Dome build: Reinforcement.

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Wednesday: Spent the day fitting top tier, vertical bracing battens. Compound, undercut miters needed care to avoid a sloppy fit. Which would rather undermine the whole point of fitting them. It took several journeys up and down the ladders to trim on the miter saw for each batten. I am paying dearly in wasted time for the dome being 'upstairs.' Had it been down on the ground it would have been far quicker. But then the finished dome would still need to be lifted up onto the rollers to within an inch or two, in 3 planes, by a complete novice at driving a telescopic loader. I wasn't willing to take that risk.

Another risk is high winds. Tomorrow promises westerly, 50mph gusts. The first real gales since I built the observatory. Fortunately there is a shelter belt of trees to the east. Though it isn't very deep it does provide some protection.

Now I am wondering if I should hastily provide a guy-line cable, or two, connected to buried concrete anchors. Precast carport anchors could be reinforced with large concrete slabs to increase their surface area against soil lift. This would offer increased resistance if needed. There is nothing westwards of the building to prevent such digging. I am suddenly aware of the rather small footprint of the octagon. It has proved remarkably stable until now. With no obvious change in level. Dare I take a risk and do nothing? Or use the time to provide some defense?

I decided against the guy-lines for the building itself. But I added four ratchet straps between the dome zenith and the pier. If the pier decides to lift, despite the hold down disks then the straps should add further restraint. The pier is massive as is the mounting on top of it. If the pier lifts then so must four more, buried,  precast concrete anchors.

The forecast is gently lowering toward 20m/s which is about 45mph. It will be an interesting test. The panel sealing is proving almost worthless. With the interior of the dome showing wet patches from rain water draining down the inside. It starts at the bottom of the top tier so I shall have to concentrate on that area with more sealant.

I fitted some net-reinforced, clear poly tarpaulin over the closed shutters to let the light in and keep the rain out. Whether it survives tomorrow's gales is quite another matter. Reaching anywhere near the top of the slit to staple the PE was completely impossible. I'm not sure what the answer is to the poor zenith access when the shutters are closed. A rope ladder? I could rejig the added top ladder. Pull out the base of the ladder to lower the angle at the top. The problem then is rotating the dome. The shutters will strike the ladder. A folding [builder's] stepladder could be cranked over the top of the dome. That would need serious support and bracing! Just getting the ladder up there would be difficult.

The dome is not strong enough locally to support separate roof rungs designed for chimney sweeping access. Once the shutters are functional and covered, the access problem goes away. That is, until I take away the tall stepladders.

It was suggested I arrange a strong support at the zenith. To allow a hoist to remove the heavy mounting. A thick wall pipe could pass right through the ribs and the shutters without affecting the weatherproofing. Water pipe with flanges bolted to the slit ribs? That would save having somebody else fabricate something with welding. Though a pipe might block the sky slightly more than  a steel strap. The steel strap would have the advantage of reinforcing the spacing of the top of the ribs. It would also tie in the zenith board of the observation slit. 

Click on any image for a enlargement.

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