1 / 15

Falling Weight Deflectometers

Falling Weight Deflectometers. Damon Brandley Graduate Research Assistant University of Illinois at Urbana-Champaign. Outline. What is a Falling Weight Deflectometer? Components Instrumentation Details Instrumentation Specifications Applications. What is the FWD?.

red
Download Presentation

Falling Weight Deflectometers

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Falling Weight Deflectometers Damon Brandley Graduate Research Assistant University of Illinois at Urbana-Champaign

  2. Outline • What is a Falling Weight Deflectometer? • Components • Instrumentation Details • Instrumentation Specifications • Applications

  3. What is the FWD? • Non-destructive test equipment for pavements • Imparts a dynamic load to a pavement structure • Simulates a moving wheel load • Measures deflection of the pavement surface

  4. What is the FWD used for? • Structural capacity/remaining life estimates • Finding in-situ layer moduli • Load transfer efficiency of joints in concrete pavements • Pavement management

  5. FWD Components • Load Cell • LVDT, Geophones, Accelerometers • Displacement measurement • Infrared temperature gages • Pavement Temperature • Air Temperature • Surface Temperature • Electronic Distance Measurement • Control/Data Acquisition Unit

  6. FWD Components • All instrumentation used simultaneously • Deflection profile is key output • Temperature and load data used with deflections to back-calculate pavement structure characteristics

  7. Load Cell Details • Load cell used to measure the impulse loading • Heavy-duty load cell required to support loading up to 60 kips in magnitude • Load created from dropping weights from specified height

  8. Load Cell Details • Load cell measures applied force with strain gages inside assembly • Measured strains on a stainless steel block allows calculation of applied force

  9. Deflection Gage Details • Geophones, LVDT’s, or Accelerometers measure deflections • Geophones and LVDT’s are most commonly used • Deflections measured at known distances from load plate

  10. Deflection Gage Details • Deflection basin is desired output • Deflections are on magnitude of 0-100 mils (mil=1/1000 in.) • High sensitivity is required for measurement

  11. Temperature and Distance Gages • Temperature • Air, Surface, and Pavement temperatures recorded • Temperature used to normalize data • Curves based on pavement type • Properties of asphalt are very temperature dependant • Distance Measuring Device • Electronic Distance measuring device is attached to the axle of the trailer • Records test locations with deflection and load data

  12. Instrumentation Specifications • Load Cells • Range: 0 - 60,000 lb. • Accuracy: 2% • Displacement • Range: 0 to 100 mils (0 to 2500 mm) • Accuracy: ±0.04 mils (1 mm) • Temperature • Range: 0 to 750°F • Accuracy: ±0.5°F

  13. FWD Applications • Pavement analysis and design • Airports • Highways • City Streets • Parking lots • Pavement Management Systems • Pavement rehab./overlay design

  14. Advantages of FWD Testing • Test large area very quickly • Run 1 test per minute • Grid pattern to get general picture • Data compiled and viewed in real-time • Entire test can be run from a laptop inside vehicle • Non-destructive test

  15. Summary • The FWD is composed of several types of instrumentation that work together. • Load cells, deflection gages, temperature gages working in unison to provide engineering insight • Provides fast, non-destructive evaluation of pavements • Provides information on condition of underlying pavement layers

More Related