BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

effectiveness of these chemicals is somewhat limited and has shown mixed results. In addition,
the potential for spills and leeching of the toxic chemical preservatives into the marine
environment raises environmental concerns with significant risk that the use of these treatments
may not be permitted.
A program of continuing to extend the service life of the bridge by way of piecemeal
replacement of timber members, although technically feasible, is generally not cost-effective.
Although it is technically feasible to replace a number of the more readily accessible timber
elements on a piecemeal basis (e.g. bridge railing, curbs, timber wearing surface, sheave poles,
lifting beams and bracing members) replacement of other timber elements that are not readily
accessible requires removal of a significant portion of other elements of the bridge. For
example, replacement of the structural deck planks requires removal of the timber wearing
surface and curbs, replacement of the stringers requires removal of the structural deck, wearing
surface and curbs, replacement of the timber cap beams requires replacement of the stringers,
structural deck, wearing surface and curbs, and replacement of the piles requires complete
removal of the superstructure and cap beams. It is sometimes possible to strengthen or replace a
deteriorated portion of an existing member (e.g. a deteriorated section of a stringer, cap beam or
pile.) However, this typically requires the addition of reinforcing plates to the members or
temporary support of the structure while the deteriorated portion is removed and a new section
inserted and spliced to the existing section to remain. This can introduce significant challenges
in some locations due to limited space, interference with other members, limited access to
fasteners, submerged connections, etc. Although technically feasible, these approaches to
extending the life of the bridge significantly increase the cost to maintain the bridge.
Although there are many examples of timber bridges where the service life has been extended in
excess of a 100 years, most of these bridges are covered bridges located in non-coastal locations.
Unlike covered bridges, where the roof structure and siding typically protect the main structural
timber members, the Mitchell River Bridge is fully exposed to the weather, where the effects of
continual exposure to moisture and sunlight accelerates deterioration and decay and reduces the
service life of the timber. In addition, most covered bridges are not located in marine
environments where timber foundations are subject to marine borer attack. In fact, many of the
covered bridges are supported on stone foundations not susceptible to deterioration due to
submersion in water.
Although technically feasible, prolonging the service life of a timber bridge beyond 30 years in
this environment requires a significant financial investment and maintenance commitment by the
community and agreements by permitting agencies to support these efforts. Furthermore, now
that it has been determined that the existing bridge is historic, the Town has a responsibility to
maintain the bridge in a manner that will prevent the continued deterioration.
Repair/Rehab. Feasibility Study March 10, 2011
Bridge No. C-07-001 (437) 51 Final Report