Published in Fall 2008 Newsletter - FRIENDS OF THE WISSAHICKON 8708 Germantown Ave., Phila, PA 19118 • tel 215-247-0417 • email@example.com
The Walnut Lane Bridge in Philadelphia’s Fairmount Park is much more than a bridge. When built between 1906 and 1908, it was not only a way across but a way forward into the new century. It made tangible many bold ideas in circulation at the time of its construction. Connecting the Germantown and Roxborough neighborhoods over the Wissahickon Gorge, it now stands as part of the park and part of the community. One usually crosses over or passes under it very quickly—it’s only about a city block long and you might miss it driving past.
When completed, the Walnut Lane Bridge was the longest and highest concrete arch in the world. Its engineers, George S. Webster and Henry H. Quimby, employed concrete to blend in with the picturesque Wissahickon section of Fairmount Park. Webster put into place years of progressive reform thinking on how to use comprehensive planning and large construction projects to connect communities with each other and with the city. This approach, which grew into the “City Beautiful Movement,” promoted cooperation, harmony, and “beautility.” The result attempted to connect opposing principles of late nineteenth-century architecture to public projects: “beauty” and “utility.” “Beautility,” the thinking went (and yes, the word was frequently used), could lift the spirit of citizens in everyday life. Workers were recruited from all over the city and represented a diverse work force of Italian Americans, African Americans, and Irish Americans. During construction a collapse of the centering falsework injured dozens and killed one local worker.
Building in the Wissahickon was not done lightly. Plans for a bridge across the Wissahickon Creek to connect Germantown and Roxborough were discussed as early as 1875, when an extension of the railroad was considered. Originally the bridge was to have looked much different. Drawings from 1899 called for a steel truss bridge, but Webster insisted that the natural beauty of the location demanded a different approach, considering a steel bridge to be inappropriate for the surroundings. This brought the use of concrete into the picture. Concrete was cheaper, required fewer trained laborers, and available locally. Of the 24 Portland cement plants in America (the most common type of cement), 20 were in eastern Pennsylvania, mostly in the Lehigh Valley. The prominence of concrete was a rapidly growing trend in construction. Soon concrete bridges became standard: in 1893 there was only one concrete bridge in Philadelphia, by 1909 there were 54. Much of the cost for the bridge went toward the centering falsework that made the dual arch construction possible. Falsework is a temporary structure used to support a spanning or arched structure until it is fully constructed and can support itself. In the case of the Walnut Lane Bridge, the falsework allowed workers to form the arches with concrete, poured from an overhead cable system, that had to dry slowly and carefully. One of the unique features of this project was that, once the first arch was completed in September 1907, the huge centering falsework was moved 34 feet to its new position and work on the north rib of the bridge started. It took 30 men three days to roll the falsework, which weighed 900 tons. After the second, north arch had been completed, the falsework collapsed while workers were removing it, killing one and injuring dozens of other workers on December 27, 1907. The sound of the tragedy was so loud that hundreds of people came out to help rescue the men dangling from the falsework.
The Walnut Lane Bridge opened on October 14, 1908 and was formally dedicated in December that same year. Local officials pulled out all the stops for the dedication ceremony and an estimated one thousand revelers attended. Students from Roxborough and Germantown met in the middle of the bridge holding American flags while singing “Hail Philadelphia.” The ceremony ended with a reception at the Indian Rock Hotel, an inn once located at the foot of Monastery Avenue along the Wissahickon Creek. The celebration featured the traditional Wissahickon meal of catfish and waffles and hoppy beer. News accounts the next day described the students as singing “songs across the chasm,” bringing the city park advocates’ notion of bridge building and harmony full circle from concept to reality.
• Largest span—233 feet
• Height from creek—147 feet
• Total length—585 feet
• Width of driveway—40 feet
• Width of sidewalks—8 feet
• 3rd largest masonry bridge in the world when built
• Modeled on the Pont Adolphe Bridge in Luxembourg
• Construction began July 5, 1906 and finished October 14, 1908
• 40,000 tons of concrete
• 370,000 board feet of timber for the falsework
• Engineers: George S. Webster (chief) and Henry H. Quimby (assistant)
• Contractors: Reilly & Riddle, Roxborough
• Cost: $259,440 (nearly $6 million—as of 2008)
In response to the last comment, the bridge that is the first major bridge in the U.S. to be built from pre-stressed/post-tensioned concrete is actually a different Walnut Lane Bridge, the one over Lincoln Drive ( http://bridgehunter.com/pa/philadelphia/bh45930/ ).
It should be noted that while this is a graceful open-spandrel arch, it was the first major bridge in the U.S to be built from Post-tensioned/pre-stressed concrete bridge, a method used in most (if not all) of today's concrete UCEBs.