| Author | Message | ||
     Rek |
I've been looking all over the www for a site that lists/explains truss designs and maximum spans. So far all I've found is information for single beams, floor joists, etc. I want to build two 28' clear-span trusses to open up my shop but cannot seem to locate the right information. anyone out there know where to find it? Rob | ||
| Mikej |
This may not help, but it should be a start: http://www.truss-frame.com/ | ||
| Signguyxb12 |
most distributors of the strusses will give you the calculations. Just call your suppler/lumber yard and they will give you the right ones for the job. signguy....former construction guy and timberframe guru wannabe | ||
| Rek |
I suppose the information I'm looking for might be considered propiatary (sp?) since none of these sites (or any I've found before) contain specific calculations for actual design. i.e. if the span=x number of feet and the load is y, then the truss needs z number of x-braces that are so deep, etc. Grrrr. If it were easy we'd have grandma and the kids out doing it. Rob BTW I'm retro-fitting these atop an exsisting wall which will be removed once the trusses are installed. S0...I can't fit pre-made trusses in the space available and they must be built in place. (Message edited by rek on November 17, 2004) | ||
| Pnut |
Rek, each truss manufacter has their own design calcs for the truss plates they use.(metal pcs holding two or more wood members together) So the clacs are not really universal. The advice of going to a lumber yard/supplier is sound. Wind and snow loads for your area also affect the design. I would ask what your doing because two trusses seems to not make sense to me? | ||
| Rek |
Pnut, I have a 48'x48' wooden grainary w/ three 12'x16' square bins down either side of an 18' wide alley. I want to remove two bins on each side and create a 32'x48' (+/-) open space. The two trusses would carry the load now supported by bin walls on each side of the alley. Rob | ||
| Bomber |
Rek -- you're local building inspector can very likely guide you in what's needed, as well -- either that, or an architect/structural engineer -- the later will cost dough, of course, but you could maybe find a new grad that's looking for work to point to as an example, and get a great deal talking to the building inspector, of course, will make sure your job get inspected, which has it's own cost, of course ;-} | ||
| Rek |
talking to the building inspector, of course, will make sure your job get inspected I don't know if I want the inspector nosing around my place or not{  Rob (Message edited by rek on November 17, 2004) (Message edited by rek on November 17, 2004) | ||
| Josh_ |
I emailed your posts to my wife, I'll let you know if she works on it | ||
| Blake |
Do yourself a BIG favor and pay a Structural Engineer (the guru you need) to size your trusses for you. Anything short of that and you are gambling, bigtime. I recall you asking about this a few months ago and raising a few concerns. There may be a lot more to what you are doing than simply ensuring adequate roof support will address. Interior walls also often provide significant lateral support against wind loads. If you remove needed lateral support, and the wind blows, that would be bad. A good structural engineer will know design loads (snow, wind) for your area and he/she will be able to solve your problem in a matter of hours, might cost you a couple hundred bucks maybe more. It will be money very well spent. You'll not find a do it yourself truss design site on the internet. WAY too much liability. It's why structural engineers attend college for four or more years and then must pass some seriously rigorous testing to gain professional certification. Example... A cursory review of design loads for your area near Lambert, MT shows that your roof snow load is as high as 30 PSF with a design wind speed as high as 80 mph. Just for reference so you can appreciate the load that your truss must be designed to safely support... For a 16'x48' tributary roof area your truss will need to be able to support upwards of 64 LB/FT or a total of over 3,000 LBs. For a 5' deep beam spanning that distance and carrying that load the upper chord would see a peak compression load of near 4,000 lbs with the lower chord seeing that same load but in tension. Put that in tangible perspective... Imagine a full size pickup truck being supported by one 2x6. How long can it be before it buckles? How do you support it laterally to prevent it from buckling? As for the wind load, at 80 mph you are looking at upwards of 25 PCF acting to push in your exterior walls. Multiply that by the enlarged work span and the height and you'll end up with around 8,000 LBs for every 10' of wall height. If your exterior walls are 16' high, that load increased by a factor of 1.6 to 12,800 LBs. Still want to rip out those walls? Avoid catastrophe, get yourself an engineer to look at the building. | ||
| Signguyxb12 |
Holy crap...Blake, you have amazed me again. I have tooth that needs pulling, i want to do it myself ...any advice???? just kidding | ||
| Pnut |
Rek So if I understand your description, you need to support 32' of existing structure that is now supported by grain bin walls (x2)But I don't know what the walls now support. Ya know the saying a picture is worth a thousand words, I think it applies. | ||
| Mikej |
Yes, please post a picture, sounds real interesting. If I could find a digital camera that works I could in short order find lots of examples around here of failed structures and twisted/collapsed barns. Neat in a photographic/artsy perspective. | ||
| Evaddave |
Rek, My mom owns & runs a truss manufacturing company, and I've done quite a bit of work there myself. The software you are looking for costs BIG BUCKS, and even once you're done, the truss design needs to be approved by an engineer. You might have more room if you take out the wall before putting the truss in. You might be able to get pre-made trusses in a couple pieces that you splice together on-site. Signguy's advice was spot-on. Talk to a local lumber yard. They often have relationships with truss manufacturers in your area, and can send a non-inspector-type person out to inspect the job site and get all the measurements needed. Here are some thoughts: - most trusses are placed 2' apart. You appear to want to span 32' with two trusses. It can be done, but it'll be expensive. - the length of the trusses will be 48'. If you have no inner load-bearing walls, then *all* the load from the roof will have to go through the trusses to the outside walls. It can be done, but it'll be expensive. - some (but certainly not all) of the factors that go into calculating the braces and size of wood in the truss are span and load, like you mentioned above, but also the number and position of load-bearing walls, spacing between trusses (the 2' distance I measured above), any overhang you might have, and the pitch of the roof. - you will need the trusses to be an exact height and length to match the existing structure. This is more difficult to do. Trusses are typically rough framing--a small variation from specification isn't a big deal as long as all of the trusses are the same. In your scenario, a small variation from the spec could be a problem. It might be more cost-effective to replace the entire roof. - depending on the pitch, a 48' truss might come in multiple pieces anyway. It's difficult to ship something that size in one piece. -Dave | ||
| Rek |
Sorry about the lack of photos, I tried several times this a.m. but I'm either too dense or my dial-up is too slow. I went into town yesterday and visited w/ a couple contractors and the lumber yard.The general consensus is that if I want to fabricate my own trusses then plywood beams are the best/only option...which will cost less($240 plywood vs $800 glue-lam vs 2x6 stick-frame=free)but double the work. The major advantage of plywood is the collar-ties that run from one eave to the other remain in situ and the lateral strength is not comprimised(windload). The biggest obstical is wrestling 4x8 sheets of plywood up into the rafters and fastening them in place. Grumble grumble. I'm just a cheap-skate and want to do it for free. Rob | ||
| Mr_grumpy |
You can't beat a good old arch for strength in any direction. And from an aesthetic point of view there is little more beautiful than a well placed arch. You may by now have guessed that I like arches, remind me to show you some of mine sometime; damn I'm starting to sound like Court, I hope there's no copyright. |
