Moment Frames
For the preliminary gravity design it was assumed that Ic / Ib = 1.75 & Ac / Ab = 1.75 to ensure strong col /
weak beam. Trial sections were obtained and the analysis repeated with the assumed sections.
-
Frames are spaced at 18'(5.49m)
-
Dead load from roof = 12.1 psf (579 N/m) on horizontal projection (See step B-2)
Columns: Loads:
The columns support the loads from the upper roof as well as the beams along grid lines B & H (one
on each side of column)
Dead Loads:
12.1 psf
(roof dead load from step B-2)
Beam Reaction = 2*(wL/2) = (2)(1325 plf)(18' /2 = 23.9 k (106 KN)
)
Live Loads:
Live loads: Lr =20R1R2
ASCE 7-95 Eq. 4-2
2
2
At = (18' (30' = 540 ft. (50.22 m )
)
)
R1 = 1.2 0.001At = 1.2 0.001(540) = 0.66
R2 = 1 (Rise of roof = 4" per foot)
Lr = (20 psf)(0.66)(1) = 13.2 psf (193 N/m2)
Beams: (Assume beam is one member for design, Length = 60'or 18.3m)
Loads;
Dead Loads:
(12.1 psf)(18' = 218 plf (3.18 KN/m)
)
The tributary area of the beams (18' (60' = 1080 ft.2 (100.4m2)
Live Loads:
)
)
The trib. area of the beams is greater than that of the columns (540 ft.2 or 50.2 m2)
A higher live load reduction could be used, however use the same live loads that the
columns to be conservative
Lr = (20 psf)(0.66)(1) = 13.2 psf = (13.2psf)(18' = 238 plf (3.47 KN/m)
)
wu = 1.2(218) + 1.6(238) = 642 plf (9.37 KN/m)
1 plf = 14.59 N/m
1 kip = 4.448 KN
Input for elastic analysis
1 foot = 0.305 m
1 inch = 25.4 mm
H3-10
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