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Author Topic: Angle Iron Connection for Post and Tie Beam Connection  (Read 590 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.
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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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Offline 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.