Slice of Americana, an engineering marvel, to be replicated across Chattahoochee River
By David Pendered
An engineering marvel of a bygone era will be retained in Rogers Bridge as its replacement is built across the Chattahoochee River to connect parks in Fulton and Gwinnett counties.
Construction has started on the project that’s been in the works since 2006. The ceremonial groundbreaking was March 29 with representatives of the four governments that joined forces to complete the bridge – the cities of Duluth and Johns Creek, and the counties of Fulton and Gwinnett.
The new pedestrian version of the Rogers Bridge is to connect parks in the two cities – the future Cauley Creek Park in Johns Creek and Rogers Bridge Park in Duluth.
As such, the new bridge is the latest in an emerging effort in metro Atlanta to build pedestrian bridges across waterways and highways in order to extend trail systems and link greenspace. Other examples include the bridge across Peachtree Creek, in Buckhead, and the planned pedestrian bridge across U.S. 41 that’s part of the Noonday Creek Trail, near Kennesaw.
After years of discussion over the benefits of preserving the old Rogers Bridge or building a new bridge, the state Department of Natural Resources determined the old bridge was too decrepit to salvage. Simultaneously, an effort was underway for the replacement to replicate its ancestor.
The design of the bridge is significant – a metal truss bridge of a design that originated in the labs of the Pennsylvania Railroad. PRR was chartered in 1846 and was the world’s largest railroad corporation before a successor went bankrupt in 1970, was folded into Conrail, which itself was split up. Conrail’s PRR assets were acquired by Norfolk Southern Railway.
Metal trusses were a favored material for bridges and other structures at the dawn of the railroad era of the mid 1800s. For railroad bridges, metal trusses could accommodate the ever-increasing weight of locomotives and rolling stock, which was a much heavier load than was required of a highway bridge.
The original Rogers Bridge was a Pennsylvania (Petit) truss design held together with metal pins. Spanning 228 feet, the bridge is the longest single-span bridge in the state and was eligible for the National Register of Historic Places, according to a report by Trust for Public Land. This potential designation is one reason DNR became involved, through its Historic Preservation Division.
In a sense, the bridge was overdesigned for its use across the Chattahoochee River when it was built, in the early 20th century.
Bridges of this design are capable of spanning from 250 feet to 600 feet. The original Petit design could stretch up to 250 feet. Modifications extended the capacity considerably – to 600 feet for both the Baltimore (Petit) and Pennsylvania (Petit) designs used from the early 1870s to the early 20th century, according to a report posted by the National Park Service, “Trusses: A Study by the Historic American Engineering Record.”
The historic significance of the Pennsylvania (Petit) metal truss bridge is described fully in an registration form submitted for a bridge of such design in Sonoma County, across the Russian River, where it was part of the famed Redwood Highway. The registration form observes:
- “In the latter part of the 19th Century, truss bridges were well established on rail lines and roads. But as the weight of trains grew, railroads needed crossings to withstand heavier loads. Thus came the Pennsylvania truss type, so named because of its origins in the design laboratories of the Pennsylvania Railroad. The design sprang from existing Pratt and Parker truss types, which placed full-length diagonal members in panels for the first time, and added bracing to the diagonal pieces.
- “The Pennsylvania truss introduced half-length struts for the bottom parts of panels or half-length ties for upper portions, and sometimes both. Both spans of the Healdsburg Memorial Bridge contain two stress-relieving ties, each positioned between full-length diagonal members on opposite sides of the center panels and the bridge’s polygonal top chord. Each tie, as well as other diagonal members, is attached with pins, instead of rivets, to enable ‘give’ as the bridge flexes and moves. The bridge gets much of its architectural flair from the sloping top chord, common to Pennsylvania and Parker truss designs. The varied height helps the bridge resist bending as weight builds near the center.
- “The Pennsylvania type, like other steel truss bridges, faded in use after 1930. In some design circles, especially among a group of urbanists of the time, truss types were seen as gaudy, an irony given the cookie-cutter blandness of many concrete crossings that took the place of truss bridges.”