Hoffman Street Bridge Replacement

From an engineering standpoint, Poughkeepsie’s new Hoffman Street Bridge appears relatively straightforward: a 122 ft simple span steel bridge over the Metro-North railroad tracks just east of the Hudson River. 
The original Hoffman Street Bridge, built in 1914, was a 97-ft two-girder span. The outdated through-girders extended seven feet above the roadway, seriously impeding drivers’ views at the approach intersections.

Modjeski and Masters (M&M) new designed span uses significantly lower profile weathered steel girders to improve intersection sight distance while meeting the clearance requirements of the tracks below. The original bridge had also been founded on the site where the underlying bedrock elevation was highest, yet misaligned with the existing approach roadways: in simple terms, the Hoffman Street Bridge did not properly align with Hoffman Street. Instead, taking Hoffman Street across the bridge meant following a zigzag route with poor intersection sight distances. The initial designs for the Hoffman Street Bridge called for a foundation of spread footings on rock. However, preliminary field tests determined that the underlying bedrock had been fractured – most likely by late 19th century dynamite blasting during the construction of the railroad. Because of this discovery, M&M investigated alternative designs. Using a single line of drilled shafts was determined to be the best solution due to their ability to resist the applied loads within a small footprint (thus helping minimize bridge span length) while also allowing the bridge to perform independently of the existing retaining walls used by the railroad, which passes below the bridge.