Buildings　are　exposed　to　multiple　natural　hazards　over　their　service　lives.　Multihazard　analysis　and　design　of　building　structures　has　become　a　research　hotspot　worldwide.　For　these　structures,　earthquake　and　progressive　collapse　are　two　of　the　most　commonly　encountered　hazards.　However,　little　research　has　been　conducted　to　examine　the　effects　of　the　seismic　and　progressive　collapse　designs　on　the　resistance　of　buildings　against　multiple　hazards.　In　this　study,　a　series　of　six-story　reinforced　concrete　(RC)　frames　are　considered,　and　their　seismic　and　progressive　collapse　designs　are　performed　independently　according　to　the　corresponding　design　codes.　Fragility　curves　are　used　to　assess　the　seismic　and　progressive　collapse　resistance.　The　interactions　between　the　two　designs　are　discussed　by　analyzing　the　fragility　curves　and　the　collapse　modes.　Results　show　that　the　progressive　collapse　design　of　the　RC　frame　may　lead　to　an　undesirable　failure　mode　(i.e.,strong-beam-weak-column)　under　earthquakes,　which　indicates　that　a　seismic　redesign　is　necessary　subsequent　to　the　progressive　collapse　design.　Note　that　sequential　use　of　different　design　codes　for　a　structure　may　result　in　material　waste　yet　a　suboptimal　structural　performance.　Therefore,　a　design　method　by　individually　considering　different　hazards　is　unsuitable　for　the　multihazard　prevention　and　mitigation　of　building　structures.　A　comprehensive　and　integrated　design　method　for　multihazards　is　thus　in　great　need.　The　outcome　of　this　study　will　lay　a　foundation　for　future　multihazard　analysis　and　design　of　building　structures.　(C)　2016　American　Society　of　Civil　Engineers.