Improved concrete structural members such as columns, piers, and piles can be manufactured by incorporating fiber-reinforced-plastic (FRP) exterior shells and FRP interior submembers. The FRP components impart greater compressive, flexural and shear strengths and ductility to a concrete structural member, relative to a similar concrete structural member made in the conventional way, without FRP. During fabrication, the FRP exterior shell also serves as a form for casting the concrete. Moreover, during use of the structure, the FRP exterior shell prevents or retards the intrusion of moisture, thereby helping to prevent or retard both environmental degradation of the concrete and corrosion of any steel reinforcement or steel structural member(s) embedded or anchored in the concrete. Thus, concrete structural members made with FRP offer greater strength and durability that should be especially advantageous for bridges and similar structures in hurricane-prone coastal areas, earthquake zones, and regions where moist concrete is damaged during freeze/thaw cycles.

Concrete structural members incorporating FRP components can be made in a wide variety of configurations, using a wide variety of polymer-matrix/fiber composite materials and composite-fabrication processes, and various concretes with or without conventional steel or advanced fiber reinforcement. A typical FRP comprises about 60 percent fibers (e.g., glass, carbon, or aromatic polyamid) and 40 percent polymeric matrix material (e.g., a polyester, vinylester, or epoxy). The concrete can be cast at the construction site, or it can be cast in a factory, possibly using centrifugation to enhance the bond between the concrete and the exterior shell.

Concrete Columns can be fabricated with FRP exterior shells. Optionally, FRP ribs or other reinforcing FRP interior components can be included. The two configurations shown here are only typical; many other configurations are also possible.

The figure illustrates some typical configurations for a round column with an FRP tube as the exterior shell, with or without interior FRP reinforcement. The shell can be made in two or more layers; for example, an inner layer containing axial fibers and an outer layer containing circumferential (hoop) fibers, both layers fabricated in a continuous filament-winding process. The ribs (if any) can be made by pultrusion. The axial fibers (if any) increase the flexural capacity of the column. Inward buckling of the axial fibers is inhibited by the concrete core. The hoop reinforcement confines the concrete and prevents outward bucking of both the axial fibers and of any longitudinal interior reinforcing ribs or bars. Alternatively, the exterior shell can be fabricated in a multilayer angle-ply configuration with winding angles of ±α, or as a sandwich of axial fibers between two hoop layers.

The interior FRP reinforcement can be in any of various forms; for example, ribs or H-columns, or else bars or cages like those of conventional steel reinforcements. A particularly advantageous design calls for pultruded longitudinal ribs formed integrally within a pultruded tube covered by an angle-ply laminate, as shown on the right side of the figure. This design can reduce or even eliminate the need for a conventional steel reinforcing cage embedded in the column, thereby reducing the time and cost of construction and enhancing durability in a saltwater or other corrosive environment.

This work was done by Amir Mirmiran of the University of Central Florida and Moshen Shahawy of the Florida Department of Transportation for Kennedy Space Center. For further information, access the Technical Support Package (TSP) free on-line at under the Materials category, or circle no. 127 on the TSP Order Card in this issue to receive a copy by mail ($5 charge). KSC-11946