This paper presents analytical assessment of the effect of vertical earthquake ground motion on RC bridge piers. A bridge structure damaged during the Northridge Earthquake and a Federal Highway concept bridge design are examined. The effects of a suite of earthquake ground motion records with different vertical-to-horizontal peak acceleration ratios on the two bridges are presented and the results are compared with the case of horizontal-only excitation. The effects of arrival time interval between horizontal and vertical acceleration peaks are also reported and compared to the case of coincident motion. It is observed that the inclusion of the vertical component of ground motion has an important effect on the response at all levels and components. It is therefore concluded that vertical motion should be included in analysis for assessment and design, especially that there are no particular challenges impeding its inclusion.