VERMONT HISTORIC BRIDGE PROGRAM
HISTORIC COVERED BRIDGE PRESERVATION PLAN
INTRODUCTION
The factors threatening
The goal of this preservation plan is for Vermonters
to be able to say, fifty or a hundred years from today, that the state’s
covered bridges are truly historic bridges, not a collection of covered bridges
that were largely rebuilt as new bridges at the turn of the 21st
century.
To pursue this goal, the Historic Covered Bridge
Preservation Committee has been established.
This committee will review the status of all historic covered bridges and
make specific recommendations for each, relying on the priority of uses
explained in Part 1 and the priority of treatments explained in Part 2.
Organization of the committee and its responsibilities are described in
Part 3. Finally, integration of the
preservation plan and the Vermont Historic Bridge Program is described in Part
4. The committee’s recommendations
for each bridge will be developed over time, as required, and will appear in
Appendix A. As new recommendations
are developed or existing recommendations modified, Appendix A will be amended
accordingly.
The committee has established five principal
objectives in developing the plan and its priorities for uses and treatments.
1.
The
historic physical and structural integrity of covered bridges should be
preserved to the maximum extent possible.
2.
Covered
bridges should remain in use on the state’s network of roads whenever
possible.
3.
Towns
provide the best opportunities for continued stewardship of covered bridges.
Partnerships between towns and the State of
4.
The
Historic Covered Bridge Committee will implement this plan through participation
in the development and review of all projects involving historic covered bridges
when state or federal funding is used.
5.
An
effective management system must be implemented and sufficient funding obtained.
This strategy should be balanced, on the one hand, identifying bridges in
very good condition and maintaining them adequately and, on the other,
identifying bridges in very poor condition and preventing deterioration from
becoming irreversible.
PART 1
PRIORITY OF USES
The following uses for historic covered bridges are
listed in order of priority. Preferences
have been established to achieve two objectives.
The first is a desire to maintain the historic use of these bridges as
part of
(A)
Special
Use on Roads. Bridges
will remain in use on roads but will be limited to very light traffic, primarily
cars. This category of use assumes
that alternative routes are available or are capable of being built at locations
near enough to historic bridges to minimize inconvenience and to eliminate, or
reduce to an acceptable level, any risk of damage by overweight vehicles.
At the same time, alternative routes must not compromise the settings for
these historic bridges. Creative
designs for bridge approaches, intended to prevent use by overweight vehicles,
are encouraged. However, these
designs must also avoid damage to settings.
Structural Integrity.
This category of use assumes that the structural integrity of historic
members of these bridges will be preserved to the maximum extent possible.
If bridges suitable for this category of use have been compromised by
extensive alterations, they should be restored to their original design.
Capacity: The capacity sought is the maximum amount obtainable
under the preservation treatments permitted for bridges in this category.
Most bridges should be confined to one-lane traffic.
(B)
Limited
Use on Roads. Bridges
will remain in use on roads and will be limited to vehicles that do not exceed
40,000 lbs. This category of use
also assumes that alternative routes are available or are capable of being built
at locations that accommodate vehicles weighing in excess of 40,000 lbs.
The proximity of alternative routes, the degree of risk that bridges will
be damaged by overweight vehicles, and the historic structural integrity of
bridges are the decisive factors in choices between Category A and Category B
– Limited Use on Roads.
Structural Integrity.
This category of use assumes that the structural integrity of historic
members of these bridges will be preserved.
If bridges suitable for this category of use have been compromised by
extensive alterations, restoration should be considered.
Structural Integrity:
This category of use assumes that the structural integrity of historic members
of these bridges will be preserved. If
bridges suitable for this category of use have been compromised by extensive
alterations, restoration should be considered.
Preservation Treatments:
Superstructure preservation treatments 1, 2, 3, and 4, in that order of
priority, are preferable for bridges in this category.
(E) Bridges Subject to Exceptional Constraints.
The circumstances of some bridges pose exceptional
constraints. A few have been so
drastically altered that repairs required for an acceptable carrying capacity
would necessitate reconstruction of the entire bridge.
In other cases, bridges have been reinforced by systems that make the
historic structure redundant. Bridges
subject to such constraints shall be assigned to this category with the hope
that acceptable alternatives for preservation will develop in the future.
During the interim, a greater variety of preservation treatments are
available for preserving these bridges.
PART 2
PRIORITY OF TREATMENTS
The following superstructure treatments for historic
covered bridges are listed in order of priority.
Preferences reveal a desire to preserve the structural integrity of
historic members of covered bridges to the maximum extent possible.
Many of
1.
Retain all existing historic materials that have not deteriorated beyond
the point of repair. Where existing
rot or other damage is not severe enough to require replacement, the materials
should be repaired rather than replaced. This
treatment should be applied to each member individually, and deterioration of a
large number of bridge elements should never justify the replacement of any
single member capable of being repaired.
2.
Replacement of existing materials in kind, meaning identical in species,
quality, and dimension to the maximum extent feasible, or restoration of
original materials and design. Preferably,
material origins should be from the Northeast region of the country.
If a different species or quality is considered and/ or materials from
the Northeast are not available, substitutions may be considered with
justification.
3.
Application of historic methods of strengthening such as the application
of sister lattices in Town lattice truss bridges.
4.
Introduction of glu-laminated beams as a co-functional, reversible
structural system. The beams must be
designed to work in conjunction with the historic structural system to achieve
required load capacity, and the historic structural system must be restored
according to Preservation Treatments 1, 2, and 3.
5.
Replacement of limited pieces of existing load-bearing members with
materials identical in species, quality, and origin, preferably from the
Northeast region of the country, to the maximum extent feasible.
Dimensions may be larger but must not cause alterations to the dimensions
of any other important bridge components. For
example, increasing the depth of bottom chords of Town lattice trusses may
increase capacity without requiring alteration to either overall bridge
dimension or the design of the floor system.
6.
Replacement of existing load-bearing members with glu-laminated members
(beams or chords) of identical dimension.
7.
Reinforcement of load-bearing members with non-obtrusive modern
materials such as steel rods or plates, glass fiber, carbon plates, or other
materials.
8.
Protection of load-bearing members by the introduction of steel beams
that provide a safety-net for the bridge. The
redundant structure must allow the existing timber frame to continue
functioning, and a minimum clearance between steel beams and floor beams should
be designed. The purpose of this
treatment is to protect the historic bridge in case of structural failure, not
to increase carrying capacity.
9.
Replacement of load-bearing members with, in order of priority: (a)
timber of larger dimension but otherwise identical in terms of species and
quality; or (b) timber of larger dimension and different species.
10.
Replacement of existing load-bearing members with modern materials.
The
following substructure treatments for historic covered bridges are listed in
order of priority. Preferences
reveal a desire to preserve the historic structural integrity of these abutments
to the maximum extent possible and to use masonry materials that are consistent
with existing materials whenever possible.
1.
Masonry
abutments, whether rubblestone or ashlar, shall be retained whenever possible
and repaired rather than replaced. Repairs
should be undertaken with like-kind materials, and all repointing should apply
appropriate mortar. Bearing seats should be repaired in kind whenever possible.
Drainage tubes or weep holes should be installed to channel runoff in all
cases to avoid hydrostatic pressure behind the abutments.
2.
If
masonry abutments, or portion of abutments, have deteriorated to the point where
repair with like-kind materials is not feasible, alternative materials may be
considered. Where abutments have
been undermined by stream flow, concrete underpinning may be installed.
Where bearing seats are inadequate, concrete caps may be added.
3.
If
masonry abutments have deteriorated beyond the point of repair, they may be
reconstructed with modern materials such as concrete.
Ornamental treatments to produce texture such as veneers, form liners,
acid washing, pneumatic blasting, bush-hammering, mechanical stamping or special
form-work may be considered.
4.
Existing
concrete abutments should be repaired whenever possible or replaced in kind if
deteriorated beyond the point of repair.
PART 3
HISTORIC COVERED BRIDGE COMMITTEE
Composition.
The permanent members of the committee shall include the Vermont Agency
of Transportation (VTrans) Structures Engineer, the VTrans Bridge Management
Engineer, the VTrans Historic Preservation Officer, a VTrans special consultant,
the two Co-Managers of the VTrans Vermont Historic Bridge Program, and two
designees from the Vermont Division for Historic Preservation.
Meetings.
The Co-Managers of the Vermont Historic Bridge Program shall call
meetings and prepare a record of committee discussions and recommendations.
Copies of meeting records shall be distributed to each participant after
the conclusion of each meeting. VTrans
project managers and staff will be invited to attend meetings when specific
projects are being discussed.
Town Participation.
One or more representatives from a town owning a covered bridge may be
invited to attend any committee meeting convened for the purpose of making
recommendations for appropriate uses or preservation treatments concerning that
bridge.
Participation by Other
Organizations and Individuals. The
committee may invite other
individuals or organizations to participate in meetings concerning specific
projects. Such participants may
include, but are not limited to, local historical societies, timber-frame
restoration specialists, and the Vermont Covered Bridge Society.
Recommendations
and Coordination with Section 106 of the National Historic Preservation Act of
1966 and its amendments. Committee recommendations reached by
consensus of all participants are desirable. In the event that consensus
is not achieved, a recommendation will be reached by vote. Permanent
members each will be entitled to one vote. Towns owning the bridge in
question will be entitled to one vote. The committee
recommendation will be recorded and notification given to the VTrans Project
Manager. Objections raised at meetings by non-voting participants will be
noted in the record. Any voting participant may request further review of
the recommendation and may take advantage of the provisions for resolving
disputed projects, as outlined by the Vermont Historic Bridge Program
Programmatic Agreement dated
Committee recommendations meet the Secretary’s Standards for Rehabilitation
and therefore are consistent with the requirements of Section 106 of the
National Historic Preservation Act (Section 106). The VTrans Historic
Preservation Officer is responsible for reviewing federally funded covered
bridge projects under Section 106 through a "Programmatic Agreement ...
Regarding Implementation of the Federal-Aid Highway Program in
Responsibilities.
The committee will oversee implementation of the Historic Covered Bridge
Preservation Plan and its incorporation into the Vermont Historic Bridge
Program. Specific tasks will
include:
1.
Preparing
and advocating for an agenda that fully funds and implements this plan as part
of the Vermont Historic Bridge Program.
2.
Identifying
suitable funding programs for special needs such as stabilization and repair of
bridges threatened with collapse.
3.
Submitting
recommendations for assigning each historic covered bridge to a specific
category of use together with the appropriate preservation treatments applicable
to that category.
4.
Advocating
that a plan is prepared for the maintenance and repair of each historic covered
bridge.
5.
Resolving
any conflict among various parties concerning specific bridge projects.
6.
Participating
as needed during both the design and construction phases of each bridge project
affecting an historic covered bridge.
7.
Participating
in presentations to the VTrans Transportation Research Committee when
appropriate.
8.
Evaluating
the merits of innovative products and ideas available for the preservation of
historic covered bridges.
9.
Such
other tasks as the committee, from time to time, determines are appropriate.
Communication. Participation
by the committee is vital, and the committee must be given adequate information
to determine whether design proposals are appropriate.
Effective methods of communication with engineers, contractors, town
officials, and members of the public who work with historic covered bridges are
essential. Toward that end:
1.
Project
managers assigned to work on specific bridge projects should provide all
documentation necessary for committee consideration.
This may include, but is not limited to:
(a)
identification
of all major structural problems and major failures;
(b)
estimates
of structural capacity assuming all components are in good condition; and
(c)
engineering
standards for determining all features and materials to be replaced in order to
achieve the required capacity.
2.
In the
case of projects for which detailed plans have not been developed by an
engineer, the bridge owner should require the contractor to provide a detailed
statement identifying all features and materials to be replaced.
That report should be supplemented by one or more field inspections by
the committee during any disassembly phase.
3.
Contractors
or engineers should notify the VTrans Historic Preservation Officer immediately
in the event that new information is uncovered during the construction phase.
4.
Towns
should notify the committee about any proposed work prior to the commencement of
that work.
PART 4
INTEGRATION OF HISTORIC COVERED BRIDGE PRESERVATION PLAN
AND THE
Ownership of
Bridges.
Partnerships among the respective towns, the Vermont Agency of
Transportation (VTrans) and the Vermont Division for Historic Preservation (VDHP)
are the preferred methods of stewardship. Towns
will remain owners of these bridges but may enroll them in the Vermont Historic
Bridge Program when projects involving substantial repairs are developed,
provided bridges remain in highway use. Enrollment
will take place when an easement agreement has been conveyed from the town to
VTrans, formalizing the town’s commitment to preserving the bridge in
perpetuity for highway use. After
bridges have been enrolled in this program, VTrans will pay for all future costs
of rehabilitation and major maintenance to the extent that federal and/or state
funds are available for such work. VDHP
will cooperate with VTrans in monitoring compliance with the preservation
easements. Towns will be required to
conduct the following routine maintenance tasks as part of the easement
agreement:
1.
Cleaning
bridge components with compressed air and removing with hand tools any deposits
of debris or dirt that may hold moisture.
2.
Keeping drainage areas free of debris and channeling deck drains and
approach run-off away from bridge elements below.
3.
Removing all small trees and shrubs growing in, on, or near substructure
units or under bridges.
4.
Removing any debris that accumulates in the channels beneath bridges.
5.
Maintaining proper load posting and advance warning signs and keeping
all signs visible.
6.
Maintaining a water-tight roof system and repairing any damaged siding.
7.
Removing any accumulated snow when such snow is of a depth to cause
concern for the stability of the structure.
8.
Maintaining smooth transition between approach roadway and bridge decks,
maintaining straight and continuous rails, and repairing minor damage caused by
accidents.
9.
Reporting significant problems concerning bridges to the co-managers of
the Vermont Historic Bridge Program and to the appropriate District
Transportation Administrator.
10.
Consulting
with the co-managers of the Vermont Historic Bridge Program prior to initiating
any emergency repairs.
All historic covered bridges owned by the State of
1.
Educate
towns about the importance of consistent preservation treatments for the
state’s collection of covered bridges and encourage town officials to enroll
eligible bridges in the Vermont Historic Bridge Program.
2.
Establish
and enforce a consistent policy regarding state and federal funding for
town-owned covered bridges that are not repaired according to treatments
recommended by this preservation plan.
3.
Increase
public awareness about the need to enforce load restrictions on historic
bridges, undertake any legislative initiatives required to assure enforcement,
and develop attractive, familiar signage that will notify truck drivers at
appropriate locations to select alternative routes.
4.
Conduct
periodic training programs for state employees, town officials, and other
interested individuals or organizations covering a broad range of topics,
including but not limited to project administration and maintenance.
Objectives.
Success of the preservation plan will also depend on
continued growth of the Vermont Historic Bridge Program and its ability to
address the specific concerns associated with preservation of covered bridges.
Toward that end, the following should be accomplished:
1.
Develop
VTrans engineering expertise in the preservation, restoration, and
rehabilitation of historic covered bridges.
2.
Develop
the ability to apply new technology and treatments to the preservation of
historic covered bridges, as those technologies and treatments become available.
3.
Conduct research and develop design specifications for the preservation,
restoration, and rehabilitation of historic covered bridges.
Research should focus on analysis of structural materials and the
interaction of components and should lead to evaluation of structural components
in place through non-destructive testing.
4.
Develop design specifications for the construction of new timber framed
covered bridges and the rehabilitation of existing historic covered bridges.
5.
Prepare design criteria for roadway approaches to historic bridges that
remain in use on the state’s network of roads and for bridges that are placed
in alternative transportation uses. Criteria
should address a number of issues including, but not limited to, discouraging
large vehicles from using these bridges. For
bridges in alternative transportation use, criteria should seek to preserve the
bridge’s original setting to the greatest extent possible.
6. Develop an appropriate policy for privately owned historic covered bridges. Preservation of these bridges is desirable, but a public interest in these structures must be assured through partnership agreements, preservation easements, or outright conveyance. Legislative initiatives may be necessary to achieve these objectives
.