International photographer (Jan-Dec 1935)

January, 1935 T h INTERNATIONAL PHOTOGRAPHER Twenty-three bridge with a clear span of 4200 feet. While the span is 700 feet longer than any ever built, it is entirely feasible from an engineering standpoint. With the two back spans the bridge proper is 6450 feet long. Characteristics of the Great Bridge Comparative Figures It has the longest single clear span in the world, 4200 feet long, four-fifths of a mile, nearly three times the length of the Brooklyn Bridge in New York, and 700 feet longer than the greatest span ever built, the famous George Washington Memorial Bridge at New York. The two side spans are each 1 125 feet in length. Thus the bridge proper has a total length of 6450 feet, or one and one-fifth miles. The steel towers are 121 feet wide at the bottom and 746 feet high above mean lower low water, the highest and largest bridge towers in the world. (Measured from the rock base of the San Francisco pier the total height is 846 feet.) The minimum vertical clearance at center is 220 feet above mean higher high water, 100 feet greater than the clearance of the Brooklyn Bridge. The total bridge width is 90 feet, center to center of cables, divided into a 60-foot roadway, with 6 lanes of vehicular traffic and two ten and one-half foot sidewalks. The grand total length of the project, including the two approach roads, or from Waldo Point in Marin County to the Marina Gate of the Presidio in San Francisco, all embraced within the project, is 7 miles. The two main cables are thirty-six and one-half inches in diameter each and 7660 feet long between anchorages. The cable sag at center is 470 feet. Principal Forces and Dimensions The total possible live load supported by the two main cables is 25,400,000 pounds, corresponding to the bridge roadway packed, curb to curb, with vehicles and both sidewalks fully loaded, for the full length of the span. The load supporting capacity of the two cables is 430,000,000 pounds, 2.6 times the maximum load. The pull on each cable at the anchorages is 63,000,000 pounds and the counteracting resistance capacity of the anchorage blocks is 126,000,000 pounds. The vertical load on each of the two main piers at the base, including the concrete pier shafts, is 400,000,000 pounds, yet the load on each square foot of the supporting rock does not exceed the established standard units. The horizontal wind force at each tower top is 1,900,000 pounds, corresponding to a velocity of 90 miles per hour. The bridge is safe at velocities far above such extremes. Each tower comprises two steel posts, built up of a series of rectangular cells in groups, the number of cells decreasing from 97 at the bottom to 19 at the top. There are 723,000 square feet of concrete roadway and sidewalk paving in the bridge proper and another 273,000 square feet in the Presidio steel viaduct. There are three and one-fifth miles of hand railing on the main and approach spans and one and five-eighths miles of additional railing on the approach roads. The steel arch over old Fort Point, clearing it by 95 feet in height, has 4 arch ribs, with a span of 319 feet and a height of 200 feet. Adjoining the arch on the San Francisco side and the bridge end of the other, are 1650 feet of steel viaducts on a curve, with a maximum height of 190 feet and deck widths of 84 and 68 feet respectively, which connect the bridge power with the toll area and the approach roads. There are two viaducts in the Presidio approach, one of steel 95 feet high and 1520 feet long and the other of concrete 3277 feet long. Method of making motion pictures on Golden Gate Bridge. Shot on elevator, top of Marin Tower, 615 feet in the air. Frank Vail at camera. Left to right, Clay Bernard, Warner McLaws, W. E. Bamberger. Photo courtesy Standard Oil Company of California. Quantities This bridge has the greatest steel tonnage of any single span bridge but one in the world— over 100,000 tons — sufficient to load a freight train 20 miles long. Each cable weighs 11,000 tons and contains 25,752 separate wires, two-tenths of an inch in diameter. The total wire length is 80,000 miles, long enough to girdle the globe more than three times. The steel in its two towers alone is more than the steel in the entire Quebec Bridge — one of the world's greatest bridges, and in addition, there are over 9,000 tons of steel in the approach spans and steel viaduct of the Presidio approach road. The San Francisco pier is one of the largest ever built, 90x185 feet, with a base carried down deep into the rock of the gate bed, and with a total height of 144 feet above this base. Each cable anchorage has twin three-tier anchor blocks. Each twin of these anchor blocks weigh 64,000 tons. The total concrete in the piers, fender and anchorages is over 260,000 cubic yards, enough to build a solid shaft of concrete 25 feet square and 2 miles high. Large additional cubic yardage is contained in the approach span footings, and in the Presidio viaduct. There are over 261,000 cubic yards of excavation required for the piers and anchorages and for the daylighting of the Marin side span, and 250,000 cubic yards more in the remaining construction. The toll terminal has provision for 16 gateways and 12 toll booths. It contains the administration buildings, fire and police equipment and maintenance depots. The main approach roads are separated from the Presidio and Fort Baker network of roads, respectively, fenced in and lighted throughout. Grade separations are Please mention The International Photographer when corresponding with advertisers.