As you say, you cannot lower the hammer onto anchor bolts due to limited headroom. Here is an idea which might work for your application: imbed tapped sleeves. Hilti offers these sleeves for use with resin grout. These sleeves are made of either carbon steel (zinc plated) or stainless ($$$). The sleeves have a coarse knurled surface on the outside to get a good mechanical bond in the resin grout. The tapped sleeves (or inserts) are often used when something has to be repeatedly removed from its location on a concrete slab (or wall), to avoid having to jack it up to clear anchor bolts. I've used these tapped inserts many times with resin grout for applications where equipment had to be unbolted and removed leaving a clear deck slab (we plugged the tappings with stainless set screws).
You can make these inserts yourself, allowing about 1/8" to 1/4" of total clearance between the OD of the insert and the ID of the holes in the concrete. If you google "Hilti" and drill down and muddle around, you will see these inserts.
In your application, I would suggest you make a bolting template out of wood to correspond to the base of your power hammer. Here is a method we used at the powerplant on this kind of work quite a number of times:
1. decide what type of resin grout you are going to us. Hilti sells quite a line of it, and some types are "gun mixed" with a spiral mixer tube (disposable, so you buy a pack). Calculate the volume of the tapped insert vs volume of the drilled holes and get the volume of resin you will need. Allow some overage, about 15-20%.
2. Screw short pieces of all thread rod with nuts into each of the tapped inserts.
3. By means of your calculations, you can get a fair idea of how deep to fill each hole with the resin BEFORE sticking the inserts in them. This prevents underfill or slopping too much resin out the tops of the holes. Some overflow is inevitable.
A 1/8" diameter rod with a piece of tape or collar as a dipstick is what we used.
4. Once you have the resin in a hole, you need to work fast as the stuff has a fairly short working time. This time varies with the ambient temp, so this time of year in Rhode Island, you may have a longer working time. With the resin in a hole, you stick in the insert on its piece of all thread and turn it a few turns and work it in the hole. This gets rid of any trapped air.
5. When you have all the inserts in the holes, you then set the wood bolting template down over the all thread studs sticking up from the inserts. Make up another set of nuts and washers just snug. Put a carpenter's level on the template and shim it as required to level it. This is your last chance to have anchor bolts coming up nice and square with the foundation.
7. After the resin grout has cured (there will be cure times furnished with the grout, but overnight at this time of year is a safe bet), strip the template. The foundation is now ready to receive your hammer.
As an aside, I am not one to set machinery, especially something like an engine ("unbalanced reciprocating forces at work"...) on the "neat line of concrete" (term for the surface of the concrete as screeded off or trowelled off to elevation).
To do so is to wind up with bearing on random points and this will lead to localized cracking of the concrete and movement of the hammer relative to the foundation. This is why a lot of machinery, turbine, and engine mainframes, bases or soleplates are grouted. The grout insures "full and complete bearing contact". You can accomplish this in a couple of ways:
1. If you do not want to go the route of grouting, you can use "Adhaesium Felt". This stuff is a heavy felt impregnated with a resin, and comes in a saturated roll, in a plastic pail. You take out what you need, cut to size with a box knife or snips, and make a bearing pad to match the base of your hammer. You then land the hammer on the Adheasium Felt, and insert studbolts in the tapped inserts. The nuts are drawn down snug. The weight of the hammer will compress the Adheasium Felt to take up any gaps or dips and dives between the hammer base and the foundation top surface. The Adhaesium resin sets up, and the hammer winds up bonded to the concrete. You then sock up on the anchor bolts. Adhaesium was used by us for indoor applications in dry locations to set machinery and some structural base plates. It is removable with hot water. Works quite well, based on my own experience using it in places where we did not want to start chipping concrete and using non-shrink grout. FlexBar should have the Adhaesium.
2. The traditional method is non shrink grouting. You will need to make an outline of the footprint of the hammer, adding perhaps 1/2" on each side. You then chip off the surface of the concrete to expose the aggregate and remove any of the slick surface finished concrete typically has. Chipping is done with air hammers, electric hammers, or by hand hammer and bull point chisel. Air or electric hammers are often used with a "bush tool"- a multi point steel which looks like a meat tenderizer. Either way, you need to expose the aggregate to get a good bond with the non shrink grout.
3. You then set the hammer and level it on steel shims. The shims also set a clearance for the grout under the base of the hammer. This is about 1" of space. On a hammer subject to impact loads and vibration, similar to a diesel engine, the ideal thing is to level the hammer with jacking screws tapped in the base. After the grout has set, the jacking screws are backed off. This makes the grout carry the whole load, no unequal support as would be the case if the jacking screws were left carrying load. I'd use square shims and try to use the minimum number to get things levelled. If you wind up with stack of lots of shims, this can act like a leaf spring in service. After levelling the hammer, tally up the shims in each stack and reduce it to a minimum by using thicker shims.
4. After shimming, you then make the decision as to whether to go with flowable grout or packed grout. either method works, but I think the flowable gives more of a guarantee of good bearing contact between the base and the grout. If you use flowable grout, the whole fancy name for it is "Cementitious, non shrink, non metallic flowable grout". Sonogrout works fine for the purpose, used it loads of times. Make a grout form out of lumber around the hammer base, and you will probably be instructed to soak the chipped surface of the concrete foundation top for 24 hours prior to grouting. The form can include a chamfered top edge and must be equal in height to the bottom surface of the hammer base plus perhaps 1/4". A pencil line inside the forms at the elevation of the hammer base's bottom surface is helpful. The finished grout must not extend above the bottom surface of the hammer base as it will only crack out if it encases the sides. The forms should be oiled with diesel fuel prior to assembling and closing them. For a small job, you can sit the forms on the concrete and seal them with something like "Duct Seal" (aka Dum Dum or Monkey S--t). Flowable grout lives up to its name, and you need tight forms. I've also held grout forms for small jobs like column or pipe support base plates to the concrete with silicon gasket eliminator.
5. Mix the grout in a wheelbarrow, per the grout maker's instructions for a flowable mix. Pour it in from one side of the foundation (you make need to get a large plastic funnel as a pouring funnel, or nail together a hopper type box on top of the forms). Rod the grout with a PLAIN steel rod to get work it in the form and make sure any air is removed. Do not use scrap rebar or all thread rod as this tends to work air into the grout. Rapping the forms with a claw hammer is also a way to settle the grout. Add grout carefully to make sure you are up to the bottom of the hammer. A little bit above the actual bottom, like maybe 1/8" is what I usually do to allow for any irregularities in an as-cast base or machinery frame.
6. When the grout has had its initial set, you can tool or cut the top surface to suit your ideas and eye using a patching trowel. The grout will have "stiffened up" to where you can cut it like you would butter. You can cut the top of the grout to a chamfer or cut it so it slopes slightly downhill from the hammer base to keep mill scale from accumulating there. On engines and turbines, we always cut the top surface of the grout so it ran downhill from the engine or turbine base. This let oil and water run right off.
7. Let the grout fully cure before you sock up on the anchor bolts. Most cementitious grouts will develop compressive strengths in excess of 5000 psi in 7 days, and be fully cured in 28 days.
If you have the bucks, you can also use an epoxy resin to set your hammer rather than the cementitious grout. An ideal product which will not only set the hammer for level but chock it against sidewards motion is "Chockfast Orange". This was formulated for setting ship's machinery and not only serves as a grout to provide full and complete bearing on the foundation (steel foundations aboard a ship), but also chocks the machinery so it will not move when the ship is pitching and rolling in heavy seas. We used Chockfast Orange on some hydro turbine work, and the stuff is quite amazing. Pricey, but with impact loadings such as a power hammer will produce, well worth the money. Philadelphia Resin produces Chockfast Orange and they have a whole line of epoxy resin machinery grouts.
Done a lot of engineering involving setting machinery and structural stuff on concrete, and putting in anchor bolts "after the fact". I believe the tapped inserts may be a good solution for your application, and the grouting on top of the foundation is something I strongly recommend.
Joe Michaels
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