first final.doc

8/14/2019 first final.doc

http://slidepdf.com/reader/full/first-finaldoc 1/31

Earthquake Resisting Building Construction ME – (Construction Technology & Management)

1.1 INTRODUCTION

Earthquake is defined as the shaking of Earth’s surface due to any reason which

results in release of large amount of energy. The energy released during an earthquake

is enormous. For example, the energy released during Bhuj earthquake was aout !""

times more than the energy released y the #$!% atom om dropped in &iroshima.

'omeody said that (Earthquakes do not kill people ut it is the structures uilt y

them that do so).

The word Earthquake is self explaining * the Earth+quakes that mean the Earth

shakes and we feel the irations caused y these motions. Earthquakes are caused

due to many reasons ut most commonly the term (Earthquake) is used when shakingof the earth’s surface is caused due to some disturances occurring inside the earth.

-irations are produced when the earth is distured,. These irations are set out

in all directions from the place of their origin. hereer these irations trael, an

earthquake is said to hae taken place. These irations are most intense near their

source. /s the distance increases these ecomes feele and slowly die out. 0ore than

#",""" earthquakes occur eery year. But most of them are not of great concern for

1iil engineers, only a few of them, haing high intensity, are a cause of major

concern. 'ome earthquakes can e ery destructie and result in collapse of

structures, thus resulting in heay loss of life and damage to the uildings. Thus it is

necessary to study the earthquake in detail and take eery precautionary measure and

protection, to minimi2e the loss of life and property. 'ince earthquakes are

unpreentale and unpredictale, so we should design the structures earthquake

resistant which means that they should withstand earthquake forces without much

damage thus loss of life and property is minimum. 'o the study of Earthquakes

engineering is important for ciil engineers to equip them with the asic knowledge of

earthquake, its effect on structures and arious principles and techniques to e

followed while designing and constructing earthquake resistant structures.

STRUCTURE OF THE EARTH:

The earthquake originates inside the earth therefore it is essential to study the

structure of the interior of the earth. The interior of the earth is diided into the

following 2ones+

S.S..B.C.!.E. & T." B#$S%%'.age




#. 1rust

3. 0antle

4. 1ore

1. Crust: The uppermost part is called crust. 5t is solid and extends up to 6"km inside

the earth. 5t mainly consist of rocks like granite, asalt etc. 7ensity is 3.% to 4.".

2. Mantle: 5s diided into two parts+ outer and inner. The upper mental extends upto

66" km and inner mental upto 3$"" km. The density aries from 4.! to %.%.This part is

in semisolid state and temperature inside the mantle is 4""" "c.

3. Core: The innermost part of the earth is called as core. 5t is also diided in to two

parts+8uter and 5nner. 5t is mantle liquid 2one. 5 9n the composition, it has :ickel and

iron. The outer core extends upto %3"" km and inner core from %3""+64;" km. The

density of core is ##." to #6." and temperature at inner core is 6""" "c. The oundary

etween the crust and core is called as 08&8.

Fig.#.# 5nside the earth

CAUSES OF EARTHQUAKE:

Earthquakes are preliminary caused due to two reasons<

#. :atural disturances

S.S..B.C.!.E. & T." B#$S%%'.age *




a= -olcanic causes

= Tectonic causes

3. /rtificial disturances

1. Natural Dstur!an"es: The natural disturances which causes earthquakes are

following<

a= #ol"an" "auses: -olcanic actiity keeps on taking place in seeral parts of the

world. -ery often, it produces sudden outurst or explosions. This impact is

sometimes strong enough to produce irations in the neary areas. >eople, liing

in ?apan and 5taly, hae experience this type of earthquake frequently. These

earthquake are not ery deep and of mild intensity. The damage caused due to this

type of earthquake is confined within a few kilometers. /ll olcanic eruptions

don’t produce earthquake.

= Te"ton" "auses: Tectonic causes are those which occur inside the earth. /n

earthquake is the iolent shaking of the Earth caused y a sudden moement of

rock eneath its surface. @ocks respond to stress Asquee2ed or pulled apart= near

the Earths surface y reaking, and when rocks moe along either side of a

fracture, it is called a fault. The land around a fault may shift hori2ontally,

ertically, or a comination of these motions The force that causes the stress

within the rock is a result of moement of giant sections of the Earths crust.

S.S..B.C.!.E. & T." B#$S%%'.age +




Fig.#.3 Types of faults

2. Art$"al Dstur!an"es: 'ometimes the surface of the earth irates due to

manmade or artificial disturance. These irations are ery mild and affect thesurrounding area only. The earthquakes of mild intensity are caused due to

these external man made agencies. 'ome of the artificial disturances

causing earthquakes are listed<

:uclear tests and explosions.

0ining lasts in the mining area.

/ massie landslide along hill slopes caused ecause of deforestation.

Carge and deep excaations.

-iration induced due to heay machinery used in industries or

moement of heay ehicles.

The irations or shaking caused due to aoe reasons is ery minor and

limited to small areas only. /ll these causes occur oer the earth’s surface so

these are called as surface causes.

S.S..B.C.!.E. & T." B#$S%%'.age ,




1.2. EFFECT OF EARTHQUAKE ON STRUCTURES

Earthquakes produce arious damaging effects to the areas they act upon. This

includes damage to uildings and in worst cases the loss of human life. The effects of

the rumling produced y earthquakes usually lead to the destruction of structures

such as uildings, ridges, and dams. They can also trigger landslides. /n example

of how an earthquake can lead to een more destruction is the #$%$ earthquake near

&egen, 0ontana. 5t caused a land slide that killed seeral people and locked the

0adison @ier. 7ue to the fact that the 0adison @ier was locked, a lake was

created which later flooded the neary town of Ennis.

Besides producing floods and destroying uildings, earthquakes that take place

under the ocean can sometimes cause tsunamis, or tidal waes. Tsunamis are high and

long walls of water which trael at a ery rapid rate. They are notorious for destroying

entire populations and cities near coastlines. 5n #D$6 'anriku, ?apan, with a

population of 3",""", suffered such a fate.

Fig.#.4 Effect 8f Earthquake

Dre"t S%a&n' Ha(ar)s an) Hu*an+Ma)e Stru"tures

0ost earthquake+related deaths are caused y the collapse of structures and

the construction practices play a tremendous role in the death toll of an earthquake. 5n

S.S..B.C.!.E. & T." B#$S%%'.age -




southern 5taly in #$"$ more than #"",""" people perished in an earthquake that struck

the region. /lmost half of the people liing in the region of 0essina were killed due

to the easily collapsile structures that dominated the illages of the region. / larger

earthquake that struck 'an Francisco three years earlier had killed fewer people Aaout

;""= ecause uilding construction practices were different type Apredominantly

wood=. 'urial rates in the 'an Francisco earthquake was aout $D, that in the

0essina earthquake was etween 44 and !%= Building practices can make all the

difference in earthquakes, een a moderate rupture eneath a city with structures

unprepared for shaking can produce tens of thousands of casualties.

/lthough proaly the most important, direct shaking effects are not the onlyha2ard associated with earthquakes, other effects such as landslides, liquefaction, and

tsunamis hae also played important part in destruction produced y earthquakes.

Geologic Effects on Shaking

hen we discussed earthquake intensity we discussed some of the asic

factors that affect the amplitude and duration of shaking produced y an earthquake

Aearthquake si2e, distance from fault, site and regional geology, etc.= and as you are

aware, the shaking caused y seismic waes can cause damage uildings or cause

uildings to collapse. The leel of damage done to a structure depends on the

amplitude and the duration of shaking. The amplitudes are largest close to large

earthquakes and the duration generally increases with the si2e of the earthquake.

@egional geology can affect the leel and duration of shaking ut more important are

local site conditions. /lthough the process can e complicated for strong shaking,

generally shaking in soft sediments is larger and longer than when compared with the

shaking experienced at a hard rock site.

Taller uildings also tend to shake longer than short uildings, which can make

them relatiely more susceptile to damage. Fortunately many tall uildings are

constructed to withstand strong winds and some precautions hae een taken to

reduce their tendency to shake. /nd they can e made resistant to earthquake

irations.

S.S..B.C.!.E. & T." B#$S%%'.age




5n many regions of limited resources andGor old structures, the structures are not

ery well suited to earthquake induced strains and collapse of adoe+style

construction has caused thousands of deaths in the last decade. The worst possile

structure for earthquake regions is the unreinforced masonry .

,an)sl)es

Buildings arent the only thing to fail under the stresses of seismic waes. 8ften

unstale regions of hillsides or mountains fail. 5n addition to the oious ha2ard posed

y large landslides, een non lethal slides can cause prolems when they lock

highways they can e inconenient or cause prolems for emergency and rescue

operations.

Fig. #.! Candslides

8ccasionally large landslides can e triggered y earthquakes. 5n #$;" an

earthquake off the coast of >eru produced a landslide than egan D" miles away from

the earthquake. The slide was large Awitnesses estimated its height at aout 4" meters

or #"" feet=, traeled at more than one+hundred miles per hour and plowed through

part of one illage and annihilated another, killing more than #D,""" people.

5n some cases, when the surface is underlain y a saturated, sand rich layer of soil,

prolonged shaking can cause the expulsion of fluid from the sand layer resulting in

large sand lows that erupt through the oerlying strata.

S.S..B.C.!.E. & T." B#$S%%'.age /




Tsuna*s

/ sometimes dramatic y product of certain types of earthquakes are tsunamis.

Tsunami is a ?apanese term that means haror wae. Tsunamis are frequently

confused with tidal waes, ut they hae nothing to do with the tides, they are the

result of a sudden ertical offset in the ocean floor caused y earthquakes, sumarine

landslides, and olcanic deformation. 5n #DD4 the olcanic eruption of Hrakatoa

resulted in the collapse of a caldera that initiated a tsunami which killed 46,"""

people on neary islands. 8n ?une 3%, #D$6 an earthquake off the ?apanese coast

generated a tsunami that hit the shore with wae heights ranging from #" to #"" feet.

/s the fishing fleets returned to shore following an oernight trip they found theirillages destroyed and 33,""" people dead. 5n the last century more than %","""

people hae died as a result of tsunamis.

The speed of this wae depends on the ocean depth and is typically aout as fast

as a commercial passenger jet Aaout ".3 kmGs or ;#3 kmGhr=. This is relatiely slow

compared to seismic waes, so we are often alerted to the dangers of the tsunami y

the shaking efore the wae arries. The troule is that the time to react is not ery

long in regions close to the earthquake that caused the tsunami.

Tsunamis pose no threat in the deep ocean ecause they are only a meter or so

high in deep water. But as the wae approaches the shore and the water shallows, all

the energy that was distriuted throughout the ocean depth ecomes concentrated in

the shallow water and the wae height increases.

Typical heights for large tsunamis are on the order of #"s of meters and a few

hae approached $" meters Aaout 4"" feet=. These waes are typically more

deastating to the coastal region than the shaking of the earthquake that caused the

tsunami. Een the more common tsunamis of aout #"+3" meters can wipe clean

coastal communities.

7eadly tsunamis occur aout eery one to two years and they hae at times killed

thousands of people. 5n #$$3+$4 three large tsunamis occurred< one in ?apan,

5ndonesia, and :icaragua. /ll struck at night and deastated the local communities.

S.S..B.C.!.E. & T." B#$S%%'.age 0




Fre

The fourth main earthquake ha2ard is fire. These fires can e started y roken

gas lines and power lines, or tipped oer wood or coal stoes. They can e a serious prolem, especially if the water lines that feed the fire hydrants are roken, too. For

example, after the Ireat 'an Francisco Earthquake in #$"6, the city urned for three

days. 0ost of the city was destroyed and 3%",""" people were left homeless.

0ost of the ha2ards to people come from man+made structures themseles and the

shaking they receie from the earthquake. The real dangers to people are eing

crushed in a collapsing uilding, drowning in a flood caused y a roken dam or

leee, getting uried under a landslide, or eing urned in a fire.

S.S..B.C.!.E. & T." B#$S%%'.age 1




1.3. EARTHQUAKE RESISTANCE -UI,DIN STRUCTURE

0asonry uildings are the most common type of traditional construction used

for housing purpose all around the world. These are mostly seen in rural, uran and

hilly regions. This type of construction has ery low seismic resistance. The recent

earthquakes hae shown that the collapse of these constructions is the main cause of

destruction. &ence, it is necessary to increase the seismic resistance of these

constructions.

5n most cases, the resistance can e improed y following simple,

inexpensie principles of good uilding construction. But already constructed in use

uildings are of concern. Thus, retrofitting of such uilding is so essential for

improing their seismic resistance. Therefore, study of all these features ecomes a

must for ciil engineer.

Sa$et/ !e$ore t%e Eart%0ua&e

• The uilding should e constructed y taking all earthquake safety measures.

• Building should not hae any crack either in foundation or in structure, if any

then it should e repaired with the consultation of ciil engineer.

• Coose ojects placed at a height or heay ojects should e affixed to the

adjoining walls so that these ojects may not harm the persons liing in the

rooms.

• >lace heay ojects or articles on the lower sheles or on floors.

• &eay hanging ojects such as head light should not e kept in edroom,

sleeping area and liing area.

• 'tore all reakale ojects, flammale products and pesticides in low closed

cainets with proper locks.

• 0ake sure that all the family memers know how to respond after earthquake

and they should hae emergency telephone numer of police and fire Fighting

stations.

S.S..B.C.!.E. & T." B#$S%%'.age 2




• /ll family memers should hae knowledge aout the location of electric main

switch and they should know how to turn off the electric main switch and gas

connection to aoid any further damage at the time of earthquake.

First aid kit, torch, flash light, some food and water, radio with attery should

e set aside for the emergency and each family memer should know aout the

storage so that these items would e helpful after the earthquake.

Eart%0ua&e resstant "onstru"ton

/n earthquake resistant construction should hae following properties for etter

seismic performance<

7uctility<

7eformaility.

Iood structural 1onfiguration.

Cateral 'trength.

7amageaility.

Du"tlt/:

7uctility is the property of a material which enales it to undergo large

elongation efore reaking. The materials generally used for construction are masonry

concrete and steel. 0asonry and concrete are rittle while steel is ductile. / good

earthquake resistance uilding should hae enough ductility. This can e done y

addition of ductile material such as wood in earthen construction and steel ars in

masonry and concrete construction.

De$or*a!lt/

7eformaility refers to the aility of the structure to undergo large

deformations without collapse. hile ductility is the inherent property of material,

deformaility pertains to the structure. The deformaility of a structure can e

increased y making regular, well proportional structure which is tied properly. Iood

deformaility of a structure is also necessarily to make it earthquake resistant. For

example+ Een when ductile material in present in the uilding components, such as

S.S..B.C.!.E. & T." B#$S%%'.age




eams and walls, the uilding may fail if the components are not well proportioned

and tied together properly.

oo) Stru"tural Con$'uraton:

The si2e, shape and structural system of uilding should e such that inertia

forces are transferred to the ground safely. /n important property of god structural

configuration is its integral action. 5ntegral action means the structure acts as one unit

and is ale to resist the earthquake forces in a etter and safer way.

,ateral Stren't%:

The earthquake results in large inertia forces. Thus, a good earthquake

resistant uilding should hae enough lateral strength, so that, it can resist the inertia

forces without collapse.

Da*a'ea!lt/:

7amageaility refers to the aility of a structure to undergo sustantial

damage without partial or total collapse. This will result in sufficient warning to the

people efore collapse, thus resulting in less loss of lies. Iood damageaility can e

achieed y proiding seeral supports to important structural components and

aoiding central columns or walls supporting large portions of uilding.

TRADITIONA,, -UI,T MASONR CONSTRUCTION

0asonry constructions hae low earthquake resistance. -arious types of

damage commonly seen in masonry uildings and their causes, some of the factors

responsile for low seismic resistance of masonry uilding are as follows<

Cack of integral action.

Cack of strong and ductile connections etween walls, walls, and roof, and walls

and foundation.

Cess strength for out of plane forces.

Cow tensile and shear strength of masonry.

&igh in+plane stiffness of wall.

Cow ductility and deformaility.

&eay mass of the structure.

S.S..B.C.!.E. & T." B#$S%%'.age *




/ll these weakness can e oercome y following simple principles and

methods gien in arious codes for the earthquake resistant design and construction of

masonry uildings.

T/es o$ "onstru"ton

Types of construction usually adopted in uildings are of two types<

#= Framed 1onstruction

3= Box Type 1onstruction.

Fra*e) Constru"ton

This type of construction is suitale for multistoried uildings and industrial

uildings. This may consist of<

• Cight framing memers which must hae diagonal racing such as wooden

frames or walls for lateral load resistance. 'teel multistoried uildings or

industrial frames and timer construction are of this type.

• The rigid or semi+rigid jointed frames. These frames are of reinforced concrete

or steel. The walls are also rigid and may e of reinforced concrete or of

reinforced rickwork.

-o4 T/e Constru"ton

This type of construction consists of masonry, concrete or reinforced concrete.

The walls support ertical loads and also act as shear walls for hori2ontal loads. /ll

traditional masonry construction falls under this type. This is also called as load

earing wall construction.

5rearn' Stru"tures $or S%a&n'

The first step in preparing structures for shaking is to understand how uildings

respond to ground motions+ this is the field of study for earthquake and structural

engineers.

hen the ground shakes, uildings respond to the accelerations transmitted

from the ground through the structures foundation. The inertia of the uilding Ait

wants to stay at rest= can cause shearing of the structure which can concentrate

S.S..B.C.!.E. & T." B#$S%%'.age +




stresses on the weak walls or joints in the structure resulting in failure or perhaps total

collapse. The type of shaking and the frequency of shaking depend on the structure.

Tall uildings tend to amplify the motions of longer period motions when

compared with small uildings. Each structure has a resonance frequency that is

characteristic of the uilding. >redicting the precise ehaior of uildings is

complicated, a rule of thum is that the period of resonance is aout equal to ".# times

the numer of stories in the structure. Thus 0acelwane &all resonates at aout ".4

seconds period, and Iriesedeck at aout #.! seconds.

Fig #.% 7ifferent 0odes 8f 'haking

eneral rn"les $or eart%0ua&e resstant !ul)n's

The earthquake resistant of uildings can e improed y following simple

principles are gien in the code and are explained elow<

,'%tness

The earthquake force depends on mass of the structure. &eaier structure means

large inertia force and collapse of these structures results in heaier damage and

loss of lies. Thus, a uilding should e as light as possile, especially the roof

and upper storeys.

-ul)n' "on$'uraton

The ehaior of a uilding during earthquake depends on its shape, si2e and

geometry. / good uilding configuration can result in less damage during

earthquakes. The arious components of uilding configuration are explained

elow<

• S/**etr/: The uilding as a whole or its arious locks should e kept

symmetrical aout oth the axes. The asymmetrical uildings are sujected to

S.S..B.C.!.E. & T." B#$S%%'.age ,




twist or torsion during earthquakes. This twist makes different portions at the

same floor leel to moe hori2ontally y different amounts. This causes more

damage. This damage can e minimi2ed y planning symmetrical uildings as

shown in Fig. 3.

Fig. #.; 'ymmetrical desirale plans.

• S*l"t/ an) re'ulart/: The uildings hae a simple rectangular plan. 5t is

seen that simple shapes ehae etter during earthquake than complex shapes like

C, T, E, &, J and T etc. shown in Fig. 4. 5t seen that during earthquakes the

uildings with re+entrant corners hae suffered great damage. These types of

uildings can e roken into rectangular locks which are separated properly.

Thus, separation of a large uilding into smaller locks can lead to symmetry and

regularity as shown in Fig. !.

Fig. #.6 Cong or unsymmetrical undesirale plans.For preenting pounding or hammering etween locks, a separation of 4 to !

cm through the height aoe plinth leel is required. This separation section is just

like an expansion joint or it may e filled with a weak material which can easily

crush during earthquake shaking.

• S*le !ul)n' 6t%out *u"% ro7e"tons an) Susen)e) 5arts !e%a8e 6ell

)urn' eart%0ua&e: Cong cornices, ertical or hori2ontal projections, facia stones

etc. should e aoided and are dangerous during earthquakes. 5f these parts cannot

S.S..B.C.!.E. & T." B#$S%%'.age -




e aoided, they should e reinforced properly and tied firmly to the main

structure. 1eiling plaster should not e done and if done, it should e as thin as

possile.

• S(e o$ t%e !ul)n': 5n tall uildings, the hori2ontal moements aoe the floor

during ground shaking are large. 5n short, ut ery long uildings the damaging

effect of earthquake are more. Buildings one of their dimensions much larger or

smaller than the other two does not perform well during earthquakes. Thus the

uildings length should not e more than three time its width. 5f longer length are

needed, two separate locks with separation should e proided.

Fig.#.D Jse of separation section for improing plans.

• En"lose) Area: / small uilding with properly interconnected walls acts like a

rigid ox and more earthquakes resistant. Therefore it is adisale to hae

separate small rooms than one long room.

Stren't% n 8arous Dre"tons

The structure should hae adequate strength along oth the axes. The design

should also e safe and take into account the reersile nature of earthquake motion.

Sta!lt/ o$ sloes

&ill side slopes are liale to slide during an earthquake. &ence

uildings should not e constructed on them only stale slopes should e

chosen. 'imilarly uildings with unequal memers will also twist underground

moement and may result in damage and collapse.

Foun)aton

The uilding should not e constructed on loose soils. These soils will

compact and susidies and result in unequal settlement of uilding and damage it.

/lthough such soil can e compacted properly for small uildings. But for large

S.S..B.C.!.E. & T." B#$S%%'.age




uildings this operation is costly. For large uildings, rigid raft foundation or piles

taken to firm stratum can e used.

Du"tlt/

7uctility is the most desirale property for good earthquake performance. The

rittle masonry can e strengthened y proiding steel reinforcing ars at critical

sections which will also improe ductility of the structure.

Fre resstan"e

5t is ery common to see fire after earthquake. 5t may e ecause of electrical

short circuits, leaking of gas pipesGcylinders kerosene lamps and kitchen fires. The

fire ha2ard is sometimes more serious than the earthquake damage. &ence, the

uildings should e made fire resistant according to 5ndian 'tandards.

Se"al Constru"ton Features

Roo$ an) $loors

Flat roof or floor should not e made of tiles or ricks supported on steel,

timer or reinforced concrete joist. There ricks or tiles can e loosened and may

fall during earthquake.

For pitched roofs, corrugated iron or asestos sheets should e used in place of

tiles or other loose roofing units. /ll roofing material should e tied properly to

the supporting memers. &eay roofing material should e aoided.

Star "ases

• Carge stair hall should e separated from the rest of the uilding.

• The interconnection of the stair with the adjacent floors should e proided y

sliding joints at the stairs to preent the racing effect on the floors.

Searaton o$ a)7on stru"tures

'eparation of adjoining structure is required for preenting pounding or

hammering. 0inimum gap width for adjoining structures is gien in tale<

Tale #.#'howing Iap idth for /djoining 'tructures

Sr.

No.T/e o$ "onstru"ton

a 6)t%9Store/ n ** $or

Des'n Ses*" "oe$$"ent

;.12

S.S..B.C.!.E. & T." B#$S%%'.age /




#Box, system or frames with shear

walls#%."

30oment resistant reinforced concrete

frame3"."

4 0oment resistant steel frame 4"."

1.<. EARTHQUAKE RESISTANT FEATURE OF MASONR

-arious code proisions of 5'< !436< #$$4 regarding material selection, design

and construction of earthquake resistant uildings are as follows<

Masonr/ unt

For earthquake resistant uildings, well urnt ricks and solid concrete locks

haing crushing strength not less than 4.% 0>a should e used. The higher

strength units may e used for taller uildings. The strength of masonry units

required depends on the numer of storeys and thickness of walls.

'quared stone masonry, stone lock masonry as per 5'< #%$;< #$$3 may also e

used.

*ortars

'ince tensile and shear strength are important for earthquake resistance, use of

mud or ery weak mortar is not suitale. / mortar mix of cement< 'and A#< 6= y

olume at least should e used.

here steel reinforcing ars are proided in masonry, the ars shall hae proper

coer in cement< sand mortar Anot less than #<4= and the minimum clear coer is

#" mm. in cement concrete of grade 0#%, minimum clear coer is #% mm or ar

diameter whicheer is more.

=alls

Oenn's n 6alls

S.S..B.C.!.E. & T." B#$S%%'.age 0




/s openings in the walls reduce their lateral load resistance so they should e

small in si2e and centrally located.

8penings in any storey should hae their top at the same leel so that continuous

and could e proided oer them.5f openings are not proided according to

standard, they should e strengthened y reinforced concrete lining with high

strength deformed ars of D mm diameter.

5f window or entilator is to e projected out, the projection should e in

reinforced masonry or concrete and tied together properly.

Jse of arches oer the openings should e aoided. 5f arches are proided then

steel ties should e proided.

Fig.#.$ 'trengthening 0asonry /round 8penings.

Ses*" stren't%enn' arran'e*ents

/ll masonry uildings should e strengthened in hori2ontal as well as ertical

direction for improing the earthquake resistance. The strengthening arrangements are

ery important and explained elow<

#= &ori2ontal reinforcement.

3= -ertical reinforcement.

Hor(ontal Ren$or"e*ent

The hori2ontal reinforcing of walls is required for imparting them hori2ontal

ending strength against inertia force. 5t also helps in tying the walls together. 5n

S.S..B.C.!.E. & T." B#$S%%'.age 1




the exterior walls hori2ontal reinforcement helps in preenting shrinkage and

temperature cracks. The following arrangements of hori2ontal reinforcement are

necessary for earthquake resistant uildings.

a= Hor(ontal -an)s or Rn' -ea*s. The most important seismic. 'trengthening

arrangement for uildings is through reinforced concrete ands. / and is

reinforced concrete or reinforced rick runner proided in the walls to tie them

together and to impart hori2ontal ending strength to them.These ands are

proided continuous through the entire load earing walls at plinth, lintel, roof

caes leel and also top of gales.

= Do6el !ars. 7owels are proided in category 7 K E of uildings. 'teel dowel

ars are proided at corners and T junctions of walls at the sill leel of windows to

a length of $"" mm. These ars must laid in #< 4 cement sand mortar with a

minimum coer of #" mm

Fig.#.#" 7owel Bar

#ert"al Ren$or"e*ent

-ertical reinforcement is also proided in walls to improe the seismic resistance

of uildings. -arious points to e considered for ertical reinforcement are

follows<

#= -ertical steel at corners and junctions of walls which are up to 4!" mm A# L

rick= thick shall e proided.

3= For walls thicker than 4!" mm area of ars can e increased proportionately. The

amount of ertical steel depends upon numer of storeys and category of uilding.

:o ertical steel is proided in category a uilding.

4= The ertical reinforcement should e properly emedded in the plinth masonry

and roof sla or roof and.

S.S..B.C.!.E. & T." B#$S%%'.age *2




!= The ertical reinforcement should e pass through the lintel ands and floor leel

ands in all storeys.

%= -ertical reinforcement for window and door openings should start from

foundation of floor and upto lintel and.

Eart%0ua&e Resstan"e Features o$ Stone Masonr/.

Cow strength stone masonry uildings are weak against earthquakes and

should e aoided in high seismic 2one. The arious features for improing the

earthquake resistance of stone masonry uildings are explained elow<

eneral "onstru"ton ase"ts

• The wall thickness should not exceed !%" mm, preferaly 4%" mm.

• The height of storey should not e greater than 4." m.

• 5n general, the stone masonry uildings should not e taller than 3 storeys when

uilt in cement mortar and # storey when uilt in lime or mud mortar.

• The unsupported length of wall etween cross walls should e limited to % m. For

longer walls, cross supports, called uttresses should e at spacing not more than

! m.

Mortar

• 1lay mud mortar should e aoided.

• 1ement+sand mortar #< 6 Aor richer= and lime sand mortar #< 4 Aor richer= should

e used for uilding construction.

=all Constru"ton

•

The masonry walls should e uilt in lifts not more than 6"" mm.

• T%rou'% Stones: 5nner and outer faces of the wall should e onded with

(through stones) Aoer full thickness of wall=. Through stones should e used in

eery 6"" mm lift at not more than #.3 m apart hori2ontally.

• 5f full length (through stones) is not aailale then and stones in pairs, Aeach

aout M of wall thickness= should e proided.

• 5n place of (through stones) steel ars of D to #" mm diameter in ' shape or a

hook may e used with a coer of 3% mm from each face.

S.S..B.C.!.E. & T." B#$S%%'.age *




• ooden ars of 4D mm x 4D mm may e used in place of through stones. The

wood used should e well presered.

• Jse of long stones should also e made at corners and junctions of wall to reak

the ertical joint and for onding perpendicular walls.

Oenn' n 6alls

These are same as in case of masonry uildings.

STRENTHENIN OF E>ISTIN -UI,DIN TO RESIST

EARTHQUAKES

-ul)n's 6t% Floors Restn' on Fra*n'

Floors simply resting on framing resulting in complete structural failure during an

earthquake. This is ery common, een when a proper concrete frame has een used.

The floor may e timer joists resting on the walls or cross eamsN or resting in joist

hangars which hae a nail or equialent holding them in place. Een in reasonale

quality flooring, precast concrete planks may e resting on earing surfaces on walls

or eams. 8r 'teel joists may e simply hooked onto supports on walls or framing

with nominal pins. The result is oious< any slight shaking and the floor falls down.

Further, any floor elow would not e ale to resist the weight of a falling floorN and

ery often the floors gie staility to the framing. ?ust look at a ideo of the orld

Trade Towers to see how well this works out. The solution to some of these prolems

is to tie adjacent floors together ery firmly so that they cannot separate either side of

the supports. 5n a proper frame, these joists are olted with full moment resisting

connections through the main supporting eamsN it is not possile to do this in

retrospect, ut joining adjacent joists oer the supports with sturdy olted steel plates

will help< as will reaking out the holes in precast hollow+core concrete plans for adistance of say !""mm either side of the support, and well grouting in deformed re+

ars across the gap. here the joists are supported on outside eams, then similar

measure must e adopted to make it impossile for them to fall off.

S.S..B.C.!.E. & T." B#$S%%'.age **




5n almost all uildings, een those designed for earthquake resistance, the shear

within the column to eam connections is greater than the shear resistance. This can

lead to catastrophic failure.

E4"ess8e -ul)n' =e'%t? Co*ro*sn' Stru"tural Stren't%

/dditional weight added to uildings leading to structural weakness and eleated

susceptiility to earthquake damage or collapse. This is ery common, particularly in

poor areas of poor countries in earthquake 2ones. >eru and &aiti spring to mind. /

uilding may hae een perfectly well uilt for one or perhaps 3 floors. 5ncreases in

family si2e with no increase in family udget leads to another floor eing jerry uilt

on top, usually as descried in paragraph # or 3. / new roof is put on, usually asdescried in paragraph 4. Further increases of more floors can follow. 5f the uilding

does not fail under the continued upwards expansion, it will certainly fail under a

slight tremorN een taking down the perhaps well uilt original uilding elow. The

est solution here is to enforce remoal of stories which make the uilding dangerous,

though the strengthening of paragraph # and 4, at eery floor, might help. 5n addition,

many such uildings hae alconies, or hae had alconies olted onN and then the

alconies hae een ricked in to create further rooms. But the extra weight is in the

wrong place. The higher weight is in the uilding, the more it shakes the uilding

aout in an earthquake. 7iscipline is needed to remoe additional weight. 5f there are

lock work and concrete roofs, they should e replace with lightweight steel and

insulation and sheeting, which may weigh ten times less.

-' Aertures Re)u"n' -ul)n' Stren't%

Big apertures at the lowest floor leel compromising the structural integrity of the

uilding particularly during an earthquake. -ery often, the ground floor leel has ig

apertures in the walls< garage doors, showroom windows, ig entrances, internal walls

cut away to make impressie loies. 8ften the wall panels that are remoed

constitute the earthquake sway racing of the uilding. 8ften, inconenient cross

racing in the new cut apertures is simply cut off, or sometimes replaced with

ineffectie racing systems. 8ften, the ground floor is the highest floor in the whole

uilding, ut the columns are a similar construction in eery floor. 8ften the columns

S.S..B.C.!.E. & T." B#$S%%'.age *+




or walls go down to pinned ases. /nd any failure of the ground to first floor is

likely to e disastrous, and is certainly the worst place to suffer a failureN and

eerything is conspiring to make this floor also the weakest. To implement earthquake

resistance, uildings need to e inspected to ensure that such weaknesses are

reinforced, with the re+introduction of racing. This may est e a four sided square

frame of steel or properly reinforced concrete, with fully rigid joints at each corner,

ertically in the aperture to gie ack sway resistance on eery wall face with large

holes. 5n all proaility the columns from ground floor to first floor also need

reinforcing, y clamping steel sections on to them, or strapping round anti ursting

concrete around them.

Co*ro*se) -ul)n' Foun)atons

The foundations of earthquake resistant uildings require special considerations to

allow for ground moement. Frequently the foundations of traditional uildings are

often designed as pinned, ut, ecause the ottom of eery wall or column ears

down onto the foundations, the ases do proide a it of fixity in the static condition.

This gies some additional strength to the walls or columns, in the static condition.

But in earthquake conditions, the ground is not static< it moes up and down, side to

side, and can change slope. 5f you can imagine a ase of a wall or column rotating out

of the hori2ontal, you can see it putting a end into the wall or column. This means

that the apparent fixity at the ase is now not giing extra strength ut, on the

contrary, is contriuting to early failure. /lso, in earthquakes, the ground can crack

and expand or ruck up within the dimensions of a uilding, and this would put

enormous forces into the structure. For this reason, foundations of uildings in

earthquake areas should always hae a grillage of reinforced concrete or steel, going

oth ways under all load supporting memers. 'uch foundations should hae full

strength connections to the columns, and should e strong enough to gie positional

and rotational restraint to all the columns. 5t is not possile to make uildings

earthquake proof, to the extent that they will resist any earthquakeN ut the remedies

proposed in this list will help any uilding, and its occupants, surie.

S.S..B.C.!.E. & T." B#$S%%'.age *,




Ren$or"e*ent $or 6ea& stru"tures to resst eart%0ua&es

5t is not possile to make eery uilding resist eery earthquakeN ut it is quick

and easy and economical to make any square or rectangular room much more

resistant. 'pecial 0oment resisting frames offer the est protection.

@E57 steel moment resisting reinforcement is a solution. For # room, the kit

consists of ! lower corners joined y four floor eams, ! corner posts, ! upper corner

pieces and ! ceiling eams.

The pieces are assemled and joined with light welds or olts to keep them in

position. 5n the eent of an earthquake, the rectangular ox of framing will gie side+

sway resistance in all directions. 5n larger rooms further T+shaped jointing pieces may

e needed

-ul)n's 6t% no Stru"tural Fra*n'

Earthquake damage caused y the uilding haing no structural framing where the

upper floors and roof are simply uilt on to masonry walls. This is difficult, ecause

some sort of framing is italN once these walls shake a it, the entire strength is lost

and the uilding will collapse or pancake during an earthquake. The solution here can

only e to strengthen each room with a #3+memer cuic frame Aon ! sides round the

floor, up the ! corners of the walls, and around the ! sides of the roof=. 'uch frames

would hae to hae sustantial moment resistance all three ways in all D corners. /nd

eery room would need the treatment, especially on the lower floors. The frames

should e tied in to walls, ceilings or roofs, floors as well as possile, with through

olts, or chemical anchors etc. 'uch frames should e in steel or in properly designed

reinforced concrete. 5t would perhaps e cheaper to demolish and reuild properly.

-ul)n's %a8n' Suse"t Stru"tural Fra*n'

The uildings hae structural framing which is suspect, leading to poor earthquake

resistance. Oou only hae to look at pictures from any earthquake to see concrete

framing which has failed< not enough steel main reinforcement, leading to ending

failure< not enough stirrups, leading to ursting failure, not enough cement in the

S.S..B.C.!.E. & T." B#$S%%'.age *-




concrete, leading to crumling under loadN and of course under+si2ed memers. 5t is

common for people to uild hollow lock walls, and leae some ertical gaps filled

with a it of concrete with a few rearsN and at eery floor, a course of locks is left

out and a similar si2ed concrete eam replaces it. Jnless a structural engineer is quite

certain that the concrete and rears are sufficiently si2ed and well enough uilt,

especially at the joints.

1.@. EARTHQUAKE RESISTANT DESIN TECHNIQUES

Intro)u"ton

The conentional approach to earthquake resistant design of uildings depends

upon proiding the uilding with strength, stiffness and inelastic deformation capacity

which are great enough to withstand a gien leel of earthquake*generated force. This

is generally accomplished through the selection of an appropriate structural

conFiguration and the careful detailing of structural memers, such as eams and

columns, and the connections etween them.

Fig.#.## Base 5solation

5n contrast, we can say that the asic approach underlying more adanced

techniques for earthquake resistance is not to strengthen the uilding, ut to reduce

the earthquake*generated forces acting upon it. /mong the most important adanced

techniques of earthquake resistant design and construction are ase isolation and

energy dissipation deices.

-ase Isolaton

S.S..B.C.!.E. & T." B#$S%%'.age *




5t is easiest to see this principle at work y referring directly to the most

widely used of these adanced techniques, which is known as ase isolation. / ase

isolated structure is supported y a series of earing pads which are placed etween

the uilding and the uildings foundation. / ariety of different types of ase

isolation earing pads hae now een deeloped. For our example, well discuss lead*

ruer earings. These are among the frequently*used types of ase isolation

earings. / lead*ruer earing is made from layers of ruer sandwiched together

with layers of steel. 5n the middle of the earing is a solid lead plug. 8n top and

ottom, the earing is fitted with steel plates which are used to attach the earing to

the uilding and foundation. The earing is ery stiff and strong in the ertical

direction, ut flexile in the hori2ontal direction.

Eart% enerate) $or"es

To get a asic idea of how ase isolation works, first examine Fig. This shows an

earthquake acting on oth a ase isolated uilding and a conentional, fixed*ase, and

uilding. /s a result of an earthquake, the ground eneath each uilding egins to

moe.

Each uilding responds with moement which tends toward the right. e say that

the uilding undergoes displacement towards the right. The uildings displacement in

the direction opposite the ground motion is actually due to inertia. The inertial forces

acting on a uilding are the most important of all those generated during an

earthquake.

5t is important to know that the inertial forces which the uilding undergoes are

proportional to the uildings acceleration during ground motion. 5t is also important

to reali2e that uildings dont actually shift in only one direction.

Because of the complex nature of earthquake ground motion, the uilding actually

tends to irate ack and forth in arying directions.

S.S..B.C.!.E. & T." B#$S%%'.age */




Fig. #.#3 0oement 7ue To Earth Ienerated Forces

5n addition to displacing toward the right, the un*isolated uilding is also

shown to e changing its shape* from a rectangle to a parallelogram. e say that the

uilding is deforming. The primary cause of earthquake damage to uildings is the

deformation which the uilding undergoes as a result of the inertial forces acting upon

it.

The different types of damage which uildings can suffer are quite aried and

depend upon a large numer of complicated factors. But to take one simple example,

one can easily imagine what happens to two pieces of wood joined at a right angle y

a few nails, when the ery heay uilding containing them suddenly starts to moe

ery quickly P the nails pull out and the connection fails.

Resonse o$ -ase Isolate) -ul)n'

By contrast, een though it too is displacing, the ase*isolated uilding retains its

original, rectangular shape. 5t is the lead*ruer earings supporting the uilding that

are deformed. The ase*isolated uilding itself escapes the deformation and damage

Pwhich implies that the inertial forces acting on the ase*isolated uilding hae een

reduced.

Experiments and oserations of ase*isolated uildings in earthquakes hae een

shown to reduce uilding accelerations to as little as #G! of the acceleration of

comparale fixed*ase uildings, which each uilding undergoes as a percentage of

graity. /s we noted aoe, inertial forces increase, and decrease, proportionally as

acceleration increases or decreases.

S.S..B.C.!.E. & T." B#$S%%'.age *0




/cceleration is decreased ecause the ase isolation system lengthens a uildings

period of iration, the time it takes for the uilding to rock ack and forth and then

ack again. /nd in general, structures with longer periods of iration tend to reduce

acceleration, while those with shorter periods tend to increase or amplify acceleration.

Finally, since they are highly elastic, the ruer isolation earings dont suffer any

damage. But what aout that lead plug in the middle of our example earingQ 5t

experiences the same deformation as the ruer. &oweer, it also generates heat as it

does so.

S%er"al Sl)n' Isolaton S/ste*s

/s we said earlier, lead*ruer earings are just one of a numer of different

types of ase isolation earings which hae now een deeloped. 'pherical 'liding

5solation 'ystems are another type of ase isolation. The uilding is supported y

earing pads that hae a cured surface and low friction.

Fig. #.#4 'pherical 'liding 5solation 'ystem

7uring an earthquake, the uilding is free to slide on the earings. 'ince the

earings hae a cured surface, the uilding slides oth hori2ontally and ertically.

The force needed to moe the uilding upwards limits the hori2ontal or lateral forces

which would otherwise cause uilding deformations. /lso, y adjusting the radius of

the earings cured surface, this property can e used to design earings that also

lengthen the uildings period of iration.

S.S..B.C.!.E. & T." B#$S%%'.age *1




Ener'/ Dssaton De8"es

The second of the major new techniques for improing the earthquake

resistance of uildings also relies upon damping and energy dissipation, ut it greatly

extends the damping and energy dissipation proided y lead*ruer earings.

The uilding will dissipate energy either y undergoing large scale moement

or sustaining increased internal strains in elements such as the uildings columns and

eams. Both of these eentually result in arying degrees of damage. 'o, y

equipping a uilding with additional deices which hae high damping capacity, we

can greatly decrease the seismic energy entering the uilding, and thus decrease

uilding damage.

/ccordingly, a wide range of energy dissipation deices hae een deeloped and

are now eing installed in real uildings. Energy dissipation deices are also often

called damping deices. The large numer of damping deices that hae een

deeloped can e grouped into three road categories<

• Friction 7ampers* these utili2e frictional forces to dissipate energy

• 0etallic 7ampers* utili2e the deformation of metal elements within the

damper

• -isco elastic 7ampers* utili2e the controlled shearing of solids

• -iscous 7ampers* utili2ed the forced moement Aorificing= of fluids within

the damper

Flu) #s"ous Da*ers

8nce again, to try to illustrate some of the general principles of damping deices,

well look more closely at one particular type of damping deice, the Fluid -iscous

7amper, which is one ariety of iscous damper that has een widely utili2ed and has

proen to e ery effectie in a wide range of applications.

S.S..B.C.!.E. & T." B#$S%%'.age +2




Da*n' De8"es an) -ra"n' S/ste*s

7amping deices are usually installed as part of racing systems. Figure % shows

one type of damper*race arrangement, with one end attached to a column and one

end attached to a floor eam. >rimarily, this arrangement proides the column with

additional support.

Fig.#.#! 7amping 7eices

0ost earthquake ground motion is in a hori2ontal directionN so, it is a

uildings columns which normally undergo the most displacement relatie to the

motion of the ground. Figure #.#! also shows the damping deice installed as part of

the racing system and gies some idea of its action.

first final.doc

Documents

Transcript of first final.doc