The release of ACI 440.11-22 building design code for concrete structures reinforced with GFRP bars comes with several challenges at various fronts. One such challenge is tackled in this paper which is the development of limit interaction diagrams for elliptical bridge columns reinforced with GFRP bars under biaxial bending plus axial compression/tension. This type of columns requires special considerations at all levels. This paper depicts the various formulations encountered herein in a detailed treatment highlighting the critical steps to build an efficient analysis algorithm. The formulation is implemented into a user-friendly software developed using object-oriented programming, namely the C# programming language. The robustness of the formulation is tested by comparing interaction diagrams of elliptical sections to those of corresponding rectangular sections. The significance of an ACI code comment requiring bar orientation being considered for circular sections with less than 8 bars is also examined in this paper. This paper also tests the ACI recommendation to neglect GFRP action in compression. Results indicate reasonable similarity among interaction diagrams of elliptical and rectangular sections leading to the conclusion that the formulation presented herein provides an accurate tool to analyze elliptical sections.

Carbon Fibre Reinforced Polymers (CFRPs) are a material of choice in the aerospace and automotive industry, but despite decades of research into their application in structural engineering applications, and in particular in new-build construction of buildings and bridges, CFRP elements remain regarded as somewhat exotic in structural engineering and their widespread take-up is mostly limited to the non-prestressed strengthening of conventional structural members. The study presented in this paper assessed the performance of CFRP bridge tendons, prestressed for 18 years at 45% of their design ultimate tensile capacity in a non-conditioned outdoor environment, over water, in Lucerne, Switzerland. The performance of the tendons is considered alongside pristine samples of the same tendons never used and stored, unstressed, indoors since 1997. Thermal characterization (matrix digestion, thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC)) was used to determine the fibre volume fraction and glass transition temperature, and tensile tests were performed and compared against available original baseline results from 1997. This comparisons show that the in-service tendons do not appear to have been adversely affected by 18 years service under sustained loading, and have retained the vast majority of their original, unstressed material properties. The in-service tendons only lost about 10.5% of their ultimate tensile capacity over time, while the pristine (unstressed) tendons also lost 7.9% of their capacity; this suggests that sustained loading and an external, unconditioned service environment do not significantly adversely affect the mechanical properties of the tendons after 18 years in service.

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.

Developments in the prestressed concrete industry evolved to incorporate innovative design materials and strategies driven towards a more sustainable and durable infrastructure. With steel corrosion being the biggest durability issue for concrete bridges, FRP tendons have been gaining acceptance in modern prestressed technologies, as bonded or unbonded reinforcement, or as part of a “hybrid” system that combines unbonded CFRP tendons and bonded steel strands. Assessments of the efficacy of hybrid-steel beams, combining bonded and unbonded steel tendons. in the construction of segmental bridges and in retrofitting damaged members has been established by several researchers. However, limited research has been conducted on comparable hybrid prestressed beams combining CFRP and steel tendons (hybrid steel-cfrp beams). This paper provides an insight on the flexural behaviour of eighteen prestressed beams tested under third-point loading until failure with the emphasis on the tendon materials (i.e., CFRP and steel) and bonding condition (i.e., bonded, unbonded). In addition, a comprehensive finite element analysis of the beams’ overall behaviour following the trussed-beam methodology is conducted and compared with the experimental results. Results show that hybrid beams, utilizing CFRP as the unbonded element maintained comparable performance when compared to hybrid steel beams. The results presented in this paper aim to expand the use of hybrid tendons and facilitate their incorporation into standard design provisions and guidelines.

The seismic performance of reinforced concrete (RC) bridge columns subjected to multidirectional ground motions is a critical issue, as these columns can experience axial compression, bending, and torsional loading. Moreover, steel corrosion is a significant concern in existing bridges, leading to deficiencies in steel-RC structural members. The use of glass fiber-reinforced polymer (GFRP) reinforcement has been established as a practical and effective solution to mitigate the corrosion-related issues associated with traditional steel reinforcement in concrete structures. However, the dissimilar mechanical properties of GFRP and steel have raised apprehensions regarding its feasibility in seismic-resistant structures. The current study involves conducting an experimental investigation to assess the feasibility of utilizing GFRP reinforcement as a substitute for conventional steel reinforcement in circular RC bridge columns subjected to cyclic lateral loading, which induces shear, bending, and torsion. One column was reinforced with GFRP bars and stirrups, while the other column, served as a control and was reinforced with conventional steel reinforcement. The aim of this investigation was to analyze the lateral displacement deformability and energy dissipation characteristics of the GFRP-RC column. The results showed that GFRP-RC column exhibited stable post-peak behavior and high levels of deformability under the applied combined loading. Additionally, with a torsion-to-bending moment ratio of 0.2, both columns reached similar lateral load and torsional moment capacities and were able to attain lateral-drift capacities exceeding the minimum requirements of North American design codes and guidelines.