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Old 11-27-2010, 08:40 PM   #31
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Avoiding sistering using wire rope?


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Originally Posted by mrgins View Post
Don't do it! It won't work. Do you have room to install a steel flitch plate on it?
Thanks for your warning!

Please see post #20. This is simply an in-shop experiment that I will attempt once I get some free time. I began by thinking I might try it as I have some rafters that are inaccessible for sistering and I'm sure many others also are faced with this or a similar situation. I have since cut a false window into the gable-end and loaded lumber into the attic that way, and sistering has begun as we speak.

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Old 11-27-2010, 09:01 PM   #32
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Avoiding sistering using wire rope?


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Originally Posted by WillK View Post
As much as I haven't really fully taken the time to comprehend what you're proposing in the initial post, when I got to this point in reading the thread, I started to think "Hmm... this is starting to sound ill-advised"

You may want to think about a real danger that might come with localized stiffening of a structural member. Let me refer you to some background material:

http://www.buildingscience.com/docum...d-but-strange/

The part I'm thinking of in particular is the nature of wood to expand and contract with moisture being absorbed and expelled. Now this is normal and natural. What concerns me is if the bottom of the wood is being constrained by anything that would stiffen the bottom, what could happen is the bottom will be relatively fixed in length, the top will be less constrained and try to expand, and what you will get is a piece of wood that wants to not be straight.
This is a thoughtful point, well described.

I would think that the wood around the rod would still absorb humidity and expand around the rod, however not as much as if the original wood that the rod replaced were still there to expand along with it.

The rod would not run the full length of the joist, just the centre 2/3rds or so, so an amount of on-axis humidity-based expansion should still occur within the joist, but likely not as much as were the rod not there.

This may be the wrench thrown into the works!

Cheers, Jp
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Old 11-29-2010, 04:28 PM   #33
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Avoiding sistering using wire rope?


I looked up steel flitch plate, as a solution offered by mrgins in an earlier post, and found, under Google Images, this interesting photo gallery of a crew taking the bend out of barn beams using rebar lowered into a slot cut into the beams from above, the rebar slot then filled with epoxy:

http://www.timber.org.uk/beamup.html

It looks as if hogging and buckling of the beam are taken into consideration since the rebar is piled up within the slot, so humidity expansion would effect the upper layers similar to how it would the lower, -the rebar is within both, similar to a flitch plate but with no steel visible from below.
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Old 11-29-2010, 04:52 PM   #34
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Avoiding sistering using wire rope?


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Originally Posted by jpwarren View Post
I have since cut a false window into the gable-end and loaded lumber into the attic that way, and sistering has begun as we speak.
AHA! If you've cut a hole in the gable end, it might be easier to build a strongback. What this is, is a 2x4 laid perpedicular to, and flat on the tops of the ceiling joists, then a 12"x8' strip of 3/4" plywood is glued and screwed to the edge of the 2x4. Make as many of these as you need to span the area that needs stiffening, but make sure the butt joints in the plywood are staggered so they don't match the butt joints of the 2x4s. Then add another layer of plywood that spans the joints in the first layer of plywood, glueing and screwing them together. Once you've assembled the whole strongback, just start screwing the 2x4 to the top of the joists. You will need to make sure each end of the beam is supported on a wall and is blocked up with 2x4s until it is supported at the same height as the tops of the ceiling joists. That is a lot easier than trying to sister joinsts and having to crawl into the eaves.
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Old 11-29-2010, 07:05 PM   #35
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Avoiding sistering using wire rope?


Too bad I'm doing rafters! Thanks anyway, that sounds a good idea.

My house is quite an odd-ball; inside the attic is a slightly shed roof, almost flat, made of layers of tarpaper with tar and gravel on top, on a raftered frame. You can walk around, dance even, on it no problem.

I think the house was once an assemblage of sheds; kitchen shed, bathroom shed, bedroom shed; then someone decided to wall them all within a traditional brick bungalow and fill in the spaces between sheds with a couple of traditional joist ceilings.

It might have been a store, with store up front at the street, then kitchen and bathroom behind, then bedroom downstairs. What I am concerned about is did they, they must have, built a foundation under the new brick wall.
It was done in '57 and you'd never know it from outside as everything appears fine, so I think they must have.

Makes it interesting putting in a bathroom fan however, as you have to ice-axe your way through the gravel and tar layers on the roof to get to the wood of the shed roof, then cut through that into the space below to get to the drywall ceiling!

Its kind of a nice thought that we have two roofs however, as there is a 350 year old oak tree that has a number of huge branches, and a scarred burr where one busted off and must have landed in our back yard one blustery night not that long ago! (We bought last May, after this happened) and we sleep with that tree in the yard next door, within branch-reach of our bedroom window.

Cheers, Jp
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Old 12-31-2010, 03:04 AM   #36
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Avoiding sistering using wire rope?


I'm sure it could work if engineered, tensioned correctly, etc. like pre-cast post tensioned concrete

however i'm not sure why you would, if your aim is just to add rigidity to the floor system.

Nailing in a line of blocking would probably work better and you wouldn't have to reinvent the wheel.

One reason why blocking is used....
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Old 12-31-2010, 08:02 PM   #37
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Avoiding sistering using wire rope?


Don't underestimate the strength that just basic cross bracing can add to floor joists.

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