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"Pilings to set the poles on"?? The whole point of "pole building" is that the embedment of the poles in the soil allows the poles to withstand a moment developed by forces perpendicular to the wall. This in turn avoids the need for knee braces, shear walls, or other means for providing resistance to lateral forces. It lets you use thin sheet metal for siding instead of plywood, for example. If you keep the pole entirely out of the ground, as by setting it on a concrete piling, what you are building becomes no longer a "pole barn", but instead a "timber frame" barn. You must now incorporate proper bracing in the frame design, and you must also arrange for uplift and sliding resistance at the juncture of the pole and concrete pier. (These issues are neatly taken care of by the soil embedded poles in a normal "pole barn".) Some pole construction, particularly in soft soils, uses concrete pads poured the bottom of the hole, to help spread out the downward forces and better resist vertical gravity loads. If the top of the pad is below the frost line, no form is really needed, as the pad only needs to be a foot thick and is the conrete is not heavily stressed. (The bottom of the pad should always be below the frostline, to avoid frost heaving). Alternatively, you may be planning on setting the poles in the ground and back-filling AROUND them with concrete. This makes for a fairly strong solution, although the constant contact with concrete tends to rot the posts. If you dig the holes with an auger so that the sides of the hole are vertical, you do not need a form. The quality of the concrete does not need to be very high, done this way. If you really do want to use piers, and any portion of the pier extends above the frostline, then I would consider it mandatory to use a form. You absolutely want vertical walls on your piers if the area you live in is subject to the ground freezing. You do NOT want walls shaped like the wide-on-top, narrow on bottom holes that naturally result from digging a hole with a shovel. Vertical walls on your piers, or even better, walls that slant inward from bottom to top, prevents the pier from being spit out of the ground like a watermelon seed, due to the action of frost. 40 years ago, when we were living in Upper Michigan, my Dad repaired an old timber frame barn on our property by jacking up the sills, digging out the now rotted cedar posts (by hand), and filling the resulting conical holes with concrete. Each freeze cycle thereafter would "jack" his piers up about about 1 inch (due to the slanting sides). Enough dirt would fall back into the hole that the pier would not settle back to where it was, leaving it raised up and out of level. After 5 years or so of this, many of the piers were way off the correct grade, and some were tilted off plumb so badly that the sills were sliding off them. At that point, I was old enough to help him jack up the frame, shovel enough dirt away from the piers to pull them out with a chain and our 9N tractor, and haul the useless, conical piers off to a convenient gully for disposal. All my Dad's work of 5 years before had been wasted, and we had build all new piers with Sonotubes. My dad, feeling the folly of learning something the hard way, joked that one of those dis-functional conical piers should be used in the future as his tombstone. The barn is still standing proud, 35 years later, on the replacement piers that we set with Sonotubes.
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