Unsteady aerodynamic forces of eccentric T-type structures under forced vibration

In wind-resistant analysis of eccentric structures, the quasi-steady assumption may lead to an underestimation of wind-induced failure risks for structures such as tower cranes and transmission angle steel towers. In this study, force-balance tests were conducted on rigid models to obtain the three-component force coefficients of T-shaped structures under three different eccentricity ratios. To evaluate unsteady effects, closed-form solutions for the aerodynamic damping and aerodynamic stiffness of an eccentric T-shaped structure under forced vibration were derived. A large eddy simulation (LES) model of the eccentric T-shaped structure was validated using experimental data and the index of resolution quality for LES(LES_IQ). The validated model was subsequently employed to assess the aerodynamic characteristics—including the three-component force coefficients, wind pressure distribution, and wind velocity distribution—of T-shaped structures with varying eccentricity ratios under forced vibration conditions. The results indicate that the influence of eccentricity on the three-component force coefficients is more pronounced under low wind speed conditions, with the torque coefficient being the most significantly affected. Increasing the eccentricity amplifies the wind pressure on the leeward side of the vertical bar at a height of 3/4H (where H is the height of the vertical bar) and induces a pressure difference across the two ends of the windward cross-arm. Furthermore, it increases the velocity gradient, elevates the generation frequency of small-scale vortices, and reduces both the aerodynamic stiffness ratio and the aerodynamic damping ratio.