The relevant authorities around the world have become seriously concerned for the safety of many items in the state’s infrastructure, especially bridges, and Hancock County has two of the worst examples: the Deer Isle and Waldo-Hancock bridges. The Maine Department of Transportation has finally acknowledged the extreme conditions in Waldo-Hancock, but not those in Deer Isle which, in the writer’s opinion, are probably worse.

The basis for this statement is:

The main cables at Deer Isle are not wrapped and the characteristic “wormhole” corrosion in the wires is easily visible, quite extensive, and very deep as is to be expected in a severe marine atmosphere. The cable anchor fittings at the abutments also are severely corroded, they have had no protection. The saddle supporting the cables at the top of the towers was a hardwood piece formed to act as a cushion between the cables and the cast iron base. It is highly probably that the wood has disappeared and the cables continue to lose wires by fretting on the base.

The vertical suspender cables which connect the main cables to the deck girders are observed to be pulling out of their individual shackles, many are already one-quarter inch out of their roughly one-inch fit.

In 1940, shortly after the completion of the Deer Isle Bridge, two significant events occurred. The first was the publication of a technical paper by a European scientist and mathematician named von Karman in which he proved that a steady force (the wind) can induce an oscillatory response (the bridge bends with the wind, then snaps back). The resulting stresses produce fatigue damage in the metal, and an elementary analysis indicates that the bridge reached the end of its “Safe-Life” period about 1990. Despite the approximations due to the absence of firm data, this analysis was presented to MDOT on Jan. 8, 1979.

Von Karman was severely criticized during the short time until the second event occurred – this was the collapse of the Tacoma Narrows Bridge in Washington state. The vortex forces simply tore the structure apart – there were no other loads on it at the time – and his theory and foresight were proved correct. In 1972 this condition obtained at Deer Isle and it is only by pure luck that the intensity of these forces was too low to destroy the bridge. As it was, the extreme deflections – the deck rose and fell some 20 feet – caused some permanent deflection, visible today as sagging.

The Tacoma Narrows and Deer Isle bridges were designed by an MIT student as part of his doctoral thesis, but said thesis was not accepted by the institute. However, the people of the respective states bought the design through their agents (DOTs), and now for the people of Maine the time has come to accept the fact that the Deer Isle structure is wholly derelict and that of Waldo-Hancock very nearly so.

The only admissible conclusion is that in the interest of public safety the two structures should be taken out of service as soon as possible – the resulting effects on the local economy, access, navigation, and so forth, notwithstanding.

Carl C. Osgood, of Surry, is a retired consultant in dynamics and metallurgy.