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8 Sensor Spacing and Target Loads FDOT follows LTPP guidelines for sensor spacing, but load levels differ. Additionally, rigid pavements are not tested; The newest version of the LTPP FWD manual details physi- "the procedure used by FDOT to predict the embankment cal setup, loads, test plans, error checks, software, and cali- Mr is applicable only to flexible pavements . . . [if a request bration protocols. Sensor spacings depend on the pavement involves composite or rigid pavements] Limerock Bearing surface being tested and the number of sensors on the FWD. Ratio tests will be used in lieu of FWD tests" (Holzschuher For basin testing, the LTPP FWD manual (Schmalzer 2006) and Lee 2006). Figure 3 gives the percentages of SHAs who requires: developed their own spacing and load guidelines. Addition- ally, histograms of sensor spacings at the project level, at the · 0, 203, 305, 457, 610, 914, 1,219, 1,524, and -305 mm network level, during research, and during other projects are (0, 8, 12, 18, 24, 36, 48, 60, and -12 in.) for nine-sensor provided in Appendix B. FWDs. · 0, 203, 305, 457, 610, 914, and 1,524 mm (0, 8, 12, 18, 24, 36, and 60 in.) for seven-sensor FWDs on flexible Falling Weight Deflectometer Manufacturers pavements. · -305, 0, 305, 457, 610, 914, and 1,524 mm (-12, 0, 12, 18, 24, 36, and 60 in.) for seven-sensor FWDs on rigid Information from four FWD equipment manufacturers was pavements. gathered for this synthesis. Those manufacturers were Carl Bro; Dynatest; Foundation Mechanics, who offers FWD Additionally, target loads of 26.7, 40.0, 53.4, and 71.2 kN equipment through its JILS division; and KUAB. The fol- (6,000, 9,000, 12,000, and 16,000 lbf) ±10% are defined for lowing paragraphs describe each of those manufacturers' LTPP pavement tests. Test locations are specified for PCC equipment and features based on the information gathered. testing at joint approach, joint leave, and corners. Because of the ever-evolving technology, other equipment and additional features may be offered by FWD manufacturers. The Florida DOT (FDOT) publishes its own guidelines for FWD use. In addition to intradepartmental report require- Carl Bro ments, the document gives FWD apparatus parameters, data analysis techniques, and crew requirements. The Carl Bro Group, acquired by the Dutch consultancy Grontmij in August 2006, offers three types of FWD: trailer- Other jurisdictions shared their sensor spacing and load mounted, vehicle-mounted, and portable FWDs. methods in the survey. As the LTPP guidelines suggest, sen- sor spacing varies depending on test type and pavement sur- The Carl Bro trailer-mounted FWD is the PRI2100. face. Most SHAs, however, follow FWD guidelines of their The FWD is mounted to the tow vehicle by a double-axle own creation rather than the LTPP guidelines. For example, trailer. According to correspondence with Carl Bro, the mass FIGURE 3 Survey response to Question 29, "What kind of flexible pavement field testing manual does your agency use?"
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9 mechanism generates force magnitudes up to 250 kN (56,200 Foundation Mechanics, Inc. lbf). Carl Bro provides a laptop personal computer (PC) with software, which controls FWD operation and records Based in California, Foundation Mechanics, Inc., sells FWDs distance measurement. The company supplies their "RoSy under its JILS nameplate. Fifteen of the 81 FWDs used by DESIGN" back-calculation software, but the FWD output survey respondents were manufactured by JILS. The com- may be used with other back-calculation packages. Three pany provides FHWA-compliant calibration services at its temperature sensors, nine deflection sensors, a four-split El Segundo, California, facility. JILS offers trailer-mounted loading plate, a time history module, and warning lights are and vehicle-mounted FWDs. also supplied (Carl Bro 2006). JILS' trailer-mounted FWD is the JILS-20. This FWD The vehicle-mounted Carl Bro PRI2100 is integrated includes a 305 mm (12 in.) loading plate, distance measurer, into a van. Otherwise, it is identical to the trailer-mounted video monitoring system, and temperature measurement PRI2100. The company recommends the vehicle-mounted hardware. JILS provides a separate gasoline engine for the FWD to reduce "mobilization time" and safety risks associ- FWD hydraulic system, allowing for independent vehicle ated with trailers. and FWD operation. Up to ten deflection sensors are sup- ported. The company provides a laptop, which includes their The PRIMA 100 by Carl Bro is a portable FWD. This JTEST FWD monitoring software. FWD data are output in device is designed to be carried by one person, with no need raw data format, but they can be converted to PDDX format for a tow vehicle. Included with the PRIMA 100 are 100 and ("JILS, Falling Weight Deflectometers: JILS 20" 2007). 300 mm (4 and 12 in.) loading plates and a 10 kg (22 lb) mass. Data are collected onto a personal digital assistant For heavier loads, the company offers the JILS-20HF. or laptop through a direct cable or Bluetooth wireless con- While supporting heavier drop loads, the features and speci- nection. A single load cell and up to two additional deflec- fications are otherwise similar to the JILS-20 ("JILS, Falling tion sensors are supported. The device is powered by four Weight Deflectometers: JILS 20HF" 2007). AA-size batteries. The company's vehicle-mounted FWD, the JILS-20T, Dynatest is otherwise identical to the trailer-mounted JILS-20. JILS provides a Ford F350 pickup with dual rear wheels as the The Dynatest Group of Denmark, the United States, and the carrying vehicle ("JILS, Falling Weight Deflectometers: United Kingdom manufactured 59 of the 81 FWDs used by JILS 20T" 2007). survey respondents. In addition to FWD equipment, Dyna- test provides FHWA-compliant FWD calibrations at its KUAB Starke, Florida, facility. Dynatest's FWDs are either trailer- or vehicle-mounted. Engineering and Research International, Inc., based in Savoy, Illinois, sells trailer-mounted and vehicle-mounted Based on information provided by Dynatest, the Model FWDs under its KUAB nameplate. The company offers 8000E FWD supports drop masses from 50 to 350 kg (110 to FWD repair and calibration services. 770 lb). The resulting applied force thereby ranges from 7 to 120 kN (1,500 to 27,000 lbf). The company supplies loading According to information provided by KUAB, four mod- plates of diameters 305 mm (12 in.) and 450 mm (18 in.), and els are sold under the KUAB name. All four models support a segmented loading plate 305 mm (12 in.) in diameter is up to seven deflection sensors. The company supplies a 300 available for separate purchase. The system supports from mm (12 in.) load plate, which is available either segmented or 7 to 15 deflection sensors. Additionally, Dynatest supplies solid. Additionally, an aluminum cover, automatic ambient a laptop PC with FWD monitoring software. The system's temperature sensors, surface temperature sensor, distance Pavement Deflection Data Exchange (PDDX)-formatted measurers, and a laptop are all included. The company pro- FWD output is compatible with Dynatest's Elmod back- vides three days of training to operators. The models are dif- calculation software package. ferentiated by their loading capacities and installation types. The KUAB 50, for example, offers a load range from 12 to The Dynatest Model 8081 applies heavier loads than the 50 kN (2,698 to 11,240 lbf). This model is only available as Model 8000E. Capable of 30 to 240 kN (6,744 to 53,954 lbf) a trailer-mounted FWD. The KUAB 120, conversely, adds a impact loads, the Model 8081 supports load masses between 450 mm (18 in.) solid or segmented load plate and has a load 200 and 700 kg (441 and 1,543 lb). Features and specifi- range from 7 to 120 kN (1,574 to 26,977 lbf). The KUAB 150 cations are otherwise similar to the lighter-weight Model brings possible loads from 12 to 150 kN (2,698 to 33,721 lbf), 8000E. Similar to Model 8000E, model 8081 outputs to and the KUAB 240 supports loads from 20 to 240 kN (4,496 PDDX format. to 53,954 lbf). Furthermore, the KUAB 120, KUAB 150,