Vehicle Live Load Calculation

[stiebert]

We are building a boardwalk and I need to do some quick calculations to redesign the joists and beam spacing.

They spec a unified live load of 85 PSF

The have a design vehicle load of 2,600 LBS, load distribution consists of 60% to rear axle, axle spacing of 6', wheel spacing of 4', and tire print area of 11" wide x 3.5" long (in the direction of travel).

I'm trying to find out if the vehicle live load is greater than the uniform 85 PSF. If you could give me a few calculations how you came about it for future reference that would be great.

Thanks

 

[Ron]

The vehicular point loads are a little less than 800 lbs, so I would design for the uniform live load AND the point load, since both could occur in proximity to each other (heavy pedestrian load plus slow moving vehicle through crowd).

 

[stiebert]

Well it's only a 10' wide boardwalk. How much would that point load be translated into a PSF? I also believe that the rear points would be 780 lbs.

 

[paddingtongreen]

This is double posted, it's not clever, it's a nuisance.

http://www.eng-tips.com/viewthread.cfm?qid=285965&page=1

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[bridgebuster]

I agree with Ron.

Does your client require the design to conform to AASHTO? I had a similar project and we were required to use AASHTO.

Here's what AASHTO Standard Specs say on tire contact area. (NOTE the last sentence; you're nowhere near HS20.)

3.30 TIRE CONTACT AREA
The tire contact area for the Alternate Military Loading
or HS 20-44 shall be assumed as a rectangle with a
length in the direction of traffic of 10 inches, and a width
of tire of 20 inches. For other design vehicles, the tire contact should be determined by the engineer.

 

[Ron]

Don't try to translate the point load into an equivalent distributed load. Use the point loads as moving loads along the probably path, checking the worst loading and response conditions.

 

[beton1]

The point load is a point load. You cannot use the vehicle area to create a uniformly distributed load. You have the wheel laods, and as Ron and Bridgebuster have stated, you must use a 'travelling' load to find max. moment and apply relevant bridge code.

 

[beton1]

There may be a clause pertaining to pedestrian bridges, which, if this is the case, may give you a alternate. (ie., If it is for service vehicle access/usage, then the design is based only on the service vehicle and is not accessed by pedestrians at the same time).

 

[steellion]

What code are you using? You may have to use a combination of a uniform load with the wheel point loads, that's the way that AASHTO does the bridge design. Even if it's not AASHTO, you probably want to put some uniform live load to go along with the wheel loads (I don't think you can say that there won't ever be other misc. loads when there is a vehicle on the boardwalk)