Which is more conservative? IBC or AASHTO?

[bquery]

I know this is a pretty broad question, but as I deal mostly in transportation related projects, we typically design per AASHTO LRFD. For a municipal project, I would like to still design that way, but was unsure if there is a quick definitive answer as to if an AASHTO LRFD design would be equal to or more conservative than the IBC?

Any thoughts?

 

[kylesito]

I'm not sure what the conservative-ness of either has to do with it. Both are acceptable codes. If it's a bridge/highway project...municipal, federal, private, or otherwise...design per the AASHTO requirements. If it is building or occupancy related, design per the IBC which is going to point you to ACI, AISC, NDS, etc.

PE, SE
Eastern United States

"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi

 

[JedClampett]

It is kind of an apple and orange comparison. For instance, building live loads are notoriously conservative. It's unlikely an office will see 50 psf or a store is going to see 75 psf (unless they're sellig anvils). So load factors are reasonable. But truck loads are dead on. A bridge is going to see a lot of 80 ton trucks in its lifetime. So the load factors are higher.
Codes are written to reduce risk to an acceptable limit. This is decided by the committees that write the code. How they get there is neither conservative or unconservative.

 

[bquery]

My apologies, I should have clarified. This is mainly for retaining walls designed with no live load surcharge from traffic. The project I am working on encompasses several different reviewing entities (DOT, RR and county code enforcement per building code). I am trying to get one design to work for all, but I am sure the county will require justification that AASHTO is at least as good as the building code requirement.

 

[grantstructure]

Just tell them it is.

Look at the load factors in IBC as compared to AASHTO. Unless AASHTO has a lower factor on its loading, it can't yield a materially different result in the concrete design. I think IBC is still 1.5 for sliding and overturning, 1.6 for ultimate load from horizontal soil loads. Check me on that.