Abstract
To ensure the seismic safety of steel bridge piers, it is realistic to check their dynamic responses under the coupling of 3D seismic wave components in terms of whether or not the responses are within the ultimate limit state. For this purpose, an interaction surface expressed in terms of three restoring force components and two restoring moment components around the two horizontal axes is proposed to express the ultimate limit state of steel bridge piers with stiffened square cross section. This interaction curve is versatile because it includes all the possible restoring force components that will act at the top of the bridge piers without eccentricity. The accuracy of the proposed interaction surface is confirmed by carrying out a dynamic response analysis under 3D seismic wave components.
