Timber frame metal connectors/shrinkage?
I am doing some very early planning for a new home and would like to incorporate some psuedo “timber frame” elements by having some of the second floor floor joists exposed to the main floor below. The joists would be heavier and on wider centers (i.e. 4×10 on 36″ centers rather than normal 2×10 16o/c).
I’ve seen some photos of timber frame construction that use custom heavy metal connectors. These appear to be cut and welded from 1/4″ bar stock and/or angle. *They often have two or more bolts across the width of one of the wooden members.
So my question is what happens when the wooden member drys out and shrinks while the dimension between the bolts is constant? This would cause it to split unless there is something I am missing. Do you bore a slightly larger hole for one of the bolts and allow the wood to move at this location? (i.e. plan for and design how the movement will be accomodated.)
(Rim joists shrink like 1/4″ in height, steel not so much!)
Thanks
John
Replies
It will work without bolts, especially if they are pseudo. The floor sheathing above, nailed to it will keep it in place. A tight bracket will limit its twisting.
I had one Architect yell at the Plumber because a 4" was cut into his nice expose ceiling. I stopped the Archi from yelling when I said "Just wait, it will be worst when he runs the exposed drain lines".
OK let me correct a few items for you
First when joints are made with metal they technically are not timberframed but rather post and beam..
Timberframe uses pegs made of wood for the connection..
Second plates are not always needed if the joint design is correct and the strength can be made with simple lag bolts rather than through bolts..
Third when wood dries out it shrinks rather than swells so the timbers loosen up and need to be retightened when dried enough.. timbers can take years even a decade or more to dry completely so periodic retightening is normal.. At least untill the wood has reached normal dryness. Further wood shrinks across width not length so splitting is unlikely..
Fourth all lag bolts need at least two and normally three differant holes drilled for each one.. the first hole drilled is the largest one to exceed the diameter of the socket needed to tighten up the bolt.. (unless you are willing to leave bolt heads exposed) you then need a hole large for the shank and finally it's required to have a pilot hole of the diameter of the core of the threads.. In addition it's highly recommended that with large timbers you use a lubricant..
This is an extremely interesting subject to me. If you want I have several pictures posted showing such details (you have to look extremly closely)
Frenchy
Thank you for you reply.
I actually like the industrial look of exposed timber washers, black metal connectors and square nuts.
If you imagine a (second) floor joist attached to the rim joist by a short length of large angle iron and four bolts, what happens when the joists shrink 1/4" and the upper and lower bolt in each leg of the angle stay put? Wouldn't this cause a long crack to form mid width the joist going from the end towards the mid-span?
(Maybe tomorrow I will sketch something.)
Yes, please send me some photos.
John
John that's fine. I'm not objecting to post and beam at all. It's a good honest look if that's what you want..
It makes drilling for connections much simpler..
Regarding the potential for cracking you're assuming that there is something to resist the shrinking Timbers will yield that 1/8 inch of shrinkage.
Heck my timbers moved 3/4 of an inch. This was a nice straight beam with no diviant grain and about a year later a 12 inch wide white oak beam had bowed in over 3/4 of an inch. It bowed in a short span too! Less than 7 foot span and it bowed that much.. In addition it also pulled 4 other 6x6 white oak beams along with it.. This was a timber which had been drying for 3 years before being put up and was nice and straight when put up.. wood moves, you need to learn to deal with it..
It pulled the SIP's in which means that it had massive power to achieve that.. Eventually the SIP's pulled it back to today it only bows about 3/8ths of an inch..
The only way to cause a big timber to split is if the way it's connected prevents the wood movement. What wood do you intend to use? what size? That will tell me how much movement you need to plan for. Which direction is it's growth rings? Remember wood swells and shrinks due to moisture changes (only) in width and not much in any other direction.. So simple orientation will eliminate the risk..
Regarding the photos they are already here all you need to do is go over to the left and enter in the advanced search function 85891.1 & 94941.1 scroll through the whole thing..
Frenchy
I have built some furniture over the years and am familiar with seasonal shrinking and swelling of wood. The wood I will probably use is local Douglas Fir. The issue I think is shrinkage across the grain (i.e. a rim joist shrinking 1/4" in the first year after close-in). My concern is bolting a piece of steel across the width of the joist/beam and then having the wood shrink and split.
If you scroll about one third down the following link they address this as "restrained bolted connections".
http://www.timber.org.au/NTEP/menu.asp?id=160
I guess the safe thing to do is fabricate joist hangers out of thicker steel and then have the bolts only clamping the joist to it (and in oversized holes). This way the load is bearing on the bottom of the hanger and the wood is relatively free to shrink and settle about the bolts.
John
Do you have a moisture meter to check on how green the timbers will be? If the wood is near 7-10% moisture content then the only adjustment needs to be for seasonal movement.. that's pretty small.
One way to ensure the connection won't split the wood is to use a slightly larger diameter tube with a lengthwise cut in it.. make the tube a tiny bit longer than the beam and when you tighten the bolts the pressure is on the floating tube which will give a great deal before the pressure can cause the wood to split..
Explain to the owners that there is absolutely nothing you can do about normal checking which is going to happen with heart centers that most timbers are made of.. The only way is to use reclaimed wood that has already dried completely and is free of checks..
I carefully dried my timbers for at least 3 years before I erected them and for a couple of years they remained relativly free of checks but about 4 years ago some timbers checked noticably.. Normal drying stuff..
Did I ever show you this job I did out in East Hampton with two other guys last winter? Took the 3 of us 3 long days. They're not holding anything up but they're real beams and the purlins are actually going into tenons we made in the main beams...very tightly!!
Looked pretty cool!
http://picasaweb.google.com/andybuildz/TimberFramingACeilingInEastHamptonLINY208?feat=directlink
http://www.cliffordrenovations.com
http://www.ramdass.org
I bet the tapers had some serious stilts to work on that ceiling. Probably had to duct tape on extra 2x4 extensions.
(that thar's some nice work!)~ Ted W ~
Cheap Tools! - MyToolbox.netMeet me at House & Builder!
Thanks....Tapers probably used rolling scaffolds like we did after they got as high as they could offa their stilts.
I just sold my stilts. Had a pair stolen then bought some new ones that went up over 48" and they freaked me out even at the lowest setting. I really didn't need stilts that big. My original stilts went up to 36" which was perfect. I'd walk up and down stairs, walk outside...even nailed gutters up once with them but the extra foot higher freaked me out. Stilts rock for all kinda work besides spackling. GREAT for painting and cutting in ceilings!!
http://www.cliffordrenovations.com
http://www.ramdass.org
Just the opposite, I had some 48" stilts that "walked away" and had to replace them with 36", the only thing I could find near the jobsite. Without them would have cost me another day on the job, so it was a trade off. I think I set the 48" full height only once, taping and painting 11' ceilings.
The real kicker is the 48" were good quality and the 36" I have now are scary cheap.~ Ted W ~
Cheap Tools! - MyToolbox.netMeet me at House & Builder!
Very cool! How were they held in place? Lag screwsfrom above? , what wood did you use? Looks like balck walnut..
The main beams are held up in the walls at each end with blocking over the plates. the purlins were lagged into braces we set between the ceiling joists. The lags basically held them in place so we could get the next main beam in. We used the giant wooden hammer to slam the purlins into the main beams. with an eyelash of space for play.
Believe it or not the owners were gonna paint them...echhhh.
http://www.cliffordrenovations.com
http://www.ramdass.org
I don't really think it is an issue. I did a Post and Beam entry porch out of freshly milled Douglas Fir, and while some checking has occurred it hasn't been anywhere near the bolts - which has also been my experience looking at other Post and Beam projects.
Have you seen the house by James Tuer in the Feb/March FHB? It uses connections similar to what you propose with out any apparent problems.
If you are still worried, why not just design the joints so that they use one bolt, or locate the bolts along the axis of the wood's grain, rather than across it.
How do I find that article?
Thanks
John
Not sure if it is online, I subscribe to the magazine.
I did a thread that linked to architect's websites featuring mainly post and beam where you might find some good ideas: 98846.1
Just to clarify another point: Post and Beam is used extensively here in both residential and commercial projects for ferry terminals, schools, libraries etc. No one adjusts their connections seasonally.
Adjusting pegs is not done with post and beam, it is done on timberframing only with those who are anal and believe highly in maintinance..
So long as the joint doesn't need to carry moment, and the metal fixture will support the weight, (I'm seeing something like a big jist hanger in my mind), you can over size the holes with no structural effect.