ST. IGNACE - We should all be as healthy as the Mackinac Bridge at age 50.

A steady regimen of parts replacement, painting, lubrication, and a form of exercise has left the span in "very good shape," with a healthy future, said Mackinac Bridge Authority Chief Engineer Kim Nowack.

"It's always amazing to me that even with the massive amount of steel and concrete, the bridge deck and the towers flex like a living thing with the changes in temperature and wind," she said.

Credit the nonstop maintenance on the bridge for its good health. This fall featured some replacement of open grating sections, as well as steel beam repairs underneath the deck. In recent years, trades workers have replaced hanger lengths and transition pieces, performed electrical upgrades, and of course, have undertaken the never-ending process of painting. Nowack said it took three years to paint the area between the towers.

"You might be able to assign a lifespan to the bridge if there had been no maintenance over the last 50 years," said Nowack. "But the bridge has had regular, ongoing inspections and maintenance. Some materials on the bridge are a day old, some are 50 years old."

The bridge has a number of parts that allow movement and flexibility. For instance, the span can rotate east and west up to 25 feet under sustained high wind conditions. And workers who use the motorized traveller (a moving platform under the bridge used to perform maintenance) feel bounces when traffic passes above.

One of the notable design elements in the Mackinac Bridge is the steel grating in the middle of the road deck. The bridge's chief engineer during its construction, David Steinman, sought to mitigate the occasional high wind forces experienced in the Straits of Mackinac region by allowing the wind to blow through the bridge deck.

From a structural standpoint, it was an unnecessary choice, the bridge was already designed with a sufficiently high wind resistance factor.

If a suspension bridge were built in the same place today, it could look like the Mighty Mac, but engineers could take advantage of lighter-weight and more rust-resistant materials. One innovation that has come along for suspension bridges, Nowack said, is the use of orthotropic technology.

The Golden Gate bridge in San Francisco, for example, switched their deck to an orthotropic system in the early 1980s, which reduced the deck's weight by 12,300 tons. An orthotropic system, according to Public Roads magazine, is a collage of steel plates welded together, stiffened by a grid of ribs, and integrated with the driving surface. It can increase the life span of the deck to 100 years.

But even without that newer technology, the good work of building trades workers 50 years ago got the Mackinac a half-century of service - and we're still counting.

"The workers then did a tremendous job of building the bridge, and we're very appreciative of their efforts," Nowack said. "Today we're doing our best to keep it in good shape."

CONSTRUCTION GROUNDBREAKING on the Mackinac Bridge took place on May 7, 1954 in St. Ignace and the next day in Mackinaw City. Construction workers had the bridge built three-and-a-half years later, on time and on budget.