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10 and KUAB 240 are available as single-axle trailer-mounted ˇ Giving operators an ownership stake in the FWD FWDs or as vehicle-mounted FWDs. equipment they operate ˇ Overhauling the equipment when needed Maintenance Practices A few SHAs reported that their FWDs have not yet needed "significant maintenance." Most SHAs perform regular maintenance on their FWD equipment and their tow vehicles. These maintenance activi- Manufacturers' Recommendations ties are separate from calibration and can include mechani- cal lubrication, replacement of consumable parts, leak FWD equipment manufacturers generally follow LTPP repair, cleaning, and other activities that keep the mechani- guidelines for equipment maintenance and offer mainte- cal devices in working order. nance services on the equipment they sell. For example, Carl Bro supplies a comprehensive maintenance list to its clients, State Highway Agency Falling Weight which breaks down maintenance activities by individual Deflectometer Maintenance FWD component. In their preventative maintenance check- list, Dynatest recommends that brake operation, hand brake Although most SHAs do not have a written FWD mainte- pump, load plate lubrication, tires, and belts be inspected on nance plan (Appendix B, Question 7), maintenance activi- a daily basis; their FWD equipment checklist is summarized ties are performed by SHA personnel. FWD equipment and in Table 4. tow vehicle maintenance is performed by SHA employees among 87% of survey respondents (Appendix B, Questions In addition to providing JILS-FWD maintenance ser- 910). Seventeen percent of SHAs reported that they fol- vices, Foundation Mechanics, Inc.'s maintenance personnel low the manufacturer's guidelines for regular maintenance. are able to log into their clients' JILS-FWD computers over Those who did not follow the manufacturer's guidelines usu- the Internet to review files and perform diagnostic tests. ally stated that maintenance activities are done when needed. Twenty-five agencies (listed in Appendix B, Question 11) KUAB offers a preventative maintenance program as an provided other suggestions on keeping their FWD equip- option with their FWDs, which includes cleaning, inspec- ment in working order, including the following (Appendix tion, and calibration. The procedures typically take between B, Questions 8 and 11): three and four weeks to complete and are done by KUAB personnel at their Savoy, Illinois, facility. ˇ Cleaning the sensors and holders with an emery cloth ˇ Storing FWD equipment and vehicles in a heated Merits of Falling Weight Deflectometer Versus garage when not in use Other Nondestructive Testing Devices ˇ Bleeding hydraulic lines annually ˇ Following a brief maintenance checklist before depart- The Missouri DOT (MoDOT) detailed the merits of FWD ing for a job usage in an undersealing study. Before employing FWDs to ˇ Including maintenance activities when FWDs are detect voids, MoDOT used to test load transfer efficiency calibrated (LTE) by the "proof-rolling method." A dump truck was filled to give a rear-axle load of 80 kN (18,000 lbf), and its TABLE 4 DYNATEST RECOMMENDED MAINTENANCE ACTIVITIES AND FREQUENCIES Frequency Activities Check brake operation, check hand brake pump for free movement, check load plate for lubrication, clean Daily, or as required clamping magnets/disks/springs. Tire pressure (approx. 32 psi), lug nuts tight (7590 ft-lb), check breakaway feature (actuator), check brake Weekly lock operation, inner catch parts lubricated with Teflon, external weight guides lubricated with Teflon, lubricate SD foam guides with silicone spray, check/refill battery level, clean infrared/air sensors. Check brake fluid level (DOT type 3 only), check rubber stabilizers for tightness, nuts and bolts tight, R/L cable checked for bends/breaks, check deflector holderstips tight, clean sensor cables with soapy water Monthly only, check charging system connections, coat terminals with corrosion inhibitor, check hydraulic fluid level, clean/inspect electronic connections, perform relative calibration, wash equipment. Annually Change hydraulic fluid, change hydraulic fluid filter, perform reference calibration. Source: DYNATEST.
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11 rear tire was placed 1 ft past a transverse joint between two ˇ Less manpower is required. slabs. Gauges then gave the deflections generated by the ˇ Lanes are closed for less time. load on each slab. When measured, LTE is less than 65% ˇ "No influence of shoulder movement to apparatus." and loaded side deflections were greater than 0.44 mm ˇ Dynamic FWD impulse loads provide a more realistic (17.5 mils), the slab was undersealed. FWDs are preferred simulation of truck movements. over the proof-rolling method, for the following reasons ˇ Multiple load levels are possible. (Donahue 2004):