For this structure #6 bars @ 40" (102 cm) were used for the vertical steel because the wall spans
vertically between the supports. Therefore, the higher reinforcing ratio is used in the direction.
Vertical steel: 1 #6 bar @ 40" (102 cm); ρv = 0.44/(8)(40) = 0.001375 > 0.0007, OK
Horizontal steel: 1 #5 bar @ 48" (120 cm); ρh = 0.31/(8)(48) = 0.0008 > 0.0007, OK
ρv + ρh = 0.0008 + 0.00138 = 0.0022 > 0.002, OK
(Note: The horizontal joint reinforcing may be used to satisfy the reinforcing steel ratio but the
strength contribution is neglected. For this example the horizontal joint reinforcing contribution to
the steel ratio is neglected.)
Steel Members
Perimeter roof beams
The roof beams must support the gravity loads from the joist in addition to acting as collectors for
longitudinal forces and chords for transverse forces. The beams were sized previously for the governing
gravity load combination 1.2D + 1.6L. They must now be checked for the seismic load case: 1.2D + 0.5L
+ 1.0E
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FEMA 302 Section 5.2.6.4.2 requires that collector elements for structures in Seismic Design
Category D be designed for the special load combination:
E = Ω oQE + 0.2SDSD
(FEMA 302 Eq. 5.2.7.1-1)
Loads:
Dead: 400 plf (5.84 KN/m) Live: 400 plf (5.84 KN/m)
QE: 2.04k (9.07 KN) (chord)
QE: 4.2k (18.68 KN) (collector)
The collector force governs the design.
wu = 1.2D + 0.5L + 0.2SDSD = 1.2(400) + 0.5(400) + (0.6)(0.2)(400) = 728 plf (10.62 KN/m)
H1-47
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