Fiber reinforced plastics

Carbon Fiber Reinforced Plastics has recently has been recognized as an alternative to conventional steel reinforcement in concrete due to its excellent resistance to corrosion. Four rectangular concrete beams and four concrete columns reinforced with CFRP bars were cast for the study of the long term behavior under uniform sustained loading. The beams were simply supported and subjected to uniform sustained loading. The columns were arranged in a steel reaction framework. The beams and columns were instrumented and monitored to observe the change in the behavior due to the creep and shrinkage of concrete. An analytical method is developed to predict the long term behavior of CFRP reinforced concrete members. The calculated deformations compare reasonably with the experimental values. A modified equation for the calculation of the long term deflection is proposed for CFRP reinforced concrete beams. A simplified equation for the calculation of the creep coefficient is also proposed.

This study evaluates the effectiveness of using externally bonded CFRP plates for repairing damaged prestressed concrete structures as an alternative to the metal sleeve splice. Currently the metal sleeve splice is the most often used method for the repair of damaged prestressed concrete bridges. The use of bonded CFRP plates could be a viable alternative to the use of steel in this type of repair because of their high strength and stiffness, resistance to corrosion and low weight. The bond strength of CFRP plates bonded to concrete was evaluated by the use of a peel test and correlated by a finite element analysis. The peel test showed that the structural system was not significantly adversely effected by harsh environmental conditions. The results of this study showed that the use of CFRP plates is a feasible alternative to steel in the metal sleeve splice repair with some limiting factors.

This report presents the experimental and theoretical studies on the feasibility of using CFRP laminates for strengthening damaged reinforced concrete beams in cold environment. Experimental work includes investigation on fatigue strength, ultimate capacity and failure modes of repaired reinforced concrete beams in cold environment and room temperature. The repaired concrete beams subjected to fatigue in cold environment exhibit fewer number of cracks than those observed in beams at room temperature. The crack propagation and resulting damage were faster in beams tested in room temperature than those at cold temperatures. The study also includes investigation of thermal response of repaired plain concrete beams with CFRP laminates subjected to thermal cycles. Analytical studies on the distributed shear forces and peeling forces of repaired reinforced concrete beams were carried out to analyze the interaction between the laminate and the concrete interface. The temperature distribution and strains developed by the temperature differential are determined in the repaired plain concrete beams subjected to thermal cycles and the analytical results compared with the measured values.

This thesis presents an experimental and analytical investigation of concrete structural members strengthened with externally bonded composite laminates with varying configurations. Parameters, such as size, type of laminate, debond, etc., are evaluated from the viewpoint of stress patterns and their influence on interfacial debonds. Stress patterns in the structure and stress intensity factors around crack tips are determined using a finite element model developed for this purpose. The study also includes a precise description of cracking and the failure function of each parameter investigated. Besides the development of an innovative finite element program, which enables the study of interfacial cracks in structures with highly nonlinear behavior and multiple irregular cracking patterns, the significant contributions include the effect of laminate geometry, the inefficiency of laminate prestressing, the negative effect of end debond, and the insignificant effect of midspan debond on the cracking and the strength of a laminated concrete structural member.

Four concrete piles prestressed with Carbon Fiber Reinforced Plastics were cast, in which two piles were fabricated with CFRP transverse reinforcement. The remaining two were provided with transverse steel spiral reinforcement. The piles were designed according to Florida Department of Transportation (FDOT) guidelines. The Pile Driving Analyzer (PDA) was chosen as the primary data acquisition system for the pile driving due to its mobility, reliability and robustness based on the high frequency excitation. The Pre-driving analysis consisted of several stages. The estimated static bearing capacity of the experimental piles was first calculated followed by SPT sampling at the pile driving site to obtain the soil conditions. The percent skin and toe friction, ultimate capacities, driving system parameters, maximum displacements, energy, integrity, tensions and static capacity were determined prior to pile driving. The piles were then driven and the data from the pile driving compared with the analysis.

In a highly corrosive environment, corrosion is the main factor leading to deterioration and eventual failure of conventional reinforced or prestressed concrete structures. Carbon Fiber Reinforced Plastics (CFRP) are considered as an alternative to steel reinforcement due to its excellent corrosion resistance. This investigation was conducted to establish the feasibility of using CFRP cables as reinforcing elements in reinforced concrete columns. Besides investigating durability of CFRP cables in adverse environments (alkali and sea water) experimental and theoretical studies were carried out to study the behavior of CFRP reinforced concrete slender columns under combined axial load and bending moment. Exposure to air, sea water and alkali environments with alternating wet/dry cycles had no adverse effect on the strength of the CFRP cables. The CFRP reinforced concrete columns subjected to eccentric loads exhibited excellent ultimate load capacity. Feasibility of using CFRP cables in the reinforced concrete columns is assessed based on deflections, strains, curvatures, crack distributions, first crack loads and ultimate loads.

Carbon Fiber Reinforced Plastics has recently has been recognized as an alternative to conventional steel reinforcement in concrete due to its excellent resistance to corrosion. Four rectangular concrete beams and four concrete columns reinforced with CFRP bars were cast for the study of the long term behavior under uniform sustained loading. The beams were simply supported and subjected to uniform sustained loading. The columns were arranged in a steel reaction framework. The beams and columns were instrumented and monitored to observe the change in the behavior due to the creep and shrinkage of concrete. An analytical method is developed to predict the long term behavior of CFRP reinforced concrete members. The calculated deformations compare reasonably with the experimental values. A modified equation for the calculation of the long term deflection is proposed for CFRP reinforced concrete beams. A simplified equation for the calculation of the creep coefficient is also proposed.

The flexural behavior of rectangular concrete beams strengthened with externally bonded Carbon Fiber Reinforced Plastic (CFRP) laminates was studied by varying the number of plates bonded to their bottom tensile face. The increases in strength and stiffness of the beams provided by the bonded plates, over control beam without CFRP plates, were evaluated. Failure loads of the beams were determined by the ACI strain compatibility method using a FORTRAN software developed for this purpose. The predicted collapsed load agrees reasonably well with the actual failure load. Precracked solid and voided slab bridge models retrofitted with varying number of CFRP laminates were used to evaluate their contribution to the flexural resistance. The increases in strength and stiffness of the retrofitted slabs were based on the deflections, strains and crack patterns at ultimate load. Theoretical analyses to predict the load-deflection behavior of the precracked sections were performed using PCFRAME software. The predicted values agree reasonably well with the experimental results.

Nonlinear finite element analyses of the reinforced rectangular beams, prestressed solid slab and prestressed voided slab retrofitted with CFRP laminates are carried out using the software ANSYS(version 5.0) on the Sunwork station. The computer analyses are based on the proposed stress-strain relationship considering the effects of tensile stress on both elastic modulus and maximum compressive stress of concrete. Several assumptions are made in predicting the loss of tensile strength due to crack, confinement due to the laminate bonding, tensile strength due to the prestress force, failure pattern due to the concentrated stress adjacent to the loading point and concrete crushing due to large compressive strain. A subroutine is developed using macro commands of ANSYS. In this research, Branson's equation or Ie procedure is assumed in the prediction of deflection of retrofitted concrete members. The modifications needed due to laminate bonding are the cracking moments of inertia (Icr) of the beams or slabs bonded with CFRP laminates, which are included in the analysis.

The feasibility studies on the use of non-metallic continuous fiber reinforcement in reinforced and prestressed concrete structures are presented herein. Experimental results from studies on relaxation, bond and transfer length of Carbon Fiber Composite Cables (CFCC) are presented followed by results of flexural load tests on concrete beams reinforced and prestressed with CFCC. Durability of the CFCC is another prime concern, and hence part of the study also focuses on establishing the durability of the CFCC exposed to aggressive environments like alkali solution and sea water. The basic mechanics that govern the structural behavior of the beams, provide important insight into the potential that CFCC has to offer.