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2. a Dynatest 8600 System Processor, and
3. a Hewlett-Packard HP-85 Table Top Computer.
3.2.1 The 8002 FWD
The Dynatest 8002 FWD consists of a large mass that is constrained
to fall vertically under gravity onto a spring-loaded plate, 11.8 in. in
diameter, resting on the pavement surface (see Figure 2.4). A load
range of about 1500 to 24000 lbs. can be achieved by adjusting the num
ber of weights or height of drop or both. The impulse or impact load is
measured by using a strain-gauge-type load transducer (load cell). The
impact load closely approximates a half-sine wave (see Figure 2.5), with
a duration of 25-30 msec which closely approximates the effect of moving
dual-wheels with loads up to 24000 lbs. (110).
Seven seismic deflection transducers or geophones in movable brack
ets along a 2.25 m raise/lower bar are used to measure the response of
the pavement to the dynamically applied load. The geophones, which are
50 mm in diameter and 55 mm high, operate at a frequency range of 2 to
300 Hz (34). One of the geophones is placed at the center of the plate,
with the remainder placed at radial distances from the center of the
plate (see Figure 3.3). In its present form, the FD0T measures deflec
tions at radial distances of 0, 7.87, 11.8, 19.7, 31.5, 47.2, and 63.0
in. from the plate center. These deflections are respectively called
D,D,D,D,D,D, and D in this study.
12 3 4 5 6 7
3.2.2 The 8600 System Processor
The Dynatest 8600 system processor is a microprocessor-based con
trol and registration unit which is interfaced with the FWD as well as
the HP-85 computer (34,110). The processor is housed in a 19-in. wide