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| cnu, Source: H. G. Wilshire for U.S. Geological Survey engineering "In October 17, 1989 the Loma Prieta earthquake hit the San Francisco Bay area, causing over $12 billion in damages and claiming 64 lives. Over half the victims were on the Cypress Street Viaduct during the quake....On October 17, 1989 at 5:04 p.m., a devastating earthquake, measuring 7.1 on the Richter Scale, rocked the city of Oakland, causing billions of dollars worth of damage and a death toll of 64....The deaths on the Cypress Viaduct, 35 in total, accounted for more than fifty percent of the 64 lives taken during the earthquake. Fortunately, only about eighty vehicles were on the affected stretch of highway during the earthquake — a fact attributed to a sporting event: the San Francisco Giants were playing in the World Series and people were indoors anticipating the commencement of the game." American Experience | PBS posted Thirty-seven years ago today [Oct 17, 1989], just before Game 3 of the 1989 World Series, fans at San Francisco's Candlestick Park felt the earth shake beneath their seats. It turned out to be the 6.9 magnitude Loma Prieta earthquake, which resonated throughout the Bay Area, ultimately responsible for 63 deaths and thousands of injuries. 📸: Collapsed sections of the Cypress Street viaduct of Interstate Highway 880 in Oakland, California, in the aftermath of the 1989 Loma Prieta Earthquake. (H.G. Wilshire/United States Geological Survey) [The comments are interesting. Several people describe what they saw during the earthquake.] |
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| localwiki engineering "During the Loma Prieta earthquake, the entire Viaduct structure began to vibrate tremendously (Peterson, 1990). Whereas well-graded soils helped to dampen vibrations (Yashinsky, 1998), the soft “bay mud” upon which most of the structure was constructed actually served to increase the amplitude of vibrations by up to five times in comparison to that of the rest of the freeway which was built on rock. In addition, it was later determined that the angular frequency of the seismic waves almost exactly matched a natural angular frequency of the individual horizontal sections of the structure (Halliday et al., 1993). It is suggested that these sediment resonances could have played a significant role in contributing to the freeway collapse, since the resulting forces were not anticipated in the original design. "The Cypress Street Viaduct was designed as a two-tier multi-lane highway constructed of reinforced concrete (Moehle, 1997). Upper and lower levels were connected by two-column bents in a combination of cast concrete and four pin (shear key) connections. The upper deck in some sections was not securely fastened to the lower deck, making this concrete susceptible to vibrations. As the bridge vibrated during the earthquake, the pins connecting the upper level to the lower level also began to vibrate, causing the concrete surrounding the pins to crumble and break away. Without the presence of concrete under the support columns, the columns slid sideways under the weight of the upper deck and allowed a large portion of the upper deck to collapse (Yashinsky, 1998)." The concrete itself tested as structurally sound. |
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| infinityeng |
Part of the land used for the spiral ramp is now the Cypress Freeway Memorial Park.
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| cnu, Source: California Highways and Public Works "The construction of the Cypress Street Viaduct displaced over 600 families and the surrounding urban renewal projects destroyed over 5000 residences." This source puts the strength of the earthquake at 7.1. The viaduct collapsed between 7th and 18th Streets. (I question this range. See the dotted red line on the USGS diagram below.) The highway was carrying 160,000 daily vehicles. The $1.1b replacement was built primarily over railroad land rather than through residential and commercial land. The old route was rebuilt as the $13m Mandela Parkway. |
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| localwikie |
I read about this collapse many years ago. I remember that some drivers deliberately parked over the columns thinking that would be the strongest part of the viaduct. Unfortunately, that is where there was a thick bent cap overhead for the upper deck. When the upper deck collapsed, those drivers were crushed. Drivers that were away from the piers survived because there was a gap between the two decks after the collapse.
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| infinityeng The earthquake lasted for 15 seconds. |
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| usgs "The part of the Cypress freeway structure in Oakland, California, that stood on soft mud (dashed red line) collapsed in the 1989 Loma Prieta earthquake, killing 42 people. Adjacent parts of the structure (solid red) that were built on firmer ground remained standing. Seismograms (upper right) show that the shaking was especially severe in the soft mud. (Photograph by Lloyd S. Cluff)" [A source that I have lost indicated that the soft mud vibrated with a frequency that matched the resonant frequency of the viaduct. Evidently, the vibration of the sand & gravel had a different frequency so that part survived. Even if they had reinforced the viaduct, it may not have sruvived because the issue of matching frequencies between the ground and structure was not a known design issue until this failure.] |
This map shows how the freeway cut through a residential neighborhood.
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| 1980/81 Oakland West Quad @ 24,000 |
A satellite image shows how the replacement highway went around the neighborhood.
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| Satellite |
