Need a help with AL design, are my interpretations correct?
Need a help with AL design, are my interpretations correct?
(OP)
Hi. I have the Aluminum Design Manual and Al Structures book as references. I'm trying to size AL 6061-T6 AL standard beams.
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S12x17.3
L=16'
Lb=16' (unbraced)
AL 6061-T6
Ftu=38 ksi
Fty=35ksi
Section 3.4.2/3.4.4
Fbt=19.5ksi (tension flange)
Fbt=28 ksi (tensino web)
Section 3.4.11 (Gross Compression)
Fbc=21 ksi (fully braced in weak axis)
Lb=16'
ry=1.03
S=Lb/ry=79 (S1=21, S2=79)
Fbc=2.50ksi
Section 3.4.15 (Flange Compression)
S=b/t=3.63 (S1=6.5, S2=10)
Fbcf=21ksi
Section 3.4.18 (Web Compression)
S=h/t=15.55 (S1=48, S2=75)
Fbcw=28ksi
Section 3.4.20 (Shear)
S=h/t=15.55 (S1=36, S2=64)
Fs=12ksi
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Assumption: Fallow=2.50ksi (minimum)
So I design based on an allowable stress (2.50 ksi)???? Or can I do a weighted average of the flange and web compression instead with the expection of getting a higher allowable design stress?
I don't design AL and I would appreciate a second opinion whether I'm interpreting the AL DM correctly. Thank you!
--------------------------------------------------------------------------------------------------------
S12x17.3
L=16'
Lb=16' (unbraced)
AL 6061-T6
Ftu=38 ksi
Fty=35ksi
Section 3.4.2/3.4.4
Fbt=19.5ksi (tension flange)
Fbt=28 ksi (tensino web)
Section 3.4.11 (Gross Compression)
Fbc=21 ksi (fully braced in weak axis)
Lb=16'
ry=1.03
S=Lb/ry=79 (S1=21, S2=79)
Fbc=2.50ksi
Section 3.4.15 (Flange Compression)
S=b/t=3.63 (S1=6.5, S2=10)
Fbcf=21ksi
Section 3.4.18 (Web Compression)
S=h/t=15.55 (S1=48, S2=75)
Fbcw=28ksi
Section 3.4.20 (Shear)
S=h/t=15.55 (S1=36, S2=64)
Fs=12ksi
--------------------------------------------------------------------------------------------------------
Assumption: Fallow=2.50ksi (minimum)
So I design based on an allowable stress (2.50 ksi)???? Or can I do a weighted average of the flange and web compression instead with the expection of getting a higher allowable design stress?
I don't design AL and I would appreciate a second opinion whether I'm interpreting the AL DM correctly. Thank you!






RE: Need a help with AL design, are my interpretations correct?
Section 3.4.11 (Gross Compression)
Fbc=21 ksi (fully braced in weak axis)
Lb=16'
ry=1.03
S=Lb/ry=186 (S1=21, S2=79)
Fbc=2.50ksi
RE: Need a help with AL design, are my interpretations correct?
I don't have the code handy to look over your list, but you can design/analyze aluminum beams in RISA. Doing so with an S12x17.3, spanning 16 ft, unbraced weak axis, I do not get such a low value as a limiter.
I do not think it is appropriate to do a weighted average, but perhaps you wouldn't need to if you can determine why RISA gives a better value than you are finding.
RE: Need a help with AL design, are my interpretations correct?
remember that the very low alloawable is for compression load on the beam. sanity check (i don't use your codes) ...
euler ... P = pi^2EI/L^2 ... s = pi^2*E/S^2 = 10*1E7/186^2 = 3 ksi ... so 2.5 ksi is "reasonable".
but remember, this is for axial compression. how much compression is in the beam ? wouldn't your allowable for bending be higher ?
different modes of failure apply against different loads.
RE: Need a help with AL design, are my interpretations correct?
RE: Need a help with AL design, are my interpretations correct?
RE: Need a help with AL design, are my interpretations correct?
RE: Need a help with AL design, are my interpretations correct?
RE: Need a help with AL design, are my interpretations correct?
and your allowable flange comression includes the effect of the unbraced length ?
RE: Need a help with AL design, are my interpretations correct?
The use of ry instead of rye is conservative. When looking through my ADM, I circled the comment about allowing rye instead of ry with a hand written note that RISA uses rye. Therefore, that would seem to explain why the RISA calculation comes up with a higher allowable stress.
RE: Need a help with AL design, are my interpretations correct?
RE: Need a help with AL design, are my interpretations correct?
Thanks :)
I download a trial copy of Digital Canal AL Design and it's computing the same S beams that I am with the AL DM. Risa must be using Rye.
RE: Need a help with AL design, are my interpretations correct?
i'm thinking Sc is section modulus = I/y, so playing a little i get rye^2*E*Sc*1.44*pi^2 = Lb^2*Me, Me = 1.44*(pi^2*E*I/Lb^2)*rye^2/y, ... not sure where this is going (and don't Really care)