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Researchers Seek to Aid Preservation Efforts for Historic Iron and Steel Truss Bridges

Attaching Strain GaugesPreservation opportunities are growing as the nation's truss bridges age. Some are being converted for pedestrian use, permitting ready public access to historic structures, which adds the advantage of providing incentives for continued maintenance. Unfortunately, the engineer for today's historic bridge preservation project often finds the structure has insufficient lateral strength to satisfy modern requirements.

With support from a PTT Grant, a team of four structural engineering graduate students led by Kevin Rens at the University of Colorado at Denver and Fred Rutz of J.R. Harris & Company, has been researching realistic lateral strength of historic truss bridges, seeking improvements over traditional analytical methods.

According to Rens, the focus of research at the University of Colorado at Denver has been on the stiffening effect of decks in historic truss bridges.

"The project's overall purpose is to aid in preservation efforts for historic iron and steel truss bridges," he said. "However, the specific goal of this research is to demonstrate a new methodology to account for increased strength provided by non-traditional—but real—load paths."

Rutz initiated the research as a graduate student at the University of Colorado with Rens serving as his adviser. When Rutz finished his thesis in 2004, his literature review showed that century-old bridges were being demolished and replaced.

"In Colorado, there were only a dozen or so historic bridges left and two of those were scheduled for replacement," Rens said. "Fred and I tried to make a difference by investigating five of those bridges to prove that they were stronger than conventional analysis indicated."

The research team investigated the problem using software tools that are readily available to practicing engineers. First analytical models using the traditional "skeleton" frame were developed to study the lateral response for each of five real bridges.

Then the same models were modified to include the stiffening effect of their respective decks and analyzed again. They confirmed that inclusion of stiffening elements such as decks into structural analysis models can aid engineers in historic bridge preservation efforts and reduce rehabilitation costs.

Civil engineering graduate students Veronica Jacobson, Shohreh Hamedian, Kazwan Elias, and Bill Swigert went into the field and prepared the bridges for study under actual wind conditions to verify their analytical findings.

The researcher team installed strain transducers and wind monitoring instruments at each bridge. Their field studies took them to bridge sites from the high plains of eastern Colorado to the Rocky Mountains to western canyons. Modern instrumentation, data acquisition and telemetry equipment were also used in the study.

Further results of this research will be published in each student's thesis work. Results have been accepted in several publications, including the Journal of Performance of Constructed Facilities and the Journal of Preservation Technology.

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Updated: Wednesday, July 18, 2007
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