Bond Stress Deformation in Pull-Out Masonry Specimens

An experimental investigation to determine bond stress, free-end slip, and relative deformation between a reference plane in the masonry and an originally coplanar point on the steel (slip) is conducted. Stack pull-out specimens constructed of grouted nominal 6-in. concrete or clay masonry units, reinforced with #4 or #7 bars, are subjected to monotonic or cyclic loadings. The method for evaluating slip incorporated slip-wires connected to linear variable differential transformers (LVDTs). Strain gages provide strain in the steel bars from which stresses in the reinforcing bar and bond stresses can be calculated. Free-end slip information is also collected. These data are useful in developing an understanding of the physical mechanism associated with bond, slip, and bond deterioration. The bond stress, which develops between the reinforcement and the surrounding grout, is a complex phenomenon dominated by the interlocking action of the reinforcing bar ribs embedded in the grout mass. To determine bond stresses and slip, six specimens are constructed and tested. Three specimens of 16-in. length are reinforced with a #4 bar, and three, of 32 in. length, are reinforced with a #7 bar. The bond stress and slip distribution curves are evaluated from experimental data. In addition, short embedment specimens, consisting of prisms of 6-in. concrete masonry units (nominal size of 6×8×8 in.) are tested. The embedment length is varied from 1 to 6 in. Ten specimen configurations were replicated three times. The nominal bond stress and free-end slip are obtained.