Covered Bridges – DuBois & King, Inc.

Wentworth Village Common Covered Bridge

Under a compressed time frame and uncertain budget, D&K provided civil-structural and permitting services for a project that replaced a severely deteriorated circa 1909 truss bridge with a covered bridge for pedestrian and other recreational traffic. The closure of the truss bridge redirected school children accessing the bus stop and others on foot onto the unprotected shoulder of NH Route 25.

Shortly after the closure, the client found a freely available covered bridge in the middle of an active demolition site in Bedford, NH and directly contacted D&K—with no clear schedule or available budget—to evaluate the structure for reuse and design shoring for transportation to the Wentworth site in a matter of a few weeks. Initial challenges included: the covered bridge had to be removed with no cost or inconvenience to the demolition contractor/owner; at 106 feet, the covered bridge was 10 feet longer than the bridge it would be replacing; due to the bridge’s design, non-destructive disassembly was not feasible; and no cranes of sufficient capacity to lift the covered bridge were available on short notice. D&K evaluated techniques to strip the bridge down to the appropriate pick weight for the available cranes; devised and implemented a design-build contract to utilize NHDOT municipal bridge aid funding to redesign the existing abutments; and designed cost-effective rehabilitation and modifications to allow for new loading conditions, exposure to the elements, and an increased hydraulic opening.

In addition to replacing a historically accurate covered bridge and providing a protected river crossing, (the truss bridge originally replaced the only covered bridge in the Town’s history) the project reused a 106’ all-timber structure that would have otherwise been landfilled. The bridge is designed for a 50-year service life. Located in the center of the Town, the bridge serves as a focal point for a municipal park and will serve additional planned outdoor recreation traffic including snowmobiles, human-powered winter recreation. The project received a 2018 Engineering Excellence Award by the American Council of Engineering Companies, New Hampshire Chapter.

Green River (Pumping Station) Covered Bridge

Conducted investigations and developed plans and cost estimates for the restoration and repair of the Green River (Pumping Station) Covered Bridge. The east abutment was severely scoured and settled as much as 6 ft as a result of a Tropical Storm Irene-related flood event, causing uneven settlement of the truss end bearings and racking and distortion of the bridge superstructure. Several main timber elements were distorted and broken. The bridge is a 93-ft-long, single span structure spanning the Green River. Constructed in 1972, the bridge utilizes Howe truss framing and has a cantilevered sidewalk. Recommendations and design for repairs include:

Temporarily shore east end of bridge superstructure
Demolish and remove east concrete abutment and wing walls
Construct new east concrete abutment on steel H-pile foundation
Jack bridge onto a new east abutment
Repair/replace broken upper lateral bracing
Replace all corroded steel truss tension rods
Replace corroded lower lateral steel bracing rods
Replace broken timber curbs
Remove and replace broken or decayed sidewalk deck planks
Replace broken or decayed cantilever sidewalk supports
Widen/expand west abutment for sidewalk bearing
Chink stone masonry at west abutment
Reconstruct east approach roadway

Principles of the Secretary of the Interior’s Standards of Rehabilitation and the Burlington Charter were followed for the renovation of this historic structure.

Wright’s Covered Bridge

Selected by the New Hampshire Division of Historic Resources (NHDHR) to provide consulting services for the historic preservation and rehabilitation of a 124-ft-long, single span truss covered bridge constructed in 1906. The timber trusses (Town Lattice) are augmented with 58-inch-deep, nail-laminated timber arches, which are integral with the chords and web members of the trusses. Project included a Section 106 historical clearance. Design of preservation measures and repairs included:

Installation of a dry sprinkler system
Installation of a linear heat detection system, power, and control
Telemetering of the heat detection system
Application of intumescent paint
Application of fire retardant
Installation of a dry hydrant for a water source
Structural repairs to deteriorated truss members and webs
Repair/replacement of timber bearings, repair of runner planks
Replacement of deteriorated (rotted) siding and timber deck
Application of insecticide at abutments

Principles of the Secretary of the Interior’s Standards for Rehabilitation and the Burlington Charter were applied to all phases of the work.

Whittier Covered Bridge Design-Build

The design-build team of DuBois & King and 3G Construction provided design and construction services for the rehabilitation the 132 ft long, single span Whittier Covered Bridge. This one lane bridge, constructed in the 1870’s, utilizes a Paddleford Truss, a unique framing style only used in a few northern New England covered bridges. The bridge superstructure was moved off the abutments and relocated on land on the south approach road. Project includes repair/replacement of deteriorated/broken timber members, increasing live load capacity to 6 tons, increasing snow load capacity of roof members to comply with current code requirements, and increasing wind resistance capabilities of all lateral bracing members.

A three-dimensional computer model was made of the superstructure for analysis of all loading conditions and to identify members needing to be strengthened. Completed field observations and condition assessment report with recommendations and cost estimates for extensive repairs. Repairs include strengthening roof purlins for snow loads; modifying lateral brace member connections for increase wind load resistance; replacing deteriorated (rotted) truss chord and truss diagonal members; and repairing/replacing stringers, floorbeams, and lower lateral bracing. Prepared preliminary repair/rehabilitation drawings and submitted to the NH Division of Historic Resources and the NH Department of Transportation for review and concurrence. The project received a National Historic Covered Bridge Preservation Grant. Services include:

Assessment of existing conditions
Preparation of investigations/recommendations report
Preparation of contract documents

Village Covered Bridge

The Village Covered Bridge, also known as the Big Eddy or Great Eddy Bridge, is a 105-ft-long, single span structure constructed in 1833. A cantilevered timber sidewalk was added on the downstream side in 1940. This bridge is Vermont’s second oldest covered bridge. The one-lane bridge spans the Mad River in downtown Waitsfield and utilizes a Queen Post and Burr Arch configuration, with trusses spaced 16-ft apart. The Village Covered Bridge is listed on the Historic National Register and the Vermont State Register of Historic Places.

Emergency Repairs – DuBois & King provided fast-track structural inspection, evaluation, and rehabilitative design for the bridge, which was damaged during Tropical Storm Irene. Damaged components include: timber siding, timber truss, timber diagonal member, north abutment backwall, north and south sidewalk approaches, and north roadway approach. The Village Covered Bridge is a vital transportation link for residents of the Town of Waitsfield. Closure of the bridge forced residents to use a 4.5 mile detour, thus making repairing the bridge a high priority for the Town.

Subsequent to the emergency repairs, DuBois & King was selected by the Town of Waitsfield to evaluate the current condition of the bridge, make recommendations for repairs, design repairs, and provide construction administration services.

The structure was showing signs of distress with noticeable sag at the outside edge of the cantilever sidewalk and negative camber in both trusses at the north end near the abutment. Noticeable spalling and deterioration of the north and south concrete abutments and wing walls was also evident.

DuBois & King completed extensive field observations and prepared a condition assessment report with recommendations and cost estimate for repairs. Recommended repairs included jacking and rehabilitating the main trusses; rebuilding and supporting the cantilever sidewalk as an independent structure; concrete repairs and patching on the abutments; and repairs and replacements to deteriorated or worn roof rafters, floor beams, and decking. Professional services include:

Inspection
Alternatives analysis
Public meetings
Historic review
Recommendation for short and long term repairs
Final design of recommended improvements
Bid phase services
Construction phase services