An amplitude-dependent nonlinear approach for vortex-induced vibration evaluation of long-span bridges with inhomogeneous cross-sections

In the design of modern long-span bridges, inhomogeneous cross sections are increasingly used to meet various requirements, posing challenges in the investigation of vortex-induced vibration (VIV). This paper introduces a nonlinear approach with a focus on amplitude dependency in VIV for inhomogeneous bridges. It presents an inhomogeneous vortex-induced force model with amplitude-dependent parameters to capture spanwise variations in aerodynamics. These parameters are identified through multiple sectional wind tunnel tests. VIV amplitudes are determined by searching for solutions under the zero-damping condition for VIV. An illustrative bridge with an inhomogeneous fairing design is employed as an engineering application. The approach is rigorously validated with experimental data and applied to assess the prototype VIV behavior of the bridge with different fairing lengths. An optimal fairing length, constituting 40% of the main girder length in the mid-span, is identified to strike a balance between VIV performance and material usage. Discussion for the prediction results provides insights into the effects of fairing length inhomogeneity on VIV. In practice, deploying fairings in the large mode shape sections of the main girder achieves VIV mitigation comparable to a full-span installation.