Steel Plates-Lag Bolts or Through Bolts

[dollar]

I am looking to add some additional steel plates and 90 Degree Steel plates to my timber frame build.

On the my scarf joints I know to use through bolts going through plates on each side of ridge beam.

My question is on the connection for the post to top chord-this is a mortice and tenon joint and I was going to add a steel plate welded at 90 degree angle under the top chord to post.

The post is 8 x 8 and the top chord is 8 x 10.

Would a 6" lag bolt work here or does it have to be through bolt?  Could I only do the through bolt on the top chord and lag bolts into post?

Or are lag bolts totally unacceptable?

[Don P]

I've read it 3 times and the jello ain't jellin  . I need a sketch with arrows and details.

But, generic stuff till then, lemme find a link...
These are the glulam folks but they do steel connections. This is some stock details and do/don't stuff.
AITC 104 all pages2 L01 (1) (plib.org)

This is their library page with this on it;
Publications | Pacific Lumber Inspection Bureau (plib.org)

The NDS at awc.org ,hit their publications tab. It has lag and bolt design capacities. Under their calculators tab is a connections calc that spits out the same results as the tables in the books.

[Brad_bb]

Why are you trying to use plates?  That's not traditional.  Why do you think you need them?

I typically see structural wood screws like the Wurth brand to reinforce a scarf, though not everyone uses hardware.

What wood is it?  Oak is very acidic and doesn't mix well with metal so you need to protect any metal.

[rusticretreater]

Over time lag bolts rust and can become loose. Expansion and contraction will also serve to loosen the bolt and also cause it to lose grip. If you must use bolts, use through bolts which you can tighten again and again without the wood giving way.

A 45 degree angle mortised support is a much better way of handling this however.

[Don P]

I'm assuming this was in reference to the kits you are thinking about?
28 x 44 Timber Frame/Post and Beam Pavilion in Timber Framing/Log construction (forestryforum.com)


I was in the Wood Handbook yesterday in chapter 8, more good reading;
Fastenings (usda.gov)

When steel side plates are used, the bolt-bearing stress parallel to grain at joint proportional limit is approximately 25% greater than that for wood side plates. The joint deformation at proportional limit is much smaller with steel side plates. If loads at equivalent joint deformation are compared, the load for joints with steel side plates is approximately 75% greater than that for wood side plates. Pre-1991 design criteria included increases in connection strength with steel side plates; post-1991 design criteria include steel side plate behavior in the yield model equations. For perpendicular-to-grain loading, the same loads are obtained for wood and steel side plates