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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.

!"#$% '(%)

!"# $ %& #' (")* &" +#,-.Satyanarayan Gangaram Pitroda

Invent a New India Using Knowledge

/0)"1 &2 324 #' 5 *)6Jawaharlal Nehru

Step Out From the Old to the New

7"#1&"8+9&"), 7:1&"8+9&")Mazdoor Kisan Shakti Sangathan

The Right to Information, The Right to Live

!"# %& ;

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875 ( Part 4 )1987

Reaffirmed 1997 )

Indian Standard

CODE OF PRACTICE FORDESIGN LOADS ( OTHER THAN EARTHQUAKE )

FOR BUILDINGS AND STRUCTURESPART 4 SNOW LOADS

(Second Revision).

Fourtll Rcprjnt OCTOBER 1997

UDC 624 042 42 :

006.7

Copyright 1988

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

NEW DELHI 110002

Gr 4 October 1988

( Reaffirmed 2003 )

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fn i n

Standard

CODEOFPRACTICE

IS:875 Bart4 -1987

FOR

DESIGNLOADS(OTHERTHANEARTHQUAKE)FORBUILDINGSAND STRUCTURES

PART 4 SNOW LOADS

(Second Revision)

0. F O R E W O R D

0.1 This Indian Standard ( Part4 ) ( SecondRevision ) was adopted by the Bureau of IndianStandards on 9 November 1987, after the draft

finalized 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; andcompliance with hygienic, sanitation, ventilationand daylight standards. The design of the build-ing is dependent upon the minimum requirements

prescribed for each of the above functions. Theminimum requirements pertaining to the structuralsafety of buildings 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 not only ensure thestructural safety of the buildings which are beingdesigned and constructed in the country andthereby reduce the hazards to life and propertycaused by unsafe structures, but also eliminate thewastage caused by assuming unnecessarily heavyloadings. Notwithstanding what is stated regardingthe structural safety of buildings, the application ofthe provisions should be carried out by compe-tent and responsible structural designer who would

satisfy himself that the structure designed inaccordance with this code meets the desiredperformance requirements when the same iscarried out according to specifications.

0.3 This Code was first published in 1957 for theguidance of civil engineers, designers and archi-tects associated with the planning and design of

buildings. It included the provisions for thebasic design loads ( dead loads, live loads, windloads and seismic loads ) to be assumed in thedesign of buildings. In its first revision in 1964,the 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 Meteo-rological Department. In addition to this, newclauses on wind loads for butterfly type structures

were included; wind pressure coefficients forsheeted roofs, both curved and sloping, weremodified; 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 the pro-visions on live load values adopted for differentoccupancies. Simultaneously live loads surveyshave been carried out in America, Canada andother countries to arrive at realistic live loads

based on actual determination of loading( mov-able and immovable ) in different occupancies.Keeping this in view and other developments inthe field of wind engineering, the Sectional Com-mittee responsible for the preparation of thisstandard has decided to prepare the secondrevision in the following five parts:

Part 1 Dead Loads

Part 2 Imposed Loads

Part 3 Wind Loads

Part 4 Snow Loads

Part 5 Special Loads and Load Combinations

Earthquake load is covered in IS :1893-1984

which should be considered along with the aboveloads.

0.3.2 This part ( Part 4 ) deals with snow loadson roofs of buildings.

The committee responsible for 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 effected

by snow-fall, In due course the characteristic

*Criteria for earthquake resistant designing of strue-trues (fourth revision .

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IS:875 Part4 -1987

snow load on ground for different regions will Basis for design of structures Determinationbe included based on studies. of snow loads on roofs, issued by the Interna-

0.4 This part is based on IS0 4355-198 ( E )tional Organization for Standardization.

1. SCOPE

1.1 This standard (Part 4) deals with snow loads

on roofs of buildings. Roofs should be designedfor the actual load due to snow or for the posedloads specified in Part 2 Imposed loads, whicheveris more severe.

NOTB -Mountainous regions in northern parts ofIndia are subjected to snow-fall.

In India, parts of Jammuand Kashmir ( BaramulahDistrict, Srinagar District, Anantnag District andLadakh District ; Punjab, Himachal Pradesh( Chamba, Kulu, Kinnaur District, Mahasu District,Mandi District, Sirmur District and Simla District ;and Uttar Pradesh ( Dehra Dun District, Tehri GarhwalDistrict, Almora District and Nainital District ) experi-ence snow-fall of varying depths two to three times ina year.

2. NOTATIONS

3.

3.1

p ( Dimensionless) Nominal values of theshape coefficients, tak-ing into account snowdrifts, sliding snow,etc, with subscripts, ifnecessary.

Ij ( in metres Horizontal dimensionswith numerical sub-scripts, if necessary.

hj ( in metres ) Vertical dimensionswith numerical sub-

. scripts, if necessary.

fii (in degrees) Roof slope.

so (in pascals ) Snow load on ground.

SI ( in pascals ) Snow load on roofs.

SNOW LOAD IN ROOF (S)

The minimum design snow load on a roofarea or any other area above ground which issubjected to snow accumulation is obtained bymultiplying the snow load on ground, s by the

shape coefficient L as applicable to the particularroof area considered.

S=c(S0

where

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

p= shape coefficient ( see 4),and

so= ground snow load in Pa( 1 Pa = lN/ma .

NOTE Ground snow load at any place depends onthe critical

combinati.m

of the maximum depth of un-disturbed aggregate cumulative snow-fall and itsaverage density. In due course the characteristic snowload on ground for different regions will be included

based on studies. Till such time the users of thisstandard are advised to

contanct

either Snow andAvalanches Study Establishment ( Defence Researchand Development Organization ) Manali ( HP) orIndian Meteorological Department ( IMD Pune inthe absence of any specific information for anylocation.

4. SHAPE COEFFICIENTS

4.1 General Principles

In perfectly calm weather, falling snow wouldcover roofs and the ground with a uniform blanketof snow and the design snow load could be

consi-

derd as .a uniformly distributed load. Truly uni-form 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 accompanied

or followed by winds. The winds will redistributethe snow and on some roofs, especially multi-level 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 far sufficient data are not available to deter-mine the shape coefficient in a statistical basis.Therefore, a nominal value is given. A representa-tive sample of

rcof

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 direction

parallel to the eaves is assumed to be uniform.

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4.2 Shape Coefficients for Selected Types of Roofs

4.2.1 Simple Flat andMonopitch Roofs

Simple Pitched Roofs(Positive Roof Slope)*

p, =0.8

4.2.2 Simple or Multiple Pitched Roofs(Negative Roof Slope)

Two-Span or MultispanRoofs

o

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4.2.3 Simple Curved Roofs

The following se s 1 and 2 must be examined:

CASE 2

Restriction:

h6

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4.2.4 Multilevel Roofs*

91

=08

s= s+

where

A- due to sliding

pw

-

due to wind

1,

= 2htbut is restricted as follows:

SmCls19 :

ps is determined from an additional load amounting to SO percent of the maximum totalload on theadjacent slope of the upper roofs and is distributed linearly as shown on the figure.

B