How do I translate ESAL to H-loading?

[perpetualjon]

I have a pavement manufacturer that has performed an accelerated wear test on a product we'd like to use in Los Angeles County but our Fire Department is requiring us to use only pavement products that are capable of H20 loading. The problem is that the engineering documentation from the pavement manufacturer used ESAL units in their testing (as I believe they should for pavement wear testing). Still, I have to come up with some sort of way to demonstrate how I can translate ESAL units to either show matching or exceeding H20 loading requirements I'm working under. Is this even possible? From what I understand, H-loading is a specific imaginary vehicle of a certain weight and dimension but ESAL units are based on a quantity of axles of a certain weight over a period of time. Am I in an impossible situation with this?

Any help would be great and I'm so glad I found this forum!!

 

[Ron]

No. You can correlate the two.

H20 is a standard bridge loading. It has an 8000lb front axle load and either a single 24000lb rear axle load or two, 16000lb rear axles spaced 4 feet apart.

Using the AASHTO ESAL load tables, you can back into the equivalent single axle loads for one standard H20 loading.

Roughly, for the tandem axle loading, one standard H20 loading is equivalent to 0.879 ESAL, while the single axle loading condition for the standard H20 is equivalent to 3.79 ESAL. As you can see, any axle loading greater than 18000lb runs the ESAL up quickly.

 

[perpetualjon]

Hmm, from what I found, it looks like the maximum axle loading of the H20 spec is 32,000 lbs. Here's where I got that from:

http://www.tfhrc.gov/structur/pubs/04098/11.htm

My problem is that, after further reading, the engineering white papers from the pavement we're wanting to use had 18,000 lbs per axles (18 kip ESALs). If you can show me some documentation that says I can divide that load into TWO 16,000 axle loads, I'd be in great shape!

Thx for the help so far!!

--Jon Roberts
Land Tech Engineering
Southern California

 

[Ron]

Look at the AASHTO Pavement Design Manual. It will give you everything you're looking for. I'm pleased to help, but you need to research and evaluate these things for yourself...it's how you'll learn.

Good luck.

Ron

 

[perpetualjon]

Well, from what I've researched, your statement of what H20 loading is seems incorrect. It is NOT a single 24,000 lb rear axle or two 16,000 lb axles but just a SINGLE 32,000 lb single axle load. There's even an HS20 spec that adds the second rear axle --but BOTH of them are still at 32,000 lbs -and this I believe is straight from the AASHTO Pavement Design Manual but I have no way of checking against the actual AASHTO manual since I don't have a copy nor can I afford a subscription. Now do you think that you may have mixed up the loading numbers between axle loads and wheel loads to get the 16,000 lb figure?

--Jon Roberts
Land Tech Engineering
Southern California

 

[Ron]

Jon....you are correct in that if you research H20 loadings, the figure that you find will show an 8000 lb. front axle and a single 32000 lb. rear axle load. This is based on the 1944 designation of standard loading for bridges. You will also see an asterisk that states that a single 24000 lb rear axle or two 16000 lb tandem loads may be used, selecting the one with the greater stress.

Most states limit single axle loads to 24000 lb and 32000 to 34000 lb for tandems (two axles at 16000 to 17000 lb each). Two 32000 lb tandems would greatly exceed allowable state highway loadings.

The H20 designation comes from the AASHTO Standard Specifications for Highway Bridges, not the AASHTO Design of Pavement Structures Manual. The Pavement Structures Manual bases all designs on an Equivalent Single Axle Load (ESAL) with the "standard" axle load being 18000 lb. All other loads on the axles are compared to that standard and each is rated based in its ratio of load, either higher or lower.

You are correct in your original post that you are somewhat comparing apples and oranges; however, depending on how they presented their data, you might still be able to correlate. The difference is that you want to know if the device can withstand 1 loading of the H20 designation and they are telling you how many times the device will withstand an 18k standard load. I see your dilemma...you might want to see if you can get more info from them. You will have to back into the correlation from material property and fatigue data.

 

[perpetualjon]

Ah yes, I had a feeling I was just making a bad comparison. Thanks so much Ron for bearing with me on this! The more I think about it, the more it looks to me like I'm using the wrong documentation (accelerated wear testing) to prove my material selection. I've already asked the manufacturer to simply provide me with a general pavement section that is designed for a 32,000 lb single axle and call it good.

Thanks again everyone. I've learned a lot through dealing with this!

--Jon Roberts
Land Tech Engineering
Southern California

 

[Ron]

Jon...it's not that simple! You can design a pavement for a 32k single axle load, but how many repetitions of that load? Pavements are designed for fatigue.

Almost any pavement section will withstand one pass of a 32k axle load, but it takes a properly designed section to accommodate one or two million repetitions of same.

Ron

 

[perpetualjon]

Actually for what we're designing, it IS that simple. This is just a private driveway for a single-family residence. The Los Angeles County Fire Department is requiring the driveway meet H20 loading so that it will be able to handle their fire trucks --but the frequency may be only once for that matter! Hell, a dirt road can handle a large 80,000 lb truck for a couple of trips!! We're just dealing with the fact that someone told them to look for "H20" somewhere or its no good so now, even if the plans indicate even better performace, if it doesn't mention H20 loading specs, its a no-go.

--Jon Roberts
Land Tech Engineering
Southern California

 

[Ron]

Jon...thanks for the clarification. I've had to design driveways for both the loading and a 60-foot turn radius to accommodate fire equipment. Really runs the cost of a simple driveway up!

Ron