What is the targeted live load capacity? Will the posted load limit or design live load capacity be increased?
The legal posted load limit of 3 tonnes will be maintained after the proposed bridge rehabilitation, regardless of the actual capacity of the bridge. The target design vehicular live load capacity will remain at the current 5 tonnes. This “design” or “actual" load capacity is the factored load capacity that takes into account statistical variations in loads and material properties, as set out in the Canadian Highway Bridge Design Code (CHBDC).
While the vehicular live load capacity would influence the extent of reinforcement on the bridge, this is not the only governing load on the structure. Forces perhaps not considered by the public include loading due to wind, snow, water and ice. In the case of the West Montrose Covered Bridge, with the relatively low posted load limit of 3 tonnes, the governing load combination for various structural members is not entirely dependent on the vehicular live load capacity. To ensure the bridge has sufficient strength to withstand the various environmental forces (such as wind and snow), the rehabilitation design will, at minimum, be designed to withstand the CHBDC specified forces. The goal of the Design Team is to ensure the rehabilitated bridge will not fail under its intended use with allowances for the occasional extreme loading events.
Some of the feedback has suggested that the design live load should be raised to a value greater than 5 tonnes as part of the rehabilitation, even if the posted load remains at 3 tonnes. The rationale for this is not clear. There have not been any requests made by emergency services for an increased capacity. Further, the experience of other jurisdictions indicates that if the actual load capacity is increased, this fact will become known and the bridge will attract more traffic, even if the legal posted load limit remains as-is. The Region and Township do not wish to attract more and heavier vehicles to West Montrose, therefore, the intention is not to design the West Montrose Covered Bridge for heavy vehicles. The existing bridge on Line 86 serves this purpose.
Based on the targeted capacity, how thick would the reinforcement of the lower chord need to be?
A wood expert will be added to the project team to provide recommendations about the specific reinforcement requirements and any impacts to the height of the bridge from the proposed rehabilitation. These results will be made available once the work has been completed.
Has a thorough inspection and analysis of the bridge timbers and the status of the structure been conducted?
Non-destructive testing and evaluation of the existing timbers will be undertaken over the next few months.
There are hundreds of wood truss bridges in Canada and a number of firms with significant expertise in this area. The design of bridges in Canada is governed by the Canadian Highway Bridge Design Code (CHBDC). CHBDC provisions are set by technical committees consisting of industry firms and experts in the relevant fields. The code provisions for wood bridges are set by a committee of persons with expertise in wood structures. The Region is familiar with some members of the Wood Committee and has reached out to the Chair of the Wood Committee to help identify firms with a breadth and depth of knowledge in wood truss bridges. Subsequently, the Region has identified a number of firms with substantive experience in the design, construction, evaluation and rehabilitation of major wood truss bridges, including historic wood truss bridges, as well as the use of carbon fibre reinforced polymers (CFRP). Several highly-qualified, highly-experienced firms have expressed interest in joining the West Montrose Covered Bridge technical team.
A request for proposals will be posted publicly for this work. The successful firm will undertake the timber-specific engineering items. A recommendation to approve the design alternative will not proceed until after this evaluation is complete.
Will the roadway elevation be raised?
The roadway elevation of the bridge will not be raised, as the floorbeam/deck elevation can be held constant. No adjustment of the approach road elevations will be required and the approach roads will meet the bridge deck at the same elevation as they do now.
Will camber be introduced?
Camber is an upward convex curvature built into the unloaded structure in order to counter the normal effects of vertical deflection under load and does not increase the load capacity. Camber is an industry standard practice for a wide variety of bridge types and materials. The original construction drawings of the West Montrose Covered Bridge do not indicate any cambering of the bridge. However, the Region believes that there is benefit to introducing camber to the structure. Regardless, this will have no bearing on the total height of the structure taken at any given cross section. Further, it is noted that the camber in any bridge is a maximum at/near the centre of the span and zero at the abutments and piers. Accordingly, any new camber introduced at West Montrose will have no effect at the approach roadway / bridge interface.
Has advice from historical experts been sought?
A Heritage Impact Assessment (HIA) is being prepared to assess potential impacts of the project and recommend mitigation measures for any identified negative impacts. Once completed, the HIA will be reviewed by the Region’s and Township of Woolwich’s Heritage Planning Committees and will be posted publicly on this page.
The consultant preparing the HIA is Unterman McPhail Associates (UMA), and they have offered some initial opinions on the two Alternatives that are being presented to the public for consideration.
UMA has noted that the focus for the bridge rehabilitation should be on considering approaches to maintaining the historic place in the community and determining interventions that preserve the character-defining elements of the built heritage resource and the cultural heritage landscape context.
There are pros and cons with each option. As noted in the evaluation table within the PCC Info Package, the steel reinforcement option (Alternative A) has the advantage of more closely matching the existing bridge, while being more reversible in nature. Conversely, the timber reinforcement option (Alternative B) more closely matches the historical form of the bridge when it was opened, but has the disadvantage of being less reversible than the steel reinforcement. Both alternatives involve retention of the existing bridge with sympathetic modification. A more fulsome explanation of the heritage impacts will be outlined upon completion of the HIA.
To what time period, structurally and aesthetically, should the bridge ideally be restored?
The Region is not undertaking a historical restoration, the Region is conserving the bridge through rehabilitation and repair. The West Montrose Covered Bridge is an example of an evolved structure that has functioned exactly as the builder intended to date. The beauty of this wooden structure and other historic bridges in Woolwich Township is that as structural components reach the end of their useful lives they can be repaired and replaced without a full-scale removal or demolition of the bridge. Picking a period to restore the bridge to is not as simple as it may seem, as it has evolved through various repair and renewal projects. The ongoing repairs and replacements to the West Montrose Covered Bridge throughout its lifetime have been extremely well documented. However, determining the character defining elements of the bridge that should continue to be conserved, and the method by which the community deems these elements should be conserved is the sole purpose of the public consultation, and will be central to Regional’s Council’s decision on how to proceed.
Can the bridge be restored to the way it was initially constructed?
No. The original 1881 design of the bridge would not meet the Canadian Highway Bridge Code, even for modest traffic loads.
Will Letson Park and/or Gole Park be used as a staging area?
The work will require a staging area to allow for storage of materials and equipment, assembly of components, and a site trailer. The Project Team is proposing that Letson Park and/or Gole Park be used for this purpose. The park will be restored to original or better condition upon completion of the project.
What is the timeline for construction?
Construction is currently expected to commence in 2023 and be completed by the end of 2024.
What happens if we don't do this major rehabilitation?
If the major rehabilitation is not undertaken, the key structural systems will continue to deteriorate to the point where the bridge will no longer be able to safely carry even its own weight.
In short, the bridge must undergo major rehabilitation if is to carry us through the current century.
Will I be able to use the bridge during construction?
Construction of the rehabilitation will require the full closure of the West Montrose bridge to all motorized vehicles and horse-and-buggy traffic for up to one full year.
It is currently believed that the bridge can remain open to pedestrians and cyclists for most of the construction period; however, there will be critical phases where the bridge will be unavailable to pedestrians and cyclists for an estimated period of up to two weeks.
Detour routes will be established and efforts will be made to make these routes as convenient and safe as possible for all road users, including horse-and-buggy traffic, pedestrians, cyclists and motorists.
More detailed information will be made available prior to construction, through letters to adjacent property owners and tenants, sign boards and postings to the Region’s web site and/or the Region’s engagewr.ca platform.