MIGHTY BRIDGES.

Pahiatua Herald, Volume XLIII, Issue 13162, 21 January 1936, Page 7

MIGHTY BRIDGES.

TWO IN PROGRESS, SAN FRANCISCO HARBOUR. OAKLAND AND GOLDEN GATE. SAN FRANCISCO, December 22. Americans are tend of doing things in a big way. Having won the title to the world’s largest dam with the great Boulder barrier on the Colorado, and having several times beaten their own record in skyscraper building, they are now building two bridges simultaneously either of which would rank as a major world engineering feat. Both bridges are being erected over the waters of San Francisco Bay. One, the Oakland Bay Bridge, will connect San Francisco with Alameda County (Oakland, Berkeley and the city of Alameda). This is the bridge which pictures have made known as the bridge which rests, in the middle of the waterway which it is spanning, on an islet. The second bridge rs being thrown across the actual headlands of the famous Golden Gate and will be the mightiest suspension bridge in the world. By May of 1937 if present plans hold, the Golden Gate Bridge will be ready to carry the teeming population of commuters between offices in San Francisco and homes in “Marvellous Marin.” It was in 1919 that Joseph B. Strauss looked across the Golden Gate and felt the challenge which had come to many another engineer before him. From Fort Point in the Presidio of San Francisco to the beetling cliffs of Marin County seemed to him no distance which the skill of man might conquer. He had to Dis credit many notable bridges in many parts of the world and he felt he could throw a span across this almost 9000-foot expanse. For ten years, however, there were innumerable legal d< lavs, though each decision reached was in favour of the bridge. Work was started in 1933, when a tower of 746 feet high began to rise on tlie Marin shore. The following facts give some idea of- the gigantic scale of the bridge: Length of main structure, 8940 feet ; height of towers above water, 746 feet ; depth of pier on Sail Francisco side, below water, 100 feet; length of main span, between towers, 4200 feet; total cost of bridge, 33,500,000 dollars; minimum vertical clearance at centre above mean high water, 220 feet. OAKLAND BAY BRIDGE. The San-Francisco-Oakland Bay Bridge, which will join San Francisco to the mainland to the east, has a total length of eight miles and a quarter, of which .tour miles and a half are over deep, navigable water. The piers beneath this bridge go further Ik4ow water than man has ever built anything before, reaching a maximum depth of 242 feet. Verba Buena- Island, in the centre of the bridge, is pierced by a double-deck tunnel of larger bore than any tunnel ever built heretofore, the dimensions after lining being 66 feet by 53 feet, which is large enough for. a four-storey building to be pulled, through upright. Midway between San Francisco and Yorba Buena Island is a block of concrete which appears almost square and which is the centre anchorage of the twin suspension bridges spanning the two miles between the city and the island. This huge concrete monolith extends 220 feet below water and rises 281 feet above, with a total height from bedrock to top of 501 feet. The interior of this anchorage is hollow, with walls tapering from 17 feet thick. The San Francisco-Oak land Bay Bridge, costing nearly £16,000,000, is being built by the California Toll Bridge Authority, of which Governor Frank F. Merriam is chairman. Construction is directed by Mr Earl Lee Kelly, State' Director of PublicWorks, and Mr C. H. Purcell, chief engineer of the project. This bridge was started in July, 1933. and is scheduled for completion in January, 1937. but it will be opened to automobile traffic- towards the end of 1936. FIN A NCI A L A R RANG EM ENTS. The bridge is being financed by revenue bonds and without taxation or liens against taxpayers. The bonds, bearing 4| per cent, interest, are now being sold to the' Reconstruction Finance Corporation at a (discount to yield j per cent, to maturity. Approaches to the' bridge are financed by the California State Legislature at a cost of over £l.<IOO,OOO as a. loan from Northern California's gasoline tax allotment. The Sa*i F*ram isoo-Oakland Bay Bridge is a double deck structure with 58 feet of roadway for automobiles on the upper deck, and 31 feet for heavy trucks and buses on the lower deck, as well as two in torurban car tracks. In the West Bay it has twin suspension bridges, each a mile long and in the East Bay a 1400-foot cantilever span, supported by five 500-foot, spans and 14 288foot spans, which are attached to tlu* land bv means of a series of shorter girder spans. The construction of the Golden Gate and San Fruncisco-Oakland Bay bridges will be celebrated by the* San Francisco Bay Bridges Exposition, scheduled for 1938. The exposition grounds will bo. located on an island to ho built by dredging sand from the bottom of the ay, just north of Verba, Buena, Island, ’file exposition is being financed bv a non-profit corporation, of which Mr Leland W. Cutler is chairman.