Rotating Equipment anchor bolt system

[pmover]

all,

a gearhead is requesting technical assistance regarding an existing anchor bolt system for an internal combustion engine gen set sitting on top of skid fuel tank. while i do not fully know the history of this installation, i do know the current installation. so bear with me . . .

for some strange reason, the entire skid is sitting on top of floor grating. so from the floor, there is the concrete pad, the floor grating (1-inch height), and then the skid itself with about 1/2-inch webbing.

the anchor bolts on one side of the skid are vertically straight and are imbedded into the concrete pad designed for the gen set (post installed anchor bolts). on the other side of the skid, the anchor bolts are installed at an angle (not vertically straight). that is, the width of concrete pad is less than width of gen set skid base. so for the length of the skid package, the anchor bolts on one side are angled inwards towards the concrete pad for the gen set and penetrate the floor concrete pad and are imbedded in the concrete pad for the gen set (post installed anchor bolts). the angle (width/vertical) is say roughly 10-15 degrees from vertical.

the civil guy wanted to embed the lower portion of anchor bolts into the pad designed for the gen set; hence, the post-installed anchor bolts are at an angle. of other importance is that spherical washers/nuts are not used. there have been a few attempts in confirming proper torque after each operation of gen set unit, with re-torquing needed each time after gen set run time. since the bottom webbing sits on top of floor grating, the webbing easily deforms where the anchor bolts are located, thus little/no torque.

i believe there are many problems associated with this installation, moreso with the anchor bolts being at an angle. my expertise is not in this realm of duties; hence, i'm asking for some assistance.

1) does anyone have any idea why the floor grating may be installed between skid and concrete pad? having all that deadweight, coupled with the dynamic loading, seems like a significant load being placed in a small area on the concrete. after some engine runtime, the paint and concrete will likely start to fail.
2) since there have been two occasions where the "angled" anchor bolts have required re-torquing and the webbing is deforming, i believe there is some shear taking place, since anchor bolt is at an angle. what i'm requesting is some technical direction/advice/suggestions/theory regarding this "unique" type of installation. does anyone have any first-hand knowledge or design experience regarding this "unique" anchor bolt system. even some readily available reference material would be helpful as my Shigley & Mitchell college textbook does not discuss/relate this "unique" installation. in other words, a second opinion is being requested.

it seems that for every piece of rotating equipment that i've seen or otherwise, most anchor bolts were cast in place and extended the length of the concrete pad (i.e. sometimes a 2-piece anchor bolt system). no angled anchor bolt system whatsoever - mainly large equipment (i.e. > 1000 hp).

this particular unit is 300 kW in size.

thanks for any help!
-pmover

 

[Barry1961]

Just a thought on the grating. If you removed the grating how would it effect the angle or placement of the anchor bolts?

Barry1961

 

[pmover]

not at all. the angle will remain as the width of skid is wider than width of concrete pad design for gen set. bear in mind, there is a concrete floor, but it is not designed for the gen set. the anchor bolt penetrates the flooring concrete until it penetrates the pad for gen set.

again, i have no idea why the grating is there in the first place.

thanks!
-pmover

 

[1969grad]

What a terrible installation!!!!!!!!!!!!!

It sounds like someone guessed at the foundation size before the generator was purchased. Often times people use one manufacturer to base the preliminary foundation size on for construction bid purposes and end up with another manufacturer having different dimensions. In this case no one put a hold on the foundation drawing until the manufacturer's drawings were received.

The grating below the generator will add some flexibility and promote vibration so get rid of it if you can. You can support the the grating from the floor with posts.

I don't think that the anchor bolts at a small angle from the vertical is a problem. The bigger problem is that the foundation does not provide a complete bearing surface for the skid. The skid runners should be in full contact with the foundation and grouted. Alternately, you could have a 3 point contact using vibration isolators.

You can double nut the anchor bolts to prevent their loosing.