The Continuous Strength Method (CSM) was developed and calibrated against experimental and numerical results as a design approach, which allows for a rational exploitation of the significant strainhardening exhibited by stocky stainless steel cross-sections, thereby leading to more economic design. In order to extend its scope of application beyond the fundamental loading cases of concentric compression and uniaxial bending, a comprehensive numerical parametric study has been conducted and the obtained numerical results have been utilized to determine suitable interaction equations for cross-sections subjected to combined loading. This paper focuses on the ultimate response of I-sections under combined loading and complements a recent relevant study on RHS under combined loading. It is concluded that the current design guidance for stainless steel cross-sections under combined compression and biaxial bending is overly conservative and significant gains can be made if the effect of strain-hardening on ultimate capacity is taken into account.