Civil Engineering Reference
In-Depth Information
PROBLEMS
20.1
Repeat Example 20.1 if the joists are spaced 1 ft 6
in. on centers, the stringers at 6 ft 0 in. on centers as are
the shores, and the live load is 100 psf. (
Ans.
sheathing
and joists OK but stringers unsatisfactory in bending,
shear, and deflection)
20.2
Repeat Example 20.1 if
20.6
Is a 4-
4-in. shore (S4S) 10 ft long satisfactory to
support an axial compression load of 4000 lb if the allow-
able compression stress parallel to the grain is 1150 psi
and
E
1,400,000 psi?
20.7
Repeat Problem 20.6 if 6-
6-in. shores made
from rough lumber 14 ft long are used, each to support
an axial compression load of 16,000 lb. (
Ans. P
14,893 lb
16,000 lb N.G.)
1
8
-in.
Class II plyform, 2
8
joists spaced 2 ft 0 in. on centers, and 2
8 stringers
spaced 6 ft 0 in. on centers are used.
20.3
It is desired to support a total uniform load of 150
psf for a floor slab with Class I plyform. If the forms
are to be used many times and the maximum permissible
deflection is
5
8
-in.
20.8
Design the forms for a 15-ft-high concrete wall for
which the concrete is to be placed at a rate of 5 ft/hr at a
temperature of 70
F. Use the following data:
1.
Sheathing is to be
/360, determine the maximum permissible
span of the sheathing, center to center of the joists, if
f
1930 psi and
E
3
4
-in.
Class II plyform,
f
1330 psi,
1,650,000 psi. Neglect shear in the
sheathing. Make similar calculations but consider shear
values for 2
and
E
1,430,000 psi.
2.
Studs and wales are to consist of Douglas fir, coastal
construction,
f
2000 psi,
H
180 psi, and
E
1,600,000 psi. Allowable compression perpendicular to
the grain is 435 psi.
3.
Ties can carry 5000 lb each and the tie washers are the
same size as those shown in Figure 20.7.
4.
Double wales are used to avoid drilling for ties.
5.
Maximum deflection in any form component is
4 joists (S4S) spaced 1 ft 6 in. on centers if
f
1815 psi,
H
180 psi, and
E
1,760,000 psi. (
Ans.
sheathing 18.25
, joists 54.40
)
20.4
Repeat Problem 20.3 if
3
4
-in.
Structural I plyform is
used.
20.5
Repeat Problem 20.3 if 1-in. Class II plyform is
used with
f
1330 psi. Assume joists are spaced 2 ft 0 in.
on center. (
Ans.
sheathing 27.00
1
360
of
, joists 47.11
)
the span.
