Support long hips from outside?

Hi folks!

I’m a long time Lurker, been reading these forums almost every day. I’m not a timber framer (really interested in it though), so there’s really not much I can contribute, but I sure have learned a lot!

I’m wondering if any of you have ever supported wide overhanging hips on the outside of the building? I’ve been messing around designing roofs with wide overhangs, in this case 4’.



I’ve run the rafter ties under the beams and out to the common rafters which seems like it’ll give me adequate support, but the hips are left unsupported.



My solution are these double 2x6 knee braces that butt into the posts on the corner, and lap each side of the hip. Seems like it would be pretty easy to cut and install, but the weak point would be the connection (TimberLok lags) where they butt into the posts. Plus, they really don’t look all that nice.







Do any of you have a better solution?? I suppose I could use 4x stock for the hips, but these rafters are curved, and cutting thru 4x on a curve would be pretty difficult.

Not being an expert I will throw in my opinion so the experts may point out the errors in my thoughts.
The key problem is the screws do not offer the strength you probably need (shear off or tear out)
I would infill the 2x6 with a 2x5 or 2x4 with the edge flush on top and receesed an inch or so on the bottom (fancies it up a little) and cut to act as a shoulder on the rafter end and jointed into the post. Epoxied together would stiffen and strengten it considerably, or bolt it in recessed holes and cap with 1 inch dowels.

Bob

Bob, those TimberLok lags are pretty strong with great pull out resistance, and I have thought about what you suggested with using infill material between those two braces, and meeting up with the post, but I'm not really happy with my design idea. I'm hoping someone's addressed this issue before and has a more time tested, traditional soulution for me.

What program are you using to create this drawing?

I think you'll need to research some wind up-lift solutions to make this building safe.....

Jim Rogers

You're right Jim, I still need to get some engneering done. Do you see any obvious issues with uplift I should address?

I'm putting the posts in to the ground for lateral stability.


I use SketchUp for these drawings!

I just created a 3D PDF of this pavilion that you can zoom on and rotate around, so you can poke around in it if you'd like. http://www.woodsshop.com/Misc.htm

sure would like to hear any observations or suggestions!

Using braces like that is certainly within the realm of possibility.

I'd try and put in a more positive connector than a pair of timlocks, however. Uplift can be a big concern; the the framing style should be able to handle it, just so long as everything is connected well.

Depending on where you are at geographically, post anchorage into the soil may be a bigger deal than anything, to keep the thing from pulling out or overturning. If the wind isn't too bad, you might be ok.

The thing that jumps out at me is there is a lot weight / surface area high up in the air, without a lot of bracing. Wind or seismic lateral forces could really get this thing to twist unless those posts are REALLY stiff.

Certainly will be neat looking, and, looks like you can really can make SketchUp work for you.

Joe

J.W. I have run into this on occasion. The braces up to the hips are a good start, but I concur with the opinion that the timlocks are inadequate. The problem with a roof like this is that only 1/4 of the weight is inside the square formed by the posts. (3/4 of the roof weight is outboard of the posts) I have solved this in the past by creating a heavy structural fascia along with heavy braced hips. I also have some concern regarding overall stability. My philosophy on exterior structures is that parts near the ground will need to be replaced someday. It is more work up front, but I recommend not sinking the posts in concrete. Design a post base connection that allows the post to be replaced in the future. Good luck.

Hey Joe, you know, I haven't really considered the posts pulling out .. is this really an issue when they're down 4' or so? You're right though about there being alot of forces high up without much bracing. This real wide 4' overhang is just something I'm exploring right now.

The posts are a little whimpy and undersized considering the racking that could happen. My other structures like these (with 2'10" and less roof overhangs), which are a little bigger in footprint, (10'x10' , 12' x12') all have 6x8 posts instead of the 6x6 I show for this one.

Not Trim Lock, but TimberLok lags. Haven't you heard about these? They seem pretty good to me as a Builder. I thought Timber Framers were using these alot these days?


I put some Technical Info and Specs about them that you can go download and view on this page http://www.woodsshop.com/Misc.htm

Say Joe, I've never run this corner connection by a Structural Engineer before, but could you tell me what you think about this post/beam connection? I'm trying to not use real visable connection hardware.




Chris, can you tell me a little more about those structural facias, and braced hips? Got any pics of either??

Oh, and that TLok pic I posted shows 4" thru 10".

Posts pulling out of the ground probably won't be a concern (that roof looks real heavy), but, depending on how windy it is there, you never know. It looks a symmetrical structure, so torsional effects may not be a concern either, depending on the site. I was just throwing out some of the things that popped into my head, some of which may or may not be relevant once investigated a little bit.

Timlocks are what we call those screws (at least around here.) They are great things, and, have a lot of uses in a modern timber frame structure. But, when loaded in shear, there ulitmate capacity is function of how big the shaft of the screw is, and, they tend to be fairly small diameter (1/4" ish). They hold things together in withdrawal real well though, and, provide some clamping when they get screwed together.

As some folks have already mentioned, a lot of the weight of that structure is in the overhang, and, if there was an additional piece of wood between the two dimensional lumber braces to provide direct bearing of that hip, you would only be relying on screws at the heal, which could make for a much better scenario.

As far as the corner connections, it may be adequate. Having the stub of the post run by is the saving grace though. Lags into endgrain tend not to be a great connection, and, isn't doing a whole lot in this case. But, screws into the stub are a good way to go. Helps tie everything together, and, certainly helps transfer any uplift from wind to the post if that is a concern. An additional screw down through the lap connection to tie the two together there may be well spent.

But, otherwise looks good, and, I'm sure you'll figure the rest out.

Joe

Thanks so much for the good advice Joe! You've given me some very good information!

Don't suppose any of you know of a Structural Engineer familiar with structures like these, in the San Diego area?

Chris, I'd still like to hear some more about those structural facias, and braced hips, sounds like they might help me out.

Derek, I design/build garden and landscape structures, and I'm especially interested in Japanese Style, especially with curved roofs. I've already designed quite a few similar structures as this one, but this time I'm, I don't know, trying to push the envelope as far as the broad overhang goes.

I don't think this will work though, too much overhang!

Thanks Derek, I really like my curved roof designs!
Here's my 10'x12' Azumaya (Dutch Hip) being built!





I'm looking in to having the rafters cut on a CNC machine, that would be interesting to watch, and I wouldn't have to clean up all the sawdust!

To Joe Wood:
I posted instructions of how to find a structural engineer through the "Resource guide" under the thread heading "Structural Engineer."

Jim Rogers

Jim, where is that Resource Guide? I found the ResourceGuide.pdf but there aren't any Threads in there.

Joe Wood, that is awesome work! Gotta love those curves.

Joe, there is no forum there, therefore no threads.
The resource guide is a database of names and addresses.
Click on the "search" link and you'll go to the search page where you can follow the instructions on the thread in this section of the Ask the Experts titled "structural engineer".

It's all there, you just clicked the wrong link...

Jim Rogers

Link to search page: Click HERE for link to search page.....

Feeling pretty dense today Jim. Do you mean I should do a search on that page like in this screenshot?


it only came back with one Engineer, way up in Truckee, Ca.

Yes, Joe that's what I meant.
You can widen your search by not entering a state, and then you'll get all listed.
Using their web page addresses you can check each one out, and you may find someone who is also licensed in CA.
You may not, but it's a start.
Good luck with your project and research.

Jim Rogers

Got it, and thanks again Jim. Appreciate all the other advice too!

I'd still like to hear some more about those structural facias, and braced hips if you could Chris.

I have Derek, but those don't help support the hip outboard I don't think, and they wouldn't help with the lateral stability either because they only tie the roof structure to the beams, and not from the posts to beams (I could be wrong about this?).

putting ypur posts into the consrete is asking for trouble down the road.for example, here in Florida we use cypress a lot for fence posts and when placed in concrete even with sloping the top it lasts maybe 4-5 years.you will never be able to keep out all the moisture. however, when set on top of a concrete footing at the bottom of a 3' deep footing with a gravel and sand back fill it will last almost indefinately and also be as solid as concrete. if strength or resistance to up lift is your goal try anchoring metal post clips into the footing and bolt them on to the post.

Do you have any pics or drawings of those metal post clips you've used before Titmas?

My reason for setting the posts into the ground is to gain lateral stability without using knee braces.

You know, like I said earlier, any rot I've ever seen with posts set in to the concrete has always been at the surface, so my thinking is that with the concrete slope for drainage at grade, and the copper wrapped around the post, rot shouldn't be able to even start.

Joe:
The issue here is the movement of the wood, from summer to winter or dry season to wet season.
Wood moves, your copper flashing will not move the same, in my opinion.
This leads to gaps between the wood and copper.
Rain water will find its way between the wood and copper and get down into the pocket created by placing the wood into the concrete.
A concrete cup below grade with a piece of wood in, will let in water, and the wood will rot.
This is why they have code rules to prevent builders from doing this as it does happen.
You'll need to end the wood above grade and do all the concrete and rebar stuff you want below grade.
There are many hold down systems for posts to concrete.
Look at Simpson strong ties at: click here for link to Simpson Strong Tie site

You'll find lots of things that will work and be allowed by code rules.

Jim Rogers

You do have a point there Jim, but, I haven't been able to find any type of hardware that would give me the lateral stability, besides having something made up at a local steel place, (which I'm not against doing), it's just that I haven't seen a good design that wouldn't be too hard to install and which would look nice.

I'd like to see anyone's pictures or drawings of post bases that give that stability ..

Joe,
Your willingness to use a local steel fabricator makes post bottoms a small bucks breeze. See the guild project in 2003 at the Vermont School Barn raising and visit their site too. You will find barn red hinges on the post bottoms. The hinge leaf fixed to the concrete pier is bolted down with the bolts imbedded in the concrete. The upper leaf is lagged to the post bottom with some bitchithane rubber between the hinge and the post. There is a 3/8" or so lip around this upper leaf which mates with the other when the hinge is closed. After the frame is true here comes the welder to permanently join the hinge leaves together. Don't and won't move in any direction . The bolts & lags are 3/4" stock if I remember correctly. The pier top, the hinge, the post bottoms are well above any water/snow line.
You set up , insert the 3/8" hinge pins and push/pull the wall/bent up. If you search the pictures about the project, including the Mountain School website,you will find these bright red goodies in various levels of detail.
If memory serves me correctly Ed Levin was the responsible design engineer on these.

Dear Joe:
A structural fascia (SF)is one where it acts as a beam spanning between the hip and a designated rafter. This rafter is usually the first one that has a back span bigger than the cantilever (or is propped up by a bracket.) The connections can be hard to develop as the overhang becomes bigger. The SF supports the outboard end of the hip jacks that have little or no backspan. To overcome the connection problems, one can drop the hip below the plane of the rafters or use a hip much deeper than the rafters. The SF can then be supported from below at the hip.
Keep in mind that on a square hipped roof, when the over hang length exceeds 1/5 of the side of the supporting square, there is more weight outside the square than inside the square. The result of this is that without braces or skyhooks to support the overhang, you have uplift at the peak (this is where a brick cupola would come in handy.) As I mentioned before, on your proposed design, 3/4 of your roof area is outboard of your supporting square. Your structure is 3/4 of the the way to resembling the structure of an umbrella.

Regards,
Chris