The　ageing　effect　in　the　life-cycle　assessment　should　be　considered　for　the　high-strength　steel　structures　constructed　in　corrosive　environments　and　high-seismicity　zones.　Additionally,　the　structures　can　suffer　multi-dimensional　seismic　excitations　because　of　the　spatial　effect　of　ground　motions.　Therefore,　this　study　aims　to　investigate　the　impact　of　different　loading　protocols　on　the　mechanical　properties　of　Q690　steel　columns　with　H-section　during　the　whole　life-cycle.　Firstly,　numerical　methods　considering　time-varying　corrosion　process　are　used　to　simulate　the　ageing　steel　columns.　After　that,　the　nonlinear　hysteretic　behaviors　of　the　ageing　steel　columns　under　different　loading　protocols　are　investigated.　The　factor　of　resistance　degradation　(the　degree　of　degradation　of　ultimate　resistance)　is　employed　to　quantify　the　effect　of　loading　protocols　on　ageing　steel　columns.　Finally,　the　biaxial　ultimate　interaction　curve　considering　the　ageing　effect　and　a　practical　design　process　are　proposed.　The　findings　demonstrate　that　the　steel　columns　exhibit　different　mechanical　properties　under　various　loading　protocols,　and　the　coupling　direction　of　bi-directional　displacement　loads　influences　the　degree　of　degradation　of　ultimate　resistance.　As　service　time　increases,　the　factor　of　resistance　degradation　of　steel　columns　gradually　reduces　by　up　to　40%.　The　proposed　biaxial　ultimate　interaction　curve　has　acceptable　accuracy.　These　findings　emphasize　the　importance　of　employing　the　unfavorable　loading　protocols　in　conducting　the　seismic　design　of　the　steel　columns　in　different　life-cycle　stages.　©　2024　Elsevier　Ltd