The Western Avenue Bridge spans the Contoocook River and is located approximately 1.5 miles southwest of the main village of Henniker. The bridge, with an overall length of 301’-4½”, is comprised of two high Pratt steel through trusses spaced at 27’-5” and has two span lengths of 149’-3” each.
The trusses were originally erected in the Town of Pembroke in 1915 and were subsequently moved to the Henniker location. As part of the construction of the bridge in Henniker in 1933, the majority of the truss members (upper and lower chords, vertical and diagonals) were retained; however, the floor system, sway bracing and upper lateral bracing members were replaced with new members.
The bridge was rehabilitated in 1988, at which time a new 3” concrete filled steel grid deck was installed, all of the exterior roadway stringers and lower lateral bracing members in the westerly span were replaced and remaining floor beams and stringers were strengthened in many locations by adding welded steel plates and bars. Additionally, plates were added to reinforce some truss members.
This bridge had an Average Annual Daily Traffic (AADT) volume of 840 vehicles per day prior to the bridge closure in 2009 due to extensive advanced member deterioration and no remaining safe live load carrying capacity. Since its closure, the traveling public has utilized the nearby single-lane Patterson Hill Road Bridge, as a detour, to cross the Contoocook River.
Due to the extremely poor condition of the structure, the bridge is being replaced. Hoyle, Tanner developed the bridge replacement design through the NHDOT Municipal Off-System Bridge Rehabilitation and Replacement (MOBRR) program, including the NEPA process, design, utility coordination, right-of-way coordination, hydraulic evaluations, geotechnical evaluations, cultural resource coordination and natural resource coordination. A programmatic Categorical Exclusion and individual Section 4(f) evaluation were also included. The bridge will be replaced with a new, two-span galvanized steel truss bridge with span lengths of about 165’ each, for a total bridge length over the river of about 330’. The new driving surface on the new bridge will be 29’-0” wide to accommodate two travel lanes and shoulders and will also have a 5’-0” overhanging sidewalk on the downstream truss.
Advertising the project for bids occurred in August 2015 with bids received in September 2015. E.D. Swett, Inc. was the low bidder and was awarded the project in September 2015. Construction commenced in December 2015 and it is anticipated will be completed in December 2017.