Has any study been made of steel fiber reinforced concrete as a tensile skin in beams? If so, what does it do to crack width?
Swamy and Al-Noori, of the University of Sheffield, United Kingdom, made test beams with a fiber concrete skin to the depth of the longitudinal reinforcement (2 inches). The concrete contained crimped steel fibers, 0.2 by 2 inches, in the amount of 3.5 percent by total weight of the mix. It was found that using fiber concrete as a tensile skin was just as effective as using it in the whole tension zone. With reinforcing steels of characteristic strength of 100,000 psi, the crack widths at design loads (steel strains of 1,600 to 2,100 millionths) varied from 0.004 to 0.0075 inch. These investigators also noted that such a tensile skin transforms a conventionally over-reinforced beam and makes it behave like an underreinforced beam with ductile characteristics. Such beams could be designed to carry a much higher service load than otherwise possible. The authors' 10-page paper, "Flexural Behavior of Fiber Concrete with Conventional Steel Reinforcement," is one of 38 papers on the theory and practice of fiber concrete construction (including other fibers as well as steel) which make up the RILEM Symposium 1975: Fiber Reinforced Cement and Concrete. This hard-covered book of 459 pages is available for $37.50 from Concrete Construction Publications.