Browsing by Author "Mervyn J. Kowalsky, Committee Member"

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    Characteristics of Innovative 3-D FRP Sandwich Panels
    (2006-02-02) Reis, Engin Murat; Sami H. Rizkalla, Committee Chair; Mervyn J. Kowalsky, Committee Member; Kara Peters, Committee Member; Ajaya K. Gupta, Committee Member
    Foam and honeycomb core sandwich composites are widely used in structural applications. Nevertheless, possibilities of core-to-face sheet delamination, crushing and buckling instability are major concerns. This study presents an innovative system for FRP panels designed to overcome delamination problems typically encountered in traditional FRP panels. The panels consist of GFRP laminates and foam core sandwich where top and bottom skin GFRP layers are connected together with through-thickness fibers. Addition of the through-thickness fibers increases the out of plane properties of the panel, delays delamination-type failures, allows low cost manufacturing and ensures full utilization of the panel strength. Fundamental material properties in tension, compression, flexure and shear are evaluated both experimentally and analytically. Failure modes and mechanisms are investigated. The influence of the panel thickness, through thickness fiber configuration and density and other parameters on the tension, compression, flexure and shear behavior of the panels will be discussed. Application of sandwich beam theories, Elementary Sandwich Theory and Advanced Sandwich Theory, are studied in the full behavior of the 3-D FRP sandwich beams. A finite element model is developed to be able to predict the behavior of sandwich panels with different panel thicknesses, through thickness fiber configurations, facing sheet thicknesses and different material properties.
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    Flexural Performance of MMFX Reinforcing Rebars in Concrete Structures
    (2003-12-18) Yotakhong, Purk; Sami H. Rizkalla, Committee Chair; Mervyn J. Kowalsky, Committee Member; Emmett A. Sumner, Committee Member
    Use of Micro-composite Multi-structural Formable Steel, commercially known as "MMFX", as a replacement for convention steel is gaining popularity in many concrete structures. The high-corrosive resistance nature and high-strength characteristics of the MMFX rebars could provide additional service life to concrete structures in areas that are prone to severe environmental conditions. The research program presented in this thesis was designed to study the flexural behavior of rectangular concrete beams reinforced by MMFX rebars. This thesis presents the experimental program carried out at the Constructed Facility Laboratory (CFL), North Carolina State University, to test a total of four large-scale concrete beams. All beams were 16 feet long, 12 inches wide, and 18 inches high. Three beams were reinforced by MMFX rebars in the tension side, and one beam was reinforced by conventional steel rebars in the tension side. All beams were equally reinforced by conventional steel rebars on the compression side. Three beams were tested under static loading conditions, while the remaining MMFX reinforcing beam was tested under a slow cyclic loading condition. All beams were tested to failure in order to investigate the behavior during the pre-cracking, cracking, post-cracking, ultimate capacities, and modes of failure.