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baza 1308 posts |
Aug 29, 2003, 13:09
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>Please let us know what problems you anticipate. Well, here`s just a couple to start with: Rowing. Assuming one tonne of lift per oar, twenty oars spread out over thirty two feet doesn`t leave much room between the oars, especially as they`d have to be closer together near the base of the upright. Towers. We wont be able to get away with a flimsy structure under present-day regulations. Serious thought must go into their construction. Where will the oarsmen stand? They`ll need to be above ground level. baz
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Steve Gray 931 posts |
Aug 29, 2003, 13:49
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Yes, I've been thinking about safety too. We might have to use scaffolding towers with guard rails and safety harnesses for the lever operators when raising the blocks. I know Gordon wants to be as authentic as possible, but if we can prove that ancient man could have raised and erected 40 ton blocks of stone, I don't think it's encumbent upon us to also demonstrate how he might have built platforms for the workforce.
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baza 1308 posts |
Aug 29, 2003, 13:58
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What I feel that we need, at the moment, are more people to volunteer and for us all to get some practical experience in shifting stones. baz
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Steve Gray 931 posts |
Aug 29, 2003, 14:19
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> Assuming one tonne of lift per oar, twenty oars spread out over thirty two feet doesn`t leave much room between the oars, especially as they`d have to be closer together near the base of the upright. That's true, but Gordon reckons that the lift is actually well in excess of 1 ton per man. There's also no reason why we can't have more than one man per lever, assuming the timber is strong enough. > We wont be able to get away with a flimsy structure under present-day regulations. Serious thought must go into their construction. True. Raising the 40 ton uprights is likely to require towers of around 5 metres high. Gordon's idea is to use logs with a ripping taken off each side to give them a uniform thickness and a flat face. The logs would be laid alternately in each tier and we would install diagonal bracing logs from ground level at periodic intervals to ensure that the tower can't topple over. I am familiar with the calculations necessary to design timber structures for planning applications (e.g. traditional purlin roofs), the only difference here is one of scale. The logs in the layer that the braces reach would need to be properly jointed to transfer the loads correctly. Raising the lintel requires greater height, but the principle is the same. The lintel weighs around 10 tons. > Where will the oarsmen stand? They`ll need to be above ground level. I've just posted a reply in another part of the thread to say that for safety reasons we may have to use modern scaffolding towers and safety harnesses. baz
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baza 1308 posts |
Aug 29, 2003, 14:47
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>Gordon reckons that the lift is actually well in excess of 1 ton per man. >There's also no reason why we can't have more than one man per lever, >assuming the timber is strong enough. The force required per lever should be easy to work out, assuming, as you say, that the levers can withstand the shearing forces involved. A workforce of 40-50 has been mentioned, more hands on the levers increases that figure. Even with 2 feet between levers, that`s not much room to manoeuvre. The BBC used 130 people to pull an upright up a 1-in-20 gradient. To halve that figure would be a substantial achievement. baz
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Steve Gray 931 posts |
Aug 29, 2003, 14:53
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> You can achieve a good result many ways by different combinations of variables – height, offset etc so I’m a bit puzzled about how to focus. Would it be right that the height variable should be pinned down to “as low as practicable”, and then the other variables can be tweaked? Or are you and Gordon undecided about height? Have you got today's update? The model has changed a bit. I saw the video of Gordon's 4 ton effort, yesterday and he basically used a very small offset so as to place the minimum load on the A frame. The tower was only as high as necessary to hit the hole and the hole was fairly close to the tower - all pretty sound thinking. The latest model has default values that use the same principles on the 40 ton stone. > Secondly, you can get the stone to just stand up, but a very marginal alteration to the parameters will take it too far and it will pitch forward or not far enough and it will fall back. So I’m wondering about margins of error – A.) should the adopted computer model be one where X% variation in the variables won’t matter, as it will still work, and B.) should the real-world arrangement include “emergency buttressing” for if the stone pitches forward unpredictably? OK, I have not yet modelled the effects of the hole. The model just stops if the angular speed is less than an arbitrary 5.7 degrees/second (0.1 rad/s) and the block is within 5.7 deg of vertical. When I do the modelling of the hole I will calculate the forces that the stone exerts on the ground due to its rotation. It should be farily easy to find out what sort of limits we can work within by waggling a small post in a hole to see how much force is needed to seriously deform the hole (we may have to repeat this at the actual site later on). Having a short slope on the right hand side (furthest from the tower) of the hole would allow the block room to pivot into the hole and make a decent area of contact with the left face of the hole. This will stop the bottom end from rotating and the momentum will carry the top of the block up towards vertical. As it reaches (or passes) the vertical its angular speed is at a minimum and by that time gravity should be pulling the stone well down into the hole. As long as we can stay within the limits of strength of the ground, as mentioned before, the block should not topple over. I don't envisage more than about one third of the hole being sloped.
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Steve Gray 931 posts |
Aug 29, 2003, 15:14
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> The force required per lever should be easy to work out, assuming, as you say, that the levers can withstand the shearing forces involved. Yes, it's not difficult to work out, but the mechanical advantage (pivot ratio) of the levers is the main criterion. You can reduce the height of the lift if you need to lift a larger weight per lever, or vice versa. > A workforce of 40-50 has been mentioned, more hands on the levers increases that figure. Even with 2 feet between levers, that`s not much room to manoeuvre. No it's 40-50 tops, including the tower builders. If we put two men per lever we halve the number of levers, not double the men. 2 feet per lever is OK since everyone moves in unison. It just gets very cosy, so we all have to remember use our underarm deoderants that morning. > The BBC used 130 people to pull an upright up a 1-in-20 gradient. To halve that figure would be a substantial achievement. So how impressive would it be to use less than a third? ;-)
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Moth 5236 posts |
Aug 29, 2003, 15:39
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Baz We were getting quite a few volunteers before the thread got dead technical. Hopefully the non-techies (like me!) have just gone quiet.... I reckon an appeal for volunteers near the time should get enough peeps. love Moth
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nigelswift 8112 posts |
Aug 29, 2003, 15:44
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I reckon there'll be enough of us in the end. If we're short then I suppose a single phone call to the nearest university archaeology or engineering department would get us a crowd in minutes. The good thing about that is that if we used students we wouldn't need to worry about safety issues...
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morfe lux 301 posts |
Aug 29, 2003, 15:59
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The good thing about that is that if we used students we wouldn't need to worry about safety issues..." Good gods man.
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