Transformer foundation
Transformer foundation
(OP)
Is it ok not to have a mass concrete foundation for a transformer about 5 tons heavy. The contractor proposed to just place the transformer above 2 parallel I-beams embedded into the RC flooring of the elect room.






RE: Transformer foundation
With what you mention, placement on an elevated concrete floor slab, I would be concerned with seismic restraint of the unit, and, if the unit is oil cooled, the location of a sump of sufficient size to catch a leak or rupture. The embedded metal beams would also have to be grounded as it sounds like at least the top flange would be exposed.
Mike McCann
McCann Engineering
RE: Transformer foundation
RE: Transformer foundation
You are designing a spread footing with overturning and a vertical P load. You cannot exceed your maximum allowable soil stress.
Start with some L, W, and T and see what your soil stresses are. Adjust from there. When the soil stresses are acceptable, calculate the steel. Check for beam and punching shear too. The footing must be thick enough to handle any embedded rods to anchor the transformer too. Special plates can be added to the ends of the rods (or other mechanisms) to increase the pullout without increasing the slab depth.
As an alternative to the hand method, RISA FOOT would handle this problem easily, except for the anchor bolts required...
Hope this helps.
Mike McCann
McCann Engineering
RE: Transformer foundation
RE: Transformer foundation
Mike McCann
McCann Engineering
RE: Transformer foundation
RE: Transformer foundation
The foundations you speak of having mass of 3 to 5 times the weight of the equipment is usually for rotating equipment. You increase the mass to ensure that the natural frequencies of the equipment and foundation do not match.
As far as for your transformer, as long as the floor slab can handle the load, you are okay.
I don't know the purpose of the beams embeded in the floor for a transformer. Transformers usually come on a skid with bolt holes for anchors. It could be that the contractor wants to weld it down, but why the extra expense of embeding the beams to weld down the transformer when it can be bolted.
Now, if the equipment is switchgear and not a transformer, then that is a different story. For switchgear, steel channels or other steel members are leveled and embedded in the concrete to insure that the switchgear is level. It is critical for the individual pieces of the switchgear to line up along the length of the embed.
RE: Transformer foundation
RE: Transformer foundation
Mike McCann
McCann Engineering
RE: Transformer foundation
thanks, right now we are waiting for the contractor's designer to present his calculation since this is a design and build contract. We suspect the designer used the wrong weight 3 tons only instead of 5.5 tons. If the design is not readily available, we intend to modify on site by making the slab under the transformer a bit thicker and add more slab reinf welded around the beam location, say make it 150 mm oc. We were not able to identify this issue earlier so other works will be dragged due to this delay if we don't act quickly. If the contractor's struc engr can prove his design is ok, then we will go ahead.