B-10 Calculate combined load effects
The load combinations from ASCE 7-95 are:
(1) 1.4D
(2) 1.2D + 1.6L + 0.5Lr
(3) 1.2D + 0.5L + 1.6Lr
(4) 1.2D + E + 0.5L
(5) 0.9D + E
Where E = ρQE 0.2 SDSD
Eq. 4-4 & 4-5
When specifically required by FEMA 302 (Collectors, their connections, and bracing connections for this
example) the design seismic force is defined by:
E = Ω 0QE 0.2SDSD
Eq. 4-6 & 4-7
0.2SDSD = 0.2(0.6)D = 0.12 D
Therefore, 0.12 will be added to the dead load factor for load combinations 4 and 5.
B-11 Determine structural member sizes
Upper roof diaphragm
Unit shear check:
The applicable load combination for diaphragm shear reduces to 1.0E.
The allowable unit shear is determined by multiplying the value from the deck manufacturer' catalog by
s
1.5 (Sec. 7.7e4(b)2.i.)
qall = 1.5 x 520 plf = 780plf (11.4 KN/m) (20-gage deck (1mm), top-seam welded at 24" (0.61m), 5
welds per end, 6' 8"span (2.03m))
-
Transverse shear = 102 plf (1.49 K/m) < 780 plf (11.4 KN/m), O.K.
Longitudinal shear = 64 plf (934 N/m) < 780 plf (11.4 KN/m), O.K.
Mezzanine diaphragm forces
Unit shear check:
The applicable load combination for diaphragm shear reduces to 1.0E.
The allowable unit shear is determined by multiplying the value from the deck manufacturer' catalog by
s
1.5 (Sec. 7.7e4(b)2.i.)
qall = 1.5 x 1745 plf = 2618 plf (38.2 KN/m)
(20-gage (1mm) deck with 3-1/2" (89 mm) n.w. concrete
fill, span = 8'(2.44m))
Transverse shear =
116 plf (1.69 KN/m) < 2618 plf (38.2 KN/m), O.K.
Longitudinal shear =
297 plf (4.33 KN/m) < 2618 plf (38.2 KN/m), O.K.
H1-36
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