where to find AASHTO traffic loads?

[ctbailey]

Hello.

I would like to find information on vehicular traffic loads as they pertain to live load surcharges over an MSE wall which is to be designed.

Which AASHTO manual should I look in?

Specifically, I need to know what surcharge I should design for HEAVY FORKLIFTs. The kind of fork truck that loads 30 Ft. boats into storage racks.

here is a good example of the fork truck I will have working on a retained parking lot:

http://www.marinetravelift.com/m2000.aspx

Ground bearing pressure is listed at 95 psi. Maximum combined weight of the vehicle and boat could reach 84,000 pounds!

thanks for any help you can provide.

___
Craig T. Bailey, PE

http://www.bailey-associates.com

 

[BigH]

Look in the Bridge Specifications - they have a section on loading and, as well, a pretty good section on MSE Walls. Is the 95psi the tire contact pressure? that is pretty high - about 7 tsf. How high is the wall? You might want to consider using the MSE wall but using elastizel or similar foamed "concrete". I have seen photos of elastizel being used behind such walls for fill. Go to

http://www.elastizell.com

for information. The elastizel is supporting your load and the MSE wall facing is basically for aesthetics. Usually used in areas of very low bearing from a global perspective.

 

[jdonville]

ctbailey,

The AASHTO Bridge specs incorporate FHWA NHI-00-043 (Design and Construction of MSE Walls and Reinforced Soil Slopes) by reference. This file can be downloaded free from

http://www.fhwa.dot.gov/bridge/geopub.htm

As for the surcharge load, you seem to have a good idea of the actual live load. You could measure and model the actual "point" loads from all four wheels associated with the forklift using Boussinesq or Westergaard theory and compute an "equivalent" uniform surcharge to use in the MSE analyses. I think that at a minimum, you should use a 250 psf live load surcharge, but your equivalent surcharge (one of those engineering judgement things, I suspect) would likely be much higher.

BigH makes a good point that depending on the height of your wall and the allowable bearing capacity of the foundation soils, you may want to use something other than MSE.

Hope this was helpful,

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

 

[BigH]

Sorry - missed a point - if you look at Elastizell's site, they use the MSE wall but use the foamed 'concrete' as the fill rather than sand. The MSE blocks become the "facing" and the wall is really the gravity of Elastizell which can support your loads - now, as in any retwall design, you need to check the global stability and settlement.
ciao

 

[jdonville]

ctbailey,

To elaborate on BigH's discussion, what you end up with is a block of the foamed concrete. During the pour, metal strips are embedded in the exterior face of the elastizell so that precast panels can be attached later for the look of a MSE structure. For analysis purposes, however, it's just a big block of lightweight foamed concrete.

Hope this wasn't confusing.

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

 

[ctbailey]

First of all, thank you jdonville for the Link to the AASHTO publications site. I had no idea that was available! A few of those refrences are being added to my library immediately. In fact, it appears that they are shipping me the hard copies as well - for free. (well, nothings free in the US.)

As far as Elastizell goes, I will look into that. Jeff, you mentioned that this material utilizes strips for facing only. No reinforcement at all?

A reply asked if the 95 psi was correct. I do not know, that is what the equipment manufacturer lists as tire contact pressure for air tires. This machine can be equipped with solid tires. Yikes, that ground pressure would be disturbingly high!

This wall will require some additional bearing capacity tests, that I am sure of. Especially since the foot of the wall will include a downslope.

___
Craig T. Bailey, PE

http://www.bailey-associates.com

 

[crossframe]

I've always treated tire pressure as a way to estimate tire contact area. 95 psi is 95 psi. Pick up that boat and watch what happens to the tires - they flatten out.

 

[jdonville]

ctbailey,

Elastizell sells foamed concrete with a designed unit weight and strength. You pick the weight range and they will tell you what range of strengths they can give you (or vice versa).

The material, as I understand it, is batched on-site and poured in lifts of several inches at a time.

To replicate the look of MSE walls, they embed metal strips in the pour. The metal strips are only used to affix a precast facing panel.

In the end, you end up with an essentially monolithic block of very lightweight unreinforced concrete. Which only looks like MSE from the front of the wall.

Clear?

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com