Strength-to-Yield Ratio of Steels and Ductility Coefficient of Steel Frame Beams

It is found that the strength-to-yield ratio of steels has a strong influence on the ductility coefficient of steel beams. The larger the ratio， the significantly higher the ductility coefficient. This is because an increased strength-to-yield ratio allows the beam to develop longer plastic yielding segments， thereby accumulating more plastic deformation.For an ideal elastic-plastic material， even if the maximum strain reaches twice the hardening strain of steel， its ductility coefficient does not exceed 1.5. This reflects the importance of specifying a minimum strength-to-yield ratio from the opposite side. Based on the above conclusions， it can be inferred that steel beams providing ductility for the overall structure will inevitably experience local buckling. Local buckling can provide ductility if the post-buckling bearing capacity maintains （with ≤15% degradation）. If the strength-to-yield ratio is small， increasing the width of the flange near the beam ends or adding cover plates can enhance beam ductility. Performance-based design requires elastic-plastic analysis. It should be recognized that while the allowable maximum strain is significantly influenced by the adopted strain-hardening modulus， such elastic-plastic analysis fails to consider both local buckling behavior and the effects of beam-end section strengthening.