Anchorage of mechanical equipment to slab.

[tmoe]

I have some mechanical equip. on a 9th story and Im designing the anchorage of the equip to the slab. The manufacturer provided anchorage locations (see attached drawing) are pretty far in from the edges of the equipment, which results in very large uplift forces if one assumes that these are the bearing points. How can use the obvious bearing of the equipment against the slab to help me reduce these large values? I can see in theory that there will be plenty of overturning resistance provided here, but Im unclear on how to calc such a thing. Is there a "safe" amount of equipment bearing area that I can assume helps me??

 

[madmantrapper]

I don't understand exactly what your after here. Looks like typical attachment to me.

 

[Triangled]

You mention "bearing" and "uplift" which are in opposite directions (at least in the northern hemisphere), perhaps I'm misunderstanding your line of thinking, but, assuming the manufacturer's provided anchorage locations, I don't see any other way.

 

[TDIengineer]

Please provide a plan layout of the anchorage relative to the equipment outline. Also need an elevation of the equipment, preferably showing center of gravity.
I will gladly attach an overturning calc for you. What building code... and what is your Sds and Ip. And you said 9th story.. how many stories total?

 

[tmoe]

Ok guys let me try to clarify. I have already gone through the calcs for lateral force on non-structural components, in this case mechanical equipment. Im tring to design the the anchorage to slab below. The angles (which locate where these anchors will be) are predetermined by manufacturer and are shown in the drawing I attached. Because of the the units heavy weight, high center of gravity, and relatively closely spaced anchorage points, I am getting really large uplift values at the tention anchors. Because of this I began to ponder how much (if any) bearing area of the unit itself against the slab ( on the compression side) I could use to help resist the OT moment in the calc. My thought process was that, because the unit is sitting flush with the slab, when a force is applied at some height H, there will always be SOME bearing pressure at the compression side of the base that is resisting overturn. Obviously if the overturning force gets too large, the unit will begin to tip, and thus the need for further anchorage. But how can I make use of this bearing pressure to reduce the OT moment the anchorage are to be design for??

 

[dhengr]

Tmoe:
Why not talk with the equip. manufacturer’s engineering dept. Half of those hold down designs were/are to prevent the equip. from vibrating across the floor and may not have been changed to reflect our greater concern for EQ loadings. It would seem that you could double your lever arm to the tension bolts, but you have to know what the sub-frame of the equip. looks like to make this determination. Maybe the shop drawing show some of this info., they should show a max. bolt load for their arrangement. You may want to shim or grout btwn. the sub-frame and the slab so you do know where the bearing points are.

 

[wannabeSE]

I assume you are wondering were to put the compression force in the TC couple resisting the overturning moment. What do the equipment cut sheet show? When the equipment has feet, I often use the center of the foot for compression and the furthest anchor for tension (neglecting any contribution from the closer anchor). If the unit has a sheet metal curb, I might use the edge of the equipment rather than the foot (even though technically it might be in a little bit in from the edge). It really depends on the equipment. These are good questions for a mentor.

 

[desertfox]

Hi

I've just been working out some concrete loading based some machine frames with loads high above the bolt positions and without much information to go on, so like WannabeSE suggests we used one bolt centre as the pivot and the other as resisting the tension generated by the overturning moment, so we ignore the contribution from the bolts nearest the pivot point.
This assumes that the machine frame is ridged however and in our case it's probably a fair assumption, this might not be the case in your situation.

 

[desertfox]

Look at page 23 on this link it might help

http://vietcons.com/uploaded/download/AISC-T-DG01-Column Base Plate.pdf

 

[Triangled]

If left edge is A, and left anchor, B, and right anchor C, and right edge D, and lateral load acting from right to left.....
I am envisioning tension on the anchor at C and a triangular distribution of compression from 0 at C to maximum at A, giving you a moment arm of the distance from C to AC/3.