Experimental Study on Direct Pull out Test: Straight Bar, Bent-Up and Headed Bar

Results from 45 bond tests conducted using the so-called direct tension pullout specimen type are presented. Anchorages of steel bars with machined deformations were tested so as to enable a targeted study of the straight bar, bent-up bar and headed bar on bond behaviour, tests were conducted with or without the combined presence of external confinement over the embedded length. The novel specimen form presented in the paper was designed to simulate the state of stress and strength arising in usual bar anchorages in the tension zones of flexural members where both cover concrete and bar are stressed in tension. This development was motivated by the need to eliminate spurious influences of the test setup on specimen behaviour, which are known to interfere with bond mechanics. Additional parameters studied in the experimental program were the development length, the cover thickness, the effect of confinement, and the tensile strength of concrete.