scec annual meeting - itr 09/17/021 1999 izmit earthquake august 17, 3:02am, 1999 mw 7.4 mw...

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1999 Izmit Earthquake

August 17, 3:02am, 1999 Mw 7.4 Mw earthquake:

>18,000 fatalities

>300,000 homeless

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North-Anatolian Fault, Turkey

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West-ward propagating series of events on the North Anatolian Fault 1939-1999

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‘Domino’ effect of earthquake sequence can largely be explained by stress

transfer/triggering

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Illustration of f(t)

North Anatolian Fault 1944 Event

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North Anatolian Fault Sequence 1939-1999

300 kmN

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Soil Amplification

A2/A1= (1c1/2c2)1/2

A1 1 c1 A2 2 c2

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Forces of Nature

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1999 Izmit Earthquake

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1999 Izmit Earthquake

A 14’th century mosque is surrounded by remains of collapsed houses. The apartment in the background was nearly undamaged

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1999 Izmit EarthquakeThe most common residential structure types in the country are 2 to 5 story low-rise buildings, concrete, reinforced with straight, or in some occasions ribbed bars. Infill walls are made of unreinforced brick walls, the use of shear walls are quite rare. The floor plans are usually symmetric, incorporating 2 to 4 apartment units on each floor.

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1999 Izmit Earthquake

Many of the buildings in the area collapsed as a result of failure in beam-column connections. This was primarily due to the poor detailing in the structural design that led to insufficient amount of reinforcing in critical parts of the structure.

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1999 Izmit Earthquake

Many of the buildings the region were not built with shear walls. In many instances, the unreinforced masonry walls resisted the lateral loads. The resulting failure is also referred to as the ‘pancake effect’, in which the frame elements cannot resist lateral loads, collapsing the building at once.

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1999 Izmit Earthquake

The design of buildings constructed on the main streets were modified in order to create more open spaces in the first floor, in order to accommodate shops and stores. This was a fatal mistake, most of these buildings collapsed on their first floors, usually damaging the floors above it as well

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Inertial Forces

F=ma Newton’s 2nd lawMass ~ Constant: increasing a -> increasing FThus, to decrease F -> decrease m or aF inertial force: mass opposes the a in an opposite direction and proportionally to the size of a

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Inertial ForcesF imposes strains on building’s structural elements:beams, columns, lead-bearing walls, floors, connecting elements

Free-standing block: move opposite to the ground motion with F=ma

Founded block: inertial force absorbed internally

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Resonance (dynamic amplification)

Building Height Typical Natural Period V, H2 story 0.2 seconds5 story 0.5 seconds f0=V/4H10 story 1.0 second fundamental 20 story 2.0 second resonance frequency30 story 3.0 second50 story 5.0 seconds

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Building Stiffness

Taller buildings tend to be more flexible than shorter

Ability to undergo distortion without complete failureMetals more ductile than stone, brick and concrete

More damping -> sooner stop vibratingAdded damping devices

Building Ductility

Building Damping

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Base Isolation

Building Height Typical Natural Period2 story .2 seconds5 story .5 seconds10 story 1.0 second20 story 2.0 second30 story 3.0 second50 story 5.0 seconds

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Base Isolation

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Base Isolation

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Earthquake Resistant Designlengthening the building’s period of vibration

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1999 Izmit Earthquake

Lessons learned:- Building structures that comply with codes and specifications is not a requirement; it is a must. Many of the failures could have been avoided with proper design and construction.

-The choice of construction site is a crucial decision in designing for earthquake resistant structures. Constructing on liquefiable sand and silt deposits requires additional measures to be taken (such as pile or flat foundations, seismic isolators.

- The performance of structures depends highly on the type of structural system chosen. 95 percent of residential structures in Turkey are built with similar structural design, consisting of reinforced concrete framing. New construction methods, such as tunnel-type-molding or use of steel structures, are proven to be more effective in such damage prone areas. Such methods should be promoted and adopted.

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1985 Mw8.0 Michoacan Earthquake

9,500 fatalities

$12-30 billion damage

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Shallow structure known from the bore-hole data:

1. Lake sediments: h 30-100 m, Vs 30-80 m/s,

2. ‘Deep’ sedimentary basin: h 300-500 m, Vs 500-1000 m/s