Designing Bridge Piers for Impact, Flood
Designing Bridge Piers for Impact, Flood
(OP)
A current project involves a footbridge with piers ~15' out of the ground to the bridge itself. It is located so that it won't flood in case of a 100 yr flood.
Some considerations:
-Designing for impact of floating debree, tree, waves, differnet water levels, etc.
-General weathering requirements for the piers.
I haven't found a good resource for minimum impact forces. General weathering requirements would seem to be using epoxy coated rebar (not sure if this is necessary), using a 3" cover, and using a low slump concrete for longer service life. Is there any code specifically addressing this? Thanks in advance for any advice / references.
Some considerations:
-Designing for impact of floating debree, tree, waves, differnet water levels, etc.
-General weathering requirements for the piers.
I haven't found a good resource for minimum impact forces. General weathering requirements would seem to be using epoxy coated rebar (not sure if this is necessary), using a 3" cover, and using a low slump concrete for longer service life. Is there any code specifically addressing this? Thanks in advance for any advice / references.






RE: Designing Bridge Piers for Impact, Flood
Your geotech should give you values for the environment to determine final concrete cover. All those things you mentioned need to be assessed by the bridge engineer.
AASHTO Stand Spec's would work as well as any.
RE: Designing Bridge Piers for Impact, Flood
I was just involved in the design of pedestrian bridges in a nature preserve. Most of the bridges were located in wetlands/floodplain areas subject to frequent flooding. I found that it really depends on what causes the flood. For example, if the flood is caused by the sudden release of water say from a water tower or dam collapsing, that is much different than a low lying area flooding due to rising levels of precipitation. On this particular site, the flood waters were almost stagnant, or moved very slowly according to the park officials. Therefore, I neglected impact of floating objects. However, I did contact the Army Corps of Engineers and obtained velocity data for the river and designed the bridge accordingly. Another feature I used was a galvanized grating for the deck to reduce uplift forces from the flood waters. Good luck.
RE: Designing Bridge Piers for Impact, Flood
RE: Designing Bridge Piers for Impact, Flood
As to practice - I can offer my experiences. We apply stream forces per AASHTO and where applicable modify per the hydraulic engineer's recommendations.
I have designed many bridges over sustaining streams and dry creeks that swell considerably during flash conditions. Some in heavily wooded areas and others in plains. I have seen debris stacked against bridge piers on major rivers and have see drift wood so thick that people can walk over it as it sits in the water.
I have found that rarely do such conditions control as other lateral forces were often greater. However, I do modify the area of the pier assuming it is locked in drift when such piers are located near the banks.
I have never used epoxy coated reinforcing in piers unless specifically requested by the client. Some use epoxy in the whole structure while others do not. I am not generally in favor of substructure steel being epoxy coated due to the conditions of the coating following delivery, siiting on the job site and then being slung around by rodbenders. Once the coating is compromised it really defeats the purpose. And getting a contractor to fix that coating is like getting a straight answer from a lawyer.
Regards,

Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
RE: Designing Bridge Piers for Impact, Flood