Arup and Payette are continuing their collaboration with Northeastern University in designing a landmark pedestrian bridge and observation deck in downtown Boston. When completed, the bridge will span active Amtrak, MBTA, and Keolis rail lines to link Northeastern University’s Huntington Avenue Campus with Columbus Avenue and its expanding campus to the southeast.
The project will also connect Boston’s Fenway and Roxbury neighbourhoods — a pivotal achievement in the university’s goal to help connect the city’s many voices and communities, particularly those from these two very diverse neighbourhoods. Our structural, geotechnical, mechanical, electrical, plumbing, and fire-safety engineers, as well as our façade and lighting consultants, solved several design challenges to create a beautiful and functional bridge for the university and the city.
Envisioned as a physical extension to the University’s recently completed Interdisciplinary Science and Engineering Complex (ISEC), this landmark new crossing presented both technical and logistical engineering challenges to the Arup team. Our mandate was to create a physical extension of the new building that read as a natural expansion of the landscape, with views focused towards the bold new façade of the ISEC and the Boston skyline beyond. The design also had to respect the stringent physical barrier requirements mandated by Amtrak and the MBTA, minimise future rail disruption through careful material specification and detailing, and create a welcoming, secure space that encourages pedestrian flow. All within extremely tight budgetary and schedule constraints.
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Formed entirely of weathering (COR-TEN) steel, the structure’s metallurgy is designed to purposely rust in a controlled, deliberate manner to form a protective corrosion-resistant surface layer. The specialty steel’s inherent corrosion resistance avoids having to paint the bridge over its lifetime, mitigating the need for routine rail line disruption.
The bridge curves as it crests over the four active rail tracks. At its south abutment, the structure expands and becomes a curved observation platform, which runs eastward along the rail alignment and serves as a threshold to the ISEC. To the north, the bridge widens into a monumental feature stair that touches down adjacent to the University’s Snell Library.
The most prominent features of the bridge are the two asymmetric parapet barriers that flank the structure along its west and east edges. Both parapets lean outwards by 10 degrees from vertical to afford views skyward while adhering to the strict geometric requirements established by the rail operators. The space between offset steel panels is in-filled with high-strength laminated glass to satisfy the barrier requirements, while also affording for both daylighting and views.
The curved, asymmetric form of the bridge created a unique structural engineering challenge. Because the bridge is curved, it naturally twists inwards. This effect is exacerbated by the architectural desire to shift the primary structural depth towards the opaque western half of the bridge — accommodating unencumbered views eastward from deck level. Both issues were addressed by employing a large hollow structural steel box girder as the primary structural member running along the bridge’s western edge.
Integrated lighting design
The lighting design for the bridge was developed as an integral part of the vision for the project, giving the bridge a signature expression at night. The lighting is designed to accent the structural composition of the bridge while also providing a comfortably illuminated environment for pedestrians. The design uses an all LED lighting solution, carefully crafted to integrate with the structure, with an intelligent lighting control system to limit energy usage and optimise brightness.