Statics: Horizontal Movements of Structures Induced by Vertical Loads

Rail bridges:

Horizontal movements of some railway bridges have been observed as trains passed over them. Because of the increasing speed of trains a number of bridges have had to be re-assessed for safety. As there are often two or more rail tracks on a bridge, the loading from any one train is effectively applied in an asymmetrical manner on the structure generating lateral horizontal movements of the bridge. There will also be some horizontal forces generated by lateral movement of the railway vehicles, even along straight tracks. With the increasing speed of trains, the vertical loading frequency will increase and this may be a problem if resonance occurs, i.e. if one of the train load frequencies in the vertical direction is close to one of the lateral natural frequencies of the bridge. It is therefore necessary to check horizontal as well as vertical natural frequencies of bridges to ensure that both are above the likely loading frequencies associated with trains running at higher speeds.