Vimala Shekar

Fatigue Response of Fabric-reinforced Polymeric Composites

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 low-amplitude 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.

Performance Evaluation of FRP Bridge Deck Under Shear Loads

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.

Fiber-Reinforced Polymer Composite Bridges in West Virginia

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

Theoretical and experimental analysis of FRP bridge deck under cold temperatures

The large temperature difference (~120°F) between the top and bottom of a fiber-reinforced polymer (FRP) bridge deck is attributed to low thermal conductivity of FRP materials and low thermal mass because of hollow core FRP decks. In this study, laboratory tests were conducted on glass FRP deck modules under low temperature gradient. A theoretical beam model was used to analyse the FRP deck-steel stringer system while closed form solutions (based on Macro Approach and Navier– Levy method) were derived using the plate bending theory for FRP deck modules. In addition, thermal stress evaluations from field test data were evaluated using theoretical models. The laboratory test data indicated that the FRP decks sag when they were subjected to negative temperature difference. Deflections and expansion of the deck top increased as the difference between the Ttop and Tbottom increased. Partial deck restraint, provided by steel stringers, resulted in partially induced stresses.

CONSTRUCTION OF FIBER-REINFORCED PLASTIC MODULAR DECKS FOR HIGHWAY BRIDGES

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.

Composites with 3-D stitched fabrics

The use of Fiber Reinforced Polymer (FRP) composites in the construction industry has been growing rapidly because they are more durable and economical over conventional materials. Currently, almost all composite products are manufactured with 1-D fibers (unidirectional) or 2-D fabrics (bidirectional), typically leading to ply-by-ply failure (due to shear-lag phenomena) or premature failure of matrix and fibers leading to the interface failure. The present paper reports on the effects of through-thickness reinforcement on the mechanical properties in the 3-D stitched fabrics. In this study, composites were fabricated using 3-D stitched fabrics with different (1) fiber architecture, (2) stitch density, (3) stitch material and (4) manufacturing process. Strength and stiffness of composites with 3-D stitched fabrics (at coupon level) under tension, bending and shear loads were experimentally established. Structural properties of composites made of 3-D stitched fabrics were compared with those composites made...