Two-layer beams from normal and fibered high strength concrete

Two-layer beams, consisting of fibered high strength concrete in compressed zone and normal strength concrete without fibers in the tensile one, are effective when the RC section carries rather big bending moments. Steel fibers have little effect on beams' elastic deformations, but increase the ultimate ones, due to the additional energy dissipation potential of fibers. Changing the fibers' content, a required ductility level can be achieved. Providing proper ductility is important for design of structures to seismic, wind and other dynamic loadings. It was demonstrated that calculation of fibers' content for such elements is important, like that of reinforcing steel bars for usual RC beams. The current study is focused on finding optimal fibre content, yielding the highest Poisson coefficient and consequently higher ductility of the beam's section. Fibre weight ratio is used as an alternative to fibre volume ratio as the first is a more accurate parameter for definition of fibre content in the concrete mixture. The experimental results, obtained in the frame of this study, form a basis for general provisions, related to manufacturing of two-layer beams.