Mechanical fatigue response of fiber-reinforced polymeric (FRP) composites is essential to better understand the durability of composite materials systems and to develop design specifications. Currently, the fatigue response of multidirectional glass composite materials is not well-understood and much needs to be done to understand their behavior under fatigue loading. In this study, three glass fabric FRP composite material coupons and systems are tested at constant lowamplitude fatigue loading. Experimental results show that for a given FRP material and load configuration, the energy loss per cycle due to fatigue damage is linear from about 10-90% of the fatigue life of the FRP composite material. The energy loss per cycle is determined to be a characteristic value of the constituent materials, and is found to vary with the induced fatigue strain levels by a power law. Based on the experimental results, a fatigue life prediction model is proposed, with internal strain energy as damage metric, to predict the useful life of FRP composites. The experimental and predicted fatigue lives at various strain levels are compared (S-N curves) and the model is found to be conservative.
Fiber-reinforced polymer (FRP) composites have been used more often over the past decade than before in new construction as well as in repair of deteriorated bridges. Many of these bridges are on low-volume roads, where they receive very little attention. It is imperative that new bridge construction or repair be long lasting, nearly maintenance free, and as economical as possible. Relative to those factors, FRP composite bridges have been found to be structurally adequate and feasible because of their reduced maintenance cost and limited environmental impact (i.e., no harmful chemicals leaching into the atmosphere with longer service life). In West Virginia, 23 FRP composite bridges have been constructed, among which 18 are built on low-volume roads that have an average daily traffic (ADT) of less than 1,000, including 7 with ADT less than 400. General FRP composite bridge geometry and preliminary field responses are presented as are some of the preliminary construction specifications and cost data of FRP composite bridges built on low-volume roads in West Virginia
Fiber-reinforced polymer (FRP) composite materials have shown great potential as alternative bridge construction materials to conventional materials such as steel and concrete. This is especially valid in the field of repair and rehabilitation of existing bridges as well as in new bridge construction. The acceptance of composites in the highway bridge industry is mainly due to their superior properties such as high strength, durability, corrosion resistance, and fatigue resistance. Moreover, FRPs are well suited for mass production of structural shapes because of their high strength-to-weight ratios, which has resulted in the rapid installation of FRP modular decks on highway bridges. Details related to the construction of FRP modular decks as replacements on existing highway bridge superstructures are provided. In addition, details on shipping, handling, erection, assembly, deck-to-deck connections, deck-to-stringer connections, joints, and wearing surfaces are discussed.
Shear behavior of glass fiber reinforced polymer (FRP) bridge deck components has been experimentally and theoretically studied under in-plane shear, out-of-plane shear, punching shear, shear of web—flange junction, and system racking shear. Experimental data revealed that the shear modulus of FRP bridge decks ranged from 2.66 to 4.14 GPa and the shear stress to failure ranged from 20.7 to 96.6 MPa. In-plane shear behavior is studied under V-notched and racking shear test (parallel and perpendicular to cell direction). Experimental results under in-plane shear loading are compared with the results from the classical finite element method. Out-of-plane shear strength and stiffness of an FRP composite deck are experimentally evaluated utilizing test data from the short beam shear test, and the beam bending test. Using experimental and numerical results, the reduction in bending rigidity due to shear deformation under several loading conditions is calculated. In addition, size limits (span to depth ratio) under transverse loading are established as: L/d>22 (for multi-cell specimen with and without joints). A theoretical model based on FRP deck types for predicting punching shear capacity is proposed and validated through experimental data. In addition, the failure modes of test specimens are identified and reported. To study the web—flange junction behavior, closed FRP sections were tested under shear-bending effect. It is clear that the web—flange junction shear strength is only one half of the shear strength obtained from flange specimens under V-notched beam testing. While testing, cracks and layer delaminations around web—flange junctions were initiated and extended along the thickness of the web portion with increasing applied loads, which eventually led to web shear-off failure. In addition, it is found that shear strengths of test specimens depend on modes of shear failures induced by different shear test methods. Higher shear strength is found on failure modes that have more influence of fiber shear.
The orientation of reinforcements in a composite system has major influence on both the elastic and inelastic properties, including failure modes. Manufacturing a polymer composite structural member can be simplified by using certain types of fiber/fabric architecture. The structural performance of a finished composite part does vary with the manufacturing process and constituent materials including fiber and resin type, fiber architecture and Fiber Volume Fraction (FVF). In this research, the structural behavior of pultruded composite plates having different fiber architecture (uni-, bi-, tri and quadri-) manufactured by the pultrusion process is investigated. Further the mechanical properties of pultruded composites are compared with performance of composites made from compression mold. The strain energy density values of composites manufactured through compression molding and pultrusion are compared with each other so as to create a database to predict the strength and stiffness of composites. In addition, the response of pultruded composites with two different resin systems namely polyurethane and vinyl ester having same fiber architecture are evaluated. Bi-linear stress-strain response under tension was observed for all composites except for tridirectional composites, which showed tri-linear stress-strain response up to the maximum stress. Under bending, the stress-strain response for uni-and quadri-directional reinforcements are trilinear, while that for bi-and tri-directional reinforcements, the stress-strain curve has four linear slopes. It is observed that under tension, change in first slope took place at 29% ~ 40% for composites with various fiber architectures (uni-, bi-, tri and quari-directional). In bending, it was observed that for composites with uni directional fabrics, the change of first slope takes place at about 50% of maximum stress, in case of bi-directional the change of first slope is at 22%, and for all other fabrics i.e, tri-and quadri-directional fabrics, the change of first slope is at about 31%-34%. iii ACKNOWLEDGEMENT First, I would like to express my gratitude to God for providing me an opportunity to do Master's Program. My sincere thanks to Dr. Hota GangaRao for his encouragement and guidance throughout course of this research program.
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