Experimental investigation on the vortex-induced vibration characteristics of long-span twin continuous steel box girder bridge

Abstract The vortex-induced vibration (VIV) characteristics of a long-span twin continuous steel box girder bridge under varying wind angles of attack (α m ), Scruton numbers (Sc), heights of beam (D = 0.078 m, 0.108 m, and 0.137 m) and layout forms (twin, single, and twin-girder fixed) are comprehensively investigated by sectional model wind tunnel tests with a scale ratio of 1:40. Results indicate that the VIV response of twin-box bridge is highly complex and shows no clear trend with changes in D or α m . Specifically, the D = 0.078 m model achieves the strongest VIV at αₘ = 5° with the downstream girder having significantly higher maximum dimensionless amplitude (Aₘₐₓ/D) than the upstream one; the D = 0.108 m and D = 0.137 m models reach maximum vibration at αₘ = -5°, where the downstream girder has higher amplitude except for a slight upstream advantage in the D=0.108 m model. The phase difference between upstream and downstream bridge is minimal at the onset of the lock-in region, increases toward approximately 180° as wind speed rises, then gradually decreases. Increasing Sc leads to reduced A max /D. Under different layout forms, the largest A max /D occur in the twin, single and twin-girder fixed models at α m = +3°, 0° and –3°, respectively