Circumferential strains of a concrete specimen in a pullout test

Pullout test of a rebar from an axisymmetric concrete specimen yields the bond-slip relationship characterizing the rebar-concrete interfacial constitutive relationship. It is assumed that inclined compressive forces are developed between the rebar ribs and the concrete during pullout. The components of the inclined forces that are perpendicular to the rebar axis create a ring action in the concrete producing radial compressive stresses and circumferential tensile stresses. The ring action develops circumferential strains on the specimen outer surface that are the subject of the present investigation. Although these strains are usually not measured, they may enhance understanding of the ring action in concrete during a pullout test, which is an important component of the bond resistance mechanism. The present study aims at investigating these circumferential strains and at examination of their dependence on different parameters. The cylindrical specimens were made of concrete without coarse aggregates to provide a relatively homogeneous material and assure the specimens axisymmetric behavior and coherent results. The investigation examines the effects of several major parameters (concrete strength, specimen diameter governing the confinement level and the number of ribs in the bonded length). Attaching a number of strain gauges along the specimen envelope to measure the circumferential strains allows investigation of their longitudinal variation during the experiment.