When checking a support beam over a rail unloading pit for deflection should I be including the impact factor? I can't find anything in AREMA or the IBC.
No. The impact is of such short duration, the forces don't have enough time to follow the load paths before they are removed.
Many years ago, my boss checked a railroad bridge by measuring it's deflection. The bridge had been rated for 5MPH by the worried owner, my boss ran a locomotive over it a 5MPH and recorded the deflection (It said the bridge was good). Just to see the effect, he had them run the locomotive over at 30MPH. The deflection gauge didn't see a thing, the load was gone before it had time to stress all the material.
Michael.
Timing has a lot to do with the outcome of a rain dance.