Unconfined bond stress and slip characteristics of steel bars embedded in masonry cement mortars

Reinforcing bars are often embedded into cement mortar layers (bed joints and surface bonded) of masonry structures to enhance their structural performance to various effects. However, there is limited research available on the bond characteristics of steel bars embedded in the masonry mortars. This study was focused on assessing the bond stress and slip characteristics of steel bars anchored within masonry cement mortars. Steel bar embedded masonry cement mortar assemblages were constructed to test them under uniaxial pull-out loading to understand their bond stress and slip characteristics. A double-lap anchorage arrangement was used for these pull-out tests. In total, 72 samples were prepared, incorporating two types of masonry mortars, three steel bar diameters (6 mm, 10 mm and 12 mm) and four anchorage lengths (2.5d, 5d, 7.5d and 10d, where d is the diameter of the bar) to examine their influence on the bonding characteristics. Two types of failure modes were observed (1) pure pull-out failure of steel bars from the mortar and (2) tensile splitting of mortar, depending on the employed mortar types and steel diameters. The bond stress between the steel bars and cement mortars varied between 1.4 MPa and 7.9 MPa for the tested samples. The analytical formulations to predict the bond strength of anchored steel bars within the masonry cement mortars were verified for pull-out and mortar splitting failures to characterise the bond slip characteristics of steel bars anchored in cement mortars.