Determining ESALs - please help!!! 2

[nutbutter]

OK, I tried to get some help on this question in another thread, but I could not.

I just need some feedback as to whether my estimation of ESALs makes sense or not.

I'm trying to determine the ESALs for an HS20-44 AASHTO loading. This truck has 3 axles, spaced 14' apart, with axle weights of 8k, 32k, and 32k.

I just want a very general ballpark estimate of what the ESALs would be for this vehicle. I'm assuming a SN=3, and a pt=2.5. Standard assumptions.

I initially estimated this truck to be 3 ESALs total. However, when I use the LEFs in my reference (CERM), I'm coming up with a much larger number. I come up with about 21 ESALs. Can anyone help me out here? I haven't done much road design so I can't use my judgment to determine which one makes sense.

Is 21 ESALs too high for a dumptruck? I came up with 158 ESALs for a dumptruck fully loaded with fill (40,000 lb). These seem REALLY high to me.

Anyway, I could really use some help. I'm going to have about 11,000 dumptrucks going over this road. So, it's going to make a HUGE difference whether I use 3 ESALs or 21-158 ESALs for each loaded dumptruck.

Can anyone shed some reason on this? I don't exact numbers here. I'm just looking for a reasonable range of what some others have determined to be a reasonable ESAL value for a dumptruck (HS20-44).

Please help.

Stoddardvilla

 

[bpattengale]

Using the LEF table from the AASHTO Guide for Design of Pavement Structures I'm getting 15.1 ESAL for HS20-44 Loading. That is using your assumed values of SN=3 and pt=2.5

Look at the definition of an ESAL (Equalivalent Single Axle Load of 18000 lbs on a single axle with two sets of dual tires)

The front axle is a 8 kips loading on a single axle from the LEF table is 0.051 ESAL. For the rear axles, I'm assuming a tandem axle with 32 kips per axle or 64 kips total load, you get 14.5 ESAL.

Using that number and your 11000 total vehicals you get 166100 ESAL's as the design ESAL's for the road.

This value assumes that the SN and pt of the pavement section you design are close to your assumptions, if not you need to recalculate your ESAL's.

 

[fattdad]

There remains some confusion: If you have a two weels on the front axle (at 8 kips) and eight wheels for each of the two rear "axles" (i.e., twin axles each with four wheels), then the ESALs for the 8/32/32 loading would be the same as 8/16/16/16/16 loading. If you then look at 11,000 trips you (well I) calculate the total ESAL is 20,120. Basically, I'm just asking if each wheel is supporting 4 kips? If so, then 20,120 would be the number I'd use. If not, then I'd like to have the problem clarified.

f-d

¡papá gordo ain’t no madre flaca!

 

[civilperson]

Try 90 psi with 90 square inch contact, or 8 kips /tire. The dual axle is worse than two axles at some distance apart with the same tire load on both systems.

 

[nutbutter]

Thank you guys for your help. I haven't done much traffic design, so this is very helpful. I didn't know the design vehicles accounted for fully loaded conditions as well...thank you for clarifying that.

We're designing an aggregate construction road for a building project on a power plant. After spending a day trying to get a very accurate estimate with HS20-44 loadings and other loadings I talked to my boss. In 2 seconds, he just told me to use 100,000 ESALs. I guess that is standard on our power plant roads.

I guess I learned to always ask my boss first. I'm new on this job, so I wanted to come to him with something instead of just asking him. My estimate was way too high (~400,000 ESALs).

Anyway, thank you guys for all of your help. I appreciate it.

Stoddardvilla

 

[eric1037]

For that type of an application, you should also consider structural loading. Some of the equipment that is delivered to the site of a power plant can be very heavy. The ESAL analysis doesn't take this into account.

You may want to search on "Haul Roads". There is a significant amount of literature out there from the mining industry.