BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

4.2.5 Railings
NBIS Condition Rating: 6 (Satisfactory)
Condition Description: The timber bridge railing members are generally sound, but contain
splits and checks in the vertical posts, horizontal rails and curbs in isolated railing members
throughout the bridge. These checks and splits retain moisture and provide an avenue for fungal
spores to enter the wood, which promotes decay. Most of the preservative treatment in the
timber railing members has leeched out of the members and thus no longer protects the timber
from decay.
The cut ends of the railings and curbs are not sealed, and although the cut ends for the railings
are not located where water typically ponds, some of the water on top of the rails drains over the
cut ends, which permits water to absorb into the ends of the rails. As the curbs rest on the
sidewalk, they are located where water that ponds on the deck and will absorb into the ends of
the curbs. Water absorption in the cut ends of the rails and curbs promotes decay near the ends.
The cut ends of the top of the posts are capped with copper sheeting to prevent moisture from
entering through the end grains.
As noted above, water absorption results in volumetric expansion of the wood when it is wet and
increased shrinkage of the wood as it dries. Significant volumetric change in the wood can act to
work fasteners loose. Loose bolts securing the horizontal rails to the posts and curbs to the posts
and sidewalk deck, would permit water retention in the small gaps between these elements,
which promotes decay.
As noted above, the bridge railings contain openings between horizontal rail elements of 8”
where the NFPA Life Safety Code specifies that the openings in guards protecting drop-off
hazards should not permit a 4 inch diameter sphere to pass.
Repair Scope: The presence of splits and checks, the lack of remaining preservative treatment,
untreated end cuts, opportunities for retained moisture and exposure introduce conditions
conducive to continuing decay. Although the existing bridge railing members currently exhibit
minimal decay, the remaining service life of the railing will be limited without corrective action.
In-place preservative treatments (see 4.3.1 below) of the timber railing are not recommended.
The railing members are too small for internal treatments. Many of the more effective
preservatives used in surface treatments include toxic chemicals that may be a concern for
human contact and that may be an environmental concern due to the potential contamination
from spills or excess preservative chemicals that leech out of the railings.
As the existing railing elements have some remaining service life, it is possible to reuse portions
of the railing, at least until deterioration has advanced to the point at which the railings are
unsafe. Eventually the railing elements will need to be replaced in entirety.
Rehabilitation Scope: The Rehabilitation Scope would be the same as that above for the Repair
Scope with the exception that it is recommended that the pedestrian railing be modified such that
the maximum opening between the horizontal rail elements not permit a 4” sphere to pass in
Repair/Rehab. Feasibility Study March 10, 2011
Bridge No. C-07-001 (437) 20 Final Report