Consequences of Strong Vertical Accelerations on Shear Demand and Capacity in Bridge Columns

Strong vertical ground motions can significantly alter axial forces in a bridge column. Axial force variations also affect the concrete contribution to the shear capacity of a reinforced concrete (RC) member. However, the effect of axial force demands on shear capacity is a fairly complex issue since the shear demand in an RC bridge column is affected by variations in the axial force. A combined experimental and numerical study was carried out in a joint project between the University of California at Berkeley and Davis to examine the effects of vertical ground motions on the shear demand and shear capacity in columns of ordinary highway bridges. The experimental study consisted of a series of shaking table simulations on quarter-scale specimens. Results of the tests indicate that tension in the columns results in degradation of shear strength, which is mainly due to the degradation of the concrete contribution to shear strength.