VORTEX-INDUCED VIBRATION AND ITS CONTROL FOR TWIN BOX GIRDER BRIDGES WITH VARIOUS SLOT WIDTHS

Although twin box girders with various slot ratios could improve the aerodynamic instability of long-span bridges, their vortex-induced vibration (VIV) performances are not explicit. The relationship of VIV performance of twin box girder with six resperentive slot ratios and slot ratio was investigated. The control effectiveness of four countermeasures including increasing structural damping ratio, installing wind barriers, installing guide vanes, and installing the grid plates were separately compared and then comprehensively evaluated. The results show that the VIV performance of a closed box girder is superior to those of twin box girders with various slot ratios. The vertical VIV amplitudes firstly increase and then decrease with the increasing of slot ratio, and torsional amplitudes are sensitive to the change of slot ratio, in which the 60% and 80% slot ratio has the largest vertical and torsional amplitude, respectively. As for the twin box girder with 60% and 20% slot ratios, increasing damping ratio and installing grid plates with small ventilation ratios could effectively decrease the verical VIV responses, while increasing damping ratio and installing the vertical and horizontal wind barriers are helpful to improve the torsional VIV performance. However, the control effect of a twin box girder with internalposition or extraposition guide vanes are depended on the slot ratio. Four countermeasures could be satisfied with the displacement requirement of torsional VIV of twin box girders, but only the grid plates with 0% ventilation ratio can be satisfied with the displacement requirement of vertical VIV according to Sperling's indicator and Wind-Resistance Specification of China.