Firetruck Loading over SWM Vault 2

[Simba13]

Afternoon all,

I am working on the design of a stormwater management vault and I was wondering how exactly to approach firetruck loading specifically with respect to the lid slab. I know there have been some older posts on this but I'm still a little unsure.

Soil depths over the slab range from 3.5' to 10.5' so despite the wheels being point loads, it's not as though the wheels are directly on the slab, the load will be transferred over a larger area by the time it gets to the slab through the soil. So I'm not sure of the best way to model this in SpSlab (modeling one way on a /ft basis btw) do I just take the overall weight of the truck/ footprint or do I bring the point loads down at a 1:1 slope and spread it over that area? Though if I do that the loads overlap somewhat and I feel like the model is becoming a little convoluted.

Any input is appreciated, thanks!

 

[WARose]

In AASHTO, if you've got at least 2 feet of soil over a buried object, you can then begin to spread the load out.

Here is some guidance from the Illinois DOT:

https://idot.illinois.gov/Assets/up...n-Guides/CM 3.4 LRFD Culvert Design Loads.pdf

 

[Simba13]

WARose Thank you! That helped a lot.

 

[Simba13]

Morning all,

I am following up on this thread, I've gone through the design of this SWM vault and everything looked good and it was checked. But something has occurred to me. The controlling case of this design for moment up until this point has been a specific firetruck outrigger loading (adjacent to a fire station) but I was looking through AASHTO today (I work at a buildings firm so I only have some knowledge of AASHTO). But I wasn't considering the design lane load of .64 klf, that wasn't mentioned in the LRFD culvert design guide at all. And that goes on top of the design truck I checked, now there is an out for culverts with spans <15' as per AASHTO 3.6.1.3.3, they don't have to have the design lane applied. The SWM vault is two span, 12.5' each in the transverse direction.

So I have two questions, how does this 3.6.1.3.3 exemption deal with multi span buried structures?

If I do have to apply the .64 klf lane load, how do I spread it through the soil? I get how the wheel loads spread, but they're acting over an area, not sure how a line load would be dealt with. Does it just go straight down to the top slab? Seems overly conservative especially in deep soil areas...

Any help is much appreciated