Wind-Induced Damages to a Three-Span, Continuous, Concrete Arch Bridge under Construction

The second Yibin bridge is a three-span, continuous, reinforced concrete arch bridge with equal span lengths of 160 m. After two reinforced concrete (RC) ribs were constructed through all three spans, during the night of June 7, 1997, the central span and the side span near Zigong city were found to have collapsed into the river on its own. The remaining side span near Yibin city collapsed later on its own, on August 29, 1997. The aeroelastic and aerodynamic investigations, including definition of design wind speed, determination of aeroelastic and aerodynamic wind loading, testing of wind-induced vibrations, evaluation of RC arch rib strength, were conducted to identify the reason for the collapse. It was finally concluded that aerodynamic instability, flutter or galloping, should be excluded in these two accidents, and the direct reason was the ultimate resistance of the cross-sections at the arch bases being less than the total load response under the joint action of structural dead loads and wind-induced loads including aerodynamic wind loading, aeroelastic wind loading and the loading based on P-Δ effects which were not considered in the design of the bridge under construction.