Bridge piers with adequate seismic capacities are considered vital to bridge construction in countries with potential earthquake threats. In order to improve bridge-pier efficiency, the authors here developed a new design concept that integrates double steel tobes with tie rods filled in to various heights with. concrete to form partially-filled sandwich box columns. This stody is focused on evaluating the ductiJity of such members. Sixteen specimens with various tube widthltbickness ratios and in-filled concrete heights were tested under combined cyclic loading. Test results showed that the ductility ratios of partially-filled sandwich box columns fell between 5 and II, greater than that required by design codes. Experimental information was also used to determine optimal concrete in-fill heights and to establish design guidelines.