IS 1893 (Part 4): Criteria for Earthquake Resistant Design of Structures, Part 4: Industrial Structures Including Stack-Like Structures

2005·2.1 MB·English

by  Bureau of Indian Standards (BIS)

इंटरनेट मानक
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.
“जान1 का अ+धकार, जी1 का अ+धकार” “प0रा1 को छोड न’ 5 तरफ”
Mazdoor Kisan Shakti Sangathan Jawaharlal Nehru
“The Right to Information, The Right to Live” “Step Out From the Old to the New”
IS 1893 (Part 4) (2005): Criteria for Earthquake Resistant
Design of Structures, Part 4: Industrial Structures
Including Stack-Like Structures. ICS 91.120.25
“!ान $ एक न’ भारत का +नम-ण”
Satyanarayan Gangaram Pitroda
““IInnvveenntt aa NNeeww IInnddiiaa UUssiinngg KKnnoowwlleeddggee””
“!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता हहहहै””ै”
Bhartṛhari—Nītiśatakam
“Knowledge is such a treasure which cannot be stolen”

IS 1893 (Part 4) : 2005
717 '? m4 4F1 Cf)
~~~=q~I3TI ~ ~Cf)Rlxlm RS\J1I~~ ~ Jil~~~
+JTTT 4 3ft ~l rTI CJ) ~1 '< =q rt I ~, "ifC,C T ~ '(1,<:q;<j I ~
Indian Standard
CRITERIA FOR EARTHQUAKE RESISTANT
DESIGN OF STRUCTURES
PART 4 INDUSTRIAL STRUCTURES INCLUDING
STACK-LIKE STRUCTURES
(Second Reprint SEPTEMBER 2008)
ICS 91.120.25
© BIS 2005
BUREAU OF INDIAN STANDARDS
MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELH1 110002
A llgllst 2005 Price Group 9
E(lrthquake Engineering Sectional Committee, CED 39
FC)REWORD
'fhis Indian Standard (Part 4) was adopted by the Bureau of Indian Standards, aftcr the draft finalized by the
Earthquake Engineering Sectional Committee had been approved by the Civil Engineering Division CounciL
H imalayan-Naga Lushai region, Indo-Gangetic Plain, Western India, Kutch and Kathiawar regions arc geologically
unstable parts of the country \vhere some devastating earthquakes of the world have occurred. A major part of
the peninsular India has also been visited by strong earthquakes, but these \vere relatively few in number occurring
at rnllch larger time intervals at any site, and had considerably lesser intensity. The earthquake resistant design
ofstTucturCS, taking into accollnt seismic data from studies of these Indian earthquakes, has become very essential,
particularly in view of heavy construction programme at present allover the country". It is to serve this purpose
tlLlt IS 1893 : 1962 'Recommendations for earthquake resistant design of structures' was published and
subsequently revised in 1966, 1970, 1975 and 1984.
In view of the present state or knowledge and in order to update this standard, the committee has decided to
cover the provisions for different types of structures ill. separate parts. This standard has been split into five
parts. Other parts in this series are:
Part I General provisions and buildings
Part 2 Liquid retaining tanks-elevated and grollnd supported
Part 3 Bridges and retaining walls
Part 5 Dams and embankments
Part I contains provisions that are general in nature and applicable to all types of structures. Also, it contains
provisions that arc specific to buildings only. Unless stated otherwise, the provisions ill Part 2 to Part 5 shall be
rC;ld necessarily in conjullction with Part I.
This standard contains provisions on earthquake resislant design of industrial structures including stack-like
structures . .Industrial structures are covered in Section I al)cI Stack-like structures are covered in Section 2.
All sub-clclLlses under the main clause 0.0 of IS 1893 (Part I) are also applicable to this part except the 0.4.1.
In the preparation orthis standard considerable assistance has been provided by SHEL, lIT Roorkee, lIT Bombay,
11'1' J<.anpur, N'fPC, ElL, TCE, DCE, NPC and various other organizations.
For the plll'pose of deciding whether a particular requirement of this standard is complied with, the final value,
observed or calculated, expressing the result of a te~;t or analysis, shall be rounded off in ac"cordance with
IS:2 : 1960 'Rules 1'01' rounding oflnull1crical values (revised)'. The IlLllllber of significant places retained in the
rOlllldeci ofT vallie should be the same as that or the specified value in this standard.
IS 1893 (Part 4) : 2005
Indian Standard
CRI1-'E:RIAFOREAR1'HQUAKE RESISTANT
DESIGN OF STRUCTURES
PART 4 INDUSTRIAL STRUCTURES INCLUDING
STACK-LIKE STRUCTURES
I SCOPE In addition to the above, the following structures are
classified as stack-like structures and are covered by
1. t The industrial structures shall be designed and
this standard:
constructed to resist the earthquake effects in
a) Cooling towers and drilling towers;
accordance with the requirements and provisions of
this standard. This standard describes the procedures b) Transmission and communication towers;
for earthquake resistant design of industrial structures.
c) Chimneys and stack-like structures;
It provides the estimates of earthquake loading for
d) Silos (including parabolic silos used for urea
design of such structures.
storage );
1.2 All sub-clauses under 1 of IS 1893 (Part 1) are
e) Support structures for refinery columns, boilers,
also applicable to this part except 1.1.
crushers, etc; and
1.3 This standard deals with earthquake resistant f) Pressure vessels and chemical reactor columns.
design of the industrial structures (plant and auxiliary
2 REFERENCES
structures) including stack-like structures associated
with the following industries:
The following standards contain provisions which,
a) Process industries; through reference in this text, constitute provisions of
this standard. At the time of publication the editions
b) Power plants;
indicated were valid. All standards are subject tC)
c) Petroleum, fertilizers and petro-chemical revision and parties to agreements based 011 this
industries; standard are encouraged to investigate the possibility
d) Steel, copper, zinc and aluminum plants; of applying the most recent editions of the standards
indicated below:
e) Pharmaceutical plants;
n IS No. Title
Cement industries;
456 : 2000 Code of practice for plain and
g) Automobile industries;
rei n forced concrete (fourth rev is ion)
h) Sugar and alcohol industries;
800 : 1984 Code of practice for genera I
j) G I(lss and ccram ic industries;
construction in steel (second
k) Textile industries; revision)
111) Foulldries: 875 Code of practice for design loads
(other than earthquake) for building
n) Electrical and electronic industries;
structures:
p) Consumer product industries;
(Part J) : 1987 Dead loads - U 11 it we ights of
q) Structures for sewage and water treatment
building material and stored
plants and pump houses;
materials (second revision)
r) Leather industries;
(Part 2) : ) 987 Itilposed loads (second revision)
s) Off-shore structures and marine/port/harbour
(Part 3) : 1987 Wind loads (second revision)
structures;
(Part 4): 1987 Snow loads (second revision)
t) Mill structures;
(Part 5): ) 987 Special loads and load combinations
u) Telephone exchanges;
(second revision)
v) Water and waste water treatment facilities; and
1343 : 1980 Code of practice for prestressed
w) Paper plants. concrete (second revision)
This standard shall also be considered applicable to 1888 : 1982 Method of load test on soils (second
the other industries not mentioned above. revision)
IS 1893 (Part 4) : 2005
IS No. Tille EL -- Response quantity due to earthquake
load
18S13 (Part I) : Criteria for earthquake resistant
2002 design of structures: Part 1 General Response quantity due to earthquake
provisions and buildings loads in X-direction
4326 : 1993 Earthq uake resistant design and
EL Response quantity due to earthquake
construction of buildings - Code of y
loads in Y -direction
practice (second revision)
Response quantity due to earthquake
4998 (Part I) : Criteria for design of reinforced
loads in Z-direction
1992 concrete chimneys: Part 1
Assessment of loads (second e. Static eccentricity at floor, i
revision) SI
g Acceleration due to gravity
6403 : 1981 Code of practice for determination
of bearing capacity of shallow ! Importance factor
foundations (firsl revision)
IL Response quantity due to imposed loads
6533 (Part 2) : Code of practice for design and
1989 construction of steel chimney: M Mass matrix of the structural system
Part 2 Structural aspects (first
A1 Mass matrix of the primary system
revision)
p
13920 : J 993 Ductile detailing of reinforced MCE Maximum considered earthquake
concrete structures su bjected to
Total mass of all the equipment that are
seismic forces
fiexible mounted at different locations
SP 6 (6): 1972 Handbook for structural engineers
in the structure
-- Application of plastic theory in
design of steel structures M Modal lllass of mode, k
k
3 GENERAL TERMINOLOGY FOR Total mass of all the equipment that are
EARTHQUAKE ENGINEERING rigidly mounted at different locations
in the structure
A" sub-clauses under 3 of IS 1893 (Part 1) are also
applicable to this standard. Iv! Total mass of structural system, which
5
supports secondary system
4 TERMINOLOGY FOR INDUSTRIAL
STRUCTURES R Response reduction factor
The following definition and the others given r - Number of modes being considered
in IS 1893 (Part 1) except 4.10 and 4.]6 are
Sa Spectral acceleration
applicable.
S,/g Spectral acceleration coefficient
4.1 Com bined Structu res
SIDL Super imposed dead loads
A structure with lateral load resisting elements
constructed from a combination of reinforced! N Standard penetration test value (SPT
prestressed concrete and structural steel. value) of the soil
5 SYMBOLS SRSS Square root of sum of squares
5.1 Symbols and notations applicable to Section 1 are T Undamped natural period of vibration
given as undcr: of the structure
Design horizontal seismic coefficient Seismic weight of floor, i
1:;'1001' plan dimension of floor ;, Z Zone factor
perpendicular to direction of force
o - jth normalized mode shape
J
c --- Indcx for closely spaced modes
Influence vector-displacement vector of
C QC Co III pIe t e qua d rat icc 0 m bin at ion the structural system
method
Mode shape coefficient at noor, i, in
DL Response quantity due to dead load mode, k
C Design eccentricity at floor, i O. Mode vector value from the pri mary
di CI
2
IS 1893 (Part 4) :2005
system's modal displacement at the N Number of locations of lumped weight
location where the secondary system is
Radius of circular raft foundation
connected
R Response reduction factor
A -- Peak response quantity due to closely
spaced modes S
a Spectral acceleration coefficient for
g
P Cross-modal correlation co-efficient: rock and soil sites
ij
Modal damping ratio Characteristic length of pile
(j)
Frequency rati•o = --J Weight lumped at itb location with the
OJ
i weights applied simultaneously with
Absolute value of quantity in mode k
the force applied horizontally
Peak response due to all modes
Total weight of the structure
considered
including weight of lining and contents
Maximum value of deflection above the base
z
Circular frequency, in rad/sec, in ith Zone factor
mode
8., Lateral static deflection under its own
Response quantity in mode i, j, k lumped weight at ith location (chimney
respectively weight lumped at to or more locations)
8 8 8 Maximum value of deflection in X, Y, v - Poisson's ratio of soil
;0\, ";I, Z Z direction respectively
1~1 Modulus of sub grade reaction of soil
5.2 Symbols and notations applicable to Section 2 in horizontal direction
are defined as under:
6 GENERAL PRINCIPLES
A Area of cross-section at the base of the
structural shell 6.1 Ground Motion
Design horizontal seismic coefficient 6.1.1 The characteristics (intensity, duration, etc) of
seismic ground vibrations expected at any location
Coeffic ient depend i ng upon the
depends upon the magnitude of earthquake, its depth
slenderness ratio of the structure
of focus, distance from the epicentre, characteristics
Coefficient of shear force depending on of the path through which the seismic waves travel,
slenderness ratio, k and the soil strata on which the structure stands. The
random earthquake ground motions, which cause the
d Thickness of pile cap or raft
structures to vibrate, can be resolved in any three
Maximum lateral detlection mutually perpendicular directions. The predominant
Dt\1ax
direction of ground vibration is horizontal.
D Don Distribution factors for shear and
y'
moment respectively at a distance X Earthquake generated vertical inertia forces are to be
from the top considered in design unless checked and proven to be
not significant. Vertical acceleration should be
E Modulus of elasticity of pile material
considered in structures with large spans, those in
Modulus of elasticity of material of the which stability is a criterion for design, or for overall
structu ra I shell stability analysis of structures. Reduction in gravity
force due to vertical component of ground motions
g Acceleration due to gravity
can be particularly detrimental in cases of prestressed
G Shear modulus of soil = pV/ horizontal members and of cantilevered members.
V Shear wave velocity of the medium Hence, special attention should be paid to the effect
s of vertical component of the ground motion on
h I-I eight of structure above the base
prestressed or cantilevered beams, girders and slabs.
Height of centre of gravity of structure
6.1.2 The response of a structure to ground vibrations
above base
is a fu nction of the nature 0 r foundat ions, so ii,
Importance factor materials, form, size and mode of construction of
structures; and the duration and characteristics of
Moment of inertia of pile section
ground motion. This standard specifics design forces
11 Number of piles for structures standing on rocks or soils, which do not
IS 1893 (Part 4) : 2005
.'lettie, liquify or slide due to loss of strength during analysis unless a more definite value is available
vibrations. for usc in sllch condition (see IS 456. IS 800
and IS 1343).
6.1.3 The design approach adopted in th is standard
is to ensure thal structures possess 111 in il1lull1 strength
SECTION 1 INDUSTRIAL STRUCTURES
to withstilnd minor eart.hquakes « DBE) which OCCLlr
frequently, without damage; resist moderate
7 DESIGN CRITERIA
earthquakes (DBE) without significant structural
damage though some nOll-structural damage may 7.1 Categorizatioll of Structures
oce LI r: all d vv i t hst a n cl a III aj or earthq 1I ake (M C E)
To perform well in an earthquake, the industrial
withollt collapse. Actual forces that appear on
structure should possess adequate strength. sl.iflllCSS,
structures during earthquakes arc much greater than
and ductility. Generally structures have large
tile design forces speci1Jed in this standard. However,
capacities of energy absorption in its inelastic regioll.
ductility. arising fwm inclastic material behaviour and
Structures wll ieh are delai led as per IS 13920 or
detailing, and overstrength, arising from the additional
SP 6 (6) and equipment which are ma(16 of ductile
reserve strength in structures over and above the design
materials can withstJnd earthquakes many folel higher
strength, are relied upon to account for this difference
than the design spectra without collapse; and damage
in actual and design lateral loads.
in slIch cases is restricted to cracking only.
Reinforced and prestressed concrete members shall be
Structures are classified into the following four
su it(lbly designed to ensure that j)\"emature fai lure due
categories:
to shear or bond docs not occur, subject to the
provisions of IS 456 (lnel IS 1343. Provisions ror a) Category Structures whose Llilure call
~lppropriale ductile detailing of reinforced concrete cause conditions that can lead
members ~lIT given in IS 13920. directly or indirectly to extensive
loss ofli fe/property to population
In steel structures, members and their connections
<It large in the areas adjacent to
should be so proportioned that high ductility is
the plant complex.
obt(lincd, as specified in SP 6 (6), avoiding premature
failure due to clastic or inelastic bLickling orany type. b) Category 2 S t r u c t LI res w 11 0 s e fa i IL I r e can
calise cond it ions that can lead
6.1.4 The design force specified in this standard shall
directly or indirectly to serious
be cOllsiuercd ill each of the two prillcip'-1l horizontal
fire hazard/extensive damage
direct ions of the structure and in vertical directioll.
\V it hi 11 the p Ia 11 teo III pie x.
6.1.5 Equipment and other systems, which arc Structures. which are required to
supported at vclriolls noor levels ortllc structure, shall halldle emergencies imlllcdiately
be subjected to motions corresponding to vibration at aftcr ~lll earthquake. are also
their support points. III important cases. it may be inc ludcd.
necessary to obtain floor response spectra for analysis
or c) Category 3 Structures whose failure,
and design equipment.
although expensive, does not
6.2 AsslImptions lead to serious hazard within the
plallt complex.
Tile following assLimptions shall be made in the
earthquake rcsistJllt design of structures: d) Category 4: A II other structures.
a) Earthquake ({llISeS impUlsive ground motions. or
Typical categorization industrial structures is given
which are complex and irregular ill charncter,
in Table 5 .
challging in period and amplitude each lasting
for ,I small eluration. cfhcreforc, resonance of NOTI': -----Ti1~ 't~rlll (ail lire used in the tieiillitioll ur categories
irnplies loss offlinetiull ,1IHIIl(lt completC" WIl;1jlSC. Pressurizcd
the type as visualized under steady-st(1[C
equipmcilt "hcre cracking call lead III rupture milV be
sinusoicbl cxci(;lIiol1s. will 110t occLir. as it would
catl'gorized by tl1~' cOI1:--equcnccs nl'rllplurc.
Ileed time to build up such amplitudes.
7.2 Design LO~ltrs
NOTL--l::\ceptioll<i1. resonallce-like conditions have been
:il'Clllll llCCllf helWCcllllll1g distance waves and tall structures 7.2.1 Dead Load (Df-)
I(HlIlt!ed Oil deep suit soils.
b) Earthquake is not likely to occur simultaneously These shall be taken as per IS 875 (Part 1).
\\' i thIn (l x i III LI III W i 11 cl 0 r 111 a x i 1l1Ll m fI () 0 d 0 r
7.2.2 Super Ill/jJosed Dead [,()ods (S[DL)
maximum sea \vaves.
c) The value of clastic modulus or materials, Industrial structures contain scveriti equiplllcnt ~lnd
wilercvcr required. may be taken as for static associated· auxiliaries and <lccessorics that ~lre
IS 1893 (Part 4) : 2005
permanently mounted all the structures. These loads response due to earthquake force (EL) is the maximum
shall be taken as per equipment spccincatiolls. of the following cases:
[L
7.2.3 Il1Iposed Loads (IL) i- 0.3 EL J:: 0.3 EL.1.
EL y
n,'
These shall be taken as per IS 875 (Part 2). EL 00 L ± 0.3 EL>:, c1.: 0.3 EL!
7.2.4 I~(/r'hqllake Loads (EL) f LI.1. ± 0.3 fl.).. -1: 0.3 EL '.
The earthquake load 011 the different members of a where x and y arc (wo orthogonal directions (lnd 1 is
structure shall be determined by carrying aLit analysis the vertical direction.
to
following the procedure described in Llsing the
7.3.2.2 As an alternative to the procedure in 7.3.2.1,
design spectra specified in 8. Earthquake loads in x
the response (EL) due to the combined effect of the
and y (horizontal) d ircctiol1s are denoted by ELx and
three components can be obtained on the square root
EI. .. and earthquake loads in vertical direction are
del~oted by EL • of the Sllm of the squares (SRSS) basis, that is
z
7.3 Load Combinations EL = !c1~L )2 + (EL )2 -+- (EL )2
, y /.
When earthquake forces arc considered on a structure,
NOTE - The combination procedures 0(' 7 .. 1.2.1 and 7.3.2.2
the response quantities due to dead load (OL), imposed apply to the samc response quanlily (say. 1l1OI11elll in a colulllll
10;ld (ll.), super imposed dead loads (SIDL) and design about its major axis. or storey shear in a i'ralllL~) due lo dillnelll
earthquake load (EL) shall be combined as per 7.3.1 componenls ui'lhe ground motion. Tlte~e cOlllbinalinns arc In
and 7.3.2. The factors defined in 7.3.1 and 7.3.2 are be made at the; member i'orce/stress levels.
applicable for Category 1 to 4 structures only under 7.3.3 For structures under Category I, wh icll are
DBE (sce 7.5). designed under MCE (see 7.5.1) and checked under
DBE, all load factors in combination with MeE shall
7.3.1 Load Faclol's for Plastic Design of Sleel
be taken as unity.
S'tructures
7.4 Increase in Permissible Stresses
In the plastic design of steel structures, the following
load combinations shall be accollntedn)r:
7.4.] Increase in Permissiblc .')'Iresses il1 Ala1erials
a) 1.7 (DL -+- SIOL + IL),
When earthquake forces are considered along with
b) I. 7 CD!. -I- SI DO ± F.L, and other normal design forces, the permissible stresses in
c) 1.3 (DL -[- S'ID!. +- IL:l: EL). material, in the clastic method of design, may be
Nt)'lT -- Ilnposed load (II,) in load combination shall not increased by one-third. However, for steels having a
include crcclion 1():lds and crane payload. definite yield stress, the stress be limited to the yield
stress, for steels without a definite yield point, the stress
7.3.2 Purtitt! S({/ely Foclotsfor Limit Slate Design q/
\,vill be limited to 80 percent of the ultimate strength
Rt'injiHced COl7crete and Prestressed C Ol1crele
or 0.2 percent proof stress, whichever is smaller; and
,,,"rue/ures
that in pre-stressed concrete members, the tens iI e stress
In the limit state design of reinforced and prestressed in the extreme fibers of the concrete may be penn ilted
concrete structures, the following load combinations so as not to exceed two-thirds oftlle modulus orrupture
shall be accounted for: of concrete.
a) 1.5 (OL -+ 5'IDL + IL), 7.4.2 Il1crease il1 Allowable Pressures in ,\'oils
b) 1.2 (DL -+ SIDL + IL :1:: EL),
When earthquake forces are illcluded, the allowable
c) 1.5 (DL + SID!. :1: EL), and bearing pressure in soils shall be increased as per
d) 0.9 (DL + SIDL) ± 1.5 EL. Table I, depending upon type of foundation of the
structure and the type of soil.
NUlL .-.- Il1Ip(lscd \(lad (n) in load combination shall not
includc cn.:clioll iliad and cram: payload.
In soil deposits consisting of submerged loose sands
7.3.2.1 When responses from the three earthquake and soils falling under classification SP with standard
components are to be considered, the response due to penetration N values less than 15 in scism ic zones Ill,
each component may be combined using the IV, V and less than 10 in seismic zone II. lhe vibration
assllmption that when the maximum response from caused by earthquake may cause liquefaction or
one component occurs, the responses from the other excessive total and differential settlcmcnts. Such sites
two components are 30 percent of the corresponding sh ou Id pre fera bly be avo ided w hi Ie loca tin g 11 ew
maximum. All possible combinations of the three set{ [C 111 en ts or i III porta n t proj eclS. Ot h erw i S('. t his
c()mponents (El." EL\, and EL) including variation~ asp.egt of the problem needs to be investigaled and
in sign (plus or minus) shall be considered. Thus, the n pprc;priatc methods 0 r com paction nr st,lb iIi z~ll ion
5
IS 1893 (Part 4) : 2005
adopted to achieve suitable N values as indicated NOTE - Structures in Category I shall be designed for seismic
in Note 3 under Table I. Alternatively, deep pile force twice that fOllnd lIsing the provisions of this clause.
foundation may be provided and taken to depths well where
into the layer. which is 110t likely to liquify. Marine Z = zone factor, given in Annex A [Th is is in
clays and other sensitive clays are also known to accordance with Table 2 of IS 1893 (Part I)].
liquefy clue to collapse of soil structure and wi!! need
S/g = spectral acceleration co.efficient for rock and
special treatment according to site condition.
soil sites given in Annex B [This is in
7.5 Design Basis Earthquakc (DBE) accordance with Fig. 1 of IS 1893 (PaI1 1) ].
I = importance factor given in Table 2 is relative
Design basis earthquake (DBE) for a specific site is to
importance assigned to the structure to take into
be determined based on either: (a) site specific
account consequences of its damage.
stud ies, or (b) in accordance with provisions of
IS 1893 (Part I). R = response reduction factor to take into account
the margins of safety, redundancy and ductility
7.5. I Structures in Category I shall be designed for
of the structure given in Table 3.
maximum considered earthquake (MCE) (which is
twice of DBE). Categorization of some individual structure and
components of typical industries are given in
7.5.2 Structures in Category 2, 3 and 4 shall be
Table 5.
designed for DBE for the project site.
8.4 Vertical acceleration values are to be taken as
8 DESIGN SPECTRUM
2/3 of the corresponding horizontal acceleration
values.
8.1 For all important projects, and all industries
dealing with highly hazardous chemicals, evaluation
9 MATHEMATICAL MODELLING
of site-specific spectra for earthquake with probability
of exccedence of 2 percent in 50 years (MCE) and 9. t Modelling Requirements
10 percent in 50 years (DBE) is recommended. All
The mathematical model of the physical structure shall
Category 1 industrial structures shall be analyzed using
include all elements of the lateral force-resisting
site-speciflc spectra. However, if site-specific studies
system. The model shall also include the stiffness
arc not carried out, the code specified spectra may be
and strength of clements. which are significant to the
L1sed with modifications as per 8.3.2. If time-history
distribution of forces. The model shall properly
analysis is to be carried out, spectra-compliant time
represent the spatial distribution of the mass and
history shall be determined based on the site-specific
stiffness oCthe structures, as well as mass of equipment,
spectra.
cable trays and piping system along with associated
8.2 For all other structures not covered in 8. t, the accessories, 25 percent of the live load shall also
spectra and seismic zone as given in Annex A and be included 8S suitably distributed mass on the
Annex B is recommended [these are in accordance structure.
with IS 1893 (Part 1) ].
9.1.1 5"oil-5'(rllctllre Intcraction
8.3 Horizontal Seismic Force
The soil..,structure interaction refers to the effects of
The horizontal seismic coefficient A shall be the supporting foundation medium on the motion of
,
obtained using the period 7: described as hunder. structure. The soil-structure intpraction may not be
considered in the seIsmIc ana1]ysis for structures
8.3.1 When lIsing site specific spectra, the seism ic
supported on rock or rock-like material.
coeflicient shall be calculated from the expression:
9.2 Interaction Effects lJetween Structure and
Equipmcnt
Ah= Interaction effects between structure and equipment
(R./!)
shall be considered as under:
Sn/
where / gg = spectral acceleration coefficient a) For Category 2, 3 and 4, simplified considera
.
tions as pCI' 9.2.1 may be used.
corresponding to site specific spectra.
b) For Category I, dctailed considerations as per
8.3.2 When llsing code specific spectra, the seismic 9.2.2 shall be adopted.
co-effiCient shall be calculated from the expression:
r 9.2.1 For the purpose of 9.2, the following notations
Ir~'. . "I: 1c'r) 3/. "II shall be used:
l 2 J L/ g J
/1,( = total mass of the structural system on which the
-----------
(R/J) . secondary system is supported,
6