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Bridge Rail Gap Size

State NE
Description Text

When we cross an expansion joint in a bridge and leave a gap in the bridge rail, what is the largest gap we can leave without considering it a snag point?


The rails are flush with each other, flat faced, and continue for several feet.


Should we allow 3" or a little more?


What width of gap is still acceptable?


Has there been testing to prove a snag or not?

  • Bridge Rails
Other Keywords none
Date June 3, 2009
Attachment bridge rail gap.jpg


Many years ago, MwRSF conducted AASHTO PL-1 and PL-2 full-scale crash testing on NDOR's open concrete bridge railing. For this testing program, impacts were performed both at interior sections as well as upstream of an expansion gap. The expansion gap was 4.5" and utilized chamfered edges. The impact angles ranged from 15 to 20 degrees. Although vehicle snag occurred at the downstream exposed edges, it was not sufficient to cause a failure of the tests.


Under the current testing criteria, pickup truck testing is performed at 25 degrees. For the future MASH testing, the impact angle for both the small cars and pickup trucks is 25 degrees. As such, a slight increase in vehicle snag could occur due to the increase in impact angle. Therefore, I would be more inclined to keep the gap width to a maximum of 4". In addition, it is recommended that the edges of the railing at the gap locations be chamfered in order to reduce the propensity for vehicle snag.

Date June 8, 2009

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