The American Concrete Institute (ACI) has developed guidelines for the design of fiber reinforced polymer (FRP) reinforced concrete structures. Current guidelines require the application of environmental and flexural strength reduction factors, which have minimal experimental validation. Our goal in this research is the development of a Monte Carlo simulation to assess the durability of glass fiber reinforced polymer (GFRP) reinforced concrete designed for flexure. The results of this simulation can be used to determine appropriate flexural strength reduction factors. Prior to conducting the simulation, long-term GFRP tensile strength values needed to be ascertained. Existing FRP tensile strength models are limited to short-term predictions. This study successfully developed a power law based-FRP tensile strength retention model using currently available tensile strength data for GFRP exposed to variable temperatures and relative humidity. GFRP tensile strength retention results are projected at 0, 1, 3, 10, 30, and 60-year intervals. The Monte Carlo simulation technique is then used to assess the influence beam geometry, concrete strength, fractions of balanced reinforcement ratio, reinforcing bar tensile strength, and environmental reduction factors on the flexural capacity of GFRP reinforced concrete beams. Reliability analysis was successfully used to determine an environmental reduction factor of 0.5 for concrete exposed to earth and weather. For simulations with higher GFRP bar tensile strength as well as larger beam geometry and fractions of the balanced reinforcement ratio, larger moment capacities were produced. A strength reduction factor of approximately 0.8 is calculated for all fractions of balanced reinforcement ratio. The inclusion of more long-term moisture data for GFRP is necessary to develop a more cohesive tensile strength retention model. It is also recommended that longer life cycles of the GFRP reinforced concrete beams be simulated. This research was conducted thanks to support from the National Science Foundation Division of Graduate Education's Interdisciplinary Graduate Education Research and Traineeship (Award # DGE-0114342) Note: The opinions expressed herein are the views of the authors and should not be interpreted as the views of the National Science Foundation. / Master of Science

The primary objective of this research was to examine the strength degradation of Glass Fiber Reinforced Polymer (GFRP) bars at high temperature and alkalinity and determine if an Arrhenius type relationship can be used as a means of projecting life. The work done includes a thorough literature review, experiments and development of strength prediction models. The experimental work involves exposure of GFRP bars incased in cement mortar to lime-water solution at 30, 45 and 57°C. Overall 100 specimens were included in the experimental program. The tensile strength and modulus of elasticity retention after 180 days of exposure at 57°C was 57% and 82% respectively. The secondary objective was to determine the moisture absorption properties of GFRP bars. The moisture absorption data available is till 80 days from the immersion of the specimens in the tank. The collected data was used in the development of strength retention models. Two strength prediction models, Time Shift Method and Fickian Model for moisture absorption are formulated. Using the Fickian Model, strength is predicted for GFRP bars, if used in bridge decks in Roanoke, Virginia. The strength loss predicted was 45% after 50 years of exposure in real life environment. A linear relationship was observed when the moisture content and strength retention were plotted. The study estimates a strength loss higher than the ACI-440H recommended environmental degradation factor of 0.7 to calculate the design ultimate tensile strength. / Master of Science

This research project on the campus of Southern Illinois University Carbondale is an extension to the inquiry into the feasibility and reliability of the technology known as Digital Laser Speckle Image Correlation (DiLSIC). This is a hybrid approach of combining two existing technologies. The first being Digital Image Correlation (DIC) which is a nondestructive evaluation commonly used to find displacement, in-plane strain, as well as deformation. The second being the of laser speckle patterns. This hybrid has achieved level of resolution measured to be 3.4μ. DiLSIC increases the application ability of the DIC technique to situations that generally would not be an option to use. DiLSIC needs no artifact speckle patterns to be applied to the specimen as a preparation for nondestructive testing. In DIC testing, the surface of a specimen must artifact speckles applied to the subject surface. Often the application of artifact speckles is not desirable or possible. DiLSIC is an acceptable alternative to the previously discussed industry-wide practice. This method broadens the usage of the DIC technique to situations which previously were not possible. This technology can identify, quantify, and detect the distribution of strain and stress concentrations in composite structures. For this study, a honeycomb-backed glass fiber reinforced polymer (GFRP) panel from a Cessna aircraft exterior luggage door was obtained and a defect panel is created. The panel is constructed with one area containing a repair compliant with manufacturer standardized methods and a repair area is not compliant and consists of multiple incorrect repair steps. An area with no repair is also tested to act as a control for comparison and quantification. The results for the inspected areas showed a linear strain increase in the noncompliant repair. The data plot for the compliant repair showed a trend of following the same basic curve as the no repair area. A verification process follows the DiLSIC testing consisting of using Infrared Thermography, Air-coupled ultrasonic, and white light artifact speckle DIC. These tests show DiLSIC is a viable alternative to the testing that is available in the industry. DiLSIC can detect defect location, size, geometry and map strain to determine the difference between compliant and noncompliant repairs when compared to a base level non-repair area

Although Glass Fiber Reinforced Polymer (GFRP) has many potential advantages as reinforcement in concrete structures, the loss in tensile strength of the GFRP reinforcing bar can be significant when exposed to the high alkali environments. Much effort was made to estimate the durability performance of GFRP in concrete; however, it is widely believed the data from accelerated aging tests is not appropriate to predict the longer-term performance of GFRP reinforcing bars. The lack of validated long-term data is the major obstacle for broad application of GFRP reinforcement in civil engineering practices. The main purpose of this study is to evaluate the longer-term deterioration rate of GFRP bars embedded in concrete, and to develop an accurate model that can provide better information to predict the longer-term performance of GFRP bars. In previous studies performed by Trejo, three GFRP bar types (V1, V2, and P type) with two different diameters (16 and 19 mm [0.625, and 0.7 in. referred as #5 and #6, respectively]) provided by different manufacturers were embedded in concrete beams. After pre-cracking by bending tests, specimens were stored outdoors at the Riverside Campus of Texas A&M University in College Station, Texas. After 7 years of outdoor exposure, the GFRP bars were extracted from the concrete beams and tension tests were performed to estimate the residual tensile strength. Several physical tests were also performed to assess the potential changes in the material. It was found that the tensile capacity of the GFRP bars embedded in concrete decreased; however, no significant changes in modulus of elasticity (MOE) were observed. Using this data and limited data from the literature, a probabilistic capacity model was developed using Bayesian updating. The developed probabilistic capacity model appropriately accounts for statistical uncertainties, considering the influence of the missing variables and remaining error due to the inexact model form. In this study, the reduction in tensile strength of GFRP reinforcement embedded in concrete is a function of the diffusion rate of the resin matrix, bar diameter, and time. The probabilistic model predicts that smaller GFRP bars exhibit faster degradation in the tensile capacity than the larger GFRP bars. For the GFRP bars, the model indicates that the probability that the environmental reduction factor required by The American Concrete Institute (ACI) and the American Association of State Highway Transportation Officials (AASHTO) for the design of concrete structures containing GFRP reinforcement is below the required value is 0.4, 0.25, and 0.2 after 100 years for #3, #5, and #6, respectively. The ACI 440 and AASHTO design strength for smaller bars is likely not safe.

Yes / The flexural performance of geopolymer concrete (GPC) T-beams reinforced longitudinally with GFRP bars under a four-point static bending test was investigated. Six full-scale simply supported T-beams were cast and tested; one control specimen was made with ordinary Portland cement concrete (OPCC), while the other five beams were made of geopolymer concrete. The G-GPC2 was designed to attain the same theoretical moment capacity as the G-OPCC6 control beam. The main parameters investigated were the reinforcement ratio of ρ_f/ρ_b= 0.75, 1.05, 1.12, 1.34 and 1.34 for G-GPC1, G-GPC2, G-GPC3, G-GPC4, and G-GPC5, respectively, and compressive strength of geopolymer concrete. Based on the results of the experiments, the ultimate strain of GPC did not show the same behaviour as that of OPCC, which affects the mode of failure. The beam capacity and deflection were, respectively, overestimated and underestimated using the ACI 440 2R-17 predictive equations.

Yes / This paper presents the experimental results of five large-scale hybrid glass fiber reinforced polymer (GFRP)-steel reinforced concrete continuous beams compared with two concrete continuous beams reinforced with either steel or GFRP bars as reference beams. In addition, two simply supported concrete beams reinforced with hybrid GFRP/steel were tested. The amount of longitudinal GFRP, steel reinforcements and area of steel bars to GFRP bars were the main investigated parameter in this study. The experimental results showed that increasing the GFRP reinforcement ratio simultaneously at the sagging and hogging zones resulted in an increase in the load capacity, however, less ductile behaviour. On the other hand, increasing the steel reinforcement ratio at critical sections resulted in more ductile behaviour, however, less load capacity increase after yielding of steel. The test results were compared with code equations and available theoretical models for predicting the beam load capacity and load-deflection response. It was concluded that Yoon's model reasonably predicted the deflection of the hybrid beams tested, whereas, the ACI.440.1R-15 equation underestimated the hybrid beam deflections. It was also shown that the load capacity prediction for hybrid reinforced concrete continuous beams based on a collapse mechanism with plastic hinges at mid-span and central support sections was reasonably close to the experimental failure load. / Higher Education of Libya (972/2007).

[pt] Este trabalho tem como objetivo investigar o desempenho de colunas com seção I em polímeros reforçados com fibra de vidro (pGFRP) submetidas a cargas de compressão concêntricas de curta duração. Uma revisão bibliográfica acerca das teorias existentes é apresentada, incluindo os conceitos básicos de instabilidade, teoria de flambagem global e local, modos de falha de colunas perfeitas, bem como o comportamento de colunas reais. Um programa experimental foi conduzido, incluindo a caracterização dos materiais. Vinte e nova colunas – com três diferentes seções I e diferentes tipos de resina, propriedades mecânicas, bem como comprimentos – foram testadas. Do ponto de vista global, as colunas foram biengastadas. As placas constituintes, por sua vez, foram testadas com três diferentes condições de contorno: biengastadas (CC), biapoiadas (SS) e simplesmente em contato com as chapas de base da máquina de compressão (CB). Foi observado que a condição de contorno CB – a mais adotada em estudos anteriores -, se aproxima mais de um engaste do que de uma condição simplesmente apoiada. A distribuição não linear de deformações elásticas ao longo da seção também foi investigada. Finalmente, recomendações para um ensaio de flambagem local apropriado foram propostas. / [en] This work aims to investigate the performance of pultruded glass fiber reinforced polymer (pGFRP) I-section columns subject to short term concentric compression. A review of existing theories is presented, including the instability concepts, global and local buckling theories, perfect columns failure modes and the behavior of real columns. An experimental program including material characterization was conducted. Twenty-nine stubs – with three different I-sections geometries, having distinct flange width-to-section depth ratios (bf/d = 0.5; 0.75 and 1.0), mechanical properties, overall lengths and matrices – were tested. In a global point of view, the columns were fixed at both ends. The constituent plates, on the other hand, were tested with different end-conditions: clamped (CC), simply supported (SS) and simply in contact with base plates of the universal machine (CB). The third analyzed boundary condition, which is the most adopted in previous studies, was concluded to be closer to a clamped end-condition. The non-linear elastic strains distribution throughout the cross-section was also investigated. Finally, guideline recommendations for successful local buckling tests were proposed.

[pt] Materiais compósitos pultrudados poliméricos reforçados com fibra de vidro (PRFV) são aplicados em diversos setores da indústria por apresentarem boas resistências mecânicas, baixo peso específico e alta resistência à corrosão. A exposição a ambientes agressivos tais como imersão em água, condicionamento sob alta umidade relativa, temperatura baixa e elevada, ciclos térmicos e úmidos, bem como a combinação desses efeitos, tornou-se cada vez mais objeto de estudo para esses tipos de materiais. A compreensão dos efeitos das condições ambientais no comportamento do material é essencial para avaliar seu desempenho e, desta forma, garantir a segurança necessária ao projeto estrutural. Com o objetivo de compreender melhor a influência de diferentes condições ambientais nas propriedades do material compósito PRFV, foram estudados os efeitos da temperatura e umidade, além da ação combinada dessas duas condições, nas suas propriedades físicas, químicas, térmicas e mecânicas. Neste estudo, foram levados em conta aspectos importantes que influenciam o comportamento do material, como a resina utilizada, o grau de cura, e características químicas e físicas do material. Os ensaios experimentais foram conduzidos em quatro condições ambientais: (i) exposição a temperaturas moderadas/elevadas (70 graus C à 330 graus C), (ii) imersão em água deionizada (25 graus C, 55 graus C e 70 graus C), (iii) exposição à névoa salina em câmaras de envelhecimento higrotérmico (35 graus C, 55 graus C e 70 graus C), e (iv) exposição a ambiente externo real. Além disso, foram aplicados modelos teóricos para avaliação dos resultados. Foi observado que a temperatura, o tempo de condicionamento e a umidade são fatores preponderantes no comportamento do material. Adicionalmente, uma questão importante para o estudo de pultrudados reside na compreensão das propriedades interlaminares do material. Nesse contexto, a fratura interlaminar, associada às fissuras no plano longitudinal entre as camadas do material, é uma das principais causas de falha em compósitos pultrudados. Consequentemente, a análise da fratura em modo II, que avalia o mecanismo da propagação da fissura no plano interlaminar, vem ganhando espaço no estudo de materiais compósitos. A análise de fratura em modo II não é trivial ou normatizada para compósitos pultrudados PRFV, de forma que poucos dados e conclusões efetivas foram obtidos até o momento a esse respeito. Com o objetivo de suprir essa lacuna, realizou-se uma extensa investigação experimental, culminando na proposição de uma nova metodologia para avaliação da fratura em modo II em materiais compósitos poliméricos pultrudados reforçados com fibra de vidro (PRFV). / [en] Pultruded glass-fiber reinforced polymer (GFRP) composites are applied in various industrial sectors due to their good mechanical strength, low specific weight, and high resistance to corrosion. Exposure to aggressive environments has become an increasingly studied topic for these materials, such as immersion in water, conditioning under high relative humidity, low and high temperatures, thermal and humid cycles, as well as the combination of these effects. Understanding the effects of environment condition on material behavior is essential to evaluate its performance and ensure the necessary safety for structural design. In order to better understand the influence of environmental conditions on the properties of GFRPs, the effects of temperature and humidity, as well as the combined action of these two effects, on their physical, chemical, thermal, and mechanical properties were studied. Important aspects that influence the material s behavior were considered, such as the resin used, the degree of curing, and the chemical and physical characteristics of the material. Experimental tests were conducted under four environmental conditions: (i) exposure to moderate/high temperatures (70 degrees C to 330 degrees C), (ii) immersion in deionized water (25 degrees C, 55 degrees C, and 70 degrees C), (iii) exposure to salt spray in hygrothermal aging chambers (35 degrees C, 55 degrees C, and 70 degrees C), and (iv) exposure to real outdoor environment. In addition, theoretical models were applied to evaluate the results. It was observed that temperature, conditioning time, and moisture are predominant factors in material behavior. Additionally, a important issue for the study of pultruded composites lies in understanding the interlaminar properties of the material. In this context, interlaminar fracture, associated with longitudinal cracks between the layers of the material, is one of the main causes of failure in pultruded composites. Consequently, mode II fracture analysis, which evaluates the mechanism of crack propagation in the interlaminar plane, has been gaining ground in the study of composite materials. Mode II fracture analysis is not trivial or standardized for pultruded GFRP composites, so few data and effective conclusions have been obtained in this regard so far. In order to fill this gap, an extensive experimental investigation was carried out, culminating in the proposal of a new methodology for evaluating mode II fracture in pultruded GFRPs.

[pt] Este trabalho tem como objetivo avaliar a resistência à força cortante de vigas de concreto reforçado com barras de fibras de vidro e investigar a contribuição dos diferentes mecanismos de transferência do esforço cortante para a resistência final da viga. Um programa experimental foi conduzido, incluindo ensaios para: caracterização do material, para avaliar o efeito de pino, para avaliar o engrenamento dos agregados e, por fim, ensaios de flexão de quatro pontos em vigas. Diferentes parâmetros foram investigados, como a quantidade de barras longitudinais para o efeito de pino, dimensão máxima do agregado graúdo para engrenamento dos agregados e a presença de estribos para os ensaios de vigas. O monitoramento do desenvolvimento da fissura crítica foi realizado com auxílio de correlação de imagem digital (digital image correlation, DIC, em inglês). Os resultados mostraram que não foi evidenciada diferença no comportamento de efeito de pino e de engrenamento dos agregados através dos ensaios realizados. Para os ensaios de vigas, observou-se que todos os espécimes apresentaram ruptura por tração da diagonal crítica e, para vigas sem estribos, a ação do efeito de pino pareceu contribuir significativamente para a resistência ao cisalhamento após a fissura, quando a carga diminui e as deflexões aumentam, resultado do menor engrenamento dos agregados à medida que a fissura se abre. Foi observado que a presença de estribos aumentou em até três vezes a resistência ao cortante das vigas ensaiadas e que houve ruptura do estribo na parte da dobra. / [en] This work aims to evaluate the shear strength of reinforced concrete beams with glass fiber reinforced polymer bars and to investigate qualitatively the contribution of the different shear transfer mechanisms to the final strength of the beam. An experimental program was conducted, including material characterization, dowel action tests, push-off tests, and finally, four-point bending tests on beams. Different parameters were investigated, such as the number of longitudinal bars for dowel action effect, maximum size of the coarse aggregate for aggregate interlock and the presence of stirrups for the beam tests. The monitoring of the development of the critical crack was performed with the aid of digital image correlation (DIC). The results showed that there was no difference in the behavior of the dowel action effect and the aggregate interlock through the tests performed. For beam tests, it was observed that all the specimens exhibited a concrete diagonal tension failure and for beams without stirrups, dowel action seemed to provide significant contribution to the shear strength after the crack, when the load reduces and the deflections increases, resulting from the loss of aggregate interlock as the crack opens. It was also observed that the presence of stirrups increased up to three times the shear strength of the beams tested and that there was rupture of the stirrup at the bent region.