What is the difference between Surge load & Drag Load ?

• Surge Load

Surge loads are lateral loads generated due to sudden starting and stopping of the movement of  Trolley or crab. This load acts in the lateral direction so this is a lateral load for Gantry girder. Surge load is resisted by the compression flange of the gantry girder alone. 

• Drag Load   

Drag loads are longitudinal loads acts longitudinal to the gantry girder. These loads is caused by sudden starting and stopping of the crane bridge while moving on the rail.

Surge load and drag load can not act simultaneously. The crab or trolley moves either in lateral or longitudinal direction.