How to Join a Bamboo Pyramid?
I am using guadua as the corner posts for a pyramid. Any suggestions as to how to join these at the top would be greatly appreciated. The lengths of the posts will be 8.5m, the pyramid base 9m x 9m. The height at the apex 6.5m. We need to get the joint exactly right to ensure the energetics of the structure are correct. Suggestions as to how to raise the posts are also appreciated.
Rob Roark replied:
I have built many pyramids and other bamboo structures, the easiest way is to cut your pieces as closely to ideal. I assume that you are using the Great Pyramid scale...
Depending upon the diameter of the poles, bend some stiff wire or cable, if you want to use tension for stability, run the cable through the entire length of the pole, and use threaded ring bolts to draw the pieces together with washers (can be made with bamboo too).
If the piece is not going to be moved a lot, just use wire angles to hold the proper angles (Duct tape will help) and spray a large amount of "Good Stuff" spray foam into the joint. Use a small bent rebar in the foam joint, and trim off the excess with a razor blade. Paint the whole piece "Bamboo Green", and the piece looks seamless!
Mark Essert replied:
Given the size of the structure I would start with a temporary, large diameter, center post. Cut each corner member to in a concave miter to meet the center post. (Using a 6x6 square post would be easier).
Once opposite members are leaning against the center, drill through all 3 members (opposing and center) and through bolt. Bolts should stagger from those in the opposite direction which join the other two corner members.
Here is my advice:
Cut two pole ends in the right angle so that they have a flat surface where they touch. Cut it about 10cm above a node in the pole to prevent it from splitting. Find a piece of bamboo that is just oversize to fit inside the bamboo poles. Scrape of the outside layer just untill you can slide it in but with a tight fit. Insert them into both ends and ut them just above the node flush with the surface you cut at the large pole end. Take a piece of strong wood large enough to cover the (ovale) pole ends about 2-3cm thick. Trim of the excess wood sticking out. Place THICK dowels in the wood sticking out on BOTH ends. Mark the holes on the bamboo pole ends and drill them to the size of the dowels. Don't drill too deep! Put a bucketload of (waterproof) glue on both ends of the wood, on the dowels, and the pole ends. (If you don't find any glue in your underpants a week later, you did not apply enough glue.) Press both ends together and keep the PRESSED together untill the glue is DRY. As in fully cured.
Provide a proper foundation for the poles that protects it from ground moisture. Either a concrete foot or a steel pipe in a bedding of gravel might do the trick. Do be cheap on the foundation. Unless you want big hospital bills from collapsing roofs etc. For this size, depending on weight of cladding, expected wind loads and snowfall I would say you need AT LEAST 1m³ for every pole.