TORSIONAL DIVERGENCE CHARACTERISTICS OF LONG SPAN BRIDGE IN TURBULENCE

Aerostatic stability of long-span cable supported bridges, especially the torsional divergence which may lead to abrupt bridge failure, are much concerned by bridge engineers during the design stage. The traditional method dealing with such problems usually adopts an iterative static finite element procedure considering the aerostatic loadings due to smooth flow only. However, airflow in nature bound layer is always turbulent and the effects of atmospheric turbulence on bridge torsional divergence need an in-depth investigation. To account for the effects of turbulence on torsional divergence, this paper adopted dynamic finite element method and performed bridge aerostatic stability analysis in time domain. The appropriate wind load expressions were also presented. Then the aerostatic stability of the longest bridge in China was investigated by the approach presented in this paper. Numerical results show that bridge torsional divergence in turbulent flow is much different from that in smooth flow. The primary difference lies in the form of torsional divergence, which manifests as an abrupt twist deformation of the girder in smooth flow, but an unstable stochastic vibration with large peak values in turbulent flow. The second difference lies in the critical divergence airspeed values. Numerical results show that turbulence decreases the critical divergence airspeed obviously, and, turbulence intensity and the spatial correlation of wind fluctuations also play an important role on that.