Wood Lattice Warping

[H57]

During the course of a project I have been asked about some interior lattice work. The lattice work is constructed of 2x12 maple that spans ~14'. Each end is supported by a hanger off of a wood beam.

My question is how often should the top and bottom flanges be braced to limit warping or bowing?

As all the framing is exposed I was thinking of using a continuous 1x top and bottom with solid blocking spaced along the length to prevent rotation.

Any thoughts?

 

[ishvaaag]

All this comes to if the beam has enough strength, LTB included. If you can't get the significant load be hanged from the bottom then I would start by making the hangers take the load from the upper part of the beam and act as guides against rotation. If the loads may derive to something prone to rotate the beam I would resource to harsher measures. Then examine if the chords are in size in accord with your ideas and acceptable to the owner; if not some transaction around bracing inmediately would start, that may be of different kinds, top or top and bottom, with rotation restraint at some points etc, all in accord with what wanted.

 

[H57]

The issue that I have is not bracing required due to the loading. It is bracing required to prevent distortion, warping, or rotating of the wood due to the cut of the wood.

 

[ishvaaag]

The designs in maple

http://www.thefind.com/search?query=lattice+panel+maple

show to have relatively coarse restraint every 2 ft aproximately, maybe it is the extent to which it works without noticeably moving.

 

[MiketheEngineer]

To add to H57 - "or changes in humidity" which affects any wood product...

 

[dhengr]

H57:
You have some image of what you are talking about, or are looking at something you want to replicate, whereas we haven’t got the vaguest idea what the hell you are calling a lattice, and made out of maple 2x12's to boot. Show us a picture or we are all spinning our wheels and wasting our time. No offense ishvaaag, you guessed and it appears you missed by a mile, since your doors don’t have much 2x12 material in them, but what you found is what I would call lattice.

If it were really a lattice wouldn’t the crossing members tend to brace each other? Is this a finished ceiling or such like? Wouldn’t the cross connection details tie the cross member together and be your real challenge? If you come across a method for calculating warping of sawn lumber please publish it because no one else has been able to do that yet. I can look at a piece of warped lumber and make a decent effort at explaining why that happened. But, I can’t look at a piece of lumber and tell you what it’s going to do in the way of warping. Some orientations of grain, in a piece of sawn lumber cause crook, some cause bowing, some cause cupping, some cause twisting, and these are all called warping. Make it out of 3/4" maple plywood, 2 plys, one side good, and face glued together, and edged. That’s about as stable as you can get with wood. And, you can hide your connection detail with the edging and trim.

 

[H57]

Please see the attached sketch. The 2x12's are interior open wood elements added by the architect for look. They are spanning between structural beams.

My concern is that they will warp, cup, twist, etc. given the span and that they are unbraced.

As the architect wants to keep these as open as possible my thought was to add solid blocking between some of the joists and then brace all of the joists to this using some continuous 1x3 material top and bottom. I have shown what I am thinking in red on the attached sketch.

What I don't know is how much of an issue the architect will have using solid maple, and in turn how much bracing to add to minimize the issues.

Any input would be appreciated.

 

[dhengr]

Good, symmetrical, quarter sawn lumber is about as stable as you can get, but it’s very pricy, and most likely not even available in 14' long maple 2x12's. I can guess 90% ± of the time how to lay flooring and decking to get it to cup, convex up, so it won’t hold water. But, it’s screwed or nailed down to inhibit most other forms of warpage at regular intervals. There really is no answer to the question you are asking, it’s a crap shoot, multiplied by the number of 2x12's you have in your assembly. And, you have to get with the Arch. and explain this, you can’t guarantee something like this, and you end up looking smarter, not incompetent, for bring this to his attention at this point in the design process. Get with him and find out how critical perfection is and what he’s willing to pay for it. Or if you are worried about nothing.

Your sketch is good and really helps with understanding, but that isn’t what I would have guessed a lattice was. But, you still leave much to the imagination. You show the glue lams as being 2' or more deep, so probably a fair distance above the fl. and I assume your fake joists only carry their own weight. Can anyone see a little warpage or even see that they are maple, for the premium that’ll cost, and given the lighting conditions? Certainly hardness and textural appearance shouldn’t be a big deal, or are they? Color contrast you get with stain. Your lines of blocking with a 1x flange t&b would help, but I can’t tell you how many. And, that introduces an aesthetic feature which I better let you and the Arch. fight out.

This looks like work for a finish carpenter, not a structural engineer. And, he would make these out of two side pieces of 1/2" plywd.; with 3/4" or 1" plywd. blocking btwn. and at side piece butt joints; with a 1x width + 1/4" ripped (1/8" reveal each side) for the t&b flanges. And, if he was real cleaver, he would cut a notch in each end of the top flange about 1&1/2" long, so he could slide these up over a knife plate, same thickness as inner blocks, and screwed to the glue lams. Thus getting rid of the ugly Simpson joist hangers.