In America there was a bridge with 2 platforms but top leval collapsed froman earhqake whats name of bridge?

Question

In america ather was a bridge with 2 platforms but the top leval collapsed crushing the bottom one due to a earthquake wich swept through the city what was the name of the bridge & the earthquake?

Answer 1

Oakland Bay Bridge

Answer 2

Many of these instances occured to many of the freeway viaducts and bridges in the SF Bay area earthquake in '89

THE CENTRAL FREEWAY:
Is part of US 101--Before 1989, the central freeway was a double decked freeway that went from the I-80/101 split all the way to Oak and Fell Streets in San Francisco-was nearly 2 miles long; Now, it only exists as a single decked viaduct that was cut down all the way to Mission and Van Ness Avenues--Only 1 Mile long--It was cut down like this because most of it's structure was damaged, and due to local opposition

THE EMBARCADERO FREEWAY
Was known as the I-480, and eventually CA-480. It was a short freeway stub that served the eastern portions of downtown San Francisco--From I-80 @ the bay bridge and ended abruptly at Broadway St.--Like the Central Freeway, it was also dual-decked, but was majorly destucted to where it couldnt be fixed, so in 1991, the state and city decided to destroy the freeway, and replace it with a Urban Artery, it now it known as the Embarcadero..

BAY BRIDGE
The top deck of the bridge had collapsed, but it was later repaired

CYPRESS VIADUCT
Freeway in Downtown Oakland, and carried Interstate 880, it was heavily destroyed, and had caused the deaths of many people--the double decked viaduct was demolished and replaced with a more secure, safer, and a single-decked viaduct that carries the same freeway, I-880

Answer 3

1989, San Francisco Bay Bridge, Loma Prieta Earthquake.

Answer 4

Cypress Street Viaducts


Cypress Street Viaduct, Collapse Section
Collapsed section of Cypress Street Viaduct, 1989


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.

What follows is an overview and analysis of the disaster, with reference to the materials and design features used in the construction of the viaduct. The knowledge gained from this tragedy has benefited subsequent structures not only in the technical data that it provided but in the research that such a public disaster is bound to initiate.

History of Bridge

In 1949, the design of a new highway that was to service the City of Oakland, California began; by 1957, the construction of the Nimitz Freeway, or I-880, was complete (Yashinsky, 1998). A portion of the Nimitz Freeway that linked the I-880 to the I-80, known as the Cypress Street Viaduct, was a 2 km two-tier highway with five lanes per deck, and traffic flowing at ground level. The path that the Cypress Street Viaduct was required to follow resulted in certain portions of the bridge being constructed on soft mud; in much of the area, the bedrock was over 150 m below the surface (Yashinsky, 1998). The bridge was constructed using cast-in-place concrete with multi-celled reinforced box girders that typically spanned 80 feet (Moehle, 1997).

At the time of construction, the California State seismic criteria required designing for a lateral force of 0.06 times the dead load (Yashinsky, 1998). Over subsequent years there was great advancement in both construction and earthquake engineering technology, and although new technology was becoming available, the Cypress Street Viaduct was not being properly restructured to withstand a large-scale earthquake. After a 1971 earthquake in the San Fernando Valley, the State of California initiated a two-phase program to increase the resistance of highways and bridges to earthquakes: Phase 1 involved strengthening the connections between elevated road ways and their support columns; Phase 2 was to strengthen the support columns themselves (Doyle, 1989). While the structure was retrofit with cable restrainer units in 1977, Phase 2 was never carried out on the Viaduct (Yashinsky, 1998).
The Loma Prieta Earthquake
Collapsed Section of Cypress Structure
Dashed red line indicates collapsed section of Cypress structure in 1989

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. Geological Scientists determined the epicenter of the quake to be in Nisene Marks State Park, along the San Andreas Fault (Doyle, 1989). During the earthquake, a 1.4 km section of the Cypress Viaduct collapsed. As the upper level fell, slabs of concrete trapped many unsuspecting motorists. A survivor gave a firsthand account of the experience as "like being inside an exploding building" and saw the vehicles ahead of her "go like dominoes" (Doyle, 1989). 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 (Doyle, 1989).

The collapse of the bridge was one the most devastating effects of the earthquake, requiring immediate action by all levels of assistance. Emergency crews worked nonstop to free people from the rubble; local residents provided ladders and helped extinguish fires and locate survivors. The final survivor was located and rescued approximately 90 hours after the initial earthquake (Doyle, 1989). The State of California and the Federal government declared the region a disaster area, making it eligible for $300 million in immediate relief (Doyle, 1989). Damage caused by the quake was extensive, and rebuilding the damaged transportation infrastructure continued for many years following the disaster.


Causes of Failure

Two major factors led to the collapse of 1.4 kilometers of the Cypress structure, part of the Nimitz freeway (Interstate I-880). The first was the geotechnical aspect of the central San Francisco Bay area. The second was the design of the concrete Viaduct and its response to strong ground shaking.

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.
Upper Deck of Cypress Street Viaduct
Collapsed section of upper deck of
Cypress Street Viaduct in 1989

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).

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