Replies

1. 
   DavidxDoud | Sep 18, 2008 06:53am | #1

   let me be the first to suggest running your plan past an engineer -

   other than that, if I'm bolting wood together, I use carriage bolts -

   big boxes carrying them?

   dunno - farm stores or good hardwares have them or can order them -

   "there's enough for everyone"
2. 
   MikeHennessy | Sep 18, 2008 03:02pm | #2

   Are these patches entirely on the exterior, or will they run past the wall?

   Mike Hennessy
   Pittsburgh, PA

3. 
   frenchy | Sep 18, 2008 03:53pm | #3

   BillA

     Are these going in blind? Then carriage bolts won't work. You will need lag bolts..

    second more smaller lags then a few large ones makes a stronger connection.

     third  predrill everything! use a drill bit equal to the shank of the screw threads plus a larger one for the untreaded shank and if you don't want the bolts to be visable use a third large enough to hold the socket you intend to use to either bring the head flush with the wood or set it below and put a peg over the hole to make the repair invisable. If you just let the threads turn themselves in you only achieve about 75% of the rated strength . 

     Fourth Cedar has tannic acids in it.. if you use regular steel bolts the tannic acid will react with the steel cause the steel to rust and the resultant will cause the wood to rot.

    You have to use stainless steel!

     My hardware store and big box store has stainless steel lag bolts up to six inches long. Beyond that you have to go to specialist stores..

      Fifth this repair is a crutch at best. It will buy you time.  If it is strong enough  depends on what the original size was.  dramatically oversized?  ok maybe it will hold for a while.  Built to the lowest possible cost?  Highly likely to fail. 

    Note, A lot of A frames were built to be relatively low cost homes. 

    

    

4. 
   joeh | Sep 18, 2008 06:15pm | #4

   Most of the PT I see is not anything I'd consider for structural use.

   It's soggy hem/fir that shrinks for months.

   All PT needs stainless fasteners.

   Your plan doesn't sound good to me, you need an engineer to advise you.

   Joe H

1. 
   BillHartmann | Sep 18, 2008 06:19pm | #5

   "Most of the PT I see is not anything I'd consider for structural use.It's soggy hem/fir that shrinks for months."That is only West coast area.Most of the US southern yellow pine is used..
   .
   A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

1. 
   joeh | Sep 18, 2008 07:19pm | #6

   Forgot about that.

   We don't see any of that here, just this soggy spongy stuff.

   Still doesn't sound like much of a plan though.

   Joe H

5. 
   Dinosaur | Sep 18, 2008 09:10pm | #7

   1. Use the same species as the original framing member. Never mix species in a structural splice.

   2. Use structurally-rated glue to make the splice, and if possible use clamps (lots of them) instead of bolts to compress the joint while the glue dries. Bolt-holes weaken the framing member.

   2a. If you must use bolts, use stainless, and spec. grade IV or better.

   3. As others have suggested, get an engineer to sign off on this; if this splice fails, the entire structure could drop right into bed with you. Not a fun way to spend your evening....

   Dinosaur

   How now, Mighty Sauron, that thou art not brought
   low by this? For thine evil pales before that which
   foolish men call Justice....
   

   

1. 
   BillA | Sep 19, 2008 07:28am | #8

   Thanks for the responses. My replies to all of the comments:

   1. The beam penetrates the wall. The reality of the area to work with is that the splices will have to be inside the house.

   2. Good catch on using corrosion resistant bolts on the PTL. I hadn't thought of that one. The recommendation of Gr IV or better is good.

   3. It looks like PTL lumber can be used structurally, although I understand some may not prefer it. According to the American Wood Council, the knockdown in strength for PTL is about 20%, and the knockdown for modulus is about 5%. So you just have to size for it. Also, they recommend contacting the mfg. to get their recommended design values. So the key will be to replace the bad wood with material of equivalent stiffness and load carrying capacity.

   4. An adhesive joint would be nice. But I'm not a big fan of adhesive bonds in major structural applications like this one, as the joint strength is sensitive to surface prep. Peel loads can also have an effect.

   5. A bolted joint can be easily designed using the values in the NDS Design Values for Wood Construction. I'm a structural engineer - of the aerospace type, so designing a bolted joint is a no-brainer for me.

1. 
   Dinosaur | Sep 19, 2008 08:13am | #9

   the key will be to replace the bad wood with material of equivalent stiffness and load carrying capacity.

   Concur. That's why I suggested using the same wood species and grade for the spliced-in pieces as the original member.

   An adhesive joint would be nice. But I'm not a big fan of adhesive bonds in major structural applications like this one, as the joint strength is sensitive to surface prep. Peel loads can also have an effect.

   Also concur about the critical nature of surface prep, but that's a fabrication issue which you should be able to deal with. (I am not familiar with the term 'peel load', however; if you could explain that I'd feel like I learned something new today.)

   A point to think about is that the scarcity of really big timbers in recent years has caused builders to develop massive glue-lams capable of very long spans and as an engineer you know how strong they are. In other words, the technology to make a solid glue joint for this splice exists. It's just a matter of applying it well, as you pointed out.

   A bolted joint can be easily designed using the values in the NDS Design Values for Wood Construction. I'm a structural engineer - of the aerospace type, so designing a bolted joint is a no-brainer for me.

   I'm sure that's true, but such a design will almost certainly require thick, bulky sistered cheeks--not an elegant solution especially for something as minimalist in æsthetic as an A-frame. And I think you said it will be inside the house, thus visible in the living quarters?

   Perhaps as a less visually intrusive alternative to a wood-sistered bolted splice, a flitch-plate splice?

   Dinosaur

   How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

1. 
   BillA | Sep 19, 2008 11:00pm | #16

   http://www.azom.com/Details.asp?ArticleID=190

    

   Peel is kind of hard to explain with words. Check out the website at the link provided. Look at Figs 1-3. As you pull on the ends of a lap joint, it wants to straighten out, which causes the over-lapped ends of each piece at the bond to want to pull away perpendicular to the adhesive bond line. Fig. 3 shows the difference between good and bad bonded joint designs. I would only use designs rated "very good" or better.

   Also, I was looking at the beams today. 2 of the 4 beams, i think, won't accomodate a double lap bolted splice. The penetration at the wall is too close to other structure for it to fit. Will probably require a bolted butt splice using metal splice plates. Asthetically, I do not mind a bolted splice on the interior. Could use a little paint and make it look kind of like timber frame construction.

   The point about the beam penetrating the wall and picking up moisture is well-taken. I bet when it was built they took a standard A-frame design and cut in an 8' vertical wall on that side. It has a door and windows.

    

1. 
   Dinosaur | Sep 22, 2008 04:38am | #17

   Thanks for that link; it was very interesting.

   All through this discussion, I've been thinking scarf joint or stepped lap; to my mind only one of those would present enough glued surface to make a repair splice structurally solid (a finger joint would too, but it's simply not feasible in a repair like this).

   So, I was pleased to see both those joints rated 'very good' or 'excellent'. It's always fun for an autodidact when the egg-heads with the diplomas agree with his dicta.... ;o)

    

    

   PS--if you do use a scarf joint, you'll do yourself a favour if you either key it or insert a few locator pins to keep it registered while you apply the clamps. Don't ask me how I know this, LOL....

   Dinosaur

   How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

2. 
   BillA | Sep 22, 2008 05:44am | #18

   good tip. I appreciate it.

2. 
   MikeHennessy | Sep 19, 2008 02:11pm | #11

   "The beam penetrates the wall. "

   That clinches it. I would NOT do any sort of splicing without an engineer designing the fix, since the spliced piece will hold up the roof load. You need to consider the length of the spliced piece, how to attach it, how the attachment method will weaken the members, shear and torsional forces -- too much going on for a "seat 'o the pants fix.

   Mike HennessyPittsburgh, PA

1. 
   frenchy | Sep 19, 2008 04:32pm | #13

   Mike

    He is an engineer!

     The book he's referring to is the standard book a structural engineer would use..  Not terribly hard to understand even for stupid 'ol me. 

   I think he's got his ducks in a row..

1. 
   MikeHennessy | Sep 19, 2008 08:37pm | #15

   "Mike, He is an engineer!"

   DOH!

   Guess he won't have to look to hard to find one then! ;-)

   Mike HennessyPittsburgh, PA

3. 
   frenchy | Sep 19, 2008 04:37pm | #14

   BillA

    I think I know what happened to your beam (which really should be the first consideration)..

    Any beam which penetrates a structure deals with various moisture levels.. that moisture is what causes the rot not a "weak Board"  or something like that. repair it well and you're like to repair it again..

    the design is flawed..

     If you read a little about moisture migration in wood you should understand what I'm trying to say..

6. 
   MisterT | Sep 19, 2008 01:30pm | #10

   If you burn it down you will be able to sift the bolts out of the ashes...

   ;oI

   .
   .
   "After the laws of Physics, everything else is opinion"

   -Neil deGrasse Tyson
   .
   .
   .
   If Pasta and Antipasta meet is it the end of the Universe???

7. 
   Catskinner | Sep 19, 2008 03:12pm | #12

   I've done these sorts of repairs under the supervision of an engineer.

   You have received a lot of good advice here already.

   Bottom line, you need an engineer.