Strength Decay of RC Columns under Shear Reversals

The decay in shear strength of tied reinforced concrete columns during earthquake loading was investigated by subjecting 12 column specimens to several reversals of loading to deflections larger than the yield deflection. The principal variables of the test program were the axial load, the transverse reinforcement ratio, and the total deflection per cycle. The test specimens were able to develop the expected yield moment in the first quarter cycle and maintain that load for some inelastic deflection. However, the repetition of these deflections resulted in a decay in the strength of the member. Experimental data are used to examine the mechanism of strength decay, which is related to crushing and spalling of the shell concrete, yielding of the transverse reinforcement, and abrasive rubbing of concrete along inclined cracks. The results of this investigation indicate that the transverse reinforcement must be proportioned to carry the total shear required to develop the ultimate moment capacity of the column.