SONG Yubing, TI Zilong, YANG Ling, LI Yongle, LI Zeteng
JOURNAL OF VIBRATION AND SHOCK. 2024, 43(7): 1-9.
During the construction of twin decks, the long-span asymmetrical twin parallel decks represent a unique design, where both the highway and railway are arranged side by side at the same elevation. Due to the disparate dynamic characteristics of the highway bridge and the railway bridge, the considerable variation in wake characteristics of the decks, as well as the pronounced and consequential aerodynamic interference between the asymmetrical twin decks, the vortex-induced vibration (VIV) characteristics of the asymmetric twin decks become considerably more intricate. To comprehensively investigate the impact of interference effects on the VIV behavior of decks, a series of wind tunnel tests and fluid-structure interaction numerical simulations were conducted on twin decks. These experiments and simulations were conducted in the context of a long-span asymmetrical twin separated parallel deck configuration, where the highway deck was designed as a Π-type superimposed deck and the railway deck was a streamlined box deck. The research findings indicate the following: (1) The Π-type highway deck exhibited significant vertical bending and torsional vibrations when exposed to the windward side, showing typical VIV "lock-in" characteristics between the wind speed range and the structural vibration frequencies. However, these vibrations diminished when the deck was on the leeward side. (2) The streamlined railway deck showed no significant vibrations when positioned on the windward side, but substantial vibrations were observed on the leeward side, with amplitudes rapidly rising and falling, without a distinct "lock-in" range. (3) The numerical flow field indicates that the scale and distribution of vortical structures near the deck vary significantly when the highway is located at different positions (windward and leeward sides). The presence of large-scale vortices in the cavity below the bridge deck and the periodic variation of vortical structures are the main reasons for vortex-induced vibration on the windward side. On the leeward side, influenced by the disturbance effect, the scale of vortices in the cavity below the bridge deck decreases, the oscillation frequency of lift changes, and the phenomenon of vortex-induced vibration lock-in disappears. (4) Flow fields and pressure distributions near the railway revealed stable flow patterns when positioned on the windward side, with self-excited lift forces approximating steady forces. However, when positioned on the leeward side, the railway surface experienced a larger negative pressure area due to the interference of the highway wake, leading to significant vibrations caused by the pulsation of the highway wake and resulting in oscillations of the railway's aerodynamic lift. This study systematically investigated the aerodynamic interference effects between asymmetrical twin parallel main girders and their impact on VIV performance. The underlying VIV and aerodynamic interference mechanisms were revealed, providing valuable insights for the engineering design of similar bridges.