Aaa earthquake engineering2

EARTHQUAKE ENGINEERING

STRUCTURE OF THE EARTH

The Earth is an oblate spheroid. It is composed of a number of different layers as determined by deep drilling and seismic evidence.

These layers are:◦ The core

◦ The mantle

◦ The crust

STRUCTURE OF THE EARTH

◦The CORE The Earth's core is the part of earth in the middle of

our planet.◦ It has a solid inner core and a liquid outer core.

◦Outer core The outer core of the Earth is a liquid layer about

2,266 kilometers thick. It is made of iron and nickel. Its outer boundary is 2,890 km (1,800 mi) beneath

the Earth's surface. The transition between the inner core and outer

core is approximately 5,150 km beneath the Earth's surface.

STRUCTURE OF THE EARTH

◦Inner core◦ The inner core of the earth, as detected

by seismology, is a solid sphere about 1,216 km (760 mi) in radius, or about 70% that of the moon.

◦ It is believed to be an iron–nickel alloy, and may have a temperature similar to the sun's surface, approximately 5778 K (5505 °C).

STRUCTURE OF THE EARTH

◦The MANTLE The mantle is the second layer of the Earth.  

It is the biggest and takes up 84 percent of the Earth.

◦ It is divided into two sections.   The Asthenosphere, the bottom layer of the

mantle made of plastic like fluid. The Lithosphere the top part of the mantle

made of a cold dense rock.

STRUCTURE OF THE EARTH

◦The MANTLE◦ The average temperature of the mantle is

3000° celsius. 

◦ It is composed of silicates of iron and magnesium, sulphides and oxides of silicon and magnesium. 

◦ It is about 2900 km thick.  It is the largest layer of the Earth, taking up 84% of the Earth.

◦ Convection currents happen inside the mantle caused by continuous circular motion of rocks in the lithosphere being pushed down by hot molasses liquid from the asthenosphere. 

STRUCTURE OF THE EARTH

◦The CRUST The crust describes  the outermost shell of

a terrestrial planet. Our planet’s thin, 40-kilometer (25-mile) deep

crust—just 1% of Earth’s mass—contains all known life in the universe.

It is the outer hard layer of the Earth, and is less than 1% of Earth's volume.

It is made up of different types of rocks; igneous, metamorphic, and sedimentary rocks. 

STRUCTURE OF THE EARTH

Earth formed around 4.54 billion years ago by accretion from the solar nebula. A volcanic  out gassing probably created the primordial atmosphere, but it contained almost no oxygen and would have been toxic to humans and most modern life. Much of the Earth was molten because of frequent collisions with other bodies which led to extreme volcanism. One very large collision is thought to have been responsible for tilting the Earth at an angle and forming the Moon. Over time, the planet cooled and formed a solid crust, allowing liquid water to exist on the surface.

HISTORY OF THE EARTH

Largely thought to be a hot, steaming, and forbidding landscape, the primitive crust of the newly condensed planet continued to cool. The crust consisted largely of igneous intrusions and volcanic rocks, and sediments that were eroded from this irregular surface. Geologic remnants from this time are the highly deformed and metamorphosed cratons of the continents. The Precambrian is subdivided, from oldest to youngest, into three eons, the Hadean (4600−3900 million years ago),Archean (3900−2500 million years ago), and Proterozoic (2500−570 million years ago).

HISTORY OF THE EARTH

Little is known about the Hadean because there are so few rocks of that age, and those that do exist are intensely deformed and metamorphosed. The Archean was dominated by crustal building and the development of extensive volcanic belts, arcs, and sedimentary basins that were probably related to plate tectonic activity. Marine rocks including chert contain the fossil remains of microscopic algae and bacteria. The Proterozoic is known for large‐scale rifting of continental crust across the world and the filling of these rifts with huge amounts of sedimentary and volcanic rocks.

HISTORY OF THE EARTH

Extensive iron deposits formed in shallow Proterozoic seas, indicating there was enough free oxygen to precipitate iron oxide minerals (for example, hematite [Fe 2O 3]) from the iron in the water. The increase in the amount of free oxygen is thought to be a result of photosynthetic action by primitive life forms in the sea. The fossil record has preserved layered algal mounds called stromatolites, an abundance of microscopic species, and trails and burrows from wormlike organisms.

HISTORY OF THE EARTH

Most earthquakes originate from the sudden movements of the earth's tectonic plates , close to the earth's surface, along zones of pre-existing weakness called faults. The animation on this page shows the main concepts that define a seismic event, as well as some of the consequent effects.

The rock fracturing determines the sudden release of elastic energy stored before the movement and producing seismic waves that radiate outwards around the fault. During travel, waves lose their energy (attenuation) so much that, for long distances, earthquake arrival can be detected and recorded only by special instruments called seismograph.

EARTHQUAKE MECHANISM

The destructive effects of an earthquake on the ground surface are not always related to the distance from the seismic source (hypocentre). Different earth materials respond differently to seismic shaking; likewise different geological and geomorphological conditions may influence the level of shaking inducing local amplification. An appropriate choice of building design and construction method can considerably mitigate the effects of the seismic shaking.

EARTHQUAKE MECHANISM

A seismic wave is a mechanical disturbance or energy packet that can propagate from point to point in the Earth. Seismic waves can be generated by a sudden release of energy such as an earthquake, volcanic eruption, or chemical explosion. There are several types of seismic waves, often classified as body waves, which propagate through the volume of the Earth, and surface waves, which travel along the surface of the Earth. Compressional and Shear waves are the two main types of body wave and Rayleigh and Love waves are the most common forms of surface wave.

PROPAGATION OF SEISMIC WAVES

Compressional Waves◦ Mechanical longitudinal waves are also called

compressional waves or compression waves, because they produce compressionand rarefaction when traveling through a medium. 

Shear Waves◦ A type of elastic wave, the S-wave,

secondary wave, or shear wave (sometimes called an elastic S-wave) is one of the two main types of elastic body waves, so named because they move through the body of an object, unlike surface waves.

PROPAGATION OF SEISMIC WAVES

Rayleigh Waves◦ Rayleigh waves are a type of surface

acousticwave that travel on solids. They can be produced in materials in many ways, such as by a localized impact or by piezo-electric transduction, and are frequently used in non-destructive testing for detecting defects.

Love Waves◦ Love waves (also known as Q waves (Quer:

German for lateral)) are surface seismic waves that cause horizontal shifting of the Earth during an earthquake.

PROPAGATION OF SEISMIC WAVES

The phenomena of earthquakes differ greatly in accordance with the number, duration, and intensity of the shocks, and with the distance of the place of observation from that of the origin of the disturbance. One of the greatest of modern earthquakes is that of northern India of 1897, which is well summed up in the official report.

Violent earthquakes, which affect extensive areas, are almost always followed by a succession of after-shocks, which may continue for weeks, months, or even years. These may be very violent, though never equaling the primary shock in this respect, but gradually die away, until the region once more comes to rest.

EARTHQUAKE PHENOMENA

In the sea the elastic waves producing shock soon die away in the water. Observations made on the several ships affected by the same quake frequently show a lineal arrangement of the disturbances. A special manifestation of earthquakes in the bed of the sea is the great sea-wave (sometimes erroneously called the tidal wave), which is a gravity wave produced by disturbances of the sea-floor or by a submarine volcanic eruption. The great sea-wave, though not strikingly displayed in the open sea, piles up on the coast into enormous breakers, which often are more terribly destructive than the earth-waves themselves.

EARTHQUAKE PHENOMENA

The vibrations produced by earthquakes are detected, recorded, and measured by instruments call seismographs. The zig-zag line made by a seismograph, called a "seismogram," reflects the changing intensity of the vibrations by responding to the motion of the ground surface beneath the instrument. From the data expressed in seismograms, scientists can determine the time, the epicenter, the focal depth, and the type of faulting of an earthquake and can estimate how much energy was released.

EARTHQUAKE MEASUREMENTS

Magnitude Earthquake Effects Estimated NumberEach Year

2.5 or lessUsually not felt, but can be recorded by seismograph.

900,000

2.5 to 5.4 Often felt, but only causes minor damage. 30,000

5.5 to 6.0Slight damage to buildings and other structures.

500

6.1 to 6.9May cause a lot of damage in very populated areas.

100

7.0 to 7.9 Major earthquake. Serious damage. 20

8.0 or greater

Great earthquake. Can totally destroy communities near the epicenter.

One every 5 to 10 years

EARTHQUAKE MEASUREMENTS

Class Magnitude

Great 8 or more

Major 7 - 7.9

Strong 6 - 6.9

Moderate 5 - 5.9

Light 4 - 4.9

Minor 3 -3.9

EARTHQUAKE MEASUREMENTS

Earthquakes are also classified in categories ranging from minor to great, depending on their magnitude

SEISMICITTY◦ the occurrence or frequency of earthquakes in a

region.

◦ the frequency, intensity, and distribution of earthquakes in a given area.

◦ seismic activity; the phenomenon of earthquake activity or the occurrence of artificially produced earth tremors.

SEISMICITY

SEISMICITY

EARTHQUAKE VIBRATIONS

SINGLE DEGREE OF FREEDOM SYSTEM◦ The simplest vibratory system can be described

by a single mass connected to a spring (and possibly a dashpot). The mass is allowed to travel only along the spring elongation direction.

FREE FORCE VIBRATIONS

Processing of vibration records is necessary because the visual inspection of a time history only reveals maximum amplitude and duration but not influences of potential noise caused by the recoding system/process and/or background (environment). Besides that, vibration records may contain various errors. Corrections of two basic errors are described in Sections 4.2 and 4.3. Douglas (2003), for example, listed types of possible non-basic errors in strong-motion records, Table 4.1: insufficient digitizer resolution , S-wave trigger , insufficient sampling rate , multiple baselines , spikes , early termination , and amplitude clipping .

STRONG MOTION VIBRATION RECORDS

EARTHQUAKE SPECTRUM◦ The response spectrum for a given ground

motion component (e.g., a(t)) is developed using the following steps: Obtain the ground motion for an earthquake. Typically the acceleration values should be defined at time steps of 0.02 second, or less.

DESIGN SPECTRUM

EARTHQUAKE SPECTRUM AND DESIGN SPECTRUM

Ground motion is the movement of the earth's surface from earthquakes or explosions. Ground motion is produced by waves that are generated by sudden slip on a fault or sudden pressure at the explosive source and travel through the earth and along its surface.

strong ground motion as the strong earthquake shaking that occurs close to (less than about 50 km from) a causative fault.The strength of the shaking involved in strong ground motion usually overwhelms a seismometer.forcing the use of accelerographs (or strong ground motion accelerometerfor recording. The science of strong ground motion also deals with the variations of fault rupture, both in total displacement, energy released, and rupture velocity.

GROUND MOTIONS

EARTHQUAKE DAMAGES TO

VARIOUS CIVIL ENGINEERING STRUCTURES

The effects of an earthquake are strongest in a broad zone surrounding the epicenter. Surface ground cracking associated with faults that reach the surface often occurs, with horizontal and vertical displacements of several yards common. Such movement does not have to occur during a major earthquake; slight periodic movements called fault creep can be accompanied by micro earthquakes too small to be felt. The extent of earthquake vibration and subsequent damage to a region is partly dependent on characteristics of the ground. For example, earthquake vibrations last longer and are of greater wave amplitudes in unconsolidated surface material, such as poorly compacted fill or river deposits; bedrock areas receive fewer effects. 

EARTHQUAKE DAMAGES TO VARIOUS CIVIL ENGINEERING

STRUCTURES

The worst damage occurs in densely populated urban areas where structures are not built to withstand intense shaking. There, L waves can produce destructive vibrations in buildings and break water and gas lines, starting uncontrollable fires.

Damage and loss of life sustained during an earthquake result from falling structures and flying glass and objects. Flexible structures built on bedrock are generally more resistant to earthquake damage than rigid structures built on loose soil. In certain areas, an earthquake can trigger mudslides, which slip down mountain slopes and can bury habitations below. A submarine earthquake can cause a tsunami, a series of damaging waves that ripple outward from the earthquake epicenter and inundate coastal cities.

EARTHQUAKE DAMAGES TO VARIOUS CIVIL ENGINEERING

STRUCTURES

EARTHQUAKE DAMAGES TO VARIOUS CIVIL ENGINEERING

STRUCTURES

Currently no single publication exists that provides up-to-date information necessary to architects, presented in a form that is attractive, readable, and intelligible to a non-specialist audience. This revised publication will fill that gap. The present publication consists of a series of chapters that provide the foundation for an understanding of seismic design, each authored by an expert in the field. The authors were given freedom to decide the scope of their chapters; and thus this publication represents expert opinion rather than consensus. Designing for Earthquakes: a Manual for Architects is intended to explain the principles of seismic design for those without a technical background in engineering and seismology. The primary intended audience is that of architects and includes practicing architects, architectural students, and faculty in architectural schools who teach structures and seismic design.

EARTHQUAKE DESIGN PROCEDURES

A design code is a document that sets rules for the design of a new development in the United Kingdom. It is a tool that can be used in the design and planning process, but goes further and is more regulatory than other forms of guidance commonly used in the English planning system over recent decades.

Examples of developments where design codes are being used include:◦ Poundbury, Dorchester◦ Fairford Leys, Aylesbury◦ Fairfield Park, Letchworth◦ Ashford Barracks, Ashford◦ Upton, Northampton

DESIGN CODES

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