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Author Topic: Angle Iron Connection for Post and Tie Beam Connection  (Read 1115 times)

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Offline Jjoness4

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Angle Iron Connection for Post and Tie Beam Connection
« on: September 05, 2017, 10:01:19 am »
We are building a small cabin for a church camp using volunteer labor for the most part.  We want to use an angle iron connection between the vertical post and tie beams.  The angle is 3" by 3" (1/4").  The tie beam will have no load except the weight of the beam which is 7x7 and 20 feet long oak.  I used this connection in a  barn loft I built many years ago and it has served well with a lot more loading than the one shown below.  The lag bolts will be 5/8" by 4 inch long.  I know this is somewhat blasphemy to suggest a joint such as this on a timber framing forum but it will be the way we have to do it.  My question is primarily concerning the angle iron size and bolt size.  There will be four foot angle braces (3"x5") across this joint. 

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Offline Roger Nair

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Re: Angle Iron Connection for Post and Tie Beam Connection
« Reply #1 on: September 05, 2017, 12:51:31 pm »
The structural context is missing.  There would be a roof above, I guess, and does that roof want to spread the plates?  The "tie beam" with very short distance from the end to bolts will not be able to resist much spreading force.  More complete drawings with roof detail is needed.  The lag screws should be replaced with through bolts, in all cases.
An optimist believes this is the best of all possible worlds, the pessimist fears that the optimist is correct.--James Branch Cabell

Offline Jjoness4

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Re: Angle Iron Connection for Post and Tie Beam Connection
« Reply #2 on: September 05, 2017, 05:43:36 pm »
The structural context is missing.  There would be a roof above, I guess, and does that roof want to spread the plates?  The "tie beam" with very short distance from the end to bolts will not be able to resist much spreading force.  More complete drawings with roof detail is needed.  The lag screws should be replaced with through bolts, in all cases.

Sorry for the missing information.  Below are some Sketch Up views (they are not precise but only conceptual) so I hope the idea for the structure can be determined. They are to scale.  We do plan on 3 by 6 collar ties about three feet down from the roof peak.  They are not shown.   We will plan on all connections being done with through carriage bolts and washers as you suggest instead of lag bolts.  There will be birds mouth on the rafter to beam intersection, secured with six inch timber lok screws through the top of the rafter and into the beam.






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Online brianJ

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Re: Angle Iron Connection for Post and Tie Beam Connection
« Reply #3 on: September 05, 2017, 06:21:36 pm »
Why wouldn't you make the post 7 inches shorter andlay the beamdirectly on top?

Offline Roger Nair

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Re: Angle Iron Connection for Post and Tie Beam Connection
« Reply #4 on: September 05, 2017, 10:11:36 pm »
Jjoness, clearly the frame you have presented will have rafter feet thrusting against the plates and you will need that thrust quantified and have the post to tie connection specified.  You will need steel gussets on both sides bolted through  or perhaps a heavy u-strap that wraps the post and gives a long end distance for the bolts in the tie.  Also outward mid span deflection my be a concern.  My opinion is to get qualified help.
An optimist believes this is the best of all possible worlds, the pessimist fears that the optimist is correct.--James Branch Cabell

Offline Don P

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Re: Angle Iron Connection for Post and Tie Beam Connection
« Reply #5 on: September 06, 2017, 08:28:22 am »
That's always good advice.
I like brianJ's idea but think I'd go the other way and put the ties on top of the plate alongside and attached to each rafter couple. Smooth strong machine bolts not an allthreaded carriage bolt. If you put a tie across each rafter pair it'll make things simpler and stronger as far as restraining the rafter outward horizontal thrust.

I'm assuming you'll have studs under the plate to help support it, otherwise you need to check it for vertical load as well.

Offline Hilltop366

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Re: Angle Iron Connection for Post and Tie Beam Connection
« Reply #6 on: September 06, 2017, 08:56:57 am »
Or a 2" by ? on each side of the rafter pair bolted through.

One concern would be the ends of the 2" by ? splitting at the bolt holes.

Offline Jjoness4

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Re: Angle Iron Connection for Post and Tie Beam Connection
« Reply #7 on: September 07, 2017, 08:33:43 pm »
Thanks for all your very helpful comments.  I am having a structural engineer  take a look at the plans now based on some of your concerns.  I will let you know what he says. 
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Offline MbfVA

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Re: Angle Iron Connection for Post and Tie Beam Connection
« Reply #8 on: September 08, 2017, 02:29:00 am »
....Smooth strong machine bolts not an allthreaded carriage bolt."

No dog in this fight ( maybe later in our design process), but I do have a ?

I think I understand the reason for not using lag screws, but why end only threaded versus fully threaded bolts--

Is it cost or engineering?

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Offline Don P

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Re: Angle Iron Connection for Post and Tie Beam Connection
« Reply #9 on: September 08, 2017, 06:31:39 am »
Look at the root diameter difference first and then the stress riser caused by the threading. As much as possible try to use a smooth dowel for bolted connections. When withdrawal is part of the equation like with a lag or nail, well, there is more going on, but for me lags have always sheared right where the threading begins.

As an aside, if you use 2x for the bottom chord I'd nail or timber screw the side plates on, spread the load out over many small fasteners in a relatively weak material like wood rather than concentrating the load onto a couple of places. Also if one nail out of a dozen fails it isn't as bad as one bolt out of two failing.

Offline MbfVA

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Re: Angle Iron Connection for Post and Tie Beam Connection
« Reply #10 on: September 26, 2017, 01:52:24 am »
 Good point on the many small vs few big ones.

Kind of the other side of "nibbled to death by ducks".

That is why I carry a bunch of short sheet rock screws and an electric screwdriver with me when I am doing maintenance, for quick easy repairs, and I use several small ones rather than one or 2 large ones.
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Offline Don P

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Re: Angle Iron Connection for Post and Tie Beam Connection
« Reply #11 on: September 26, 2017, 04:24:47 am »
now you've gone and done it  :D one more thing to think about in that.
brittle vs ductile failures. drive a sheetrock screw partially into a board and smack it sideways with a hammer. do the same to a nail. the brittle screw fails suddenly in shear with no warning where the ductile nail distorts, groans, gives all kinds of warning that it is in distress. the sheetrock screw is good in withdrawal, it does its job well, but don't use it structurally.

Offline MbfVA

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Re: Angle Iron Connection for Post and Tie Beam Connection
« Reply #12 on: September 26, 2017, 09:37:15 am »
 relax Don, I only use them for repairs or putting up electrical boxes surface mount, etc.  The point I was making was something like, one ductile nail might do it, but I woukd use two or three sheet rock screws, that way if one does fail, the other two will hold.

Also, I use the term sheet rock screw generically--there are a number of sheet rock "style" screws, variations which can be used just like nails or other more venerated fasteners, and which have great sheer strength.  The blue ones that Lowes sells come to mind, drill a pilot hole for one of those, and it'll go in great and hold better than a nail. And it won't split the wood, nor will you need a monkey claw to pull it out &  start over when it bends an inch or so from seating itself  smiley_tom_dizzy03

I have noted that screw specs are usually included by the architect/engineer.
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Offline Don P

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Re: Angle Iron Connection for Post and Tie Beam Connection
« Reply #13 on: September 26, 2017, 10:53:34 am »
go carefully with screws used structurally. the NDS specs on the steel for those tables, such as the awc connections calc, call for the same type of ductile steel used in nails, those are the soft screws that are miserable to drive. Many are now hardened to improve driving but become brittle, drywall and deck screws. then there are the engineered high tensile steel screws, the fastenmasters, ledgerlock and simpson hanger screws, etc. you'll find an ESR building code approval number and usually allowable load tables on the box. those are expensive but are the real deal when you're doing structural work.

Offline Don P

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Re: Angle Iron Connection for Post and Tie Beam Connection
« Reply #14 on: October 01, 2017, 11:32:19 am »
Maybe beating the horse but a good example reared its head
we are shopping for deck type screws to attach the sheathing on the roof of the barn. With screws we can do a little trial end error shimming if needed on top of the skimmed log rafters. Withdrawal strength is needed for uplift, when the wind gets under the tin but good shear strength is also needed when the wind racks the building. The metal panels if screwed in the valleys as per manufacturer provide diaphragm bracing to the roof, if the sheathing connections can take shear. I looked for specs/approvals on the screws at the building supply, none. I have no connection to this company but will probably order theirs, this is the ESR report giving loads/strengths and approval for structural use. it shows that the steel used exceeds the minimum bending yield strength called for in a structural screw. That report is what I look for with engineered components.
http://www.icc-es.org/reports/pdf_files//ESR-3201.pdf

in the esr I found something that didn't make me glad. the shear table is based on wood with a specific gravity of .67,,, white oak. I'm going through and into tulip poplar .42. i'll use the tables in the NDS, which is also the connections calc on the awc website to check those screw dimensions at poplar specific gravity. This is conservative where if I used the esr number for dense wood the connection capacity would be 176 lbs i'll use the nds number of 90 lbs for this screw in poplar.

Offline MbfVA

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Re: Angle Iron Connection for Post and Tie Beam Connection
« Reply #15 on: October 04, 2017, 05:42:14 am »
 OK, Don, here's a new fastener  solution  for you, or at least new to me: Timberlinx.   Canadian-based.   They're not cheap (though the exchange rate helps), but they look like an interesting alternative solution, somewhere between true timber framing and post and beam.

www.timberlinx.com

The straight in 1.125 inch holes required to use them look pretty easy to drill using the jig that they sell for $450.  It appears that these fasteners can allow for some bad behavior by the green wood OFTEN used for timber framing. Hold your fire, Don.

 The sales person recommended also using an HD tongue and groove arrangement at big joints, I'm going to get more of a description from him soon I hope. He suggested that that cuts down on twisting problems common to timber framing.  I am probably mooshing the terminology here.

 I intend to acquire a sample and show it to our building inspector, our designer and to an engineer 'round here.  I am also going to try to get a ruby extension or whatever it's called to use with sketchup.  There will need to be several since these things come in various lengths.

They have a US distributor in North Carolina which is also a timber framing company.  I spoke with a salesman there today, very interesting.

 Searching the fforum before posting this did not reveal a lot of experience, though there were a lot of comments. The hard-core timber framers don't like them right away of course.   I saw lots of argument about how much labor they would save.  However I also saw where someone said it takes 45 minutes to do a quality mortise and tenon joint, cannot imagine this system takes that long, especially after practice.  I suspect this post  might re-ignite that debate.  Got my helmet on.

I note they're available in stainless steel, which should avoid the problem of the wood interacting with the metal.   Probably good for our planned oak framing, but they look to be about 50% more expensive.   we'll see as this plan progresses, if we decide to use these fasteners.

The same salesperson gave me a $90 per square foot ballpark bid on timber framing a 4000 square-foot, four corners only, simple box.  Yeeouch!  Glad I've got my saw mill & my own forest, and several experienced timber frame carpenters to help, who also like to hunt on our game infested property.  Heh, heh!
www.ordinary.com (really); Jim
Always learning & questioning authority
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Liebherr 621C, Bobcat A300, 430
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Ford/Chevy/Porsche
and a few more...
Did I mention, a very small bank account?