Modification of IS code 1893

8/13/2019 Modification of IS code 1893

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Modifications in IS 1893Criteria For Earthquake Resistan

Design Of Structures

Presented By:

Arvind Thakur (801222001)Jaskaran Singh (801222006)

Salman Siddique (801222016)

Vipin Sharma (801222022)


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Disaster Vulnerability and Mitigation

India is one of the most disaster prone countries, vulnerablealmost all natural and man made disasters. About 85% areavulnerable to one or multiple disasters and about 57% area seismic zone including the capital of the country. Disaster prinvolves engineering intervention in buildings and structurethem strong enough to withstand the impact of natural haza

impose restrictions on land use so that the exposure of the the hazard situation is avoided or minimized.


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Himalayan-Nagalushai region, Indo-Gangetic plain, WesternKutch and Kathiawar regions are geologically unstable parts country and some devastating earthquakes of the world hav

occurred there. A major part of peninsular India has also beby strong earthquakes, but these were relatively few in numhad considerably lesser intensity. It has been a long felt neerationalize the earthquake resistant design and constructionstructures taking into account seismic data from studies of tearthquakes. It is to serve this purpose, Bureau of Indian Stahas rendered invaluable services by producing a number of standards in the field of Design and Construction of EarthquResistant Structures and also in the field of measurement anconnected therewith.


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Introduction to IS 1893

This standard contains provisions that are general in nature applicable to all structures. Also, it contains provisions that specific to buildings only. It covers general principles and decriteria, combinations, design spectrum, main attributes of dynamic analysis, apart from seismic zoning map and seismcoefficients of important towns, map showing epicentres, m

showing tectonic features and lithological map of India.

The first Indian seismic code (IS 1893) was published in 196has since been revised in 1966, 1970,1975,1984 and 2002.


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Bhuj Earthquake

2001 Gujarat earthquake was a wake up call for many seismchanges and modifications in building codes after 18 years.

t


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osop ca c anges n t e newcode Seismic zone map is revised with only four seismic zones. Zo

upgraded to Zone II. Killari area is enhanced to Zone III. Bellaisolated zone is removed. East coast is enhanced to Zone III

connected with Zone III of Godavari Graben area.

IS 1893:1984

IS 1893:2002


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Seismic zone factor is changed reflecting more realistic valueground acceleration.

Zone Factors as per IS 1893:1984

S.

NoZone No.

Seismic

Coefficient

method

Response

Spectrum

method

1 V 0.08 0.40

2 IV 0.05 0.25

3 III 0.04 0.20

4 II 0.02 0.10

5 I 0.01 0.05

Zone Factors as per IS 189

S.

NoZone No.

Seismic

Intensity

1 II Low

2 III Moderate

3 IV Severe

4 V Very severe


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Response acceleration spectra are now specified for three tyfounding strata viz. Hard, Medium and Soft. In older versionaverage acceleration spectra is mentioned.

As Per IS 1893:1984 As Per IS 1893:2002


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The design spectrum shape now depends on the type of soil and thfoundation-soil factor () has been dropped. Instead a clause has bintroduced to restrict the use of foundation vulnerable to differentsettlement in severe seismic zones.

As Per IS 1893:1984The value of shall be taken as

As Per IS 1893:20The use of foundations vulnsignificant differential settleto ground shaking shall be astructures in seismic ZonesIn seismic Zones IV and V, i

spread footings or pile capsinterconnected with ties, exindividual spread footings asupported on rock.

S.no Type of

soil

Piles

passing

through

any soil

but

resting

on Type

1

Piles

not

covered

Raft

Foundatio

n

Combine

d or

Isolated

RCC

footings

with tie

beams

Isolated

RCC

footings

without

tie

beams

Well

Foundatio

n

1 Type I

Rock or

hard soils

1.0 1.0 1.0 1.0 1.0

2 Type II

Medium

soils

1.0 1.0 1.0 1.0 1.2 1.2

3 Type III

Soft

soils

1.0 1.2 1.0 1.2 1.5 1.5


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Empirical expression for estimating the fundamental naturaof multi-storeyed buildings with regular moment resisting frbeen revised.

= 0.1 (as per IS 1893:1984)

n= number of storeys including basement.

(Taas per IS 1893:2002)

= 0.075. .

= 0.085. .

h=Height of building, in m. This excludes the bastoreys, where basement walls are connected with the groundeck or fitted between the building columns. But it includes tbasement storeys, when they are not so connected.


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The concept of response reduction due to ductile deformatiofrictional energy dissipation in the cracks is brought into the explicitly, by introducing the response reduction factor in plearlier performance factor.

As Per IS 1893:1984 As Per IS 1893:20S.No Lateral Load Resisting System

1 Ordinary RC moment-resisting frame ( OM

2 Special RC moment-resisting frame ( SM

3 Steel frame with

a) Concentric braces

b) Eccentric braces

4 Steel moment resisting frame designed as p

5 Load bearing masonry wall buildings)

a) Unreinforced

b) Reinforced with horizontal RC band

c) Reinforced with horizontal RC bands and v

bars at corners of rooms and

jambs of openings

6 Ordinary reinforced concrete shear wa

7 Ductile shear walls

8 Ordinary shear wall with OMRF

9 Ordinary shear wall with SMRF

10 Ductile shear wall with OMRF

11 Ductile shear wall with SMRF

S.No STRUCTURAL FRAMING SYSTEM VALUES OF

PERFORMANCE

FACTOR, K

1 Moment resistant frame with appropriate

ductility in reinforced concrete

or steel

1.0

2 Frame as above with R. C. shear

walls or steel bracing members designedfor ductility

1.0

3 Frame with either steel

bracing members or plain or

nominally reinforced concrete infill

panels

1.3

4 Frame in combination

with masonry infills

1.6

5 Reinforced concrete framed buildings 1.6


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The code now requires that there be a minimum design force basempirical fundamental period(Ta) of the building even if the dynaanalysis gives a very high value of natural period and thus low sei

As per IS 1893:1984

=

VB = Base shear

K= Performance factor

C= Coefficient defining the

flexibility of structure

h= Design seismic coefficient

W= D.L+L.L

As per IS 1893:20

=

VB= Base shear

Ah= Design horizontal acc

spectrum valueW= Seismic weight of the


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Torsional eccentricity values have been revised upwards inserious damages observed in buildings with irregular plans

As per IS 1893:1984

Provision shall be made for theincrease in shear resulting from thehorizontal torsion due to aneccentricity between the centre ofmass and the centre of rigidity. Thedesign eccentricity shall be taken as

1.5 times the computed eccentricitybetween the centre of mass and thecentre of rigidity. Negative torsionalshears shall be neglected.

As per IS 18

The design eccen = 1.5

Or =

Whichever

= Static Eccentric

= Floor plan dime

In case of irregular beccentricity of 0.0


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Modal combination rule in dynamic analysis of buildings hrevised.

As Per IS 1893:20

Regular buildings Th

greater than 40m in heZones IV and V and thogreater than 90m in heZones II and III.

Irregular buildings A

buildings higher than 1Zones IV and V and thogreater than 40m in heZones II and III.

As per IS 1893:1984Building Height Seismic zones Recommended Method

Greater than 40 m III, IV and V Detailed dynamicanalysis

Greater than 90 m I and II Modal analysis using

response spectrum

method

Greater than 40 m and

up to 90 m

All zones Modal analysis using

response spectrum

method. (Use of

seismic coefficientmethod permitted for

zone I, II and III)

Less than 40 m All zones Modal analysis using

response spectrum

method.(Use of seismic

coefficient

method permitted in all

zones)


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Editorial and Typographical Errors Direction of horizontal ground motion in design (Clause 6.3.

A minor typographical error in this Clause needs to be correct

replacing direction at time by "direction at a time. Fundamental natural period (Clause 7.6.2)

In first printing of the code, in equation T = 0.09h/(d), the tewas missed and this should be corrected. In this Clause brickpanels should be replaced by masonry infill panels

Clause 7.8.1

There is a typographical error in section (b) in Clause 7.8.1. Abuildings higher than 12m. should be replaced by All buildhigher than 12m.


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Modal combination (Clause 7.8.4.4)

In the equation for CQC method, there is a typographical errofirst printing of the code. The equation should be as follows:

Seismic zone map

In first printing of the code, some errors got introduced in the

zone map.

(i) Locations of Allahabad and Varanasi have been interchangemap. Varanasi should be in zone III and Allahabad in zone II.

(ii) Kolkata is shown in zone IV, it should be in zone III.


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References

Indian standard criteria for earthquake resistant design of stIS 1893 : 1984, Bureau of Indian Standards, New Delhi.

Indian standard criteria for earthquake resistant design of stIS 1893 : (Part 1) 2002, Part 1 General Provisions and BuildinRevision), Bureau of Indian Standards, New Delhi.

Jain SK and Murty SVR, Proposed Changes in Indian SeismicCode,IS:1893 (Part 1) 2002. IITK-GSDMA Project on Building

Jain SK, Review of Indian seismic code, IS 1893 (Part 1) : 20Indian Concrete Journal (November 2003)


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Modification of IS code 1893