TM 5-818-1 / AFM 88-3, Chap. 7
(1) Use equations (10-5) and (10-6) to
10-7c. The repetitive loading will consist of the dead
compute-
load pressure, with the live load increment applied for 1
(a) Minimum and maximum footing sizes
minute. Then release the live load increment and allow
using Es = 1000 and 5000 kips per square foot,
to rebound at the dead pressure for 1 minute. This
respectively.
procedure constitutes one cycle of live load pressure
(b) Two intermediate footing sizes using
application. Deformation readings will be taken at three
values intermediate between 1000 and 5000 kips per
points: at the start, after the live load is applied for 1
square foot.
minute, and after the plate rebounds under the dead load
Use these four values of B or D in the following
pressure for 1 minute. Live load applications will be
equations to compute the increase (or pressure change)
repeated for 15 cycles.
in the live load, ∆L.
(4) Increase the dead load pressure, q0, to
the second lowest value, allow to consolidate, and then
square footing ∆L =
apply the respective live load increment repetitively for 15
17.0M (pounds per
cycles.
3
square foot) (10-7)
B
(5) Repeat step 4 for the remaining two
dead load pressure increments.
round footing ∆L =
20.3M (pounds per
(6) An uncorrected modulus of elasticity
3
D
square foot) (10-8)
value is computed for each increment of dead and live
load pressure as follows:
(2) The Es value depends on the depth of the
25.5 ∆L (1 - )
2
Es' =
footing below grade, the average dead load pressure on
S
the soil, and the maximum pressure change in the live
Es' =
uncorrected effective modulus of
load, ∆L, on the foundation due to wind moments. A
elasticity for the loading condition used, pounds per
determination of the E, value will be made at the
square foot
proposed footing depth for each footing size computed.
S
=
average edge deformation of the plate
(3) The dead load pressure, q0, is computed as
for the applied load, determined from the slope of the last
the weight, W, of the radar tower, appurtenances, and
five rebound increments in the repetitive load test, inches
the footing divided by the footing area, A.
=
Poisson's ratio (see table 3-6).
ΣW
=
(10-9)
q0
(7) The above-computed uncorrected
A
modulus of elasticity will be corrected for bending of the
plate as described in TM 5-824-3/AFM 88-6, Chapter 3,
The selection of loadings for the field plate load test will
where E' is defined above, and E, is the effective
be based on qo and ∆L.
modulus of elasticity for the test conditions.
d. Field plate load test procedure.
The
e. Selection of required footing size. The
following plate load test will be performed at the elevation
required footing size to meet the allowable rotation
of the bottom of the footing, and the test apparatus will
criteria will be determined as follows:
be as described in TM 5-824-3/AFM 88-6, Chapter 3.
(1) Plot on log-log paper the minimum and
(1) Apply a unit loading to the plate equal
the maximum footing size and the two intermediate
to the smallest unit load due to the dead load pressure
footing sizes versus the required (four assumed values)
q0. This unit loading will represent the largest size
effective modulus of elasticity for each footing size.
footing selected above.
(2) Plot the measured effective modulus of
(2) Allow essentially full consolidation
elasticity versus the footing size corresponding to the
under the dead load pressure increment. Deformation
loading condition used for each test on the same chart
readings will be taken intermittently during and at the end
as above.
of the consolidation period.
(3) These two plots will intersect. The
(3) After consolidation under the dead
footing size indicated by their intersection is the minimum
load pressure, perform repetitive load test using the live
footing size that will resist the specified angle of tilt.
load pressure ∆L computed by the formulas in paragraph
10-6
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