φv Vn = 77.5k (344.7KN)
(calculated previously)
∴ Vu,column = 9.66k < 77.5k = φv Vn (42.97KN < 344.7KN)
O.K.
B-12 Check allowable drift and P ∆ effect.
Transverse direction;
Drift;
In the transverse direction, allowable drift was checked during the moment frame design.
P ∆ effect;
Px ∆
θ=
(EQ. 5.3.7.2-1 FEMA 302)
Vx hsx Cd
By inspection, the worst case condition occurs at the first story of the interior high roof moment frame
because it has the largest total vertical load "Px" and the largest design story drift "∆ ".
Px = Total vertical design load without load factors
= 15'0.225+0.280+0.600+1.272)klf+2(0.974k+0.649k)
(
= 38.9k (73.0KN)
∆ = 0.565" (14.4mm)
Vx =1.17k + 0.90k + 0.004= 2.074k (9.23KN)
hsx = 11' 12"/1' = 132" (3.36m)
(
)
Cd = 5.5
38.9 k (0.565" )
∴ θ=
= 0.015 < 0.10
2.074 k (132" )5.5
Therefore, P ∆ effects need not be considered in the transverse direction.
Longitudinal direction;
Check Drift;
Low Roof;
The stiffness for a single ` ' brace (one per building side) consisting of two braces in the horizontal
x
direction is;
2(3.59 - in2 )29,000ksi
2AE
2
cos2 (37o) = 444 - k / in (77.8KN/mm)
=
cos φ =
K horiz
L
25' (12"/1' )
1.25k
Pu
∴ δalc
=
=
= 0.003" (0.08mm)
c
K horiz 444 - k / in
∆ allow = 0.025hsx = 0.025(15' (12"/1' )) = 4.5" (114.3mm)
Cd xδalc = 5.0(0.003" ) = 0.015" < 4.5" = ∆ allow (0.38mm < 114.3mm)
O.K.
c
High Roof;
The stiffness of two diagonal braces (two per building side per story) in the horizontal direction is;
H4-37
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