This paper presents a parametric study of the effect of vertical ground motion on a simple RC frame with different geometric configurations including span length, span ratio and story height. The effects of a suite of earthquake ground motion records on RC frames are presented and the results are compared with the case of horizontal-only excitation. The structural response was investigated at both the global and the local levels. Interstory drift was considered as a global failure criterion, while the curvature ductility and shear capacity of structural members were monitored to assess failure on a local level. The effect of vertical ground motion on axial force and shear capacity is also investigated.