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Publication Number: FHWA-HRT-06-132
Date: December 2006
The physical setup described in this manual is mandatory for all LTPP-owned FWDs. Other FWDs collecting data on behalf of LTPP may not be capable of the setup described. In those cases, the setup should be followed as closely as possible.
For all LTPP testing, maintain the same placement of the geophones on the FWD. Measure geophone offsets from the center of the load plate to the center of the geophone holder. Measure the location of each geophone directly from the center of the load plate to avoid accumulated error. Offsets in front of the load plate (i.e., in the direction of the hitch) are considered positive. Offsets behind the load plate (i.e., in the direction of the rear bumper) are considered negative. The required offsets are shown in Table 1.
|1mm = 0.039 inch|
If testing is to be performed on behalf of LTPP by an FWD that mounts only seven deflection sensors, use the sensor spacings shown in Table 2.
|Deflection Sensor||Offset |
|D1||0 mm||0 mm|
|D2||203 mm||–305 mm|
|D3||305 mm||305 mm|
|D4||457 mm||457 mm|
|D5||610 mm||610 mm|
|D6||914 mm||914 mm|
|D7||1,524 mm||1,524 mm|
|1mm = 0.039 inch|
Non LTPP-operated FWDs and LTPP-operated FWDs that have undergone overhaul or replacement of the sensor bar or deflection sensor holders must have the deflection sensor offset measured and set accurately using the following procedure.
Configure the weight package the same for all LTPP testing. For Dynatest model 8002 FWDs, use three standard weights per side. Use two buffers per side. When new buffers are installed on the FWD, fill out form F04 and submit it to the FHWA LTPP FWD task leader.
If testing is to be performed on behalf of LTPP by an FWD other than a Dynatest model 8002 FWD, select a combination of buffers and weights that achieves the load requirements described in manual section 4.2 and comes as close as possible to a 13-millisecond (ms) pulse rise time.
Four load levels are defined here for LTPP testing. The acceptable load range for each drop height is between 90 percent and 110 percent of the target value. Experience has shown that drop loads for a given drop height tend to decrease slightly over the course of a day of testing. Setting the drop load at 103 percent of the target load at the beginning of the day will minimize the deviation over the course of the day for most cases.
Each drop height must be within the acceptable range shown in Table 3 for all testing. Table measurements are in kilonewtons (kN) and kips (1 kip = 1 × 103 lb). Drop heights may not be adjusted during a test pass.
|Drop Height||Target Load, kN (kips)||Acceptable Range, kN (kips)|
|1||26.7 (6.0)||24.0 to 29.4 (5.4 to 6.6)|
|2||40.0 (9.0)||36.0 to 44.0 (8.1 to 9.9)|
|3||53.4 (12.0)||48.1 to 58.7 (10.8 to 13.2)|
|4||71.2 (16.0)||64.1 to 78.3 (14.4 to 17.6)|
|Note: Drop height 1 is not used for testing on rigid pavements.|
This section includes specific software settings required for LTPP testing. Instructions on how to enter these settings into the data collection software are given in the LTPP FWD Data Collection Software Manual.
All FWD data collected for LTPP should be in International System (SI) units, with the exception of station units, which should be in feet. Specifically, temperature should be recorded and displayed in Celsius (C), load in kilonewtons (kN), deflection in micrometers (µm) (microns), and deflection sensor offsets in millimeters (mm).
Data collected with LTPP FWDs should be in the FWDWin MDB format. Data collected with non-LTPP seven -sensor FWDs should be in the R80-20 format, where possible. For FWDs not supporting either of these formats, contact the FHWA LTPP FWD task leader for instructions with a copy to the Technical Support Services Contractor (TSSC) before testing begins.
Collect data with all filters and smoothing turned off.
Enable the following checks:
Further information on what these checks are and what to do if they fail appears in manual section 6.
Two different drop sequences are used for LTPP testing:
|Where||C is a seating drop (no data saved) from drop height 3,|
|1 is a drop from drop height 1,|
2 is a drop from drop height 2,
3 is a drop from drop height 3,
4 is a drop from drop height 4,
H indicates that the full-time history for that drop is to be saved.
In addition, one of the following drop sequences is used to warm up the buffers before testing:
Furthermore, the reference calibration and the relative calibration drop sequences from the "SHRP-LTPP FWD Calibration Protocol" should be preprogrammed into the LTPP-owned FWDs.
The file name for an FWD data file should be eight characters in the following format: XXYYYYZN
|Where||XX is the state code for section location,|
|YYYY is the LTPP section ID for the section,|
Z represents the site visit (A for the first visit, B for the second visit, and so on), and
N represents the pass number.
For example, for the first pass of the first visit to section 3807 in North Carolina, the file name should be 373807A1. Test passes are described in detail in manual section 5.2.
Topics: research, infrastructure, pavements and materials
Keywords: research, infrastructure, pavements and materials, Deflection measurement, falling weight deflectometer, LTPP
TRT Terms: research, facilities, transportation, highway facilities, roads, parts of roads, pavements