Journal of Composites for Construction

The shear behavior of basalt fiber–reinforced polymer-reinforced seawater–sea sand concrete (BFRP-SSC) beams was investigated experimentally. The effects of several factors, including stirrup diameters (8, 10, and 12 mm), stirrup spacings (100, 125, and 150 mm), and shear span-to-depth ratios (1.55, 1.95, and 2.35), were considered. The results demonstrated that the shear mechanism of the diagonal section of BFRP-SSC beams could be explained using the arch truss model. Moreover, the shear span-to-depth ratio significantly influences the shear capacity, bending stiffness, diagonal crack width, and shear failure mode of beams, with diagonal compression failure occurring in beams with a ratio of 1.55 and shear compression failure occurring in beams with a ratio between 1.95 and 2.35. In addition, the actual shear capacities of 72 BFRP-reinforced concrete (BFRP-RC) beams were compared to the results obtained by five design provisions. Correction coefficient of shear span-to-depth ratio, modification to stirrup spacing, correction equation of stirrup strain, and shear contribution coefficient of stirrups were proposed to modify the shear equation in ACI 440.1R-15. The results of the modified shear equation showed a good agreement with the actual shear capacities of beams. The findings of this research have theoretical significance for the design and practical application of BFRP-SSC beams in marine construction.

Resistance factors (ϕ-factors) are reliability-based factors of safety used in load and resistance factor design (LRFD) of structural systems. The ϕ-factors specified in the consensus standard for the structural design of pultruded fiber-reinforced polymer (FRP) structural members and connections are generally lower than the ϕ-factors used for more conventional materials (e.g., structural steel, reinforced concrete, and wood) for comparable limit states, consequently potentially limiting the application of pultruded FRP as a structural material. This work describes a review of 350 published experimental tests of bolted connections in pultruded FRP and compares these test results with the nominal strengths from equations in the consensus standard. Subsequently, a first-order reliability method analysis—following the methodology proposed by Ellingwood for pultruded FRP composites—was performed to re-examine ϕ-factors for the most common limit states of bolted connections in pultruded FRP. All relevant limit states for bearing-type connections as defined by the consensus standard were considered in the study and the derived ϕ-factors were compared with the ϕ-factors prescribed in the consensus standard with the goal of highlighting the need for additional research.

In this study, we evaluate the seismic performance of concrete columns reinforced with lap-spliced glass fiber–reinforced polymer (GFRP) bars through simulated earthquake loads. Six 400 × 400 mm columns with an overall height of 1,850 mm were tested. Five columns were reinforced with lap-spliced GFRP bars and one was reinforced with continuous GFRP bars to serve as a reference for comparative purposes. The primary test variables were the transverse reinforcement spacing, tie configuration, and number of bars spliced at the critical section. The experimental investigation was followed by an evaluation of the provisions of related North American design standards on the effect of the confinement and staggering of the lap-splice length. The test results show that the level of confinement and staggering affected the hysteretic response, load-carrying capacity, and bond performance of the column specimens. The influence of the amount of transverse reinforcement on the deformability of the columns was found to be considerable. Staggering, however, did not significantly affect the deformability. A comparison of the results with existing design standards demonstrated that the current provisions in the CAN/CSA S6-19 and ACI 440.11-22 standards for monotonic loading need improvement in order to provide accurate results when considering confinement and staggering in predicting the lap-splice length of GFRP-RC columns under seismic loading.

The ratio of fiber-reinforced polymer (FRP) confinement stiffness to concrete strength (confinement stiffness ratio) has been widely accepted to determine the postpeak stress‒strain behavior of FRP-confined concrete. It has been established that the effects of confinement efficiency are significantly different for normal-strength concrete (NSC) and high-strength concrete (HSC). This paper presents an experimental study of the stress‒strain behavior of carbon FRP (CFRP)-confined circular and square HSC columns. Various FRP confinement stiffnesses were designed for concretes with different strengths to achieve the same confinement stiffness ratios. The test results indicate that although the specimens had similar confinement stiffness ratios, the criterion values of the confinement stiffness ratio to distinguish the postpeak strain hardening/softening transition increased with increasing HSC strength. However, for FRP-confined NSC, it is suggested that a constant value of approximately 6.5 be used. In addition, this study also revealed that for specimens with weak confinement or nonuniform confinement (square cross sections), the change in confinement efficiency at the postpeak stage results in the recovery of the postpeak strain hardening behavior from the strain softening behavior. By incorporating the confinement efficiency parameter in the ultimate condition models for CFRP-confined HSC, the proposed model demonstrated satisfactory performance when compared with the test results.

This paper aimed to study the compatibility between E-glass of chemical resistance (ECR-glass) fibers and the polymer matrix and the influence of different matrix types on the durability performance of ECR-glass fiber–reinforced polymer (GFRP) bars in a marine concrete environment. Two types of matrices, epoxy and vinyl ester, were employed to fabricate GFRP bars, which were then subjected to accelerated exposure by immersion in a simulated seawater sea-sand concrete (SWSSC) pore solution. The degradation performance and damage mechanism were thoroughly investigated. The results indicated that hydrolytic degradation of the cured epoxy and vinyl matrices and subsequent chemical etching to glass fibers are the primary damage mechanisms affecting GFRP bars in the SWSSC environment. Based on these mechanisms, two damage models were proposed: a chemical etching-based model and a hydroxyl ion diffusion-based model. These models enabled the prediction of the residual tensile strength of GFRP bars in the SWSSC pore solution environment at different temperatures. The accuracy of the proposed models was validated through comparisons with experimental data.