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• A method for estimating full set of amplitude-dependent FDs at the whole wind speed regime from free vibration wind tunnel tests is proposed and validated. • The evolution characteristics of the nonlinear coupled and uncoupled aerodynamic damping with wind speed and vibration amplitude were revealed. • The influence of structural parameters on the post-flutter performance were investigated based on the developed 2D nonlinear flutter analysis method. • The influences of vertical DOF (mode) and 3D effects on nonlinear flutter response were revealed based on the developed 3D nonlinear flutter analysis method. To estimate nonlinear flutter response of long-span bridges, this study established a method for identifying full set of amplitude-dependent flutter derivatives (FDs) from free vibration wind tunnel tests. Taking a typical double-deck truss bridge as a Case study, the amplitude-dependent FDs of the bridge deck at the whole wind speed regime are identified and cross-validated based on large-amplitude free vibration wind tunnel tests of its single degree of freedom (SDOF) torsional and 2DOF vertical-torsional section models. The influential mechanism of vertical DOF on nonlinear flutter was revealed by quantitatively comparing the nonlinear aerodynamic damping of the SDOF and 2DOF systems. The amplitude-dependent FDs are then used to calculate the nonlinear flutter responses of the 2D bridge section and a prototype long-span suspension bridge (1650m) with four main cables based on developed 2D and 3D nonlinear flutter analysis methods. Finally, the influence of structural parameters and 3D effects on nonlinear flutter are quantified and discussed. The results show that the 2DOF system has a lower critical wind speed and higher torsional stable amplitudes compared with the SDOF system since the participation of vertical DOF introduces the negative coupled aerodynamic damping to the system. The aerodynamic nonlinearity becomes stronger and stronger as the wind speed increases and it mainly leads to the significant amplitude dependence of the uncoupled aerodynamic damping, which is the key factor to cause the limit cycle oscillation (LCO)-type of flutter. While the coupled aerodynamic damping appears to be a relatively linear damping with weak amplitude-dependence within the studied wind speed and it mainly plays the role of reducing the stability of the system. The 3D effects of the vibrating bridge deck will reduce the system stability mainly by increasing the negative uncoupled aerodynamic damping. Therefore, the amplitudes of nonlinear flutter will be seriously underestimated if the 3D effects are ignored. [ABSTRACT FROM AUTHOR]

• The upper and lower surfaces of the deck are the vibration-induced parts. • The phase raise of lift leads to unsteady galloping instability. • Barriers' porosity or height change aerostability while their processes differ. • Mechanical damping is not a decisive parameter affecting critical wind speed. The long-span bridges with truss beam are widely recognized as typical wind-sensitive structures, and its wind-induced divergence events may become a very predominant issue. This work evaluates the galloping performance of a typical truss beam with wind barriers, which is detected to be susceptible to the infrequent vertical instability at specific attack angles, as evidenced by experimentation and numerical analysis. Since the truss beam constitutes a complex cross section, this study employs energy analysis to distinguish the crucial parts affected by vibration and discovers that the galloping vibration is mostly caused by the surfaces of the deck. Rather than relying on conventional quasi-steady theory, this study explores the unsteady aerodynamic forces to identify the underlying galloping driving mechanism. Our findings reveal that the instigator of galloping instability is the phase rising of lift with increasing wind speed. Additionally, the nonlinear mechanical damping is not a decisive parameter. Furthermore, we have investigated the impact of an essential ancillary facility, the wind barrier, and discovered that its galloping stability can be enhanced by increasing its porousness and decreasing its height. However, the underlying mechanisms behind this improvement are distinct. [ABSTRACT FROM AUTHOR]