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7
chapter two
Falling Weight Deflectometer Equipment
This chapter provides information on FWD ownership, types · One or more deflection sensors. (Note: Deflection basin
and configurations, manufacturers, and maintenance practices. tests require at least seven sensors.)
· A system for collecting, processing, and storing deflec-
tion data.
FALLING WEIGHT DEFLECTOMETER Ownership
Recorder systems, discussed in Section 8 of ASTM
The 45 SHAs that responded to the survey reported own- D4694-96, should display and store load measurements with
ing 82 FWDs. Most were manufactured by Dynatest, but a 200 N (45 lbf) resolution. Such systems should display and
Carl Bro, JILS, and KUAB were also represented. Table 3 store deflection measurements with ±1 m (0.039 mil) or less
summarizes SHA FWD ownership by manufacturer of resolution.
(Appendix B, Questions 26).
Most of the FWDs used by SHAs are either towed by
TABLE 3 a vehicle or are built into a vehicle's cargo area. Figures 1
QUANTITIES OF FWDS OWNED BY STATE HIGHWAY and 2 depict one of each such FWD.
AGENCIES, BY MANUFACTURER
Quantity of FWDs Ages of FWDs
Manufacturer in Service (total) (years, average)
Dynatest 61 14
JILS 15 6
KUAB 6 14
Carl Bro 0 Not applicable
Other 0 Not applicable
Total 82 11
Falling Weight Deflectometer Types and
Configurations
Falling Weight Deflectometer Components FIGURE 1 Trailer-towed FWD (Courtesy: Carl Bro).
The basic components of a FWD are defined by reference
documents such as AASHTO and ASTM standards. For
example, in ASTM D4694-96, the apparatus described is
composed of the following ("Standard Guide for General
Pavement Deflection Measurements" 2005, pp. 487488):
· An impulse-generating device with a guide system.
This device allows a variable weight to be dropped
from a variable height.
· Loading plate, for uniform force distribution on the test
layer. When the weight affects this plate, this loading
plate ensures that the resulting force is applied perpen-
dicularly to the test layer's surface.
FIGURE 2 Vehicle-mounted FWD (Courtesy: Foundation
· A load cell for measuring the actual applied impulse. Mechanics).
