This study introduces a novel test apparatus that can be used to test the adhesive bond between fiber-reinforced polymer (FRP) laminate and concrete in both double shear and mixed mode (shear/peeling). It was deployed to evaluate the behavior of carbon FRP (CFRP)–concrete interfaces at six peel angles. The apparatus is usable with any servohydraulic load test frame and requires only one-half of the traditional concrete block specimen used in both double shear and mixed-mode tests. Experimental results revealed a decrease in bond capacity as peel angle increased. The reduction is quantified using a power-law relationship with respect to the tangent of the peel angle. A three-dimensional (3D) finite-element model utilizing a cohesive zone model to characterize the FRP–concrete interface was developed to corroborate experimental results and carry out parametric studies. The percentage increase in CFRP–concrete bond capacity resulting from an increase in the FRP modulus or its thickness declined as the peel angle increased.

The practice of using fiber-reinforced polymer laminates and fabric to repair and strengthen concrete structures is well established. What limits the application of fiber-reinforced polymer materials, especially in flexural strengthening, is the equipment and man power needed for continuous application when retrofits take place over waterways or multilane roadways. A carbon fiber–reinforced polymer rod panel system consisting of 1220-mm (48-in) panels made continuous through a finger joint/splice was developed to overcome these limitations. The system’s performance hinges on whether forces can be transferred from one panel to another. This study investigated the bond characteristics of carbon fiber–reinforced polymer rods, as well as the flexural behavior of concrete members strengthened with carbon fiber–reinforced polymer rod panels, to improve knowledge of the finger joint’s behavior. Bond tests were conducted using double-lap shear specimens on individual rods with both steel and concrete substrates. Further bond tests were performed on small carbon fiber–reinforced polymer rod panels on steel substrate. Flexural tests were carried out under four-point bending on small-scale reinforced concrete beams that were strengthened using continuous carbon fiber–reinforced polymer rod panels and carbon fiber–reinforced polymer rod panels spliced using a finger joint. Case studies of four field applications are presented to provide a better understanding of the system. The new carbon fiber–reinforced polymer rod panels effectively reduce labor and equipment costs for work conducted on bridges with limited access, as they enabled the performance of repair/retrofit operations by a small crew working out of a single work platform.

Short ultrahigh-modulus (UHM) carbon fiber–reinforced polymer (CFRP) strip panels connected through a finger joint configuration offer a convenient modular method for strengthening steel girders. Three-dimensional nonlinear finite-element (FE) analysis was conducted to characterize the interfacial and flexural behavior of strip panels. The calibrated FE model provides an efficient and economical method of evaluating different parameters related to the material properties and strengthening configuration of the UHM CFRP strip panels, for which experimental data are not available. Analysis implemented robust features, including debonding of CFRP using a mixed-mode bond–slip model, CFRP rupture, steel yielding, and concrete slab crushing. Predictions were calibrated and validated against experimental results from double lap shear tests and flexural tests of steel beams and steel–concrete composite beams. The FE model was used to investigate the effects of finger joint location, joint length, and laminate thickness. Strip panels with 300-mm-long finger joints and thicknesses of up to 2 mm equaled the strength of a continuous laminate with the same CFRP area. Both failed by CFRP rupture. At greater thicknesses, debonding occurred at lower ultimate loads than for a continuous laminate. The finger joint splice was also compared to the traditional splice plate method. The splice plate length required to achieve the same level of load transfer was longer than the finger joint length when the connection was in the maximum moment region. For a given CFRP thickness and splice plate length (or finger joint length), strip panels with finger joints provide greater load-carrying capacity.

CFRP Rod Panels (CRPs) have been recently developed to externally strengthening concrete structures in flexure, especially over multi-lane highways. Both exterior beams of a reinforced concrete (RC) bridge traversing southbound Interstate 71 (I-71) in Kentucky were damaged by an over-height truck impact. Rebars within the bottom mat of each exterior beam were severely bent due to the impact. CRP 195, with CFRP rods 3.96-mm (0.156 in) in diameter, and having a capacity of 870 kN (195.6 kips) per 300 mm (12 in) width of panel, were selected for flexural strengthening. CRPs were chosen due to their modular construction capability permitting a smaller work crew to carry out the retrofit construction while requiring closure of only a single lane of traffic on I-71. As current codes do not address CRPs, the retrofit design was based on American Association of State Highway and Transportation Officials (AASHTO) guidelines for externally bonded FRP. A load rating of the impacted girders was carried out for the as-built, damaged, and retrofitted stages. This paper details the retrofit construction of the bridge girders, highlighting the advantages of the CRPs.