Reinforced　concrete　(RC)　single-column　piers　(SCPs)　and　double-column　piers　(DCPs)　are　widely　used　in　highway　girder　bridges.　However,　the　seismic　behavior　of　conventional　RC　DCPs　has　not　received　sufficient　attention.　This　study　aimed　to　investigate　the　seismic　behavior　of　DCPs,　especially　the　comparison　of　the　failure　mechanism,　hysteretic　behavior,　and　dynamic　response　between　SCPs　and　DCPs.　To　this　end,　the　critical　performance　parameters　between　SCPs　and　DCPs　in　the　elastic　phase　were　first　calculated　according　to　the　simplified　calculation　formulas.　Eight　1/3　scaled　SCPs　and　DCPs　were　then　fabricated　and　tested　under　quasi-static　cyclic　loading,　and　the　effective　height　of　the　DCPs　was　twice　that　of　the　SCPs.　The　test　results　showed　that　the　failure　modes　and　damage　mechanisms　between　the　SCPs　and　DCPs　are　obviously　different.　In　particular,　the　plastic　damage　states　at　the　top　and　bottom　of　each　column　in　the　DCP　were　asymmetric,　and　this　behavior　was　also　observed　on　both　sides　of　each　plastic　hinge　region.　Subsequently,　the　relationship　between　the　performance　parameters　of　SCP　and　DCP　in　the　plastic　phase　differed　from　that　of　the　elastic　phase　and　was　not　proportional.　Existing　formulas　for　calculating　the　plastic　hinge　length　of　SCPs　cannot　effectively　predict　DCPs　and　may　even　underestimate　it.　Furthermore,　numerical　simulations　were　analyzed　to　investigate　the　effects　of　various　design　parameters　and　ground　motions　on　the　seismic　behavior　of　the　SCPs　and　DCPs.　©　2024　American　Society　of　Civil　Engineers.