Combined Sections in AISCM ASD 9th Edition
Combined Sections in AISCM ASD 9th Edition
(OP)
Part 1 of AISCM ASD 9th Edition tabulates properties for combined sections.
I know the general practice is to weld the beams to form the combined sections.
However, is there a method, procedure, or calculation, to determine bolt size and spacing for joining two beams so they may be considered a combined sections (i.e their moment of inertia may be combined)?
I know the general practice is to weld the beams to form the combined sections.
However, is there a method, procedure, or calculation, to determine bolt size and spacing for joining two beams so they may be considered a combined sections (i.e their moment of inertia may be combined)?






RE: Combined Sections in AISCM ASD 9th Edition
RE: Combined Sections in AISCM ASD 9th Edition
RE: Combined Sections in AISCM ASD 9th Edition
I found shear flow in my mechanics of material by Beer. Looking forward to doing the math.
RE: Combined Sections in AISCM ASD 9th Edition
RE: Combined Sections in AISCM ASD 9th Edition
Combined Section W12 x 40 on bottom and C15 x 33.9 bolted on top of it (long side of C15 x 39.9 up)
Input
Beam 1: W12 x 40
I1 = 310 in^4
A1 = 11.8 in^2
yc1 = 11.94 in / 2 = 5.97 in
Beam 2: C15 x 33.9
I2 = 315 in^4
A2 = 9.96 in^2
yc2 = yc1 + 15 / 2 = 19.4 in
Shear Load: V = 10.3 kip
Bolts: 5/8” dia. A325 with 30 ksi allowable per AISCM Table I-D
Calculation
The centroid of the combined section is( as measured from the bottom of the W12 x 40):
yc = A1 * yc1 + A2 * yc2 / (A1 + A2) = 12.1 in
Using parallel axis theorem,
Ic1 = I1 + (yc – yc1)^2 * A1 = 310 in^4 + (12.1 – 5.97)^2 * 11.8 in^2 = 759 in^4
Ic2 = I2 + (yc2 – yc)^2 * A2 = 315 in^4 + (19.4 – 12.1)^2 * 9.96 in^2 = 846 in^4
I_comb_sect = Ic1 + Ic2 = 1605 in^4
Q = (yc2 – yc) * A2 = 72.8 in^3
q = V * Q / I_comb_sect = 5.6 kip / ft
Abolt = (PI/4) * dbolt^2 = 0.31 in^2
V_bolt_allow = 30 ksi X 0.31 in^2 = 9204
s_bolt_min = V_bolt_allow / q = 19.7 inch
RE: Combined Sections in AISCM ASD 9th Edition
BA
RE: Combined Sections in AISCM ASD 9th Edition
I lnow buckling may be a concern as TLHS mentioned.
RE: Combined Sections in AISCM ASD 9th Edition
Beam 1: W12 x 40
I1 = 310 in^4
A1 = 11.8 in^2
yc1 = 11.94 in / 2 = 5.97 in
Beam 2: C15 x 33.9
I2 = 315 in^4
A2 = 9.96 in^2
yc2 =
yc1d1 + 15 / 2 = 19.4 okay inShear Load: V = 10.3 kip
Bolts: 5/8” dia. A325 with 30 ksi allowable per AISCM Table I-D
Calculation
The centroid of the combined section is( as measured from the bottom of the W12 x 40):
yc = A1 * yc1 + A2 * yc2 / (A1 + A2) = 12.1 in
Using parallel axis theorem,
Ic1 = I1 + (yc – yc1)^2 * A1 = 310 in^4 + (12.1 – 5.97)^2 * 11.8 in^2 = 759 in^4
Ic2 = I2 + (yc2 – yc)^2 * A2 = 315 in^4 + (19.4 – 12.1)^2 * 9.96 in^2 = 846 in^4
I_comb_sect = Ic1 + Ic2 = 1605 in^4
Q = (yc2 – yc) * A2 = 72.8 73.1? in^3
q = V * Q / I_comb_sect = 5.6 kip / ft
Abolt = (PI/4) * dbolt^2 = 0.31 in^2
V_bolt_allow = 30 ksi X 0.31 in^2 = 9204
s_bolt_min = V_bolt_allow / q = 19.7 inch
Looks good to me except as noted.
BA
RE: Combined Sections in AISCM ASD 9th Edition
RE: Combined Sections in AISCM ASD 9th Edition
BA
RE: Combined Sections in AISCM ASD 9th Edition
RE: Combined Sections in AISCM ASD 9th Edition
BA
RE: Combined Sections in AISCM ASD 9th Edition
RE: Combined Sections in AISCM ASD 9th Edition
Thanks for the feedback.
I was not aware the Manual of Steel Construction, Allowable Stress Design, 9th Edition was an obtuse code.
Anyway, the application is assembling a purchased enclosure provided with C Channels onto a skid frame composed of W flange beams. Bolting is preferred so they may be shipped separate. Loading is from lifting which is about eight point loads. The W flange beams on the bottom are sized for the whole lifting load but I wanted a basis for bolt spacing.