International Concrete Abstracts Portal

The geometry of arched (vertically curved) reinforced concrete (RC) members contributes to the development of additional stresses, affecting their flexural and shear strengths. This aspect of curvilinear RC members reinforced with glass fiber-reinforced polymer (GFRP) bars has not been reported in the literature. In addition, no specific design recommendations consider the effect of curvilinearity on the flexural and shear strengths of curved GFRP-RC members. This study has performed pioneering work in developing models to predict the flexural and shear strengths of curvilinear GFRP-RC members, with a focus on precast concrete tunnel lining segments. Eleven full-scale curvilinear GFRPreinforced tunnel segment specimens were tested under bending load as the experimental database. Then, a model was developed for predicting the flexural strength of curvilinear GFRP-RC members. This was followed by the development of two shear-strength prediction models based on the Modified Compression Field Theory (MCFT) and critical shear crack theory (CSCT). After comparing the experimental and analytical results, a parametric study was performed to evaluate the effect of different parameters on the flexural and shear strengths of curvilinear GFRP-reinforced members. The results indicate that neglecting the curvilinearity effect led to a 17% overestimation of the flexural strength, while the proposed models could predict the flexural strength of the specimens accurately. The proposed models based on the MCFT—referred to as the semi-simplified Modified Compression Field Theory (SSMCFT) and the improved simplified Modified Compression Field Theory (ISMCFT)—predicted the shear strength of the specimens with 28% conservativeness. In addition, the modified critical shear crack theory (MCSCT) model was 10% conservative in predicting the shear strength of curvilinear GFRP-RC members.

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.

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.

Statistical process control (SPC) procedures are proposed to improve the production efficiency of precast concrete tunnel segments. Quality control test results of more than 1000 ASTM C1609/C1609M beam specimens were analyzed. These specimens were collected over 18 months from the fiber-reinforced concrete (FRC) used for the production of precast tunnel segments of a major wastewater tunnel project in the Northeast United States. The Anderson-Darling (AD) test for the overall distribution indicated that the data are best described by a normal distribution. The initial residual strength parameter for the FRC mixture, f D 600, is the most representative parameter of the post-crack region. The lower 95% confidence interval (CI) values for 28-day flexural strength parameters of f1, f D 600, and f D 300 exceeded the design strengths and hence validated the strength acceptability criteria set at 3.7 MPa (540 psi). A combination of run chart, exponentially weighted moving average (EWMA), and cumulative sum (CUSUM) control charts successfully identified the out-of-control mean values of flexural strengths. These methods identify the periods corresponding to incapable manufacturing processes that should be investigated to move the processes back into control. This approach successfully identified the capable or incapable processes. The study also included the Bootstrap Method to analyze standard error in the test data and its reliability to determine the sample size.

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.