HEREFORD – The white stone bridge was erected in 1933, according to plaques at either end of the span, and it carries Big Falls Road over Gunpowder Falls.
The plaques don’t tell you, however, whether the bridge, identified as being in poor condition by a Capital News Service study, was constructed as an arch or a T-beam, and the answer to that question means a lot when talking about the safety of the bridge.
Even the bridge’s inspectors haven’t always agreed on what to call it.
In 1992, the county got into a dispute when it hired a new contractor to inspect the bridge, and the new contractor declared that the bridge was a T- beam, and unsafe for use, said James Arford, chief of structures with Baltimore County’s Department of Public Works’ Bureau of Engineering and Construction’s Structures Section.
But the previous contractor had listed the bridge as an arch, which could carry greater weight, and was therefore safe to cross, he said.
A T-beam has the potential to bend without proper support, while an arch relies on internal compression to hold its shape, and shouldn’t crack if it’s working properly.
The county doesn’t have the original design documents for the bridge anymore, said Arford, and how to classify it became a matter of professional judgment.
The county sent its own inspectors out to the bridge, and they decided it was an arch. They accepted the previous inspector’s judgment, and detailed their decision in a letter to the Maryland State Highway Administration.
Although the situation was “unusual,” the county did the right thing, said Joe Miller, chief of the State Highway Administration’s Bridge Inspection and Remedial Engineering Division.
As the bridge owner, it was the county’s prerogative to make the final decision, although it could have asked the state for an opinion, Miller said.
The bridge has performed without incident through its March 2001 inspection, when cracks were found in the superstructure, said Arford.
Unlike some bridges, where crumbing concrete reveals rusted rebar, this bridge appears sound from above, although from the side and underneath, cracks in the stone become apparent.
Those cracks mean that the bridge is no longer under compression, which an arch should be, Arford said, and as a result, “(the department’s) argument doesn’t hold anymore, and that’s why we’re replacing the bridge.”