Historic Structures

significant structures of the past

Golden Gate Bridge – 75th Anniversary. Courtesy of Reinhard Ludke.

With many great achievements, the end result is the sum of the contributions made by all that participate. Neil Armstrong and Edwin “Buzz” Aldrin, the Apollo 11 The Real Story – Structural astronauts that stepped on the moon on July Engineers and Architects of 20, 1969, got there the Golden Gate Bridge through the efforts of 1000s of engineers and scientists. Engineers worked behind the Part 1 scenes for years developing and supporting the moon landing program, but only Armstrong By Reinhard Ludke, S.E. and Aldrin receive the tribute and went down in history for this accomplishment. Joseph B. Strauss, visionary and promoter to span the Golden Gate, receives the credit as the Engineer of the Golden Gate Bridge. Mr. Strauss, owner Reinhard Ludke, S. E. is a Bridge Engineer, Principal Structural Engineer, for Creegan + D’Angelo Engineers, San Francisco, CA. He was the Past President of the Structural Engineers Association of Northern California, served as the Director and Secretary of the Structural Engineers Association of California, and was elected FELLOW of the Structural Engineers Association of California in 2010. of his own engineering firm, Strauss Engineering Corporation, in Chicago, Illinois, was appointed the Chief Engineer by the Golden Gate Bridge and Highway District Board of Directors on August 15, 1929. Joseph Strauss is the “statue” near the bridge toll plaza, and he receives the credit for spanning the gate. In 1916, more than four decades after railroad entrepreneur Charles Crocker proposed a bridge across the Golden Gate Strait, James H. Wilkins, a structural engineer and newspaper editor for the San Francisco Call Bulletin, suggested spanning the Gate. San Francisco City Engineer, Michael M. O’Shaughnessy, the lead engineer of the San Francisco Hetch Hetchy water system, contacted bridge engineers to consult with them about the feasibility and cost of bridging the Golden Gate. Most speculated that a bridge would cost over $100 million. Joseph Strauss, who had designed nearly 400

The online version of this bridges, claimed it could be built for $25 to $30 article contains detailed million. This man, “Joseph Baermann Strauss references. Please visit was an undersized man with a Napoleonic ego, www.STRUCTUREmag.org. yearning for a career in the arts, with only the most modest amount of formal engineering training…”, says John Van Der Zee. “Strauss was a strange, at times almost a self cancelling mixture of conflicting traits: promoter, mystic, tinkerer, dreamer, tenacious hustler, publicity seeker, and recluse. He was not a member of the American Society of Civil Engineers nor was he a graduate of a college of engineering.”

Strauss Hybrid Bridge Concept

His answer to spanning the gate, Joseph Strauss imagined a hybrid concept for the span that included a steel truss bridge from the shore with cantilevered steel truss from the main towers. Two suspension cables would be attached at the ends of the top chord of the cantilever, with a stiff steel truss road deck suspended from the cables. Strauss submitted a design proposal for bridging the Golden Gate Strait to O’Shaughnessy in June 1921, with a cost estimate of $17 million. Strauss called his solution a symmetrical cantilever-suspension hybrid bridge. Once his design was made public by O’Shaughnessy in December 1922, the public voiced little opposition, even though the local press described it as ugly. In 1921, Strauss hired Charles A. Ellis, Professor of structure and bridge engineering at the University of Illinois, to head up his engineering staff in Chicago. Ellis joined Strauss

1931 Suspension Bridge Elevation by Irving F. Morrow. Collection of the Golden Gate Bridge, Highway and Transportation District. Photo by Robert David.

Engineering Corporation after a 14 year teaching career in Civil Engineering at the Universities of Michigan (1908 to 1912) and Illinois (1914 to 1921). The University of Illinois had the preeminent civil engineering faculty in the United States in first half of the 20th century. He had studied mathematics and structural engineering theory and authored a textbook, Essentials in the Theory of Framed Structures, which was a popular university textbook of that time. Ellis quickly advanced to Vice President at the Strauss company where he was in charge of all bridge engineering, design and construction supervision. The original September 1937 Report of the Chief Engineer did not include detailed information about the roles played by Ellis and by Leon S. Moisseiff, a New York bridge engineer, who was developing new mathematical methods for the analysis of suspension bridges. In Ellis, Joseph Strauss found the structural engineer he needed for his dream of a bridge across the Golden Gate. Unlike Strauss, Ellis had no inclination to seek fame. The pair was quite odd – the sly businessman and a academic and professor, who found satisfaction in completing complex mathematical analysis and engineering. Ellis and Moisseiff had a profound influence in the evolution of the final design for the Golden Gate Bridge. In 1925, Strauss had Ellis arrange for Leon S. Moisseiff, designer of New York’s Manhattan Bridge, to serve on a “Board of Consultants” for the bridge district. He reviewed Strauss’s plans for a cantilever-suspension hybrid bridge, and found them to be practical from an engineering standpoint and capable of being built within the estimated budget of $21 million. Moisseiff had some concern about the hybrid bridge design and asked Strauss to consider an alternate “all cable” design. Moisseiff noted this in his letter to Strauss dated November 15, 1925: Dear Sir:

In accordance with your letter of acceptance of June 8, 1925, I present herewith to you a report on a comparative design for a suspension bridge with a single span stiffening truss based on identical specifications and prices as the cantilever-suspension type proposed by you for the Golden Gate Bridge at San Francisco and on which I made a report to you on July 27, 1925.

Respectfully submitted, /s/ Leon Moisseiff This letter included the Report on Comparative Design of a Stiffened Suspension Bridge over the Golden Gate at San Francisco, California. The seven-page report describes an all wire cable bridge of the stiffened suspension type, consisting of two parallel wire cables spanned over two towers and anchored on each side into bedrock. The bridge had a span of 4,000 feet between towers and provided a clearance of 200 feet above the high tide water. Two 36-inch diameter main cables were described as 91 strands, made with 25,700 high strength wires, spaced 90 feet apart supporting the suspended steel roadway. Together, Moisseiff and Ellis explored a practical application of Moisseiff’s deflection theory of suspension bridges. They made their bridge design flexible enough to withstand the gales that often blew through the Golden Gate. The bridge would be lighter, longer, and narrower than any of its predecessors. Moisseiff believed that up to half the stress caused by winds could be absorbed in a suspension bridge by the bridge cables and suspender ropes, and transmitted to the bridge towers and abutments. If a bridge were designed to bend and sway with the winds, the suspended structure – the roadbed – would act as a counterweight and restore the bridge to equilibrium. At the time of his report, Moisseiff was working as a consultant on the design of the George Washington Bridge, New York

Joseph B. Strauss Bridge Engineer Charles A. Ellis

Bridge Consultant Leon S. Moisseiff Bridge Architect Irving F. Morrow

City, and he was in close contact with O. H. Ammann, Chief Engineer, Port of New York Authority. Moisseiff’s design incorporates several key features of the George Washington Bridge design, including traffic live loads for long span suspension bridges, the allowable stresses, and anchorage of the cables in rock tunnels. The 1925 report suggests a bridge that is very similar to the one that was built. A continuous steel stiffening truss bridge deck is suspended from the main cables. The towers rise from piers constructed in the water. Each tower is constructed of multiple riveted steel plate cells that form two large columns. The two columns are braced together at multiple levels, into a transverse frame. Architectural features were added during the design to create the Art Deco style that was popular at the time. The 435-foot tall towers have a trapezoidal plan shape that tapers from 40 feet at the base to 20 feet top. Moisseiff estimated the suspension bridge construction cost as $19,400,000. Eventually Strauss would speak of these conceptual ideas, who’s technical engineering was beyond his capabilities, as if they were his own. continued on next page

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The suspension span concept did not immediately become the leading design for the bridge. As late as 1929, Strauss continued to campaign for a bridge using his original symmetrical cantilever-suspension hybrid design. On August 15, 1929, the Board appointed prominent engineers Leon Moisseiff and Othmar H. Ammann, and Professor Charles Derleth, Jr. of the University of California Engineering School at Berkeley, to serve as the Bridge District Advisory Board of Engineers alongside Chief Engineer Strauss. Strauss also appointed Charles Ellis to the Advisory Board of Engineers, serving as its Secretary. On August 27, 1929, the first meeting of the Board of Engineers took place. A year later, on August 27, 1930, Mr. Strauss submitted his Report of the Chief Engineer with Architectural Studies, Volume I, to the Board and made his presentation of a suspension span. The preliminary plans illustrated the distinctive shape of the main towers and the elevation of the suspended span that is very similar to what was eventually built, as proposed in Moisseiff’s 1925 report. Ellis signed all the design drawings, and he is included on the official letterhead of the Office of the Chief Engineer which lists the Officers and Engineers of the District, naming Charles A. Ellis as Designing Engineer. Mr. Strauss noted in his cover letter accompanying his report:

The staff in charge of the detail work of the Golden Gate Bridge has been the staff of the Strauss Engineering Corporation of

Chicago, under the immediate direction of Mr. Charles A. Ellis and with other heads of the Strauss staff advising … The work of the Company is directed by myself as President and Chief Engineer through two Engineering Vice Presidents; namely,

Mr. Ellis, above referred to, and Mr. C.

E. Paine, assisted by a large force of engineering specialists. Mr. Ellis has acted as

Chief Assistant to myself on the Golden

Gate bridge, and on other similar projects...while Mr. Paine has similarly acted as Chief Assistant on such projects as the

Columbia Longview bridge... From Strauss’s original design of a symmetrical cantilever-suspension hybrid bridge to Moisseiff’s 1925 suspension bridge design, to the suspension span design presented to the Advisory Board of Engineers in August 1930, Ellis played a fundamental role in this design evolution. November 4, 1930, signaled the start of the final design for the Bridge and Strauss submitted an Outline of Engineering Procedure, for District General Manager Alan MacDonald’s approval. This document details the bridge engineering staff organization as follows:

Computation of Stresses and the preparation of stress sheets is assigned to the

Computation Division under the direction of M. Charles A. Ellis of the Strauss Staff.

General Plans: Preparation of the general plans and checking of the contractor’s working plans is assigned to the Plans Division under the direction of Mr. Clifford E. Paine of the Strauss Staff.

Specifications, Contract and Proposal

Forms: The specifications, contract and proposal forms are assigned to the

Computation Division under the direction of Mr. Ellis, reviewed by Mr. Paine of the Plans Division. Lateral forces, from the wind and earthquake, were a major analysis, design and engineering challenge of the time. The engineer had to determine the wind force, the forces in the cable and deck and towers, and the lateral movement. In the 1920s, complex manual calculus mathematics computation was required to solve for multiple unknown variables. Ellis was the engineer who understood the new theories and spent many hours of his own labor to complete the analysis and “design every stick of steel on that bridge”, according to his record at Purdue University. Construction of bridge tower foundations in the deep water and swift currents of the gate also required innovative engineering and construction. Engineers calculate predictable static forces and designed their structures with strength, stiffness, and stability to support those forces. They had to also consider forces that change over time, temperature, traffic, and wind which added complexity to their calculations. Charles Ellis and Leon Moisseiff calculated forces for the Golden Gate Bridge with only a slide rule and a manual adding machine. Ellis worked for months solving equations and designing the structural members of the bridge. Over 75 years ago, the bridge design and structural calculations provided by Charles Ellis and Leon Moisseiff persuaded Strauss to abandon his own design in favor of a suspension bridge, which is celebrated in 2012. The Golden Gate Bridge, Report of the Chief Engineer, September 1937, written by Mr. Strauss, provides no details on the transition from his originally proposed symmetrical cantilever-suspension hybrid bridge to the Moisseiff inspired suspension span design that was eventually built, and simply states on page 37:

Eberson’s Bridge Tower Sketch. Golden Gate Bridge, Elevation study of tower, ca. 1930. Pencil on vellum. Courtesy of The Architectural Archives, University of Pennsylvania by the gift of Drew Eberson, 1984.

“... In the interval which had elapsed any advantages possessed by the cantileversuspension type bridge had practically disappeared and on recommendation of the

Chief Engineer, the cantilever-suspension type was abandoned in favor of the simple suspension type.” The timing of the change from the original Strauss proposal to a suspension bridge design is not exactly known, but it had to have been accomplished sometime between Mr. Moisseiff’s report of November 15, 1925, and the August 27, 1929, meeting of the Board of Engineers. An upcoming issue of STRUCTURE® will continue this Golden Gate Bridge structure engineering history and the contributions of Charles Ellis, Leon Moisseiff and Irving Morrow.▪

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