Thursday, October 26, 2017
Structural engineering projects come in all shapes and sizes. Sometimes they even serve to reunite a community with its symbolic center.
When the Wanakena Footbridge was destroyed by an ice jam on the Oswegatchie River in January 2014, the hamlet of Wanakena mourned its loss. The bridge was first built in 1902 by the Rich Lumber Company to provide access across the river for lumber mill employees. The 171-foot, wood-framed suspension bridge had been damaged several times over the years by river ice, but this time it was a total loss.
Bolstered by community spirit and multiple fundraisers plus grants and gifts from around the world, this project sought to reconstruct the bridge to match the configuration of the original design. The bridge had been placed on the National Register of Historic Places in 1999. However, only the steel cable was original, and fatigue was identified when the cable was tested. Klepper, Hahn & Hyatt engineers, along with Crawford & Stearns Architects, decided to replace the cable in the new design. The bridge deck was also raised two-and-a-half feet above the original to mitigate further ice damage. These two factors led to the removal of the bridge from the Historic Register.
The replacement of an historic pedestrian suspension bridge was a unique and interesting project for the firm. KHH engineers studied photos and a drawing which detailed the bridge dimensions. Design drawings for the new bridge were based on these.
In an effort to save on the project cost, the KHH team planned to reuse the existing shoreline anchors and anchor rods. However, there was no information available about the design or condition of these anchors. A load test confirmed that the original anchors were unable to support the load required for the new bridge and were inadequate for the present Building Code of New York State. New anchor blocks were designed and detailed to support the replacement structure and also to deflect ice, which had imperiled the prior bridge.
On the Fourth of July, the rebuilt Wanakena Footbridge was celebrated with a dedication and ribbon cutting. Hundreds of residents were drawn to the shoreline for the event. It was the culmination of a three-year effort by the community, and the attention to detail and dedication of the design team.