An　experimental　and　numerical　study　on　the　residual　stresses　and　the　cross-sectional　behavior　of　Q1100　ultrahigh　strength　steel　welded　I-sections　is　reported　in　this　paper.　The　experimental　tests　included　nine　tensile　coupons,　eight　stub　column　tests　and　measurements　of　the　residual　stresses　and　geometric　imperfections　of　welded　I-section　stub　columns.　Based　on　the　test　results,　finite　element　(FE)　models　were　developed　and　validated,　which　were　then　employed　in　a　parametric　study　to　expand　the　available　test　data　pool.　The　slenderness　limits　and　design　methods　for　high　strength　steel　stub　columns　in　the　European,　North　American,　Australian　and　Chinese　design　codes　and　the　DSM　method　were　examined　by　the　test　and　FE　data.　Furthermore,　a　new　modified　DSM　method　offering　improved　accuracy　for　the　design　of　Q1100　welded　I-sections　was　proposed　and　validated　via　reliability　analyses.