Build a Geodome from some bamboo sticks and plastic hubs during a pandemic? There are many pros and cons but in the end I hope to have a lot of satisfaction at having completed a greenhouse, outdoor socialising area and a bit of a challenge.
A bad day for the dome. I watched from the safety of the house to see the dome initially handle the buffetting of the high winds but eventually succumb to the forces of nature.
Initial weathering of Storm Barra
Eventually succumbing to extereme buffeting
The storm was intense and ongoing for many hours on that fateful day. For many many hours the wind strengthened and waned changing direction as the storm passed over Ireland. The shelter from the surrounding buildings , trees and hedges protected the dome from the worst of the gusts of wind but at certain orientations the protection is very limited.
It is difficult to know what the point of failure was.... During the storm it was unsafe to investigate , my sole activity being to dismantle / flatten the geodome remnants as portrayed above to try and prevent further damage and material flying away. However, it was clear that the frame had not broken as such....ie no bamboo sticks had fractured ...rather the connecting hubs had given way under the repeated flexing of the joints from the buffetting wind.
Dislodged Hub Connections but no Bamboo breakages / failures
The metal 90 degree brackets used to attach the bamboo frame to the circular pattern of concrete blocks were deformed due to the forces involved ...and this may well be the source of the first catastrophic failure. Indeed from the video of the just collapsed dome you can see that the face nearest the camera, the location where the above bracket was situated.
It is also likely that one of the hubs loosened and the 'dome' shape was lost creating a large sail - like sheet of polythene to capture more energy from successive gusts of wind to repeat the process. 2 or 3 of the hubs were found to be completely opened up ...the following day....so maybe a tighter hub...would/could have prevented the collapse.
What Now?
I have recovered all of the frame elements and cleaned them up of all the mud and rinsed with a dilute bleach solution in order to remove any ongoing micro biological attack over the winter months.
Most of the 'bamboo' is in great shape though there may be more lengthwise splits than was observed during the first embodiment of the structure. (hard to tell) . I had a little spare so should be able to rebuild the frame completely with no more cost. The polythene cover ended up woth some local damage that has still to be fully assessed. It only ripped to a degree in a small area though a tape seam or two may have given up the ghost. Again, I have ample polythene and tape to repair whatever may be revealed when fully unravlled on a warm windless spring day in a few weeks time.
Dome II will therefore be different in 3 ways...
1) I will replace the small through bolts used to attach the polythene cover to the frame with quick release poppers. (if a big storm is forecast...I'll remove the cover and recover on storm passing)
2) Metal bracket strength will be increased to try and avert potential buckling leading to subsequent hub loosening.
3) A slight increase in ventillation holes will be made to try and lower humidity levels slightly through greater airflow through the structure.
The completed structure So.....In the words of Talking Heads....How did I get here. From earlier posts you will have seen the assembly of the polythene cover unit cells of Hexagons, Pentagons and 1/2 Hexagons......that allow the build to be easier to visualise and ultimately build correctly. Using the UV resistant mega strong tape and the gadget below (see earlier post) start connecting the unit cells into bigger fragments. (the gadget will take the strain of when trying to form a 3D structure from flat sheets). Its easy to get lost so I'd recommend joining 5 pairs of 2 hexagon cells as the basic 5 vertical stripes that you have to joing together via intervening pentagons. The repetition of this operation will hopefully result in less (0 errors) Gadget developed to join flat sheets to form a 3D cell. Once the whole structure is completed ....wait for a dry, windless day and go for it. I was assisted by my daughter who kept tension on 2 ropes straddling the top of the geodom...
Well....I did a lot of what I said I would after demise of DOME I in storm Barra 7/12/2021 and rebuilt the dome with only a few small repairs to the cover and a couple of bamboo poles. Somewhat bizzarrely , rather than using stacks of cement blocks to raise the dome to allow the underlying layer to be added....I happened to have a set of dining room chairs resting in my garage. Anyway, though this was a larger strain on the structure the vertical ,movement of the dome onto the chair seats could be acheived far more quickly than moving loads of blocks ...and so was a shorter and less periolous assembly. Second time around the slackening and straighten and re-tightening operation of each of the hexagonal and pentagonal connectors was realised more efficiently and I am convinced Dome II is more inherently stable than Dome I. With Polythene cover in place and raring to go. Only 2 or 3 days before annual holiday....so need to protect against wind catching under edge of dome and arrange...
Physical construction of bamboo. This results in the appearance of a solid core if your rod cut lies on a node. These are usually thin enough to be drilled out to reveal the natural diameter of the bamboo. Various dimensions and shapes OK, due to the construction of bamboo the plugging of the ends of the rods you cut is not so easy. The above shows a typical variation of what each rod end will present to be filled by a dowel trimmed to size. As you can see the sidewalls can be thin (2-3mm). While this is still mechanically very strong...especially under longitudinal forces...you can see that you cant just drill out irregular ends to form easily plugged circles. This means you need to have a lot of dowel diameters to hand and trim them to the irregularities of the bamboo. My Set up Gorilla Tape to wrap round ends of rods to protect against splitting. Wood Glue to secure dowel in bamboo rod. A variety of dowel diameters A sharp craft knife for scoring the inner rods. Hand-drill for...
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