Drexel University engineers are researching methods to establish the safe load capacity of aging concrete bridges.
The research of A. Emin Aktan, John Roebling Professor of Infrastructure Studies at Drexel University, and Dr. Franklin L. Moon, assistant professor in the College of Engineering’s Department of Civil, Architectural and Environmental Engineering, is part of a Federal Highway Administration-funded project that will continue for six years. Their findings could lead to the development of evaluation equipment that might help prevent tragedies such as the Minneapolis bridge collapse.
Aktan, Moon and their students recently evaluated two bridges in West Virginia using tests of truck loads to characterize the behavior and estimate the present and future weight capacities of bridges in West Virginia’s Coal Resource Transportation System (CRTS). The CRTS comprises more than 600 reinforced concrete bridges, some up to 100 years old. To help maintain bridges, the state designed the CRTS to keep coal trucks weighing more than the legal limit off certain roads.
About 100 bridges in the CRTS can accommodate less weight than the allowable CRTS loads. Because of the large number of CRTS bridges, conducting load tests of each bridge is cost-prohibitive. The Drexel engineers therefore also used an off-the-shelf, wireless data-acquisition system and falling-weight deflectometer to determine their effectiveness in producing rapid and cost-effective findings.
Also involved in inspections of the Tacony-Palmyra and Burlington-Bristol bridges in New Jersey following the Minneapolis tragedy, Aktan and Moon will return to West Virginia next month to re-evaluate one bridge and evaluate another.
The lack of documentation for the aging bridges presents a challenge for the Drexel engineers in collecting adequate information about the bridges’ materials and reinforcement properties. The challenges Aktan and Moon face are formidable but not unique: Thirty percent of U.S. bridges lack critical documentation.
Aktan and Moon say the wireless system is not reliable to be used during load testing but encourage the development of this technology because it could offer time and cost savings for bridge evaluators. They say the falling-weight deflectometer, which drops weights onto a grid marked on a bridge, could be transformed into a useful tool to complement visual inspections, the common practice of determining bridge safety.
Aktan and Moon determined that the load carrying capacities of the bridges they evaluated exceed the demands of established CRTS loads. They recommend, however, that the bridges’ foundations be inspected annually and that the development of a prototype falling-weight deflectometer be given top priority to expedite testing the great number of CRTS bridges.