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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).