In this work, hybrid composite having linear gradation of carbon and glass fibers (functionally graded hybrid (FGH)) is made and its material properties are compared with classical sandwich hybrid (SH) laminates, i.e., carbon fibers in between glass fibers or vice versa. The performance of FGH composite is evaluated in tensile, compressive, and flexural loadings. Using analytical approach (rule of mixtures), hybrid effect w.r.t. carbon fiber or glass fiber laminates is determined in terms of strength and stiffness. It is observed that failure of FGH specimen is progressive, i.e., layer by layer failure, due to this high ductility is noticed in comparison with SH specimens except in compression. Stiffness and strength of FGH specimens are higher than SH specimens under tension, compression, and flexural. The FGH has shown 7–8% positive hybrid effect in flexural modulus w.r.t. carbon fiber reinforced polymer laminates. In terms of compressive strains, SH and FGH specimens have shown 526% and 380% positive hybrid effect w.r.t. carbon fiber laminates, respectively. Overall FGH is proved better in comparison with classical SH laminates.

Recent research trends focus on developing bio-based (derived from agricultural byproducts) fiber-reinforced polymer (FRP) composites for structural applications. Fire resistance is one of the key issues that need to be addressed for the use of these FRP materials in buildings. The thermal and mechanical properties of the constituent materials essentially determine the fire performance (and the fire resistance rating) of a structural member, and these properties vary with temperature. Further, the properties of composite materials such as the FRP are highly influenced by the composition and type of fibers and matrix, and these thermo-mechanical properties also vary significantly with temperature. Due to this variation, the fire resistance of FRP materials (both conventional and bio-based) poses a major concern for use in buildings. Currently, very few standardized test procedures are available for evaluating the high-temperature material properties of FRP composites. In this paper, a review of testing protocols and procedures for undertaking tests on FRP materials at various elevated temperatures for evaluating their properties is carried out. Recommendations are provided on the most suitable test methods, specimen conditions, testing regime, and other issues associated with testing at elevated temperatures. In addition, the applicability of the proposed test methods is illustrated through a case study on conventional FRP specimens. Further, the applicability of the recommended test procedures for measuring high-temperature properties of bio-based FRP composites is highlighted.

The main objective of this study is to investigate the effect of combining natural and synthetic fibers on the mechanical characteristics of hybrid and novel functionally graded hybrid composites by considering hemp as natural fiber and carbon and glass as synthetic fibers. Before manufacturing, the natural fibers were treated with sodium hydroxide (NaOH) solution to remove the impurities on the fiber surface. The fibers were reinforced in an epoxy‐based matrix using a hand‐layup technique. The volumetric fraction of the hybrid composites was 40% fibers and 60% matrix. Different types of composites, such as plain fiber reinforced polymer (FRP), sandwich hybrid (SH), alternative hybrid (AH), and functionally graded hybrid (FH), were manufactured from hybridizations of hemp/carbon and hemp/glass. In accordance with ASTM standards, the tensile, compression, flexural, short beam shear, water absorption, and wettability properties of composites were determined. FH composites with hemp fiber at the top surface had the highest improvement in tensile strength, stiffness and compressive strength compared with pure hemp FRP (HFRP) composites. Hemp SH composites had the highest improvement in flexural and short beam properties in both hybridizations compared with HFRP composites due to the stacking of synthetic fiber at the outer layers. Scanning electronic microscopic (SEM) studies identified the failure mechanism of the tensile failure specimens and also the effect of mercerization on fiber surfaces. In conclusion, this work identified the structural capacity of hybrid composites and emphasizes that FH and hemp SH composites can replace glass FRP composites in structural applications.Highlights: Treating hemp fiber with 2 g/L of NaOH for an hour had a better impact. Functionally graded composites had better in‐plane strength and stiffness. Composites made with synthetic fiber on the outer layers were good at bending. In structural applications, hemp/carbon hybrid composites can replace GFRP.

This paper focuses on the flexural behavior of masonry walls strengthened with precast engineered cementitious composite (ECC) sheet. The walls were subjected to out-of-plane static loading and analyzed using ABAQUS. For the validation of numerical results, four masonry walls of size 762 × 480 × 230 mm were cast using burnt clay bricks and cement mortar. Out of four, two masonry walls were strengthened with precast ECC sheet using epoxy as adhesive, and the remaining two acted as control specimens. The validation of numerical results with the experimental results shows that the model can effectively capture the nonlinear behavior of masonry and ECC to predict the strength and failure mechanism. The influence of mesh size on the numerical results is also reported. Further, a parametric study has been carried out to observe the effect of several parameters such as percentage of ECC reinforcement ratio, span/depth (L/d) ratio and width/thickness (b/h) ratio of the strengthened masonry walls. This study reveals that the precast ECC sheet increases the load-carrying capacity and ductility of brick masonry walls and hence demonstrates its performance as a strengthening element for brick masonry structures.

This paper presents a numerical study to evaluate the fire resistance of concrete beams and slabs incorporating natural fiber-reinforced polymers (FRP). A validated finite element model was applied to carry out a series of numerical studies on fire-exposed reinforced concrete (RC) beams and slabs strengthened with conventional and bio-based FRP composites. The model calculates the temperature-dependent moment–curvature relationship for various segments of the member at each time step, which are then used to calculate the moment capacity and deflection of the member. The variables in the beams and slabs include different strengthening techniques (externally bonded FRP and near-surface mounted FRP), different fiber composites, and fire insulation schemes (uninsulated and insulated). The results from the study indicate that the bio-based FRP-strengthened RC members undergo a faster degradation in moment capacity and also experience higher deflections under fire exposure. This leads to a lower fire resistance in RC members with bio-based FRP composites compared to beams and slabs with conventional FRP-strengthened concrete members. The addition of fire insulation to the bio-based FRP-strengthened members can enhance their fire performance and help achieve the required fire resistance ratings for use in building applications. In this study, the NSM CFRP-strengthened RC beams were found to have a fire resistance of 3 h without any fire insulation; however, the bio-based FRP-strengthened beams required a layer of vermiculite–gypsum-based fire insulation material (of about 25 mm) to achieve similar fire resistance.