Pennsylvania Department of Transportation—Walnut Land Bridge Rehabilitation

The Walnut Lane Bridge is an engineering marvel, as well as an iconic structure in the City of Philadelphia, for 110 years. Yet, as with all older bridges, the Walnut Lane Bridge But needed rehabilitation. The big challenge: replacing the intricately-detailed concrete balustrade, a character defining feature of this century-old structure without impacting its historic integrity.

Using a scheme of stainless steel threaded rods embedded in newly-placed structural concrete sidewalk slabs, precast concrete balustrade sections were securely anchored to the structure. By incorporating a crashworthy traffic barrier at the curblines, the precast balustrade system could be designed to resist minimal loadings which greatly reduced the required capacity of the anchoring system. The use of precast concrete permitted the detailed architectural lines and shapes of the original balustrade to be cost effectively replicated in a controlled setting.  An exposed aggregate finish, as well as the inclusion of a fine black aggregate in the concrete mix to provide a dull granite-like veneer, became integrated the design. This all allowed PennDOT to update the bridge, boosting safety and longevity, while also keeping the integrity of the historic structure at a cost of about $14.76 million.