Effect of reinforcing steel bond on the cracking behaviour of lightly reinforced concrete members

• Influence of reinforcement bond strength on lightly reinforced concrete members.
• Pull out and prism tests using reinforcement with different deformation patterns.
• Greater yield penetration when using half rib height reinforcement.
• Greater crack distribution (secondary cracking) when using standard reinforcement.

The ductility of lightly reinforced concrete (RC) members is dependent on the distribution of cracks, as well as the strain penetration of reinforcement at each crack. A series of experimental tests were conducted to investigate how the bond characteristics of reinforcing steel would influence the strain penetration and crack distribution in lightly reinforced concrete members. To vary the bond characteristics, reinforcement with three different deformation patterns were investigated, including a standard deformation pattern and two modified bars with either half the rib height or double the rib spacing of a standard bar. Pull-out tests were conducted to quantify the bond strength of the reinforcement with different deformations patterns, followed by direct tension prism tests that represented the end region of an RC wall with minimum vertical reinforcement. The pull-out tests indicated that the standard deformation pattern achieved the highest initial bond stiffness, whereas the double rib spaced deformation pattern achieved the highest ultimate bond strength. The direct tension prism tests showed similar crack distributions for the two modified bar types, but increased secondary cracking for the standard bar due to higher initial bond strength. However, only the half rib height bar displayed a higher ductility than the standard bar, with significantly greater yield penetration at each crack causing larger ultimate crack widths prior to bar fracture.