Lateral torsional buckling design of dumbbell-shaped steel strip dampers

The concept of “structural fuse” for seismic energy dissipation has been widely adopted in both design standards and research worldwide. Among the metallic structural fuses, slit-yielding dampers, which dissipate energy through in-plane yielding of steel strips, have shown significant promise due to their high ductility and stable hysteretic behavior. However, their effectiveness can be compromised under bi-directional deformations, which may trigger lateral-torsional buckling. This study examines how geometric parameters influence the distribution and accumulation of plastic strains, the onset of buckling, and the energy dissipation capacity of dumbbell-shaped steel strip dampers. A refined non-linear finite element model (FEM) was developed, validated against experimental results, and used to perform non-linear buckling analyses considering initial geometric imperfections. A comprehensive parametric study was carried out on dumbbell-shaped steel strips with varying geometries to assess their susceptibility to yielding and lateral-torsional buckling. The findings highlight the importance of precise geometric control in the design of dumbbell-shaped steel strip dampers to ensure stable energy dissipation under cyclic loading. This is due to the high sensitivity of buckling-induced strength degradation to geometric parameters such as the length-to-thickness ratio, slenderness, aspect ratio, and initial imperfection amplitude. For example, at an aspect ratio of 5.5, an 8 % increase in slenderness resulted in a 39 % reduction in strength, while increasing the initial imperfection from L 0 /1000 to L 0 /500 led to a 30 % drop in peak strength for slenderness of 105.63. To address this, acceptance criteria based on buckling-induced resistance degradation were defined to determine a critical slenderness threshold. A regression analysis revealed a strong correlation between critical slenderness and initial imperfection, with regression coefficients linearly dependent on the aspect ratio. The model achieved coefficients of determination ( R 2 ) ranging from 0.9818 to 0.9969 under monotonic loading, and from 0.8980 to 0.9881 under cyclic loading. Based on this analysis, a practical design formula was developed to predict the critical slenderness of dumbbell-shaped steel strips under cyclic loading. Calibrated using the FEM dataset and validated across a range of imperfections and aspect ratios, the formula demonstrated strong accuracy, with standard deviation from 0.0145 to 0.0452, and standard error varying from 0.0065 to 0.0202.