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- To: <seaint(--nospam--at)seaint.org>
- Subject: Seated Beam Connections
- From: "John P. Riley" <jpriley485(--nospam--at)peoplepc.com>
- Date: Thu, 5 Apr 2001 23:29:28 -0500
1. If it is an HCMU wall, my preference is pockets with bearing plates (see SJI specification 5.3(a)). I have a standard detail, want it?
2. If you're asking what allowable bending stress to use for the horizontal leg as a cantilevered beam, my answer would be 0.75Fy.
3. I'd use e = 1/2 bf, where e is the eccentricity of applied load relative to face of wall and bf is width of horizontal angle leg. As the joist deflects and the cantilever deflects, the effective e will move around, but I think it will eventually be less than 1/2 bf. Of course, I'd detail the end of the joist at about 1/4" clear of the wall.
4. Effective width of cantilevered section . . . I'd use 6 or 8 inches, depending upon my mood. This is engineering, not science. Do you know how wide the joist bearing is? Must be about 5" for a K-series joist. If the end of the joist is sufficiently stiff to distribute the load 5", then 8" for the cantilever seems OK to me.
5. After you do all your number crunching, don't be shy about going thicker just for the heck of it. My experience is that these things tend to appear appropriate in details and breathtaking in the field. For what you've described, my minimum angle would be L 4 x 4 x 3/8. The joist manufacture wants 4" bearing (masonry), but will settle for 2 1/2" (steel). If you detail the clearance between joist end and face of masonry at 1/4", it seems unlikely that actual conditions will result in too much heartburn.
6. Just roughing this out, without considering bending between anchorages (which I'd minimize by showing the anchor bolts at the joists . . . because I don't think an angle is worth a hoot in bending), assuming 55 psf roof load (30 psf snow):
S = b t^2 / 6 = (8)(3/8)^2 / 6 = 0.188 in^3
M = Fb S = 0.75(36)(0.188) = 5.06 in-k
P = M/e = 5.06 / 2 = 2.53 k
P/5' = 2,530/5 = 506 plf
L/2 (max) = 506 plf / 55 psf = 9.2 ft
L max = 18.4 ft (max. joist span for 3/8" thick horiz. leg)
L max = 25.1 ft (max. joist span for 7/16" thick horiz. leg)
L max = 32.7 ft (max. joist span for 1/2" thick horiz. leg)
7. Hopefully, I did the math right. If I did, then I'll say, "This is the easy part." Do you have any questions about the anchorages? LOL
John P. Riley, PE, SE
20 Oakwood Drive, Blue Grass, Iowa 52726
Tel & Fax: 319-381-3949
I would like some asistance to resolve a design question. I am designing an angle used as a beam seat. I checked my college steel book and Gaylord was using Fsubb = 0.66Fsuby. I checked some more sources and Salmon and Johnson was using 0.75Fsuby, Fisher's Vulcraft book was using 0.75Fsuby. Which one is right???
With a little more looking I found in the ASD Specs F2.1 (Compact) Fsubb = 0.75Fsuby or F2.2 (Noncompact) Fsubb = 0.60Fsuby. These sections refer to Section B5. Is the appropriate test b/t < 76/Sqrt(Fsuby)???
Finally, My real question, this angle is not a single beam seat but a ledger angle supporting multiple purlins or bar joists. What is the effective length of support to subsitute into fsubb = (6*M)/(lsube*t^2)??? Surely it is not the 5' spacing of purlins, the 2' spacing of bar joists, or the spacing of bolts or welds which attach the ledger to the wall. How does one determine the effective length of support on a continous ledger angle???
Thanks in Advanc
Jim Hannah, EIT
Butler Manufacturing Company
- Seated Beam Connections
- From: James Hannah
- Seated Beam Connections
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