International Concrete Abstracts Portal

Ultra-high-performance concrete (UHPC) features tensile strain-hardening behavior and a high compressive strength. Existing studies on the shear behavior of UHPC structural members have been focused on prestressed UHPC girders. More experimental data of the shear behavior of non-prestressed UHPC beams are necessary to quantify the safety margin of shear designs for structures. Moreover, while the UHPC members in most studies did not contain coarse aggregate to strengthen their microstructure, the inclusion of coarse aggregate has been shown to substantially reduce the autogenous shrinkage and enhance the elastic modulus for UHPC materials, which is beneficial for structural applications of UHPC. This study experimentally investigated the shear failure behavior of eighteen non-prestressed rectangular UHPC beams. The experimental variables included the volume fraction of fibers, shear span-to-depth ratio of the beams, and coarse aggregate. The detailed shear failure responses of the UHPC beams were discussed in terms of the damage pattern, shear modulus, shear strength, shear strain, and strain energy. The test results showed that the inclusion of coarse aggregate increased the beam shear strength, and its enhancement became more significant with a higher volume fraction of fibers and a lower shear span-to-depth ratio of the beam. In addition to the experimental investigation, a shear strength model for non-prestressed rectangular UHPC beams that accounts for the interactive effect of the key design parameters was developed. An experimental database of the shear strength of the UHPC beams in existing studies was established to assess the performance of the proposed model. It was shown that the proposed model reasonably predicted the shear strength of the UHPC beams in the database with a higher accuracy and lower scatter compared to the results of existing models.

Most of the research related to interface shear transfer in concrete elements has utilized steel bars as reinforcement, while GFRP reinforcement has received little attention experimentally and analytically. For this reason, only a few design specifications include provisions for the calculation of the interface shear transfer when using GFRP. In this project, an experimental campaign is being conducted to determine the contribution of GFRP bars to the mechanism of shear transfer by using push-off specimens. The literature review and the test methodology are reported in this paper. The obtained results indicate that the use of GFRP reinforcement significantly enhances the interface shear strength, resulting in a capacity that exceeds those of the specimens without reinforcement. When the GFRP-reinforced specimen reaches the first crack at a load similar to that of the unreinforced specimens, it continues carrying load until it reaches a peak, thus indicating that the reinforcement is providing both dowel action and clamping force prior the shear failure. Additionally, once the peak strength is reached, the use of GFRP reinforcement allows the specimen to deform in a pseudo-ductile fashion thus preventing sudden failure.

This paper presents an experimental study that investigated the physical and mechanical properties of the helical wrap glass fiber-reinforced polymer (GFRP) bars. The physical tests are conducted to check the feasibility and quality of the production process through the cross-sectional area and evaluation of the fiber content, moisture absorption, and glass transition temperature of the specimens. While the mechanical tests in this study included testing of the GFRP specimens to determine their tensile properties, transverse shear, and bond strength. Four bar sizes (#3, #4, #5, and #6), representing the range of GFRP reinforcing bars used in practice as longitudinal reinforcement in concrete members subjected to bending, are selected in this investigation. The GFRP bars had a helical wrap surface. The tensile failure of the GFRP bars started with rupture of glass fibers followed by interlaminar delamination and bar crushing. The bond strength of the GFRP bars satisfied the limits in ASTM D7957/D7957M. The test results reveal that the helical wrap GFRP bars had physical and mechanical properties within the standard limits.

The near surface-mounted (NSM) technique utilizing fibre-reinforced polymer (FRP) reinforcements has gained significant popularity in enhancing the shear resistance of reinforced concrete (RC) beams. Various models have been proposed to predict the shear contribution of NSM FRP reinforcement in RC beams. In this study, the performance of five well-established models, namely those proposed by De Lorenzis and Nanni, Rizzo and De Lorenzis, Dias and Barros, Bianco et al., and Mofidi et al., is assessed. A comprehensive database comprising 137 beams from published works is compiled for this assessment. The findings reveal that the model proposed by Bianco et al. exhibits superior predictive performance but tends to produce extremely conservative predictions. On the other hand, the model proposed by Dias and Barros performs well for beams shear strengthened with FRP laminates, although it is not specifically calibrated for specimens shear strengthened with FRP rods. Notably, the latter model results within an appropriate safety domain, avoiding extreme conservatism. Further research is warranted to develop a comprehensive model with enhanced predictive accuracy.

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.