Joist question... drop-in or dovetail

[Jim_Rogers]

I like that design a lot and I use that as a tying joist to hold the sills and tie beam to each other.

Jim Rogers

[Jay C. White Cloud]

Hi timberwrestler,

You are correct, it is called a soffit tenon, (soffit meaning the underside of an architectural structure such as an arch, a balcony, or overhanging eaves, etc.)  It is a wonderful joint if you are doing a "member reduction."  The tusk is the first one in my example and can even be done using a spline that would connect both inserting members coming into the receiving member from opposite sides.  These are a wonderful family of joints that can really tie and strengthen a frame.

[Aikenback]

Hi everyone,
Yes I am aware of neutral axis but also was thinking of the shear area down the center between the compression and tension areas (obviously, lol). I always considered the shear area to be as wide as the beam is, but if the forces are hourglass shaped, I can see there is less concern.

Some new LVL beam material in conventional framing is marked in that area as an area drilling is allowed to some degree. It was more a full row of mortises I was leery about. Especially from both sides.

I can always run numbers, and I guess advice is a click away. usually the beams I am mortising into are oversized just for aesthetics anyway. It could be an extra advantage. As far as the beam/joist reductions, that is one of those counter intuitive things.

We were taught never to notch the bottom of a supporting member without supporting the full thickness of the member in front of the notch. Otherwise the member is only considered as deep as the notch.

Then an engineer told me how much I could reduce a fairly major beam one time and I was amazed. I was reading a pdf I downloaded from the tfg, and they actually gave a simple formula for the radius they would like to see based on the amount of reduction. Not only a great look, but spreads the shear from the reduction over a larger area. Like you guys didn't know.

I probably read it recently in one of Jim Rogers posts from years ago. Lol.

P.S. I said I downloaded the thesis, didn't say I got thru it, lol.

[Aikenback]

By the way, very informitive discussion for me. One of these days I will start compiling reference materials from the tfg etc. I do have several recommended books. People really have no idea how educated true carpenters really are. Its a shame.

[Jay C. White Cloud]

Hi Aikenback,

Check out this link: http://blog.ftet.biz/2009/01/keyed-and-key-laminated-beams.html. on "key-laminated beams."  There has been several "keyed" and "tooth" lamination techniques through the ages to make small beams into big beams.  When you consider the dynamic at play when designing one of these "traditional laminated" beams, you begin to understand the brilliance behind "tusk" and "soffit" joinery.

I can't remember where on here I shared the "rules of 2s and 3s -3s and 4s" but the day I was taught it, they also taught me "less is more," when reducing a the end of a beam to avoid "concentrated shear" at a notch or to save from taking more out of a receiving member.

Regards,

jay

[Aikenback]

Yes I have seen the keyed beams, they are pretty cool. And totally make sense. I notice, after thinking a bit, the amount of material between tenons in a row of soffit/tusk mortises would control a significant amount of shear anyway. Thanks for the link.

Sorry Dan we hijacked your thread, I guess your going to have to decide yourself, this could go on for ever! Lol

[Jay C. White Cloud]

I'm sorry too, I have only been here a short time, and now think maybe I should make suggestions about moving certain conversation, (tangents,) to a new post.  Maybe once I'm more familiar with the forums culture, I will suggest that when we begin to "hijack" a thread.

Hi Aikenback,

I knew once you thought about the two together you would make the connection! ;)

Regards,

jay.