Small-scale plain concrete precracked beams strengthened with glass fiber reinforced polymer (GFRP) sheets underwent testing in 3-point flexure to assess variations in the FRP-concrete Mode II interfacial fracture energy after 6 and 13 years of sustained loading in indoor and outdoor environments. The Mode II fracture energy of the interfacial region, GF, was determined by analyzing strain profiles along the length of the FRP sheet, which were obtained using digital image correlation and photoelastic techniques. In the experiments conducted after conditioning, higher GF values were observed as the debonded zone progressed from the region of sustained shear stress transfer to the unstressed section of the interfacial region, particularly in beams subjected to outdoor conditioning. In the interfacial region near the notch, GFRP beams showed reductions in GF in both indoor and outdoor environments. For outdoor beams with GFRP sheets, there was no additional degradation in GF when the FRP was exposed to direct sunlight, in comparison to beams with the FRP exposed to indirect sunlight.

The use of fiber-reinforced polymer (FRP) composites for external bonding has become a popular and widely accepted technique for enhancing the strength of concrete structures due to its excellent mechanical performance, corrosion resistance, and ease of construction. However, premature debonding is a major challenge as it prevents the full capacity of FRP composites from being achieved, resulting in material waste. Recently, grooving the surface of concrete before bonding FRP has emerged as a potential solution to this problem. Several experimental studies have evaluated the bond strength of FRP-to-concrete joints with grooves. To facilitate the practical application of this technique, it is necessary to develop comprehensive reliability-based design guidelines that account for the uncertainty arising from various aspects such as materials, model errors, and loading. A critical factor of such analysis is the calibration of model uncertainty which significantly affects the accuracy of reliability-based design and analysis. The objective of this study was to measure the model uncertainty of the existing prediction model for FRP-to-concrete joint with a longitudinal groove by involving the model factor which is defined as the ratio of observed values from experimental test to calculated values from prediction models. To eliminate the potential correlation from critical parameters, the residual model factor was isolated from model factor by separating the systematic part. The lognormal distribution was found to be the most suitable distribution function to describe the residual model factor, and the mean and variance were determined. With this newfound knowledge, we are better equipped to account for uncertainties in the design and construction of FRP-to-concrete connections with grooves, which will ultimately result in more durable and reliable structural improvements.

his paper presents preliminary experimental and numerical results of a research program aimed at investigating the residual capacity of 60-year-old reinforced concrete bridge girders strengthened using CFRP sheets. Two 4.5 m and 5.0 m long, bridge girders were deconstructed from a bridge located in Canada. The two 60-year-old girders have been strengthened with CFRP for the last six years of the service life of the bridge. The two full-scale girders were tested at the structural lab of Sherbrooke’s University after having suffered under real service conditions. A finite element model using the ANSYS program had been validated with the experimental results before it was used as a control sample for non-strengthened conditions. The test results revealed that the CFRP strengthening technique can extend the service life of the bridge element by keeping their shear capacity safe. The CFRP strengthening configuration of the two girders increased the maximum shear capacity by 35.5 % and 30 % over the finite element control model. The presented outcomes show the effectiveness of using the external CFRP sheets as an external technique for bridge rehabilitation. The test results were compared with the ACI 440 2R-17 and CSA S6-19 design guidelines. The theoretical comparison between guidelines, experimental and numerical results shows that the two guidelines are considered overly conservative.

The first phase of this work uses experimental evidence to critique some shortcomings of the so-called improved double-lap bond shear tests regarding their limited application to wet layup fiber-reinforced polymer (FRP) and their inapplicability to pultruded FRP laminates. Even in the case of the wet layup FRP, the study provides some evidence of high chances of obtaining undesirable fiber rupture that preclude the use of the results as reliable means for interpreting the FRP-concrete bond-slip models. Further proposed modifications to overcome these challenges are provided by designing a convertible bond tester applicable to both wet layup and pultruded FRP laminates. Apart from the application of the apparatus to FRP-concrete bond assessment under pure double shear, it proved to be applicable to conducting mixed-mode bond tests. The second phase of the work upgrades the so-designed test apparatus to make it convertible to bond testing of other variants (near-surface mounted [NSM] FRP bars/strips, fiber-reinforced cementitious mortar [FRCM], etc.) of strengthening systems without developing a different apparatus for each. The apparatus allows testing the NSM FRP-concrete bond in a novel manner compared to the traditional practice. Also, given the absence of mixed-mode studies for FRCM, the apparatus provides a pioneer means of conducting the same.

In the last decades, the devastating effects of earthquake events in seismic prone regions increased the attention on the vulnerability of existing constructions. Masonry walls especially experienced severe damage, both considering out-of-plane and in-plane mechanisms. To increase their resistance to horizontal forces, different strengthening systems can be applied. The objective of the present work is to study the efficiency of an innovative strengthening solution, involving the use of fiber reinforced polymer (FRP) pultruded bars. An experimental campaign is presented, in which clay-brick single-leaf masonry panels are retrofitted by carbon FRP rebars, inserted into grooves cut within the masonry panel with a cementitious mortar, and CFRP sheets applied on the panel external surfaces. A total of seven direct shear tests (ST) and four diagonal compression tests (DC) were performed on unreinforced and strengthened samples. The results of the tests showed that the strengthening technique can be effective for the improvement of the shear sliding and diagonal cracking resistances, also allowing to deepen the knowledge of the principal failure mechanisms characterizing the FRP-retrofitted masonry elements.