Introduction on

IS 1893 (Part-1) : 2002

Dr. S. K. Prasad

Professor of Civil Engineering

S. J. College of Engineering, Mysore

prasad_s_k@hotmail.com

Revised IS Code for Earthquake Resistant Design of Structures

IS 1893 (Part 1) : 2002

INDIAN STANDARDS FOR EARTHQUAKE DESIGN

IS : 1893 – 2002 Criteria For Earthquake Design of Structures

IS : 4326 – 1976 Code Of Practice For Earthquake Resistant Design And Construction of Buildings

IS : 13920 – 1993 Code Of Practice For Ductile Detailing Of Reinforced Concrete Structures Subjected To Seismic Forces

SP: 22 Explanatory Handbook on Codes For Earthquake Engineering

Different Parts of IS:1893

Part 1 General Provisions and Buildings

Part 2 Liquid Retaining Tanks– Elevated and Ground Supported

Part 3 Bridges and Retaining Walls

Part 4 Industrial Structures Including Stack Like Structures

Part 5 Dams and Embankments

1. Specifies Seismic Design Force

2. Seismic requirements for Design,Detailing and Construction are coveredin other codes, e.g., IS:4326, IS:13920,

3. For an Earthquake Resistant Structure,one has to follow IS:1893 (Part-1)together with Seismic Design andDetailing Codes.

What does IS:1893 Cover?

Seismic Zonation of India

Zone Factors for Indian Cities

City Zone Factor City Zone Factor

Mysuru II 0.10 Bhuj V 0.36

Bangalore II 0.10 Port Blair V 0.36

Delhi IV 0.24 Srinagar V 0.36

Mangalore III 0.16 Roorkee IV 0.24

Ahmadabad III 0.16 Gulbarga III 0.16

Mumbai III 0.16 Bijapur III 0.16

Kolkata III 0.16 Goa III 0.16

Belgaum III 0.16 Chennai III 0.16

Dharwad III 0.16 Kochi III 0.16

Seismic Hazard & Zone Factor

Zone Shaking Intensity

Zone Factor (Z)

II VI (and Lower)Low

0.10

III VIIModerate

0.16

IV VIIISevere

0.24

V IXCatastrophic

0.36

MAGNITUDES OF PAST EARTHQUAKES

S No

Year Earthquake Magnitude

1 1897 Assam earthquake 8.7

2 1938 Bihar – Nepal earthquake 8.4

3 1950 Assam – Tibet earthquake 8.7

4 1967 Koyna earthquake 6.5

5 1988 Bihar – Nepal earthquake 6.6

6 1991 Uttarkashi earthquake 6.6

7 1993 Latur earthquake 6.4

8 1997 Jabalpur earthquake 6.0

9 1999 Chamoli (UP) earthquake 6.8

10 2001 Bhuj (Gujarat) earthquake 7.9

Major modifications

1. Zone I is merged with Zone II.

2. Values of seismic zone factors are changed considering MCE & service life of structure.

3. Response spectra are specified for THREE types of soils - Rock & Hard Soil, Medium Soil and Soft Soil.

4. Empirical equations for time period of multi storeyed buildings is revised.

Assumptions in IS 1893 – Part 1

1. Resonance will not occur during earthquake as the force is random & impulsive, not steady state.

2. Earthquake does not occur simultaneously with maximum wind, flood or sea wave.

3. Static properties (modulii, strength etc.) represent behavior during earthquake.

Load Combinations

• Steel Structures– 1.7(DL + LL)– 1.7(DL ± EL)– 1.3(DL + LL ± EL)

• RCC and PSC Structures– 1.5(DL + LL)– 1.2(DL + LL ± EL)– 1.5(DL ± EL)– 0.9DL ± 1.5EL

• Combination for 3 component motion– ±ELx±0.3ELy±0.3Elz– ±ELy±0.3ELz±0.3Elx– ±ELz±0.3ELx±0.3Ely

BASIS OF SEISMIC COEFFICIENT METHOD

VB = m aVB = (W/g) aVB = W (a/g)VB = W Ah

Ah = Basic horizontal seismic coefficientVB = Base shearW = Total weight of the structurea = Acceleration induced at the base during

earthquakeg = Acceleration due to gravity

R

I

g

SZA

WAV

ah

hB

..2

• Z=Zone Factor

• Ss/g = Spectral Acceleration taken fromResponse Spectrum

• I= Importance Factor

• R=Ductility/Over-Strength Reduction Factor

CALCULATION OF SEISMIC FORCE

Zone factor Z is for MCEFor DBE, it is Z/2

Damping percentage

0 2 5 7 10 15 20 25 30

Factors 3.2 1.4 1.0 0.9 0.8 0.7 0.6 0.55 0.5

Table 3 : Multiplication factor for Sa/g at other dampings

SlNo

Structure Importance Factor

1 Service, Community & Emergency Buildings (Hospital, School, Monument, Telephone exchange, Television / Radio Station, Fire station, Railway station, cinema hall, power station etc)

1.5

2 All other buildings 1.0

Table 6 : Importance Factor, I

SlNo

Lateral Load Resisting System R

1 Ordinary RC Moment Resisting building Frame (OMRF) 3

2 Special RC Moment Resisting building Frame (SMRF) 5

3 Steel frame with concentric braces 4

4 Steel frame with eccentric braces 5

5 Steel moment resisting frame designed as per SP6 5

6 Load bearing unreinforced masonry wall building 1.5

7 Load bearing masonry wall building with reinforced horizontal band

2.5

8 Load bearing masonry wall building with reinforced horizontal band & vertical bars at corner

3

9 Ordinary shear wall with OMRF 3

10 Ordinary shear wall with SMRF 4

11 Ductile shear wall with OMRF 4.5

12 Ductile shear wall with SMRF 5

Table 7 : Response Reduction Factor, R for Building Systems

Response spectra for different soil types at 5 % Damping

Fundamental Natural PeriodSl No Description Natural Period (s)

1 R C frame buildings 0.075 h0.75

2 Steel frame buildings 0.085 h0.75

3 Other buildings (eg masonry) 0.09h/√d

4 Earth embankments 2.9H/Vs

For Hard Soil Sa/g = 1+15T when 0≤T≤0.1

For Hard Soil Sa/g = 2.5 when 0.1≤T≤0.4

For Hard Soil Sa/g = 1/T when 0.4≤T≤4

For Medium Soil Sa/g = 1+15T when 0≤T≤0.1

For Medium Soil Sa/g = 2.5 when 0.1≤T≤0.4

For Medium Soil Sa/g = 1.36/T when 0.4≤T≤4

For Soft Soil Sa/g = 1+15T when 0≤T≤0.1

For Soft Soil Sa/g = 2.5 when 0.1≤T≤0.4

For Soft Soil Sa/g = 1.67/T when 0.4≤T≤4

0 1 2 3 4 50.0

0.5

1.0

1.5

2.0

2.5 Rock or Hard Soil

Medium Soil

Soft Soil

Sa/g

Time Period (secs)

Response Spectrum IS : 1893 :2002

R

I

g

SZA

WAV

ah

hB

..2

Structural Response Factor, Sa/g

DAMPING FOR DIFFERENT STRUCTURES

Type of Structure Damping Ratio

Steel structure 2 - 5%

Concrete structure 5 - 10%

Brick structure 5 - 10%

Timber structure 2 - 5%

Earthen structure 10 - 30%

Comprehensive Intensity Scale (MSK 64)

• Type of Structures

– Type A (Rural low quality houses)

– Type B (Ordinary Brick houses)

– Type C (R C Buildings)

• Quantity Definition

– Single, Few 5 %

– Many 50 %

– Most 75 %

Comprehensive Intensity Scale (MSK 64)

• Classification of Building Damage

– Grade 1 (Slight Damage)

– Grade 2 (Moderate Damage)

– Grade 3 (Heavy Damage)

– Grade 4 (Destructive Damage)

– Grade 5 (Total Damage)

• Intensity Scale (M M Scale)

– I to XII

I Insignificant Only detected by instruments

II Very LightFelt by sensitive persons, Oscillation of hanging objects

III Light Small vibratory motion

IV ModerateFelt inside building, Noise produced by moving objects

V Slightly Strong Felt by most persons, some panic, minor damages

VI Strong Damage to non seismic resistant structures

VII Very Strong People panic, serious damage to poor construction

VIII Destructive Serious damage to structures in general

IX RuinousSerious damage to well built structures, almost total destruction of non-seismic resistant structures

X Disastrous Only seismic resistant structures remain standing

XIDisastrous in

ExtremeGeneral Panic, almost total destruction, ground cracks & opens

XII Catastrophic Total destruction

Intensity of Earthquake – Modified Mercalli’s Scale

Ground conditions

Distribution of design force at different floors

Qi = Design lateral force at floor iWi = Seismic weight of floor ihi = Height of floor i measured from baseN = Number of storeys in the buildingVB = Design Base shear

It is impossible to stop or predict earthquake. As engineers, let us all unite and move forward & work for reducing calamities due to natural

and man made hazards