Polymer Beam

Fiber reinforced polymer (FRP) is a new kind of material for structural engineering in recent year. The partial inferiority of the bond and mechanical properties for FRP bars, however, leads to wider cracks compared with those of steel-reinforced concrete structures. Therefore, current design methods for predicting crack widths developed in concrete structures reinforced with steel bars at service load may not be used for concrete structures reinforced with FRP bars. This paper presents an analytical formula that calculates the maximum crack with in FRP- reinforced concrete beam, taking into account both the bond and the mechanical properties of FRP bars. The experimental results compared well with those proposed by the model.

Behavior of hybrid (steel-CFRP) and CFRP bar-reinforced concrete beams in fire

The establishment of fire resistance of the fiber-reinforced polymer (FRP) bar-reinforced concrete (RC) is a prerequisite to the widespread applications of these bars. The use of FRP bars in residential and commercial buildings could result in their increased applications. This article presents an experimental study on the performance of carbon FRP (CFRP) and hybrid (steel—CFRP) RC beams at elevated temperatures. The beams were tested in a floor furnace and carried a load of 40% of ambient load capacity. Temperature rise in the compression concrete was found insignificant and its mechanical properties were nearly unaffected. All the tested beams failed in flexure which was also the intended failure mode at ambient temperature. The slip of CFRP bars was a major contributing factor to the beam failure. Influence of temperature rise was not found on the bar slip. A hybrid bar-reinforced beam showed better strength and stiffness characteristics in comparison with the steel- or FRP-reinforced beams. The beam reinforced with two CFRP bar layers was the strongest but the least ductile beam.

Development of corrosion-free concrete beam–column joint with adequate seismic energy dissipation

The use of Fibre-Reinforced Polymer (FRP) as reinforcement in concrete structures has received much attention owing to its higher resistance to corrosion compared to that of regular steel reinforcement. Since FRP is a brittle material, its use in seismic resisting structural elements has been a concern. FRP RC structures can be made ductile by utilizing a ductile material such as steel at the plastic hinge regions. However, the use of steel negates the corrosion resistance purpose of FRP. On the other hand, Nickel–Titanium (Ni–Ti) shape memory alloy (SMA) is highly resistant to corrosion. It also brings about an added advantage in seismic regions since it has the unique ability to undergo large deformation, but can regain its undeformed shape through stress removal. In this study, a SMA–FRP hybrid RC beam–column joint has been proposed to address not only corrosion resistance, but also seismic related problems. This joint is reinforced with a super-elastic Ni–Ti SMA bar at the plastic hinge regions of the beam and FRP in the other regions of the beam and column. To validate the proposed joint, an experimental investigation has been carried out to develop such a joint and test it under reversed cyclic loading. The results are compared in terms of load–storey drift, moment–rotation and energy dissipation capacity to those of a similar RC beam–column joint specimen reinforced with conventional steel. The SMA–FRP beam–column joint proved to have adequate energy dissipation under earthquake type loading.

Effects of Bonded Splice Joints on the Flexural Response of Pultruded Fibre Reinforced Polymer Beams

Three Pultruded Fibre Reinforced Polymer (PFRP) 152 x 152 x 6.4mm Wide Flange (WF) beams were fabricated with a central two-plate splice joint. The 6.4mm thick PFRP splice plates were 210, 410 and 610mm long. Each beam was tested in symmetric four-point bending about its major and minor-axis and deflections, rotations and surface strains were recorded. Beam transverse stiffnesses, support rotations and splice rotational stiffnesses were quantified and compared with theoretical predictions. Predicted deflections were 3.5% to 18.5% larger and support rotations were 10% smaller to 14.2% larger than the experimental values. Splice end rotations were generally poorly predicted.

Combined Analytical and Finite Element Beam Model for Wind Turbine Blades

Finite element method (FEM) has been widely used in recent years to analyze fiber-reinforced polymer (FRP) beams such as wind turbine blades. Although it is generic and convenient, FEM does little to shed light on the mechanical behavior of structures. Moreover, it is inefficient in calculation. This study presents a combined analytical and finite element beam (CAFB) model with an inclination angle correction to solve the non-prismatic, blade-like FRP beam problem. It not only substantially reduces computational time, but also helps us comprehend the mechanical behavior. Also, the inclination angle correction is supposed to correct the overestimated axial stiffness due to the topology of beams. In the presented cases, the CAFB model can accurately analyze the FRP thin-walled beams with all results being certified by finite element analysis software, and the correction is especially effective in small fiber orientation angles.

Deflection Calculation of Frp-Strengthened Reinforced Concrete Flexural Members

SummaryExternally bonded fibre-reinforced polymer (FRP) composite plates can enhance the flexural strength, as well as stiffness to a limited degree, of reinforced concrete (RC) flexural members. Understanding the behaviour of these strengthened members at the serviceability and ultimate load ranges of response is of particular importance to engineers. The description of such behaviour is best described via plotting of the complete moment-curvature, as well as load-deflection responses from initial load to member failure. Based on the assumption of a tri-linear moment-curvature relationship, closed-form analytical solutions are presented in this paper for calculating the complete load-deflection response of FRP flexurally-strengthened one-way RC slabs and beams, which are simply-supported (three- and four-point bending), as well as cantilevered (free-end point load). The analytical predictions compare well with test results and the basis of a new “quad-linear” moment-curvature relationship is proposed that may better capture a so-called “pseudo-ductile” response occasionally observed in experiments. The influence of anchorage of the FRP strengthening for the prevention or delaying of debonding and a procedure for its inclusion in the analytical model is also discussed. Finally, the results of parametric studies are presented.

Nondestructive Evaluation of Full-Scale FRP Bridge Beams Prior to Construction

Two innovative hybrid bridges having conventional reinforced concrete slabs combined with fiber-reinforced polymer (FRP) beams have been designed and built in the Corpus Christi District. The first structure had two spans each of 30 feet and the second structure length is 50 feet; the width of each bridge is 32 feet. The first hybrid structure was designed by researchers at the University of Texas at Austin working closely with Texas Department of Transportation (TxDOT) and the second was designed by researchers at the University of Texas in Arlington and the University of South Carolina. For both bridge structures, beams were nondestructively evaluated at the manufacturing facility using Acoustic Emission (AE) as the primary evaluation method. This article presents a description of the structures and the methods and results of the nondestructive evaluation (NDE). AE testing proved to be a useful tool for helping to establish the fitness for service of the FRP beams prior to implementation and for identifying areas requiring special attention during the quality assurance phase.

Strength Modeling of Reinforced Concrete Beam with Externally Bonded Fibre Reinforcement Polymer Reinforcement

This research study presents the evaluation of the structural behaviour of reinforced concrete beams with externally bonded Fibre Reinforced Polymer (FRP) reinforcements. Three different steel ratios with two different Glass Fibre Reinforced Polymer (GFRP) types and two different thicknesses in each type of GFRP were used. Totally fifteen rectangular beams of 3 m length were cast. Three rectangular beams were used as reference beam (Control Beams) and the remaining were fixed with GFRP laminates on the soffit of the rectangular beam. The variables considered for the study includes longitudinal steel ratio, type of GFRP laminates, thickness of GFRP laminates and composite ratios. Flexural test, using simple beam with two-point loading was adopted to study the performance of FRP plated beams interms flexural strength, deflection, ductility and was compared with the unplated beams. The test results show that the beams strengthened with GFRP laminates exhibit better performance. The flexural strength and ductility increase with increase in thickness of GFRP plate. The increase in first crack loads was up to 88.89% for 3 mm thick Woven Rovings GFRP plates and 100.00% for 5 mm WRGFRP plated beams and increase in ductility interms of energy and deflection was found to be 56.01 and 64.69% respectively with 5 mm thick GFRP plated beam. Strength models were developed for predicting the flexural strength (ultimate load, service load) and ductility of FRP beams. The strength model developed give prediction matching the measurements.

Measurement of the Timoshenko Shear Stiffness. I: Effect of Warping

Fiber-reinforced polymer (FRP) composite beams are increasingly finding use in construction. Due to their lower stiffness relative to steel sections, the design of FRP structures is usually deflection controlled. Furthermore, shear deformation can be significant in FRP beams, thus, requiring the use of the Timoshenko beam theory to estimate deflections. However, the Timoshenko shear stiffness can be difficult to measure. Part of the measurement error has been attributed to shear warping effects. It has been hypothesized that warping restraints at loading points and supports increase the apparent shear stiffness to a degree that is significant at relatively short spans, e.g., L∕h<10 to 15. In this study, the influence of warping on short to moderate length FRP beams under various types of loading and boundary conditions is considered using finite-element analysis. In particular, a commercially available thin-walled FRP beam was investigated. The results suggest that warping has a negligible effect for thin...

Experimental validation of the higher-order derivative discontinuity method for damage identification

A damage identification method based upon fourth derivatives of the mode shapes is proposed and demonstrated on laboratory and field applications. The higher-order derivative discontinuity (HODD) method is based on the premise that localized damage will cause large discontinuities in the magnitude of the fourth derivative. The HODD method, which is applicable to beam-like structures, does not require a reference to the undamaged state of the structure. The method includes algorithms to estimate the fourth derivatives, to detect possible damage locations, and to assess statistical significance and objectively eliminate false-positive indications of damage. The HODD method is demonstrated on an aluminium beam, and fibre-reinforced polymer beam, and a full-scale plate girder bridge. Crack and delamination damages are physically simulated and successfully located in the presence of real-life noise. The HODD method is accurate in locating damage corresponding to stiffness reductions as low as 0.15%. The results also demonstrate the importance of the statistics-based parameters for accurate damage detection. Copyright © 2007 John Wiley & Sons, Ltd.

Evaluation of In-Service Performance of Tom’s Creek Bridge Fiber-Reinforced Polymer Superstructure

The Tom's Creek Bridge is a small-scale demonstration project involving the use of fiber-reinforced polymer (FRP) composite girders as the main load carrying members. It is a simply supported, short-span bridge located along Tom's Creek Road in Blacksburg, Virginia. As a result of discussions among Virginia Tech, Strongwell, the Virginia Department of Transportation, and the Town of Blacksburg, the existing deteriorated superstructure of the Tom's Creek Bridge was replaced with a glue-laminated timber deck on 8 in. (20.3 cm) deep pultruded FRP beams. The project was intended to address two issues. First, by calculating bridge design parameters such as the dynamic load allowance, transverse wheel load distribution and deflections under service loading, the Tom's Creek Bridge will aid in modifying current AASHTO bridge design standards for use with FRP composite materials. Second, by evaluating the FRP girders after being exposed to controlled laboratory and service conditions, the project will begin to answer questions about the long-term performance of these advanced composite material beams when used in bridge design. A dynamic load allowance, IM, of 0.90 is recommended for the Tom's Creek Bridge. This value is the largest average IM observed and is therefore conservative. This value is significantly higher than those set forth in the AASHTO standards of 0.33 (AASHTO, 1998) and 0.30 (AASHTO, 1996). It is recommended to use a value of L/425 (LRFD Specification) or L/500 (Standard Specification). This value is consistent with AASHTO deflection control criteria for an all timber bridge. It is recommended to use the AASHTO wheel load distribution factors for a glulam timber deck on steel stringer bridge. There is no indication of loss of FRP girder ultimate strength after 15 months of service. Given the low service loads (no more than 10% of the ultimate capacity) and traffic volume the fatigue life prediction model suggests that fatigue will not be a major concern during the life of service (10 to 15 years).

Testing of hybrid FRP composite beams in bending

This paper presents tests where hybrid composite beams have been investigated. The hybrid beam consists of a glass fibre I-beam with carbon fibre strengthened bottom flange and a rectangular concrete block in the compressive zone. The interaction between the concrete and composite beam were obtained in two ways; casting in shear connectors of steel and bonding by epoxy adhesive. As a reference, a beam without concrete in the compressive zone was also tested. The idea of combining carbon, glass and concrete was to utilize the stiffness contribution from the carbon and the compressive strength from the concrete. The glass fibre I-beam would then take up the main part of the shear force. The results from the test showed that a good composite action could be achieved between carbon, glass and concrete. However, it could also be noticed, as expected, that an I-beam is not the ultimate form due to stability problems. In the tests, problems arose due to lateral instability, but this was solved by placing stiffeners manufactured from wood between the flanges of the Fibre Reinforced Polymer beam over the supports. With a few modifications of the hybrid beam it is believed, that it would be possible to create both a technical and economical hybrid profile that benefits from carbon, glass and concrete.

The Clear Creek Hybrid Composite I-Girder Pedestrian Bridge

An 18.3 m (60 ft) pedestrian I-girder bridge was analyzed, designed, tested, and constructed. The main load-carrying members for the bridge are two 61-cm (24-in.) deep composite fiberglass I-girders with embedded carbon fibers in the flanges. Laboratory testing quantified the increased stiffness of the hybrid glass/carbon fiber-reinforced polymer beams over those manufactured solely with glass fibers. Typical joint connections were tested to investigate their performance, and a dynamic analysis was performed to check the bridge's vibration under pedestrian load.