I have been reading through the postings for a couple of things, one is regarding my own interest in tape. While researching the other non filament tapes that might be functional, I was thinking that things might be over-engineered. I suppose with the possible winds, over-engineering may not always be a bad thing. But tonight, I came across a comment from Vinay in 2011, mentioning that hexayurt failures are uncommon. Or almost unheard of. Is that still the case. The only attibutable cause, so far, has been poor construction practices.
There are a few failure mechanisms I can think of. But sideways release of tape has not been one that comes to mind. Adhesion failure: Causes - contaminated surface, non compatible surfaces. Non-shear loads, or peeling. Most of these tapes have fairly significant peel strengths, but an adhesion failure from peeling would be a truly monumental achievement in poor construction techniques. Like hanging something from the ceiling, stuck to one end of a piece of tape, with the other stuck to the ceiling. But shear strength of adhesion would be like hanging same said object from the wall. The load is not trying to peel, it is trying to shear. Very different scenario. And the shear strength will come from both the tensile strength of the tape, and the shear strength of the bond. A good bond, under tensile load, also depends on a good length of anchor. Example: Make up a moving box and tape the bottom. You will see pros wrap 12 inches up the side. Amateurs will use 3 pieces of tape, with only 3 inches up the side on each side. Which is stronger? I have seen more than a few blowouts on the three piece method. There is only 3 inches of tensile / shear, and once the middle starts to fail, there go the sides. The 3M bi filament tape states a peel strength of 100 lbs per inch width to steel. Tensile failure. Breaking tape. I don't think any of these are going to break sideways. Maybe if the roof were connected only by a ring of tape and the wind was able to grab an edge. But I speculate that the adhesion would fail before tensile. So for that, some Longitudinal (top to bottom) straps connecting the two, or of course, the anchors. The monodirectional tapes, and the bidirectional tapes have around 150 psi tensile strength per inch width. Bi filament has it of course in both directions. But we're not really relying on tensile strength laterally. At least I don't believe so. And it's the wide bi filament tape that gets really expensive. I don't see any shear strength ratings, but I would imagine that it could be higher than the tensile strength, given that peel strength is 66% (for the 8959 tape). So that would mean that width is your friend. And even if you do get lateral loading, that would be across great lengths, so regardless of the tape, the strength is significant. There are other tapes that I have found. High molecular weight (expensive), and some high strength polyethylene tapes. I would hazard a guess that some of the "ultra clear" premium packaging tapes would work, though 6 inch width woudl be a minimum. That being said, am I going to bank my shelter on it. Nope. But, it might be a worthwhile experiment. Another failure mechanism is structural. To some degree, I think the tape lends rigidity to the structure, and the structural mechanics take over. I put together my foamcore model today. Flip flopping around, falling over, shifting around. Then, with a few very small pieces of tape, I got the roof on. You can bear down on that sucker, and the load holds very well. Where would it be weak? Where ever it could buckle. And that depends on the model, and the roof. I think that the resulting equilateral triangle sections would be better served with an inside tight tape bonding. That is a large segmented flat surface. The inside tape prevents the hinge from opening. If you were to use a weaker tape, I would further augment that joint with some cross lengths, perpindicular to the seam, going a couple of feet to either side. Over engineering, maybe. But if you saved money on the tape, it would be well spent tossing some of it into over engineering. I'm all for over building: if things remain aesthetic, functional, and economical. I planning on an H13, with a full door. Lots of discussion in 2011 on questions, breaking the tape ring. I don't see much from 2012. Though I do think that the plywood panels on either side of the doorway addresse that issue. I like one comment about bringing the tape ring over the plywood and wrapping around to the inside (bonding length). I think by leaving a couple of inches of intact plywood at the bottom, and many inches at the top, then keeping the door around 30 inches or less in the 48 inch panel, and you have a good amount of integrity both for the tape ring, and for that huge flat surface and seam that get compromised by cutting into it. If you were to forgo the plywood, I would think that some metal L channel might be good in the doorway, on either side, straddling the seams. And maybe a plate of plywood or metal to either side of the door to shore up that joint. You want to prevent buckling at that wall, and those would help to support the weak spot. For that matter, you may want to put plates on the adjacent high wall, as that is still a large surface that could be taking tangential load. While the roof has large surfaces, the wind loading is not direct, and the loads are transferred to the walls. Tangential to the wall, some will want to go the adjacent walls, but that is a long horizontal seam directly in the load path. I'm just throwing some of my thoughts out there. If someone does have any knowledge of, or stories about failures, I would be very interested. But the failure mode is important. Stronger glue using the same crappy materials won't help anything. I think that some of the experiments with fabric hinges, etc., stand a greater chance of failure than tapes that are less strong than bi filament tape. While you a square inch of fabric versus a square inch of tape film, the fabric does not have a uniform flat surface, so your effective bonding area is very likely far lower than an inch. Plus, the outer parts of the fabric are not homogeneous with the inner parts. You could have a lint deposit on the adhesive, post bonding failure. It would be interesting to hear about some peel tests for that type of joint. I'm simply speculating on possible sources of failure. If it were to have a peel strength in excess of the bi filament tape, then you are probably good to go. If you have a consistent application method. Anyway, if you do go that path, run some experiments with your fabric. Glue it down, how you intend to and leave a strip hanging. The try to pull it off, pulling tangentially to the surface. If the foil comes off, you're probably good. If the foil adhesion is failing, it don't matter what tape, material or adhesive you are using. Also try the test under shear. If you get some filament tape (regular filament will be fine), you can compare it to that, but use identical widths. People are spending tons of money on tape, and the tape of choice deteriorates rapidly. I think we are surrounded by solutions if we were to look and share. It's not worth it to save a few percent of cost on your structure, only to have it be marginal. But removing the old bi filament is more work. Adding aluminum tape over it is more cost. I think we can still build with a comfortable load margin, yet save some time and money. -- You received this message because you are subscribed to the Google Groups "hexayurt" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/hexayurt?hl=en. For more options, visit https://groups.google.com/groups/opt_out.
