Chief engineer of the Greatest bridge in the world: San francisco-Oakland Bay Bridge
CHARLES HENRY PURCELL
Charles H. Purcell (1883-1951) was educated in civil engineering at Stanford University and specialized in bridge design. In 1927, he was appointed as California’s State Highway Engineer, a post he held until 1942. While he presided over many notable projects in California, including the building of the first freeways, nothing occupied his skills and time as thoroughly as the Bay Bridge. In 1929, Purcell had been appointed technical advisor to the Hoover-Young Commission and in 1931, Governor Jim Rolph appointed him Chief Engineer of the Bay Bridge.
Purcell drew his leadership team chiefly from the Division of Highways along with an advisory board that included the most respected bridge engineers in the nation. Upon completion, the San Francisco – Oakland Bay Bridge was renowned for being the longest and most expensive bridge ever built ($77,600,000). More than 6,500 employees worked on the project that was completed several months ahead of schedule.
Support cables are an essential part of any suspension bridge design as they bear the load of the decks and traffic. Four spools, each containing 60 miles of steel wire and mounted on axles, were set up on the cable anchorages at the tops of the towers. Each wheel had two grooves and the wire was unreeled from two spools simultaneously, placing four wires in the cable on each trip of the spinning wheel. Guide wires were carefully laid into position, with the workers making constant adjustments so that all the wires were laid to the same sag, thereby sharing the load equally. When 472 wires were laid, they were bound with metal bands forming one strand. Thirty-seven strands were compressed by powerful compacting machines into one 28 ¾ – inch suspension cable. Repairs to the cable wires are impossible once the cable has been completed.
Illustration from The San Francisco Oakland Bay Bridge : A Technical Description in Ordinary Language. E. Cromwell Mensch, c1936.
Source: Harmer E. Davis Transportation Library.
AUTOS AND TRAINS
Originally divided into three lanes in each direction, the upper deck of the Bay Bridge was designed for automobiles and other light vehicles. Trucks and buses used three lanes on the lower level of the bridge, sharing it with the Key System and Interurban Electric (Southern Pacific), which operated trains using two standard gauge electric railway tracks, separated from vehicular traffic. Ten-car trains ran directly from Alameda, Berkeley and Oakland to the newly constructed terminal in San Francisco. The trains were scheduled to run as closely as 63 seconds apart in order to handle the passenger load. The first year of bridge traffic was estimated to be approximately 6 million vehicles. This number would gradually increase until it reached 9 million by 1950. However, the bridge actually carried 9 million vehicles the first year. The train tracks were removed from the Bay Bridge, and the bridge decks were converted to their present traffic configuration, during a 4-year project begun in 1958 (at a cost of $35 million), after the Key System abandoned transbay service due to decreased patronage.
Illustration from Facts About the San Francisco-Oakland Bay Bridge. Bay Bridges Educational Bureau, c1935.
Illustration from The San Francisco Oakland Bay Bridge : A Technical Description in Ordinary Language. E. Cromwell Mensch, c1936.
Chief engineer of San Francisco-Oakland Bay Bridge helped pioneer interstate highway system
Copyright © 2005 by E.A. Kral
One of the most distinguished civil engineers of the 20th century was Charles H. Purcell, a native of North Bend, Nebraska. He became renowned as the chief engineer of California’s monumental San Francisco-Oakland Bay Bridge, the first ever to cross San Francisco Bay.
And during his career from 1906 to 1951, the era in which the automobile emerged as a prominent factor in American society, he also was a national highway authority who helped initiate the development of the Interstate Highway System.
At first, he held ten different positions designing or supervising construction of bridges and highways in several states, mostly in the Pacific Northwest. Notable achievements included completion in 1914 of Oregon’s first paved highway, and three years later his innovative 170-foot-long concrete arch bridge on the Columbia River Highway near Portland.
He was also district engineer for the U.S. Bureau of Public Roads for seven years. In 1928, Purcell became California State Highway Engineer, and was responsible for the design and construction of the $78 million double-deck 8 1/4-mile-long bridge between San Francisco and Oakland, completed ahead of schedule in November 1936 and realization of local dreams since 1850.
The western portion of the Bay Bridge–from San Francisco to Yerba Buena Island–consists of four towers and two main suspension spans joined end-to-end and connected with a massive central anchorage. Each tower extends nearly 500 feet above water, more than the height of the Nebraska State Capitol.
Unprecedented is the depth of the central anchorage, a 500-foot-tall structure, 220 feet of which lie below the surface of the water. It is the world’s largest pier. It crosses Yerba Buena Island through a 540-foot-long tunnel, and at the time was the largest bore tunnel in the world.
The dirt from the tunnel formed the landfill for adjacent Treasure Island. The eastern portion continued to Oakland with one cantilever span 1400 feet long (regarded at present as the sixth longest cantilever span in the world) and a series of trusses. Because of damage during the 1989 earthquake, the eastern span is now being replaced with a newly designed suspension span. The $6 billion project, a joint venture headed by Peter Kiewit Company of Omaha, may be completed by 2013.
As State Highway Engineer and later Director of Public Works, he also transformed the California Highway System from 4,800 miles of rural main roads in 1928 to 14,000 miles of vastly improved rural and urban highways by 1950.
Included among the 640 miles of metropolitan freeways at the time were the Pasadena Freeway, completed in 1940 and considered the first freeway in the West, and the world’s first four-level interchange in 1953 in Los Angeles. Thus Purcell had established California as a pioneer in metropolitan freeway development that anticipated interstate highway design standards by at least a decade.
He was also a national highway authority, serving from 1928 to 1951 as a member of the executive committee of the American Association of State Highway Officials, which worked closely with the U.S. Bureau of Public Roads, now called the Federal Highway Administration. In 1937, he was appointed by the U.S. Secretary of Agriculture to the twelve-person Committee on Planning and Design Policies.
And in 1941 he was selected by U.S. President Franklin Roosevelt to serve on a seven-man National Interregional Highway Committee, whose final report in 1944 influenced Congress that year to authorize establishment of the national system of interstate highways. During President Dwight Eisenhower’s Administration, federal funding of a 41,000-mile network of limited access expressways was authorized in 1956.
Honors were accorded to Purcell, including posthumous recognition. In November 1955, the American Society of Civil Engineers selected the Bay Bridge as one of the seven modern civil engineering wonders of the United States. A review of the construction of the Bay Bridge may be found in Richard H. Dillon, High Steel:
Building Bridges Across San Francisco Bay (Celestial Arts Publishing, 1979). A lengthy biography was published in the June 2, 1999 Wilber /NE/ Republican, pp. 5-6. An entry on Purcell appeared in American National Biography, Supplement 1 (Oxford University Press, 2002) 493-494.
And an article was published in the August 19, 2003 Omaha World Herald. Born in 1883 at North Bend, Dodge County, Nebraska, he was one of two children who survived to adulthood of John and Mary Gillis Purcell. Though his father died three years later, Charles remained in North Bend, where he liked to draw pictures, especially bridges, and graduated from North Bend High School in 1900.
He attended the University of Nebraska-Lincoln for his freshman year, followed by one year of employment near his uncles in Chicago, then one semester at Stanford University. After his mother’s death in January 1903, he returned to the University of Nebraska-Lincoln, and earned his bachelor’s degree in 1906.
In 1914, he married Minnie Pullen, daughter of a Portland, Oregon farmer. The couple had no children. Charles Henry Purcell died in Sacramento, California in 1951, just five weeks after his retirement due to ill health. His cremated remains were placed at East Lawn Memorial Park in that city. For more information, consult “900 Famous Nebraskans” on the Internet at www.nsea.org or www.beatricene.com/gagecountymuseum or www.nebpress.com.
Golden Gate Bridge Statistic
Length, Width, Height, Weight
Total length of Bridge including approaches from abutment to abutment: 1.7 miles = 8,981 ft = 2,737 m
Total length of Bridge including approaches from abutment to abutment, plus the distance to the Toll Plaza: 9,150 ft = 2,788 m
Length of suspension span including main span and side spans: 1.2 miles = 6,450 ft = 1,966 m
Length of main span portion of suspended structure (distance between towers): 4,200 ft = 1,280 m
Length of one side span: 1,125 ft = 343 m
Width of Bridge: 90 ft = 27 m
Width of roadway between curbs: 62 ft = 19 m
Width of sidewalk: 10 ft = 3 m
Clearance above mean higher high water: 220 ft = 67 m
Total weight of each anchorage: 60,000 tons = 54,400,000 kg
Original combined weight of Bridge, anchorages, and approaches: 894,500 tons = 811,500,000 kg
Total weight of Bridge, anchorages, and approaches (1937): 894,500 tons = 811,500,000 kg
Total weight of Bridge, anchorages, and approaches (1986)*: 887,000 tons = 804,700,00 kg*
Weight of Bridge, excluding anchorages and approaches, and including the suspended structure, main towers, piers and fenders, bottom lateral system and orthotropic redecking (1986): 419,800 tons = 380,800,000 kg*
* The total bridge weight listed for 1986 includes the reduction in weight due to the redecking in 1986. The weight of the original reinforced concrete deck and its supporting stringers was 166,397 tons (150,952,000 kg). The weight of the new orthotropic steel plate deck, its two inches of epoxy asphalt surfacing, and its supporting pedestals is now 154,093 tons (139,790,700 kg). This is a total reduction in weight of the deck of 12,300 tons (11,158,400 kg), or 1.37 tons (1133 kg) per lineal foot of deck.
Bridge Deflection, Load Capacity
Watch this video to see how the Golden Gate Bridge can move up and down by as much as 16 feet depending on the temperature.
Maximum transverse deflection, at center span: 27.7 ft = 8.4 m
Maximum downward deflection, at center span: 10.8 ft = 3.3 m
Maximum upward deflection, at center span: 5.8 ft = 1.77 m
Live load capacity per lineal foot: 4,000 lbs. = 1,814.4 kg
As an example of how the Bridge is built to move, during the winter storms in 1982, the main span bowed approximately 6 to 7 feet
The three maximum deflections noted above at the center of the suspension bridge are due to the following loading conditions:
- The transverse deflection is due to a sustained transverse wind load. The maximum transverse movement of 27.7 ft is based on the maximum allowable longitudinal movement of the wind locks at the support towers;
- The maximum downward deflection is due to a condition with maximum live load on the center span, no live load on the side spans and maximum design temperature to elongate the main cables; and
- The maximum upward deflection is due to a condition opposite to condition 2 above, with maximum live load on side spans, no live load on center span and minimum design temperature to shorten the cable length.
The Golden Gate Bridge has two main towers that support the two main cables.
Height of tower above water: 746 ft = 227 m
Height of tower above roadway: 500 ft = 152 m
Tower base dimension (each leg): 33 x 54 ft = 10 x 16 m
Load on each tower from main cables: 61,500 tons = 56,000,000 kg
Weight of both main towers: 44,000 tons = 40,200,000 kg
Transverse deflection of towers: 12.5 inches = 0.32 m
Longitudinal deflection of towers: shoreward: 22 in = 0.56 m and channelward: 18 in = 0.46 m
The south tower foundation depth below mean low water is: 110 ft = 34m
To build south tower pier to support the south tower, construction workers pumped 9.41 million gallons or 35.6 million liters of water out of the fender that was constructed first.
Main Cable Stats
The Golden Gate Bridge has two main cables which pass over the tops of the two main towers and are secured at either end in giant anchorages.
The main cables rest on top of the 746-foot main towers in huge steel castings called saddles.
Diameter of one main cable including the exterior wrapping: 36 3/8 in. = .92 m
Length of one main cable: 7,650 ft = 2,332 m
Total length of galvanized steel wire used in both main cables: 80,000 mi = 129,000 km
Number of galvanized steel wires in one main cable that are 0.192 inches in diameter: 27,572
Number of bundles or strands of galvanized steel wire in one main cable: 61
Weight of both main cables, suspender cables and accessories: 24,500 tons = 22,200,000 kg
The galvanized steel wire comprising each main cable was laid by spinning the wire using a loom-type shuttle that moved back and forth as it laid the wire in place to form the cables. The spinning of the main cable wires was completed in 6 months and 9 days.
The galvanized steel wire used for the main cables is carbon steel with the following average chemical composition and physical properties
Ladle test results (specified) C: 0.81% (0.85) Mn: 0.66% (—) P: 0.026% (0.04) S: 0.028% (0.04) Si: 0.24% (—) Tested properties (specified) Tensile Str, Fu = 235,600 psi (220,000 psi min) Yield Str, Fy = 182,600 psi (160,000 psi min) Elongation in 10″ at rupture = 6.3% (4.0% min)
Suspender Rope (vertical ones) Stats
The Golden Gate Bridge has 250 pairs of vertical suspender ropes that are spaced 50 feet apart across both sides of the Bridge. Each suspender rope is 2-11/16 inches in diameter. All of the ropes were replaced between 1972 and 1976, with the last rope replacement completed on May 4, 1976.
Cu. yd. Cu. m. San Francisco Pier and Fender 130,000 99,400 Marin Pier 23,500 18,000 Anchorages, Pylons, and Cable Housing 182,000 139,160 Approaches 28,500 21,800 Paving 25,000 19,115 Total 389,000 297,475
Tons Kg. Main Towers 44,400 40,280,000 Suspended Structure 24,000 21,772,000 Anchorages 4,400 3,991,000 Approaches 10,200 9,250,000 Total 83,000 75,293,000