Failure of foundation due to earthquake

Kuldeep kumar meena107CE028

What’s earthquakeAn earthquake is the trembling or shaking of

the ground caused by the result of a volcanic activity. it is when the movement of molten material and by gas pressure inside a volcano. An earthquake is also the breaking or slippage of large rock masses below or at the surface of the earth. An earthquake's point of initial rupture is called its focus or hypocenter. The term epicenter refers to the point at ground level directly above the hypocenter

how earthquake come?

Earthquakes happen when stresses built up between tectonic plates in the earth's crust finally release in an instantaneous fashion

Types of earthquakesTectonic earthquakes Tectonic earthquakes are the most common type of earthquake. It may be of small or of extremely high magnitude.

Volcanic earthquake occur usually after a volcanic activity has taken place. The magma that erupts during an earthquake leaves a space, to fill the space left by the magma the rocks move towards the space to fill it in, causing severe earthquakes.

Collapse earthquakes Collapse earth quakes are comparatively small earthquakes and they take place around underground mines.

Explosion earthquakes The explosion earthquakes are caused due to the nuclear explosions.

Effects of earthquakes

Shaking and ground rupture The severity of the local effects depends on the

complex combination of the earthquake magnitude, the distance from the epicenter

High frequency body waves shake low buildings more. Low frequency surface waves shake high buildings more. Intensity of shaking also depends on type of subsurface material.

Column failure, Loma Prieta earthquake Column failure on interstate highway overpass, Northridge earthquake

Landslides

describes a wide variety of processes that result in the downward and outward movement of slope-forming materials including rock, soil, artificial fill, or a combination of these. The materials may move by falling, toppling, sliding, spreading, or flowing.

La Conchita, coastal area of southern California

House destroyed by landslide,Santa cruz mountains

LiquefactionLiquefaction is a physical process that takes place during some

earthquakes that may lead to ground failure. liquefaction takes place when seismic shear waves pass through a saturated

granular soil layer

Collapse highway bridge (close-up of support columns), california

Fires

Earthquakes can cause fires by damaging electrical power or gas lines.

Gas fire , san francisco 1906

Reduce earthquake effect techniques

External post-tensioning Under the PRESS (Precast Seismic Structural Systems), a large-scale U.S./Japan joint research program, unbonded post-tensioning high strength steel tendons have been used to achieve a moment-resisting system that has self-centering capacity. An extension of the same idea for seismic retrofitting has been experimentally tested for seismic retrofit of California bridges under a Caltrans research project

Base isolators Base isolation is a collection of structural elements of a building that should substantially decouple the building's structure from the shaking. This earthquake engineering technology, which is a kind of seismic vibration control, can be applied both to a newly designed building and to seismic upgrading of existing structures. Normally, excavations are made around the building and the building is separated from the foundations. Steel or reinforced concrete beams replace the connections to the foundations, while under these, the isolating pads, or base isolators, replace the material removed. While the base isolation tends to restrict transmission of the ground motion to the building, it also keeps the building positioned properly over the foundation.

Supplementary dampers Supplementary dampers absorb the energy of motion and convert it to heat, thus "damping" resonant effects in structures that are rigidly attached to the ground. supplementary damping can reduce the displacement and acceleration demand within the structures. supplementary dampers act similarly to Shock absorbers used in automotive suspensions.

Tuned mass dampers Tuned mass dampers (TMD) employ movable weights on some sort of springs. These are typically employed to reduce wind sway in very tall, light buildings. Similar designs may be employed to impart earthquake resistance in eight to ten story buildings that are prone to destructive earthquake induced resonances.

Slosh tank

A slosh tank is a large tank of fluid placed on an upper floor. During a seismic event, the fluid in this tank will slosh back and forth, but is directed by baffles - partitions that prevent the tank itself becoming resonant.

Active control system very tall buildings when built using modern lightweight materials, might sway uncomfortably(but not dangerously) in certain wind conditions.Adhoc addition of structural reinforcementThe most common form of seismic retrofit to lower buildings is adding strength to the existing structure to resist seismic forces. it may involve adding primary resisting elements such as walls or frames, particularly in the lower stories.

Connections between buildings and their expansion additions

building additions will not be strongly connected to the existing structure, but simply placed adjacent to it, with only minor continuity in flooring, siding, and roofing. The addition may have a different resonant period than the original structure, and they may easily detach from one another.

References

http://earthqaukesix.wordpress.com/2009/11/18/earthquake6/

http://hubpages.com/hub/Types-Of-Earthquakes

http://en.wikipedia.org/wiki/Earthquake#Earthquake_fault_types

http://www.google.co.in/images?q=teconic%20earthquake&safe=active&um=1&ie=UTF-8&source=og&sa=N&hl=en&tab=wi&biw=1680&bih=889

http://www.ngdc.noaa.gov/seg/hazard/slideset/earthquakes/

References cont..

http://en.wikipedia.org/wiki/Magma http://www.platetectonics.com/book/page_4.

asp http://en.wikipedia.org/wiki/Earthquake#Eart

hquake_fault_types http://pubs.usgs.gov/fs/2004/3072/fs-2004-3

072.html http://en.wikipedia.org/wiki/Seismic_retrofit

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