Finite element method investigation of seismic design for enlarged beam section (EBS) connection in steel structures under cyclic loading

Abstract The Enlarged Beam Section (EBS) connection has emerged as a superior solution for enhancing the seismic resilience of steel moment-resisting frames. Finite element analyses, validated by experimental results, demonstrate that optimizing the beam flange width adjacent to the connection zone and increasing the web thickness to 12 mm can achieve cumulative rotation angles of up to 1.82 rad, with peak von Mises stress nearly 408 MPa and the damage index, expressed in terms of equivalent plastic strain (PEEQ), remaining below 0.7. A critical design improvement is the relocation of the plastic hinge away from the column face, which effectively reduces stress concentrations and mitigates the risk of damage at the beam-to-column connection. The design procedure for the EBS connection involves an iterative approach that systematically adjusts key geometric parameters to ensure that the flexural capacity (M cap ) exceeds the moment demand (M dem ), thereby optimizing both rotational performance and structural integrity. Damage evaluation results further highlight the advantages of the EBS configuration. Across all models, the damage incurred at the end of the 4% and 6% rad drift cycles remained well below the failure threshold, with a maximum damage index of approximately 0.7 at the 6% rad drift cycle, significantly lower than the PEEQ threshold of 3.32. This confirms that the EBS connection maintains its structural integrity under significant cyclic loading, which is crucial for seismic resilience. These quantitative findings provide clear design guidelines that can be readily implemented to develop safer, more reliable structures in earthquake-prone regions, paving the way for innovative seismic design strategies.