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.

The two-way shear equation in ACI CODE-440.11 was originally developed nearly two decades ago using experimental data from early fiber-reinforced polymer (FRP) materials, most of which are no longer representative of modern glass fiber-reinforced polymer (GFRP) reinforcement. With current GFRP bars exhibiting significantly improved mechanical and surface properties, the validity of the existing equation requires reassessment to ensure practical and economical design. This study evaluates the ACI CODE-440.11 two-way shear provisions using a comprehensive database of 49 GFRP-reinforced concrete (GFRP-RC) interior slabs and 14 edge column connections. The current code equation was found to be highly conservative, yielding an average test-to-predicted ratio of 2.13. Updated equations are proposed for both interior and edge conditions, reducing the ratio to 1.02 and 1.04, respectively, while maintaining acceptable statistical variation. Additionally, symbolic regression (SR) is used to develop machine-learning-based expressions that show high predictive accuracy. The proposed models provide reliable, physically grounded, and less-conservative predictions of punching shear capacity, supporting broader implementation of GFRP reinforcement in structural concrete applications.

An experimental study was conducted to compare the long-term performance of two partially prestressed concrete (PC) beams reinforced with either bonded carbon fiber-reinforced polymer (CFRP) tendons (CFRP-PC) or steel strands (steel-PC) under 1200-day sustained loading. The deflections increased rapidly during the first 200 days and then at a slower rate. The final-to-initial deflection ratio was 1.58 for the CFRP-PC beam and 1.45 for the steel-PC beam. The final-to-instantaneous maximum crack-width ratio was approximately 2.00 for both beams. Based on the age-adjusted effective modulus method (AEMM), a finite element analysis (FEA) program was developed and calibrated using the experimental results. Parametric simulations were subsequently performed on 14 beams. A modification of the suggested equation in ACI 440.1R-15 was proposed to predict the time-dependent deflection of PC beams, which exhibits an improved correlation with the experimental results as compared to the design standards.