Determining Bridge Clearance?

mudpuppy · Jan 23, 2019

Asking for Mrs. mudpuppy.... how do you determine the minimum clearance of a bridge above a navigable waterway? She says some of the waterways have a published height by the Coast Guard, but the one she's working with does not.

As an EE I'm totally lost here.

kevo_55 · Jan 24, 2019

The AASHTO Bridge design code should have it in there.

I'm a buildings guy though.

bwin12 · Jan 24, 2019

I was involved in Design Build project in Alaska once. I wish I could find the direct quote from the Forest Service but it went something along the line of "This river is known to have iceberg travel due to calving from the nearby upstream glacier. The nearby downstream Railroad Bridge has but affected by glancing blows periodically, so please design this bridge slightly higher than the RR Bridge. We opine that height will be sufficient.".

My answer, based on experience- guess, then go a little higher for safety.

mudpuppy · Jan 25, 2019

bwin12 said:
I was involved in Design Build project in Alaska once. I wish I could find the direct quote from the Forest Service but it went something along the line of "This river is known to have iceberg travel due to calving from the nearby upstream glacier. The nearby downstream Railroad Bridge has but affected by glancing blows periodically, so please design this bridge slightly higher than the RR Bridge. We opine that height will be sufficient.".

My answer, based on experience- guess, then go a little higher for safety.

My wife was finally able to get a hold of someone from the Corps of Engineers yesterday and this was basically their answer. Except they don't know how high the next bridge over is. Apparently the Coast Guard is the ultimate authority on this (for navigable waterways), but they're furloughed.

P-E · Jan 25, 2019

This method works

nope not enough

youngmotivatedengineer · Jun 29, 2019

mudpuppy said:
Asking for Mrs. mudpuppy.... how do you determine the minimum clearance of a bridge above a navigable waterway? She says some of the waterways have a published height by the Coast Guard, but the one she's working with does not.

As an EE I'm totally lost here.

Whoever governs the waterway should be able to provide the answer. They should know what the other bridge heights are and what suze water crafts usually travel that water path. Ideally, you would want to at least match or be higher than the next bridge up and down stream from where you are.