Mornin’ All,
I’m about to start building a large Cape Cod that requires a structural ridge beam. I’ll be using GPI’s for the rafters and am comfortable with the necessary framing details. I was planning on running the rafters long and bearing on top of the ridge beam on a bevel plate (per mfg. detail). My problem is, the rear roof has a shed roof section so my front/back pitches are 12/12 and 5.5/12. In this case, the bevel plate of the shallow pitch has to be very tall and I don’t know if that’s ok. The easy answer is to hang the rafters from the beam, but I’m considering using steel instead of LVL’s, to get a longer clear span. SO, the questions are:
1. Is the tall bevel plate ok? If so, how would I anchor it?
2. If I must hang the rafters, how do I hang GPIs from a steel I beam?
Thanks,
Andrew
Replies
I have no idea why if the tall beveled plate would fly with GP or not. It would probably be best to run it by their engineering division. I don't think they charge for the service.
I looked around briefly at their website:
http://www.gp.com/englumber/ibeam.html
You might contact them through the website, or call the toll free number on their literature.
As for hanging on an I-beam - I've seen details on plans where the open space between the top and bottom flange was filled solid with ripped 2X lumber, then stuff was hung on the lumber. You'd definitely want to run that by your local code officials, though.
Whatever you do with your house, would you consider posting pics? We all like to see what others are doing..........
If you think health care is expensive now, wait until you see what it costs when its free. -- P.J. O'Rourke
Thanks for the quick feedback. I've been through all the literature I could find, with no luck, and I've never gotten any response from the web contact form. Never thought of calling tech support... I'll try that on Monday and post results.
Re: hanging rafters from beam... packing the web will work, allthough I'm looking at a 7" W series beam so that's 4 layers of 2x... hmmm... Another drawback to hanging from a beam that wide is, I would need to frame something on top of the beam to support the rest of the sheathing up to the ridge.
I'd be happy to post pictures and descriptions as we progress, we should start cutting the 1/4 mile road next week. There are several interesting aspects to the design that should be of interest. Mainly, I'm going to clearspan 28' floors so there will be no load bearing walls or columns. This seemed simple at first, just use open web floor trusses. The ripple effect on footing size, wall thickness, header dimensions, etc. has been significant. Imagine doubling the loads on an 8' wide header that supports 2 floors and a roof! Plus footings have to be up sized because there's no center footing taking half the load. Also, we're putting a full basement under the detached garage/breezeway for about 1000 s.f. of cheap extra storage space. This one's a personal project so the timeline will stretch out, but it should be fun :)
Regards,
Andrew
Hope you get some response from them by calling.
One thing you mentioned caught my attention - The 28' clear span floor. Have you read the thread about floor vibration? Don't let anyone talk you into a floor that's too shallow...........
Here's the thread:
http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=21010.1I stayed up all night worrying about why I've been so tired
I remember reading a great article on perceived bounciness related to frequency and our bodies' resonance, either in FHB or JLC... In any case, thanks for the reference. I have had this discussion with the truss co. but had not referenced the article as a refresher. I know they used at least L/480, but need to see if they can stiffen it up even more because that's still almost 3/4" @ mid-span. Currently, the first floor is spec'd at 18" trusses, 24" o.c. and the 2nd floor at 20", 24" o.c. The second floor has some point loads due to a bump out, knee walls in an intersecting gable and a bridge across two-story space.
Your link was very imformative and I'm very interested in getting a copy of your spreadsheet, thanks.
The L/480 doesn't mean a great deal on floors, IMHO. It only limits the deflection, which means little.
Also IMHO, 18" trusses should NOT be used on 28' clear spans. I'll try to show you why I feel that way with the spreadsheet.
I'm at home now, and can't come up with a copy of the floor vibration spreadsheet. I'll have to send it to you from work Monday. If history repeats itself, I should think we can expect the same thing again.
Most long spans are designed to an absolute deflection limit (often 1/2") rather than a deflection ratio.
From my point of view, most vibration "guesses" are myth. They may work for producing a good floor, but they predict the very wrong vibration frequencies.
I think Truss Joist has a good analysis program. I have not looked at the details, but they seem to be good engineers.