Journal of Composites for Construction

In this article, we examine the influence of bolt threads on the tensile rupture strength of the net section corresponding to single-bolt double-lap connections in pultruded materials made of dicyclopentadiene-based unsaturated polyester resin reinforced with E-glass fibers in the forms of roving, continuous-strand mats and triaxial fabrics that incorporate chopped strand mats and plies oriented in the ${45}^{\circ }$, ${90}^{\circ }$, and ${-45}^{\circ }$ directions with respect to the longitudinal direction (i.e., roving direction). Thirty-six single-bolt double-lap connection tests were carried out on plates in which the bolt-hole diameter to plate width ratios were 0.5, 0.6, and 0.75. All these connection tests incorporated finger-tight A307 zinc-coated bolts fully threaded in one case and partially threaded in another case. The results from these experiments revealed that bolt threads in contact with the bolt-hole surface influence the tensile resistance of the net section. This influence is evident as the bolt-hole diameter to plate width ratio decreases. Analysis of our findings highlights a notable discrepancy: current design guidelines in both the United States and Europe can considerably underestimate the net section tensile rupture strength of single-bolt connections made from pultruded materials with an offaxis reinforcement scheme. Recommended design guidelines that can be adopted by practicing engineers are proposed.

This paper presents the results of an experimental study to investigate the effects of two types of graphene, dried (DG) and hydrated graphene (HG), when enhancing the interfacial and tensile mechanical properties of fabric-reinforced cementitious matrix (FRCM) composites. The inclusion of DG and HG could produce an improvement in the tensile strength of the FRCM composites by increasing the tensile strength of the mortar paste and the amount of fibers that participate in load bearing due to the increased penetration of mortar (cement hydrates) into the fiber bundle. The better dispersion of HG produces better results than DG. The maximum increases in the overall tensile strengths of the FRCM composites with DG and HG are 18% and 31%, respectively, with the majority of these improvements coming from the increase in the number of fibers that participate in load bearing. The microstructure images indicate increases of up to 20% and 44% in the mortar penetration thickness into the fiber bundles using DG and HG, respectively.

The combination of glass fiber–reinforced polymer (GFRP) and ultrahigh-performance concrete (UHPC) to form structural members has generated significant interest due to their excellent durability and mechanical properties. This paper presents the flexural behavior and design methodology of GFRP-reinforced UHPC beams. Eight reinforced UHPC beams were tested to failure, varying in longitudinal reinforcement type (steel and GFRP), flexural reinforcement ratio, and steel fiber volume fraction (1% and 2%). Two flexural failure modes, including crack localization followed by rupture of GFRP (tension failure) and progressive crushing of UHPC followed by rupture of GFRP (compression failure), were observed in the tested GFRP-reinforced beams. Substitution of steel bars with GFRP bars resulted in delayed crack localization and a significant improvement in flexural strength by 54.9% and ultimate displacement by 55.7%. Increasing the GFRP reinforcement ratio showed a trend of increased flexural capacity, ultimate deformation, and energy dissipation capacity. Increasing the steel fiber volume in UHPC improved the flexural capacity of the tension failure–controlled beam, but had a slight effect on the flexural capacity of the compression failure–controlled beam. In addition, two different models were used to calculate beam deflection, and were compared with experimental results at the service load levels. Considering the fiber-bridging mechanism, a flexural strength model for GFRP-reinforced UHPC beams was developed. Finally, a minimum reinforcement ratio was proposed to ensure progressive failure of GFRP-reinforced UHPC beams.

Fiber-reinforced polymer (FRP) wraps of reinforced concrete columns might be vulnerable to accidental damage or vandalism. This study aims to develop a simple empirical tool that is based on experimental results to aid in the condition assessment and establish the reduced axial strength ratio (P/P_o) of short columns that are loaded at small eccentricities. A total of 47 cylinders, 152 mm in diameter (D), were wrapped with carbon–FRP sheets of 1–3 layers [i.e., producing confinement effectiveness $(f_{cc}^{\mathrm{\prime }}/f_c^{\mathrm{\prime }})$ of 2.3–4.0] and were then subjected to a vertical cut of length (x) that varied from 0.20D to 0.61D at midheight. The loading eccentricity (e) varied from zero to 0.1D. The cut location around the perimeter, for the angle (θ) that was measured from the point of extreme compression, was varied from 0° to 180°. The jacket cuts affect eccentrically loaded cylinders more severely than concentrically loaded ones. As e increased from zero to 0.1D, P/P_o reduced from 1.0 to 0.81 for intact samples and from 0.56 to 0.40 for samples with jacket cut. As the cut location traveled around the circumference starting from extreme compression (θ = 0°), less strength reduction was observed where P/P_o increased, and at θ = 180° it even exceeded P/P_o at zero eccentricity. This suggests a reduction in eccentricity due to a shift in the cross-sectional centroid due to the disturbed confinement on one side. Design models that account for e/D, θ, x/D, and inclined cuts have been developed and calibrated for cylinders of up to 22 slenderness ratio. In addition, a design example is presented.

This paper presents the first seismic tests on a full-scale all-composite frame structure, constituted by pultruded glass fiber–reinforced polymer (GFRP) profiles, to the best of the authors’ knowledge. These tests were performed in the scope of the FRP-Quake project, which aimed to provide an in-depth understanding of the dynamic and seismic behavior of all-GFRP structures, and to develop structural systems with adequate seismic resistance. Therefore, an extensive research program was conducted, from the material and component scales to the structural full-scale, which encompassed the development of appropriate beam-to-column bolted connection systems. The experimental campaign presented in this paper was composed of shaking table tests on a full-scale, two-story, three-dimensional (3D) frame of I section pultruded GFRP profiles connected with bolted stainless steel parts. First, modal identification tests were performed, which show the influence of adding floor masses, bracings, or both on the dynamic characteristics of the structure, which were accurately predicted with relatively simple linear finite-element (FE) models. Then, the frame structure was subjected to 18 base displacement histories with increasing intensity, which was based on the design earthquake for mainland Portugal. The results showed that the structure maintained its integrity for intensities up to 37% higher than the normative requirements. This showed the feasibility of using this type of all-GFRP structures in seismic areas.

Predicting the shear contribution of a fiber-reinforced polymer (FRP) strengthening system in a reinforced concrete (RC) beam strengthened using the embedded through-section (ETS) method remains challenging due to the complex shear mechanisms involved. The present study proposes a new approach that analyzes the shear resistance mechanism for ETS-FRP strengthening bars by investigating their bonding behavior with concrete. First, the consistency of existing bond models and parameters for simulating the bond profile for ETS-FRP bar-to-concrete joints was studied using a simplified finite discretization method (FDM). After validation using pullout tests, the maximum bond stress, slip at peak bond stress, and slip at complete debonding were found to be consistent for all bond laws. This allows researchers and engineers to conveniently obtain suitable bond parameters for their designs. A bonding-based approach coupled with the FDM that considers various bond rules and crack compatibility for analysis of the ETS shear contribution was then developed. The proposed approach can analyze the behavior and failure progress for single ETS strengthening elements. Based on corroboration using 46 sets of beam data, the proposed method was found to more accurately predict the ETS-FRP shear contribution than current shear design models. The results of this study indicate that using the proposed method, the ETS shear resistance can be reliably estimated by applying bilinear, trapezoidal, and nonlinear bond laws considering the compatibility of nonuniform crack widths.

Abstract

This paper presents a pioneering experimental investigation of the fatigue behavior of a full-scale (15.24 m × 3.89 m) concrete bridge deck reinforced with glass fiber–reinforced polymer (GFRP) rebar under rolling (R)-load cycles applied using the Rolling Load Simulator (ROLLS) at Queen's University, Canada. The study compares this type of fatigue with conventional fixed-point pulsating (P)-loads. The deck is supported by two Steel I-girders spaced at 3.05 m. A 3.81-m-long section on one end was subjected to R-loads and a similar section on the other end, to P-loads, both up to 3 million (M) cycles. Monotonic tests were performed periodically. The study showed that R-load results in far more fatigue damage than P-load, as reflected by 71% and 54% stiffness degradation (k/k_o), respectively. This suggests that cumulative damage of one R-cycle is equivalent to 120 P-cycles. Live load deflection limit of span/800 was reached in the R-loading section after 0.78M cycles, and at 3M cycles was exceeded by 15%, but the P-loading section remained below the limit. GFRP reinforcement performed very well, with maximum strain remaining below 10% of the guaranteed tensile strain. The R-load section showed far more extensive and dense grid-pattern cracking with concrete pitting at the soffit, while the P-load section showed minor longitudinal and some radial cracks. A conversion factor (ξ) is established to enable researchers and designers convert (k/k_o) from readily and easily available P-loading to an equivalent R-loading of GFRP-reinforced deck at any number of cycles, since P-loading is not conservative and R-loading capabilities are not easily available. In this study, ξ is 0.59 at 3M cycles and is projected to be 0.5 at 10M cycles.

Practical Applications

It has been well-established that fixed-point pulsating loads cannot accurately replicate the fatigue damage resulting from traffic loads on bridge elements. The degradation behavior of bridge decks’ stiffness should be studied using rolling loads. However, conducting a rolling load fatigue experiment often requires a specialized apparatus that is not readily available. This paper presents the establishment of a conversion factor (ξ) that can be used to convert the normalized stiffness data of bridge decks tested under traditional pulsating loads into real stiffness degradation data under rolling loads.

Hybrid fiber-reinforced polymer (FRP) composites, combining different types of fibers within a polymeric matrix, have piqued the research community’s interest due to their enhanced mechanical properties and functional performance. These materials offer optimized fiber usage, tailored failure responses, and potential for pseudoductile behavior. Furthermore, hybridization avoids catastrophic tensile failure despite the composites being composed entirely of brittle materials. Empirical evidence from previous research conducted on hybrid FRP composites for civil engineering applications suggests their potential as a promising asset to the field. This review paper collates extensive research and development work on hybrid FRP composites for civil engineering applications, providing a comprehensive summary since their inception. It covers areas including the development of reinforcing bars for reinforced concrete (RC) structures, externally bonded strengthening systems for RC structures, pultruded profiles for novel structures, and cables for long-span bridges. The paper begins with a concise overview of the influential developments that paved the way for hybrid FRP composites, followed by an in-depth discussion of their utilization in the construction sector. The paper concludes by extrapolating the potential future trajectory of hybrid FRP composites, providing insights into their future outlook.

This study examined nine concrete members reinforced with glass fiber–reinforced polymer (GFRP) bars, exploring the impact of combined bending moment and low axial loads. Three reinforcement ratios (1.7%, 2.5%, and 3.3%) were considered under various axial loads (0, 125, and 250 kN). In the absence of a standardized test method for determining the compressive properties of rebars, a simple approach was adopted. GFRP bars demonstrated a compressive modulus of elasticity that was roughly equivalent to their tensile modulus, along with a compressive strength reaching approximately 70% of their tensile strength. The main tests on members showed that increasing the reinforcement ratio to 3.3% resulted in a 4% reduction in bending resistance with a 2% axial load, while a ratio of 2.5% led to a 7% decrease; conversely, a lower ratio of 1.7% showed a 2% increase in bending resistance under the same load. An analytical model incorporating GFRP bar compression contributions was developed for cross-sectional analysis. It was verified against experimental and literature data, to conduct parametric studies on the impact of reinforcement ratio, concrete strength, GFRP modulus, and strength on the interaction diagram shape under low axial loads. The results demonstrated that there are two major cases of interaction diagram slope in the proximity of the pure moment axis. At higher reinforcement ratios, the moment resistance diminishes at low axial loads when compared with pure moment conditions. However, more research is needed to verify the repeatability of the test results and draw conclusive empirical evidence.

One of the common deficiencies of pre-70s reinforced concrete (RC) moment frames is the shear failure of beam–column (BC) joints. In addition to that, joints with high tension demand have limited shear capacity to resist seismic actions, according to the New Zealand (NZ) seismic assessment guidelines. Fiber-reinforced polymers (FRP) have been widely used in research and practice for seismic retrofitting of BC joints prone to shear failure. However, in many cases, the tests were conducted on two-dimensional BC joints, which does not necessarily represent the limitations structural engineers face in practice, such as the presence of the diaphragm slab, transverse beams, and access limitations to the joint panel. The American Concrete Institute guidelines for FRP strengthening only mention that strengthening joints is possible but do not provide design guidance. The European fib Bulletin 90 provides design guidance but assumes that the joint panel is always available to install FRP, which is rarely the case in real structures. We have proposed a design method for shear strengthening of beam–column joints using FRP sheets and FRP anchors based on the adaptation of aforementioned design documents, published research, and first principles of engineering. The intention is for this case study to inspire other engineers who face the same issue and to encourage further research in this area.