B-9 Determine need for overstrength factor, Ω o .
Per paragraph 8.6.2 of FEMA 302, connections for diagonal bracing members and collectors shall have a
design strength equal to or greater than the nominal tensile strength of the members being connected or
Ω o times the design seismic force.
Therefore, for these force controlled elements the following seismic load will be used;
E = Ω oQ E 0.2S DS D
Longitudinal direction;
(EQ. 4-6)
E = 2Q E 0.2(0.57)D
E = 2Q E 0.114D
E = Ω oQ E 0.2S DS D
Transverse direction;
(EQ. 4-7)
E = 3Q E 0.2(0.57) D
E = 3Q E 0.114D
B-10 Calculate combined load effects.
Load combinations per ANSI/ASCE 7-95 and TI 809-04 are as follows;
(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
However, per paragraph 4-6 of TI 809-04;
E = ρQ E 0.2S DS D
= 1.0Q E 0.2(0.57)D
= Q E 0.114D
Therefore, equations 4 and 5 become;
(4a)
1.314D+QE+0.5L
(4b)
1.086+QE+0.5L
(5a)
1.014D+QE
(5b)
0.786D+QE
H4-20
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