A bridge to a glorious past

Erie Canal Harbor Commercial Slip, Buffalo, N.Y.

Civil engineer
Parsons Brinckerhoff, Buffalo, N.Y.

Product application
Designers use photos and patent drawings to recreate a 19th century truss bridge using modern materials.

Design of the Erie Canal Harbor Commercial Slip makes a case for cost-effective historic recreation.

Establishing an all-water passage from the Great Lakes to the port of New York City, the Erie Canal transformed Buffalo from a frontier village into a thriving port city. Along Buffalo’s Commercial Slip, a port culture emerged with wharves, grain elevators, warehouses, shops, residences, and hotels. After railroads started to take over the transportation of goods in the late 19th century, the Erie Canal was no longer used as a commercial transport venue; by the 1930s, the Commercial Slip was paved over to accommodate traffic.

Old photos of the original Whipple Truss Bridge, built in the 1850s, helped designers recreate the structure. The new bridge has become a signature piece for Buffalo’s inner harbor redevelopment.

But in 2001, the Empire State Development Corporation, the city of Buffalo, Erie County, and several federal and state agencies decided to restore this historically relevant area where the Erie Canal once connected to the Buffalo River with Lake Erie. Designed to recreate the historic character of the site, the project involved construction of a series of landside improvements to facilitate and enhance public access to the water, connect existing pedestrian and bicycle paths, and provide opportunities for private development.

Reconstructing the Commercial Slip required relocation and mitigation of the Hamburg Drain, a large combined sewer overflow (CSO), which was constructed in the Commercial Slip’s right-of-way when it was abandoned in the 1920s. To remove a portion of the drain, Parsons Brinckerhoff developed a detailed and intricate plan that allowed the Hamburg drain to operate during its demolition, ensuring efficient and effective sewage overflow management under adverse weather conditions. New fixed and floating docking facilities were designed to address the varying water level of Lake Erie and provide low-level access for recreational watercraft.

The walls of the new Commercial Slip were constructed using stone similar to the original on top of a modern bulkhead structure that meets current navigational needs, making the site eligible for the National Register of Historic Places.

While all this work required creative, state-of-the-art engineering, the most creative aspect—in the traditional sense of the word—was the design and construction of a new footbridge. Rather than build a new bridge of prefabricated components, the design team successfully proposed to revive the design of the original bridge that spanned the Commercial Slip.

The original Whipple Truss Bridge across the Commercial Slip in Buffalo, built circa 1850, featured three arches with nine truss panels each, separating two traffic lanes and two outboard pedestrian walkways. Using photographs of the original bridge and the patent drawings, the project team recreated the accurate geometry in a 3-D AutoCAD model. The team then exported the model to another program (RISA 3D) for structural analysis. The CAD model was also used to create weldment and construction drawings.

The team’s original design concept used rectangular steel tubes to mimic the original bridge’s timber deck beams. Since this proved too costly, wide flange shapes were used instead, changing the construction from a single hanger rod to a cluster of four rods that straddle the web of the wide flange beam. In addition, arch segments were fully welded together, while the original cast iron segments rested on each other and were held together by the hanger rod passing through both segments at the panel point.

Arch segments were fabricated with steel angles close in size to the original cast iron sections. Dimensions were taken directly from the 1859 patent drawings. Openings in the deck under the arches were closed with two planks of wood, forming a gable roof-like cap with the ridge on the arch’s centerline. The boards were then notched at the ridge to fit around the hanger and diagonal rods. In the replica, bar grating was used, allowing the lighting designer to place up-lighting under the bar grating to illuminate the arch at night.

Bar grating along the centerline of each arch allows up-lighting to illuminate the arch at night.

The handrail was designed last and in close collaboration with the landscape architect, since the architectural team had requested that the bridge’s handrail design be similar to that used on the rest of the site. Photographs indicated that the original handrail was made from wrought iron and featured a picket-type design with spring scrolls at the posts. As it turned out, the spring scrolls not only added aesthetic interest, but also provided additional strength to the post against horizontal load. To give the bridge design a "finished edge," top rail wood dowels were designed to match the rest of the site.

The three arches were fabricated in halves and welded together off-site. Except for the finish decking, the bridge was fully assembled on a barge, and, with a fire boat leading the way and breaking the ice, the barge was tugged into the slip. A 500-ton hydraulic crane then lifted the bridge off the barge and into position on the abutments. Timber decking was then installed with galvanized carriage bolts, the tops of which were exposed in an aesthetic pattern.

Not only did PB’s custom-designed historic replica come in below budget for the originally selected, prefabricated off-the-shelf bridge, the new structure has become a signature piece for Buffalo’s inner harbor redevelopment. More than simply connecting two pieces of land bound by water, it provides a link between the city’s storied past and its efforts to rebuild the harbor in support of commercial and residential development.

Joe Fonzi is a senior structural engineer and John Hubert a senior project manager in the Buffalo, N.Y., office of Parsons Brinckerhoff.

Designer of the Whipple Truss Bridge
Squire Whipple was one of the most famous engineers of his time, and the first to develop theoretical formulae to calculate stresses in articulated trusses. His truss was the first to use cast iron for compression members and wrought iron for tension members. In 1841, Whipple patented a design that became so well regarded that the state of New York accepted it as its official bridge design, using it extensively on the Erie Canal.

Posted in Uncategorized | January 29th, 2014 by

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