Tips to Design Earthquake Resistant Building_Jean-Rayner Kuswadi

8/17/2019 Tips to Design Earthquake Resistant Building_Jean-Rayner Kuswadi

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Tips to Design EarthquakeResistant Structures

Designing Earthquake Resistant Structures is indispensable.Every year, earthquakes take the lives of thousands of people, anddestroy property worth billions. It is imperative that structures aredesigned to resist earthquake forces, in order to reduce the loss oflife. Structural design plays an important role. ere, we willdiscuss different tips and techniques used in designing EarthquakeResistant structures.

What is an Earthquake?

!n earthquake is a sudden, rapid shaking of the Earth caused by thebreaking and shifting of rock beneath the Earth"s surface. #orhundreds of millions of years, the forces of plate tectonics haveshaped the Earth as the huge plates that form the Earth"s surfacemove slowly over, under, and past each other. Sometimes themovement is gradual. !t other times, the plates are locked together,unable to release the accumulating energy. $hen the accumulatedenergy grows strong enough, the plates break free causing the

ground to shake. %ost earthquakes occur at the boundaries wherethe plates meet& however, some earthquakes occur in the middle ofplates.

'round shaking from earthquakes can collapse buildings andbridges& disrupt gas, electric, and phone services& and sometimestrigger landslides, avalanches, flash floods, fires, and huge,destructive ocean waves (tsunamis). *uildings with foundationsresting on unconsolidated landfill and other unstable soil, and

trailers and homes not tied to their foundations are at risk becausethey can be shaken off their mountings during an earthquake. $henan earthquake occurs in a populated area, it may cause deaths andin+uries and etensive property damage.

It is for this reason that it is often said,

"Earthquake don't kill people, buildings do."



-he dynamic response of building to earthquake groundmotion is the most important cause of earthquakeinduced damageto buildings. -he damage that a building suffers primarily depends

not upon its displacement, but upon acceleration. $hereasdisplacement is the actual distance the ground and building maymove during an earthquake, acceleration is a measure of howquickly they change speed as they move. -he conventionalapproach to earthquake resistant design of buildings depends uponproviding the building with strength, stiffness and inelasticdeformation capacity which are great to withstand a given level ofearthquakegenerated force. -his is generally accomplished throughthe selection of an appropriate structural configuration and thecarefully detailing of structural members, such as beams and

columns, and the connections between them.

In contrast, we can say that the basic approach underlying moreadvanced techniques for earthquake resistance is not to strengththe building, but to reduce the earthquakegenerated forces actingupon it. *y decoupling the structure from seismic ground motion itis possible to reduce the earthquakeinduced forces in it. -his canbe done in two ways/

Increase natural period of structure by " BASE ISOLATION".

Increase damping of the system by " ENERGY DISSIPATING DEVICES".



Tips to Design Earthquake Resistant

Buildings

Designing Earthquake Resistant Structures is indispensable. Everyyear, earthquakes take the lives of thousands of people, and destroyproperty worth billions of dollars. -his loss of life and property canbe prevented by using latest techniques and developments in thefield of Earthquake Engineering. It is imperative that structures aredesigned to resist earthquake forces, in order to reduce the loss oflife. Structural design plays an important role. $hat are EarthquakeResistant structures0 ow do we design them0 $hich techniques areefficient0 $hich techniques are practical. you will find out all this inthe following report, first published by %r. !dit 1. $arange, under

the guidance of 2rof. S. 3. 4oshi.

Earthquakes and Natural Calamities

5atural calamities are the phenomenon which can"t beprevented, but we can take precautions. 6alamities such as #loods,6yclones, volcanoes, -sunamis, Earthquakes, over heat, causesdisturbance to our daytoday life. Science and -echnologies arelooking forward to counteract these disasters.

CALAMTES

!L""DS# Floods are the natural dsaster !aused due to oer#lo$ o#rers due to hea% ran#all or &eltn' o# sno$ $h!h !auses a lar'e

destru!ton n !tes and lla'es.



C$CL"NES# A !%!lone s a rotatn' stor& that !an (e a hundreds o#)lo&eters $h!h !an (e er% destru!te and t loo)s l)e a hu'e s*nnn'dou'hnut o# !louds. The !o&(naton o# $nd+ ran+ and $aes )no!)do$n trees+ #latten houses+ and $ash out roads.

%"LCAN"ES# Vol!anoes are the lar'e o*enn's on the to* o# a&ountan and so&et&es on sdes+ throu'h $h!h &elted ro!)s and 'aseses!a*e $th 'reat #or!es #ro& Earth,s !rust.

TS&NAM# A tsuna& s a er% lon'-$aelen'th $ae o# $ater $h!h s 'enerated (% a sudden ds*la!e&ent o# sea #loor or dsru*ton o# an%(od% o# standn' $ater. Tsuna&s o!!ur suddenl%+ o#ten $thout an%$arnn'+ the% are etre&el% dan'erous to !ostal !o&&untes.



EART'(&A)ES

An earth/ua)e s the (raton+ so&et&es olent+ o# Earth,s sur#a!e that #ollo$s a release o# ener'% n Earth,s !rust.

Earthquakes are one of the most devastating forces innature. 1ibrations of Earth"s surface, caused by seismic wavescoming from a source of disturbance in side the Earth is known asEarthquake. 7r in other words.

"Earth/ua)es are s&*l% 'round os!llatons o# er% lar'ea&*ltude and rather lo$ #re/uen!%. The *redo&nant &ode o# e!taton

s hor0ontal+ not ert!al as n nor&al 'round-(orne nose."



Causes o* Earthquakes

Earthquakes are caused by active faults, which are, causedby the sudden movement of the two sides of a fault with respect toanother. -he occurrence of tectonic earthquakes can be eplained bythe theory of elastic rebound. $hich was first advanced by . *.REID. -he motion along the fault is accompanied by the gradualbuildup of elastic strain energy within the rock along the fault. -herock stores this strain energy like a giant spring being slowlytightened.

Eventually, the strain along the fault eceeds the limit ofthe rocks at that point to store any additional strain. -he fault thenruptures that is, it suddenly moves a comparatively large distancecomparatively short amount of time. -he rocky masses which formthe two sides of the fault then snap back into a new position. -hissnapping back into position, upon the release of strain, is the8E9!S-I6 RE*7:5D8 of Reid"s theory. -he rupture of fault results insudden release of the strain energy that has been built up over theyears. -he most important form which this suddenly released energytakes is that of seismic waves.

ACT%E !A&LTS# -hey are caused because of fault lines passing through thetectonic plates.

M"%EMENTS "! TECT"NC +LATES# -hey are caused because of tectonicplates are continuously floating on the mantle and thus they are set in motion.

%"LCANC ER&+T"NS# -hey are caused due to internal pressure buildingup inside the Earth"s crust.

S&R!ACE AND S&,S&R!ACE E-+L"S"NS# -hey are caused due to man

made eplosions such as blasts, tunneling, etc.

EART'(&A)E 'A.ARDS



/R"&ND M"T"N

-he most destructive of all earthquake ha;ards is

caused by seismic waves reaching the ground surface at placeswhere humanbuilt structures, such as buildings and bridges, arelocated. $hen seismic waves reach the surface of the earth at suchplaces, they give rise to what is known as strong ground motion.Strong ground motions cause"s buildings and other structures tomove and shake in a variety of comple ways. %any buildingscannot withstand this movement and suffer damages of variouskinds and degrees.

%ost deaths, in+uries, damages and economic losses caused byearthquake result from ground motion acting on buildings and othermanmade structures not capable of withstanding such movement.

/R"&ND !AL&RE

Strong ground motion is also the primary cause of damages to theground and soil upon which, or in which, people must build. -hese

damages to the soil and ground can take a variety of forms/cracking and fissuring and weakening, sinking, settlement andsurface fault displacement.

7ne of the most important types of ground failure is known asliquefaction. 9iquefaction takes place when loosely packed, waterlogged sediments at or near the ground surface lose their strengthin response to strong ground shaking. 9iquefaction occurringbeneath buildings and other structures can cause ma+or damageduring earthquakes.

Ground Sliding

Strong ground motion is also the primary cause of damages to the ground and soil

upon which, or in which, people must build. These damages to the soil and ground

can take a variety of forms: cracking and fissuring and weakening, sinking, settlement

and surface fault displacement.



Ground Tilting

Sometimes, due to earthquake, there is tilting action in the ground. This causes plain

land to tilt, causing excessive stresses on buildings, resulting in damage to buildings.

Differential Settlement

If a structure is built upon soil which is not homogeneous, then there is differential

settlement, with some part of the structure sinking more than other. This induces

excessive stresses and causes cracking.



Liquefaction

uring an earthquake, significant damage can result due to instability of the soil in the

area affected by internal seismic waves. The soil response depends on the mechanicalcharacteristics of the soil layers, the depth of the water table and the intensities and

duration of the ground shaking. If the soil consists of deposits of loose granular

materials it may be compacted by the ground vibrations induced by the earthquake,

resulting in large settlement and differential settlements of the ground surface. This

compaction of the soil may result in the development of excess hydrostatic pore water

pressures of sufficient magnitude to cause liquefaction of the soil, resulting in

settlement, tilting and rupture of structures

BUILDING STINESS !ND

LE"IBILIT#

-he taller a building, the longer its natural period tendsto be. *ut the height of a building is also related to anotherimportant structural characteristic/ the building fleibility. -allerbuildings tend to be more fleible than short buildings. (7nlyconsider a thin metal rod. If it is very short, it is difficulty to bend itin your hand. If the rod is somewhat longer, and of the same

diameter, it becomes much easier to bend. *uildings behavesimilarly) we say that a short building is stiff, while a taller buildingis fleible. (7bviously, fleibility and stiffness are really +ust the twosides of the same coin. If something is stiff, it isn"t fleible andviceversa).

#igure shows the Displacement of *uilding according to theireight < Stiffness



Ductility is the ability to undergo distortion or deformation withoutresulting in complete breakage or failure. -o see how ductility canimprove a building"s performance during an earthquake, consider#ig =.>.b. In response to the ground motion, the rod bends butdoes not break. (of course, metals in general are more ductile thanmaterials such as stone, brick and concrete) -he ductility of a

structure is in fact one of the most important factors affecting itsearthquake performance. 7ne of the primary tasks of an engineer



designing a building to be earthquake resistant is to ensure that thebuilding will possess enough ductility to withstand the si;e andtypes of earthquakes it is likely to eperience during its lifetime.

SEIS$I% EE%TS

NERTA !"RCES N STR&CT&RES

!n earthquake causes shaking of ground. Soa building resting on it will eperience motion at its base. #rom5ewton"s first law of motion, even though the base of the buildingmoves with the ground, the roof has a tendency to stay in itsoriginal position. *ut since the walls and columns are connected to

it, they drag the roof along with them.

This is much like the situation that you are faced with when the bus you

are standing in suddenly starts, your feet move with the bus, but your

upper body tends to stay back making you fall backwards!!!

-his tendency to continue to remain in the previous position isknown as inertia. In the building since the walls or columns arefleible, the motion of roof is different from that of ground.

6onsider a building, whose roof is supported oncolumns. 6oming back to the analogy of yourself on the bus& when

the bus suddenly starts, you are thrown backwards as if someonehas applied a force on the upper body. Similarly, when the ground



moves, even the building is thrown backwards, and the roofeperiences a force, called inertia force. If the roof has the mass %and eperiences an acceleration a, then from 5ewton"s second lawof motion, the inertia force #? is mass % times acceleration a, andits direction is opposite to that of the acceleration.

"ore mass means higher inertia force"

E!!ECT "! DE!"RMAT"NS N

STR&CT&RES



-he inertia force eperienced by the roof istransferred to the ground via the columns, causing forces incolumns. -hese forces generated in the columns can also beunderstood in another way. During earthquake shaking, the columnsundergo relative movement between their ends. In figure thismovement is shown as quantity u between the roof and the ground.*ut, given a free option, columns would like to come back to thestraight vertical position, i.e. columns resist deformations. In the

straight vertical position, the columns carry no hori;ontalearthquake force through them. *ut, when forced to bend, they



develop internal forces. -he larger is the hori;ontal displacement ubetween the top and bottom of the column, the larger this internalforce in columns. !lso, the stiffer the columns are (i.e. bigger is thecolumn si;e), larger is the force. #or this reason, these internalforces in the columns are called stiffness forces. In fact, the

stiffness force in the columns is the column stiffness times therelative displacement between its ends.

&'RI('NT!L !ND )ERTI%!L S&!*ING

Earthquake causes shaking of ground in all three directions along the two hori;ontal directions (@ and A, say), and the verticaldirection (B, say). !lso during the earthquake, the ground shakesrandomly back and forth ( and C) along each of this @, A and Bdirections. !ll structures are primarily designed to carry the gravityloads, i.e. they are designed for a force equal to the mass % (thisincludes mass due to own weight and imposed loads) times theacceleration due to gravity g acting in vertical downward direction (B). -he downward force %g is called the gravity load. -he verticalacceleration during ground shaking either adds or subtracts from

the acceleration due to gravity. Since factors of safety are used inthe design of structures to resist the gravity load, usually moststructures tend to be adequate against vertical shaking.

owever, hori;ontal shaking along @ and Adirections (both C and directions of each) remains a concern.Structures designed for gravity loads, in general, may not be able tosafely sustain the effects of hori;ontal earthquake shaking.

L'+ ' INERTI! 'R%ES T' 'UND!TI'NS



:nder hori;ontal shaking ofground, hori;ontal inertia forces are generated at a level of themass of the structure (usually situated at the floor levels). -heselateral inertia forces are transferred by the floor slab to the walls orthe columns, to the foundations, and finally to the soil system

underneath. So, each of this structural elements (floor slabs, walls,columns, and foundations) and the connections between them mustbe designed to safely transfer these inertia forces through them.

$alls or columns are the most critical elements intransferring the inertia forces. *ut, in traditional construction, floorslabs and beams receive more care and attention during design andconstruction, than walls and columns. $alls are relatively thin andoften made of brittle material like masonry.

'"W EART'(&A)ES A!!ECTRein*orced Concrete

,uildings ! typical R6 building is made of hori;ontal

members (beams and slabs) and vertical members (columns andwalls), and supported by foundations that rest on ground. -hesystem comprising of R6 frame. -he R6 frame participates inresting the earthquake forces. Earthquake shaking generates inertiaforces in the building, which are proportional to the building mass.Since most of the building mass is present at floor levels,earthquake induced inertia forces primarily develop at the floor

levels. -hese forces travel downwards through slabs and beams tocolumns and walls, and then to foundations from where they are



dispersed to ground. !s inertia forces accumulate downwards fromthe top of the building, the columns and walls at lower storeyeperience higher earthquake induced forces (fig ?) and aretherefore designed to be stronger than those in storeyabove.



R"LE "! !L""R SLA,S AND MAS"NAR$

#loor slabs are hori;ontal plate likeelements, which facilitate functional use of buildings. :sually, beamsand slabs at one storey level are cast together. In residential multistory buildings, thickness of slabs is only about ???mm. whenbeams bend in the vertical direction during earthquakes, these thinslabs bend along with them (fig>a). !nd, when beams move withcolumns in the hori;ontal direction, the slab usually forces the

beams to move together with it. In most buildings, the geometricdistortion of slab is negligible in the hori;ontal plane& this behavioris known as the rigid diaphragm action (fig >b).

!fter columns and floors in a R6 building arecast and the concrete hardens, vertical spaces between columnsand floors are usually filledin with masonry walls to demarcate afloor into functional spaces (rooms). 5ormally, these masonry walls,also called infill walls, are not connected to surrounding R6 columnsand beams. $hen columns receive hori;ontal forces at floor levels,

they try to move in hori;ontal direction, but masonry walls tend toresist this movement. Due to their heavy weight and thickness,these walls attract rather large hori;ontal forces. owever, sincemasonry is a brittle material, these walls develop cracks once theirability to carry hori;ontal load is eceeded. -hus masonry walls isenhanced by mortars of good strength, making proper masonrycourses, and proper packing of gaps between R6 frame andmasonry infill walls.



'"R."NTAL EART'(&A)E E!!ECTS

:nder gravity loads, tension in the beams is at the bottomsurface of the beam in the central location and is at the top surfaceat the ends. -he level of bending moment due to earthquakeloading depends on severity of shaking and can eceed that due togravity loading. -hus, under strong earthquake shaking, the beam

ends can develop tension on either of the top and bottom faces.Since concrete cannot carry this tension, steel bars are required onboth faces of beams to resist reversals of bending moment.

STREN/T' 'ERARC'$

#or a building to remain safe during earthquake shaking,columns should be stronger than beams, and foundations should be

stronger than columns.

If columns are made weaker, they suffer severe localdamage, at the top and bottom of a particular storey.



+LANNN/ 0 A T""L "!

ARC'TECT&RE

!R%&ITE%TUR!L E!TURES

-he behavior of building during earthquakes dependscritically on its overall shape, si;e and geometry. ence, at planningstage itself, architects and structural engineers must work togetherto ensure that the unfavorable features are avoided and a goodbuilding configuration is chosen. If both shape and structural system

work together to make the structure a marvel.

"f we have a poor configuration to start with, all the engineer

can do is to provide a bandaid improve a basically poor solution as best

as he can. #onversely, if we startoff with a good configuration and

reasonable framing system, even a poor engineer cannot harm its ultimate

performance too much".

SI(E ' BUILDINGS



In tall buildings with large weighttobase si;e ratio thehori;ontal movement of the floors during ground shaking is large. In

short but very long buildings, the damaging effects duringearthquake shaking are many. !nd, in buildings with large planarea, the hori;ontal seismic forces can be ecessive to be carried bycolumns and walls.

&'RI('NT!L L!#'UT ' BUILDINGS

*uildings with simple geometry in plan perform well during

strong earthquakes. *uildings with reentrant corners, like :, 1, and C shaped in plan sustain significant damage. -he bad effects ofthese interior corners in the plan of buildings are avoided by makingthe buildings in two parts by using a separation +oint at the +unction.

)ERTI%!L L!#'UT ' BUILDINGS

Earthquake forces developed at different floor levels in abuilding need to be brought down along the height to the ground bythe shortest path, any deviation or discontinuity in this load transferpath results in poor performance of building. *uildings with verticalsetbacks cause a sudden +ump in

earthquake forces at the level of discontinuity. *uildings that havefewer columns or walls in a particular storey or with unusually tallstorey tend to damage or

collapse which is initiated in that storey. *uildings on sloppy groundhave unequal height columns along the slope, which causes twistingand damage in shorter

columns that hang or float on beams have discontinuity in loadtransfer. *uildings in which R6 walls do not go all the way to theground but stop at upper levels get severely damaged

!D,!%EN%# ' BUILDINGS



$hen two buildings are close to each other, they maypound on each other during strong shaking. $hen building heightsdo not match the roof of the shorter building may pound at the midheight of the column of the taller one& this can be very dangerous.

Construction Techniques *orEarthquake Resistance

EART'(&A)E RESSTANCE DES/NA++R"AC'

%on-entional !pproach

Design depends upon providing the building with strength, stiffness

and inelastic deformation capacity which are great enough towithstand a given level of earthquakegenerated force.



-his can be accomplished by selection of an appropriate structuralconfiguration and careful detailing of structural members, such asbeams and columns, and the connections between them.

Basic !pproach

Design depends upon underlying more advanced techniques forearthquake resistance is not to strengthen the building, but toreduce the earthquake generated forces acting upon it.

-his can be accomplished by decoupling the structure from seismicground motion it is possible to reduce the earthquake inducedforces in it by three ways.

Increase natural period of structures by *aseIsolation.

Increase damping of system by Energy Dissipation Devices.

*y using !ctive 6ontrol Devices.

EART'(&A)E DES/N +'"S"+'$

Severity of ground shaking at a given location duringan earthquake can be minor, moderate and strong. -hus relativelyspeaking, minor shaking occurs frequently& moderate shakingoccasionally and strong shaking rarely. #or instance, on averageannually about F earthquakes of magnitude ..G occur in theworld while about ?F for magnitude range H.H.G. So we shoulddesign and construct a building to resist that rare earthquake

shaking that may come only once in years or even once in >years, even though the life of the building may be or ? years0

Engineers do not attempt to make earthquakeproof buildings that will not get damaged even during the rare butstrong earthquake& such buildings will be too robust and also tooepensive. Instead the engineering intention is to make buildingsearthquakeresistant& such buildings resist the effects of groundshaking, although they may get damaged severely but would notcollapse during the strong earthquake. -hus, safety of people and

contents is assured in earthquakeresistant buildings, and thereby a



disaster is avoided. -his is a ma+or ob+ective of seismic design codesthroughout the world.

DESIGN .&IL'S'.&#

a) :nder minor but frequent shaking, the main members of thebuildings that carry vertical and hori;ontal forces should not bedamaged& however buildings parts that do not carry load maysustain repairable damage.

b) :nder moderate but occasional shaking, the main membersmay sustain repairable damage, while the other parts that do notcarry load may sustain repairable damage.

c) :nder strong but rare shaking, the main members maysustain severe damage, but the building should not collapse.

Earthquake resistant design is therefore concerned aboutensuring that the damages in buildings during earthquakes are ofacceptable variety, and also that they occur at the right places andin right amounts. -his approach of earthquake resistant design is

much like the use of electrical fuses in houses/ to protect the entireelectrical wiring and appliances in the house, you sacrifice somesmall parts of electrical circuit, called fuses& these fuses are easilyreplaced after the electrical overcurrent. 9ikewise to save thebuilding from collapsing you need to allow some predeterminedparts to undergo the acceptable type and level of damage.

Earthquake resistant buildings, particularly their main elements,need to be built with ductility in them. Such buildings have theability to sway backandforth during an earthquake, and to

withstand the earthquake effects with some damage, but withoutcollapse.

Construction Materials *or

Earthquake Resistance

In India, most nonurban buildings are made in masonry. Inthe plains, masonry is generally made of burnt clay bricks andcement mortar. owever in hilly areas, stone masonry with mudmortar is more prevalent. *ut now a day we are very familiar with



R.6.6. buildings, and a variety of new composite constructionsmaterials.

C"NSTR&CT"N MATERALS

I/ $!S'NR#



%asonry is made up of burnt clay bricks and cement or mudmortar. %asonry can carry loads that cause compression (i.e.pressing together) but can hardly take load that causes tension (i.e.pulling apart). %asonry is a brittle material, these walls developcracks once their ability to carry hori;ontal load is eceeded. -hus

infill walls act like sacrificial fuses in buildings/ they develop cracksunder severe ground shaking but they share the load of the beamsand columns until cracking.

II/ %'N%RETE

6oncrete is another material that has been popularly usedin building construction particularly over the last four decades.6ement concrete is made of crushed stone pieces (calledaggregate), sand, cement and water mied in appropriate

proportions. 6oncrete is much stronger than masonry undercompressive loads, but again its behavior in tension is poor. -heproperties of concrete critically depend on the amount of water usedin making concrete, too much and too little water both can causehavoc.

III/ STEEL

Steel is used in masonry and concrete buildings asreinforcement bars of diameter ranging from mm to Jmm.

reinforcing steel can carry both tensile and compressive loads.%oreover steel is a ductile material. -his important property ofductility enables steel bars to undergo large elongation beforebreaking. 6oncrete is used with steel reinforcement bars. -hiscomposite material is called as reinforced cement concrete. -heamount and location of steel in a member should be such that thefailure of the member is by steel reaching its strength in tensionbefore concrete reaches its strength in compression. -his type offailure is ductile failure, and is preferred over a failure whereconcrete fails first in compression. -herefore,

Providing more steel in R.C. buildings can be harmfuleven!!

EART'(&A)E RESSTANTDES/N C"NCE+T



If two bars of same length and same crosssectional

area one made of ductile material and another of a brittlematerial. !nd a pull is applied on both bars until they break, thenwe notice that the ductile bar elongates by a large amount before itbreaks, while the brittle bar breaks suddenly on reaching itsmaimum strength at a relative small elongation.

$mongst the materials used in building construction, steel is ductile, while

masonry and concrete are brittle.

-he correct building components need to be made

ductile. -he failure of columns can affect the stability of building,but failure of a beam causes locali;ed effect. -herefore, it is betterto make beams to be ductile weak links then columns. -his methodof designing R6 buildings is called the strongcolumn weakbeamdesign method. Special design provisions from IS/ ?=G>?GG= forR6 structures ensures that adequate ductility is provided in themembers where damage is epected.

(&ALT$ C"NTR"L NC"NSTR&CT"N

-he capacity design concept in earthquake resistant design of buildings will fail if the strengths of the brittle links fall below theirminimum assured values. -he strength of brittle constructionmaterials, like masonry and concrete is highly sensitive to thequality of construction materials. $orkmanship, supervision, andconstruction methods. Similarly, special care is needed in

construction to ensure that the elements meant to be ductile areindeed provided with features that give adequate ductility. -hus,



strict adherence to prescribed standards, of construction materialsand processes is essential in assuring an earthquake resistantbuilding. Regular testing of materials to laboratories, periodictraining of workmen at professional training houses, and onsiteevaluation of the technical work are elements of good quality

control.

,ASCS "! EART'(&A)E

RESSTANCE

6onventional seismic design attempts to make buildings that

do not collapse under strong earthquake shaking, but may sustaindamage to nonstructural elements (like glass facades) and to somestructural members in the building. -his may render the buildingnonfunctional after the earthquake, which may be problematic insome structures, like hospitals, which need to remain functional inthe aftermath of earthquake. Special techniques are required todesign buildings such that they remain practically undamaged evenin a severe earthquake. *uildings with such improved seismicperformance usually cost more than the normal buildings do.

-wo basic technologies are used to protect buildings fromdamaging earthquake effects. -hese are *ase Isolation Devices andSeismic Dampers. -he idea behind base isolation is to detach(isolate) the building from the ground in such a way thatearthquake motions are not transmitted up through the building orat least greatly reduced. Seismic dampers are special devicesintroduced in the buildings to absorb the energy provided by theground motion to the building (much like the way shock absorbersin motor vehicles absorb due to undulations of the road)

,ase solation *or EarthquakeResistance

It is easiest to see the principle at work by referring directly tothe most widely used of these advanced techniques, known as baseisolation. ! base isolated structure is supported by a series ofbearing pads, which are placed between the buildings and buildingfoundation.



-he concept of base isolation is eplained through an eamplebuilding resting on frictionless rollers. $hen the ground shakes, therollers freely roll, but the building above does not move. -hus, noforce is transferred to the building due to the shaking of the ground&simply, the building does not eperience the earthquake. 5ow, if the

same building is rested on the fleible pads that offer resistanceagainst lateral movements, then some effect of the ground shakingwill be transferred to the building above. If the fleible pads areproperly chosen, the forces induced by ground shaking can be a fewtimes smaller than that eperienced by the building built directly onground, namely a fied base building. -he fleible pads are calledbaseisolators, whereas the structures protected by means of thesedevices are called baseisolated buildings. -he main feature of thebase isolation technology is that it introduces fleibility in thestructure.

Traditional Earthquake MitigationTechniques

,ase solation Technique



Due to the fleibility in the structure, a robust mediumrise masonryor reinforced concrete building becomes etremely fleible. -heisolators are often designed, to absorb energy and thus adddamping to the system. -his helps in further reducing the seismic

response of the building. %any of the base isolators look like largerubber pads, although there are other types that are based onsliding of one part of the building relative to other. !lso, baseisolation is not suitable for all buildings. %ostly low to medium risebuildings rested on hard soil underneath& highrise buildings orbuildings rested on soft soil are not suitable for base isolation.

Lead0ru11er 1earings are the frequentlyused typesof base isolation bearings. ! lead rubber bearing is made fromlayers of rubber sandwiched together with layers of steel. In the

middle of the solid lead 8plug8. 7n top and bottom, the bearing isfitted with steel plates which are used to attach the bearing to thebuilding and foundation. -he bearing is very stiff and strong in thevertical direction, but fleible in the hori;ontal direction.

Working +rinciple

-o get a basic idea of how base isolation works, firsteamine the K(fig b). -his shows an earthquake acting on base

isolated building and a conventional, fiedbase, building. !s aresult of an earthquake, the ground beneath each building begins to



move. In (fig b) it is shown moving to left. Each building respondswith movement which tends towards the right. -he buildingsdisplacement in the direction opposite the ground motion is actuallydue to inertia. -he inertia forces acting on a building are the mostimportant of all those generated during an earthquake.

In addition to displacing towards right, the unisolatedbuilding is also shown to be changing its shape from a rectangle toa parallelogram. $e say that the building is deforming. -he primarycause of earthquake damage to buildings is the deformation whichthe building undergoes as a result of the inertial forces upon it.

RES+"NSE "! ,ASE S"LATED,&LDN/S

-he baseisolated building retains its original,rectangular shape. -he base isolated building itself escapes thedeformation and damagewhich implies that the inertial forcesacting on the base isolated building have been reduced.Eperiments and observations of baseisolated buildings inearthquakes to as little as L of the acceleration of comparablefiedbase buildings.

!cceleration is decreased because the base isolationsystem lengthens a buildings period of vibration, the time it takesfor a building to rock back and forth and then back again. !nd ingeneral, structures with longer periods of vibration tend to reduceacceleration, while those with shorter periods tend to increase oramplify acceleration.

SEC"ND T$+E "! ,ASE S"LAT"N



Spherical sliding isolation systems are another type of base isolation. -he building is supported by bearing pads that havea curved surface and low friction. During an earthquake the buildingis free to slide on the bearings. Since the bearings have a curvedsurface, the building slides both hori;ontally and vertically. -heforces needed to move the building upwards limits the hori;ontal orlateral forces which would otherwise cause building deformations.!lso by ad+usting the radius of the bearings curved surface, thisproperty can be used to design bearings that also lengthen thebuildings period of vibration.

Energ2 Dissipation De3ices *orEarthquake Resistance

!nother approach for controlling seismic damage in buildings andimproving their seismic performance is by installing SeismicDampers in place of structural elements, such as diagonal braces.-hese dampers act like the hydraulic shock absorbers in cars muchof the sudden +erks are absorbed in the hydraulic fluids and onlylittle is transmitted above to the chassis of the car. $hen seismicenergy is transmitted through them, dampers absorb part of it, andthus damp the motion of the building.

6ommonly used types of seismic dampers include/



%iscous Dampers (energy is absorbed by silicone-based fluid passing between piston cylinder arrangement

!riction Dampers (energy is absorbed by surfaces with frictionbetween them rubbing against each other

$ielding Dampers (energy is absorbed by metallic componentsthat yield

%iscoelastic dampers (energy is absorbed by utiliing thecontrolled shearing of solids

-hus by equipping a building with additional devices whichhave high damping capacity, we can greatly decrease the seismicenergy entering the building.



Working +rinciple

-he construction of a fluid damper is shown in (fig). Itconsists of a stainless steel piston with bron;e orifice head. It isfilled with silicone oil. -he piston head utili;es specially shapedpassages which alter the flow of the damper fluid and thus alter theresistance characteristics of the damper. #luid dampers may be



designed to behave as a pure energy dissipater or a spring or as acombination of the two.

! fluid viscous damper resembles the common shockabsorber such as those found in automobiles. -he piston transmits

energy entering the system to the fluid in the damper, causing it tomove within the damper. -he movement of the fluid within thedamper fluid absorbs this kinetic energy by converting it into heat.In automobiles, this means that a shock received at the wheel isdamped before it reaches the passengers compartment. In buildingsthis can mean that the building columns protected by dampers willundergo considerably less hori;ontal movement and damage duringan earthquake.

%luid &iscous amper



SE%'ND T#.E ' ENERG# DISSI.!TI'N

DE)I%ES

-he innovative methods for control of seismic vibrations suchas frictional and other types of damping devices are importantintegral part of seismic isolation systems as they severe as a barrieragainst the penetration of seismic energy into the structure. In this

concept, the dampers suppress the response of the isolated buildingrelative to its base.

-he novel friction damper device consists of three steelplates rotating against each other in opposite directions. -he steelplates are separated by two shims of friction pad material producingfriction with steel plates.

$hen an eternal force ecites a frame structure the girderstarts to displace hori;ontally due to this force. -he damper will

follow the motion and the central plate because of the tensile forcesin the bracing elements. $hen the applied forces are reversed, theplates will rotate in opposite way. -he damper dissipates energy bymeans of friction between the sliding surfaces.

-he latest #riction1iscoElastic Damper Device (#1EDD) combines the advantages of pure frictional and viscoelasticmechanisms of energy dissipation. -his new product consists offriction pads and viscoelastic polymer pads separated by steel platesas shown below. ! prestressed bolt in combination with disk springs

and hardened washers is used for maintaining the requiredclamping force on the interfaces as in original #DD concept.



Acti3e Control De3ices *orEarthquake Resistance

!fter development of passive devices such as base isolationand -%D. -he net logical steps is to control the action of thesedevices in an optimal manner by an eternal energy source theresulting system is known as active control device system. !ctivecontrol has been very widely used in aerospace structures. Inrecent years significant progress has been made on the analytical

side of active control for civil engineering structures. !lso a fewmodels eplains as shown that there is great promise in thetechnology and that one may epect to see in the foreseeable futureseveral dynamic 8Dynamic Intelligent *uildings8 the term itselfseems to have been +oined by the 3a+ima 6orporation in 4apan. Inone of their pamphlet the concept of !ctive control had beeneplained in every simple manner and it is worth quoting here.

2eople standing in swaying train or bus try to maintainbalance by unintentionally bracing their legs or by relaying on themussels of their spine and stomach. *y providing a similar functionto a building it can dampen immensely the vibrations whenconfronted with an earthquake. -his is the concept of DynamicIntelligent *uilding (DI*).

-he philosophy of the past conventional a seismicstructure is to respond passively to an earthquake. In contrast inthe DI* which we propose the building itself functions activelyagainst earthquakes and attempts to control the vibrations. -hesensor distributed inside and outside of the building transmitsinformation to the computer installed in the building which can

make analyses and +udgment, and as if the buildings possessintelligence pertaining to the earthquake amends its own structuralcharacteristics minutes by minute.

Acti3e Control S2stem

-he basic configuration of an active control system isschematically shown in figure. -he system consists of three basicelements/



?) Sensors to measure eternal ecitation andMor structuralresponse.

>) 6omputer hardware and software to compute control forces onthe basis of observed ecitation andMor structural response.

=) !ctuators to provide the necessary control forces.

-hus in active system has to necessarily have an eternalenergy input to drive the actuators. 7n the other hand passivesystems do not required eternal energy and their efficiencydepends on tunings of system to epected ecitation and structuralbehavior. !s a result, the passive systems are effective only for themodes of the vibrations for which these are tuned. -hus theadvantage of an active system lies in its much wider range of

applicability since the control forces are worked out on the basis ofactual ecitation and structural behavior. In the active system whenonly eternal ecitation is measured system is said to be in openlooped. owever when the structural response is used as input, thesystem is in closed loop control. In certain instances the ecitationand response both are used and it is termed as openclosed loopcontrol.

Control !orce De3ices %any ways have been proposed to apply control forces to astructure. Some of these have been tested in laboratory on scaleddown models. Some of the ideas have been put forward forapplications of active forces are briefly described in the following/

45 Acti3e tuned Mass Dampers 6TMD5#

these are in passive mode have been used in a umber of structures

as mentioned earlier. ence active -%D is a natural etension. Inthis system ?N of the total building mass is directly ecited by anactuator with no spring and dash pot. -he system has been termedas !ctive %ass Driver (!%D). -he eperiments indicated that thebuilding vibrations are reduced about >N by the use of !%D.

75 Tendon Control#

1arious analytical studies have been done using tendons for activecontrol. !t low ecitations, even with the active control system off,



the tendon will act in passive modes by resisting deformations inthe structures though resulting tension in the tendon. !t higherecitations one may switch over to !ctive mode where an actuatorapplies the required tension in tendons.

85 "ther Methods#

-he liquid sloshing during earthquakes has assumed significanceimportance in view of over flow of petroleum products from storagetank in post earthquakes. 7ne of the important consideration withsloshing is that is associated with a very low damping. -he waveheight was controlled through force applied to the side wall by ahydraulic actuator. -he active control successfully reduced wave

heights to the level of N of those without control, for harmonicecitations at sloshing frequency. #or earthquake type ecitationthe wave heights were reduced to ?GN level.

%'N%LUSI'N

6onventional approach to earthquake resistant design ofbuildings depends upon providing the building with strength,

stiffness and inelastic deformation capacity. *ut the new techniqueslike Energy Dissipation and !ctive 6ontrol Devices are a lot moreefficient and better.

?. *uilding should be of regular shapes. 6ylindrical structures

perform better in highwind areas.

>. !rchitect should try to design the building as aerodynamic as

possible. -his reduces the effect of $ind load on tall

structures.

=. -here should no odd shapes in elevation and the whole

building should be in balance. -he center of gravity of

building should not move.

J. 6antilever pro+ections should be minimum and their length

should not be more than = to J feet.

. -he span between the columns should be as small as

possible.



. 2oint loads on loadcarrying beams should be avoided.

H. -he dead loads on the cottagebuilding should not be

increased unnecessarily. #or Eample, -errace garden or

terrace swimming pools should be avoided, if possible.F. -he sunk portions of $6 and bath should be minimum.

G. *uilding should be a Reinforced 6oncrete framed structure. It

provides better stability and reliability in Earthquakeprone

areas.

?. 6ottagebuilding"s foundation should be placed on hard

and level ground.

??. -here should not be very large overhead water tanks

than are required. If it has to have larger capacity, then it

should be divided into two three smaller tanks and should be

kept at different locations to maintain balance of cottage

building.

?>. If the column length is more than ?> feet, then bracing

beams should be provided in between the column at regular

intervals. *racing beams strengthen a column, and allow

construction of multistoried buildings.

?=. -he columns should be connected at each level.

?J. #or strengthening the brickwork, a sill or a lintel should

be provided at every = feet level, and R.6.6. wall should be

taken where it is possible.

?. 6ottage building should not contain very large andheavy windows. -hey are bound to weaken the structure.

?. -he cottage building"s electrification should contain a

main switch and circuit breakers so as to avoid fire ha;ards

because of short circuit in the earthquake.

?H. -he glass used any structure should be fiberreinforced

glass or wire glass.



?F. :se of new and better materials like #iberreinforced

6oncrete and fiberglass should be recommended. -hese new

materials decrease dead load and increase the structure"s

strength.

Documents

Tips to Design Earthquake Resistant Building_Jean-Rayner Kuswadi