3/8” Hilti kb3 & kB-tz - did the strength change?
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Did the tension and shear strength of the 304SS ⅜” hilti kb3 and kb-tz change? I was about to order a few boxes yesterday and was reviewing the tension and shear strengths. Unless I’m reading the charts wrong, it seems like their numbers are quite weak. Is the design strength different than ultimate strength? KB-Tz technical info KB3 technical info |
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There are a lot of numbers in those PDFs. Which numbers (i.e. which table from, say, the KB3 reference) are you reading? |
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David Gibbs wrote: Table 11. Page 353 |
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Adobe Page 9 of 21, Table 9 Yes it appears that design is not ultimate. I remember when we had a meeting with some Hilti engineers about anchors bolts, they were shocked we were working in ultimate strength. |
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the best way to ease you mind about bolt strength is to forget the numbers. place a bolt in a BAB (Big Assed Boulder) then tie a fig8 loop on each end of a 15m rope. clip one end of the rope to the bolt, clip the other end to the rear bumper of a BAT (Big Assed Truck) coil the rope on the ground. Rev up BAT and dump the clutch. Flinch when you hear your rope explode. If the bolt fails and the rope does not break you know dam well that those bolts are no good. if your rope explodes with a loud bang you know damn well that those bolts are Truck. :) |
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Nick Goldsmith wrote: Good way to blow a tranny too! |
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Actually no. Red Bessie breaks climbing rope like nobodys buisness. barely even feel her work hard. just drive away and hear that BANG when the rope breaks much less work than dragging big trees out of the woods with logging chain. the whole point being that your rope will almost always break at the fig 8 knot unless you get gate flutter in which case your biner will break but that is pretty rare. usually the rope breaks at the knott. I would be very alarmed if the bolt failed without breaking the rope as rope breaks pretty easy. so by very simple deduction if the bolt is strong enough to break your rope don't worry about the bolt. The actual numbers really don't mean anything once the rope breaks. |
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Nick, you should do a guest appearance on Hownottohighline with your break test setup! |
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Nick Goldsmith wrote: Well normally when we fall off there's two strands of rope taking the force....... Single strand of climbing rope can be down below 10kN which isn't much in bolt terms. |
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Jim, wouldn't you agree that when the rope breaks everything else is a moot point? |
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Nick Goldsmith wrote: Two strands. |
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when you double the rope up sometimes the biners break before the rope but usually they just stretch a bit. it's still a moot point. that Never Ever happens while actually climbing unless the biner is cross loaded or the gate is open. I totally get it that if you are a manufacturer you have to meet certain numbers but from a consumers viewpoint if the rope breaks every other link in that system that did not break is complety Fckn Truck. |
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The concept that the rope is the strongest link in the system was abandoned in the late 1960's. |
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Rope may not be the strongest link in the system but if it breaks nothing else matters. Game over. My point is that while 3/8th in wedge bolts have relatively weak looking numbers they are probobly the most widely used bolt in the USA and we do not have a problem with them failing. On the rare occasions that they do fail its improperly placed and or in soft sandstone. We have those same problems with any mechanical bolt. I love glue ins and feel that they are the go to rig for popular steep sport climbs and super busy areas but wedge bolts get it done just fine for the adventure climbing that I do. While I get what you are saying about two strands it is important to note that in a real climbing scenario only one end of those two ropes is fixed to the belay. the other end is weighted by the climber so dynamic. In red neck break testing the strand that runs from the anchor to the truck and then back to the anchor again both ends of the rope are fixed which is completly unrealistic for a climbing scenario and gobs more force that you could ever generate climbing unless you took Red Bessie up the cliff with you. This of course is the reason we don't have a rash of broken rope accidents. The one wedge bolt I will Never use again is Rawl Powerwedge. the newer cone has a very sharp angle to it which can lead to the sleeve popping off the cone and the bolt loosening up. I never had that issue with the red head WW3830 or the Hilti kwick bolts. |