Plywood Hexayurt Tensegrity Cable Tie-Down: Hurricane Survivability? The plywood hexayurt is probably far more appropriate for Haiti than the foam board construction, but how well would it survive a strong hurricane with 100+ mph winds, or 130 mph? Or more? Described below is an idea of how to build one that will survive:
Two issues concern me: 1. How well do the panels need to be fastened to each other to survive a hurricane? I don't think that screwed-together panels will stay connected, and when they separate and fly away they will become lethal projectiles. 2. How will the entire structure be anchored so it doesn't all fly away? Working with this calculator: http://timber.ce.wsu.edu/Supplements/WindDesign/PAGE1.asp It appears that the wind force on a standard 8x8' side panel hexayurt in 100mph winds is something like 20,000 pounds. My initial calcuations with this tool are only approximate, and I can only say that the forces are HUGE and I think that the structure will require more than just screws to survive. Here are the drawings of the cabling system that resulted from discussing all this with Vinay the other day, followed below by an explanation: http://richardginn.us/gallery/hexayurt Basically, every panel is tied to another panel by cable or strong rope, through holes drilled in the plywood. The holes are covered over later by flattened metal cans or any solid material, and then tarred or caulked. The whole structure could be tarred or painted for waterproofing, etc., but this discussion and test is about structural strength. There are three cabling elements: Whole structure tie-down, tensegrity internal webbing, panel-to-panel joinery (for the two side panels that make up the square face). 1. The whole structure can be tied down using a standard cargo-net hitch anchored to very solid rebar anchors. Very very solidly anchored rebar. The cabling runs over the edge of the roof so that the entire roof is anchored down to the walls, and none of it can move. If this is done strongly enough it will stay put in a hurricane. Of course, the panels themselves have to stay connected, and this will not work with foam boards because the edges are too fragile. One-inch thick plywood should be strong enough for anything, but engineering analysis must be done, and actual real-world testing too. 2. Two triangular cabling patterns tie the corners together at the top and the bottom of the wall panels. This results in a 6-pointed star tensegrity system. It also creates the base for a raised floor and a ceiling storage area when covered with plywood. 3. The wall panels should be made by two horizontal sheets of plywood, so that they can be tied together at the side edges and withstand strong winds. Maybe vertical panels would tie together just as well, and the faces with the doors can be vertical, with the door cut into one panel. The wall panels are tied together with X-pattern cabling, as illustrated. This is a first sketch of the idea, but the principle is that if it's tied together well enough, and made of solid enough material, it could survive a hurricane. It would also be relatively cheap, and strong rope could replace steel cabling if it tested out OK. That brings us to the testing phase: Where can we test these out? Build them and see what they will take. [end] Richard Ginn - [email protected] -- You received this message because you are subscribed to the Google Groups "hexayurt" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/hexayurt?hl=en.
