International Concrete Abstracts Portal

This paper presents post-fatigue residual punching shear strength experiments of two identical sections reinforced by glass fiber-reinforced polymer (GFRP) rebar in a large bridge deck (15.24 m x 3.89 m x 0.21 m) supported by steel girders spaced at 3.05 m. The experiment was designed to isolate the influence of fatigue loading type on residual punching shear strength. The sections have experienced 3 million cycles of service loads, one using pulsating loads (PL) and the other using rolling loads (RL). Although the RL section suffered more stiffness degradation (71%) than the PL section (54%), both had comparable punching shear strengths (Vu), within 4%. Available equations, including ACI and CSA code regulations, underestimated Vu by 24-54% because they do not account for end restraints, which generate compressive membrane effects that significantly increase the punching shear capacity of concrete slabs. Nonlinear finite element analysis was conducted and used to examine interactions between multiple loading axles as well as offset of the loads from the center. Vu under 2 half axles spaced at 1.2 m (i.e., the 2 axles likely to interact in design truck CL-625 of the Canadian Highway Bridge Design Code) increases by only 34% compared to a single load.

Hollow concrete columns (HCCs) are an effective structural system in construction, offering high strength and stiffness while maintaining low self-weight. Limited research to date has focused on hollow square concrete columns reinforced with fiber-reinforced polymer (FRP) bars. This paper investigates the structural behavior of hollow square concrete columns (HSCCs) reinforced with glass FRP (GFRP) bars and ties under eccentric loading. Twelve hollow square reinforced concrete (RC) columns were cast with a square cross section of 400 x 400 mm and an inner circular hollow of 150 mm in diameter and 2000 mm in height. The tested specimens were divided into three groups based on the longitudinal reinforcement ratio (1.2%, 1.6%, and 2.9%). Each group consisted of four identical columns tested under four levels of eccentricity (e/h = 10%, 20%, 40%, and 80%) to investigate their influence on the structural behavior of the columns. The test results reveal that the eccentricity level had a more significant effect on the structural performance of these columns than the reinforcement ratio. The failure mode of the specimens tested under low eccentricity levels was compression-controlled, starting with concrete crushing. Contrarily, the failure mode of the specimens tested under high eccentricity levels was tension-dominated failure. Furthermore, increasing the eccentricity level from 10% to 20%, 40%, and 80% decreased the axial load capacity of the column by approximately 13%, 52%, and 80%, respectively. Lastly, increasing the reinforcement ratio enhanced the post-peak behavior of the columns. These findings offer critical insights into the structural behavior of hollow square concrete columns (HSCCs) reinforced with GFRP bars and are expected to guide design engineers and contribute significantly to North American standards and design guidelines for HSCCs reinforced with GFRP reinforcement.

The interference between steel fiber and coarse aggregate reduces the homogeneity of fiber distribution and orientation, which may compromise the expected reinforcing effectiveness of steel fibers in concrete. Traditional destructive testing techniques constrain the quality control of steel fiber distribution in prefabricated concrete segments; developing an inductance-based technique contributes to non-destructive characterization of steel fiber distribution. This work uses a Helmholtz coil to solve the magnetic field non-uniform distribution, thereby designing an inductor device to improve the accuracy of steel fiber distribution monitoring within concrete. On this basis, a multi-parameter experiment was designed to study the coupling effect of coarse aggregate and steel fiber, with key variables including water-to-binder ratio, coarse aggregate gradation, steel fiber mixing sequence, vibration duration, and casting flow distance. The C50 concrete mixture incorporates fly ash (75 kg/m³) as a supplementary cementitious material to improve workability and particle packing density. The primary findings are as follows: the induction-based method enables non-destructive evaluation of steel fiber content and orientation in steel fiber‑reinforced concrete containing coarse aggregate (SFRC‑CA), demonstrating high detection efficiency. The larger the aggregate size and water-binder ratio, the worse the steel fiber distribution uniformity. Improper vibration will lead to steel fiber thickness-related settlement, while the longer the flow distances, the more uneven the orientation of the fiber. These results offer important reference for material design and quality control of precast SFRC-CA components.

Limited studies explored the shear friction behavior of reinforced concrete (RC) elements using glass fiber-reinforced polymer (GFRP), mostly using bent bars. This study investigates the behavior incorporating GFRP headed-end bars with varying reinforcement ratios and interface conditions. Twenty-one push-off specimens were tested to evaluate the influence of interface condition (i.e., as-cast, intentionally roughened, and monolithic joints), reinforcement type (i.e., steel stirrups, GFRP headed-end bars), and ratio (0.33 to 1.00%). The results revealed that interface condition and reinforcement stiffness significantly impact the behavior. Surface roughening slightly increased the capacity of the GFRP-RC specimens by 2 to 23%, while the monolithic GFRP-RC specimens reached peak loads up to 118% higher than the as-cast specimens. The GFRP-RC specimens exhibited significant load recovery, with secondary peak loads exceeding the first peak by up to 60%. Comparisons with existing models indicated that, in most cases, they inaccurately predict the capacities when GFRP connectors are utilized.

The calculation of the nominal flexural strength of concrete members prestressed with hybrid (that is, a combination of bonded and unbonded [steel and/or carbon fiber-reinforced polymer (CFRP)]) tendons is dependent on determining the stress in the unbonded prestressed reinforcement. Current provisions in ACI CODE-318-25 are only applicable to members with either unbonded or bonded steel tendons. Additionally, while ACI 440.4R-04 is adopted for unbonded CFRP tendons, neither ACI provision addresses the use of hybrid tendons. This paper presents a closed-form analytical solution for the stress at ultimate derived based on the modified deformation-based approach (MDBA) that is applicable to beams prestressed with unbonded, hybrid (steel or FRP), external with deviators or internal tendons, with and without nonprestressed reinforcement. An assessment of its accuracy and applicability in calculating the nominal flexural strength is examined using a large database of 330 beams and slabs (prestressed with steel and/or CFRP tendons) compiled from test results by the authors as well as those available in the literature. Results predicted by the proposed approach exhibited excellent accuracy when compared to those predicted using ACI CODE-318 or ACI 440.4R stress equations. They also show that the approach is universally applicable to any combination of bonded and/or unbonded (steel and/or CFRP) tendons, span-depth ratio, and loading applications.