Vertical Component of Live Load Surcharge

[NotDeadYet]

I have asked around my office, read the applicable sections of LRFD-BDS, read multiple text books, and done multiple google searches but for some reason have not been able to find an explanation that I can wrap my head around to explain the idea of a vertical component of Live Load Surcharge.

Horizontal make perfect sense. If you put your fist on a lump of playdough and push down it expands out creating a lateral force against any obstacles to that expansion.

Where does the downward component come from though? If traffic is close enough there could be a downward force from Live Load, but that is a separate load. Is the vertical component of LS some sort of shear reaction where Live Load pushes down the soil beneath the lane and that pulls down the adjacent soil behind the wall? What is causing the vertical component of LS in real world terms? Apparently I need an explanation written in crayon.

Any help is appreciated...

 

[jhnblgr]

it’s the distributed wheel load.

https://connect.ncdot.gov/resources/Geological/Documents/6B-1_Modeling%20Traffic%20and%20Construction%20Equipment%20Surcharges_Lien.pdf

 

[NotDeadYet]

Thanks for the quick response, but I'm still not sure I'm getting it.

Is this saying that LS should be used instead of LL? Like it is a simpler method of determining what part of the LL distributed at 45deg through the fill is over the footing?

 

[jhnblgr]

It is resolving the point load into a psf load which you can use in the unit width design of your wall. Typically codes provide design live load surcharge.