A-7 Determine Seismic Design Category. With SDS = 0.57, SD1 = 0.37, and a Seismic Use Category of
IIIE, enter tables 4-2a and 4-2b to obtain a Seismic Design Category of ` '
D.
A-8 Select Structural System.
Gravity: Steel frame with metal deck roof and reinforced concrete second floor slab. Roof deck spans
between interior open web steel joists and perimeter edge beams. Open web steel joists span to transverse
beams. Perimeter edge beams and interior transverse beams span between columns. Second floor slab
spans between interior beams and perimeter edge beams. Second floor beams span to girders that span
between columns.
Lateral: As permitted by Table 7-1:
Transverse direction: Special steel concentrically braced frames.
Longitudinal direction: Special steel moment frames.
A-9 Select R, Ω 0 , & Cd factors.
From Table 7-1:
R = 8, Ω 0 = 3, Cd = 5.5
Transverse direction - Special Steel Moment Frames
R = 6, Ω 0 = 2, Cd = 5.0
Longitudinal direction Special Steel Concentrically Braced Frames
A-10 Determine preliminary member sizes for gravity load effects.
(1) Roof Decking.
Live Load (per Table 4-1 of ANSI/ASCE 7-95):
20
psf
Dead Load (estimated):
Roofing;
5
psf
Rigid Insulation;
3
psf
Decking;
2
psf
Misc. (Mechanical & Electrical);
3
psf
psf (0.62KN/m2)
Total =
13
Dead + Live = 20 + 13 = 33 psf (1.58KN/m2)
Total Load:
Per steel deck manufacturers catalog with 3 or more 5-ft (1.53m) spans;
Choose 1-1/2" (38.1mm)-22 gage HSB36
(2) Roof Joists.
33 psf (1.58KN/m2) + self weight
Loading:
Assume self weight ≈5 plf (0.073KN/m), and a spacing of 4-ft (1.22m) on center
Loading = 33psf(4' +5plf
)
= 137plf (2.00KN/m)
Per steel joist manufacturers catalog with span = 20'(6.10m), a total load = 137plf (2.00KN/m), and a live
load = 80plf (1.17KN/m);
Choose 10K1 Joists @ 4-ft (1.22m) o.c.
(3) Longitudinal Roof Edge Beams. Use Fy = 36ksi. One design will be produced for the worst case and
used throughout. The beam must have a minimum depth of 12" (304.8mm) to ensure installation of 3 bolts
per connection in anticipation of chord/collector forces. Worst cases situation occurs at the low roof that
has the longest span and largest tributary area. Also, all beams are simply supported.
H4-4
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