This article addresses a time-domain method for the postflutter analysis of long-span suspension bridges. The energy input properties of indicial functions (IFs) were first analyzed, and based on the findings, the concept of multistage IFs was brought forward to describe the nonlinear aeroelastic properties of bridge decks. The application of the multistage IFs to the nonlinear postflutter analysis entails resolution of two basic issues: smooth switching between groups of IFs and the integration of the mean wind loads. To avoid nonphysical transient responses that result from the abrupt involvement of a group of IFs, a strategy was developed that shows that groups of IFs participate in the aeroelasticity simulation simultaneously and independently; however, in this strategy, only two appropriate groups of IFs were engaged in denoting the aeroelasticity. To avoid double counting of the mean wind loads and to reflect the nonlinear properties of the loads correctly, separation of the pseudosteady effects from the aerodynamic loads denoted by IFs is suggested. The numerical example presented in this paper indicates that multistage IFs can be applied successfully to describe amplitude-dependent nonlinear aeroelastic effects and to conduct a time-domain postflutter analysis.

Buffeting-induced oscillations of hangers at a suspension bridge have been addressed in this work. The buffeting is obtained by a dynamic finite-element analysis procedure in the time domain, with simulated turbulent wind fields and experimentally obtained load parameters. Wind loadings inherent to the hangers are neglected intentionally to exclude potential interference. Dynamic properties of hangers are simulated by discretizing them into a number of elements. The numerical results show that a number of long hangers can experience large-amplitude oscillations due to the main structure’s buffeting at a moderate wind speed. Motions of the hangers are mainly contributed by their first-order modal shapes. The hangers oscillate in both directions in the horizontal plane, with motions in the longitudinal direction being more violent than in the lateral direction. Moreover, it is found that the dominant frequency of a single hanger in one direction differs slightly from that in the other, thereby causing an ever-changing phase angle between the two motions. Fourier transforms of the time series indicate that excitations resulting in the resonances are from the main cables. The functional motion component at cable-hanger intersections can be as small as a couple of millimeters, which can result in hangers’ motions as large as 300 mm. Replacement of steel wire hangers with carbon fiber-reinforced polymer (CFRP) ones can restrain effectively the resonance. However, replacements over an insufficient range of hangers may result in transferring of the resonance to neighboring ones, and a comprehensive mitigation necessitates replacements over quite a wide range along the bridge deck.

This article presents the results of an investigation of the wind-induced resonance of hangers on a long-span suspension bridge. The data from field observations, numerical simulations, and wind tunnel experiments presented in this article show that the hangers experience buffeting-induced resonance oscillations and that the source of the excitation is the buffeting of the main cables to which the hangers are attached. Because of the dense natural frequencies of the main cables and the broad-spectrum structural buffeting that takes place, it appears that these oscillations occur as energy is transferred from the main cables to the hangers. Hence, it is the main cables rather than the hangers that trap energy from the oncoming turbulent wind field. The numerical results presented indicate that the resonance of the hangers could be sensitive to positions along the bridge deck, wind speeds, and damping ratios. This article also includes the results of simplified wind tunnel experiments that verified...

The vortex-induced vibration (VIV) properties of a π-shaped bridge girder are addressed in this study through wind tunnel tests. Attention is paid to the influence of torsional-bending frequency ratio on the VIV, while the mass-damping property (Scruton number) of the vertical motion remains unchanged. The torsional-bending frequency ratios of the model covered in this study were 0.872, 0.971, 0.988, 1.035, 1.085, and 1.245. The results show that, when the ratio is close to 1.0, the girder exhibits coupled vibration in the vertical and torsional directions. However, the coupling significantly reduces the vortex-induced vertical amplitude, which had been supposed to remain unchanged, owing to a fixed Scruton number. Further, the results indicate that the torsional motion results not only in the transference of a small amount of energy from vertical to torsional vibration, but also in a substantial reduction of the total amount of mechanical energy trapped by the system from the wind field. The energy reduction effects should be understood as a result of the altered flow pattern around the section, which is caused by coupling of the model's degrees of freedom.