Vaulted Hip Roof

[XR250]

Got an 18x18 ft. carport with a pyramid, vaulted hip roof. I am showing a dogleg W8x24 beam to support the 1 3/4” LVL hips. Trying to create a clean detail for attaching the hips to the beam. I am thinking welding a 1/4” backing plate to the beam flanges and then plug welding a Simpson HRC1.81 to the plate. Anyone got any better ideas?

Thanks!

 

[KootK]

With respect to cost and ease of construction, I'm not sure that it gets any better than that. Are you happy with the durability aspect in what will, I presume, essentially be a sheltered, outdoor environment? Does aesthetics matter here? If so, I might tend towards knife plate connections coming off of the beam to the sides of the LVL. Depending on the degree of cost consciousness at play, I might also double up the LVL just so that they could sandwich the knife plates.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[XR250]

With respect to cost and ease of construction, I'm not sure that it gets any better than that. Are you happy with the durability aspect in what will, I presume, essentially be a sheltered, outdoor environment? Does aesthetics matter here? I

Everything is covered in 1x T&G so aesthetics do not matter if it all fits within the hip and rafters space.

I though about the knife plates, but worry about them getting the angles correct.

 

[XR250]

Another idea.....

 

[KootK]

Meh. Not very pretty. Will the tension side notches on the LVL check out?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

Just saw your post about it not needing to be sexy. I like the first option better unless you really are concerned with durability.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[dhengr]

XR250:
If your kinked steel beam is carrying any load, it loads the top tie beams at mid span vertically and laterally. Maybe not so easy to deal with. You have the tie (tension) beams atop the columns all around. Why not put a bearing shoe over each column and in line with each hip (hip ridge line)? Then the four LVL have a horiz. bearing seat cut (gravity load) , and a vert. plumb cut (for thrust) and the lower end of the LVL just sits down into that shoe, with a couple bolts. Then some fairly simple steel cross up at the top ties the four sets of LVL’s together.

 

[KootK]

dhengr makes a convincing argument. That's probably the natural load path based on stiffness anyhow. Although I suppose that the steel beam might aid erection.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[XR250]

@dhengr - great idea - I think I will run with it. Don't know if i even need an iron cross at the top. Might be able to use a 4x4 wood support post that could be cut off after framing.

As far as the kinked beam goes, why is it loading the tie beams laterally?

 

[txeng91]

XR250 is right, if there is a moment connection at the ridge there is no need for lateral restraint at the beam connection, the W8x24 would just need to be stiff enough to prevent too much horizontal displacement at the supports.

That being said I have done pretty much the same design dhengr described before and I think it's more than adequate provided the spans are not too long, which in this case you are probably right at that threshold. You would just need to make sure to size the lvls and connections for gravity and thrust.

 

[XR250]

Just looked at the Arch. section a little closer. The raised heel might make the shoe idea more challenging...

 

[rdubs]

Since you have steel tie beams and columns, would it be possible to make those the moment connections thus reducing the moment at the base of the columns? Looks like you have the makings of a tension ring with the steel tie beams. The LVLs, if fitted tightly at the peak with the proper bracket, will be self-supporting. The LVL lateral will go into the tension ring tie beams. The rafters will be simply-supported off the LVLs and the tie beams.

 

[KootK]

Raise the beams up or lower the heel. This is one of those situations where the architecture should adapt to allow for sensible structure. As a four sided hip, I can't imagine that it's terribly important for the thing to have it's heel configuration perfectly matching neighboring stuff.

So, backing it up a bit, did the glulam guys suggest a base detail that you can share with us? Or communicate the process that would be involved?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[XR250]

Raise the beams up or lower the heel. This is one of those situations where the architecture should adapt to allow for sensible structure. As a four sided hip, I can't imagine that it's terribly important for the thing to have it's heel configuration perfectly matching neighboring stuff.

So, backing it up a bit, did the glulam guys suggest a base detail that you can share with us? Or communicate the process that would be involved?

Just got off the phone with the Arch. He ain't budging on that as it works best with his uplighting. I may go back to the kinked beam.

The glulam folks said they could either provide a moment resisting base or I could bury the post in concrete. I did go too deep into the base with them as the use of glulams was still up in the air.

 

[KootK]

Raise the beams and add some packing on the bottom to get back to the uplighting advantageous profile?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[XR250]

Raise the beams and add some packing on the bottom to get back to the uplighting advantageous profile?

The beams are an exposed architectural element. They seem wed to the current plan. No real skin off my back either way (as I am doing it hourly) other than I prefer efficient structures.

 

[KootK]

Yeah, sometimes you just gotta give the people what the people want...

Still I worry that the pyramid/tension ring path will be the stiffest and you'll end up drawing lots of load to the ridge tail connections no matter what you do with the cranked steel beam.

What if you left the ring beams where they are but then cantilevered the columns up past them a bit to improve the rafter connections? On some beefy, moment frame steel columns, that shouldn't hurt anything with respect to the columns.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[BAretired]

Why not get rid of the W8x24 cranked beam and let the structure work like a pyramid? A temporary column could be used to support the hip beams at midspan.

BA

 

[XR250]

What if you left the ring beams where they are but then cantilevered the columns up past them a bit to improve the rafter connections? On some beefy, moment frame steel columns, that shouldn't hurt anything with respect to the columns.

That is a great idea. Lemme mess around with it. You have any ideas for a shoe that can be easily fab'ed? I was thinking about switching to dbl. 2x8's for the hips as they will fit in the rafter space better. For the shoe i was thinking of slicing the face off a vertical HSS3 1/2x3 1/2x1/4. Might be better to just weld up some plates. I have not calc'ed out the hip thrust yet so I should prolly start there.

 

[KootK]

That is a great idea...You have any ideas for a shoe that can be easily fab'ed?

Yeah, I feel compelled to revisit the issue of my previous firing at this juncture.

If it were my baby, I'd just weld three vertical plates to the column cap plate. You know, so long as they were reasonably sized plates. 1"-1.5" minimum.

If you want to go bargain basement on this -- and I know that you do -- I suppose that you could weld a face mount Simpson hanger horizontal to the cap plate and call it good. You might need to supplement uplift capacity but that's easy enough.



I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.