REVISIONS IN IS 1893-Part 1 ON ERD OF TALL BUILDINGS

Dr. D.K. Paul Retd. Professor

Department of Earthquake Engg IIT Roorkee andDepartment of Earthquake Engg., IIT Roorkee andChairman, Earthquake Engineering Sectional

Committee, BIS CED 39 ,

IS 1893 P 1 2016IS 1893-Part 1: 2016 onon

CRITERION FOR EARTHQUAKE RESISTANT DESIGN OF STRUCTURESDESIGN OF STRUCTURES

Part 1 General Provisions and Buildingsg(Sixth Revision)

TALL BUILDINGSTALL BUILDINGSAccording to draft Code on Structural Safety of Tall Buildings d fi R C B ildi f h i h h 45 d ldefine R.C. Buildings of height greater than 45 m and less than 250 m as Tall Buildings

Tall reinforced concrete buildings are now increasingly used as residential, official and commercial buildings

Earthquake safety of tall buildings are carried out as per IS: 1893-Part 1 based on its dynamic behavior1893 Part 1 based on its dynamic behavior

Some of these new residential towers rely on a substantial t h ll t id th k i tconcrete shear-wall core to provide earthquake resistance

The newly designed buildings have not experienced major y g g p jearthquakes and therefore have not been tested for its performance

3

MAX IMUM BUILDING HEIGHT FOR DIFFERENT STRUCTURAL SYSTEMDIFFERENT STRUCTURAL SYSTEM

Seismic zone

Structural systemStructural wall

t Fl tMoment f

Moment f

Structural ll t

Structural ll t bsystem + Flat

slab floor system with

frame system

frame + structural

wall

wall system wall + tube frame

systemperimeter

moment framesystem

V NA NA 100 m 100 m 150 mV NA NA 100 m 100 m 150 mIV NA NA 100 m 100 m 150 mIII 70 m 60 m 160 m 160 m 220 mIII 70 m 60 m 160 m 160 m 220 mII 100 m 80 m 180 m 180 m 250 m

4

IS 1893 P t 1 2016IS 1893 Part 1: 2016Revised in 2016 (Sixth revision)Revised in 2016 (Sixth revision)Discuss the sixth revision applicable to ERD of Tall BuildingsBuildingsThe basic design philosophy remains the same i.e. intended to provide life safetyintended to provide life safetyThe structures designed as per this Standard is expected t t i d d t th kto sustain damage under strong earthquakeThe Standard is not applicable to Buildings with base isolation and Energy Dissipative devices

5

O t i fOverturning of Multi Storey R.C. Frame B ildingFrame Building

6

Margalla tower gcollapsed. A R.C. Frame building, Islamabad

7

This new buildingThis new building was not yet occupied at theoccupied at the time of the earthquake. qAgain, the bearing failure of its mat foundation was related to its relatively large height-to-width ratio

8

Badly damaged concreteBadly damaged concreteshear wall building

9

EARTQUAKE EXCITATIONEARTQUAKE EXCITATIONThe buildings under random ground motion consisting ofThe buildings under random ground motion consisting of several frequencies and of varying amplitude vibrate in different frequenciesdifferent frequencies

Resonance condition may arise between long distance d t ll t t ti d ft ilwaves and tall structures resting on deep soft soil

Soil-structure interaction becomes important for buildingSoil structure interaction becomes important for building resting on flexible soil-foundation system

Building supported on rock or rock like material, soil-structure interaction may be ignored

10

INTENSITY OF GROUND MOTIONINTENSITY OF GROUND MOTION

Intensity depends on following parameters

Peak ground accelerationFrequency content of ground motionq y gDuration of shaking

11

SEISMIC ZONE MAP

The zoning map is based on expected maximumseismic intensity in a regionseismic intensity in a region

Current trend world wide is to specify the groundacceleration that has a certain probability of beingexceeded in a given number of years. It is underdevelopment.

The country has been divided into four Zones, ZoneThe country has been divided into four Zones, ZoneII, III, IV & V.

12

PRESENTATION

Int. Z

VI 0 10VI 0.10

VII 0.16

VIII 0 24VIII 0.24

> IX 0.36

13

DESIGN RESPONSE SPECTRA2.5

3.0Type I: Rock or Hard SoilType II: Medium Soil

1 0

1.5

2.0S

a/g

Type III: Soft Soil

Spectra for Equivalent Static Method

0.0

0.5

1.0

0 1 2 3 4 5 6

3 0

0 1 2 3 4 5 6

Natural Period T (s)

2.0

2.5

3.0Type I: Rock or Hard SoilType II: Medium SoilType III: Soft Soil

1.0

1.5

Sa/

g

Spectra for Response Spectra Method

0.0

0.5

0 1 2 3 4 5 6

N t l P i d T ( )

14

Natural Period T (s)

Classification of Types of Soils for determining the Spectrum (Clause 6 4 2 1)

Soil Type RemarksI Well graded gravel (GW) or well graded sand (SW) both with less than 5

Spectrum (Clause 6.4.2.1)

IRock or

Hard Soils

Well graded gravel (GW) or well graded sand (SW) both with less than 5percent passing 75 m sieve (Fines)Well graded gravel – sand mixtures with or without fines (GW-SW)Poorly graded sand (SP) or clayey sand (SC), all having N above 30

μ

y g ( ) y y ( ), gStiff to hard clays having N above 30, where N is Standard Penetration Test value

II Poorly graded sands or Poorly graded sands with gravel (SP) with little or Medium or Stiff Soils

no fines having N between 10 and 30Stiff to medium stiff fine-grained soils, like Silts of Low compressibility (ML) or Clays of Low Compressibility (CL) having N between 10 and 30

IIISoft Soils

All soft soils other than SP with N<10. The various possible soils areSilts of Intermediate compressibility (Ml);Silts of High compressibility (MH);Silts of High compressibility (MH);Clays of Intermediate compressibility (CI);Clays of High compressibility (CH);Silts and Clays of Intermediate to High compressibility (MI-MH or CI-CH);y g p y ( );Silt with Clay of Intermediate compressibility (MI-CI); andSilt with Clay of High compressibility (MH-CH).

15

CODAL DESIGN PHILOSOPHY• Elastic design for very high lateral forces due to a major• Elastic design for very high lateral forces due to a major

earthquake would be very uneconomical

• An economically acceptable design under severe earthquake• An economically acceptable design under severe earthquakecan be achieved by allowing structure to undergo limiteddamage without collapse

• The most acceptable approach would be to design structuresto resist most frequent moderate earthquake and

• then check the resistance for infrequent most severeearthquake allowing limited damage without collapse whichmay occur in useful life time of a structuremay occur in useful life time of a structure

• To account for ductility as above, the elastic average spectra isreduced by a Reduction Factorreduced by a Reduction Factor

16

F

yel qFF =Structures to remain elastic in major earthquakes is likely to bemajor earthquakes is likely to be uneconomical – force demand is likely to be high

yF

More economical design can be achieved by making use of the ductility of the structure and over-strength to reduce the

E i l t f D tilit d B h i F t ith

yxx μ=maxyx x over strength to reduce the force demand

Equivalent of Ductility and Behaviour Factor with Equal Elastic and Inelastic Displacement

17

Building Damage States

Bas

e (V

b)

Capacity Curve

Shea

r B Collapse

C l i i d S f

Capacity Curve

Yield point

Damage Control Limited Safety

Displacement

Immediate OccupancyLevel

Life SafetyLevel

Structural StabilityLevel

Performance Level

Capacity Curve for Nonlinear Structure and Associated Damage States.18

Design Hori ontal Seismic Coefficient )/)(2/( gSZ

Design Horizontal Seismic Coefficient

)/()/)(2/(

IRgSZA a

h =

=Z Zone factor, refers to zero period acceleration value. Country has been

divided into four Zones divided into four Zones

gSa / = Design acceleration coefficient forga Design acceleration coefficient for different soil type and natural time period of building normalized to PGA

=I Importance factor depending upon functional use of the structure functional use of the structure

=R Response reduction function

d di th d tilit depending on the ductility

19

IMPORTANCE FACTOR, I,(Clause 7.2.3)S no Structure IS no. Structure I

1. Important service and community buildings or structures (for example critical governance buildings schools) signature buildings monumentcritical governance buildings, schools), signature buildings, monument buildings, lifeline and emergency buildings (for example hospital buildings, telephone exchange buildings, television stations buildings,

di t ti b ildi b t ti b ildi d t il b ildi )radio station buildings; bus station buildings and metro rail buildings), railway stations, airports, food storage buildings (such as warehouses), fuel station buildings, electric power station buildings and fire station buildings), and large community hall buildings (for example cinema halls, shopping malls, assembly halls and subway stations) and power station buildings 1.5g

2 Residential or commercial buildings (other than those listed in Sl No2. Residential or commercial buildings (other than those listed in Sl. No. 1 with occupancy more than 200 persons 1.2

3 All other buildings 1 0

20

3. All other buildings 1.0

RESPONSE REDUCTION FACTOR

f h b b l bl lIn view of the energy absorbing capacity available in inelasticrange, ductile structures will be able to resist alternate lateralload without much damageload without much damage

In addition to ductility, over strength and redundancy ofl d h f h h kstructure lead to the fact that an earthquake resistant

structure can be designed for much lower force

Depending on the perceived seismic damage performance ofthe structure, characterized by over strength, redundancy andd l b l d f f d dductile or brittle deformations, a factor R is introduced

21

RESPONSE REDUCTION FACTOR, R( l )(Clause 7.2.6)

S.N. Lateral Load Resisting System R

(1) (2) (3)(1) (2) (3)Moment Frame Systems

1. RC Buildings with Ordinary Moment Resisting Frame (OMRF)1 3.02. RC Buildings with Special Moment-Resisting Frame (SMRF) 5.03. Steel Buildings with Ordinary Moment Resisting Frame (OMRF)1 3.04. Steel Buildings with Special Moment Resisting Frame (SMRF) 5.0

Braced Frame Systems2

5 Buildings with Ordinary Braced Frame (OBF) having Concentric Braces 4 05. Buildings with Ordinary Braced Frame (OBF) having Concentric Braces 4.06. Buildings with Special Braced Frame (SBF) having Concentric Braces 4.57. Buildings with Special Braced Frame (SBF) having Eccentric Braces 5.0

Structural Wall Systems3y8. Load Bearing Masonry Buildings

(a) Unreinforced Masonry (designed as per IS 1905) without horizontal RC Seismic Bands1 1.5(b) Unreinforced Masonry (designed as per IS 1905) with horizontal RC Seismic Bands 2.0

(c) Unreinforced Masonry (designed as per IS 1905) with horizontal RC Seismic Bands and vertical reinforcing bars at corners of rooms and jambs of openings (with reinforcement as per IS 4326)

2.5

(d) Reinforced Masonry [refer SP 7 (Part 6) Section 4] 3.0(e) Confined Masonry 3.0

9. Buildings with Ordinary RC Structural Walls1 3.010 Buildings with Ductile RC Structural Walls 4 0

22

10. Buildings with Ductile RC Structural Walls 4.0

D l S t 3Dual Systems3

11. Buildings with Ordinary RC Structural Walls and RC OMRFs1 3.012. Buildings with Ordinary RC Structural Walls and RC SMRFs1 4.013 Buildings with Ductile RC Structural Walls with RC OMRFs1 4 013. Buildings with Ductile RC Structural Walls with RC OMRFs 4.014. Buildings with Ductile RC Structural Walls with RC SMRFs 5.0

Flat Slab – Structural Wall Systems4

15. RC Building with the three features given below: 3.0(i) Ductile RC Structural Walls (which are designed to resist 100% of the design

lateral force),(ii) Perimeter RC SMRFs (which are designed to independently resist 25% of

the design lateral force) and preferablythe design lateral force), and preferably(iii) An outrigger and belt truss system connecting the core Ductile RC Structural

Walls and the perimeter RC SMRFs1.

NOTES:NOTES:1.RC and Steel structures in Seismic Zones III, IV and V shall be designed to be ductile.

Hence, this system is not allowed in these Seismic zones.2.Eccentric Braces shall be used only with SBFs.3 B ildi i h S l W ll l i l d b ildi h i S l W ll d M3.Buildings with Structural Walls also include buildings having Structural Walls and Moment

Frames, but where:(a) Frames are not designed to carry design lateral loads, or(b) Frames are designed to carry design lateral loads, but do not fulfill the requirements of(b) Frames are designed to carry design lateral loads, but do not fulfill the requirements of

'Dual Systems'.4. In these buildings, (a) punching shear failure shall be avoided, and (b) lateral drift at the

roof under design lateral force shall not exceed 0.1%.

23

DESIGN IMPOSED LOADSDESIGN IMPOSED LOADS (Clause 7.2.7)The design seismic force shall be estimated using full dead load plusThe design seismic force shall be estimated using full dead load plus percentage of imposed load

Percentage of Imposed Load to be considered in Calculation of Seismic Weight (Clause 7.3.1)

Sl. No. Imposed Uniformity Distributed Floor Loads

Percentage of Imposed LoadFloor Loads

(kN/m2)Imposed Load

)i) Upto and including 3.0 25ii) Above 3.0 50

24

LOAD COMBINATIONSEven when load combinations that do not contain earthquakeEven when load combinations that do not contain earthquake effects, indicate larger demands than combination including them, the provisions shall be adopted related to design, ductile detailing and construction relevant for earthquake conditionsdetailing and construction relevant for earthquake conditions.

Design horizontal earthquake loads: When lateral load resisting elements are oriented along two mutually orthogonal horizontalelements are oriented along two mutually orthogonal horizontal directions, the building should be designed for full design earthquake load in one horizontal direction at a time

When lateral load resisting elements are not oriented along two mutually orthogonal horizontal directions, the following set of earthquake effects should be taken as

ELX ± 0.3 ELY

ELY ± 0.3 ELX

25

LOAD COMBINATIONS (cont….) Following load combinations shall be taken for 3D e/q ground motion

1) 1 2(DL + IL ± (ELX ± 0 3 ELY ± 0 3 ELZ))1) 1.2(DL + IL ± (ELX ± 0.3 ELY ± 0.3 ELZ))1.2(DL + IL ± (ELY ± 0.3 ELX ± 0.3 ELZ))

2) 1.5(DL ± (ELX ± 0.3 ELY ± 0.3 ELZ))1.5(DL ± (ELY ± 0.3 ELX ± 0.3 ELZ))

3) 0.9DL ± 1.5 (ELX ± 0.3 ELY ± 0.3 ELZ))

0 9DL 1 5 (ELY 0 3 ELX ± 0 3 ELZ))0.9DL ± 1.5 (ELY ± 0.3 ELX ± 0.3 ELZ))

26

BUILDING MODELLINGBUILDING MODELLINGTh i l tiff f th fl d f l b h ll b dThe in plane stiffness of the floor and roof slabs shall be assumed rigid

Each rigid floor shall be modeled as SDOFS in the direction earthquake excitation

The beam and column members shall be modeled as beam and column elements with appropriate sectional properties

The structural walls shall be modeled as plane stress/ shell elements

Th URM i fill ll h ll b d l d b i i l t di lThe URM infill walls shall be modeled by using equivalent diagonal struts taken to be pin jointed on either end

27

MDOFS - MULTI DEGREE OF FREEDOMMDOFS MULTI DEGREE OF FREEDOM SYSTEM

28

BUILDING MODELLINGEquivalent width of the diagonal strut

BUILDING MODELLING

F

F

wLds

wds

dshds Lw 4.0175.0 −= α

⎟⎟⎠

⎞⎜⎜⎝

⎛= 4

42sinhIE

tEh

f

mh

θα

29

⎟⎠

⎜⎝ 4 hIE cf

Sectional Properties

F t t l l i th t f i ti h ll b t kFor structural analysis, the moment of inertia shall be taken as:

(1) I RC d M t t 70% f I(1) In RC and Masonry structures: 70% of of columns, and 35% of of beams; andgrossI

grossI

(2) In Steel structures: of both beams andl

grossIcolumns

S il t t I t tiSoil-structure InteractionSoil-structure interaction becomes important for building resting on flexible soil foundation system The soil shall be modeled byflexible soil-foundation system. The soil shall be modeled by equivalent soil spring system

30

FOUNDATIONFOUNDATIONFailure of foundation can take place due to

Excessive pressure and excessive settlementSliding failure of founding stratag gFailure due to liquefaction; such cases are not covered by the present codeIsolated RC footings without tie beams or unreinforced strip footings should not be adopted in buildings rested on soft soil (with corrected N < 10) in any seismic zoneN < 10) in any seismic zone.Individual spread footings or pile caps should be interconnected with ties except when individual spread footings are directly supported on rock in Zones IV & V.All ties shall be capable of carrying, in tension and in compression, an axial force equal to times the larger of the column or pile cap4/Aaxial force equal to times the larger of the column or pile cap load in addition to the normal calculated forces, subject to minimum of 5% of larger of column or pile cap load.

4/hA

31

METHOD OF ANALYSISMETHOD OF ANALYSISFollowing methods are adopted for analysis of building for design earthquake loadsearthquake loads

(1) Equivalent Static Method, and ( ) q ,(2) Dynamic Analysis Method.

D i l i b f d i thDynamic analysis can be performed in three ways,

(i) Response Spectrum Method(i) Response Spectrum Method, (ii) Modal Time History Method, and (iii) Time History Method.

For Tall Buildings, Response Spectrum Method and Time History Method are adoptedMethod are adopted.

Equivalent Static Method may be used for analysis of regular t t ith i t t l i d T l th 0 4

32

structures with approximate natural period Ta less than 0.4s.

Desirable minimum corrected field values of N

If soils of lower N values are encountered than those specified in the table above, then suitable ground improvement techniques shall be adopted to achieve these values Alternately deep pile foundationsadopted to achieve these values. Alternately, deep pile foundations should be used, which are anchored in stronger strata, underlying the soil layers that do not meet the requirement

S.N Seismic Depth (m) N Remarkso. Zone below GL Values1 III, IV

and V= 5=10

1525

For values of depths between 5 m and 10 mand V =10 25 between 5 m and 10 m, linear interpolation is recommended.2 II = 5

> 101020> 10 20

33

Classification of Types of Soils for determining Percentage Increase in Net Bearing Pressure and

Soil Type Remarks

Percentage Increase in Net Bearing Pressure and Skin Friction (Clause 6.3.5.2)

Soil Type RemarksA

Rock or Hard Soils

Well graded gravel (GW) or well graded sand (SW) both with less than 5 percent passing 75 μm sieve (Fines)Well graded gravel – sand mixtures with or without fines (GW-SW)Poorly graded Sand (SP) or Clayey Sand (SC) all having N above 30Poorly-graded Sand (SP) or Clayey Sand (SC), all having N above 30Stiff to Hard Clays having N above 30, where N is corrected Standard Penetration Test value

B Poorly graded sands or Poorly graded sands with gravel (SP) with little or no fines having N Medium or Stiff Soils

y g y g g ( ) gbetween 10 and 30Stiff to medium stiff fine-grained soils, like Silts of Low compressibility (ML) or Clays of LowCompressibility (CL) having N between 10 and 30

C All soft soils other than SP with N<10 The various possible soils areCSoft Soils

All soft soils other than SP with N<10. The various possible soils areSilts of Intermediate compressibility (Ml);Silts of High compressibility (MH);Clays of Intermediate compressibility (CI);Clays of High compressibility (CH);Clays of High compressibility (CH);Silts and Clays of Intermediate to High compressibility (MI-MH or CI-CH);Silt with Clay of Intermediate compressibility (MI-CI); andSilt with Clay of High compressibility (MH-CH).

DUnstable,

Collapsible, Liquefiable

Requires site-specific study and special treatment according to site condition (See 6.3.5.3)

34

qSoils

INCREASE IN NET PRESSURE ON SOILS IN DESIGN OF FOUDATIONSIN DESIGN OF FOUDATIONS

In design of foundations unfactored loads shall beIn design of foundations, unfactored loads shall be combined while assessing the bearing pressure in soilsWhen earthquake forces are included net bearingWhen earthquake forces are included, net bearing pressure in soils can be

Sl. No.(1)

Soil Type(2)

Percentage increase allowable

(3)i) Tape A: Rock or hard soils 50ii) Type B: Medium or stiff soils 25iii) Type C: Soft soils 0

35

DESIRABLE ATTRIBUTES OF ANDESIRABLE ATTRIBUTES OF AN EARTHQUAKE RESISTANT BUILDING

Robust structural configurationAt least a minimum elastic lateral stiffnessAt least a minimum lateral strength, and Adequate ductility

36

REGULAR AND IRREGULAR CONFIGURATIONSBuilding with simple regular geometry and uniformlyBuilding with simple regular geometry and uniformly distributed mass and stiffness in plan and elevation suffer much less damageelevation, suffer much less damage

- Plan Irregularity

Torsion Irregularity

g y

Re-entrant CornersFloor slabs having excessive cut-outs or openingsOut of plane offsets in vertical elementsNon-parallel lateral force system

37

- Vertical IrregularityStiffness Irregularity – Soft Storey

(larger of bare frame and frame with URM analyses, drift 0.2%)

Mass Irregularity ( f fl 150% f th f fl b l )Mass Irregularity ( mass of floor >150% of the mass of floors below)

Vertical Geometric Irregularity (horizontal dimension of the lateral force resisting system in any storey is > 125% of the storey below)

In-plane Discontinuity in Vertical Elements Resisting Lateral Force (when in plane offset of the lateral force resisting elements is greater than 20% of plan length of those elements)p g )

Strength Irregularity – Weak Storey (lateral strength is less than that of the storey above)

Fl ti t b lFloating or stub columnsIrregular modes of vibration in two principal plan directions (First three modes contributes less than 65% mass participation factor in each principal plan p p p p pdirections)

38

RC FRAME BUILDINGS WITH OPEN STOREYSSTOREYS RC moment resisting frame buildings, which have open storey(s) may be fl ibl d kflexible and weak

In such buildings, suitable measures shall be adopted , which increase both stiffness and strength of the open storeystiffness and strength of the open storey

These measures shall be taken in both the principal directions

The said increase may be achieved by providing (i) RC structural walls, and (ii) braced frames in selected bays

Wh RC t t l ll id d th d i d h th t thWhen RC structural walls are provided, they are designed such that the building does NOT have (i) additional torsion irregularity, (ii) lateral stiffness in open storey is less than 80% of that in storey above and (iii) lateral strength in the open storey(s) is less than 90% of that in the storey above.

RC wall plan density of the building should be at least 2% along each i i l di ti i i i III IV d Vprincipal direction in seismic zones III, IV and V.

The structural walls shall be designed and detailed with the requirement of IS 13920

39

IS 13920.

EQUIVALENT STATIC METHOD

D i B Sh (L t l F )

EQUIVALENT STATIC METHOD

WAV

Design Base Shear (Lateral Force)

)/)(2/( SZ

WAV hB =

)/()/)(2/(

IRgSZA a

h =

Distribution of Base Shear – lateral force

∑= N

iiBi

hWVQ

2

2

∑=j

jj hW1

2

40

FUNDAMENTAL NATURAL PERIODThe approximate fundamental natural period of vibration for momentresisting frame building without brick infill panels in seconds is given by

aT

i) ⎪⎨

⎧

= buildingMRFCompositeSteel-RCfor0800building MRF RCfor 075.0

75.0

75.0

hh

T)⎪⎩

⎨=building MRF Steelfor 085.0

buildingMRFCompositeSteel-RCfor 080.075.0h

hTa

iii) for building with RC structural walls

hhT 09.0075.0 75.0aTaT

⎤⎡ ⎪⎫⎪⎧ ⎞⎛N 2

dh

AhTw

a09.0075.0

≤=

∑= ⎥

⎥⎦

⎤

⎢⎢⎣

⎡

⎪⎭

⎪⎬⎫

⎪⎩

⎪⎨⎧

⎟⎠⎞

⎜⎝⎛+=

wN

i

wiwiw h

LAA

1

2

2.0

iii) for all otherhTa

09.0=

41

da

DESIGN LATERAL FORCEB ildi h ll b d i d f th d i l t l f i bVBuildings shall be designed for the design lateral force given byBV

WAV hB = hB

Buildings should be designed for at least for Minimum Design Earthquake Horizontal Lateral Force (Clause 7 2 2)

Seismic Zone Percent

Earthquake Horizontal Lateral Force (Clause 7.2.2)

Percent

(1) (2)II 0 7

(3)0 50

mH 120≤ mH 200≥

II 0.7III 1.1IV 1.6

0.500.751.25IV 1.6

V 2.41.251.75

42

DEFINITION OF HEIGHT AND BASE WIDTH OF BUILDINGS

43

RESPONSE SPECTRUM METHODRESPONSE SPECTRUM METHODThis method of analysis is based on the dynamic response of the buildingid li d h i l d d iff i i i h hidealized as having a lumped mass and stiffness in various storeys with eachmass having one degree of freedom, that of lateral displacement in thedirection under consideration. Response in each mode is determined byusing the following relationship

Design lateral force at each floor

where design horizontal acceleration spectrum value using the natural

ikikikik WPAQ φ=

Awhere, = design horizontal acceleration spectrum value using the naturalperiod of vibration of mode k.

= mode shape coefficient at floor i in mode k

ikA

φ = mode shape coefficient at floor i in mode k= modal participation factor of mode k

iki

N

Wφ∑

ikφkP

=

= seismic weight of floor i

[ ]21

1

iki

N

i

i

W φ∑

∑

=

=

W = seismic weight of floor i

44

iW

b Modal Mass of mode k is given byb. Modal Mass of mode k is given by2

iki

N

Wϕ∑ ⎥⎦

⎤⎢⎣

⎡

[ ]21

1

iki

N

i

i

WgM

φ∑=

= ⎦⎣=

c. Storey shear forces in each modeN

QV ∑

d d l b

jkij

ik QV ∑+=

=1

d. Modal combination

The peak response quantities (e.g., storey forces, storey shears, andb ) h ll b b d l dbase reactions) shall be combined as per Complete QuadraticCombination (CQC) method

45

MODE COMBINATIONSMODE COMBINATIONSAccording to this method the total response is obtained as

jiji

r

j

r

iλρλλ ∑∑

==

=11

λwhere, is the response quantity in mode i, and

is the response quantity in mode j

iλ

λ is the response quantity in mode jjλ

( ) 5.12 18 ββς +

r = number of modes considered

( )( ) ( )22222 141 ββςβ

ββςρ++−

=ij

r = number of modes consideredς = modal damping ratio

= frequency ratioβ = frequency ratioβ

46

MODE COMBINATIONSMODE COMBINATIONSAlternatively, the peak response quantities may be combined by:y p p q y y

Square Root of Sum of Squares (SRSS) method: is applied when the building does not have closely spaced modes, then the peak quantity (λ) due to all modes considered shall be obtained as

[ ]2r

λλ ∑where, λk = absolute value of quantity in mode k

[ ]21

kk

λλ ∑=

=

r = number of modes being considered

Absolute sum (ABSSUM) rule: if the building has a few closely spacedAbsolute sum (ABSSUM) rule: if the building has a few closely spaced modes, then the peak response quantity (λ*) due to these modes shall be obtained as

where the summation is for the closely spaced modes (λ*) is then combined c

cλλ ∑=

47

with those of the remaining well separated modes by the SRSS method.

3. Lateral forces at each storey due to all modes yconsidered:

1+−= iii VVF

roofroof VF =

where, = shear at the ith floor

ff

iV

In either method the design base shear ( ) shall becompared ith base shear ( ) calc lated sing

BVcompared with base shear ( ) calculated using fundamental period . Where is less than , all the response shall be multiplied by

BV

VV /BVaT BV

the response shall be multiplied by BB VV /

48

Determination of mode shape coefficient (φir)

A popular method for determination of the fundamental mode is theit ti St d l M th d Th ti f ti f f ib tiiterative Stodola Method. The equation of motion for a free vibratingmotion of a multi-storeyed lumped mass can be written as:

…..(a)

i hi h i th di l t i th tiff t i i l ti t

0=+ xKxM &&

in which is the diagonal matrix, the stiffness matrix in relation tolateral displacement and, and are displacement vectorcorresponding to storey displacement and acceleration vector

M Kx&& x

corresponding to storey displacement and acceleration vectorcorresponding to storey acceleration matrices, respectively. Assumingthe free vibration is simple harmonic,

…..(b)tx ωφ sin=

represents the shape of vibrating system, which does not changewith time but varies only with amplitude, represents circularf f th t

φω

frequency of the system.49

Equation (a) can be written asEquation (a) can be written as,

02 =+− φφω KMwhich can be solved to

whereφφ 1=MG

1−= KG

this equation is of the form

φω

φ 2=MG

this equation is of the form

xxK λ=

which represents an eigen value problem whose solution leads toevaluation of natural frequency and corresponding mode shape. Knowingω the fundamental period for mode can be computed as:ω, the fundamental period for mode can be computed as:

2π=T

11 ω

=T

50

DAMPINGDAMPING(Clause 7.2.4)

The value of damping shall be taken as 5 percent of critical damping for the purposes of estimating in the D i L t l F f b ildi i ti f thDesign Lateral Force of a building irrespective of the material of construction (namely steel, reinforced concrete, masonry, or a combination thereof of these , y,three basic materials).

Thi i i il b th b ildi iThis is primarily because the buildings experience inelastic deformations under design level earthquake effects, resulting in much higher energy dissipation , g g gy pthan that due to initial structural damping in buildings.

Thi l f d i h ll b d i ti fThis value of damping shall be used, irrespective of the method of the structural analysis employed, namely Equivalent Static Method or Dynamic

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y q yAnalysis Method

DYNAMIC ANALYSIS

Linear dynamic analysis shall be performed to obtain the design

DYNAMIC ANALYSIS

Linear dynamic analysis shall be performed to obtain the design

lateral force for all building other than regular buildings lower than 15

i i i IIm in seismic zone II.

Dynamic analysis may be performed either by time history method or

by the response spectrum method. In either method the design base

shear shall be compared with base shear calculated using BV BVp g

fundamental period . Where is less than, , all the response

quantities (for example member forces displacements storey shearBV

B B

BVaTquantities (for example member forces, displacements, storey shear

and base reactions) shall be multiplied by BB VV

Time history method shall be based on an appropriate ground motion

preferably compatible with design response spectrum

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INTER STOREY DRIFTINTER STOREY DRIFTStorey drift in any storey shall not exceed 0 004 times theStorey drift in any storey shall not exceed 0.004 times thestorey height under the action of design base shear with noload factorsload factors

Separation between adjacent units

2211 Δ+Δ=Δ RR

Where is the reduction factor and is the storeydisplacement

1R 1Δdisplacement

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TORSION OF BUI DINGSTORSION OF BUILDINGS

Provision shall be made for increase in shear forces on the lateral force resisting elements resulting from twisting about the vertical axis of an

funsymmetric building, arising due to eccentricity between the centre of mass and the centre stiffness at all floor levels.

The design eccentricity to be used at floor i shall be taken asdie

or

isidi bee 05.05.1 +=be 050−or

The factor 1.5 represents dynamic amplification factor, while the factor

isi be 05.0−

The factor 1.5 represents dynamic amplification factor, while the factor 0.05 represents the extent of accidental eccentricity. The factor 1.5 need not be used when time history analysis is carried out.

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Assessment of Liquefaction Potential

(i) Relation between CRR and (N1)60 for sand for Mw 7.5 earthquakesq

(ii) Relation between CRR and (qc1N)csfor Mw 7.5 earthquakes

(iii) Relation between CRR and Vs1 for(iii) Relation between CRR and Vs1 for Mw 7.5 earthquakes

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REVISIONS INCORPORATEDDesign spectra defined up to natural period 6.00 sg p p pSame design spectra corresponding to 5% damping are specified for all buildings, irrespective of materialIntroduced intermediate importance category of buildings to consider the density of occupancyBuildings designed for at least a minimum lateral forceAdditional clarity about different types of irregularity of structural

tsystemEffect of masonry infill walls includedN t l i d f b ildi ith b t t b k b ildi dNatural period of buildings with basement, step back buildings and buildings on hill slopes includedSimplified procedure for evaluating liquefaction potential is addedSimplified procedure for evaluating liquefaction potential is added

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Th kThanks

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