| Summary: | <p>Advanced nondestructive inspection techniques like stress wave timing and
resistance microdrilling have been used to successfully inspection timber bridges, but it
is most effective on girder style bridges. There is a noted need to develop additional
inspection techniques for longitudinal deck/slab timber bridges, which comprise about
20% of the national bridge inventory. One technique that holds potential is ground
penetrating radar, a recognized nondestructive testing technique that has been used
effectively for many different environmental and transportation applications. It has
been utilized successfully to identify buried objects, internal defects and material
changes. The objective of this research was to assess the potential for using GPR to
identify and assess simulated deterioration in longitudinal timber deck timber bridges.
GPR scans were completed in the longitudinal and transverse directions of a screwlaminated
timber bridge deck before and after a bituminous layer was added to assess
embedded defects that simulated voids, decay, insect damage and horizontal shear
splitting. Assessment of the GPR wave energy signal was completed using visualization
software that was provided with the commercial GPR unit used for the testing. The
radar signal was analyzed in both the longitudinal direction (antenna front to back) and
the transverse direction (antenna side to side). Interpretation of the radar signals
allowed for the identification of various internal defects present in the deck. Based on
the results, GPR has the potential to identify internal defects in timber bridge decks
before and after a bituminous layer was added. Large, rectangular void defects (at least
6‐ by 12‐ by 5 in. (15.2‐ by 30.4‐ by 12.7 cm)) that were hollow, filled with foam, or filled
with sawdust/adhesive were most easily identified under all scanning conditions. The
addition of a bituminous layer, common to slab bridge construction, damped the signal
response and made it more difficult to identify defects. Several smaller defects that
were found in the deck without a bituminous layer were not identified in scanning
completed after the bituminous layer was added.</p>
|
|---|
