Posting a load sign on an existing bridge

[SKJ25POL]

Hi,
The is an existing bridge (steel girder and concrete deck), 87ft span and 14 ft wide.
There is no load-rating on the drawings for this bridge, however I am very sure that was designed for HS-20 truck.

1-When I contacted the consulting that designed the bridge, they said at that time (1978 to 1982) there was no requirement to state the bridge load rating on the drawings or specs !!! Does anybody it is true?

2- Will I be correct to tell the owner to put a sign of 72000 lbs. on the bridge ?
An Hs -20 : 8000+32000+32000 = 72000 lbs.
Is that a correct sign and load rating for the bridge?

Thank you for your comment and direction. I am not a bridge engineer and my practice is regular structural engineering. I apologize to all bridge engineers and don't mean that I am stepping on their toe. This request just came to me to assist the bridge owner.

Sincerely,
SKJ

 

[bridgebuster]

and this

 

[SKJ25POL]

HotRod10 (Structural) and bridgebuster (Civil) thank you very much for your effort to help me. I am very grateful.
I finally got a little bit information and want to may be ask this question for the truck in below pic with total growth weight of 44,300 lbs, is the existing bridge (designed for HS-20)okay?
I mean is the below truck below or within the designed load for the bridge?

Thank you for your continuing help.
bridgebuster (Civil), thank you for the attachments. They were so informative.
HotRod10 (Structural), thank you for your great comment. I couldn't find legal load truck for KY. Seems this state is working on it. I believe HS-20 can be considered legal load truck !!!

 

[TehMightyEngineer]

I couldn't find legal load truck for KY.

You didn't look very hard then; found this in about 30 seconds:

https://drive.ky.gov/motor-carriers/Pages/OWOD-Legal-Dimensions.aspx

Here's their bridge design page:

https://transportation.ky.gov/StructuralDesign/Pages/default.aspx

HS-20 is a design load that should exceed or meet the worst case of legal loads. For the weight/truck you indicated it's difficult to tell unless you know how much load is on that tandem rear axle.

Based on the questions you are asking I feel you shouldn't be undertaking this design and should consult with a qualified bridge engineer. I'd also reach out to KYDOT as they likely can assist you in the legal requirements you must undertake to load rate and post the bridge.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL)
American Concrete Industries

https://americanconcrete.com/

 

[BridgeSmith]

I can't say for sure whether that truck would rate as well as the HS-20. Technically, it would depend on the weight distribution and the length of the bridge. What I can tell you is that it appears very similar to our Type 3 legal load rating truck, which typically rates over 50% higher than the HS-20 for our bridges. I can't see that changing much except for maybe a bridge with very short spans (less than 30ft).

I can also tell you that somewhere around half of the public highway bridges in service in the US were designed for HS-20 live load. Those hundreds of thousands of bridges are used by millions of trucks of every legal configuration on a daily basis. There are maybe a few with major damage or severe deterioration that may be posted, but the vast majority are not. If the DOTs in all 50 states are not concerned about that, why is the owner of this bridge?

As I said, if the owner wants a load rating, my suggestion is refer them to an engineering firm that does load ratings. They have the expertise and the software to do it efficiently. Unless you plan on doing alot more ratings or start designing highway bridges, you're going to overcharge them or short-change yourself, due to the time it would take you to learn the process and the code requirements, and what it would cost you to buy the software package.

 

[BridgeSmith]

Or, you could take this approach...