equipment pad
equipment pad
(OP)
for seismic design ASCE requires components to be securely fasten to the supporting structure. sometimes we design concrete pads to support an HVAC units outside buildings. it seems funny we anchor the unit to the pad but the pad itself is not securely attached to something else. since the pad is embeded very shallow to the soil to me the pad and the equipment can be thrown the air together during an earthquake. is there a min embedment requirement for shallow foundations? thanks.






RE: equipment pad
Beyond that, you have passive soil pressure resisting any movement.
In northern areas, minimum embedment is governed by frost depth. Here in the southwest, it's more of a common sense issue, and one or two feet deep feels right.
RE: equipment pad
RE: equipment pad
RE: equipment pad
RE: equipment pad
Cedar Bluff Engineering
http://cedarbluffengineering.webs.com
RE: equipment pad
Watch out potential for shear failure (one & two way) if the pad seemd thin. Also, can the equipment tollerate uneven settlement caused by frost heave? Throw some thoughts on these.
RE: equipment pad
You could take that line of reasoning with any structure. The result would be ridiculous. The buck has to stop somewhere and it is with the foundation.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: equipment pad
RE: equipment pad
Earthquake is the movement of earth plates, structural damages are due largely to non-synchronized/random motion/displacement between earth and structures.
The phenomenon of dynamic earth-structure interface alone is complicate enough by itself, I sincerely hope the AIR wouldn't get into this mix. But, what a theory, and what I know! Maybe given another 100 years the Air Dynamic (not related to wind, but earthquake), Soil Dynamic and Structural Dynamic would be linked together in the scientific textbook. Glad that I won't be there to see it.
RE: equipment pad
RE: equipment pad
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that is why i think we may need a min embedment for the pad.
RE: equipment pad
Judgement is more important than code.
RE: equipment pad
Every geotech. report I have read allows the use of both passive and friction to resist loads, unless the soil are so bad or there is undocumented fill. The IBC also allows the use of friction. There is no reason, when soil are not an issue that, friction and passive pressure can not be used to resist loads.
RE: equipment pad
The equipment must be anchored to the slab through mechanical means, not friction, per the code.
The seismic load is applied at the C.G. of the equipment to calculate the overturning moment. The foundation/mat slab will provide resistance to the overturning moment through the weight of the slab itself...so the anchorage or connection to the slab must be able to resist these overturning forces (these will be tension loads).
The seismic load must also have shear or lateral resistance, this is accomplished through the foundation interacting with the soil, usually friction will be enough in equipment pads such as this.
So the equipment anchors have to be designed for the tension due to the uplift due to overturning and the shear due to the lateral load.
Usually the pads are about 12" thick, sometimes with a turned down edge to get the minimum 12" below lowest adjacent grade. The soil needs to be sufficient to support the anticipated soil pressures due to dead, live and seismic loads, and is usually far less than the code minimum of 1500 psf.
The code also says that any structure must be separated so that adjacent structures do not pound against each other. But equipment pads are usually on the exterior, ground mounted and away from the structure. This is usually not a concern at all in equipment pads.
The weight of the equipment and pad are what keeps everything in place, further anchorage is not required such as soil anchors, piles, deepened foundations etc...
That's my 2 cents, although I usually charge 3 cents for all that...
RE: equipment pad
RE: equipment pad