BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

The bracing members typically exhibit moderate to heavy deterioration and corresponding loss in
section within the tidal zone due to marine borer attack. The south end of Bent 3, the north end
of Bent 5, and the south end of Bent 8 represent the most severe conditions with the lower end of
the bracing member exhibiting complete deterioration for a length of 4 to 5 feet.
All of the existing bracing members contain creosote preservatives; however, much of the
creosote has leeched from the bracing members in the tidal zone and thus no longer protects the
bracing members from surface decay and marine borer attack. The creosote preservative in the
upper portion of the bracing is in greater quantity; however, there is evidence that the quantity
has reduced somewhat due to ongoing leeching of the material.
The galvanized steel bolts that attach the bracing members to the piles exhibit heavy surface
corrosion and moderate section loss in the tidal zones and light surface corrosion at other
locations.
Repair Scope: As the bracing members throughout the bridge include significant deterioration
from marine borer attack, it is recommended that the timber bracing members including
corresponding spacer boards be replaced. As the bracing members are partially submerged in
saltwater and creosote preservative treatment of piles is restricted for use in marine
environments, the bracing members will need to be replaced with dimensional lumber with
water-borne preservative chemicals permitted for use in this environment. As the water-borne
preservatives are less effective in protecting the timber, the bracing members are likely to have a
limited service life. The use of tropical timber may increase the service life somewhat, but
recent experience in similar applications indicates that the service life is still likely to be limited.
It is recommended that the bolting hardware throughout bracing system be replaced with more
corrosion resistant material such as Type 316 stainless steel that does not rely on sacrificial
material with a limited service life (e.g. zinc coatings) to protect the bolts.
Rehabilitation Scope: The Rehabilitation Scope is the same as that for the Repair Scope.
Functionality and Safety: The bracing members do not affect the functionality and safety of the
bridge.
Load Capacity: The bracing members are required for the lateral stability of the structure and to
reduce deflections that might make motorists and pedestrians feel uncomfortable. The lateral
bracing does not otherwise directly affect the load carrying capacity of the structure.
Maintenance: Replacing the timber bracing 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.
Repair/Rehab. Feasibility Study March 10, 2011
Bridge No. C-07-001 (437) 43 Final Report