As it became clear that a bridge across the strait was not only possible but also affordable, Strauss began to plan. In 1921 Strauss hired Charles Ellis to lead his team and later placed Ellis in charge of bridge design and construction management. In 1925, the newly constructed Board of Consultants examined Strauss' design and concluded that they were practical from an engineering standpoint and could be built.
The original cantilever-suspension hybrid design of Joseph Strauss
Soon thereafter, one of the consultants expressed concern to Strauss. While he approved of the original design, he also submitted his Report on Comparative Design of a Stiffened Suspension Bridge over the Golden Gate Strait at San Francisco, CA. At some unknown point, the bridge design shifted to the stiffened suspension bridge suggested by Leon S. Moisseiff in the aforementioned report. The exact date of this design change is not known. However, we do know that Strauss campaigned his cantilever design until at least 1929. The shift most certainly occurred at some point between the publishing of the report in 1925 and the first meeting of the Board of Engineers on August 27, 1929. Speaking of this shift at a later date, Strauss simply stated, “... In the interval which had elapsed any advantages possessed by the cantilever-suspension 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.”
In the years prior to construction, Strauss and his fellow engineers spent most of their time doing calculations. Unknown until after construction, the majority of the calculations were done by Charles Ellis. He was responsible for the thousands of required calculations, the computations of the stresses, and many other tasks that were generally attributed to Strauss. Strauss later fired Ellis prior to construction, and he would not receive the immense credit due to him until after his death in 1949.
Construction began on January 5, 1933 and was completed on May 27, 1937.
Interesting construction facts:
A huge construction challenge the builders faced involved the transportation of the bridge components. Some of the larger parts of the bridge and building materials were constructed off-site. These were sent through the newly-built Panama Canal from areas such as New Jersey, Maryland, and Pennsylvania. The Panama Canal, opened in 1914, proved to be pivotal in assisting the delivery of materials for construction. The environmental factors of the area caused several issues with construction. The dense fog proved to be dangerous, decreasing visibility in the mornings. Construction on such a large structure would be nearly impossible without full visibility. The currents in the bay were also incredibly strong. Building the foundations of the bridge were very difficult with strong currents. The wind also created hazardous situations when building at increasing height. The structure was not fully stabilized until construction was completed. Because of passing boats and the Navy port at the harbor, the bridge needed to be 220 feet tall. This unfortunately almost ensured the death of any worker that fell during construction, if not for the safety net. A final but important challenge was the obvious fact that there were no computers at the time. The immense force calculations took many months to work out by hand.
One area impacted greatly by new innovations was safety during construction. Strauss firmly insisted on safety precautions that were unheard of at the time. All construction workers were required to wear hard hats on site. This most likely led to greater safety and set the standard for future construction policy.
Bridge worker wearing the required hard hat
The most innovative safety feature was the mammoth-sized safety net spanning below the bridge. This was an incredibly new idea that saved nineteen lives. These 19 survivors are known as the "Halfway to Hell Club." Based on general patterns at the time, planners predicted at least thirty-five deaths during construction. However, the use of these safety innovations cut that estimate down to only eleven deaths. Without a doubt, the implementation of this net inspired countless future construction safety requirements.
Another innovation was the method of spinning wire. The builders developed parallel wire construction specifically for the Golden Gate Bridge Project. This allowed for the combination of thinner wires into a larger cable and, in theory, would allow engineers to construct cables of infinite length. In the end, the cables took six months to spin on-site and consisted of 27,572 strands of wire. The diameter of the cable's cross section is 36 and 3/8 inches. The cables were completed eight months ahead of schedule (the bridge was completed ahead of schedule as well).
Another interesting addition was the fog horns. Due to the natural tendency for fog to envelop the bay and San Francisco, the builders placed foghorns on the middle of the span and south tower. These foghorns are intended to guide ships through the bridge safely. Also, the bridge was painted "International Orange" to be aesthetically pleasing and stand out in the fog.
Engineering Disciplines Involved
Structural engineering is a discipline of civil engineering that deals with the analysis and design phase of construction. The structural components of this engineering marvel took an immense amount of time. Everything from the overall design to the strength of the rivets had to be taken into account, resulting in an incredibly complicated structural analysis/calculations. As noted previously, there were no major calculators or design simulation programs. Everything had to be done by hand. The structural engineers had to account for the complicated external forces such as wind, ocean currents, weight loading and earthquakes that were inevitably coming. In such a project, the engineers in charge had to start by making sure a bridge across the strait was even structurally feasible.
Construction Engineering and Project Management
The complexity of the construction for the Golden Gate Bridge never ceases to amaze. The project was physically large, over water, and groundbreaking. This meant that the project was broken up into distinct larger stages that consisted of numerous smaller projects. The construction lasted roughly four years. Not all of the materials were made on site; therefore some project managers were required to be off-site, coordinating shipments. The north approach tower was constructed first because of earthquake concerns. Construction of the south tower followed, and then the roadway/span was built between the two towers.
Workers during an early stage of construction
For a detailed construction timeline, go here.
The geotechnical aspect of this project, while fairly minimal, plays an important role in function and design. Because of the region and proximity to a fault line, the Golden Gate Bridge had to be able to withstand earthquakes. To allow for these hazards, engineers needed to over-design to ensure a greater factor of safety. Because of this, the foundations in all areas needed to be stronger and deeper. The coastal connections were excavated to allow for deeper foundations and geotechnical engineering was very much a part of this.