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Parapet Heights at Thrie Beam Transitions

State IA
Description Text

We have a project showing the following detail (77-1631-087_BridgeEnd.pdf), where it is a bridge deck overlay and they are upgrading the bridge ends from Type C (page 3 of BA-202) to a more updated Type B (page 2 of BA-202). New bridge ends are
normally specified at 34” (per BA-107) but the project in question is showing 32” to match the height of the existing bridge rail.

On past projects where we are only replacing guardrail, we’ve allowed the bridge side of our BTS (BA-201) to sit at 30” or 31” to match the old transition height as reconstructing new bridge ends was beyond the scope of the project. However, since this project is updating the bridge ends, in which order are the alternatives from most preferable to least?

a)      Stay at 32” to the top of the bridge end and install 32” BTS. This leaves only 2
3/8” from center of top bolt hole to top of rail and puts the top of the BTS at
the top of rail.

b)      Stay at 32” to the top of the bridge but lower the bolt hole pattern by 1” or 2” to
gain clearance and still fall within adjusted tolerances for the BTS (30” or

c)      Taper the new bridge end from 32” existing up to 34” by the first bolt holes (three
vertical) and install BTS at normal height. The 2” transition would have to
take place over 20.5”.

d)      Another option?

Thanks for your assistance on this and future applicable instances.

  • Approach Guardrail Transitions
Other Keywords concrete end parapet
Date May 8, 2015
Attachment eba202.pdf
Attachment eba201.pdf
Attachment eba107.pdf
Attachment 77-1631-087_BridgeEnd.pdf


We had a similar discussion to this  just last week at our annual Midwest States Pooled Fund meeting.  At that time, multiple State DOTs had said they have transitioned the ends of the bridge parapet up a few inches to provide a few more inches of cover to the attachment bolts/hardware of the thrie beam transition.  This is very similar to your Option C, and I recommend this method for use.  You vertical height transition of 1/10 seems well within reasonable bounds to prevent snag and vehicle instability during reverse direction impacts.

Date May 8, 2015

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