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Disclosure to Promote the Right To Information

Whereas the Parliament of India has set out to provide a practical regime of right to

information for citizens to secure access to information under the control of public authorities,in order to promote transparency and accountability in the working of every public authority,

and whereas the attached publication of the Bureau of Indian Standards is of particular interest

to the public, particularly disadvantaged communities and those engaged in the pursuit of

education and knowledge, the attached public safety standard is made available to promote the

timely dissemination of this information in an accurate manner to the public.

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The Right to Information, The Right to Live

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Knowledge is such a treasure which cannot be stolen

IS 875 (Part 4) (1987, Reaffirmed 2003): Code of Practice

for Design Loads (Other Than Earthquake) For Buildings and

Structures. Part 4: Snow Loads (Second Revision). UDC

624.042.42 : 006.76

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Indian StandardCODE OF PRACTICE FOR

IS 875 (Part 4) : 1987(Reaffirmed 2003)

DESIGN LOADS (OTHER THAN EARTHQUAKE)FOR BUILDINGS AND STRUCTURES

October 1988

PART 4 SNOW LOADS(Second Revision)

Ninth Reprint DECEMBER 2010

UDC 624.042.42 : 006.7

BIS 1988B U R E A U O F I N D IA N S T A N D A R D SMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002Price Group 4

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IS : 875 ( Part 4 ) - 1987Illdian Standard

CODE OF PRACTICE FORDESIGN LOADS (OTHER THAN EARTHQUAKE)FOR BUILDINGS AND STRUCTURES

PART 4 SNOW lOADS

(Seconei Revisiolljo. FOR E W 0 R D

0.1 This lndian Standard (Par t4 ) (SecondRevision) was adopted by the Bureau of IndianStandards on 9 November 1987. after the draftfinalized by the Structural Safety SectionalCommittee had been approved by the CivilEngineering Division Council.0.2 A building has to perform many functionssatisfactorily. Amongst these functions are theutility of the building for the intended use andoccupancy. structural safety, fire safety; an dcompliance with hygienic, sanitation, ventilationand daylight standards. The design of the building is dependent upon the minimum requirementsprescribed for each of the above functions. Theminimum requirements pertaining to the structuralsafety of build ings are being covered in this Codeby way of laying down minimum design loads whichhave to be assumed for dead loads, imposed loads,wind loads, snow loads and other external loads,the structure would be required to bear. Strictconformity to loading standards recommended inthis Code, it is hoped, will no t only ensure thestructural safety of the buildings w h i ~ h are beingdesigned and constructed in the country andthereby reduce the hazards to life and propertycaused by unsafe structures, but also eliminate th ewastage caused by assuming unnecessarily heavy10adinQs. Notwithstanding what is stated regardingthe structural safety of buildings, the application ofthe provisions should be carried out by competent and responsible structural designer who wouldsatisfy himself that the structure designed inaccordance with this code meets the desiredperformance requirements when th e same iscarried out according to speCifications.0.3 This Code was first published in 1957 for theguidance of civil engineers, designers an d architects associated with the planning and design ofbuildings. It included the provisions for th ebasic design loads (dead loads, live ioads, windloads and seismic loads) to be assumed in thedesign of build ings. In its first revision in 1964.th e wind pressure provisions were modified onthe basis of studies of wind phenomenon and itseffects on structures undertaken by the special

committee in consultation with the Indian Meteorological Department. In addition to this, newclauses on wind loads for butterfly type structureswere included; wind pressure coefficients forsheeted roofs, both curved and sloping, weremodifled; seismic load provisions were deleted( separate code having been prepared) and metricsystem of weights and measurements was adopted.

0.3.1 With the increased adoption of the Code,a number of comments were received on th e provisions on live load values adopted for differentoccupancies. Simultaneously live loads surveyshave been carried ou t in America, Canada andother countries to arrive at realistic live loadsbased on actual determination of loading ( movable and immovable) in different occupancies.Keeping this in view and other developments inthe field of wind engineering, the Sectional Committee responsible for the preparation of thisstandard has decided to prepare the secondrevision in the follOWing five parts:

Part 1 Dead LoadsPart 2 Imposed LoadsPart 3 Wind LoadsPart 4 Snow LoadsPart 5 Special Loads and Load CombinationsEarthquake load is covered in IS : 1893-198-t*which should be considered along with the above

loads.0.3.2 This part ( Part 4 ) deals with snow loads

on roofs of buildings.The committee responsibJe fo r the prepara

tion of the code while reviewing the availablesnow-fall data, felt the paucity of data on whichto make specific recommendations on the depthof ground snow load for different regions effectedby snow-fall. In due course the characteristic

.Criteria for earthquake resistant designing of structrues (fourth revision ).

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IS : 875 ( Part 4 ) - 1987snow load on ground for diffe rent regions willbe included based on studies.0.4 This part is based on ISO 4355-1981 (E )

1. SCOPE1.1 This standard (Part 4 ) deals with snow loadson roofs of buildings. Roofs should be designedfor the actual load due to snow or for the imposedloads specified in Part 2 Imposed loads, whicheveris more severe.

NOTE --- Mountainous regions in northern parts ofIndia are subjected to snow-fall.In India, parts of Jammu and Kashmir ( BaramulahDistrict, Srinagar District, Anantnag District andLadakh District); Punjab, Himachal Pradesh( Chamba, K ulu, Kinnaur District, Mahasu District,

Mandi District, Sirmur District and Simla District);and Uttar Pradesh ( Dehra Dun District, Tehri GarhwalDistrict, Almora District and Nainital District) experience snow-fall of va rying depths two to three times ina year.2. NOTATIONS

I-' ( Dimensionless) - Nominal values of theshape coefficients, taking into account snowdrifts, sliding snow,etc, with subscripts, ifnecessary.

h ( in metres) - Horizontal dimensionswith numerical sub-scripts, if necessary.hi ( if} metres) - Vertical dimensionswith numerical sub-scri pts, if necessary.

(i n degrees) - Roof slope.So ( in pascals) - Snow load on ground.SI ( in pascals) - Snow load on roofs.

3. SNOW LOAD IN ROOF (S)3.1 Th e minimum de"ign snow load on a roofarea or any other area above ground which issubjected to snow accumulation is obtained bymUltiplying the snow load on ground, So by theshape coefficient 1-', as applicable to the particularroof area considered.

S = I-' SQ

'Basis for design of structures - Determinationof snow loads on roofs', issued by the International Organization for Standardization.

wheres = design snow load in Pa on plan areaof roof,

I-' = shape coefficient ( see 4) , andSo = ground snow load in Pa( 1 Pa = IN/m!!).

NOTE - Ground snow load at any place depends onthe critical combination of the maximum depth of undisturbed aggregate cumulative snow-fall and itsaverage density. In due course the characteristic ~ n o wload on ground for different regions will be inCludedbased on studies. Till such time the users of thisstandard are advised to contanct either Snow andAvalanches Study Establishment (Defence Researchand Development Organizatio n) Manali ( H P) orIndian Meteorological Department ( IMD), Pune inthe absence of any specific information for anylocation.

4. SHAPE COEFFICIENTS4.1 General Principles

2

In perfectly calm weather, falling snow wouldcover roofs and the ground with a uniform blanketof snow and the design snow load could be considerd as a uniformly d istributed load. Truly uniform loading conditions, however, are rare andhave usually only been observed in areas that aresheltered on all sides by high trees, buildings, etc.In such a case, the shape coefficient would beequal to untiy.In most regions, snow falls are accompaniedor followed by winds. The winds will redistributethe snOW and on some roofs, especially multilevel roofs, the accumulated drift load may reacha multiple of the ground load. Roofs which aresheltered by other buildings, vegetation, etc, maycollect more snow load than the ground level.The phenomenon is of the same nature as thatillustrated for multilevel roofs in 4.2.4.So fa r sufficient data are not available to deter

mine the shape coefficient in a statistical basis.Therefore, a nominal value is given. A representative sample of Toof is shown in 4.2. However, inspecial cases such as strip loading, cleaning of theroof periodically by deliberate heating of the roof,etc, have to be treated separately.The distribution of snow in the directionparallel to the eaves is assumed to be uniform.

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4.2 Shape Coefficients for Selected Types of Roofs4.2.1 Simple Flat and

4.2.2

Monopitch Roofs~flt

I

tO O < f J ~ 3 0 o

1 S o < ~ ~ 3 0 1A1 = O'B

30o

'2= l'SpA,:: (}

i

*For asymmetrical simple pitched roofs, each side of the roof shall be treated as one half of correspondingsymmetrical roofs. 3

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IS : 875 ( Part 4 ) 19874.2.3 Simple Curved Roofs

The following cases 1 and 2 must be examined:

Restriction:/1s ~ 2'3/1 = 0 if (3 > 600

4

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4.2.4 Multilevel Roofs'"

/11 = 0'8/1a = J.ls + J.lw

where/18 = due to slidingIlw = due to wind

la = 2ht but is restricted as follows:5 m < la < 15 m

I} + fa khJ.lw = --ffl < -s;;-with the restriction 0'8 < Ilw .;;;: 4'0

whereh is in metresSo is in kilopascals ( kilonewtons pe r square metre)k = 2 kN/ma

IS : 875 ( Part 4 ) - 1987

> 15 : Jis is determined from an additional load amounting to 50 percent of the maximum total load on theadjacent slope of the upper rooft, and is distributed linearly as shown on the figur e,

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IS : 875 ( Part 4 ) - 19874.2.5 Complex Multilevel Roofs

I = 2h l: Is = 2hs: /11 = O'SRestriction:

5 m < 13

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IS : 875 ( Part 4 ) - 19874.2.6 Roofs with Local Projections an d Obstructions

wherekh11, = - o

h is in met resSo is in kilopascals (kilonewtons per square metre)k = 2 kNjm3fl.l = 0-81= 21z

Restrictions:0'8 < l1a

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IS : 875 ( Part 4 ) - 1987APPEND IX A

( Clauses 4.2.4 and 4.3 )SHAPE COEFFICIENTS FOR MULTILEVEL ROOFS

A more comprehensive formula for the shape coefficient for multilevel roofs than thatgiven in 4.2.4 is as follows:........___ .., WIND DIRECTIONS

1Jlw = 1 + -h - ( ml 11 + ma I. )( II - 2 h )Jl1 = 0'8I. = 2 h(h and I being in metres)

Restriction :

wherekhPw