Building for Earthquakes

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Building for Earthquakes

• Chances are 2 out of 3 that youll be home when
  the next earthquake strikes, and 1out of 3 that
  youll be in bed. So your homes ability to
  withstand an earthquake affects not only your
  pocketbook but also your life and the lives of
  those who live with you.

Collapse of brick structure during 1983 Coalinga
Earthquake
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• Imagine for a moment that your house is anchored
  to a flatcar on a moving train. Suddenly the
  train collides with another train and the flatcar
  stops abruptly. What happens to your house? If
  its a wood-framed house, as most houses in
  California are, it probably would not collapse,
  although your brick chimney might topple over.

Damage to chimneys resulting from magnitude 7.1,
1992 Petrolia Earthquake
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• This analogy introduces an important concept.
  The jolt to your house during the train wreck is
  analogous to the shocks the house would receive
  during a large earthquake. The response of the
  house and its contents (including you) to these
  jolts follows the principle of inertia. The
  principle of inertia says that a stationary
  object will remain stationary. A home not bolted
  to its foundation will slip of the foundation
  because of its inertia.

This house along Jefferson Street in the Marina
District shifted more than 10 cm on its
foundation due to 1989 Loma Prieta Earthquake
Wooden structure located on Jefferson Street in
Watsonville has shifted on its foundation due to
1989 Loma Prieta Earthquake
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Damage to unreinforced masonry structures in Los
Gatos (above) and San Jose (below) resulting from
the 1989 Loma Prieta Earthquake

• Ductile buildings such as wood and steel-frame
  structures tend to bend and sway during an
  earthquake. In contrast, brittle structures made
  of brick or concrete block joined together with
  mortar, or adobe buildings from Californias
  pioneer days are unable to deform during an
  earthquake with out collapsing.

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The Armenian SSR Earthquake

• On December 7, 1988, at 1141 a.m. local time a
  magnitude 6.9 earthquake shook northwestern
  Armenia and was followed four minutes later by a
  magnitude 5.8 aftershock. Swarms of aftershocks,
  some as large as magnitude 5.0, continued for
  months in the area around Spitak. The vast
  majority of the damage occurred in unreinforced
  masonry structures.

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• In this earthquake both design deficiencies and
  flawed construction practices were blamed for the
  large number of building collapses and resulting
  deaths. Many of the modern multi-storied
  buildings did not survive. Twenty-five thousand
  were killed and 15,000 were injured by the
  earthquake. In addition 517,000 people were made
  homeless.

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• During the 1994 Northridge Earthquake, similar
  damage patterns to those in Armenia were observed
  throughout the San Fernando Valley.

Partial collapse of Bullocks Department Store
Collapsed roof near Northridge Mall
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• A common failure in Californias recent
  earthquakes was the two- or three-garage with
  living space overhead. Many condominiums have
  most of the first floor devoted to parking, with
  apartment space in the upper floors. The large
  amount of empty space at the garage door means
  less bracing against earthquake forces than in
  standard walls, so these open areas are the first
  to fail in an earthquake.

Detail of shoring to garage area in building on
Beach Street in the Marina District. The practice
of using the first floor for garages left the
building with inadequate lateral bracing on the
ground level.
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Carport beneath the collapsed apartment building
in Northridge. Collapse of buildings into
carports was a common cause of apartment damage
in the epicentral area. The carports, because
they were open on one side, did not have the
resistance to shaking.
This apartment building in Reseda collapsed over
the garage due to 1994 Northridge Earthquake
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• Similar problems arise, although on a smaller
  scale, with large picture windows, sliding-glass
  patio doors, double doors or patio covers.

Porch Damage, Wood Frame House, Santa Cruz
Mountains, Loma Prieta Earthquake, 1989
Total Collapse of Front of Residence, Coalinga
Earthquake of 1983
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Soil Types and Shaking Amplification

• Because of certain conditions, seismic waves may
  cause certain areas to shake up to 10x harder
  during an earthquake, this is called site
  amplification. The chief contributor to the site
  amplification is the velocity at which the rock
  or soil transmits shear waves (S-waves). Shaking
  is stronger where the shear wave velocity is
  lower.

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Fire!

• There is also a formidable threat of fire, such
  as resulted from the 1906 San Francisco, the 1923
  Tokyo, and the 1995 Kobe earthquakes.

Citizens of San Francisco watch fires burn out of
control following the 1906 earthquake
Fires burn in the city of Kobe following the 1995
quake there
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This panoramic view shows San Francisco in
flames, five hours after the earthquake. The
photograph was taken from Mason Street at 1000
A.M., April 18, 1906. There is little evidence of
earthquake damage. Most of the city's downtown
buildings appear to be intact, yet these were
later partially or wholly destroyed by flames.
The fire continued unchecked for three days.
This view of the San Francisco ruins shows many
square blocks completely leveled. The photograph
was taken on May 1, 1906, almost a month after
the disaster. Much of the debris had already been
hauled away leaving only empty ash-blackened
blocks. Rebuilding of small buildings had begun.
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• Great Kanto quake (Tokyo-Yokohama) 1923
• killed at least 140,000
• tens of thousands burnt to death
• Great Hanshin quake (Kobe) 1995
• fires started in old, cramped parts of city
• many wooden buildings
• 146 fires started
• 23,000 homes destroyed
• Tokyo today
• 1 million wooden homes

Kobe
Tokyo
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