Civil Engineering Reference
In-Depth Information
Stringers
Properties of 2
8 stringer with finished dimensions
1
2
7
4
:
A
10.87 in.
2
,
I
47.63 in.
4
,
S
13.14 in.
3
load/ft
(4)(225)
900 lb/ft
Bending and shear stresses:
10
(900)(4)
2
M
w
2
1440 ft- lb
10
(12)(1440)
13.14
f
b
1315 psi
1875 psi
OK
2
12
4
2
7.25
12
V
0.6
w
(0.6)(900)
1507 lb
f
v
(3)(1507)
(2)(10.87)
208 psi
180 psi
No good
Deflection:
1
360
Permissible deflection
(12
4)
0.133
12
)(12
4)
4
(128)(1.76
(
900
Actual
10
6
)(47.63)
0.0371
0.133
OK
20.10
DESIGN OF FORMWORK FOR FLOOR AND ROOF SLABS
From the same principles used for calculating the flexural and shear stresses and the de-
flections in the preceding section, it is possible to calculate maximum permissible spans
for certain sizes of sheathing, joists, or stringers. As an illustration, it is assumed that a
rectangular section is used to support a total uniform load of
w
lb/ft over three or more
continuous equal spans. The term
used in the equations to follow is the span, center to
center, of supports in inches, while
f
is the allowable flexural stress.
Moment
The bending moment can be calculated in inch-pounds and equated to the resisting mo-
ment, also in inch-pounds. The resulting expression can be solved for
, the maximum
permissible span, in inches.
2
10
in foot- pounds
2
120
in inch- pounds
w
w
M
M
res
f
S
in inch- pounds
