Experimental investigation of post-flutter properties of a suspension bridge with a π-shaped deck section

Paralleled experimental tests of a full-bridge model and a sectional model are conducted to investigate nonlinear post-flutter properties of a suspension bridge, including structural damping, motion amplitudes, phase angle, motion frequency and coupling effects. Structural damping is found to increase nonlinearly and remarkably as the motion amplitude increases. Modal shapes are found to evolve as the motion amplitudes increase. Nonlinear structural damping properties differ significantly between the two models. Flutter instability of both models end up with limit cycle oscillations (LCOs), which increase progressively with the oncoming wind speed. LCO amplitudes of the sectional model are significantly smaller than those of the aeroelastic model. LCOs of the full-bridge model are coupled motions among 3 major structural modes, one torsional (symmetric) and two vertical (symmetric and asymmetric). Comparisons between the two models indicate that the underlying mechanism is single DOF torsional flutter. Phase angles between the vertical and torsional motions are found to be non-zero and differ significantly between the two models. Further, the amount of time evolving from a flutter onset to a LCO state decreases obviously as the wind speed increases, and the evolution time differs obviously between the aeroelastic and section models.