Direct Digital Image Analysis of Local Displacements and Strains in a Pull-out Test

The effect of local rebar geometry on global strain measurements in pull out tests

“…The maximum circumferential strain value is obtained at almost the same stage of the experiment (e.g., TOLF‐20‐2‐1 ( τ / τ max = 0.90 on the postpeak descending branch) and TOLF‐20‐2‐2 ( τ / τ max = 0.86 on the postpeak descending branch see Figure b). However, because of the gradual development of the damage mechanism near the ribs (has been identified and reported in a previous article) a different circumferential strain–slip curve is expected, as shown in Figure b. At a smaller confinement level (smaller specimen diameter) larger circumferential strains are developed, as expected. For example, compare the strain (~74 micro‐strain) measured on a 100 mm diameter specimen TOLF‐10‐2‐4 with the strain (~18 micro‐strain) measured on a 200 mm diameter specimen TOLF‐20‐2‐1.…”

“…The gradual development of the damage near each of the ribs had been identified and reported in a previous article . It is expected that the circumferential strain–slip curve for each rib will be different, as the maximum strain is expected to develop at a different slip, however their descending branch, after full damage development, is expected to be similar and coincide at larger slips.…”

“…The gradual development of the damage near each of the ribs had been identified and reported in a previous article. 8 It is expected that the circumferential strain-slip curve for each rib will be different, as the maximum strain is expected to develop at a different slip, however their descending branch, after full damage development, is expected to be similar and coincide at larger slips. The strain gauges on these specimens were installed at larger gauge-rib relative distances than the slips at maximum bond stress (i.e., the relative distance is closed during the descending branch stage of the bond-slip curve).…”

Predicting the circumferential strains on a cylindrical concrete specimen during a pull‐out test

“…Assuming a circular rib geometry, full axial symmetry is maintained, and the longitudinal location of each rib is clearly determined. In a recent investigation with a new experimental technique using a Digital Image Correlation (DIC) system, the strain field in the concrete around the ribs could be followed 10–12 and inclined local compressive strains of high intensity were identified at the ribs sides. This observation supports the assumption of inclined compressive forces concentrated at the ribs sides 6 and leads to an idealized representation of a radial pressure band of narrow width acting at the side of each rib, representing the radial component of the inclined compressive force.…”

“…Recent studies 10,11 have shown that during the pull‐out process high shear strains are developed in the concrete, in the longitudinal plane of symmetry, in a zone of limited width in the radial direction around the rebar. The shear strains decrease sharply with the radial distance until reducing to zero.…”