CEMP-E
TI 809-07
NOVEMBER 1998
Where:
L = Floor span in inches
(2) Calculate the predicted deflection of a single joist,
due to a 255 lb concentrated
ot
load at midspan:
255L3
(Eq 2-9)
ot
48EI
Where:
L = Floor span in inches.
E = Modulus of Elasticity of the joist.
I = Moment of Inertia of a single joist.
from the Steel Joist Institute (SJI)
(3) Calculate the number of effective joist, N
eff
equation:
x
1 2 cos
(Eq 2-10)
Neff
2x o
Where:
x = Distance from the center joist to the joist under consideration (inches).
x = Distance from center joist to the edge of the effective floor = 1.06eL (inches).
o
L = Joist span (inches).
0.25
e = (D /D )
x
y
3
D = Flexural stiffness perpendicular to the joist = E t /12
x
c
D = Flexural stiffness parallel to the floor joists = EI /S
y
t
E = Modulus of elasticity of the sub-flooring.
c
E = Modulus of elasticity of the joists.
t = sub-flooring thickness.
I = Moment of inertia of joists alone.
t
S = Joist Spacing.
:
(4) Calculate the predicted central floor deflection,
o
ot
(Eq 2-11)
o
Neff
Where:
= Deflection of floor at mid-bay.
o
= Deflection of a single joist due to 255 lb. concentrated load at midspan.
ot
N
= Number of effective joists in the floor system.
eff
(5) Compare the
value to the critical deflection, y :
o
crit
If
<y :
Acceptable
o
crit
If
y
<
1.1 y :
Marginal
crit
o
crit
If
> 1.1 y :
Unacceptable
o
crit
2-11
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