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AASHTO Inventory and Operating Rating values

AASHTO Inventory and Operating Rating values

(OP)
What are these two number values expected to be normal?

RE: AASHTO Inventory and Operating Rating values

If you are using the Standard Specs, Inventory Rating is based on 0.55Fy; it's considered "normal" traffic. Operating is an "occasional" overload and the rating is based on 0.75Fy.

Under the LRFD spec, same principle. The IR is based on a live load factor of 1.75 and the OR is based on a factor of 1.35.

RE: AASHTO Inventory and Operating Rating values

(OP)
Bridgebuster, So an inventory rating of 1.35 and operating rating of 1.75 is a well designed bridge?

RE: AASHTO Inventory and Operating Rating values

No, for a load rating with no bridge posting requirements the inventory and operating ratings should be greater than 1.0 with a structural analyzed using a live load factor of either 1.75 or 1.35

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/

RE: AASHTO Inventory and Operating Rating values

edward1 - Under LRFD 1.35 and 1.75 are Load Factors applied to the live load as Teh pointed out.

RE: AASHTO Inventory and Operating Rating values

(OP)
So if the inventory rating is 1.0 the bridge is ok for design?

RE: AASHTO Inventory and Operating Rating values

A Design Inventory Rating of 1.0 is usually required for new bridges. If it's greater than or equal to 1.0 that should be OK unless the owner has specific requirements. I don't know if I would want it to be exactly 1.0. If you want to be super cool I supposed you could design for a future condition factor of 0.85 and shoot for 1.18 which would be 1/0.85. This is for LRFD, not LFD.

It's also important to remember that a Design Load Rating is not the same thing as a Legal Load Rating. The design rating is only for the HL93 loading, while the legal load rating is done for specific trucks specified in the Manual of Bridge Evaluation.

RE: AASHTO Inventory and Operating Rating values

edward1: You might want to consider taking the Load rating of Superstructures course offered by National Highway Institute (NHI). It deals with all topics related to load rating such as inventory, operating ratings for HL93; legal and permit load ratings; specialized hauling vehicles; load posting etc.

RE: AASHTO Inventory and Operating Rating values

(OP)
OSUCivilEng, Congrats that is the right answer. I conferred with a P.E. that works for Michael Baker and he gave me that answer.

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