BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

Load Capacity: The current loss in section of the piles is not currently considered severe enough
to reduce the load carrying capacity of the bridge to a capacity less than the other governing
members of the bridge. However, if the piles are permitted to continue to deteriorate, it is likely
that this condition will eventually be reached.
The foundation capacity of many of the piles is unknown as there are no pile driving records
indicating the depth to which the piles were installed or the driving resistance that was achieved.
Although it is likely that the piles were driven to dense sandy glacial till material found 40 to 50
feet below the river bed, this cannot be confirmed. There is also no information regarding the
design capacity of the 1925 piles. The predicted local scour (approximately 4 feet) will further
reduce the load carrying capacity of the piles and the lateral stability. Although there is no
reported significant settlement or loss in stability, the factors of safety for both axial capacity and
lateral stability are unknown and thus there is a risk that the piles can settle under heavy loads or
lose stability due to scour from a major storm event.
Maintenance: Installation of FRP jackets to the piles may increase maintenance as it may be
necessary to provide minor maintenance of the jackets. Based on the limited experience with
these jackets, it is difficult to fully gauge the maintenance impacts.
Replacing the timber piles now would reduce maintenance in the short-term by reducing the need
to make periodic repairs to the deteriorating timber or to reapply in-place preservative
treatments. However, based on the limited anticipated service life of timber piles in this
environment, maintenance would likely continue to be a significant long-term concern with the
less effective water-borne preservatives. Use of tropical timber may increase the service life
slightly and thus reduce maintenance somewhat, but because the durability of this timber is
unreliable, the long-term maintenance is still anticipated to be a significant concern.
Visual Impacts: The installation of FRP jackets on the piles may introduce a visual impact, as
the timber piles will be completely obscured by the jackets. Furthermore, the jackets will be
significantly larger in diameter than the existing piles (approximately 18” to 20” in diameter
instead of the current 12” diameter timber piles.) With the FRP jackets installed, the piles will
effectively no longer be considered timber piles as they will be considered composite piles (i.e.
FRP shell with a timber core.)
4.4.4 Timber Bracing
NBIS Condition Rating: 4 (Poor)
Condition Description: The timber lateral bracing members throughout the bridge were
replaced, with the exception of the bracing members in Bents 4A and 6A, when the bridge was
reconstructed in 1980. There are diagonal lateral bracing members secured to the piles in every
pile bent with the exception of Bent 8 and diagonal longitudinal bracing members attached to the
piles at the outside edge of the bridge between Bents 2 and 3, Bents 5 and 6 and Bents 8 and 9.
The bracing sometimes include spacer boards to offset the bracing from the piles needed to
accommodate misalignment of the piles.
Repair/Rehab. Feasibility Study March 10, 2011
Bridge No. C-07-001 (437) 42 Final Report