A Connection to History: Historic Bridge Saved by Lehigh Alumni Gets National Designation

Nearly 30 years ago when a group of Lehigh graduate engineering students discovered the historic Walnut Street Bridge in Hellertown, Pennsylvania, the structure was corroding away on the banks of Saucon Creek where it was moved after being decommissioned in the 1970s.

The students recognized the span as one of the few cast-and-wrought-iron bridges remaining in the United States and undertook a years-long journey to save it. In October 2023, they returned to the borough to celebrate the rehabilitated bridge’s inclusion on the National Register of Historic Places.

It was 1994 when the graduate students took a field trip to survey bridges in the area. They realized the 55-foot-long span might be something special when they found it described in the book “Landmark American Bridges” by Eric DeLony.

“Starting in 1994 and culminating in 1998, the [Walnut Street Bridge] became a test of ingenuity, applied and practical knowledge, design principles, experience and our willingness to see this rehabilitation project to its desired conclusion,” said Perry Green ’79G ’01 Ph.D. during his keynote speech at the event.

Green, who now lives in South Carolina and is retired after more than 35 years working in civil engineering, was among the students who helped rehabilitate the bridge. The other students include William Bruin ’95G, Robert Connor ’96G ’02 Ph.D., Richard Garlock ’93G, Mike Hebor ’94G, Christopher Higgins ’97 Ph.D., Ian Hodgson ’94 ’96G, Robert Tiberi ’91 ’93G, Paul Tsakopoulos ’99G and James Van Dien ’93 ’96G. The engineers live all over the country. All but one of them was able to return for the ceremony.

Hodgson, a senior research engineer with Lehigh’s Advanced Technology for Large Structural Systems (ATLSS) Engineering Research Center, is involved in structural testing and research in the laboratory there.

Hodgson noted the bridge has cast-iron members: floor beams, which are very unusual; verticals, top chords, lateral struts and end posts. It originally had wrought iron horizontal and vertical round rod bracing and bottom chord members that were all replaced with in-kind steel members.

“I certainly learned a lot during my time spent on this project. The project required a lot of hands-on physical work, and so we learned quite a bit about how the bridge was put together,” Hodgson said. “I made lifelong friendships during my time working on the bridge and at Lehigh, and these connections eventually brought me back to the ATLSS Center after a number of years working as a structural engineer in San Francisco.”

The bridge was fabricated in 1860 by the Beckel Foundry and Machine Shop of Bethlehem near what is today known as Sand Island. It formerly connected a dirt road that eventually became West Walnut Street in Hellertown.

In 1950, Northampton County paid for repairs to the bridge that lasted another 20 years. When the Hellertown and Lower Saucon school districts merged in 1970, the county moved the bridge to make way for a paved concrete girder bridge that would be safe to carry school buses. The bridge was lifted in one piece by a crane and placed in a vacant field 150 feet from its original site near the Heller-Wagner Grist Mill.

In 1994, the Lehigh engineering students began the process of helping the Hellertown Historical Society, which owned the bridge, dismantle, rehabilitate, and reassemble it over a mill race next to the grist mill.

“It was truly a time to put what we learned in our classes to the real test,” Green said during his speech. There were no quizzes or exams that were graded, there wasn’t any homework that needed to be turned in. What there was, was something that we discovered, and upon closer physical examination after this first trip to see this bridge, was a unique structure and worthy of further study.”

When the students first came upon the bridge they thought it was “just another truss,” until they started to do research, Green said. They found it was one of a group of bridges that were listed in DeLony’s book as the 75 cast-and-wrought-iron spans remaining in the United States. Those bridges were all built from the 1840s through 1880s.

The students began by disassembling the entire bridge, identifying what was damaged and figuring out what needed to be repaired or replaced. The work started in the fall of 1994. The students came up with a labeling system. Parts that could be repaired were transported to the ATLSS Center on the Mountaintop campus for further attention.

Green said the students made an optimistic promise to the historical society that if they took the bridge down, they’d be able to get it back up again.

The first major efforts to reassemble the bridge took place in the summer and fall of 1995. A new site was chosen for the bridge not more than 200 yards from its original location. It was decided a bridge of such stature had to be spanning a body of water, so it was placed at the trailhead of a nature trail, crossing the mill race from Wagner’s Grist Mill on the south side of Walnut Street.

In September 1998, the bridge was re-erected at its new location. During the 2000 Hellertown Historic Days, a ribbon cutting was held.

Hodgson said the bridge provides a connection to the area’s past, and the former students always knew how special it was.

“It was important to save the Walnut Street Bridge to celebrate its place in the history of the area, the contributions to bridge engineering made by the builders, and to preserve it for future generations to enjoy,” he said.

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