Improvement to Calculation Method of Flood Force on T-Girder Considering Entrapped Air in Chambers

Abstract

Entrapped air in the chambers of a T-girder bridge generates a considerably large vertical force which is harmful to the safety of the bridge superstructure. The contribution of the entrapped air is not considered when calculating flood force in the related specifications, and also it has not been taken into account by researchers. Two-dimensional, scaled-down models at a 1:40 scale are selected as the research object. Analytical and numerical methods are employed to investigate the contribution of entrapped air in T-girder chambers to flood forces. Results show that the entrapped air in the rear chambers could escape easier than that in the front chambers and the compressibility of entrapped air has a small influence on drag force and vertical force (generated by dynamic pressure) coefficients, but it reduces the buoyancy of the T-girder. Considering the entrapped air compressibility and entrapped air escape, the calculation method of the buoyancy of entrapped air is proposed to improve the precision of the existing flood force calculation method.