taha load patren 3

8/18/2019 Taha Load Patren 3

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shapes of buildings and come to conclusion as to which is moststable and economical shapes under given condition forwind and earth#uake loads.

).*.6 750(0T0+( +5 TA88 90870(:

The tall building can be described as a multistory building generallyprovided with high speed elevators, constructed using a structuralframe, and combining extraordinary height with ordinary roomspaces such as could be found in low'buildings. 0n aggregate, it is aphysical, economic, and technological expression of the city&s powerbase, representing its private and public investments.

).*.) ;0(7 55/T2 +( TA88 90870(:2

The wind is the most powerful and unpredictable force a"ectingtall buildings. Tall building can be dened as a mast anchored in theground, bending and swaying in the wind. This movement,known aswind drift , should be kept within acceptable limits. $oreover, for awell'designed tall building, the wind drift should not surpass theheight of the building divided by 1A?0AT0+( +5 ;0(7 237 ;0T@ @0:@T


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An important characteristic of wind is the variation of its speedwith height 5igure *B. The wind speed increase follows a curvedline varying from zero at the ground surface to a maximum at somedistance above the ground. The height at which the speed stops toincrease is called the gradient height, and the corresponding speed,

the gradient wind speed . This important characteristic of wind is awell understood phenomenon that higher design pressures arespecied at higher elevations in most building codes. Additionally,at heights of approximately )CC m from the ground, surface frictionhas an almost negligible e"ect on the wind speed4 as such the windmovement is only depend on the prevailing seasonal and local winde"ects. The height through which the wind speed is a"ected by thetopography is called atmospheric boundary layer. The wind speedprole within this layer is in the domain of turbulent ow and couldbe mathematically calculated.

).*.< 1+?TD'2@770(: 3@(+$(+( Along wind and across wind are two important terms, used toexplain the vortex'shedding phenomenon. Along wind or simplywind is the term used to refer to drag forces. The across windresponse is a motion, which happens on a plane perpendicular tothe direction of wind. ;hen a building is sub!ected to a wind ow,the originally parallel wind stream lines are displaced on bothtransverse sides of the building 5ig 6B, and the forces produced onthese sides are called vortices.


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5ig 6. Simplifed wind ow

At #uite a low wind speeds, the vortices are shed symmetrically oneither transverse side of the building 5ig 6 aB, and so building doesnot vibrate in the across wind direction.

5ig 6. 1ortices in di"erent wind speed conditionsE aB vortices in lowspeed of wind there is no vibration in the across wind directionB4bB vortices in high speed of wind F vortex'shedding phenomenonthere is vibration in the across wind directionB +n the other hand,at higher wind speeds, the vortices are shed alternately rst fromone and then from the other side. ;hen this occurs, there is animpulse both in the along wind and across wind directions. Theacross wind impulses are applied to the left and then alternativelyto the right. Therefore such kind of shedding which causesstructural vibrations in the ow and the across wind direction is

called vortex-shedding, a phenomenon well known in uidmechanics. This phenomenon of alternate shedding of vortices for arectangular tall building is shown schematically in 5igure 6b.

).*.C A?T@G9AH 55/T2 +( TA88 90870(:2 As earth#uakes can happen almost anywhere, some measure of earth#uake resistance in the form of reserve ductility andredundancy should be built into the design of all structures to


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prevent catastrophic failures. $oreover, during the life of a buildingin a seismically active zone, it is usually expected that the buildingwill be sub!ected to many small earth#uakes, including somemoderate ones, one or more large ones, and possibly a very severeone. uilding massing, shape and proportion, ground acceleration,

and the dynamic response of the structure, inuences themagnitude and distribution of earth#uake forces. +n the otherhand, if irregular forms are inevitable, special design considerationsare necessary to account for load transfer at abrupt changes instructural resistance. Therefore, two general approaches areutilized to determine the seismic loading, which take intoconsideration the properties of the structure, and the past record of earth#uakes in the region. ;hen compared to the wind loads,earth#uake loads have stronger intensity and shorter duration.

).*.I 720:( /+(207?AT0+(2

$oreover, despite the advancements in earth#uake engineeringduring the last three decades, many uncertainties still exist. Theplan layout of a building plays a vital role in its resistance to lateralforces and the distribution of earth#uake forces. xperience hasshown that the buildings with an unsymmetrical plan have a greatervulnerability to earth#uake damage than the symmetricalones.Therefore, symmetry in both axes, not only for the buildingitself but also for the arrangement of wall openings, columns, andshear walls is very important. 5or irregular featured buildings, suchas asymmetry in plan or vertical discontinuity, assumptionsdi"erent from the buildings with regular features should be used in

developing seismic criteria.

).*.J TA88 90870(: @A10+? 79?0(: A?T@G9AH2 2eismic motion response of tall buildings is to some extentgenerally di"erent than low'rise buildings. The magnitude of inertiaforces generated by an earth#uake depends on the building mass,ground acceleration, the nature of foundation, and the dynamiccharacteristics of the structure 5igure )B. Although tall buildingsare more exible than low'rise buildings, and usually experienceaccelerations much less than low'rise ones, a tall building sub!ectedto ground motions for a prolonged period may experience much

larger forces if its natural period is near that of the ground waves.


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5igure ). Schematic representation o seismic orce

).*.K 2@A3 28/T0+(A tall building, whose shape is unsuitable, often re#uires a greatdeal of steel or a special damping mechanism to reduce its dynamicdisplacement within the limits of the criterion level for the designwind speed. 9nderstandably, an appropriate choice of buildingshape and architectural modications are also extremely importantand e"ective design approaches to reduce wind induced motion byaltering the ow pattern around the building, hence for thisresearch work four shaped buildings are generally studied namelycircular, rectangular, s#uare and triangle as shown in 5igure > to5igure IB.


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5igure > Circular Shape

5igure C Square Shape


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5igure I Triangular Shape

).6 8+A72 /+(207?7).6.* 7A7 8+A72E

).6.*.* 7ead loads shall include self'weight of all items of

permanent nature that will act continuously throughout the

service life of the building, street, building works, street

works, and the variations of its magnitude with time are

insignicant. 0t shall be taken to include but not limited to the

followingE

aB the structure

bB all other structural elements that are axed to the

structure e.g. windows, claddings and other forms of

permanent constructionB4


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cB non'structural elements e.g. nishes, roong, surfacing

and coverings, linings, kerbs, suspended ceilings, insulation,

earth and ballastB4

dB permanent e#uipment including xtures and ttings e.g.

permanently xed wiring and reticulated servicesB4

eB partitions the positions of which are indicated on the

building plans submitted to the uildings 7epartment L7MB

for approval4 and

fB soil ll, waterproong and drainage system for gardening,

greenery or planting.

All permanent constructions of the structure form the dead

loads. The dead load comprises of the weights of walls,

partitions oor nishes, false ceilings, false oors and the

other permanent constructions in the buildings. The dead load

loads may be calculated from the dimensions of various

members and their unit weights. the unit weights of plain

concrete and reinforced concrete made with sand and gravel or

crushed natural stone aggregate may be taken as 6> k(NmM

and 6< k(NmM respectively.

).6.*.6 The weights of tanks and other receptacles shall be

considered as dead loads. The contents of tanks and

receptacles shall be considered as imposed loads.

).6.*.) ;hen there is doubt to the permanency of loads, such

loads should be treated as imposed loads while reduction of

which under clause ).I should not be taken on beams and

vertical members.

).6.6 7etermination of 7ead 8oads

).6.6.* :eneral

7ead loads shall be calculated from the design or known

dimensions of the structures and the density of the materials

used. The density of some common materials is given in

Appendix A for reference. 5or materials not included in

Appendix A, the determination of their density shall be based


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on reliable data. 2ome common items for assessment of dead

loads are described in more details in clause

).6.6.6 3artitions

A' 3artitions indicated on the building plans submitted to 7for approval are considered as permanent partitions. Their

weight shall be considered as dead loads and calculated

according to the layout shown on the building plans.

' ;here partitions are envisaged but the location of which are

not indicated on the building plans, the weights of these

partitions shall be considered as imposed loads and to be

calculated in accordance with clause ).C.

).6.6.) ?oong&s

aB' The weight of roong&s such as waterproong membrane,

protective screeding, and tiles shall be calculated from the

weight of the component materials and their geometry such as

the thickness and area.

bB' ;here a roof is to be provided with greenery, the weight

of soil, waterproong and drainage system, and plants for

greenery shall be taken as dead loads.

).6.6.> /laddings and 5inishes

aB' /laddings shall include aluminum or metal cladding,

polished granite slabs or limestone cladding, marble facing

and their xings. 5inishes shall include in'situ nishes e.g.

plaster, screedsB, pre'fabricated wall'panel nishes, suspended

ceilings, timber and other oor nishes.

bB' The weight of niches in columbaria shall be determined

according to the material used for the construction of niches

and the weight of the urns. 5or lightweight niches, such as

niches made of wood or lightweight metals, the weight shall be

not less than 6.= k(Nm length for each meter height. 5or heavy

weight niches, such as niches made of concrete, the weight

shall be not less than >.< k(Nm length for each meter height.


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).6.6 0$3+27 8+A72E0mposed load is produced by the intended use or occupancy of a building including the weight of movable partitions,distributed and concentrated loads, load due to impact andvto, creep and shrinkage of the structure, the di"erential

settlements to which the structure may undergo.

).6.6.* :eneral

aB'9nder the uilding /onstructionB ?egulations, theimposed load on any building, street, building works or street

works shall be the greatest applied load likely to arise from

their intended use or purpose during the service life of the

building, street, building works or street works including

forces exerted by the ad!acent ground but excluding dead

loads and wind loadsB.

bB' The values of imposed loads are categorized and given inthis 2ection according to specic use of the related oor or

structure, and they shall be considered as the minimum values

to be adopted in design. ;here higher values are anticipated

or considered more appropriate, based on knowledge of the

intended use of the oor or the intended installation of

e#uipment, machinery or displayed items, they shall be

considered in determining the imposed loads on the oor.

).6.6.6The imposed loads as given shall beE

aB a uniformly distributed load, #k, in k3a4 or

bB a concentrated load or line load, Gk, in k( or k(Nm, as

appropriate4 whichever shall produce the most adverse e"ect.

).6.6.)The uniformly distributed load, #k, and theconcentrated load or line load, Gk, shall be considered

separately.

).6.6.> The uniformly distributed load, #k, shall be applied toone or more areas such that the most adverse e"ect will be

produced for the design parameter under consideration.

).6.6.


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for the design parameter under consideration. The

concentrated load shall be assumed to be uniformly

distributed over a contact area as specied in this /ode. The

line load shall be applied in the manner as specied in this

/ode.

).6.6.C ?eduction of distributed imposed loads in accordancewith clause ).I may be applied as appropriate.

).6.6.I Allowance for partitions where positions of which arenot indicated on building planB and horizontal imposed loads

as specied in clause ).C and ).J respectively shall be

considered as appropriate.

).6.6.J 5loor uses are categorized into eight classes as

shown in Table ).*

).6.) /lass * to


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Notes: 1 Specific uses that are not specified in the Building (Construction) Regulations.2 For stacking or storage area, reference shall e !ade to the appropriate e"a!ple of specific use and the

corresponding i!posed load gi#en in Class $.% Storage height in Class $ shall e the height of the space et&een the follo&ing: the floor, and a ph'sicalconstraint to the height of storage for!ed ' a ceiling, soffit of a floor, roof or other ostruction.


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A oor should be designed for the most adverse e"ect of uniformly distributed load and concentrated load over =.) m by=.) m as specied in Table').*, but they should not beconsidered to act simultaneously. All other structural elements

such as beams and columns are designed for thecorresponding uniformly distributed loads on oors.

?eduction in imposed liveB load may be made in designingcolumns, load bearing walls etc., if there is no specic load likeplant or machinery on the oor. This is allowed to account forreduced probability of full loading being applied over largerareas. The supporting members of the roof of the multi'storeyed building is designed for *==O of uniformly distributedload4 further reductions of *=O for each successive oor downto a minimum of


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3.2.3 WIND LOAD:

The wind loading is the most important factor thatdetermines the designof tall buildings over *= storeys, wherestorey height approximately lies between

6.I F ).= m. uildings of up to *= storeys, designed for gravityloading can accommodate wind loading without any additionalsteel for lateral system. 9sually, buildings taller than *=storeys would generally re#uire additional steel for lateralsystem. This is due to the fact that wind loading on a tallbuilding acts over a very large building surface, with greaterintensity at greater heights and with a larger moment armabout the base. 2o, the additional steel re#uired for windresistance increases non'linearly with height as shown in 5ig.).I.

Fig.3.2.3.1Weight of steel in multi-storeyed buildings

As shown in 5ig.).I the lateral sti"ness of the building is amore important consideration than its strength for tall multi'storeyed structures. ;ind has become a ma!or load for thedesigner of multi'storeyed buildings. 3rediction of windloading in precise scientic terms may not be possible, as it isinuenced by many factors such as the form of errain, the


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shape, slenderness, the solidity ratio of building and thearrangement of ad!acent buildings. The appropriate designwind loads are estimated based on two approaches. 2taticapproach is one, which assumes the building to be a xed rigidbody in the wind. This method is suitable for buildings of

normal height, slenderness, or susceptible to vibration in thewind. The other approach is the dynamic approach. This isadopted for exceptionally tall, slender, or vibration pronebuildings. 2ometimes wind sensitive tall buildings will have tobe designed for interference e"ects caused by theenvironment in which the building stands. The loading due tothese interference e"ects is best ascertained using windtunnel modeled structures in the laboratory.@owever, in the 0ndian context, where the tallest multi'storeyed building is only about )< storeys high, multi'storeyedbuildings do not su"er wind'induced oscillation and generally

do not re#uire to be examined for the dynamic e"ects.5ordetailed information on evaluating wind load, the reader isreferred to 02EJI


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+i#ure 3.2.3.2 Fluctuating wind orces based on wind turbulence and orte!generation

in wa"e o building

5luctuating wind pressures act on building surfaces due to theabove factors. 5luctuating wind pressures change temporally, andtheir dynamic characteristics are not uniform at all positions on thebuilding surface. Therefore, it is better to evaluate wind load onstructural frames based on overall building behavior and that oncomponentsNcladding based on the behavior of individual buildingparts. 5or most buildings, the e"ect of uctuating wind forcegenerated by wind turbulence is predominant. 0n this case,horizontal wind load on structural frames in the along'winddirection is important. @owever, for relatively exible buildings witha large aspect ratio, horizontal wind loads on structural frames inthe across'wind and torsional directions should not be ignored. 5orroof loads, the uctuating wind force caused by separation owfrom the leading edge of the roof often predominates.Therefore, wind load on structural frames is divided into two partsEhorizontal wind load on structural frames and roof wind load onstructural frames.


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+i#ure 3.2.3.3 Classifcation o wind loads

3.2.3.)Desi#n Wind %peed ,-&The "asic ind speed ,-& for any site shall "e o"tained from and shall "e modifiedto include the folloin# effects to #et desi#n ind velocity at any hei#ht ,-& for thechosen structure:a /is0 level1bB Terrain roughness, height and size of structure4 and

cB 8ocal topography.

It can "e mathematically e(pressed as follos:Where:- -" 0l 0 0s design &ind speed at an' height * in !+skl proailit' factor (risk coefficient)

k terrain, height and structure si*e factor andks topograph' factor

?isk /oecient k0 5actorB gives basic wind speeds for terrain

/ategory 6 as applicable at *= m above ground level based on


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or ridges which can signicantly a"ect wind speed in theirvicinity. The e"ect of topography is to accelerate wind near thesummits of hills or crests of cli"s, escarpments or ridges anddecelerate the wind in valleys or near the foot of cli", steepescarpments, or ridges.

3.2.3.2WIND 6/7%%8/7% AND +O/97% ON 8ILDIN;% 9pi A 6d-here,

/pe % e!ternal pressure coe&cient'

9pi internal pressure coefficient,A surface area of structural or cladding unit, and6d design &ind pressure ele!ent


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3.2.? %7I%@I9 LOAD:

3.2.3.)Desi#n Lateral +orceThe design lateral force shall rst be computed for the building

as a whole. This design lateral force shall then be distributedto the various oor levels. The overall design seismic force

thus obtained at each oor level shall then be distributed to

individual lateral load resisting elements depending on the

oor diaphragm action.

3.2.3.2Desi#n %eismic ase %hearThe total design lateral force or design seismic base shear

1bB along any principal direction shall be determined by thefollowing expressionE

1b P Ah ;

-here,

Ah hori*ontal acceleration spectru!W seis!ic &eight of all the floors

3.2.3.3+undamental Natural 6eriodThe appro(imate fundamental natural period of vi"ration ,T&& in seconds& of a

moment5resistin# frame "uildin# ithout "ric0 in the panels may "e estimated "ythe empirical e(pression:

Ta*.*B h*.B for RC fra!e uildingTaP=.=J< h=.I< for steel fra!e uildingWhere&h P @eight of building, in m. This excludes the basement

storeys, where basement walls are connected with the ground

oor deck or tted between the building columns. ut it

includes the basement storeys, when they are not so

connected. The approximate fundamental natural period of

vibration T,B, in seconds, of all other buildings, including

moment'resisting frame

buildings with brick lintel panels, may be estimated by theempirical xpressionE


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T.*C4


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3.2.3.B.2.) Dynamic Analysis5Dynamic analysis shall "e performed to o"tain the desi#n seismic force& and itsdistri"ution to different levels alon# the hei#ht of the "uildin# and to the variouslateral load resistin# elements& for the folloin# uildin#s:

aB Regular buildings 'Those greater than >= m in height inRones 01 and 1 and those :reater than K= m in height in Rones00 and ***.bB Irregular buildings F All framed buildings higher than *6m inRones 01 and 1 and those greater

The analytical model for dynamic analysis of buildings withunusual conguration should be such that it ade#uatelymodels the types of irregularities present in the building

conguration. uildings with plan irregularities cannot bemodelled for dynamic analysis. 5or irregular buildings, lesserthan >= m in height in Rones **and 000, dynamic analysis, eventhough not mandatory, is recommended. 7ynamic analysis maybe performed either by the Time @istory $ethod or by the?esponse 2pectrum $ethod. @owever, in either method, thedesign base shear 1B shall be compared with abase shear1B


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3.2.3.B.2.).) Time 4istory @ethod5

. Sou nd the response of the structure internal forcesB as afunction of time for a specicground motion.

. 0t re#uires to have the accelerogram of the designearth#uake or have several representative ace


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Time history method of analysis shall "e "ased on an appropriate #round motionand shall "e performed usin# accepted principles of dynamics.

3.2.3.B.2.).) /esponse %pectrum @ethod5)5Definition

2o what is a spectrum in the context of this discussion Aspectrum is a collection of sine waves that, when combinedproperly, produce the time'domain signal under examination.


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5igure *'* shows the waveform of a complex signal. 2upposethat we were hoping to see a sine wave. Although the waveformcertainly shows us that the signal is not a pure sinusoid, it doesnot give us a denitive indication of the reason why. Thefre#uency'domain display plots the amplitude versus the

fre#uency of each sine wave in the spectrum. As shown, thespectrum in this case comprises !ust two sine waves. ;e nowknow why our original waveform was not a pure sine wave. 0tcontained a second sine wave, the second harmonic in this case.7oes this mean we have no need to perform time'domainmeasurements (ot at all. The time domain is better for manymeasurements, and some can be made only in the time domain.5or example, pure timedomain measurements include pulse riseand fall times, overshoot and ringing The fre#uency domain alsohas its measurement strengths.3eople involved in wirelesscommunications are extremely interested in out'of'band and

spurious emissions. 5or example, cellular radio systems must bechecked for harmonics of the carrier signal that might interferewith other systems operating at the same fre#uencies as theharmonics. ngineers and technicians are also very concernedabout distortion of the message modulated onto a carrier. Third'order intermodulation two tones of a complex signalmodulating each otherB can be particularly troublesome becausethe distortion components can fall within the band of interest,which means they cannot be ltered away. 2pectrum monitoringis another important fre#uency'domain measurement activity.:overnment regulatory agencies allocate di"erent fre#uencies

for various radio services, such as broadcast television andradio, mobile phone systems, police and emergencycommunications, and a host of other applications. 0t is criticalthat each of these services operates at the assigned fre#uencyand stays within the allocated channel bandwidth. Transmittersand other intentional radiators often must operate at closelyspaced ad!acent fre#uencies. A key performance measure forthe power ampliers and other components used in thesesystems is the amount of signal energy that spills over intoad!acent channels and causes interference. lectromagneticinterference $0B is a

term applied to unwanted emissions from both intentional andunintentional radiators. These unwanted emissions, eitherradiated or conducted through the power lines or otherinterconnecting wiresB, might impair the operation of othersystems. Almost anyone designing or manufacturing electricalor electronic products must test for emission levels versusfre#uency according to regulations set by various government.The pea0 or ma(imum response ,acceleration& velocity& displacement of all possi"le


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linear sin#le de#ree of freedom ,%D+ system to a particular component of #roundmotion for a #iven level of dampin#.

+i#ure ). 0isplace!ent response spectru! for 2 percentda!ping (after Chopra).


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. (ow, it is necessary to construct the design response spectrum.

. A plot of the peak value of a response #uantity eg.accelerationBas a function of the natural vibration period of the system is called

the response spectrum for this #uantity.. This response spectrum will depend on the damping ratio and theground motion selected.

2. 8ses of the response spectruma. The response spectrum provided a convenient and practical ay to summari$ethe fre=uency content of a #iven acceleration& velocity or displacement time history.". It provides a practical ay to apply the 0noled#e of structural dynamics todesi#n of structures and development of lateral force re=uirements in "uildin#

codes.3. Types of /esponse %pectra

,a5 /esponse %pectra calculated from actual time histories


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+i#ure 3. cceleration i!e /istor' for 3era Buena 4sland fro! the 1565 7o!a 8rieta9arthuake.

+i#ure 2. cceleration Response Spectru! for 3era Buena Record.


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+i#ure ?. 0isplace!ent Response Spectru! for the 3era Buena Record.%teps for calculatin# a

,a5)response spectrum from a time history

The response spectrum for a #iven #round motion component ,e.#.& a,t is developed usin#the folloin# steps:

,) O"tain the #round motion ,a,t for an earth=ua0e. Typically the acceleration valuesshould "e defined at time steps of *.*2 second& or less.

,2 2elect the natural vibration period, T , and damping ratio, for

27+5 system. ( 9sually < percent damping is selected.B,3 Determine the ma(imum displacement response for a %DO+ structure ith the selectedpercent dampin# for a #iven period or fre=uency of vi"ration.

To do this& you must solve the folloin# differential e=uation mM2u


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. +ourier transform

. Inverse +ourier transform ,d Numerical methods ,linear and nonlinear systems

. Numerical time steppin# methods

,? /epeat step 3 and vary the fundamental period of the structure "y chan#in# the mass,m& the stiffness ,0& or "oth. 6lot the ne results.

7(ample of 8sin# NONLIN to create a displacement response spectrum

+irst linear analysis

! 1;; kipsk 1;; kips + in

c $ percent of critical da!ping

earthuake record is 4!perial alle' 9l Centro Record (4!p#al1.acc)

period ;.%2 s, f %.1% /*, ω )C.HB rad


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k 2;; kips + in

c $ percent of critical da!ping

earthuake record is 4!perial alle' 9l Centro Record (4!p#al1.acc)

period ;.2% s, f


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+i#ure H. 0isplace!ent Response Spectru! for 9l Centro Record.


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+i#ure . 0isplace!ent Response Spectru! fro! N>N74N.

,B 9alculate the other pseudo spectral velocity values usin#:

- ω D

+i#ure G. elocit' Response Spectru! for e"a!ple.


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+i#ure C. elocit' Response Spectru! fro! N>N74N

,H 9alculate the pseudo acceleration response values from:

A ω D

It is common to e(press A in units of #& thus:

A,in # ω2D


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+i#ure )*. cceleration Response Spectru!


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+i#ure )). cceleration Response Spectru! fro! N>N74N

," . Deterministic /esponse %pectra from attenuation relations

.7eterministic spectrum are usually developed for themaximum credibleearth#uake $/B.

.The maximum credible earth#uake is the largest earth#uakepossible from the

active faults in the region.

+i#ure )2. Co!parison of 0eter!inistic Rock Spectra for ? @.;, R $ k! earthuake fro! attenuation relations.

,c. 6ro"a"ilistic %pectra for 6ro"a"ilistic %eismic 4a$ard Analysis ,6%4A


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+i#ure )3. Seis!ic /a*ard and 8ercent Contriution of ? and R pairs for 2$;; 'ear return period e#ent (2

percent proailit' of e"ceedance in $; 'ears) for peak ground acceleration.


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+i#ure )?. 8roailistic Anifor! /a*ard Spectra for input*ipcode 6


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taha load patren 3

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