The flexural (or bending) capacity of structural members can be easily enhanced by bonding a layer of FRP to the tension face of the element. In the case of a reinforced concrete structure, for example, the FRP resists tension forces that supplement the tension force being resisted by the existing reinforcing steel. Thus, the moment capacity of the member is calculated by taking into account the contributions of both steel and FRP.
Shear strength in concrete is resisted by diagonal tension; it is this principle that allows FRP to be used as shear reinforcement. Bonding fabrics of FRP to the sides of a reinforced concrete beam, for example, allow the fibers of the fabric (which are parallel to the legs of the stirrups of the beam) to resist tension, and thus shear forces. Most design guidelines limit the allowable strain in the FRP for shear to very small values; this is to ensure that the shear crack does not become too wide and that the aggregate interlock remains present.
The fibers of FRP buckle at relatively small loads; thus, most design guidelines do not allow direct contribution of the FRP to axial load enhancement. However, when a concrete column is wrapped with FRP, the confinement provided by the FRP increases both the strength and the failure strain (ductility) of the column. It is this contribution that can enhance the overall axial strength of the member.
The presence of FRP can reduce deflections under service loads. Numerous tests by researchers (including those at the University of Arizona) have demonstrated that the gain in stiffness is more than what one would calculate based on transformed section properties of the beam section to account for the FRP.
For columns, where the FRP is primarily used for confinement, the ductility of the members is significantly enhanced. These are demonstrated in many of the research papers that are available on this website. For flexural members, however, the gain in strength is often accompanied by a reduction in deflection at failure (i.e. ductility). Nevertheless, by proper design, one can ensure that the steel reinforcement in the beam yield before failure, giving advanced warning prior to failure of the beam.
FRP products are very effective in repair of corrosion-damaged structures. Because oxygen is the fuel for the corrosion process, by totally encasing a member in FRP, this fuel is shut off. This will significantly reduce the rate of corrosion. At the same time, FRP products can be used to repair and strengthen structures where corrosion has reduced the area of steel reinforcement. QuakeWrap™ products have been successfully used for such applications in extremely severe conditions in the mining industry.
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