Reinforced concrete members in structures are typically subjected to a combination of bending, shear and axial compression (tension) loads. A simplified bending–shear–axial compression (tension) interaction formula based on bending–axial compression, bending–shear and bending–axial tension interactions was proposed to obtain the strength envelope of symmetrically reinforced concrete members under bending, shear and axial compression (tension). The interaction formula is verified by a comparison with experimental data. A sample planar-frame calculation result indicates that the envelope can be used as a failure criterion in symmetrically reinforced components to determine the safety of the members and calculate the residual capacities of components under bending, shear and axial compression (tension).