anominal
Structural
- Jul 10, 2009
- 40
I'm designing a partial through girder bridge that carries four tracks. The interior through girders share the live load from two tracks.
AREMA's limiting live load deflection criteria is L/640. It says to compute the deflection using live loading plus impact. Does anyone have an opinion about including rocking effect in this deflection computation?
Here's the scenario: two locomotives that produce force effects equal to the AREMA alternative live load (the notional load with 100k axles) pass each other at midspan of my bridge with full impact AND full RE (rocking towards each other, loading up an interior through girder). This scenario might seem unlikely, but some engineers prefer to design for "the worst case".
Considering that this is a serviceability concern, I don't believe this remote possibility justifies increasing my primary member's section modulus by 20%. Heck, I'm already using 2.5" plates for the flanges...
-Chris
AREMA's limiting live load deflection criteria is L/640. It says to compute the deflection using live loading plus impact. Does anyone have an opinion about including rocking effect in this deflection computation?
Here's the scenario: two locomotives that produce force effects equal to the AREMA alternative live load (the notional load with 100k axles) pass each other at midspan of my bridge with full impact AND full RE (rocking towards each other, loading up an interior through girder). This scenario might seem unlikely, but some engineers prefer to design for "the worst case".
Considering that this is a serviceability concern, I don't believe this remote possibility justifies increasing my primary member's section modulus by 20%. Heck, I'm already using 2.5" plates for the flanges...
-Chris
