published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Master / Master of Philosophy

published_or_final_version / abstract / Civil Engineering / Master / Master of Philosophy

The high cost of repairing reinforced or prestressed concrete structures due to steel corrosion has driven engineers to look for solutions. Much research has been conducted over the last two decades to evaluate the use of Fiber Reinforced Polymers (FRPs) in concrete structures. Structural engineering researchers have been testing FRP to determine their usability instead of steel for strengthening existing reinforced concrete structures, reinforcing new concrete members, and for prestressed concrete applications. The high strength-to-weight ratio of FRP materials, especially Carbon FRP (CFRP), and their non-corrosive nature are probably the most attractive features of FRPs. In this study, an experimental program was conducted to investigate the flexural behavior of prestressed concrete beams pre-tensioned with CFRP strands. The bond characteristics were examined by means of experimentally measuring transfer length, flexural bond length, and bond stress profiles. A total of four rectangular beams pre-tensioned with one 0.5-in. diameter CFRP strand were fabricated and tested under cyclic loading for five cycles, followed by a monotonically increasing load until failure. In investigating bond properties, the experimental results were compared to the equations available in the literature. The results from the four flexural tests showed that the main problem of CFRP strands, in addition to their liner-elastic tensile behavior, was lack of adequate bonding between FRP and concrete. Poor bonding resulted in early failure due to slippage between FRPs and concrete. As a result, a new technique was developed in order to solve the bonding issues and improve the flexural response of CFRP prestressed concrete beams. The new technique involved anchoring the CFRP strands at the ends of the concrete beams using a new "steel tube" anchorage system. It was concluded that the new technique solved the bond problem and improved the flexural capacity by about 46%. A computer model was created to predict the behavior of prestressed beams pre-tensioned with CFRP. The predicted behavior was compared to the experimental results. Finally, the experimental results were compared to the behavior of prestressed concrete beams pre-tensioned with steel strands as generated by the computer model. The CFRP beams showed higher strength but lower ductility.

This thesis has investigated the application of CFRP and GFRP bars as longitudinal reinforcement for continuously supported concrete beams. Two series of simply and continuously supported CFRP and GFRP reinforced concrete beams were tested in flexure. In addition, a continuously supported steel reinforced concrete beam was tested for comparison purposes. The FRP reinforced concrete continuous beams were reinforced in a way to accomplish three possible reinforcement combinations at the top and bottom layers of such continuous beams. The experimental results revealed that over-reinforcing the bottom layer of either the simply or continuously supported FRP beams is a key factor in controlling the width and propagation of cracks, enhancing the load capacity, and reducing the deflection of such beams. However, continuous concrete beams reinforced with CFRP bars exhibited a remarkable wide crack over the middle support that significantly influenced their behaviour. The ACI 440.1R-06 equations have been validated against experimental results of beams tested. Comparisons between experimental results and those obtained from simplified methods proposed by the ACI 440 Committee show that ACI 440.1R-06 equations can reasonably predict the load capacity and deflection of the simply and continuously supported GFRP reinforced concrete beams tested. However, The potential capabilities of these equations for predicting the load capacity and deflection of continuous CFRP reinforced concrete beams have, however, been adversely affected by the de-bonding of top CFRP bars from concrete. An analytical technique, which presents an iterative procedure based on satisfying force equilibrium and deformation compatibility conditions, has been introduced in this research. This technique developed a computer program to investigate flexural behaviour in particular the flexural strength and deflection of simple and continuously supported FRP reinforced concrete beams. The analytical modelling program has been compared against different prediction methods, namely ACI 440, the bilinear method, mean moment inertia method and Benmokrane's method. This comparison revealed the reliability of this programme in producing more enhanced results in predicting the behaviour of the FRP reinforced beams more than the above stated methods.

Call number: LD2668 .T4 1986 S53 / Master of Science / Civil Engineering

Call number: LD2668 .T4 1986 Y362 / Master of Science / Civil Engineering

This study presents and illustrates a methodology to calculate the capacity of an existing reinforced concrete bridge under a non-conventional blast load due to low and intermediate pressures. ATBlast program is used to calculate the blast loads for known values of charge weight and stand off distance. An excel spreadsheet is generated to calculate ultimate resistance, equivalent elastic stiffness, equivalent elastic deflection, natural period of the beam, the maximum deflection, and the maximum rotation in the support for a simple span solid slab and T-Beam bridges. The allowable rotation could be taken as to two degrees. Naval Facility Engineering Command (NAVFAC) approach was adopted, where the inputs were material properties, span length, and area of reinforcement. The use of the Fiber Reinforced Polymer for increasing the capacity of an existing bridge is also presented in this study. Parametric studies were carried out to evaluate the performance of the solid slab and T-Beam bridges under the assumed blast load. / by Firas A. Abdelahad. / Thesis (M.S.)--Florida Atlantic University, 2008. / Includes bibliography. / Electronic reproduction. Boca Raton, FL : 2008 Mode of access: World Wide Web.

Muitas edificações têm apresentado degradação ao longo dos anos em todo o mundo, gerando situações de risco e causando acidentes, de modo que se têm estudado alternativas para se recuperar ou reforçar estruturalmente suas vigas, pilares e lajes. Entre as técnicas desenvolvidas para essas finalidades, destacam-se, atualmente, as que utilizam compósitos de polímeros reforçados com fibras (PRF), de modo que, desde as últimas décadas do século passado, desenvolveram-se os sistemas de reforço estrutural por colagem externa de tecidos e laminados de PRF de carbono (PRFC). Isto deve-se a este tipo de fibra apresentar o melhor conjunto de propriedades necessárias para se reforçarem as estruturas de concreto armado, como altas resistência à tração e módulo de elasticidade longitudinal. Na última década, surgiu o sistema de inserção de laminados de PRFC em entalhes executados no concreto de cobrimento de elementos estruturais preenchidos com resina epóxi. Embora haja resultados de outros pesquisadores, há a necessidade de maiores investigações no Brasil sobre o desempenho dessa nova técnica. Assim se propôs o planejamento experimental desta dissertação, cujo objetivo principal foi a análise experimental do desempenho de sistemas de reforço estrutural à flexão com laminados de PRFC aplicados a vigas de concreto armado ensaiadas com carregamento estático. De um total de dez vigas pré-moldadas, quatro foram testemunhos e seis foram reforçadas à flexão com dois laminados de PRFC através de três sistemas: colagem externa, inserção em entalhes longitudinais preenchidos com resina epóxi e com argamassa com sílica ativa. Analisa-se comparativamente o seu desempenho quanto às cargas máximas, aos deslocamentos verticais no centro do vão e às aberturas de fissuras. Constata-se que as reforçadas com laminados de PRFC inseridos em entalhes longitudinais preenchidos com resina epóxi apresentam os maiores valores de carga máxima e de rigidez. Entretanto as preenchidas com argamassa com sílica ativa obtêm desempenho inferior ao das vigas testemunhos por falta de aderência. Também se conclui que as reforçadas com colagem externa de laminados de PRFC têm os menores deslocamentos verticais no centro do vão. / Many buildings have shown deterioration over the years around the world, creating a hazardous situation and causing accidents, so that they have studied alternatives to recover or strengthen their structural beams, columns and slabs. Among the techniques developed for these purposes, stand out, currently, those using fiber reinforced polymer (FRP) composites. Since the last decades of the last century, it has been developed structural reinforcement systems of externally bonded carbon FRP (CFRP) textiles and laminates. This is due to the type of fiber having the best set of properties that are necessary to strengthen reinforced concrete structures, such as high tensile strength and longitudinal elastic modulus. In the last decade, the near-surface mounted CFRP laminates system executed in grooves in the concrete cover of structural elements filled with epoxy resin came up. Although there are results from other researchers, there is a need for further investigation in Brazil on the performance of this new technique. Thus, the experimental program of this thesis has been proposed, which main objective was the experimental analysis of the performance of bending structural reinforcement systems with CFRP laminates applied to reinforced concrete beams tested under static loading. From a total of ten precast beams, four were for control and six were strengthened in bending with two CFRP laminates composites through three systems: externally bonded, near-surface mounted insertion into longitudinal grooves filled with epoxy resin and mortar with silica fume. Their performance is comparatively analyzed for maximum loads, vertical displacements at mid-span and crack openings. It is concluded that those reinforced with near-surface mounted CFRP laminates inserted into longitudinal grooves filled with epoxy resin shows the highest maximum load and stiffness. However those filled with mortar with silica fume obtained lower performance than the control beams for lack of bonding. In addition, it is concluded that the ones strengthened with externally bonded CFRP laminates have the lowest mid-span vertical displacements.

Utilizing the higher capacity steel in design can provide additional advantages to the concrete construction industry including a reduction of congestion, improved concrete placement, reduction in the required reinforcement and cross sections which would lead to savings in materials, shipping, and placement costs. Using high-strength reinforcement is expected to impact the design provisions of ACI 318 code and other related codes. The Applied Technology Council (ATC-115) report "Roadmap for the Use of High-Strength Reinforcement in Reinforced Concrete Design" has identified key design issues that are affected by the use of high-strength reinforcement. Also, ACI ITG-6, "Design Guide for the Use of ASTM A1035 Grade 100 Steel Bars for Structural Concrete" and NCHRP Report 679, "Design of Concrete Structures Using High-Strength Steel Reinforcement" have made progress towards identifying how code provisions in ACI 318 and AASHTO could be changed to incorporate high-strength reinforcement. The current research aims to provide a closer investigation of the behavior of beams reinforced with high-strength steel bars (including ASTM A615 Grade 100 and ASTM A1035 Grades 100 and 120) and high-strength concrete up to 12000 psi. Focus of the research is on key design issues including: ductility, stiffness, deflection, and cracking. The research includes an extensive review of current literature, an analytical study and conforming experimental tests, and is directed to provide a number of recommendations and design guidelines for design of beams reinforced with high-strength concrete and high-strength steel. Topics investigated include: strain limits (tension-controlled and compression-controlled, and minimum strain in steel); possible change for strength reduction factor equation for transition zone (Φ); evaluation of the minimum reinforcement ratio (þmin); recommendations regarding limiting the maximum stress for the high-strength reinforcement; and prediction of deflection and crack width at service load levels. Moreover, this research includes long-term deflection test of a beam made with high grade concrete and high-strength steel under sustained load for twelve months to evaluate the creep deflection and to insure the appropriateness of the current ACI 318 time-dependent factor, λ, which does not consider the yield strength of reinforcement and the concrete grade.