Bond over direct support of deformed rebars in normal and high strength concrete with and without fibers

This paper describes results of the second stage of a research on the bonding of deformed bars in normal and high strength concrete with and without fibers. The current study focused on the effect of confinement conditions, which are present over a direct support of a reinforced concrete beam, and compares these results with data obtained in the first stage of the research. The experimental work consisted of pullout tests, which were based on the standard RILEM flexural bond test (??beam test??) of deformed steel bars with diameters of 12 and 20?mm. Results revealed an increase in the normalized bond strength due to support conditions. An unstable post-peak slip of the tested rebar was observed when located over the support, whereas bars bonded near mid-span exhibited controlled bond?Cslip throughout the test. Up to peak load, however, bond?Cslip relations exhibited higher energy absorption over the support than near mid-span. Inclusion of fibers had only a minor effect on bond strength but had a significant influence on pre-peak energy absorption. A previously developed model of bond strength shows good agreement with current results when applying an increase factor due to the support effect.