4½ MILES OF STEEL

Te Awamutu Courier, Volume 52, Issue 3771, 19 June 1936, Page 9

4½ MILES OF STEEL

BRIDGING SAN FRANCISCO BAY A MARVEL OF ENGINEERING (By Charles F. Hoppe, in Brisbane Mail). The completion this year, or early in 1937, of the San Francisco Bay Bridge, linking the cities of San Francisco and Oakland, California, will be -of special interest in Australia, in view of the fact that Sydney possesses a bridge which is justly considered one of the greatest engineering feats of the present century. The San Francisco Bay Bridge consists of two vast - structures, each lenger than the largest existing bridge. East of Yerba Buena Island, in the middle of the bay, there has arisen a cantilaver bridge more than two miles long. Between the island and San Francisco two suspension bridges, each about a mile in length, are nearing completion. The total length of the cantilever and suspension bridges is four and a half miles. Statistics are seldom interesting. Nevertheless, passing niention must be made of the staggering figures of the material which have gone into the building of the world’s largest bridge. Even the most imaginative of Australians might find it difficult to visualise the colossal foundations of the great towers arisen from San Francisco Bay, and dwarfing even the 30 storied skyscrapers of the city’s downtown business district. But statistics must suffice, in some small way, to indicate the hugeness of one of the engineering marvels of the world. For instance, the 152,000 tons of steel used in the bridge represent about six per cent of the United States’ yearly steel output, and the 70,800 miles of cable wire, about 19,000 tons, would encircle the earth three times. The timber, 30 million board feet, would build three thousand five-room dwellings, dr a residential section of a town of 15,000 people. The concrete and steel used are sufficient to build 35 skyscrapers, each 28 stories high. .Three hundred thousand gallons of paint is being used. Dredging and excavation consist of over 6,000,000 cubic yards. And the cost will be 77,200,000 dollars, or approximately £l5l millions. These figures may enable one to gain some faint idea of the gigantic span which is slowly but surely rising over the gleaming waters of San Francisco Bay. THE MIGHTY TOWER" It was with natural pleasure and excitement that I grasped the invitation extended to me by Bay Bridge engineering chiefs to visit the topmost heights of the structure and gain material for a special article for The Courier-Mail. Accompanied by a young engineer on the project, I made my way through the hurry and

bustle of San Francisco’s harbour front, where Jack London spent his adventurous boyhood days. Cargoes from China, from Japan, from Australia, from all the Seven Seas were being unloaded at the great wharves. The odour of musk and copra, the wailing of syrens of ocean-going liners and tug-boats, the ever-pre-sent belam of sound, which is the natural accompaniment to the music of commerce of every large port, brought to memory Robert Louis Stevenson, who wandered these selfsame docks during his several years in San Francisco. Suddenly, rounding the corner of a warehouse, there loomed above us the hundreds of feet of steel and riveting of Tower No. 1 of the bridge —one of the four immense towers which form the main overwater crossing of the structure. We entered an electric elevator at the base, and were whirled to the topmost tier. Far below lay the great dock area. The world-famed San Francisco ferry boats, with their cargoes of automobiles and humanity, left fleecy wakes of foam on the blue waters. San Francisco’s great skyscrapers had become architects’ pasteboard models. The thirty thousand ton liners, at the quays, for all the world might have been the ten foot models of steamship company’s offices, so dwarfed were they by the spectacular height of Tower Number One. The height of this tower, and that of its accompanying structures, is 502 feet from the concrete foundations—ll 7 feet higher than the pylons of the Sydney Harbour Bridge. BRIDGE AND TUNNEL From our vantage point on the tower were the two massive cables which festooned their swaying lengths to Yuerba Buena Island, almost in the centre of the bay. Actually the Bay Bridge will be eight and a half miles long from the western approach. It is, however, bisected by Yuerba Buena Island, and thus the bridge proper will be 23,000 feet long, or about four and a half miles. Through the highest part of the island a huge vehicular tunnel, 76 feet wide and 58 feet high, is being bored to connect the two sections of the bridge. The vastness of the project becomes apparent as one gazes at the network of steel girders and cables which stretch their way across the four and a half mile of water. Gaunt arms of derricks and cranes move weirdly, tentatively across the sky. Great pumps cough and groan as myriads of steel cables are being] spun together to form the main tensions of the two principle cables which will eventually hold the traffic runways. Each of the niain cables is 283 inches in diameter, and contains 17,464 wires spun into place on site, on the bridge itself! WORK NEVER STOPS Little black figures, like fantastic black gnomes, dart along the perilous runways, hundreds of feet above water. These little black gnomes are men—the men who are building the bridge, jjoing the actual work, the dangerous work, the dirty work, the skilled work which calls for so much

experience and brain, as well as strength and—courage. I glanced down at the watery death below and again at the steel towers looming over the bay. Little blackdots, hammering and welding, climbing, swaying precariously. And one false step! Oblivion! They earn their money, these 6500 men employed on the San Francisco Bay Bridge. Work goes on incessantly, as it has done ever since the bridge commenced three years ago. One shift goes off, and another commences where the last downed tools. While the great city, with its towering skyscrapers, luxurious hotels, and exclusive appartment houses on Nob Hill is lightup at night, and while San Francisco sleeps, these men carry on with their work, apparently unconcerned with the death which lies ever at their feet. A number of books could be filled with a detailed account of the many features and engineering problems which confronted the engineers in charge of the work, including the sinking of the great caissons through the harbour mud to rock bottom, in one instance 235 feet below the surface of the bay. The bridge will have a double-deck-er runway. The lower will carry trains, street cars, and electric trains and the upper with its six lane traffic runway, will carry automobiles and freight lorries. Incidentally, both runways will be twice as broad as an average main street. The cost has been defrayed by the sale of 42 per cent, bonds, issued against prospective tolls from the bridge. These bonds have been purchased at a discount, increasing the yield to 5 per cent, by the United States Federal Reconstruction Cor.poration, a government organisation, and may eventually be sold to the public. The hourly capacity of the 16,000 motor vehicles and a yearly capacity of 30,000,000 passenger cars and trucks will bring tolls which should amply suffice to pay off the cost of the bridge within about 20 years. The chief engineer of the bridge is Mr Charles H. Purcell. ENORMOUS CABLES The young engineer seemed more interested in Australia than in the bridge, which had become old news to him. However, every now and then I was able to drag him away from “down under” and subject him to questioning! He informed me that the two main suspension cables between the towers will eventually exert a live and a dead load of 37,000,0001 b. in their anchorage! The amazing factor in the manner in which these two cables have been constructed is that if one of the two suspension spans, which exert a balanced pull of tens of thousands of tons, were to be destroyed, the unbalanced pull of the remaining span would not affect it in any way! Descending from the tower, we took a launch across the bay, to the concrete centre anchorage. Mr Edward Rowe, the famous American engineering expert in concrete work, paused a moment to chat, when we ascended the vast concrete monolith by elevator. “I’ll say it’s pretty big,” he answered. “They say this baby is just about the biggest thing of its kind ever built, and I guess that’s correct. And believe me, she’s built to last!” Most of the structural ironworkers employed on the Bay bridge were previously engaged m the building of America’s skyscrapers, a specialised form of work and dangerous in the extreme. All of them wear hats which resemble the steel helmets of wartime days. They told me that their greatest danger lay in falling riverts. I forbore to ask how many millions of rivets have gone into the building of the steel towers. Their immensity is spectacular enough to the eye, without further bewildering the emotions with infinitesimal figures. But as for the steel workers’ labour of riveting, clinging like flies to the latticed steel laced hundreds of feet in the air—that was nothing at all, the said. That was their life, an everyday life, just like that of a steeplejacks. But falling rivets—they were something else. JUST ANOTHER JOB To me the erection of the suspension towers was a tremendous job, as I walked fearfully along the swaying catwalks. But to these human flies on the girder it was—just another job. Leaving the centre anchorage, my engineer guide and I chugged back in the launch to the mainland. Far above me the giant bridge reared its immensity to the darkening .evening sky with its ceaseless labour going on, on, on. Suddenly thousands of electric lights and broad floodlit expanses flickered on, illuminating the bridge from end to end for the night’s labour. The spectacle was breathtaking, like some Aladdin’s Lamp dream come true. To the left, at the majestic entrance to the Golden Gate, was another bridge, also in the process of construction. It is named the Golden Gate Bridge, and will be the largest single span bridge in the world. However, as the late Rudyard Kipling might have said when he lived in San Francisco, and was .ironically enough, turned down by the city’s newspapers in his efforts to get a job as a reporter—“that is another story.”