Journal of Composites for Construction

The lower elastic modulus of fiber-reinforced polymer (FRP) bars over steel rebar renders the postcracking deflection of FRP concrete beams critical under serviceability limit states. To predict the deflection of FRP prestressed concrete (PSC) beams, the American Concrete Institute (ACI) utilizes a semiempirical equation of effective moment of inertia ($I_e$), originally developed and calibrated for steel reinforced concrete beams, and applies a reduction factor to account for the low elastic modulus of FRP bars. In this paper, a mechanics-based relationship for $I_e$ is developed using the moment-curvature behavior of FRP PSC sections. From this a beam deflection equation is derived for general loading conditions. The proposed equation is verified using experimental observations that cover various ratios of the cracked-to-gross moment of inertia ($I_{cr}/I_g$). The comparative results reveal that the ACI equation unrealistically underestimates the deflection for low $I_{cr}/I_g$ ratios ($<0.04$), which is the case for lightly reinforced FRP PSC beams and one-way slabs. However, for higher $I_{cr}/I_g$ ratios ($>0.08$), for which the semiempirical ACI equation was originally calibrated, reasonable predictions are observed. The proposed equation, which offers an implicit flexibility formulation as opposed to the stiffness formulation adopted by ACI, provides more accurate predictions of deflection regardless of the $I_{cr}/I_g$ ratio.

This paper introduces an innovative composite railway sleeper with an optimal material usage for a narrow-gauge railway track under static loading condition. The composite sleeper is designed using sandwich panels that were bonded and coated with epoxy polymer matrix. The sleeper’s optimized shape was obtained using topology optimization. The vertical deflection and sleeper-ballast contact pressure of the optimized sleeper were analyzed by finite-element simulation and compared with a traditional timber sleeper. Prototype sleepers were then manufactured and their performance was evaluated experimentally. Results showed that the optimal sleeper shape only needs 50% volume of materials required for a standard rectangular timber sleeper. The performance of the optimal sleeper satisfactorily met the Australian standard requirements and was very similar to a timber sleeper indicating the high potential of this sleeper technology to replace the existing timber sleepers. This new sleeper is currently being tested in the Queensland Rail network as part of their sleeper maintenance program.

This paper presents the experimental results of seven full-scale glass fiber-reinforced polymer (GFRP) reinforced concrete (RC) slab–column edge connections. The dimensions of the slabs were $\mathrm{2,800}\times \mathrm{1,550}\times 200\mathrm{mm}$ with a square column measuring $300\times 300\times \mathrm{2,200}\mathrm{mm}$. The test connections were divided into two series. Series 1 included three high-strength concrete (HSC) connections, investigating the effect of the flexural reinforcement ratio (0.90, 1.35, and 1.80%); and Series 2 included four normal-strength concrete (NSC) connections, investigating the effect of the GFRP shear-reinforcement type (headed studs or corrugated bars) and pattern (six or eight lines of shear reinforcement). The test results showed that increasing the reinforcement ratio increased the punching capacity and the postcracking stiffness of the HSC connections. The test results also showed that the use of headed studs and corrugated bars increased the punching capacity and the deformability of the NSC connections. The test results were compared to the predictions of the Canadian and American design provisions for FRP-RC structures.

Fiber-reinforced polymer (FRP) bars and fiber-reinforced concrete (FRC) are composite materials that have found acceptance in current construction systems due to their high strength-to-weight ratio, durability, and ease of installation. This study presents an experimental and analytical study on the potential of these materials to improve the seismic behavior of low-rise shear walls. Two low-rise concrete shear walls with similar geometry were tested up to failure under pseudostatic lateral cyclic loads. The first wall was a steel-RC low-rise shear wall, compliant with seismic considerations of North American codes for structural reinforced concrete. The second was a steel fiber-reinforced concrete (SFRC) wall reinforced with a hybrid scheme of FRP-steel bars as flexural reinforcement. The FRP bars had the purpose of enhancing the self-centering capacity of the wall, while the SFRC helped to mitigate the damage experienced by the concrete. The goals were achieved reasonably in the testing phase. A finite-element analysis model for low-rise hybrid shear walls was developed and verified with experimental results. The analysis model is able to predict system performance variables with satisfactory accuracy for both walls, such as force-displacement relationship, stiffness, and energy dissipation. The experimental and analytical results show that the hybrid glass fiber-reinforced polymer (GFRP)-steel reinforced walls can achieve similar strength, stiffness, and ductility levels to RC construction while experiencing less residual displacements.

This study addressed the feasibility of reinforced-concrete squat walls totally reinforced with glass fiber-reinforced polymer (GFRP) bars achieving the strength and drift requirements specified in various codes. Using noncorrodible GFRP bars represents an effective method for overcoming deterioration due to corrosion problems. The previous experimental studies on GFRP-reinforced midrise shear walls showed that GFRP reinforcement can control shear deformation, which is a major problem in steel-reinforced squat walls. Five full-scale concrete squat walls with an aspect ratio (height to length ratio) of 1.3, one reinforced with steel bars (as a reference specimen) and four totally reinforced with GFRP bars, were constructed and tested to failure under quasi-static reversed cyclic lateral loading. The reported test results clearly show that properly designed and detailed GFRP-reinforced concrete squat walls can reach high deformation levels with no strength degradation. The results also show that the achieved drift satisfies the limitation in most building codes. Acceptable levels of energy dissipation, compared to the steel-reinforced squat wall, were observed. The promising results can provide impetus for constructing concrete walls reinforced with GFRP and constitute a step toward using GFRP reinforcement in such lateral-resisting systems.

An overview of an experimental program investigating the effectiveness of fabric-reinforced cementitious matrix (FRCM) to limit the damage in shear critical unreinforced hollow concrete masonry assemblages is presented. The experimental program involved the mechanical testing of the constituent materials and the diagonal shear testing of 16 masonry panels constructed to replicate the masonry types prevalent in nonductile reinforced concrete frames with masonry infill buildings. The test variables investigated included the masonry type, the FRCM fabric material, and the number of FRCM layers. Three FRCM fabrics (basalt, glass, and carbon) and two masonry types (200 and 150 mm thick) were used. The FRCM strengthening changed the failure mode from brittle bed joint sliding to a more gradual distributed diagonal cracking and/or toe crushing, with a shear strength increase of 104–258% for 150-mm thick masonry panels and 69–156% for 200-mm thick masonry panels. A substantial increase in the ductility and energy dissipation capacity was also noted for the FRCM-strengthened masonry panels. The shear stress-strain behavior, deformation capacity, pseudoductility, energy dissipation, and stiffness characteristics were analyzed and discussed. The behavior of the FRCM-strengthened panels was predicted using analytical equations, and the predicted values were compared to the experimental results.