Bridges, Tunnels and other Transportation Structures
Conventional (plain, unreinforced) concrete is a quasi-brittle material that is strong in compression, relatively weak in tension, and exhibits low strain capacity. In traditional rebar reinforced concrete (R/C), a limited number of steel reinforcing bars, with lengths comparable to key dimensions of the structural element, are strategically embedded to carry tensile stresses and to prevent sudden (brittle) failure. In contrast, fiber-reinforced concrete (FRC) utilizes a large number of small discontinuous fibers mixed within the concrete, typically made of steel, synthetic, glass, or natural materials. Adding distributed discrete fibers has been found to improve hardened mechanical properties such as tensile strength, ductility, toughness, and impact resistance.
In highway bridge construction, concrete bridge rails (i.e., longitudinal safety devices intended to redirect errant vehicles) may be constructed using slip forming. Concrete slip forming is an on-site construction technique in which fresh concrete is placed, formed, and finished in a single continuous motion, resulting in a continuous structural element. When applied to the construction of concrete bridge rails, conventional steel reinforcing bars contained within the rail cross-section must be installed prior to the start of slip forming. Consequently, the efficiency of slip formed bridge rail construction is diminished, due to the expense of time, labor, and cost on rebar installation. In this study, FRC is investigated as a possible means of eliminating the need for installation of a rebar cage (consisting of flexural and shear steel), instead using distributed steel fibers as the primary form of reinforcement within the railing.
Results from standardized, small-scale laboratory static tests and moderate-scale pendulum impact tests will be presented. Test data are used to characterize the improved material properties of the developed FRC mixture, specifically designed for low-slump slip forming. The characterized FRC material properties are used to validate complementary high-resolution, nonlinear finite element analysis (FEA) models which are analyzed using LS-DYNA. The validated FRC modeling techniques are employed to design a full-scale FRC railing for truck impact loading, per impact conditions specified in AASHTO MASH.