Air turnover system of large bridge steel structural unit and air turnover method

A space turn-over method for the large steel member of bridge includes such steps as putting said large steel member on two L-shaped hanging tools, using a dual-hook gantry crane to lift it up to a certain height, and slowly lifting one hanging hood while slowly lowering another to turn over the large steel member by 90 deg.C. It features low cost and high efficiency. Its system is also disclosed.