GENERAL

The Kansas FWD Calibration Center is a 1,000 sq. ft, indoor facility in a new building and is a part of the Civil Infrastructure Systems Laboratory (CISL).  CISL is located on 924 Carlson St. just off McCall Road in Manhattan, Kansas. The calibration laboratory floor space is approx. 1,000 sq ft. (32 ft x 32 ft) and has a height clearance of 12 ft.  It is accessible by a 10 ft x 10 ft retractable door.  This indoor space provides easy access for FWD and towing vehicle, large level floor, controlled temperature and humidity, heating, and good security for the calibration equipment.

    The floor slab is 15 feet by 15 feet, with and 8-foot wide clear zone around perimeter (for maneuvering FWDs and the reference data acquisition system) and was built as a smooth, crack-free Portland cement concrete surface. The slab consists of a 5-inch thick Portland cement concrete slab resting on an 8-inch open-graded crushed stone base.  This slab thickness was intended to achieve slab deflection of at least 16 mils due to a 16,000 lb load at the position of the deflection sensor holder when the FWD is in the specified position for calibration. To increase the fatigue life, fiber-reinforced concrete was used in the slab.  A layer of filter fabric was placed below the base to protect it from intrusion of subgrade fines. The slab when tested upon completion showed a deflection of more than 17 mils under a 16,000 lb load at the location of the sensor holder. The senor holder was located not closer that two feet from the edge of the test pad.

REFERENCE CALIBRATION EQUIPMENT

The following items were fabricated at the shop of the Civil Engineering Department at Kansas State University for the Kansas FWD calibration laboratory following the blue prints supplied by the SHRP/LTPP program:

A 3' wide x 22" high x 5' long concrete inertial block weighing approximately 4,000 lbs. was cast. The block was lightly reinforced with No. 3 and No. 5 rebars and rests on 4" x 4" Air Cel low frequency rubber isolation pads. The block is equipped with 4 trailer jacks for easy and precise vertical positioning. Photo #1 shows the concrete inertial block for the Kansas FWD calibration center.

A 5-foot long, wide flange aluminum reference beam was attached to the concrete block through a base plate as shown in Photo #2. On the other end of the beam, the LVDT mounting hardware was fabricated which consists of the deflection sensor holder assembly (LVDT Clamp, Top Plate, Bottom Plate, Spacer, KUAB Seismometer Mount, Washer, Stainless Steel Bolts, Hex Head Cap Screws and Magnetic Tip for LVDT) as shown in Photo #3.  A fish eye bubble has been placed to ensure that the top plate is level after the sensor is in place in the holder.

A Schaevitz Model GCD-121-125 DC Linear Variable Differential Transformer (LVDT) with 0.125-inch stoke and Cannon connector was used. A Schaevitz metric LVDT calibrator, C-41M (micrometer), was used in an in-house assembly for calibrating the LVDT as shown in Photo #4. A magnetic tip is used on the top of the LVDT while in  the calibration assembly.

  A KUAB Seismometer holder assembly consisting of KUAB Seismometer holder frame, KUAB Seismometer mount, base plate, steel rod and machined screws, was also fabricated.

  The fabricated Dynatest Geophone holder consists of aluminum frame, steel clip, circular base plate, aluminum base, steel rods, and machined screws.

  A Measurements Group, Inc. Vishay Model 2310 signal conditioner, shown in Photo #5, with modification for + 15 V DC and - 15 V DC excitation, was installed with line cord and stabilizer, and extra am phenol plug with options V & Y.

  A Keithly-MetraByte Model DAS-16 G2 data acquisition board, with STA-16 screw terminal board and C-1800 ribbon cable was installed in the dedicated computer which is an IBM-compatible microcomputer with 80486 processor with 40 MHZ  processor speed, 1.6 megabyte RAM and 400 megabyte hard drive. An 8-bit expansion slot was used for the MetraByte board. The computer has a VGA color monitor, and a good quality, ink jet printer is used for printing. The complete data acquisition and out put assembly is shown in Photo #6.

Connecting cables, Vishay to LVDT and Vishay to MetraByte, were purchased from a local Radio Shack (RS) store.

A reference load cell (300 mm diameter, 40,000 lbs. capacity) was fabricated following the structural and cabling diagrams furnished by the LTPP program. The following are the components of the load cell: aluminum body and lid, box (RS #270-230), cable (3 conductor, shielded), 2 Kohm resistor (RS #271-1321), push button switch (RS #275-609), cable strain relief (RS #278-1636), 3 lug strip (RS #274-688), strain gages, Am phenol receptacle, Am phenol plug, cable, cable clamp, ribbed rubber sheet, and guide posts. For signal light, the following components were used: box (RS #270-230), cable (RS #278-513), LED (RS #276-022), LED holder (RS #276-079), and cable strain relief (RS #278-1636). The strain gages were installed in the load cell by the B & Q Technical Services in Philadelphia, Penn. Photos #7 and 8 shows the complete load cell. Connecting cables were also needed for connection from Vishay Signal Conditioner to the load cell. Circular wooden blocks (Photo #9) matching diameter of the load cell were also assembled in the shop. The annual calibration of the load cell is performed at Cornell University in Ithaca, New York.

FWD reference calibration software (FWDREFCL) and documentation were obtained from the LTPP program.
 
 
 

Photo # 1 Concrete inertial block for the Kansas FWD calibration laboratory.
 
 

Photo #2 Wide flange aluminum reference beam
 
 

Photo #3 Deflection sensor holder assembly
 
 
 

Photo #4 Micrometer assembly for calibrating the LVDT
 

Photo #5 Vishay model 2310 signal conditioner
 

Photo #6 Data acquisition and out put assembly
 
 

Photo #7 Reference Load Cell

Photo #8 Reference Load Cell
 

CURRENT STATUS:

The calibration center is now operational.  An independent quality assurance visit by PCS/LAW Inc. of Beltsville, Maryland has confirmed that the equipment and setup are working correctly.  KSU, from now on, will provide KDOT with continued FWD reference and relative calibration services as per a Memorandum of Understanding (MOU) between KDOT and KSU till year 2002. The MOU defines the mechanics of cooperation between the Secretary of the Kansas Department of Transportation and KSU regarding the use and maintenance of the proposed facility. Kansas State University will continue to operate this facility well beyond this date. The facility is also available for calibration of FWD's from other states and private industry.
 

Download Precalibration Trip Checklist here.
 

Watch the FWD Calibration Movie
 

Last Updated: September 23, 2002.