Seismically Resistance Building Designs

8/18/2019 Seismically Resistance Building Designs

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Building Failure and SeismicallyResistance Building Designs

Erik Blaser

ID# 51032347

Tuesday and Thursday 4-6pm


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Abstract ˗˗˗

Stemming from the tectonic forces that cause earth’s lithosphere to shift and

terraform, earthquakes are one of the most destructive natural disasters.

They cause more than one illion dollars in damages and thousands of

deaths annually. !hen earth’s plates aruptly move past one another they

release vast amounts of energy in the form of four types of earthquake

"aves. These "aves are "hat can e felt "hen an earthquake occurs and

they are also the cause of damage to uildings and in turn people. !hen the

"aves interfere they create a unique "ave pattern that cause a variety of

failures "hich end up damaging structures. The main failures a uilding can

e#perience are soil, foundation, and structural failure. $s engineers have

studied the causes of each of these failures they have een ale to design

several uilding features that negate the e%ects of earthquakes. By isolating

the ase from the rest of the structure, engineers are ale to de&ect much of

the energy from the structure into energy sinks. $lternatively engineers are

using damping systems similar to "hat a car uses to reduce shocks to reduce

the lateral movement of uildings during earthquakes due to the seismic

"aves. The use of seismic resistance design is already in use in many of the

"orlds countries' it continues to evolve as more is learned aout

earthquakes and ho" to minimi(e their damaging e%ect.


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Table of Contents

Page Number

1) Introduction to Earthquakes and Building Failure

a) Types of Building Failure

i) Soil Failure

ii) Foundational Failure

iii) Structural Failure

2) Seismic Resistance Technology of Today

a) Base Isolation

i) ead Ru!!er Bearings

ii) e"itating Foundation

!) #i!ration $amping

i) Frictional $amper

ii) Tuned %ass $amper

&) 'onclusion

() References

1

2

2

2

3

3

4

4

55

5

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Introduction to Earthquakes and Building Failure

)


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$s the earth’s lithosphere is created' the tectonic plates slo"ly shift

along the earths fault lines. $n accumulation of energy results from the

friction et"een t"o plates that are interacting "ith each other. This energy

uilds up to a point "here the plates can no longer remain static and

aruptly dissipate all of their stored energy. The energy is released in the

form of "aves "hich drastically deform earth’s terrain for a short period of

time' these periodic releases of energy and resulting deformations are called

earthquakes. $n earthquake’s "aves *+move in a nearly random fashion in

all directions, oth hori(ontally and vertically +)- as a result of the

superposition of four types of seismic "aves. arthquakes release /, S, 0ove,

and Raleigh "aves' the 1rst t"o eing ody "aves and the latter ones eing

surface "aves. Body "aves are the faster of the t"o types of "aves and

have only one degree of freedom' either compressional in the case of /

"aves or vertical deformation in the case of S "aves. 2o"ever, most of the

damage to structures is caused y 0ove and Raleigh "aves ecause they

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have a slo"er frequency and as a result the "aves have a higher amplitude

than / and S "aves. Raleigh "aves propagate in a rolling motion, "hile the

0ove "aves shear the terrain hori(ontally +4. !hen these four types of

"aves are released they create a unique "ave interference pattern that can

trigger one of many types of failure for a uilding.

Types of Building Failure

5any uilding are

susceptile to collapse during or

shortly after an earthquake ut

not all uildings fail for the same

reasons. The causes of failure

can range from insu6cient

compaction of the ground "here

a uilding’s foundations are laid

to catastrophic failure of the

uildings structural integrity +7.

Soil Failure

Soil failure is often called

liquefaction, *+referring to a loss of strength in saturated, cohesionless soils

due to the uild8up of pore "ater pressures during dynamic loading +9.-

0iquefaction is especially common in soil that is on a slope such as an alluvial

fan or areas "here the soil grains are not adequately compacted and are

ale to decrease volume "hen undergoing shear stress +:. ;nce soil has

4

Figure 1 !"#


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lique1ed it can no longer support the "eight of the uilding "hich slumps

into the soil and lose structural staility +7.

Foundational Failure

Buildings that have not een uilt or retro1tted according to modern

uilding code often have foundations that are not designed to "ithstand the

irregular impulse forces that are the result of an earthquake. $ uilding’s

height also plays a large role in foundational failure since it is a principle

component of a structure’s resonance frequency.

+simply slides o% its foundation +7.’’

Structural Failure

Structural failure occurs "hen a uilding’s structural material is

damaged and undergoes a reduction in load earing capaility.


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$eismic %esistance Technology of Today

$s engineers have studied the reasons ehind uildings failure they

have created speci1c uilding codes for areas that are prone to earthquakes.

These codes have een evolving "ith the advancements made in

understanding e#actly ho" earthquakes cause damage to uildings. The

)@A: San Francisco earthquake prompted *revisions to the city of Santa

Barara’s uilding code in )@39 +"hich "ere the 1rst e#plicit policy and

legal consideration of the seismic safety of structures in alifornia [email protected] Since

the )@A: earthquake there have een multiple revisions, usually follo"ing a

large earthquake such as the 0oma /rieta or Corthridge earthquakes, and

each revision increases the pulic’s safety. The uilding codes are no"

thorough enough for smaller and less critical structures in moderate

earthquakes. 2o"ever there must e special precautions taken for structures

such as hospitals and high rises "here the danger of a uilding failure is

compounded y the numer of lives at risk.


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*decouple +the structure from the hori(ontal components of the earthquake

ground motion-, thus reducing the shear forces a uilding must endure +)A.

Lead Rubber Bearings

sing the principle of resonance frequency a lead ruer earing

system is design to *+give the structure a fundamental frequency that is

much lo"er than

its 1#ed8ase

frequency and

also much lo"er

than the

predominant

frequencies of

the ground

motion +)A-.

ngineers accomplished this feat y creating a spring that is very sti% in the

vertical direction ut can plastically deform a great deal hori(ontally. sing

many layers of oth ruer and steel "ith a central core of lead the earing

is ale to dissipate or de&ect most of an earthquake’s energy +)3.

Levitating Foundation

Similar to the lead ruer earing the concept of a levitating

foundation is to dissipate an earthquake’s energy y separating the top of a

structure from the ase. The levitating foundation does this y in&ating an

air ag "hich lies on the uildings foundation that *ultimately +lifts the

:

Figure " !11#


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entire house a good three centimeters o% its +)4- foundation. This form of

ase isolation is fairly ne" and has only een tested in limited quantities.

;nce the houses that have no" een 1tted "ith a levitating foundation

e#perience an earthquake the designers "ill e ale to "ork out ho" to use

the technology to isolate the ase vertically as "ell as hori(ontally.

&ibration 'amping

$n alternative to isolating the ase from the rest of the structure is to

dampen the earthquakes "aves as it passes through the uilding. This can

e done y turning the energy from the earthquake into heat, in the case of

the frictional dampers or into a controlled motion in the case of a tuned mass

damper +)7.

Frictional Damper

Frictional dampers come in many styles and si(es, ranging from friction

ase isolators to tension cross racing. ach of these acts as a *frictional

rake +"hich is "idely used to e#tract kinetic energy from a moving ody as

it is the most e%ective, reliale, and economical mean to dissipate energy

+)9-. Friction rakes dissipate energy y having an assemly "hich is ale

to slide and distort "hen a force is applied. Through this movement, the

maEority of an earthquake’s forces are converted to heat and not transferred

to the rest of the structure.

Tuned Mass Damper

nlike the frictional damper, a tuned mass damper is ale to *reduce the

dynamic response of +a structure- through the use of a mass, springs and a

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type of damper +):. During an earthquake a tuned mass damper egins to

s"ing "ith a frequency that is tuned to e out of sync "ith the frequency of

the rest of the uilding.

Through this o%set of

frequencies the damper is

ale to asor some of

the earthquakes energy

"ith its inertial energy

and return the uilding to

its original position.

Conclusion

!orld"ide, earthquakes

cause *annual average

losses +that range from ).4 illion to 9.= illion +)?-. $ large portion of

this loss can e mitigated through the use of seismically resistance uilding

technology. ;nce engineers "ere ale to understand the reasons ehind

structural failure in uildings they "ere ale to come up "ith "ays to keep

uildings upright.


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*):: countriesGnations have some form of seismic code +)@- "hich have

helped reduce the destruction caused y earthquakes and "ill continue to

improve as earthquake engineering advances as a 1eld.

@


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%EFE%ENCE$

+)C. Ce"mark, H%ects of arthquakes on Dams and mankmentsH,Geotechnique, vol. )9, no. 3, pp. )4@8):A, )@:9.

+3 !est /ulishing ompany, Types of Earthquake Waves. .+4I. ndsley, H!hat


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+)?I. Mranes and R. /ielke, )ormali/ed Earthquake Damage and 'atalitiesin the #nited !tates, )st ed. niversity of olorado Boulder, 3AA@.

+)@L. Daniell, H$ !;R0D!

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