THE ’FRISCO BRIDGES

Evening Star, Issue 21628, 25 January 1934, Page 1

THE ’FRISCO BRIDGES

GOST MANY MILLIONS Tile city of San Francisco is situated oil the northern tip of a peninsula separating the Pacific Ocean from the southern half of San Francisco Bay. This serene arm of the sea coupled with the Golden Gate has proved an effective barrier to the growth of the city; its only means of communication with the communities to the east and north being by a ferry system. In an age of radio and aeroplane, the ferry is too slow and uncertain a method of transportation across four and one-half miles of water, particularly in times of I storm and fog. Ferries will continue I to exist but they must be supplemented Iby bridges and tunnels (writes Pro- | fessor Charles Derleth, Dean of the College of Engineering at the University of California, in the ‘ Literary Digest’). Consequently, construction of two superlatively great bridges is now in progress to connect San Francisco with its neighbouring communities across San Francisco Bay. One, a 78,000,OOOdol combination double suspension and cantilever bridge that will be the greatest in the world, will extend to Oakland and Berkeley on the east; the other, a record-breaking suspension span dwarfing in size the huge George Washington Bridge in New York, will join the city with Marin County on the north, across the Golden Gate'. It will cost 35,000,000d01. • Tbe, huge trt'nsbay structure knowif as_ 'Die : «an Frahcisico-Oakland Bay bridge is in reality;'composed of five bridges and a tmiuel. It stretches from Rincon Hill in San Francisco to Yerba Buena Island, in the middle of the bay, and from the island to Oakland, a total length of slightly over eight miles. Bv far the most spectacular is the West Bay section, two complete suspension bridges with a common central anchorage. Each of the two main spans is 2,310 ft long, and the four side spans 1,160 ft each. Nearly two miles in length, it is the longest double suspension bridge yet to be built. Supported by two steel cables thirty inches in diameter, its two-level decks will accommodate without serious congestion 16,000 vehicles per hour, seven times greater than the present transbay traffic. THE TUNNEL. On reaching Yerba Buena Island the traffic will pass through a doubledecked tunnel eight feet wide and sixty feet high, the largest vehicular tunnel bore in the world to-day. Across the East Bay, beyond the island, a 1,400 ft cantilever bridge with 510 ft side spans over the shipping channel is the principal feature. The bridge, on a descending grade, reaches street level at Oakland’s waterfront. More than 1,600 men are now busy pouring concrete in the cable anchorages and caissons for the towers and piers of this bridge. The deepest caisson in the West Bay will extend 220 ft to bedrock in 70ft of water, an unprecedented feat. The roadway will be at the height of a twenty-storey building above the water. The 17,464 seoarate wires in each cable would l extend nearly 70,000 miles if stretched out in one piece. The structure will require 190.000 tons of wire cables and steel, a million cubic yards of concrete, 30,000,000 board feet of lumber, and 200.000 gallons of paint. It will be completed in 1937.. The other link in the San Francisco project is the Golden Gate Bridge. For years engineers have dreamed of spanning the swift waters of the Golden Gate, but hitherto the distance had been considered too great, and the fairway too deep for the materials available. In 1928 the leading bridge engineers of the United States were invited to submit proposals for spanning the treacherous water barrier, and Joseph B. Strauss was selected as chief engineer to make the designs for the longest suspension span ever constructed.

The clear span between the two | main towers is 4,200 ft long. It will exceed the main span of the George Washington Bridge by 700 ft. Because of its position over the only entrance to one of the world’s great harbours, the War Department required that the roadway clear the water by 220 ft, more than enough to pass the highest mast on any ship afloat or now projected. Construction began last January, when the gigantic cofferdam for the Maria pier at Lime Point was started l . This pier was completed the latter part of June. The San Francisco pier, one of the largest ever built in an ocean exposure, will extend thirtyfive feet into bedrock in the sixty-five feet of water, I,oooft offshore. _ On top of these two piers will rise the sky-piercing steel towers, 746 ft above water, to support the main suspender cables. These exceed the height of the George Washington Bridge towers by 150 ft, and are the highest and largest in the world. Over I these towers and anchored into the rock at each end of, the bridge, 55,144 separate strands of wire, each nearly a mile and a-half long—enough to circle the earth three times at the Equator—are to be hung two at a time and formed into two cables, each

more than a yard in diameter. These are the cables which, placed ninety feet apart, support the roadway an<J carry the six lanes of vehicular traffic. The 100,000 tons of steel in the towers and cables is alone sufficient to load a freight train twenty miles long. The cement required for the’ piers and anchorages if placed in barrels and piled one on the other would make a stack 110 miles high. It would make enough concrete -to build a five-foot sidewalk from New Yorfc ■ to San Francisco.