Fiber-reinforced plastic grids for the structural reinforcement of concrete beams

• Main Author: Yost, Joseph Robert
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1993
• Subjects: Civil engineering
• ISBN: 9798207973647

The research presented in this dissertation evaluates the performance of simply supported concrete beams reinforced with a 2 dimensional Fiber Reinforced Plastic (FRP) grid. The non-corrosive, high strength properties characteristic of FRP materials make them a desirable structural reinforcement for concrete in environments where high concentrations of chloride ions are present. The FRP grid under investigation is called NEFMAC and it is manufactured by Turay Industries of Tokyo Japan. NEFMAC is dimensionally fabricated as orthogonally intersecting longitudinal and transverse bars. The bars are continuous at the intersection points and, as such, there exists no preferred or strong direction within the grid. Tensile strengths of the material used to reinforce test beams range from 99 ksi to 178 ksi and modulus values range from 6000 ksi to 12300 ksi. These properties suggest that substituting NEFMAC for steel on an equal area basis will result in significantly higher deflections and correspondingly greater flexural capacity. As a consequence, deflection limitations will be an important component in design considerations. Test data from 31 beams reinforced with NEFMAC is presented in detail. Comparison of test results and current ACI strength predictions conclude that flexural strength is accurately quantified but shear strength is being significantly overestimated. A modification to the code shear strength prediction is proposed for design with NEFMAC. Deflection compatibility between test results and theoretical predictions employing the Branson equation for calculating the cracked-section effective moment of inertia was dependent upon the percentage of reinforcement provided. For sections reinforced greater than 2 times a balanced design, deflection prediction was good for the duration of the test. For section below this level deflection was significantly underestimated. Unlike steel, FRP material behave nearly linearly elastically to ultimate, at which point a brittle failure occurs. As such, application of an ACI flexural design criterion that is founded upon the yield capabilities in the reinforcement is not appropriate for FRP. Knowing that FRP reinforced beams can only experience brittle failure, a design criterion that considers energy reserve as a measure of safety is proposed. The result is low working stress levels in the reinforcement providing a high degree of reserve strength and acceptable compliance with deflection criteria.