Capacity of a bolt through a flitch plate

[SeanTee]

I have a U bracket connecting to a flitch plate with bolts and I'm trying to understand what my bolt capacity will be.

To me it seams that I cant just use a standard shear capacity because the steel members are separated by 1.75" wood members.
I haven't been able to find any guidance on this. Any suggestions?

Thanks!

 

[SeanTee]

Is there a way to quantify the rotational stiffness of the bolted connection or is it just related to the relative "play" in oversized holes.

What if instead of bolting to the flitch I had some angles shop welded to the flitch that were then field bolted to a top plate on the post? That seams like it would take care of rotational stiffness issues, right?

My original plan for this was to have a post and beam system with moments resisted at the base of the post. But then the Architect said that he didn't want the posts to go to the concrete and instead would sit on the wood subfloor. That gave me the chills, but he said that its normal. Is that normal?

 

[KootK]

Is there a way to quantify the rotational stiffness of the bolted connection or is it just related to the relative "play" in oversized holes.

It is related to the play in the holes and, perhaps, other things. I'm sure there's a timber guru in Germany someplace that knows how to quantify the stiffness but I do not.

What if instead of bolting to the flitch I had some angles shop welded to the flitch that were then field bolted to a top plate on the post?

If you know how, your best bet is to post a sketch for everybody to comment on. It's that little tool ribbon icon with the purple camera. I'm struggling to visualize what you've got in mind.

But then the Architect said that he didn't want the posts to go to the concrete and instead would sit on the wood subfloor. That gave me the chills, but he said that its normal. Is that normal?

It's certainly normal for a wood post in a wood building. A little less normal for a steel post, depending on how heavily loaded it is and what it's function is. Keep in mind that the posts of your frame may well see some uplift and need to be tied down to something below the floor building.

It might be beneficial to share a little more information about your building:

1) What's the occupancy? Somebody's house? Hospital? Car dealership?

2) Where's the project located? Brisbane? Pittsburgh?

3) How many stories is this building?

4) What's the predominant structural typology here? Light frame wood? Post & beam? Steel?

We thrive on detail.

 

[KootK]

Just spit balling here. Don't even bother asking me how to quantify it. In soft-ish materials like wood, it's often advantageous to spread your moment connections out some.

 

[SeanTee]

1)It's a fancy house that is mostly windows.
2)its in the Appalachians near Boone. 150 mph wind zone kzt=2.11.
3) one story.
4) alot of light frame with some post and beam and steel worked in where required.

 

[KootK]

Maybe a wide flange steel beam wrapped with timber? Is the member visible anywhere?

Could you make something like a Simpson Stong-Wall work? You builder will whine about the cost of course.

 

[phamENG]

Did the architect mention why he doesn't want the post going through to the foundation? If I had to guess, I'd say it's fear of a thermal bridge from the crawl/basement up into the house through the steel. A legitimate concern (Boone gets pretty cold), but so is making sure the building doesn't fall down. If you can't make a connection work with confidence given the limits the Arch has imposed, you need to renegotiate those limits. The Arch is not a god (though many think it of themselves) and he's relying on you to make his vision a reality. Be careful, of course - push back too hard on too many things and he'll find somebody else to make his next vision a reality.

I like KootK's sketch - kinda what I was thinking, though I'm not sure you'd need the stiffeners. A heavy plate should be good for residential loads. What's the relative depth of the joists framing into this? If you can make the beam slightly shallower than the joists, then it'll leave some room to recess the plate. If you can't, the arch will have to get fancy furring it out.

If you can't make the connection at the top work, consider finding a solution that lets you take the post all the way down to the foundation. You could try to fix it at the base to resist the lateral loads, or you could try to use the force couple of the foundation and where it passes through the floor diaphragm to resist the moment. Might take some special detailing in the floor and it would probably behave more like a partially restrained connection (some moment resistance but not quite enough to call it perfectly rigid).

 

[SeanTee]

Yep thermal bridging was the reason. Are there some kind of plastic/FRP/etc. plates that are rigid and can transfer forced that are made to prevent thermal bridging? I guess you would still have steel bolts going through and creating a bridge.

I also like KootK's sketch with the GRKs but with a thick baseplate instead of the stiffener, but I'm not understanding what forces the bolts are resisting?. Or I could also use 2 angle brackets that would create a U-bracket that would be stiffer than a plate (fig 1).

The beam is made from 1.75x24" LVLs with 2x12s for the roof and 2x8s for the celling so they could be moved as required for detailing.

Would I be able to notch the beam for the baseplate since there will be GRKs to prevent splitting of the grain (fig. 2)?

I need to get 15 ft-k of capacity out of the connection, but since its so screwy I plan to overshoot that by a bit.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1579613915/tips/wood_moment_connection_h7sayw.pdf[/url]

This is a drawing of my other thought stemming from dhengr's idea but shop welding the angles:
[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1579619137/tips/moment_connection_welded_akpjhg.pdf[/url]

Thanks!

 

[phamENG]

That's a big LVL. Probably special order. And heavy. So I think all steel will be your best bet here. By the time you put in the steel plate and build it up with the 24" deep LVLs, you'll have a big, heavy beast that probably won't save any money over a wide flange beam (check the weight of your flitch beam vs. an acceptable steel shape - the concern about steel is often weight and the crane needed to lift it). You already have steel on the job, so it shouldn't be a big deal to use a steel beam. And your connection will be a lot easier (search for AISC design calculation example for moment connections, continuous beam over column connection).

Simpson makes top flange hangers that can be welded to the beam flange, or you can detail a nailer to be fastened to it with bolts or PAFs.

As far as the thermal bridge issue goes - there aren't a lot of great options right now. I'm not aware of a structurally rated material that has zero thermal conductivity - if you can think of one you'll be a millionaire real quick. Unfortunately, most architects seem to think we have access to such materials. It may come down to wrapping it in insulation below the floor level (but be careful about if/where condensation forms). I'd also suggest using a wide flange column or other open section if you can - that would prevent creating a path for heat to move freely up the cavity of an HSS column.