Building the Octagon Pt.31. Piering into the past.

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The perfect pier design still hasn't presented itself.  There are so many alternatives but none says "choose me!" No arrangement of diagonal braces, tried so far, offers much in the way of headroom downstairs.

With four loose, 4x4 vertical posts to play with, it is not difficult to imagine sandwiching other timbers between them. By using a halving joint two planks can be nested, vertically on edge, between the posts at right angles to each other. It is assumed the four posts are sunk into concrete in the large concrete pipe for stability. Though the dimensions of the pipe are very unlikely to offer enough stability on its own as a foundation block. A large plastic bin bag can provide a waterproof membrane for the inside of the pipe to avoid the upright posts from rotting over time.

The downstairs floor is still not finalized so larger timbers could easily be set on edge as horizontal 'feet' for diagonal braces to be attached. Thus making an oversized telescope pier more normally constructed from metal. Through bolts will ensure a complete lack of relative movement as the braces are firmly clamped in place.

A timber cross of [say] 2x6 just below obs. floor level would help to push out the braces to allow a little more headroom under the braces. A halving joint allows them to cross each other without hindrance and exit the four post pier at the same level.The diagonal braces could even be duplicated form [say] 2x4 for increased stiffness but without making the braces too deep and intrusive.

The image shows the proposed timber feet, upper cross and bracing in orange superimposed on a similar arrangement. The upper cross allows more headroom than direct stays joining the pier posts. Only the two nearest feet and braces are shown for clarity.

Separating the upright posts increases their moment. The greater dimension provides greater stiffness provided they are firmly fixed over spacers and braces over their length. Adding 2" wide braces increases the 8" square format to 10"x10".

The timber feet can be lost beneath the ground floor. Or even sunk into gravel if that is the choice of flooring at ground level. A sheet plastic membrane in the form of a tray can ensure the gravel remains dry inside the building. So rot can be avoided. Using gravel of the usual angular chipping variety will enure it settles compactly. Placing the outer ends of the timber feet on concrete footings will ensure a lack of rocking. Separating the footings from the octagonal building's footings will reduce vibrations travelling between them.

The next image shows the 2x6 cross one meter [40"] in diameter inserted between the posts. The posts have also been spaced by 2" at the bottom and clamped with ratchet straps. The diagonal stays are 2x4s clamped to the timber cross to get a feel for the latest pier arrangements.

The pier still rocked because the braces were not properly anchored at ground level. Anchoring would seem to be vital even if heavy timber feet are employed. Though the heavy timber feet are still only optional if the diagonal braces are bolted directly to concrete footings. The triangulation provided by the diagonal braces is the vital feature. Whether they are attached to feet or concrete footings is [hopefully] irrelevant. Though the timber [feet] pier joists would probably provide further leverage against the pier rocking if firmly anchored.

It is fascinating how the wooden pier stays upright just standing on sand. You certainly wouldn't want to do this anywhere it can fall and injure someone.  It weighs a couple of hundred pounds and has 12' to fall from the top! With the floor aperture easily restraining it, the pier seems remarkably docile when upright. Otherwise it wouldn't be remotely so easy [nor safe!] to keep experimenting with different stays.

Click on any image for an enlargement. 

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