Journal of Composites for Construction

This paper presents a procedure based on the Arrhenius relation to predict the long-term behavior of glass fiber-reinforced polymer (GFRP) bars in concrete structures, based on short-term data from accelerated aging tests. GFRP reinforcing bars were exposed to simulated concrete pore solutions at 20, 40, and 60°C. The tensile strengths of the bars determined before and after exposure were considered a measure of the durability performance of the specimens. Based on the short-term data, a detailed procedure is developed and verified to predict the long-term durability performance of GFRP bars. A modified Arrhenius analysis is included in the procedure to evaluate the validity of accelerated aging tests before the prediction is made. The accelerated test and prediction procedure used in this study can be a reliable method to evaluate the durability performance of FRP composites exposed to solutions or in contact with concrete.

In the case of heavily reinforced concrete structural members, bundled bars are required rather than spaced bars. The use of spliced bundled bars is necessary when available bar lengths are limited. No design recommendations regarding the use of bundled or spliced bundled FRP bars are available. The results of four-point flexural testing of nine concrete beams reinforced with spliced bundled CFRP bars are presented herein. The effects of the type of bundle and splice length on the bond strength of bundled CFRP bars are investigated. Based on the experimental results, a procedure for determining the critical splice length of FRP bars is presented and the corresponding values of bond stresses can be predicted. Moreover, the ultimate strength analysis method is used to predict the maximum stress in spliced bundled CFRP bars. Finally, comparisons with the existing recommendations regarding the use of bundled steel bars and the recommended modifications for bundled CFRP bars are presented.

Near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) laminate strips are used to increase the load-carrying capacity of concrete structures. This is done by inserting the CFRP strips into slits made in the concrete cover of the elements to be strengthened and gluing the strips to the concrete with an epoxy adhesive. In several cases the NSM technique has substantial advantages when compared with externally bonded laminates. To assess the bond behavior between the CFRP and concrete under monotonic and cyclic loading, an experimental program was carried out based on a series of pullout-bending tests. The influence of the bond length and loading history on the bond behavior was investigated. In this work the details of the tests are described and the obtained results discussed. Using the experimental data and an analytical-numerical strategy, a local bond stress-slip relationship was determined. A finite-element analysis was performed to evaluate the influence of the adhesive on the global response observed in the pullout-bending tests.

Numerous recent research findings evidenced the success of retrofitting existing RC columns using fiber-reinforced plastic (FRP) jacketing. However, little is known about the residual performance of FRP-retrofitted RC columns following limited seismic damage. In this paper, the residual performance of FRP-retrofitted columns damaged after simulated seismic loading is studied. Eight model columns with a shear aspect ratio of 5.0 were tested first under cyclic lateral force and a constant axial load equal to 20% of the column gross axial load capacity. The main parameters considered were the type of FRP jacket and peak drift ratio where the lateral loading was interrupted. Glass fiber-reinforced plastic (GFRP) and carbon fiber-reinforced plastic (CFRP) were both used for retrofitting. Five of the model columns were subjected to long-term axial loading after being subjected to limited damage by lateral cyclic loading. From the results of long-term loading test, it was found that FRP-retrofitted columns had much smaller creep deformation than the counterpart as-built model. The deformation of retrofitted columns under long-term axial loading depended on the previous damage intensity and the modulus of elasticity of FRP. The effective creep Poisson’s ratios of the retrofitted columns were much smaller than the as-built column but identical for GFRP and CFRP retrofitted columns. Under the testing conditions of this study, the long-term axial deformation of retrofitted columns tends to be sufficiently stable, despite the simulated earthquake damage.

This paper deals with reinforced concrete beams strengthened by means of externally bonded fiber-reinforced polymer (FRP) sheets. The scope of the work is to discuss and compare an exact and an approximate approach to the computation of the flexural load-carrying capacity of the strengthened beam. The two approaches differ from one another in the way they take into account the extent of the load already acting throughout strengthening operations. To achieve this goal a numerical model is presented and validated by comparing its output with that of 46 experimental tests taken from the literature. The numerical model is then adopted to perform a numerical parametric analysis of a wide range of practical applications, excluding all cases of FRP delamination, and useful conclusions are drawn.

The construction boom over the last century has resulted in a mature infrastructure network in developed countries. Lately, the issue of maintenance and repair/upgrading of existing structures has become a major issue, particularly in the area of bridges. Fiber- reinforced polymer (FRP) has shown great promise as a state-of-the-art material in flexural and shear strengthening as external reinforcement, but information on its applicability in torsional strengthening is limited. The need for torsional strengthening in bridge box girders is highlighted by the Westgate Bridge in Melbourne, Australia, one of the largest strengthening projects in the world for externally bonded carbon FRP (CFRP) laminates. This paper reports the experimental work in an overall investigation of torsional strengthening of solid and box-section reinforced concrete beams with externally bonded carbon FRP. This was found to be a viable method of torsional strengthening. Photogrammetry was a noncontact measuring technique used in the investigation. The deformation mechanisms were found to be unchanged in the strengthened specimens. Furthermore, it was found that the crack widths were reduced and aggregate interlocking action improved with the strengthened beams.

Based on experimental data of tension lap splices confined with fiber reinforced polymer (FRP) sheets in normal and high strength concrete (HSC) specimens, a new FRP confinement parameter, $K_{\mathrm{tr},f}$ , was recommended. It accounts for the increase in bond strength due to the presence of FRP sheets. In this paper, a correlation is presented between the confining effects of FRP flexible sheets, transverse reinforcement, and steel fibers to improve the bond capacity and ductility of the mode of failure of tension lap splices. The correlation is based on research programs conducted at the American University of Beirut in recent years using identical specimens except for the confinement method used: FRP sheets, transverse steel stirrups, or steel fibers. Other variables included the amount of confinement provided and concrete strength. Analysis of test results indicated that an equivalent improvement in bond strength of tension lap splices in normal and high strength concrete specimens is provided by an amount of FRP sheets corresponding to a $K_{\mathrm{tr},f}$ value of 2.5, or an amount of transverse reinforcement corresponding to $K_{\mathrm{tr}}$ of $1.0d_b$ . For HSC specimens, an amount of steel fibers corresponding to a volume fraction of 1% would provide an equivalent improvement in bond strength.

An innovative use of fiber-reinforced polymer composite materials to control the manifestation of local buckling in a steel section during plastic hinging is discussed in the present work. This discussion focuses on a technique wherein the constituent plate components in a steel I-shaped cross section are braced against local plate buckling modes through the imposition of thin longitudinal strips whose function is to enforce a nodal line along a plate element. This work demonstrates that such an approach increases the critical load for individual steel plate elements and helps to constrain plastic flow for these same elements so that the structural ductility of the overall cross section is enhanced. The research work discussed herein is analytical in nature. Detailed nonlinear finite element models are created using traditional techniques implemented on the commercially available software system ADINA. Specifics pertaining to bond-line response are not treated.

This paper reports on a feasibility study of splicing techniques for precast concrete-filled fiber-reinforced polymer (FRP) tubes (CFFT). A total of four spliced beams were tested. Three were internally spliced using grouted steel bars, grouted FRP bars, or unbonded posttensioning bars, and the fourth was spliced with FRP socket, commonly used in the piping industry. A control CFFT beam with no internal reinforcement was also tested as a reference. The experiments showed the superior effect of FRP tube continuity on system performance. Although initially stiffer, none of the spliced beams tested in this program was as strong as the control specimen. This may be primarily attributed to the lack of continuity of the FRP tube, as well as the quality of the cement grout for dowel reinforcement. Posttensioning proved to be efficient in improving system performance. The system may benefit from FRP continuity through either a longer and more effective socket or a threaded coupler insert or sleeve. Internal reinforcement can further increase the stiffness and strength of the connection, if grouting quality is controlled. Splicing may be improved by combining the methods tested in this program. Further understanding of the implications of composite action between FRP and concrete was achieved. Finally, the behavior of spliced CFFT beams was closely described using a combination of beam theory and rigid body deformations; the extent of the latter depends on joint stiffness.

The design of a deck-and-stringer bridge system is usually reduced to the analysis of a T-beam section, loaded by concentrated loads corresponding to an equivalent fraction of the applied truck load. This equivalent load is defined by wheel load–distribution factors, which approximate the overall behavior of the bridge superstructure. In this paper, a one-term approximation of a macroflexibility series solution including deformations for fiber-reinforced polymer (FRP) deck-and-stringer orthotropic bridge systems, is used to develop explicit expressions for symmetric and asymmetric load distribution factors. It is significant that the equations presented herein include important parameters that represent, as accurately as possible, the response characteristics of the super structure, such as the geometry and material properties of the FRP deck and stringers, bridge aspect ratio, and number and spacing of stringers. As an illustration in actual design applications, the formulation presented in this paper is used to develop an analytical method for FRP deck-and-stringer bridge systems, and the method is verified by predicting the response of an all FRP model bridge in the lab and an FRP deck on steel stringers in the field. The results of the present formulation compare well with experimental lab and field results. The simplified analysis presented in this paper can be used with sufficient accuracy for the design of composite FRP deck on stringers bridges.