Private bridge open to the public
Private bridge open to the public
(OP)
So, I've got a little bit of a conundrum. We're designing a private bridge for heavy construction vehicles to access a wind farm construction site. The "bridge" is going to be short span precast concrete box culverts of 10 feet span or less. The loads we're designing for are H-20 loads, heavy articulated truck loads, and a 488 ton crane. Thus, the bridge will easily meet the load rating requirements of a public roadway. We're also designing them to the latest AASHTO LRFD 2012 specification. Now, the bridge is a private bridge but will be open to the public and is expected to be used by ATVs, pedestrians, light vehicles, and probably additional H20 construction equipment down the road.
Now, my question is the contractor and precast manufacturer want to save some cost by not designing it to the full song and dance of AASHTO. For example AASHTO prescribes 2" exterior cover on precast culverts, however they want to use 1.5" as they're not concerned about maintaining a 75 year bridge life and the structure will not be exposed to deicing salts. What are your thoughts on items like this? I can find no guidance from the local DOT website on issues such as this and I know this is going to be above the head of the local code official. As we're not changing the load rating would you say it's acceptable to use AASHTO modified as they request?
And, yes, the PE in charge has requested that unless we can find a good argument otherwise to just design for the full AASHTO. However, if that's the case I really need a good reason to tell the contractor why we had to use the full AASHTO specification beyond just "my boss told me so and it covers our butt".
Now, my question is the contractor and precast manufacturer want to save some cost by not designing it to the full song and dance of AASHTO. For example AASHTO prescribes 2" exterior cover on precast culverts, however they want to use 1.5" as they're not concerned about maintaining a 75 year bridge life and the structure will not be exposed to deicing salts. What are your thoughts on items like this? I can find no guidance from the local DOT website on issues such as this and I know this is going to be above the head of the local code official. As we're not changing the load rating would you say it's acceptable to use AASHTO modified as they request?
And, yes, the PE in charge has requested that unless we can find a good argument otherwise to just design for the full AASHTO. However, if that's the case I really need a good reason to tell the contractor why we had to use the full AASHTO specification beyond just "my boss told me so and it covers our butt".
Maine EIT, Civil/Structural.






RE: Private bridge open to the public
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RE: Private bridge open to the public
I do tend to agree, though. Doubly so as this is a private, remote area and I would be shocked if people were inspecting this structure regularly 50 years from now.
Maine EIT, Civil/Structural.
RE: Private bridge open to the public
RE: Private bridge open to the public
RE: Private bridge open to the public
RE: Private bridge open to the public
In these sorts of cases how do you guys usually determine what the applicable standard is? Do you just go strictest standard or play it on case-by-case basis.
Maine EIT, Civil/Structural.
RE: Private bridge open to the public
I used concrete cover as an example. Some other things they wanted to push was use of ACI 318 vs AASHTO (not gonna happen), not using impact factors (maybe), ignoring the cutoff for box culvert design rules in AASHTO below 2 feet soil cover (not happening), and designing for reduced service life (probably not), etc. Most of them we can't do for obvious reasons but concrete cover was the one I was most on the fence about.
Maine EIT, Civil/Structural.
RE: Private bridge open to the public
From an Owner's perspective, a case-by-case-basis. Depends on the size (value) of the project, its complexity, magnitude of the savings, effects on schedule, long-term consequences of the change (sometime for the better), and other non-technical factors. In my experiences, never rule out a proposed change (well, almost never) but take a careful look at all aspects to see if the savings (to the Owner) are worth the change - many times they are.
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Private bridge open to the public
RE: Private bridge open to the public
Maine EIT, Civil/Structural.
RE: Private bridge open to the public