Fatigue loading for steel bridge under light rail.

[yakpol]

I am assessing existing highway steel box-girder bridge for light rail loads. The fatigue loading is not well defined in the project design criteria. It references fatigue design to AASHTO which deals with highway loads. The main dilema is: how many trains shall be on two-track bridge? According to AREMA: two, if to follow AASHTO ideology: only one.
Greatly appreciate sharing experience on this subject!

Yakpol

 

[davidbeach]

I'm not a bridge engineer, but I've seen enough of lightrail operation to say that if it's possible for both tracks to be occupied at the same time, there will be times where both are occupied. Signaling systems could limit use to one track at a time.

 

[wiktor]

You should use two trains as loading. You may follow AASHTO for the fatigue design, as far as detailing and allowable stresses ranges. Keep in mind, that for steel structures allowable stress method is used, and for concrete (any kind) load factor design is considered.
Also, for railway structures indefinite number of load cycles is always used.
With steel box girder typical details to be carefully checked will be the diaphragms and cross braces.

 

[yakpol]

wictor,
Thank your for reply. I am dealing with an existing roadway bridge.Infinite number of cycles for two trains kills every single detail. This criteria is very good for a new bridge, but too conservative for existing.

Yakpol

 

[VoyageofDiscovery]

See if you can find the anticipated usage (people per hour per direction) and design life for the system. Then depending on the fully loaded car capacity you can make a determination.

HTH

VoD