Effect of reinforcing steel bond on the seismic performance of lightly reinforced concrete walls

Abstract

During the Canterbury earthquake series, several reinforced concrete (RC) walls formed a limited number of cracks at the wall base as opposed to the expected distributed cracking in ductile plastic hinge regions. The ductility of a lightly reinforced concrete wall is dependent on the distribution of cracks, as well as the reinforcement bond and yield penetration at each crack. A series of experimental tests were conducted to investigate how the bond characteristics of reinforcing steel would influence the yield 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 deformation patterns, followed by direct tension tests of prisms that represented the end region of an RC wall with minimum vertical reinforcement. The pull out tests indicated that halving the rib height and doubling the rib spacing had similar effects of reducing the reinforcement bond strength. The direct tension tests showed similar crack patterns for the two modified bar types, but increased secondary cracking for the standard bar due to the higher 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. Using half rib height bars as vertical reinforcement would potentially improve the ductility of lightly reinforced concrete walls.