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#1
Posted to alt.home.repair,sci.electronics.repair,rec.woodworking
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
John Robertson wrote, on Fri, 17 Oct 2014 23:46:50 -0700:
Better check the specs of the wire rope, the owner may be going by the rated maximum capacity (12,200 lb for 3/8" wire rope) and only derating it 50%. Note the manufacturer recommends only a 20% load factor I asked the owner about the weight of the deck, where this came back: https://c2.staticflickr.com/6/5608/1...8d70ba58_b.jpg Hello Danny: Thanks for your help last week. I couldn't have done it without you.h You seemed skeptical about my estimate of the first bridge section. Given a 2x10 weighs 3.37 lbs per foot. Given a 2x6 weighs 2.00 lbs per foot. 3x16x3.37 = 162 lbs for the three long boards 2x10x3.37 = 68 lbs for the two end boards 2x6 2.00 lbs/ft 10x2x32 = 640 lbs for the decking 870 lbs per 16 foot section. So if there are 5 sections (80 feet), or 6 sections (96 feet) we have 4,350 lbs or 5,220 lbs for the deck. The cables can support 28,000 lbs. That gives us 22,780 lbs for the house and occupants, assuming the only support is the cable. If we allow that some of the weight is supported by the posts and the trees, we have even more leeway. If the house is 24 feet long and ten feet wide, it will weigh about 8,000 pounds. Add 4,000 pounds for furnishings and appliances. That gives us 10,780 pounds of leeway for occupants. But I plan to have most of the house weight supported by the redwoods, not by the cable. |
#2
Posted to alt.home.repair,sci.electronics.repair,rec.woodworking
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
On 10/21/2014, 1:10 PM, Danny D. wrote:
John Robertson wrote, on Fri, 17 Oct 2014 23:46:50 -0700: Better check the specs of the wire rope, the owner may be going by the rated maximum capacity (12,200 lb for 3/8" wire rope) and only derating it 50%. Note the manufacturer recommends only a 20% load factor I asked the owner about the weight of the deck, where this came back: https://c2.staticflickr.com/6/5608/1...8d70ba58_b.jpg Hello Danny: Thanks for your help last week. I couldn't have done it without you.h You seemed skeptical about my estimate of the first bridge section. Given a 2x10 weighs 3.37 lbs per foot. Given a 2x6 weighs 2.00 lbs per foot. 3x16x3.37 = 162 lbs for the three long boards 2x10x3.37 = 68 lbs for the two end boards 2x6 2.00 lbs/ft 10x2x32 = 640 lbs for the decking 870 lbs per 16 foot section. So if there are 5 sections (80 feet), or 6 sections (96 feet) we have 4,350 lbs or 5,220 lbs for the deck. The cables can support 28,000 lbs. That gives us 22,780 lbs for the house and occupants, assuming the only support is the cable. If we allow that some of the weight is supported by the posts and the trees, we have even more leeway. If the house is 24 feet long and ten feet wide, it will weigh about 8,000 pounds. Add 4,000 pounds for furnishings and appliances. That gives us 10,780 pounds of leeway for occupants. But I plan to have most of the house weight supported by the redwoods, not by the cable. It again all hinges on the diameter of the cable (wire rope) they are using and how it is secured. If it is 3/8" then I wouldn't go near it assuming he is going by the maximum load. Based on his reasoning (28,000 load spread over two cables) he needs at least 7/8" (12,900 lb safe load each), but 1" (16,700 lb) would be better. Attaching the house to the tree will save a lot of weight, however trees grow larger in diameter so the support must allow for that somehow. Also his securing of the wire rope must be flawless, and the fact that he has already stressed the rope in a few places with the clamps has weakened the original wire rope significantly. However he doesn't appear to be willing to get an inspector, so I'll assume I'll read about this upcoming disaster in the newspaper in the near future (next couple of years). Just because you are clever doesn't mean you are right. Some of us can be quite smug...(ducking) John :-#(# -- (Please post followups or tech inquiries to the newsgroup) John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out." |
#3
Posted to alt.home.repair,sci.electronics.repair,rec.woodworking
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We started the 100-foot long 10-foot wide deck high up in the California redwoods
"John Robertson" wrote: It again all hinges on the diameter of the cable (wire rope) they are using and how it is secured. If it is 3/8" then I wouldn't go near it assuming he is going by the maximum load. Based on his reasoning (28,000 load spread over two cables) he needs at least 7/8" (12,900 lb safe load each), but 1" (16,700 lb) would be better. Attaching the house to the tree will save a lot of weight, however trees grow larger in diameter so the support must allow for that somehow. Also his securing of the wire rope must be flawless, and the fact that he has already stressed the rope in a few places with the clamps has weakened the original wire rope significantly. However he doesn't appear to be willing to get an inspector, so I'll assume I'll read about this upcoming disaster in the newspaper in the near future (next couple of years). Just because you are clever doesn't mean you are right. Some of us can be quite smug...(ducking) ---------------------------------------------------------- You can buy them books, BUT if they eat the covers. Lew |
#4
Posted to alt.home.repair
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We started the 100-foot long 10-foot wide deck high up in the California redwoods
On Tue, 21 Oct 2014 14:25:46 -0700, John Robertson
wrote in However he doesn't appear to be willing to get an inspector, so I'll assume I'll read about this upcoming disaster in the newspaper in the near future (next couple of years). The lawyers are going to love it. Everyone from the wire rope manufacturer to the water-boy will be sued. -- I kill-file all messages posted through Google Groups. |
#5
Posted to alt.home.repair,sci.electronics.repair,rec.woodworking
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
On 10/21/2014 4:35 PM, Lew Hodgett wrote:
"John Robertson" wrote: It again all hinges on the diameter of the cable (wire rope) they are using and how it is secured. If it is 3/8" then I wouldn't go near it assuming he is going by the maximum load. Based on his reasoning (28,000 load spread over two cables) he needs at least 7/8" (12,900 lb safe load each), but 1" (16,700 lb) would be better. Attaching the house to the tree will save a lot of weight, however trees grow larger in diameter so the support must allow for that somehow. Also his securing of the wire rope must be flawless, and the fact that he has already stressed the rope in a few places with the clamps has weakened the original wire rope significantly. However he doesn't appear to be willing to get an inspector, so I'll assume I'll read about this upcoming disaster in the newspaper in the near future (next couple of years). Just because you are clever doesn't mean you are right. Some of us can be quite smug...(ducking) ---------------------------------------------------------- You can buy them books, BUT if they eat the covers. Lew Now days Lew you buy them books and they eat the Teacher! |
#6
Posted to alt.home.repair,rec.woodworking
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
On 10/21/2014 3:10 PM, Danny D. wrote:
John Robertson wrote, on Fri, 17 Oct 2014 23:46:50 -0700: Better check the specs of the wire rope, the owner may be going by the rated maximum capacity (12,200 lb for 3/8" wire rope) and only derating it 50%. Note the manufacturer recommends only a 20% load factor I asked the owner about the weight of the deck, where this came back: https://c2.staticflickr.com/6/5608/1...8d70ba58_b.jpg .... 870 lbs per 16 foot section. So if there are 5 sections (80 feet), or 6 sections (96 feet) we have 4,350 lbs or 5,220 lbs for the deck. The cables can support 28,000 lbs. The problem as others have been saying generally and that Morgans points out in another posting is this doesn't account for the geometry. Consider for simplicity the condition if the cables were mounted on telephone poles on level ground 100-ft apart. Say you tension the cable so there's 10-ft sag in the middle. Using the tabulated weight for 3/8" cable, I estimated that it takes only about 30 lbf to achieve that sag so we'll ignore that for the time being. With 10 ft drop at midpoint of 100 ft run, and considering that the applied load will essentially straighten the cable, if the load were at the center rather than distributed the angle between the horizontal and the cable is invtan(10/50) -- angle ~11 degrees. Now to support that load, the vertical component of the tension has to balance the weight of approximately 5000 lb. That vertical component is Tv=T sin(angle) or the cable tension T is Ty/sin(angle). Substituting numbers and noting that for small angles sin(theta)~theta, the tension to support that 5000 lb is T=W/sin(angle) = (W/2)/sin(11) -- 2500/0.2 -- 12,500 lb So, you've taken up roughly half the total strength of the cable simply by the decking. That's only a safety factor of ~2X and minimum generally accepted is 3X while for overhead rigging and personal safety of support 5X is considered prudent. As said, this isn't going to approach that kind of margin and is extremely risky going forward without more serious engineering than has happened to date. There are excellent design guides in the various handbooks that have been linked to extensively before in the previous threads; no point in reproducing them yet again if they're not going to be heeded. But, your friend really needs some input from an engineer who understands statics well enough to make some reasonable calculations for the actual geometry and design. -- That gives us 22,780 lbs for the house and occupants, assuming the only support is the cable. If we allow that some of the weight is supported by the posts and the trees, we have even more leeway. If the house is 24 feet long and ten feet wide, it will weigh about 8,000 pounds. Add 4,000 pounds for furnishings and appliances. That gives us 10,780 pounds of leeway for occupants. But I plan to have most of the house weight supported by the redwoods, not by the cable. |
#7
Posted to alt.home.repair
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We started the 100-foot long 10-foot wide deck high up in the California redwoods
On Thu, 23 Oct 2014 07:36:12 -0500, dpb wrote in
T=W/sin(angle) = (W/2)/sin(11) -- 2500/0.2 -- 12,500 lb So, you've taken up roughly half the total strength of the cable simply by the decking. That's only a safety factor of ~2X and minimum generally accepted is 3X while for overhead rigging and personal safety of support 5X is considered prudent. As said, this isn't going to approach that kind of margin and is extremely risky going forward without more serious engineering than has happened to date. There are excellent design guides in the various handbooks that have been linked to extensively before in the previous threads; no point in reproducing them yet again if they're not going to be heeded. But, your friend really needs some input from an engineer who understands statics well enough to make some reasonable calculations for the actual geometry and design. Good analysis. Unfortunately Danny D and Friends just don't seem to understand what the effect of the catenary configuration has in increasing the tension in the cable. I really hope someone convinces them to have a engineer look at their exact config and do some simple calcs as you have done above. -- Web based forums are like subscribing to 10 different newspapers and having to visit 10 different news stands to pickup each one. Email list-server groups and USENET are like having all of those newspapers delivered to your door every morning. |
#8
Posted to alt.home.repair,rec.woodworking
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
On 10/23/2014 7:36 AM, dpb wrote:
.... Consider for simplicity the condition if the cables were mounted on telephone poles on level ground 100-ft apart. Say you tension the cable so there's 10-ft sag in the middle. Using the tabulated weight for 3/8" cable, I estimated that it takes only about 30 lbf to achieve that sag so we'll ignore that for the time being. With 10 ft drop at midpoint of 100 ft run, and considering that the applied load will essentially straighten the cable, if the load were at the center rather than distributed the angle between the horizontal and the cable is invtan(10/50) -- angle ~11 degrees. Now to support that load, the vertical component of the tension has to balance the weight of approximately 5000 lb. That vertical component is Tv=T sin(angle) or the cable tension T is Ty/sin(angle). Substituting numbers and noting that for small angles sin(theta)~theta, the tension to support that 5000 lb is T=W/sin(angle) = (W/2)/sin(11) -- 2500/0.2 -- 12,500 lb So, you've taken up roughly half the total strength of the cable simply by the decking. That's only a safety factor of ~2X and minimum generally accepted is 3X while for overhead rigging and personal safety of support 5X is considered prudent. .... ERRATUM: I forgot to divide the cable limit by the two above -- the actual limit per cable is (optimistically) as used by your friend 14000, not 28000. So, the decking alone is roughly 90% of the rated breaking strength and adding a 200 lb person is 100/0.2--500 lb. You'll gain a little by considering the decking as a distributed instead of point load, but that'll be only a marginal improvement and you'll likely lose some (and potentially a lot) for the non-uniform geometry on the downhill side as that side may be almost perfectly horizontal so the amplification factor of 1/sin(theta) goes way up as Morgans feared (hence his 10X estimate). THIS IS VERY BAD... -- |
#9
Posted to alt.home.repair
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
On 10/23/2014 8:05 AM, CRNG wrote:
On Thu, 23 Oct 2014 07:36:12 -0500, wrote in T=W/sin(angle) = (W/2)/sin(11) -- 2500/0.2 -- 12,500 lb So, you've taken up roughly half the total strength of the cable simply by the decking. That's only a safety factor of ~2X and minimum generally accepted is 3X while for overhead rigging and personal safety of support 5X is considered prudent. .... Good analysis. Unfortunately Danny D and Friends just don't seem to understand what the effect of the catenary configuration has in increasing the tension in the cable. I really hope someone convinces them to have a engineer look at their exact config and do some simple calcs as you have done above. Excepting I divided the load by 2 for each cable but then compared that to the total rating of the two cables. So actually, the decking is 12,500 lb out of 14,000 breaking strength not 28,000 for the two. See my followup to myself wherein I noted the fault... -- |
#10
Posted to alt.home.repair,rec.woodworking
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
On 10/23/2014 8:13 AM, dpb wrote:
On 10/23/2014 7:36 AM, dpb wrote: ... .... T=W/sin(angle) = (W/2)/sin(11) -- 2500/0.2 -- 12,500 lb .... ERRATUM: I forgot to divide the cable limit by the two above -- the actual limit per cable is (optimistically) as used by your friend 14000, not 28000. So, the decking alone is roughly 90% of the rated breaking strength and adding a 200 lb person is 100/0.2--500 lb. You'll gain a little by considering the decking as a distributed instead of point load, but that'll be only a marginal improvement and you'll likely lose some (and potentially a lot) for the non-uniform geometry on the downhill side as that side may be almost perfectly horizontal so the amplification factor of 1/sin(theta) goes way up as Morgans feared (hence his 10X estimate). .... On the last point -- the angle at which the total tension amplification factor reaches 10X the applied load is invsin(10) -- 5.7 degrees as opposed to the 11 degrees. That's not a lot of difference. -- |
#11
Posted to alt.home.repair
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We started the 100-foot long 10-foot wide deck high up in the California redwoods
On Thu, 23 Oct 2014 08:13:06 -0500, dpb wrote in
On 10/23/2014 7:36 AM, dpb wrote: ... Consider for simplicity the condition if the cables were mounted on telephone poles on level ground 100-ft apart. Say you tension the cable so there's 10-ft sag in the middle. Using the tabulated weight for 3/8" cable, I estimated that it takes only about 30 lbf to achieve that sag so we'll ignore that for the time being. With 10 ft drop at midpoint of 100 ft run, and considering that the applied load will essentially straighten the cable, if the load were at the center rather than distributed the angle between the horizontal and the cable is invtan(10/50) -- angle ~11 degrees. Now to support that load, the vertical component of the tension has to balance the weight of approximately 5000 lb. That vertical component is Tv=T sin(angle) or the cable tension T is Ty/sin(angle). Substituting numbers and noting that for small angles sin(theta)~theta, the tension to support that 5000 lb is T=W/sin(angle) = (W/2)/sin(11) -- 2500/0.2 -- 12,500 lb So, you've taken up roughly half the total strength of the cable simply by the decking. That's only a safety factor of ~2X and minimum generally accepted is 3X while for overhead rigging and personal safety of support 5X is considered prudent. ... ERRATUM: I forgot to divide the cable limit by the two above -- the actual limit per cable is (optimistically) as used by your friend 14000, not 28000. So, the decking alone is roughly 90% of the rated breaking strength and adding a 200 lb person is 100/0.2--500 lb. You'll gain a little by considering the decking as a distributed instead of point load, but that'll be only a marginal improvement and you'll likely lose some (and potentially a lot) for the non-uniform geometry on the downhill side as that side may be almost perfectly horizontal so the amplification factor of 1/sin(theta) goes way up as Morgans feared (hence his 10X estimate). THIS IS VERY BAD... I don't think they are taking heed. They have been successful with their little neighborhood projects, and they are starting to get over confident. -- Web based forums are like subscribing to 10 different newspapers and having to visit 10 different news stands to pickup each one. Email list-server groups and USENET are like having all of those newspapers delivered to your door every morning. |
#12
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
On 10/23/2014 12:40 PM, CRNG wrote:
On Thu, 23 Oct 2014 08:13:06 -0500, wrote in .... So, the decking alone is roughly 90% of the rated breaking strength and adding a 200 lb person is 100/0.2--500 lb. You'll gain a little by considering the decking as a distributed instead of point load, but that'll be only a marginal improvement and you'll likely lose some (and potentially a lot) for the non-uniform geometry on the downhill side as that side may be almost perfectly horizontal so the amplification factor of 1/sin(theta) goes way up as Morgans feared (hence his 10X estimate). THIS IS VERY BAD... I don't think they are taking heed. They have been successful with their little neighborhood projects, and they are starting to get over confident. I think Danny D is reading responses but the friend-in-charge is apparently bullheaded-enough to not be willing to reconsider there's anything to consider other than tensile strength in straight loading. I do suggest that Danny not be committing himself to relying on this for support from this point on as it's getting at least marginal already. Of course, if the droop angles are significantly larger than the assumed 10 degree or so, then they gain a fair amount by there being a larger vertical component but it's too spooky by far as described and shown. -- |
#13
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We started the 100-foot long 10-foot wide deck high up in the California redwoods
On Thu, 23 Oct 2014 13:35:20 -0500, dpb wrote in
On 10/23/2014 12:40 PM, CRNG wrote: On Thu, 23 Oct 2014 08:13:06 -0500, wrote in ... So, the decking alone is roughly 90% of the rated breaking strength and adding a 200 lb person is 100/0.2--500 lb. You'll gain a little by considering the decking as a distributed instead of point load, but that'll be only a marginal improvement and you'll likely lose some (and potentially a lot) for the non-uniform geometry on the downhill side as that side may be almost perfectly horizontal so the amplification factor of 1/sin(theta) goes way up as Morgans feared (hence his 10X estimate). THIS IS VERY BAD... I don't think they are taking heed. They have been successful with their little neighborhood projects, and they are starting to get over confident. I think Danny D is reading responses but the friend-in-charge is apparently bullheaded-enough to not be willing to reconsider there's anything to consider other than tensile strength in straight loading. I do suggest that Danny not be committing himself to relying on this for support from this point on as it's getting at least marginal already. Of course, if the droop angles are significantly larger than the assumed 10 degree or so, then they gain a fair amount by there being a larger vertical component but it's too spooky by far as described and shown. +1 on that -- Web based forums are like subscribing to 10 different newspapers and having to visit 10 different news stands to pickup each one. Email list-server groups and USENET are like having all of those newspapers delivered to your door every morning. |
#14
Posted to alt.home.repair,sci.electronics.repair,rec.woodworking
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We started the 100-foot long 10-foot wide deck high up in the California redwoods
On Tue, 21 Oct 2014 20:10:10 +0000 (UTC), "Danny D."
wrote: John Robertson wrote, on Fri, 17 Oct 2014 23:46:50 -0700: Better check the specs of the wire rope, the owner may be going by the rated maximum capacity (12,200 lb for 3/8" wire rope) and only derating it 50%. Note the manufacturer recommends only a 20% load factor I asked the owner about the weight of the deck, where this came back: https://c2.staticflickr.com/6/5608/1...8d70ba58_b.jpg Hello Danny: Thanks for your help last week. I couldn't have done it without you.h You seemed skeptical about my estimate of the first bridge section. Given a 2x10 weighs 3.37 lbs per foot. Given a 2x6 weighs 2.00 lbs per foot. 3x16x3.37 = 162 lbs for the three long boards 2x10x3.37 = 68 lbs for the two end boards 2x6 2.00 lbs/ft 10x2x32 = 640 lbs for the decking 870 lbs per 16 foot section. So if there are 5 sections (80 feet), or 6 sections (96 feet) we have 4,350 lbs or 5,220 lbs for the deck. The cables can support 28,000 lbs. That gives us 22,780 lbs for the house and occupants, assuming the only support is the cable. If we allow that some of the weight is supported by the posts and the trees, we have even more leeway. If the house is 24 feet long and ten feet wide, it will weigh about 8,000 pounds. Add 4,000 pounds for furnishings and appliances. That gives us 10,780 pounds of leeway for occupants. But I plan to have most of the house weight supported by the redwoods, not by the cable. I see a complete failure to account for wind loads. Wind loads on this tree house will be larger than the dead loads. Ask the owner to calculate the wind loads as well. ?-) |
#15
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
On 10/23/2014 8:21 AM, dpb wrote:
On 10/23/2014 8:05 AM, CRNG wrote: On Thu, 23 Oct 2014 07:36:12 -0500, wrote in T=W/sin(angle) = (W/2)/sin(11) -- 2500/0.2 -- 12,500 lb So, you've taken up roughly half the total strength of the cable simply by the decking. That's only a safety factor of ~2X and minimum generally accepted is 3X while for overhead rigging and personal safety of support 5X is considered prudent. ... Good analysis. Unfortunately Danny D and Friends just don't seem to understand what the effect of the catenary configuration has in increasing the tension in the cable. I really hope someone convinces them to have a engineer look at their exact config and do some simple calcs as you have done above. Excepting I divided the load by 2 for each cable but then compared that to the total rating of the two cables. So actually, the decking is 12,500 lb out of 14,000 breaking strength not 28,000 for the two. See my followup to myself wherein I noted the fault... ERRATUM 2: I outsmarted meself...I left the other 2X out on purpose originally and then whiffed when came back. The free body diagram has T1 and T2 supporting the load, the tension force in each direction. Hence the actual magnitude _is_ half the total, one half going each way. So we're back to the ~2X SF for the decking which, while likely not collapsing while they're building the basic deck, isn't a good starting point for the overall structure. |
#16
Posted to alt.home.repair,sci.electronics.repair,rec.woodworking
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
Danny D. wrote, on Tue, 21 Oct 2014 20:10:10 +0000:
But I plan to have most of the house weight supported by the redwoods, not by the cable. We finished rigging up the second 16 foot section, which missed the next set of redwood trees by about a foot or two. https://c2.staticflickr.com/6/5611/1...49344c53_b.jpg Unfortunately, those two redwoods straddling the end of the 32-foot suspended section are just a tad under ten feet apart. So, we're gonna have to engineer a slight bevel inward, to squeeze in between those two trees, and then it's on to the next three or four 16-foot long 10-feet wide sections, all of which is suspended by ropes and temporary cables, at the moment, as we build it as we walk out to the edge... https://c4.staticflickr.com/4/3953/1...b58d5ecf_b.jpg |
#17
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
josephkk wrote, on Thu, 23 Oct 2014 18:23:37 -0700:
I see a complete failure to account for wind loads. Wind loads on this tree house will be larger than the dead loads. Ask the owner to calculate the wind loads as well. This is a good point so I will mention it to him. We worked on the second floating 16-foot section today, by the way. https://c4.staticflickr.com/4/3955/1...2b960f68_b.jpg So now we're suspended 32 feet straight out. Only 60 or so feet to go! |
#18
Posted to alt.home.repair,rec.woodworking,sci.electronics.repair
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
dpb wrote, on Thu, 23 Oct 2014 07:36:12 -0500:
T=W/sin(angle) = (W/2)/sin(11) -- 2500/0.2 -- 12,500 lb Wow. Those were wonderful calculations. I forwarded it all to my friend, and will reply back with his response. Meanwhile, we worked on the second section today, and we ended up stopping about 2 feet away from redwoods which we need to squeeze through. https://c4.staticflickr.com/4/3937/1...bffcce41_b.jpg |
#19
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
CRNG wrote, on Thu, 23 Oct 2014 12:40:15 -0500:
I don't think they are taking heed. They have been successful with their little neighborhood projects, and they are starting to get over confident. I think the owner is taking heed, it's just that he's a third party to this conversation (he doesn't know Usenet). BTW, here's a view from below today, when I dropped my glasses and had to climb down the steep hill to retrieve them. https://c4.staticflickr.com/4/3943/1...a8481615_b.jpg |
#20
Posted to alt.home.repair,rec.woodworking,sci.electronics.repair
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
dpb wrote, on Thu, 23 Oct 2014 13:35:20 -0500:
Of course, if the droop angles are significantly larger than the assumed 10 degree or so, then they gain a fair amount by there being a larger vertical component but it's too spooky by far as described and shown I'm sorry I haven't responded in a while. I hurt my back and was laid up but hopefully I'm better now ... The whole thing is supposed to hang from the cables, but we did anchor one end because we needed a way for people to get "on" the decking. Here's where we left it today... https://c4.staticflickr.com/4/3945/1...22bf0914_b.jpg |
#21
Posted to alt.home.repair,rec.woodworking,sci.electronics.repair
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
CRNG wrote, on Thu, 23 Oct 2014 08:05:45 -0500:
Good analysis. Unfortunately Danny D and Friends just don't seem to understand what the effect of the catenary configuration has in increasing the tension in the cable. I really hope someone convinces them to have a engineer look at their exact config and do some simple calcs as you have done above. I'm sorry I haven't been able to respond lately. We had to readjust all the cables today, with a set of 5 winches, as we had to re-balance everything once the second 16-foot section was planked. Unfortunately, I ruined my clothing, as I hadn't expected the oil to still be soaking wet ... even though it was drying outside for a day ... https://c2.staticflickr.com/6/5616/1...c2665284_b.jpg |
#22
Posted to alt.home.repair,rec.woodworking,sci.electronics.design
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
dpb wrote, on Fri, 24 Oct 2014 08:22:06 -0500:
So we're back to the ~2X SF for the decking which, while likely not collapsing while they're building the basic deck, isn't a good starting point for the overall structure. I'm forwarding all this to the owner. The only thing I can say is that it "seems" sturdy when we're both on it, and that's almost 500 pounds of people alone ... It's being supported, at the moment, by 6 separate winched vertical cables (the winches are for level adjustments). https://c2.staticflickr.com/6/5599/1...d812a890_b.jpg |
#23
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
VinnyB wrote, on Wed, 22 Oct 2014 05:58:58 -0500:
The lawyers are going to love it. Everyone from the wire rope manufacturer to the water-boy will be sued. You forgot the screw manufacturers! https://c4.staticflickr.com/4/3935/1...e1cc2650_b.jpg Notice we gave up on the lower screw (the one with the longer thread). It was just too hard to drive into the wood. Even with this nice pile driver thing from Harbor Freight! https://c4.staticflickr.com/4/3934/1...3a566c90_b.jpg The screw on top, with the shorter thread, goes in without pounding! |
#24
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We started the 100-foot long 10-foot wide deck high up in the California redwoods
"Danny D." wrote in
: josephkk wrote, on Thu, 23 Oct 2014 18:23:37 -0700: I see a complete failure to account for wind loads. Wind loads on this tree house will be larger than the dead loads. Ask the owner to calculate the wind loads as well. This is a good point so I will mention it to him. We worked on the second floating 16-foot section today, by the way. https://c4.staticflickr.com/4/3955/1...2b960f68_b.jpg So now we're suspended 32 feet straight out. Only 60 or so feet to go! See http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940) The chances of your bridge deck fluttering in a blow are fairly high. -- Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED) ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- & [dot]=. *Warning* HTML & 32K emails -- NUL |
#25
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
Ian Malcolm wrote, on Tue, 28 Oct 2014 00:21:08 +0000:
See http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940) The chances of your bridge deck fluttering in a blow are fairly high. We actually joked, a few times, about the Tacoma Narrows bridge, and, yes, I think just about everyone has seen that video of the car on the bridge and the person getting out and making it just in time. This bridge isn't nearly as long. It's only about 100 feet long, by 10 feet wide, supported on one end on the ground and on the far end about 40 or 50 feet up in a tree on a (very) steep slope. Here's what the first two 16-foot-long sections looked like today, when we ran out of oiled wood: https://c4.staticflickr.com/4/3945/1...22bf0914_b.jpg I'm currently learning how to wash good clothes to get the oil out! |
#26
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We started the 100-foot long 10-foot wide deck high up in the California redwoods
"Danny D." wrote in message ... CRNG wrote, on Thu, 23 Oct 2014 12:40:15 -0500: I don't think they are taking heed. They have been successful with their little neighborhood projects, and they are starting to get over confident. I think the owner is taking heed, it's just that he's a third party to this conversation (he doesn't know Usenet). BTW, here's a view from below today, when I dropped my glasses and had to climb down the steep hill to retrieve them. https://c4.staticflickr.com/4/3943/1...a8481615_b.jpg Pardon me for a silly suggestion but ... .... in view of the - how shall we put it - challenging ? - nature of the site, wouldn't it be a good idea to have your specs on one of those strings around your neck ? And tools like hammers, roped to your belt ? Arfa |
#27
Posted to alt.home.repair,rec.woodworking
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
On 10/27/2014 6:34 PM, Danny D. wrote:
CRNG wrote, on Thu, 23 Oct 2014 12:40:15 -0500: I don't think they are taking heed. They have been successful with their little neighborhood projects, and they are starting to get over confident. I think the owner is taking heed, it's just that he's a third party to this conversation (he doesn't know Usenet). BTW, here's a view from below today, when I dropped my glasses and had to climb down the steep hill to retrieve them. https://c4.staticflickr.com/4/3943/1...a8481615_b.jpg Where are the supporting cables in the picture--on top or just hidden by the view? What I'd like to know is can you measure the height differential between the upper and lower mounting locations and the approximate distance from the straight line between them to the low point and where that point turns out to be between the two end points. In a _very_ crude sketch.. | | A-|- | | | | -|-B | | = | | X | ____ C = xxxx _____ xxxxx A and B represent the two tieoff points, the relative height between them and then the distance from the lowpoint C in the middle somewhere to either of those plus the horizontal distance from C to the two trees represented by the vertical lines. With that could at least crudely approximate the loadings and the tension amplification from the angle of dangle, so to speak. As you can see from the previous as the angle gets smaller, the multiplier gets large quickly because there isn't much of a component of the total tension in the vertical direction to support the load. You also need to consider how much side load this is putting on those trees and how large they are at that point to handle the lateral load plus how well their root systems are capable of that additional continuous load, particularly when the ground gets saturated when it finally does rain again... -- |
#28
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
dpb wrote, on Thu, 23 Oct 2014 08:13:06 -0500:
ERRATUM: I forgot to divide the cable limit by the two above -- the actual limit per cable is (optimistically) as used by your friend 14000, not 28000. Here's the response from the neighbor building the deck... https://c4.staticflickr.com/4/3953/1...1f28763d_b.jpg The 3/8" steel suspension cable is a good deal higher than 10 feet above the deck at the ends. Currently that 3/8" steel cable is anchored at a tree about 25 feet above the deck at the beginning end of the deck. Also, the 100 foot final length of the deck was a guess that is probably a bit high, where perhaps 80 feet might be closer to the final length. So the 11 degrees may no longer still be the result of the calculations. Looking at the photos, the angle of the cable looks like around 30 degrees to me. If the height of the suspension cable above the deck is 25 feet, and the length of the deck is 80 feet, we now have 32 degrees. Using his tension formula, we get a tension of 4,718 pounds. So, I believe, that means the 3/8" suspension cable can support almost six times what we are assuming. While the deck was originally supposed to be free floating, since we decided to anchor the close end of the deck on the dirt path (so that people could just step onto the deck from the path), that end of the deck is now supported by the two fence posts, so half of its weight goes away. If, additionally, we add another fence post, in a "T" shape support, at the end of the first 16-foot-long section, then the weight of that first 16-foot-long section goes away completely, as does half the weight of the next 16-foot-long section. And we still have the option of supporting the other half by attaching it to the small redwood trees, along with half of the third section. If we really did get to 28,000 pounds of tension, the trees would pull closer together, reducing the distance, and making the angle steeper. It thus gets asymptotically harder to actually put that much tension on the cable. The treehouse itself, when it's built, will be supported mostly by the redwood trees. |
#29
Posted to alt.home.repair,rec.woodworking,sci.electronics.repair
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
Arfa Daily wrote, on Tue, 28 Oct 2014 02:05:05 +0000:
... in view of the - how shall we put it - challenging ? - nature of the site, wouldn't it be a good idea to have your specs on one of those strings around your neck ? And tools like hammers, roped to your belt ? That's a good suggestion, as we have tools all over the place! https://c4.staticflickr.com/4/3948/1...c6370a50_c.jpg Usually, we tie in when we're out on the cable, with no firm footing: https://c4.staticflickr.com/4/3947/1...fee9cb37_b.jpg And, we tie in when we're working on the steep slope below the deck: https://c4.staticflickr.com/4/3950/1...b042e8a8_b.jpg The harnesses we use are the same ones we use for climbing the hills: https://c2.staticflickr.com/6/5602/1...2eb1ee32_b.jpg Here's my setup, for example, as I was digging the fence post holes: https://c4.staticflickr.com/4/3950/1...b042e8a8_b.jpg And, here's what I used when I had to double-line rappel downslope: https://c4.staticflickr.com/4/3932/1...03b1b22c_c.jpg Even so, we've had a few of the typical gotchas, from dropping the spool of wire (where it rolled a hundred or so feet downhill before getting wedge under a fallen tree) to the inevitable search for missing glasses and hammers. Such is the nature of working in the trees... |
#30
Posted to alt.home.repair,rec.woodworking,sci.electronics.repair
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
dpb wrote, on Mon, 27 Oct 2014 21:06:58 -0500:
https://c4.staticflickr.com/4/3943/1...a8481615_b.jpg Where are the supporting cables in the picture--on top or just hidden by the view? All the supporting cables are above the deck. It's a bit hard to see in that picture from below today, but the 3/8" steel cable is glinting in the sunlight a few feet *above* the deck. https://c4.staticflickr.com/4/3943/1...a8481615_b.jpg The deck is not attached to *anything* other than the cable on the free- floating end, as we build it out. In fact, while it's hard to tell from the angle of this picture, but the end of the second 16-foot-long section is still shy of the leftmost redwood by about a foot, and maybe it's two feet shy of the right-most redwood tree: https://c2.staticflickr.com/6/5600/1...a7136264_c.jpg Here is a picture taken earlier in the day, before we planked the second 16-foot-long section, showing how the 10-foot-wide deck is suspended from the steel cables (this is the second of the two 16-foot-long sections): https://c2.staticflickr.com/6/5601/1...53aa5e3e_c.jpg |
#31
Posted to alt.home.repair,rec.woodworking,sci.electronics.repair
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
dpb wrote, on Mon, 27 Oct 2014 21:06:58 -0500:
You also need to consider how much side load this is putting on those trees and how large they are at that point to handle the lateral load plus how well their root systems are capable of that additional continuous load, particularly when the ground gets saturated when it finally does rain again... This is a good point, in that sometimes it pours out here, and this is a steep slope, so the runoff could be great. We just had a half inch of rain over the weekend, and this is a shot of the cables and the people on the decking (the dog won't go on the deck): https://c4.staticflickr.com/4/3953/1...1f28763d_b.jpg We're still about a foot from the left-most redwood here, and about two feet from the right-most redwood, so we "can" attach to them (if decided) with the third 16-foot deck section: https://c2.staticflickr.com/6/5600/1...a7136264_c.jpg |
#32
Posted to alt.home.repair,rec.woodworking,sci.electronics.repair
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We started the 100-foot long 10-foot wide deck high up in the California redwoods
"Danny D." wrote in message ... Arfa Daily wrote, on Tue, 28 Oct 2014 02:05:05 +0000: ... in view of the - how shall we put it - challenging ? - nature of the site, wouldn't it be a good idea to have your specs on one of those strings around your neck ? And tools like hammers, roped to your belt ? That's a good suggestion, as we have tools all over the place! https://c4.staticflickr.com/4/3948/1...c6370a50_c.jpg Boy oh boy ... I thought I was making a bit of a silly suggestion there ... Usually, we tie in when we're out on the cable, with no firm footing: https://c4.staticflickr.com/4/3947/1...fee9cb37_b.jpg Work clothes ? And, we tie in when we're working on the steep slope below the deck: https://c4.staticflickr.com/4/3950/1...b042e8a8_b.jpg That's concrete, yes ? Looks a little lean on the mix ... ? The harnesses we use are the same ones we use for climbing the hills: https://c2.staticflickr.com/6/5602/1...2eb1ee32_b.jpg Here's my setup, for example, as I was digging the fence post holes: https://c4.staticflickr.com/4/3950/1...b042e8a8_b.jpg And, here's what I used when I had to double-line rappel downslope: https://c4.staticflickr.com/4/3932/1...03b1b22c_c.jpg Even so, we've had a few of the typical gotchas, from dropping the spool of wire (where it rolled a hundred or so feet downhill before getting wedge under a fallen tree) to the inevitable search for missing glasses and hammers. Such is the nature of working in the trees... Hmmmm ... Arfa |
#33
Posted to alt.home.repair,rec.woodworking,sci.electronics.repair
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We started the 100-foot long 10-foot wide deck high up in the California redwoods
"Danny D." wrote in message ... dpb wrote, on Mon, 27 Oct 2014 21:06:58 -0500: You also need to consider how much side load this is putting on those trees and how large they are at that point to handle the lateral load plus how well their root systems are capable of that additional continuous load, particularly when the ground gets saturated when it finally does rain again... This is a good point, in that sometimes it pours out here, and this is a steep slope, so the runoff could be great. We just had a half inch of rain over the weekend, and this is a shot of the cables and the people on the decking (the dog won't go on the deck): Animals have a sort of 'sixth sense' about this sort of thing. Perhaps this should tell you something ... d:-} Arfa |
#34
Posted to alt.home.repair,rec.woodworking
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
On 10/27/2014 10:56 PM, Danny D. wrote:
dpb wrote, on Thu, 23 Oct 2014 08:13:06 -0500: ERRATUM: I forgot to divide the cable limit by the two above -- the actual limit per cable is (optimistically) as used by your friend 14000, not 28000. Here's the response from the neighbor building the deck... https://c4.staticflickr.com/4/3953/1...1f28763d_b.jpg The 3/8" steel suspension cable is a good deal higher than 10 feet above the deck at the ends. Currently that 3/8" steel cable is anchored at a tree about 25 feet above the deck at the beginning end of the deck. Also, the 100 foot final length of the deck was a guess that is probably a bit high, where perhaps 80 feet might be closer to the final length. So the 11 degrees may no longer still be the result of the calculations. Looking at the photos, the angle of the cable looks like around 30 degrees to me. If the height of the suspension cable above the deck is 25 feet, and the length of the deck is 80 feet, we now have 32 degrees. Using his tension formula, we get a tension of 4,718 pounds. So, I believe, that means the 3/8" suspension cable can support almost six times what we are assuming. While the deck was originally supposed to be free floating, since we decided to anchor the close end of the deck on the dirt path (so that people could just step onto the deck from the path), that end of the deck is now supported by the two fence posts, so half of its weight goes away. If, additionally, we add another fence post, in a "T" shape support, at the end of the first 16-foot-long section, then the weight of that first 16-foot-long section goes away completely, as does half the weight of the next 16-foot-long section. And we still have the option of supporting the other half by attaching it to the small redwood trees, along with half of the third section. If we really did get to 28,000 pounds of tension, the trees would pull closer together, reducing the distance, and making the angle steeper. It thus gets asymptotically harder to actually put that much tension on the cable. The treehouse itself, when it's built, will be supported mostly by the redwood trees. Some validity to the above but... While it is true that the end that is resting on the ground does have that support, it's not necessarily so that the remaining load on the cable is only half; it depends on the actual geometry of the configuration. It _might_ be half; could be more, could even be less. The previous "analysis" was simply intended as a demonstration of the effect geometry has on the overall tension required in the cable (actually, any supporting member--that it is cable in that sense is a distraction) is that which will, for the given arrangement, provide a vertical component that balances the gravity forces plus applied loads. The key lesson intended to be shown is that the vertical component is dependent upon the angle of the tension force. Thinking that "it's harder to put that much tension on the cable" isn't really so--while the trees may move some, the actual counteracting force is whatever it needs to be given the loading. If the distance is shortened enough, yes, the angle will increase but that's going to exacerbate the other issues raised of whether the root structure can sustain that continued side load (increased moment at the base) indefinitely, particularly with the addition of wind load and ground saturation and all the other things that go on. I do agree that with the one end supported that certainly helps and the idea of the second ground support at the outer end is also a good one but I'd still think it only prudent to get the input of a competent engineer to evaluate the overall structure, including the questions of the ability of the soil to hold and what would be realistic wind loads and so on. While one would presume nobody would be silly enough to be out there during a storm, it seems a sizable investment in both time and money to risk losing it all the first thunderstorm or the next coastal front with a good blow. It's certainly not unheard of uncommon for them to have 90 mph in WA where daughter is; don't know how far this is from coast nor elevation and such but would think it not unreasonable guesstimate. It's just imprudent imo to not have more than just a "seat o' the pants" look at something this ambitious and that has such a potential for serious consequences if these guesstimates are wrong. Given the $$ that have and are obviously going to be expended, a few more thrown at the design/safety issues would seem a good investment. (Or, is the issue that if does that it'll get stopped because it isn't within whatever covenants are in place for the location?) Anyways, I've had my say; simply hoping nothing does go wrong but it seems a very risky venture as is... (*) The unique thing about cable is that unless the loading is such as was presumed before that the cable is essentially straightened by the load, the tension is variable along the cable -- |
#35
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
On 10/28/2014, 2:57 AM, Arfa Daily wrote:
"Danny D." wrote in message ... dpb wrote, on Mon, 27 Oct 2014 21:06:58 -0500: You also need to consider how much side load this is putting on those trees and how large they are at that point to handle the lateral load plus how well their root systems are capable of that additional continuous load, particularly when the ground gets saturated when it finally does rain again... This is a good point, in that sometimes it pours out here, and this is a steep slope, so the runoff could be great. We just had a half inch of rain over the weekend, and this is a shot of the cables and the people on the decking (the dog won't go on the deck): Animals have a sort of 'sixth sense' about this sort of thing. Perhaps this should tell you something ... d:-} Arfa The dog is the only one paying attention to load factors. John :-#(# -- (Please post followups or tech inquiries to the newsgroup) John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out." |
#36
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
Arfa Daily wrote, on Tue, 28 Oct 2014 09:53:11 +0000:
https://c4.staticflickr.com/4/3947/1...fee9cb37_b.jpg Work clothes ? We're all retired, and, getting a bit complacent, so, we tend not to own (real) work clothes.... But, we're getting real good at buying army surplus static line! https://c4.staticflickr.com/8/7474/1...aaff11cc_b.jpg Maybe we should pick up a pair of these Ghillies as fitting work clothes, since we're always hanging around in the trees: https://c4.staticflickr.com/4/3943/1...d8aa3fd1_b.jpg |
#37
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We started the 100-foot long 10-foot wide deck high up in the California redwoods
On Mon, 27 Oct 2014 23:46:30 +0000 (UTC), "Danny D."
wrote: https://c4.staticflickr.com/4/3935/1...e1cc2650_b.jpg Notice we gave up on the lower screw (the one with the longer thread). Those screws are from GRK Fasteners... http://www.grkfasteners.com/index.php/en/ Videos on Youtube: http://www.youtube.com/user/grkfasteners/videos |
#38
Posted to alt.home.repair,rec.woodworking
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
On 10/28/2014 9:21 AM, dpb wrote:
.... (*) The unique thing about cable is that unless the loading is such as was presumed before that the cable is essentially straightened by the load, the tension is variable along the cable Ignore the above; I thought I had deleted it before posting...I was beginning an involved discussion regarding multiple loading points and all and decided against it... -- |
#39
Posted to alt.home.repair,rec.woodworking,sci.electronics.repair
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
dpb wrote, on Tue, 28 Oct 2014 09:21:42 -0500:
While it is true that the end that is resting on the ground does have that support, it's not necessarily so that the remaining load on the cable is only half; it depends on the actual geometry of the configuration. It _might_ be half; could be more, could even be less. Thanks for all the insight. Below is the owner's response to your concerns. BTW, I created an animated GIF of the entire process, as I see it, but I can't get Flickr to show the animations since Flickr turns an animated GIF into a static JPG. I'll post the animation separately, if I can figure out how to preserve the animation, but here is the starting point static JPG: https://c2.staticflickr.com/6/5605/1...4969faac_z.jpg Here is where we are right now: https://c4.staticflickr.com/8/7575/1...ed414ac3_z.jpg And here is the penultimate ending point static JPG: https://c2.staticflickr.com/6/5600/1...66bb66b1_z.jpg Here's the owners response to your valid concerns ... I wonder if they realize how huge the final redwood tree is? The tree probably weighs in excess of 2,000 tons, and has a 30 foot circumference. The smaller set of redwood trees I would estimate weighs 15 tons. In a wind of 50 mph, the small tree experiences 200,000 pounds of force due to the wind. The idea that 28,000 pounds of tension on a cable is more than it encounters in a light wind does not seem tenable. The root structures of both trees routinely handle much larger forces during a typical day. A wind blowing at 100 miles per hour generates 25 pounds of force per square foot. If that wind were blowing straight down on 800 square feet of deck, we'd have 20,000 pounds of force. I consider that unlikely. :-) Edge-on, we have 67 square feet, or 1,666 pounds of force. But that is also somewhat unlikely. Sideways forces will add a little to the cable tension, but will mostly be taken up pushing against the trees and the support posts. The deck will weigh in the neighborhood of 5,000 pounds, and has 800 square feet of maximum surface area. Lifting that, requires 6.25 pounds per square foot, or a wind speed straight up of 50 miles per hour. But the deck is held down at the ends and in the middle by either trees or posts, which also limit the amount it can tilt or twist. The surrounding trees limit the wind considerably. The assumption that the engineering is "seat of the pants", or that the mathematics have not been done is incorrect, but the ideas are all good because I don't want to miss something, by not thinking about it at least. Let them know that I appreciate their advice! (Please invite them to lunch on Wednesdays in Redwood City if they're local.) |
#40
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We started the 100-foot long 10-foot wide deck high up in theCalifornia redwoods
Oren wrote, on Tue, 28 Oct 2014 10:37:43 -0700:
Those screws are from GRK Fasteners... The ones with the longer threads were really stinky because you needed four hands, while suspended on the cable, to screw them in. The ones with the shorter threads only take 3 hands. Here's an animated GIF, I just made, of the suspension bridge... http://i62.tinypic.com/ieeakx.gif |
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