A　curve-approximated　hysteresis　model　of　the　lateral　load-displacement　behavior　of　steel　bridge　columns　is　proposed　for　nonlinear　seismic　response　assessment　of　single-column-type　bridges　using　single-degree-of-freedom　(SDOF)　analysis.　Instead　of　multiple　straight　lines,　a　series　of　curves　are　adopted　to　precisely　describe　complicated　force-displacement　hysteresis　behavior　of　the　column.　The　P-delta　effect,　hardening　effect　in　unloading-reloading　hysteresis　loops,　deterioration　of　strength,　and　stiffness　are　taken　into　account.　Parameters　of　proposed　hysteresis　model　for　three　types　of　steel　column　specimens　used　in　this　study　are　calibrated　by　six　quasi-static　cyclic　tests.　To　verify　the　accuracy　of　the　proposed　model,　eleven　pseudodynamic　tests　are　conducted.　By　comparing　the　simulation　and　the　test　results,　the　differences　between　the　predicted　nonlinear　seismic　response　using　the　proposed　model　and　pseudodynamic　tests　are　found　to　be,　on　average,　5%　in　maximum　response　displacement,　22%　in　residual　displacement,　and　4%　in　the　amount　of　energy　dissipation.　(C)　2014　American　Society　of　Civil　Engineers.