April 15, 2000
Long before a Mackinac Bridge was even conceived, it was possible to walk across the straits. Still is. Each year, sometime in January or February, the waters freeze solidly enough for hikers, cross-country skiers and snowmobilers to cross. The ice will be tested for thickness and strength, then a trail will be blazed, using previously enjoyed Christmas trees as markers. As long as the ice lasts, anywhere from two days to several months, intrepid souls cross over to Mackinac Island from both upper and lower peninsulas, make their way into town, where some restaurants and B & Bs have remained open, and then head back to the mainland again. Fun, but not practicable year round. So, to work.
On May 7, 1954, ground was broken at St. Ignace, then at Mackinaw City the following day. 14 survey teams were assembled, eight on land and six on the water, to triangulate the 34 foundations the bridge piers would rest on. While this was going on. companies from surrounding states were busily constructing giant caissons, as well as segments of the bridge itself. Fleets of construction vessels and land trucks converged on the site from as far off as Pennsylvania and Indiana. Foundation after foundation was created by the Merritt-Chapman & Scott Corporation, as caissons were lowered onto the carefully prepared bedrock then filled with cement and stone. The foundations were completed in 1955 then, on July 2nd, the American Bridge Division of United States Steel Corporation began erecting the superstructure, including the 46-story towers atop piers 19 and 20 and cable anchors in piers 17 and 22. Creeper cranes on the tower piers hoisted themselves up along their own creation, telescoping into the Michigan sky. When the time came for the two main 24.5-inch cables, composed of 12,580 .19 inch diameter wires each, and weighing 12,500 tons, to be stretched across the strait the engineers solved the impossible problem of elevating all of that weight by spinning the cables on site, one wire at a time. Finally, on November 1, 1957, everything was in place. From the foundations 206 feet beneath the surface of the straits, to the tower tops 500 feet above the surface, across the 26,444 feet of the bridge's length, and back and forth along the 41,000 miles of cable wire, the Mighty Mac was ready. Governor Williams cut the ribbon.
Instead of the 462 cars per hour of the ferry service, 6,000 cars an hour could now cross the straits. Gone were waiting periods as long as 19 hours. Almost. There are still times when gale force winds whistle across the lakes, and the bridge is temporarily shut down. At such times the bridge can sway twenty horizontal feet to the east or west. Jim Harrison describes it in his novel Sundog, "I could barely hold the lane and was whipped back and forth with my stomach and heart jumping and thumping and sweat itching around my ears. The tumultuous water below looked at least a mile away." Dramamine anyone?
For Classical ninety-one five, this is David Minor
© 2000 David Minor / Eagles Byte
URL OF THE WEEK
Do It Yourself. You can try your hand at building bridges. Just go to Nova's Super Bridge site, learn how it's done, see some of the best-known bridges (including Galloping Gertie) and read the transcript of the two-hour PBS documentary. Your kids will enjoy this site as well. A list of resources and a teachers' guide are also part of the site.
The Game's Afoot !