[music] Narrator: Lake Superior, the monarch of America’s inland waters. Largest of the Great Lakes, it allows cargo ships to penetrate the heart of the American continent, bringing manufactured goods to the Northern Great Plains and taking out grain and mineral oils from the plains and forests of the United States and Canada. Superior is a temperamental lake. It can be serene and wildly beautiful, or violently stormy, the equal of any of the oceans of the world. Thrust into the middle of the lake, like a giant finger, is Michigan’s Keweenaw Peninsula. Early Great Lakes sailors regarded it as a hazard to navigation. But, men of vision saw that it could also be a boon to the shipping traffic. More than a century ago, a channel was cut southward from Portage Lake to Keweenaw Bay. In 1873, another channel was cut northward. Ever since, the Keweenaw waterway has served Great Lakes mariners as a short cut on the long voyage up and down the lake and as a harbor of refuge in stormy weather. Today, the Keweenaw Peninsula is a natural, unspoiled playground in both winter and summer. Each year, more and more tourists discover its rugged beauty. Besides playing host to visitors, the peninsula's main activities are lumbering and copper mining. This is one of only two places in the world where copper occurs naturally in the metallic state. Its copper mines produce some 20,000 tons of copper annually. The transportation needs of the peninsula are met by two railroads and a system of county, state, and federal highways. And all of them, railroads and highways alike, gather at one point to cross the Keweenaw waterway. In the early days of the waterway, the crossing was made on wooden tressles. The first steel bridge was built in 1895. It had a pivoted middle span, which swung out of the way of ships. There were two levels. The lower for railroad tracks, the upper for vehicles and pedestrians. Over the years it had its share of hard knocks. Here’s what it looked like in 1905 after a ship ran into it. But for 64 years, this bridge was the lifeline of the Keweenaw Peninsula, the only means of crossing the waterway. And each time a vessel came through, the land traffic halted while the bridge swung open. Only 5 feet above the water, it required an opening for even small pleasure boats. Water traffic was given the right of way over land traffic. The bridge opened more than 700 times a year. Each opening brought delay, usually a half-hour or more. Delay and congestion as traffic backed up to clog the streets of Houghton and Hancock. Even closed, it was a traffic bottle neck. Two lanes wide, it was too narrow for todays’ cars and trucks. But in 1957, while traffic crept above them on the old bridge, Michigan State Highway Department surveyors were staking out the remarkable structure that was to replace it. The new Houghton-Hancock Bridge was to cost $11 million. And because of the unusual conditions it had to meet, it was to be unlike any other bridge in the world. It was to be 1,310 feet long and, like the old bridge, have two decks: automobiles on top, trains below. The center span, instead of swinging like a gate, was to rise like an elevator. To reduce the number of traffic interruptions, the bridge was designed to operate in an intermediate position. In this position the railroad deck of the center span aligns with the upper levels of the fixed span at either end. Auto traffic moves freely while boats up to 32 feet high use the waterway. This clearance will accommodate nearly all pleasure craft and fishing boats. When trains cross, the bridge drops to its lowest position. Automobile traffic now uses the top deck of the elevator span. When a large ship comes, the bridge can be raised to its full height, giving a clearance of 100 feet. Only then is automobile traffic completely halted. And because the new bridge operates much more rapidly than the old one, the delays will be only short ones. The design was the beginning, but only a beginning. On Dec. 18, 1957, the construction work began. The first necessity of any bridge is something for it to stand on. The Houghton-Hancock Bridge was to rest on a series of concrete piers. The three deepest ones reaching down to the water and the mud to a layer of solid gravel 75 feet below the surface of the water. The three large piers were to be built by the caisson method. That is, the piers were to be hollow and the excavation would take place inside them. Here is how these giant structures were built. To begin, the contractor built an artificial island over the spot where the pier was to stand. The island was made by driving sheet pilings in a circle 106 feet in diameter. When the enclosure was completed, it was filled with sand. Then began the actual building of the pier. It starts on top of the sand island where wooden forms are placed at the exact location of the pier. Inside the forms goes the concrete. The first of the 9,000 tons which went into each pier. And along with the concrete, come the men vibrating it so that it leaves no unfilled spaces. This first pour of concrete forms the bottom end of the pier. A hollow chamber surrounded by a wall tapering to a sharp edge. Five circular shafts will run upward from the chambers. After the first layer of concrete has hardened, another is added on top of it. The layers are 10 feet high. These men are fastening the network of reinforcing steel which will be imbedded in the concrete. Wooden forms are built around it. The building of the pier continues on top of the sand island until the structure is about 25 feet high. Then the sinking operation begins. Cranes drop their clam shell buckets down the shaft and begin to dig sand and mud from the chamber at the bottom of the pier. As the material is removed the pier begins to settle. Its own great weight and the cutting edge at the bottom allow it to twist downward through the sand like a giant cookie cutter. But it moves slowly. Three inches an hour is top speed. After it has settled a ways, the excavation stops and another layer of concrete is added to the top and then the digging resumes. Besides the clam shell, another device is used to remove material from beneath the pier. It's called an air lift. Compressed air forced down a pipe blows the semi-liquid sand and mud up through another pipe. The excavation and the addition of concrete to the top of a pier continues as alterna operations as the structure pushes down through the sand island and into the muddy floor of the lake. It’s a slow laborious process, but with three piers to build this way it went on summer and winter. In winter, the contractor built an enclosure over the work to protect the men and materials from the cold. To keep the concrete from being damaged by freezing, the sand, gravel, and water that went into it were heated. This covered pile of gravel is warmed by steam pipes under the ground. The concrete was prepared at a plant in the nearby village of Ripley and hauled to the bridge site in mixer trucks. The standards for the concrete were so rigid that the mixing drum of the truck had to make a specified number of revolutions before the concrete could be poured. Michigan State Highway Department inspectors at the site kept up a running series of tests on the quality of the mixture. After many weeks of building and digging, the pier has reached a depth only 2 or 3 feet above its final position. Here, it encounters boulders and hard gravel, which neither the air lift nor the clam shell can remove. So the shafts are sealed and air is forced into the chamber, pushing the water out through the bottom. And now, men will go down 50 feet below the lake bottom to complete the digging by hand. The compressed air is their safety factor. The pressure keeps the chamber from filling with water. In effect, the men will be working inside a huge bubble. Men chosen for this work undergo rigid physical examinations. Before descending to the work area, the workers must spend about a half hour in a compression tank. The pressure in the tank is increased gradually until it equals that in the work chamber. Then the men go down to work. The pressure here is 32 pounds per square inch, more than inside your automobile tires. Only those in top condition, without circulatory ailments or excess fat, can safely work in compressed air. The loaded buckets are hoisted to the surface. Going up and down the shaft, the bucket passes through an air lock, which prevents escape of the compressed air. Their work periods are limited to two hours at a time. When they return to the surface, they must wait in the tank while the pressure is slowly reduced to normal. Slow decompression safely releases the excess nitrogen their body tissues have absorbed. Too rapid release damages the circulator system and brings on the excruciating disease called "the bends." It can strike many hours after they leave the job. The only treatment is return to the pressure tank. As the pier reaches its final position, Michigan State Highway Department engineers test the strength of the earth to make sure it will settle no farther. With the pier firmly in place, the compressed air equipment is removed and water flows back into the caisson. The cavity at the bottom is filled with concrete and the top is sealed with a concrete cap. Then, the artificial island is removed. A crane removes the steel sheets which held the sand. But some of them refused to be pulled, so a diver goes down to cut them off. When the steel and sand have been removed, this little concrete island, 4 feet high and 90 feet long, is all that shows of a structure six stories tall, which costs more than a half million dollars. Three piers were built by the caisson method. Seven others situated in shallower water or dry land, were built by simpler means. For those in the water, coffer dams were built around the pier site. Here, the ready-made steel frame for one of them is lowered to the lake bottom. It is enclosed with steel sheeting, forming a water-tight box. Then the water is pumped out. This leaves the lake bottom free for excavation. Steel pilings are driven down into the earth until they will support a load of at least 55 tons. If a piling fails to meet this resistance, another one is spliced onto it and it is driven deeper until the required load-bearing strength is reached. The pilings are the foundation for the piers. These piers are built of the same material as giant underwater piers. Concrete reinforced with steel. When the piers are complete, their surfaces get a finishing treatment. And the points at which the steel will rest are finished with a grinder. The piers of the bridge are now ready for the steel superstructure. But first, timeout for winter and 150 inches of snow. Work comes practically to a standstill, but here is a hearty surveyor out checking lines. The winter was a time of preparation. In February, the steel began to arrive from U.S. Steel fabricating plants. Each piece bears a number indicating its exact position in the bridge. The steel is stockpiled on the Hancock side of the lake. Meanwhile, tall derricks are being raised. Assembly of the steel begins. And soon the first members of the bridge are being pushed into position. It’s a good show for the sidewalk superintendents. The bridge begins to grow taller as the first vertical columns of the towers are set in place. Towers which will rise 200 feet above the surface of the water. Trusses for the stationary part of the bridge are assembled on shore and floated into place on barges. Meanwhile, a mile away, work starts on the center lift span for the bridge. It is being built aboard barges moored to the shore of the lake. More and more steel is put in place and the bridge grows rapidly. The huge towers are put together piece by piece and the bridge thrusts its silhouette against the skyline. The bridge is assembled with bolts and nuts so that its members can be pulled tightly together. But this is only temporary. As soon as the parts are in place, the bolts are replaced with rivets. More than 230,000 of them were used in the bridge. And each one of them was tested this way. If the washer bounces, the rivet is loose. The loose ones will be cut out and replaced. The bridge has two decks, this is the upper one. Metal forms to hold the concrete are welded in place. They will remain as a permanent part of the structure. The lower deck is the one the railroads will use. It requires enormously strong girders to carry the weight of the trains. Near the shore, the railroad tracks curve away from the rest of the bridge. Here is a concrete mixer truck returning from the bridge along the railroad deck. While the stationary parts of the bridge are nearing completion, the center span is taking shape on a floating platform of barges. It will span the 250 foot gap between the two towers. Since it must carry both automobile and rail traffic without support from beneath, its steel beams are generally larger than those in the rest of the bridge. This extra strength will make it the heaviest vertical lift bridge span in the world. Four-and-one half-million pounds. And its great size and weight will add to the difficulty of moving the span nearly a mile and fitting it into an opening only 8 inches bigger than it is. As the center span nears completion, the towers are being made ready to receive it. Here, being lifted to the top is a bearing for a giant pulley. The span will hang from four sets of cables, two on each tower. The pulley will support the cables. There will be two of these on each tower. In the language of the bridge men, they are called sheaves. The great wheel is lifted slowly, it weighs 65 tons. By telephone, a signal man on top of the tower guides the sheaves into position. It is lowered onto a temporary support until it can be fitted into the bearing. The center span will hang from one end of the cables. From the other end will hang steel boxes filled with concrete. These are the counter weights. There will be one in each tower and their combined weight will exactly equal the weight of the center span. The boxes are hoisted into place empty. They will be filled with concrete after they are attached to the cables. The man with the telephone guides the hoisting operation. In the distance, the center span is nearly ready for its trip to the bridge. Below, the old bridge still carries traffic but its days are now numbered. And below also, circles an ever present rescue boat ready to pick up any of the workmen who might fall. Fortunately, its services were never needed. This chute, called an elephant trunk, will carry the fresh concrete into the box. The concrete comes from far below, hoisted by a crane. These big chains are part of the counterbalancing mechanism. As the span moves up and down, the size of the loop changes to off-set the weight of the lifting cables. With the counterweights and balancing chain in place, the time has come for the center span to be moved into place. Dawn of Sept. 9 is cool and cloudy on the Keweenaw Peninsula. In the first early daylight, rumbling tugboats ease the great, great span away from the shore. The span moves slowly down the water way escorted by a fleet of boats. Because it will disrupt traffic on the old bridge, the placing of the center span has to be a one-day operation. As it nears the opening, its movement becomes almost imperceptible. It’s like threading a huge needle. There are only 4 inches of clearance at either end. For the sidewalk superintendents, this was the most exciting day of them all. Slowly, very slowly, the span is worked into position. Then the cables are hooked up. The span is still resting on the barges but it isn’t ready to be lifted yet. So the barges are partially flooded to lower them in the water. Then they are towed away. The bridge isn’t finished yet, but within a few days its lifting mechanism is tested. And now it looks just like it did on paper two years earlier. The bridge will be operated from a control room about half-way up the south tower. Here are some of the controls and indicators. The bridge underwent a period of rigorous testing before it was opened to traffic. About three months after the center span was put in place, the testing was completed and the bridge was ready. The new bridge was opened at 8 a.m. on Dec. 20, 1959, two years and two days after construction began. Four lanes of traffic began flowing uninterruptedly between Houghton and Hancock. The 65-year reign of the old bridge was at an end. On the following day, the old structure headed for the junk yard. And of course, the faithful sidewalk superintendents were there to witness the destruction. The new bridge was opened after navigation on the Great Lakes had closed for the winter. With no ships passing, it remained in its lowered position all winter. In the spring of 1960, when the big ships returned, the bridge got its first chance to show what it can do. Michigan’s Houghton-Hancock vertical lift bridge is a key link in Michigan’s accelerated highway modernization program. Built for the Michigan State Highway Department, the bridge is the result of the intelligence, the skill, the imagination of many men. State Highway Commissioner John C. Mackie, dedicated Highway Department engineers, who supervised construction for the state, bridge-building know-how from the Al Johnson Construction Co., and the American Bridge Division of the United States Steel Co. Consulting design engineering service supplied by the firm of Haslett and Erdal. Federal participation by the United States Army Corps of Engineers and the United States Bureau of Public Roads. The team work of all these organizations was needed to build the bridge. Along with the energy and courage of 200 workmen of many different trades. Raised for ships, lowered for trains, in the middle for cars and small vessels. Ponderous and yet nimble, the new bridge moves quickly to meet the demands of both land and water traffic, carrying three times the traffic of the old bridge it replaces. For many years, the people of the copper country dreamed of a new bridge to link the peninsula with the rest of Michigan. Now the dream is a reality. A triumph of engineering and a major tourist attraction add to the scenic wonders of the colorful Keweenaw area. The traffic jams are gone, the delays are only brief pauses, as Michigan moves ahead with its highway and bridge-building program and motorists cross the Keweenaw waterway on one of the world's most unusual bridges.
