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Federal Highway Administration Research and Technology
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This report is an archived publication and may contain dated technical, contact, and link information
Publication Number: FHWA-RD-03-093
Date: August 2006

Study of Long-Term Pavement Performance (LTPP): Pavement Deflections

Chapter 2. LTPP Data Screened and Reviewed

Data Request

The level E FWD load-deflection data (Data Release 9.0, November 23, 1998) were requested and received when this project began in 1998. Included with this requested information were up-to-date FWD loads and deflections, along with all pertinent ancillary FWD data. All data were then processed as described below.

Data Organization for Screening and Processing

The data obtained from the database were organized for detailed analyses. Specifically, the largest volume of LTPP data in the database, the FWD load-deflection data from the “*.M06” data tables, was reorganized as follows:

  1. Each level E load-deflection data record was retrieved from the database tables in comma-delimited format, with four directories (i.e., one *.M06 subdirectory for each of the four LTPP regions). For each regional *.M06 file, the data were reorganized into “sections” and “dates of test” while retaining the original format (comma delimited, columns A through W or 1 through 23).
  2. For each LTPP region, subdirectories were then created using a six-character section identification name, with the first two characters being the State number and the last four being the LTPP section identification number. For example, an analysis subdirectory in Region 4 called “040122” denotes State #04 (Arizona) and LTPP section #0122 (Specific Pavement Studies (SPS)–1, section 22). In this report, an individual test section (for instance, section 040122) may also be referred to as section 04–0122.
  3. For each subdirectory identifying the LTPP section, a series of “day” files then were generated. The file names correspond to the date of test at that section, using a six-digit file name in “yymmdd” format. For example, one of the files under subdirectory 040122 is 930726, which contains the load-deflection data records from Arizona’s SPS section #0122, tested on July 26, 1993.
  4. All subsequent data processing began with the above-outlined file format for the FWD load-deflection data. All other ancillary FWD data were left in the format in which it was received, as the size of the remaining database data files was small enough to manage on a personal computer (PC) for use in a standard spreadsheet program.

Individual FWD instruments, or machines, are identified by serial number (SN). Thus FWD SN #129 refers to the FWD with the serial number 129. In this report, serial number is sometimes referred to as unit. Thus FWD SN #129 is also identified as unit #129.

The pre-autumn 1998 comma-delimited structure of each line of load-deflection data, as recorded in the database at level E, is shown in table 1.


Table 1. Format of FWD load-deflection records from the pre-autumn 1998 database.
FWD Load-Deflection Records (Data Lines)
  Data Structure in the Database
Contents of Data Fields Field Max. # of Characters Units
LTPP section identification number A 4 String
State number B 2 Integer
Construction number C 1 Integer
Date of test D 9 yymmdd
Time of test (24-hour clock) E 4 String
FWD SN (FWD serial number) F 8 String
Station number G 6 Floating.1
Lane designation H 2 String
Drop sequence number I 2 Integer
Drop height J 1 String
Peak load plate pressure (kilonewtons) K 4 Integer
Whole history stored offline? L 1 String
#1 deflection sensor reading (µm) M 4 Integer
#2 deflection sensor reading (µm) N 4 Integer
#3 deflection sensor reading (µm) O 4 Integer
#4 deflection sensor reading (µm) P 4 Integer
#5 deflection sensor reading (µm) Q 4 Integer
#6 deflection sensor reading (µm) R 4 Integer
#7 deflection sensor reading (µm) S 4 Integer
(Not used) T 0 Empty
(Not used) U 0 Empty
(Not used) V 0 Empty
Data quality level W 1 String
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