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The behavior of precast concrete tunnel lining (PCTL) segments reinforced with glass fiber-reinforced polymer (GFRP) bars under punching loads is one area in which no research work has been conducted. This paper reports on an investigation of the punching-shear behavior of GFRP-reinforced PCTL segments induced by soil conditions, such as rock expansion or the geotechnical conditions surrounding a tunnel. Six full-scale rhomboidal PCTL specimens measuring 1500 mm (59 in.) in width and 250 mm (9.8 in.) in thickness were constructed and tested up to failure. The investigated parameters were: 1) reinforcement type (GFRP or steel); 2) reinforcement ratio (0.46 or 0.86%); 3) stirrups as shear reinforcement; and 4) segment length (2100 or 3100 mm [82.7 or 122 in.]). The experimental results are reported in terms of cracking behavior, punching-shear capacity, deflection, strain in the reinforcement and concrete, and failure modes. The results reveal that the GFRP-reinforced PCTL segment was comparable with its steel counterpart with the same reinforcement ratio and satisfied serviceability limits. Increasing the reinforcement ratio and decreasing the segment length enhanced the punching-shear strength. The shear stirrups improved the structural performance and increased the punching and deformation capacities of the GFRP-reinforced PCTL segments. In addition, theoretical predictions of the punching-shear capacity using the current design provisions were compared to the experimental results obtained herein. The theoretical outcomes show the suitability of using current FRP design provisions for predicting the punching capacity of PCTL segments reinforced with GFRP bars. [ABSTRACT FROM AUTHOR]

Although estimating the post-cracking torsional stiffness is vital for distributing the torsional moment in analyzing statically indeterminate reinforced concrete (RC) structures, none of the North American codes provide an analytical approach for determining the torsional stiffness after cracking. Moreover, the scarcity of experimental work has resulted in the lack of torsion design provisions for concrete box girders reinforced with glass fiber-reinforced polymer (GFRP). Therefore, the purpose of this research was to study the stiffness characteristics of RC box girders reinforced with GFRP reinforcement and to provide a simple analysis technique that can be used to predict post-cracking torsional stiffness. Fourteen concrete box girders were fabricated and tested under a pure torsional moment. In addition, data on 10 solid rectangular RC beams with GFRP reinforcement was collected from the literature. The test results indicate that the concrete strength, as well as the ratio, type, and configuration of the web reinforcement, substantially affected the post-cracking torsional stiffness of the tested specimens. An analytical model was developed for estimating the torsional stiffness after cracking. This model was based on a thin-walled tube and space truss analogy using a concept of postcracking shear modulus. The proposed model considers the effect of concrete strength, the configuration and ratio of the GFRP web reinforcement, and the ratio of the GFRP longitudinal bars. In addition, an equation to calculate the ultimate twist of the GFRP-RC members was developed. The validity of the proposed model was investigated by analytically regenerating the torque-twist curves of the tested box girders and the other specimens available in the literature. [ABSTRACT FROM AUTHOR]

The hysteresis response of precast concrete tunnel lining (PCTL) segments reinforced internally with fiber-reinforced polymer (FRP) bars under quasi-static cyclic flexural loading is an area for which no experimental research results are available. This paper reports on an investigation on the hysteresis behavior of PCTL segments reinforced internally with glass fiber-reinforced polymer (GFRP) bars. Full-scale curvilinear GFRP-reinforced PCTL segments were designed, fabricated, and tested under quasi-static cyclic flexural loading. The segments measured 3100 mm (122 in.) in length, 1500 mm (59 in.) in width, and 250 mm (9.8 in.) in thickness. The test parameters were the longitudinal reinforcement ratio, the transverse reinforcement configuration, and the concrete compressive strength. The hysteresis response, cracking pattern, and ductility of the PCTL segments were identified and experimentally evaluated. The experimental results of the current study demonstrate that the hysteresis response of the curvilinear GFRP-reinforced PCTL segments had stable cyclic behavior with no or limited strength degradation until failure. In addition, analytical prediction of the load-carrying capacity, deflection, and unloading stiffness of the test segments was carried out. The segments' analytically predicted responses were validated and compared to the experimental results. The segments' analytically predicted models for the post-cracking loading tangent stiffness and unloading stiffness for the curvilinear GFRP-reinforced PCTL segments are proposed herein. The analytically predicted hysteresis response shows accurate predictions with comparable loading stiffness, unloading stiffness, and residual deformation at the end of each loading cycle. [ABSTRACT FROM AUTHOR]

This paper reports the results of a comprehensive analytical study implemented to develop deflection prediction methodologies for curvilinear reinforced concrete (RC) members with glass fiber-reinforced polymer (GFRP) reinforcement, focusing on precast concrete tunnel lining (PCTL) segments. The first step involved modifying the procedures for estimating elastic deflection, cracking moment, and cracked moment of inertia, which were then introduced for use with curvilinear members. In the next step, three methodologies of effective moment of inertia, integration of curvature, and integration of curvature considering tension stiffening were developed for curvilinear members. Then, the analytical results were compared to the experimental database, and a novel method was developed for predicting deflection in curvilinear GFRP-RC members. In the third and final step, a procedure was developed to adapt the presented methodologies for use with a tunnel segment under real load and boundary conditions. The results indicate that the proposed method could predict the deflection of curvilinear GFRP-RC members with high accuracy. [ABSTRACT FROM AUTHOR]

The torsional behavior of solid reinforced concrete (RC) members reinforced with fiber-reinforced polymer (FRP) bars has been the subject of several experimental studies. No experimental research, however, seems to have focused on RC box girders reinforced with FRP bars under a pure torsional moment. This paper reports the results of an experimental investigation on the torsional strength and behavior of full-scale RC box girders reinforced with longitudinal glass FRP (GFRP) bars. All specimens measured 380 mm (15 in.) in height, 380 mm (15 in.) in width, 100 mm (4 in.) wall thickness, and 4000 mm (157.48 in.) in length. They were tested under pure torsional loading over a clear span of 2000 mm (78.74 in.). The test specimens consisted of four RC box girders with longitudinal GFRP bars and one RC box girder with longitudinal steel bars as a reference. All the specimens were constructed without web reinforcement to study the contribution of the longitudinal reinforcement to torsional strength. The test variables included the longitudinal reinforcement ratio (ranging between 1.10 and 2.74%) and the type of longitudinal reinforcement (GFRP or steel). The test results indicate that increasing the GFRP longitudinal reinforcement ratio increased the torsional strength after the initiation of the first diagonal crack, especially for specimens with a high reinforcement ratio. In addition, theoretical torsional moment-twist curves were developed and gave predictions consistent with the experimental test results. Lastly, the ultimate torsional strength of the GFRP-RC box girders without web reinforcement was estimated with the CSA S806-12 (R2017) design equation with a modification related to the GFRP tensile strain limit. [ABSTRACT FROM AUTHOR]

Integrating glass fiber-reinforced polymer (GFRP) bars into lightweight self-consolidating concrete (LWSCC) would effectively contribute to producing lighter and more durable reinforced concrete (RC) structures. Nonetheless, the shear behavior of GFRP RC structures cast with LWSCC has not yet been fully defined. This paper reports experimental results on the behavior and shear strength of LWSCC beams reinforced with GFRP bars. The beams measured 3100 mm (122.05 in.) long, 200 mm (7.87 in.) wide, and 400 mm (15.75 in.) deep. The test program included six beams reinforced with GFRP bars and one control beam reinforced with conventional steel bars for comparison purposes. The test variables were the reinforcement type and ratio and concrete density. The experimental results indicate that using LWSCC allowed for decreasing the self-weight of the RC beams (density of 1800 kg/m3 [112.4 lb/ft3 ]) compared to normalweight concrete (NWC). All beams failed as a result of diagonal tension cracking. Increasing the axial stiffness of the longitudinal GFRP reinforcing bars improved the concrete shear capacity of the LWSCC beams. The test results of this study and the results for 42 specimens in the literature were compared to the current fiber-reinforced polymer (FRP) shear design equations in the design guidelines, codes, and literature. Applying concrete density reduction factors of 0.8 and 0.75 in the ACI 440.1R-15 and CSA S806-12 shear design equations, respectively, to consider the influence of concrete density achieved an appropriate degree of conservatism equal to that of the equations for NWC beams. [ABSTRACT FROM AUTHOR]

This study investigated the behavior of hollow concrete columns (HCCs) reinforced with glass fiber-reinforced polymer (GFRP) bars and spirals under axial loading. Nine columns were constructed with a hollow circular cross section having 305/113 mm outer/inner diameter and 1500 mm height, while five solid columns were fabricated as references. Test parameters included the influence of the longitudinal reinforcement ratio (1.89, 2.53, and 3.79%), type (GFRP and steel), and cross-section configuration (hollow and solid) on the behavior of HCCs. The test results show that increasing the reinforcement ratio had no significant effect on the peak load but significantly enhanced the confinement efficiency and ductility of the HCCs reinforced with GFRP bars and spirals. The GFRP longitudinal reinforcement contributed to resisting the peak loads by an average of 11% of the ultimate capacity. Thus, considering the contribution of GFRP bars in the recent design guidelines can safely estimate the ultimate capacity of the HCCs. [ABSTRACT FROM AUTHOR]

Using glass fiber-reinforced polymer (GFRP) reinforcement in precast concrete tunnel lining (PCTL) segments is a practical approach to overcome corrosion problems in underground tunnels. This study involved fabricating full-scale PCTL segments 3100 mm (122 in.) in length, 1500 mm (59 in.) in width, and 250 mm (10 in.) in thickness reinforced with curvilinear sand-coated GFRP bars and testing them under three-point bending load. The investigated parameters were the reinforcement type (GFRP and steel) and reinforcement ratio (0.48, 0.9, and 1.3%) with different configurations of GFRP bar spacing and size. The structural performance of the tested PCTL segments was evaluated in terms of cracking behavior, failure mechanism, load-deflection curve, strain analysis, and deformability. The test results indicate that the structural performance of GFRP-reinforced specimens under bending load was satisfactory in terms of cracking and deflection behavior at service load, ultimate load-carrying capacity, ultimate deflection, and deformability. In addition, increasing the reinforcement ratio changed the failure mode while enhancing the load-carrying capacity, stiffness, and cracking behavior. Lastly, an analytical investigation was conducted to evaluate the ACI 440.1R design provisions for predicting the flexural strength, shear capacity, and crack width of GFRP-reinforced PCTL segments. The experimental and analytical results are presented and discussed herein. The test results and outcomes of this study can serve in assessing and exploring the feasibility of using curvilinear GFRP bars in precast concrete tunnel segments in underground tunnel applications. [ABSTRACT FROM AUTHOR]

The design provisions of reinforced concrete (RC) circular columns in ACI 318 are based on the work done by ACI Committee 105 in 1933 for steel spiral reinforcement. The provisions for volumetric reinforcement ratio and spacing were intended to ensure sufficient confinement after spalling of the concrete cover. This paper presents the development of similar provisions for columns reinforced with glass fiber-reinforced polymer (GFRP) reinforcing bar and spirals that could be adopted in the upcoming version of the ACI 440.1R design guide. A comprehensive database of 56 experiments on concentrically loaded circular columns reinforced with GFRP was assembled from 12 studies with a wider range of parameters. The analysis carried out focused on the confined concrete strength and considered the softening response of the concrete cover, which was presumably omitted in the reported data. An assessment of the available confinement models was made. These models were mostly calibrated with a limited number of specimens. A simpler design-oriented confinement model was developed and accurately predicted the confined strength of the database columns. Additionally, the minimum volumetric ratio of steel spirals in ACI 318 was reviewed and modified for applicability to columns spirally reinforced with FRP. [ABSTRACT FROM AUTHOR]

This paper presents the test results of an experimental investigation conducted on 14 full-scale circular lightweight self-consolidating concrete (LWSCC) columns reinforced with glass fiberreinforced polymer (GFRP) bars and spirals. The 300 mm (12 in.) diameter columns were designed according to CAN/CSA S806-12 code requirements. The columns were constructed using new designed and developed LWSCC and tested under axial and eccentric loading. The test variables were the eccentricity-to-diameter ratio, longitudinal reinforcement ratio, and type of reinforcement (steel versus GFRP). Four eccentricity-to-diameter ratios were estimated and applied (8.2, 16.4, 32.8, and 65.6%) to develop the nominal failure envelope. Test results indicate that increasing the GFRP longitudinal-reinforcement ratio enhanced the post-peak performance of LWSCC columns. On the other hand, the failure mechanism of the tested LWSCC columns was similar to that reported previously for conventional reinforced normalweight concrete columns. Based on the fundamentals of equilibrium of forces and compatibility of strains, the available equivalent stressblock parameters and design provisions in the literature were used to predict the axial-flexural capacity of the tested GFRP-reinforced LWSCC columns. The predicted i interaction diagrams are presented and discussed. [ABSTRACT FROM AUTHOR]

Replacing defective reinforced concrete railway sleepers has reportedly been urged by several businesses and maintenance agencies. The harsh environmental conditions, especially in North America, trigger material degradation and steel corrosion. Glass fiber-reinforced polymer (GFRP) bars have been increasingly used in a wide variety of applications. The present study presents an original, promising application of GFRP as prestressed reinforcement in concrete railway sleepers. For prestressed GFRP sleepers to be accepted as replacements for defective sleepers made with timber and concrete, they must pass several short- and long-term tests. Full-scale GFRP- and steel-reinforced concrete sleepers were designed, tested, and compared according to the requirements of the American Railway Engineering and Maintenance-of-Way Association (AREMA). The test results show that GFRP- and steel-reinforced concrete sleepers achieved similar cracking levels and ultimate loads in the rail-seat negative and positive tests. The tested GFRP specimens met AREMA's requirements for static and fatigue loading for use in freight and commuter rail systems with the designated loads, spacings, and train speed used in this study. The failure of the prestressed GFRP-RC sleepers was governed by shear-compression failure, while the prestressed steel-RC sleepers failed by crushing of the concrete due to the slippage of steel strands. Moreover, field inspection of GFRP-reinforced concrete sleepers after 3 years under actual service conditions reveal very competitive performance and no cracks. Lastly, the results of this study constitute a basic step toward establishing code provisions for using GFRP bars as prestressing reinforcement in concrete sleepers for railway applications. [ABSTRACT FROM AUTHOR]

The well-established moment magnification procedure in ACI 318 for the structural analysis of slender steel-reinforced concrete (steel-RC) columns was reexamined to accommodate concrete columns reinforced with glass fiber-reinforced polymer (GFRP) bars. This could encourage North American codes and guidelines (ACI 440.1R; CSA S806) to include detailed sections dealing with the design and analysis of RC columns entirely reinforced with GFRP bars. Consequently, a second-order analytical model was derived to assess the structural performance of more than 9500 slender GFRP-RC columns with a wide range of design parameters. The developed analytical model correlated well with the experimental data of 72 large-scale FRP-RC columns assembled from this study and the literature. The investigated parameters were the applied eccentricity ratio, slenderness ratio, longitudinal GFRP-reinforcement ratio, elastic modulus of GFRP bars, concrete compressive strength, column cross section geometry, and GFRP bar arrangement. Then, a multiple linear regression analysis of the simulated theoretical data was conducted to propose a simple and practical design equation for the effective flexural stiff-ness of slender GFRP-RC columns. Lastly, the stiffness reduction factor used to reduce the critical buckling load of a single isolated slender GFRP-RC column was recommended as 0.6 based on the performed one-percentile statistical analysis. [ABSTRACT FROM AUTHOR]

This paper reports on an investigation of the flexural behavior and serviceability performance of long-span square concrete members with a shear span-to-effective depth ratio (a/d) greater than 5, internally reinforced with uniformly distributed fiber-reinforced polymer (FRP) bars. The study comprised testing of four large-scale square members up to failure under four-point bending. The specimens measured 400 mm (16 in.) in width, 400 mm (16 in.) in depth, and 6000 mm (236.22 in.) in length. The test parameters included the longitudinal reinforcement ratio and the longitudinal reinforcement type, including glass FRP (GFRP), carbon FRP (CFRP), and steel bars. Test results show that the deformability of the tested FRP-reinforced concrete (FRPRC) specimens ranged between 7.0 and 10.4, which significantly exceeds the requirements of North American codes. Moreover, the nominal flexural strength of the specimen reinforced with GFRP bars was 1.9 times that of the steel counterpart specimen when the reinforcement ratios were similar. An analytical strain-compatibility model capable of predicting the flexural strength of the tested specimens was developed and compared to the experimental results. In addition, the measured crack widths and deflections were analyzed and compared at service load conditions to those predicted using models in the literature as well as in design guidelines and codes. The effect of uniformly distributed bars on the flexural strength and serviceability of square FRPRC members was also investigated, revealing that the presence of side bars significantly enhanced the serviceability performance in terms of crack width and deflection. On the other hand, the contribution of these side bars to flexural strength was minimal. [ABSTRACT FROM AUTHOR]

This paper intends to experimentally and theoretically support the North American technical committees engaged in developing design provisions for slender glass fiber-reinforced polymer-reinforced concrete (GFRP-RC) columns. Consequently, 22 full-scale slender GFRP-RC columns with slenderness ratios of 23 and 33 were produced and tested at four different initial eccentricities (0, 16, 33, and 66% of the column diameter). Moreover, the levels of GFRP-longitudinal and transversal reinforcement were also observed and are presented. During all testing phases, the GFRP-reinforcement proved its capacity to maintain stability and resistance to the applied loads. An analytical second-order model accounting for material and geometrical nonlinearities was then developed to extend the parametric study and include additional parameters such as the longitudinal tensile modulus of the GFRP bars. A model for slender GFRP-RC columns was developed by discretizing the section into several integration layers. The ACI stability index corresponding to the ratio of the secondary to the primary moment of 1.4 is applied to GFRP-RC columns to define the permissible tensile design strains at which acceptable lateral deformations are expected. The derived model correlated substantially with the test results. Lastly, based on the experimental results and the developed model, the permissible tensile design strain of the GFRP bars was proposed to be limited to 0.9% to avoid stability failure. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental and analytical investigation of the splice length of glass fiber-reinforced polymer (GFRP) bars under compression in concrete. The experimentation comprises 29 full-scale circular concrete columns. The experimental parameters evaluated in this study were composed of the compressive strength of concrete, bar diameter, splice length, and amount of transverse reinforcement. The experimental results indicated that the requisite splice length of GFRP bars would be less than that of steel. In addition, the bond strength of GFRP bars to concrete was improved by increasing the bar diameter of transverse reinforcement and compressive strength of concrete. Reducing the spacing of transverse reinforcement and longitudinal bar diameter can also lead to decreasing the splice length. However, splice length was independent of the ultimate strength of transverse reinforcement. The obtained experimental data of the present study was augmented with the results of 39 additional specimens collected from the literature to develop design recommendations for lap splicing of GFRP bars under compression. In addition, a relation for splice length was derived by applying methodologies similar to those already used for steel bars. The proposed equation for design purpose of the splice length of GFRP bars under compression was found to be in a reliable agreement with the available experimental data. [ABSTRACT FROM AUTHOR]

The design of concrete members reinforced with fiber-reinforced polymer reinforcement (FRPRC members) is typically governed by serviceability-limit-state requirements rather than ultimate-limitstate requirements. ACI 440.1R deflection design equations were introduced and assessed based on experimental work on FRPRC members with rectangular sections. These equations have not been assessed for circular sections for inclusion in an anticipated FRPRC design code currently being prepared by ACI Committee 440. This research program was designed to evaluate the deflection predictions of circular FRPRC flexural members using the available design equations. A total of eight full-scale circular RC flexural members measuring 500 mm (20 in.) in diameter and 6000 mm (236.22 in.) in length were constructed and tested up to failure under four-point bending load. The test parameters included the type of FRP reinforcing bars and the reinforcement ratio. Three specimens were reinforced with glass FRP (GFRP) bars, three were reinforced with carbon FRP (CFRP) bars, and two were reinforced with basalt FRP (BFRP) bars. The measured deflections and experimental values of the effective moment of inertia (Ie) were analyzed and compared with those predicted using models in the literature as well as those in design guidelines and codes. Based on the analysis of the test results, a new equation was developed to accurately predict the deflection of the tested circular specimens. Moreover, an analytical model was developed using a layer-by-layer curvature analysis approach based on cross-sectional analysis satisfying strain compatibility and equilibrium conditions. The load-deflection relationship for circular FRPRC flexural members can be generated based on the calculation of curvature with an incremental strain technique. The comparisons with the experimental results indicate the model's capability of reproducing the experimental load-deflection responses of the tested circular specimens. [ABSTRACT FROM AUTHOR]

ACI 440.1R design provisions provide conservative estimates for the flexural design strength of glass fiber-reinforced polymer (GFRP) reinforced concrete (RC) members with rectangular sections. These provisions do not apply equally well to nonrectangular sections, which motivated this study. This study investigated the flexural strength and behavior of concrete members with circular section and reinforced with GFRP bars and spirals both experimentally and theoretically. Large-scale specimens with a total length of 6000 mm (236.22 in.) and diameter of 500 mm (20 in.) were constructed and tested under four-point bending. The test parameters included reinforcement flexural stiffness (GFRP versus steel) and GFRP longitudinal reinforcement ratio. In this paper, ductility and deformability of the tested specimens were defined, calculated, and evaluated. Test results show that the deformability of the tested GFRP-RC circular members ranged between 19 and 40, which significantly exceeds the requirements of North American codes. Moreover, the nominal flexural strengths of the GFRP-RC specimens were 1.5 and 3.0 times that of the steel counterpart specimen, when considering a similar reinforcement ratio and equivalent longitudinal axial stiffness, respectively. An analytical strain compatibility model capable of predicting the flexural strength of circular GFRP-RC members, including the sequential progressive failure, was developed and verified with the experimental results. Moreover, a simplified method, including design equations and a design chart, is presented using noniterative analysis. This method accurately and simply predicted the flexural capacity and can be considered a simple and more straightforward method for practicing engineers. [ABSTRACT FROM AUTHOR]