BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

4.4.2 Pile Caps
NBIS Condition Rating: 6 (Satisfactory)
Condition Description: The cap beams for the pile bents are typically sound with no apparent
significant decay, although the caps typically contain 1/16” wide splits and checks throughout on
all surfaces. On Bents 3 and 4, the cap beams contain larger splits and checks up to 1/4” in width
with these extending the full height. The larger splits and checks are of a depth that permits
fungal spores to access the center of the timber, where there are no preservatives, which
increases the risk for decay. Much of the preservatives have leeched from the surfaces of the
timber increasing the risk of surface decay as well. Moisture leaking through the deck, as
evidenced by the moisture staining, is retained on the horizontal top surface of the cap beams,
which promotes fungal decay. The underside of the cap beams over the piles and the top of the
cap beams directly below the timber stringers are not accessible for visual inspection, and thus
the condition of these surfaces cannot be directly verified. The cut ends of the cap beams are not
sealed, and although the cut ends are not located where water typically ponds, water running
over the edges of the deck also runs over the cut ends of the members permitting water to absorb
into the ends of the members, which promotes decay near the ends. Several of the cap beams
exhibit initiation of decay near the ends of the cap.
The cap beams in all but Bents 4A, 6A and 7A were spliced when the bridge was widened in
1949. The galvanized steel bolts used to make the splice exhibit light surface corrosion
indicating that most of the zinc coating on the bolts has been consumed.
Repair Scope: Although the timber cap beams are currently sound with no significant apparent
decay, the size and depth of the current splits and checks, the limited remaining preservatives in
the wood, and the current exposure introduces conditions conducive to fungal decay. As such,
the remaining service life of the existing timber cap beams may be limited without corrective
action.
Similar to the timber stringers, there are options for in-place preservative treatment of the timber
cap beams including both internal and surface treatments. However, many of the same risks and
concerns for in-place preservative treatments exist for the cap beams with exception that the
drilled holes for internal treatment are not likely to be significant and there are no access
concerns. Due to the location of the timber cap beams directly above the waterway, there are
significant concerns with the toxic chemicals and the potential for environmental contamination
from spills or run-off of chemicals that leech from the cap beams. As such, in-place preservative
treatments are not recommended for the timber cap beams.
Rehabilitation Scope: In addition to the work addressed in the Repair Scope replace the cap
beams in Bent 7A with larger members. As noted above, the cap beams will need to be made
approximately 4’-0” longer (2’-0” on each end) to accommodate the required shift in the
operating winches and sheave poles needed to improve accessibility. If the decision is made not
to shift the masts, the cap beams at Bent 7A could be strengthened using fiber reinforced
polymer (FRP) sheets applied to the exterior faces of the members.
Repair/Rehab. Feasibility Study March 10, 2011
Bridge No. C-07-001 (437) 35 Final Report