Ductility-Based Stiffness Optimization of Transmission Tower–Line Systems for Wind-Induced Collapse Resistance

To enhance the collapse resistance of transmission tower–line systems under strong-wind loads, this study develops a ductility-based stiffness optimization framework for weak structural segments. A finite-element model of a practical three-tower, four-span transmission system is established, and nonlinear dynamic analyses under different wind attack angles are first conducted to identify the weak segments. Pushover analysis combined with the equal-energy method is then used to determine the initial and target ductility coefficients, while incremental dynamic analysis (IDA) provides the collapse ductility coefficients of the weak segments. Their stiffness is subsequently adjusted according to the deviation between the collapse and target ductility coefficients, and the required stiffness is implemented by modifying member cross-sectional dimensions. The optimized intersegment stiffness agrees with the target stiffness within 0.01%. Vulnerability analyses further show that the critical collapse wind speed increases by 18.4%, 15.6%, 9.7%, and 9.1% at wind attack angles of 0°, 30°, 45°, and 90°, respectively. These results demonstrate the effectiveness of the proposed framework in improving the collapse resistance of the investigated tower–line system under the considered wind conditions; its broader applicability requires further validation.