Side Splitting Failure of RC Beams and Columns under Seismic Action As a Form of Shear Failure

Abstract

Recently bond splitting failure prior to the yielding of stirrups has attracted more attention for reinforced concrete (RC) structures located in seismic areas due to the increased popularity of high strength steel. However, bond splitting failure is complicated, particularly in RC beams with multiple layers of reinforcement with different cutoffs. Pullout tests indicate the bond strengths of bars in the second (inner) layer of RC beams are weaker than those in the first (outer) layer. In contrast, test results of RC beams indicate that the bond strengths of cutoff bars in the second layer are larger than those in the first layer. To examine this contradiction, previous studies of pullout test in which deformed bars were embedded in concrete were reviewed. In contrast to the conventional method of evaluating the surface bond strength of each bar, a new method for evaluating bond resistance is developed, in which a discussion point is focused on the shear strength at a potential failure plane below the reinforcement layer. The proposed method shows good results when compared with test results of RC beams and columns that failed in bond splitting prior to yielding of longitudinal reinforcement, with an average ratio of measured-to-predicted failure stress of 1.23 and a coefficient of variation of 14%. In contrast, ACI 318-19 shear equation slightly underestimated some of the test results of single-layered beams, with an average ratio of measured-to-predicted failure stress of 0.98 and a coefficient of variation of 15%. These findings suggest that side splitting failure of RC beams and columns under seismic action can be treated as shear failure.