In this study, the investigation of maximum inelastic displacement demands in steel moment resisting (SMR) frames designed using the Performance-Based Plastic Design (PBPD) method is conducted under both near-fault and far-fault earthquake records. The PBPD method utilizes a target drift and predetermined yield mechanism as the functional limit state. To accomplish this,6 steel moment frames having various heights were scaled using well-known 𝑠𝑎(𝑇1) method and, then, were analyzed by OPENSEES software. A total of 22 far-fault records and 90 near-fault records were compiled and employed for parametric nonlinear dynamic analysis. The near-fault records were classified into two categories: 𝑇1/𝑇𝑝 ≥ 1 and 𝑇1/𝑇𝑝 < 1 . The study aimed at investigate their impacts on the inter-story drift and the relative distribution of base shear along the height of the structure. The results revealed that the records with 𝑇1/𝑇𝑝 ≥ 1 exerted the greatest influence on the drift demands of upper stories in all frames. Conversely, the near-fault records with 𝑇1/𝑇𝑝 < 1 demonstrated the most significant impact on the lower stories of mid-rise frames. Additionally, the distribution of relative story shears was examined through genetic programming for optimum PBPD design of steel moment frame structures. As a result, a proposed relationship, denoted as b (seismic parameter for design lateral force distribution), was developed and optimized for both near-fault and far-fault records. This relationship depends on the fundamental period of vibration and the total height of the structure. The accuracy of the predicted model was assessed using 𝑅2, which confirmed the reliability of the proposed relationship.
