In North America, bridges are not typically designed for vertical earthquake ground motion. Design codes, AASHTO in the USA and S6-06 in Canada, do not explicitly consider the effect of vertical earthquake ground motion in the design of highway bridges. However, analytical and field evidences have often drawn engineers' attention to the damage potential of vertical earthquake ground motion to engineered bridges. This paper proposes a simplified method to calculate elastic support reactions under vertical earthquake ground motion. Support reactions are first calculated by exact dynamic method. By applying a few assumptions, a simplified method has been developed. The developed method can be readily used in the design of typical bridges with regular span distribution. This simplified method has been demonstrated with several examples.