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Jun 302020
 

DuBois & King received a Silver Award in the Structural Systems Category for the Lilac Bridge Replacement project in Hooksett. The award was presented by the American Council of Engineering Companies of New Hampshire Engineering Excellence Awards Program, a showcase of exemplary engineering projects completed in the state and/or by New Hampshire firms.

DuBois & King provided investigation, evaluation of alternatives, and design for a replacement of the Lilac vehicle bridge with a new pedestrian bridge. The new bridge maintained the viewscape of the previous bridge—a historic high Pratt through truss bridge constructed in 1909—and served as a crossing over the Merrimack River. The existing bridge was bypassed and closed to vehicles in 1976 and closed to pedestrians in 1995. In August 2014, the NHDOT advised the Town of Hooksett that a recent inspection revealed the existing bridge had failed, citing four locations where critical truss members had fractured, and the bridge was in imminent danger of collapse. While closed to vehicles and pedestrians, the bridge still supported a major sewer line.

D&K led planning, design, and permitting of this project while simultaneously balancing the needs of eight stakeholder groups that had interest and jurisdiction in the project. Managing the stakeholder groups’ conflicting needs added complexity during the project’s compressed schedule. The replacement bridge satisfies pedestrian and sewer crossing requirements while providing an economical, long-lasting structure that mimics the appearance of the historic structure it replaces.

Construction Contractor E. D. Swett developed an aggressive construction schedule that demolished and removed the superstructure, rehabilitated the substructure and erected the new bridge to carry the sewer line before the bridge succumbed to collapse and failure of the supported sewer line and impending environmental disaster.

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