CA -- San Francisco -- Golden Gate Bridge (South Side):
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Specific picture descriptions: Photos above with "i" icons next to the bracketed sequence numbers (e.g. " ") are described as follows:
GGBS_180714_06.JPG: Golden Gate Bridge
Physical Suicide Deterrent System
GGBS_180715_041.JPG: Keeper of the Gate
GGBS_180715_048.JPG: The Bottom of the Bay
GGBS_180715_069.JPG: Seismic Isolation
Much new knowledge was gained over the decades about earthquake engineering after the Bridge was completed in 1937. Two retrofit strategies have been used recently on the Bridge: (1) making some key elements stronger, and (2) using seismic isolators on approaches to the Bridge to reduce the earthquake motions that they experience.
The isolators reduce the severity of shaking transmitted up into the structure and make the vibrations slower and less jerky. You can see seismic isolators, short black cylinders about 3 feet (1 m) in diameter, under the roadway decks of approach spans at the north and south ends of the Bridge.
When a bridge is rigidly connected to the ground, it directly experiences the rapid, jerky earthquake shaking. If the bridge is mounted on seismic isolators, the isolators deform back and forth during the earthquake allowing a bridge to rock back and forth, softening the vibrations that the structure experiences. When a bridge is isolated, the forces can be reduced by as much as two-thirds as compared to a non-isolated bridge.
Invented in New Zealand in the 1970s, a common type of isolator like the one shown above is made of layers of steel and rubber bonded together. Sometimes there is a hole in the middle in which a lead plug is inserted to increase energy absorption. These are also called lead-rubber bearings.
GGBS_180715_077.JPG: Ships of the Golden Gate
The Golden Gate Strait is the only entrance to San Francisco Bay and is one of the best places in the world to watch ships.
PILOT BOAT - Built to handle rough seas, these boats are painted with bright colors and often with the word Pilot boldly printed on them. They transport a pilot, skilled in navigating the waters of the Golden Gate and Bay, out beyond the Gate where the pilot climbs aboard a large ship. The pilot then takes over steering the ship into the Bay.
OIL TANKERS - The longest and heaviest ships in the world are oil tankers. The steel bulb or bump on the bow is slightly submerged under the water when the ship is heavily loaded. That bulb causes the water to pass around the ship with less resistance, improving the ship's speed. In this photo, because the bow bulb is under the water, you can tell that this tanker is full, not empty.
CONTAINER SHIPS - These long ships have flat decks for stacking steel intermodal containers filled with products. Intermodal means the same container can use multiple modes of transportation, such as rail, truck, and/or ship. You can see giant cranes used to load and unload these ships at the Port of Oakland.
COAST GUARD VESSELS - Coast Guard vessels are marked with a distinctive diagonal orange stripe on the bow. Their mission is to coordinate the safe and efficient movement of vessels in San Francisco Bay and out beyond the Gate on the ocean.
SAILBOATS - San Francisco Bay is one of the world's best places for sailing. Especially in the warmer months, and during the afternoon hours, a strong breeze often blows in through the Golden Gate.
TOUR BOATS - These boats can be seen cruising around Alcatraz Island and sailing under the Golden Gate Bridge before turning back, giving passengers a unique view of the Bridge.
TUGBOATS - Built with large engines, these sturdy boats are used to push and pull much larger ships to get them where they need to go. Tugboats are also used to slow down large ships, like oil tankers, which can otherwise take up to 3 miles (5 km) to come to a stop.
FERRY BOATS - The Golden Gate Bridge, Highway and Transportation District operates a fleet of commuter ferry vessels, lessening traffic on the Bridge.
GGBS_180715_084.JPG: Plate Tectonics
Earth's crust is broken up into about a dozen large sections called plates. These plates make up the continents and seafloor. They move slowly but steadily over millions of years.
Plate Tectonics - Present
At this location, you are standing on the North American Plate. The San Andreas Fault is about 6 miles (11 kilometers) away to the west, under the ocean. The other (far) side of the San Andreas Fault is the Pacific Plate. On a clear day when you look west over the ocean, you can see the Farallon Islands 30 miles (48 kilometers) away. As strain in the plates builds up and is released, causing earthquakes, the crust on the far side of the San Andreas Fault from where you are standing moves to the right. The Farallon Islands are thus slowly moving northward toward Alaska at the rate of about one mile (1.6 km) in 40,000 years.
Plate Tectonics - Future
300,000 Years From Now
If this geologic movement is "played backwards," going back about 15 million years, the Farallon Islands would be located in Southern California. Granite is not native to the San Francisco Bay Region, but the Farallon Islands are made of granite -- granite made about 400 miles (650 kilometers) away in Southern California and transported here by tectonic movement over that time span.
GGBS_180715_087.JPG: Bridge Deck Aerodynamics
The weight, torsional stiffness, and especially the shape of the cross section of a suspension bridge deck determine the stability of the bridge in strong winds. Subtle changes to the cross section of the bridge have a big effect on how stable the bridge is in strong winds.
The importance of cross-sectional shape on bridge stability during winds was demonstrated in 1940 when the newly completed Tacoma Narrows Bridge in Washington State collapsed on a moderately windy day (about 40 miles per hour or 64 kilometers per hour). One model on display is a scale model of the deck of the Tacoma Narrows Bridge that collapsed.
The other model is a modern design using today's knowledge of aerodynamics. Both small-scale models of the bridge decks are equally stocky in cross section, with the same height and width. But if the wind is blowing, the model at left (Tacoma Narrows Bridge) will probably be twisting, sometimes violently; while the model at right, with a shape that responds to the wind in a stable way, may bounce a little because of gusts but quickly "calms down." Even if you push or tap the model on the right, it will return to its original position. These models show how subtle differences in the shape of bridge decks can have a significant effect on how bridges respond to strong winds.
Because of the small scale of these models, they simulate (with some exaggeration) the behavior of full-size bridge decks exposed to a wind speed about 10 times greater. For example, when the wind speed here is 5 miles per hour (8 kilometers per hour), the models simulate the effect on full-size bridge decks exposed to winds of about 50 miles per hour (80 kilometers per hour).
GGBS_180715_096.JPG: Seismic Retrofits and Historic Preservation
Much has been learned about earthquake engineering since the Bridge was designed and built in the 1930s. Today, mathematical analysis techniques help calculate how a structure will perform when subjected to various levels of ground shaking. In addition, physical tests are run on specimens that represent portions of the structure. Comparing and validating mathematical analysis with test results is a standard engineering method.
To test the strength of an existing bridge piece called a lattice strut on the Golden Gate Bridge, a large replica was made and tested by the University of California at Berkeley Civil and Environmental Engineering Department. A piece of that bent and buckled test specimen is displayed here. With accurate figures for the strength of these pieces, decisions can be made to replace or strengthen particular portions of the Bridge to preserve it against damage in future earthquakes.
The original lattice struts have a crisscross pattern of many small pieces of steel riveted together. When one of these struts is replaced, the new, stronger, one-piece steel member has holes cut in it to preserve the historic appearance of the Bridge.
GGBS_180715_107.JPG: Crisis Counseling
Crisis Text Line
Text GGB to 741741
Free support 24/7
There is Hope
GGBS_180715_110.JPG: Taken while driving over the bridge
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