TRAFFIC RATED MANHOLE

[Erasa]

Hi Engineers,
I have been asked to design a manhole size 1.5m x 2m x 2.5m deep which will receive traffic loading.
I am designing the walls and base as propped cantilever retaining structure with H20-44 loading (wheel load as my imposed load).
My question is, do i have to use the wheel load as static on the wall or dynamic; if dynamic can someone help me out with the estimation of the dynamic load? Any reference, publications and codes will be appreciated.

 

[EireChch]

Seems like major over kill.

Why cant you just buy an off the shelf product?! Its a small manhole, there is surely a type that fits your size or bigger.

Anyways, I would just design it as a static load and be conservative.If your wall go from 100mm to 150mm its not a big deal. I think you are over complicating it trying to look at dynamic load. It would be difficult to determine and you will have to look at dynamic stiffness etc. which complicates things.

 

[fel3]

I once used a City of ****** standard manhole on private property (a petroleum tank farm) and the City of ****** building department required me to provide calculations for the structural adequacy of the manhole. Never mind that the City of ****** already had thousands of these manholes in city streets, most of which were much deeper than mine. Never mind that my manhole was in a raised traffic island, so technically not subject to full traffic loading.

So, I did two things. First, I showed that the traffic loading produced compressive stresses in the concrete that were but a fraction of the concrete's compressive strength.* Second, I did a calculation that showed that the manhole was good to about 1500 ft of burial (IIRC) until failure by hoop compression (this calculation incorrectly, but usefully, assumed that the equivalent fluid model for the soil would still be valid at depth). The point of the exercise was to show (subtly) that requiring such calculations was stupid.

* For example, a 48" diameter manhole with 6" walls has a cross-sectional area of 1,018 sq in. A 16k load on this area results in an average compressive stress of only 15.7 psi. The compressive stresses on the neck and cone sections will be higher, of course, and cone sections can be subject to eccentric loadings, but none of this is enough to matter.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[bridgebuster]

I think by dynamic load he meant impact, which I would include as 30% of the wheel load.

 

[hokie66]

You fellows are assuming that the OP is located where precast manholes are available. That may not be the case.

Erasa,
A propped cantilever is not the appropriate model for your walls, as the cover will be removable, I assume. Design the walls to span horizontally.
bridgebuster has given you the answer in regard to impact load.

 

[r13]

As bridgebuster mentioned, impact should be considered when designing the manhole cover and its base. A surcharge (without impact) should be imposed on the ground level when designing the wall.

 

[chicopee]

To retired13 "...A surcharge (without impact) should be imposed on the ground level when designing the wall." I take it that you would be concerned from a surcharge from a nearby parked truck or even from a lattice boom crane.

 

[r13]

To Chicopee: Yes, the surcharge load is safety against unforeseen events, anything can happen to a manhole located in an open area.