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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
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“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 ~, "ifCCT , ~ '(1,<:q;
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
1. t The industrial structures shall be designed and constructed to resist the earthquake effects in accordance with the requirements and provisions of this standard. This standard describes the procedures for earthquake resistant design of industrial structures. It provides the estimates of earthquake loading for design of such structures.
In addition to the above, the following structures are classified as stack-like structures and are covered by this standard: a) Cooling towers and drilling towers; b) Transmission and communication towers; c) Chimneys and stack-like structures; d) Silos (including parabolic silos used for urea storage );
1.2 All sub-clauses under 1 of IS 1893 (Part 1) are also applicable to this part except 1.1.
e) Support structures for refinery columns, boilers, crushers, etc; and
1.3 This standard deals with earthquake resistant design of the industrial structures (plant and auxiliary structures) including stack-like structures associated with the following industries:
f) Pressure vessels and chemical reactor columns.
a) Process industries; b) Power plants; c) Petroleum, fertilizers and petro-chemical industries; d) Steel, copper, zinc and aluminum plants; e) Pharmaceutical plants;
n Cement
industries;
g) Automobile industries; h) Sugar and alcohol industries; j) G I(lss and ccram ic industries;
2 REFERENCES
The following standards contain provisions which, through reference in this text, constitute provisions of this standard. At the time of publication the editions indicated were valid. All standards are subject tC) revision and parties to agreements based 011 this standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below: IS No.
456 : 2000
Code of practice for plain and rei n forced concrete (fourth rev is ion)
800 : 1984
Code of practice for genera I construction in steel (second revision)
k) Textile industries; 111) Foulldries: n)
875
Electrical and electronic industries;
p) Consumer product industries; q) Structures for sewage and water treatment plants and pump houses; r) Leather industries; s) Off-shore structures and marine/port/harbour structures; t) Mill structures;
u) Telephone exchanges; v) Water and waste water treatment facilities; and w) Paper plants.
This standard shall also be considered applicable to the other industries not mentioned above.
Title
Code of practice for design loads (other than earthquake) for building structures:
(Part J) : 1987
Dead loads - U 11 it we ights of building material and stored materials (second revision)
(Part 2) : ) 987
Itilposed loads (second revision)
(Part 3) : 1987
Wind loads (second revision)
(Part 4): 1987
Snow loads (second revision)
(Part 5): ) 987
Special loads and load combinations (second revision)
1343 : 1980 1888 : 1982
Code of practice for prestressed concrete (second revision) Method of load test on soils (second revision)
IS 1893 (Part 4) : 2005
18S13 (Part I) : 2002
4326 : 1993
Criteria for earthquake resistant design of structures: Part 1 General provisions and buildings Earthq uake resistant design and construction of buildings - Code of practice (second revision)
Response quantity due to earthquake loads in X-direction EL y
1992
Code of practice for determination of bearing capacity of shallow foundations (firsl revision)
6403 : 1981
6533 (Part 2) : 1989
Code of practice for design and construction of steel chimney: Part 2 Structural aspects (first revision) Ductile detailing of reinforced concrete structures su bjected to seismic forces
e.SI
Static eccentricity at floor, i
g
Acceleration due to gravity
!
Importance factor
IL
Response quantity due to imposed loads
M
Mass matrix of the structural system
A1p
Mass matrix of the primary system Maximum considered earthquake
MCE
Total mass of all the equipment that are fiexible mounted at different locations in the structure
SP 6 (6): 1972 Handbook for structural engineers -- Application of plastic theory in design of steel structures 3 GENERAL TERMINOLOGY EARTHQUAKE ENGINEERING
Response quantity due to earthquake loads in Y -direction Response quantity due to earthquake loads in Z-direction
Criteria for design of reinforced concrete chimneys: Part 1 Assessment of loads (second revision)
4998 (Part I) :
13920 : J 993
EL -- Response quantity due to earthquake load
Tille
IS No.
Modal lllass of mode, k
Mk
Total mass of all the equipment that are rigidly mounted at different locations in the structure
FOR
A" sub-clauses under 3 of IS 1893 (Part 1) are also applicable to this standard.
Total mass of structural system, which supports secondary system
Iv!5
4 TERMINOLOGY FOR INDUSTRIAL STRUCTURES
The following definition and the others given in IS 1893 (Part 1) except 4.10 and 4.]6 are applicable.
R
Response reduction factor
r -
Number of modes being considered Spectral acceleration
Sa
Spectral acceleration coefficient
S,/g
4.1 Com bined Structu res
Super imposed dead loads
SIDL
A structure with lateral load resisting elements
constructed from a combination of reinforced! prestressed concrete and structural steel.
Standard penetration test value (SPT value) of the soil
N
SRSS
5 SYMBOLS 5.1 Symbols and notations applicable to Section 1 are given as undcr:
Square root of sum of squares Undamped natural period of vibration of the structure
T
Seismic weight of floor, i
Design horizontal seismic coefficient
o
J
c --- Indcx for closely spaced modes
CQC DL C
di
Zone factor
Z
1:;'1001' plan dimension of floor ;, perpendicular to direction of force
-
jth normalized mode shape
Influence vector-displacement vector of the structural system
Co III pIe t e qua d rat icc 0 m bin at ion method
Mode shape coefficient at noor, i, in mode, k
Response quantity due to dead load Design eccentricity at floor, i
O.
CI
2
Mode vector value from the pri mary
IS 1893 (Part 4) :2005 system's modal displacement at the location where the secondary system is connected
N
A -- Peak response quantity due to closely spaced modes
R
Pij
Cross-modal correlation co-efficient:
Number of locations of lumped weight Radius of circular raft foundation
Sa
g
Modal damping ratio
Response reduction factor Spectral acceleration coefficient for rock and soil sites Characteristic length of pile
(j) •
Frequency ratio
J
= --
Weight lumped at itb location with the weights applied simultaneously with the force applied horizontally
OJ i
Absolute value of quantity in mode k Peak response due to all modes considered
Total weight of the structure including weight of lining and contents above the base
Maximum value of deflection Circular frequency, in rad/sec, in ith mode
z
Zone factor
8.,
Lateral static deflection under its own lumped weight at ith location (chimney weight lumped at to or more locations)
v -
Poisson's ratio of soil
Response quantity in mode i, j, k respectively
8 8 8 ;0\,
";I,
Z
Maximum value of deflection in X, Y, Z direction respectively
5.2 Symbols and notations applicable to Section 2 are defined as under: A
Area of cross-section at the base of the structural shell Design horizontal seismic coefficient Coeffic ient depend ing upon the slenderness ratio of the structure Coefficient of shear force depending on slenderness ratio, k
d
Thickness of pile cap or raft
Dt\1ax
Maximum lateral detlection
Dy ' Don
E
Distribution factors for shear and moment respectively at a distance X from the top Modulus of elasticity of pile material Modulus of elasticity of material of the structu ra I shell
g
Acceleration due to gravity
G
Shear modulus of soil = pV/
Vs
Shear wave velocity of the medium
h
I-I eight of structure above the base
Height of centre of gravity of structure above base Importance factor Moment of inertia of pile section 11
Number of piles
1~1
Modulus of sub grade reaction of soil in horizontal direction
6 GENERAL PRINCIPLES
6.1 Ground Motion 6.1.1 The characteristics (intensity, duration, etc) of seismic ground vibrations expected at any location depends upon the magnitude of earthquake, its depth of focus, distance from the epicentre, characteristics of the path through which the seismic waves travel, and the soil strata on which the structure stands. The random earthquake ground motions, which cause the structures to vibrate, can be resolved in any three mutually perpendicular directions. The predominant direction of ground vibration is horizontal. Earthquake generated vertical inertia forces are to be considered in design unless checked and proven to be not significant. Vertical acceleration should be considered in structures with large spans, those in which stability is a criterion for design, or for overall stability analysis of structures. Reduction in gravity force due to vertical component of ground motions can be particularly detrimental in cases of prestressed horizontal members and of cantilevered members. Hence, special attention should be paid to the effect of vertical component of the ground motion on prestressed or cantilevered beams, girders and slabs. 6.1.2 The response of a structure to ground vibrations is a fu nction of the nature 0 r foundat ions, so ii, materials, form, size and mode of construction of structures; and the duration and characteristics of ground motion. This standard specifics design forces for structures standing on rocks or soils, which do not
IS 1893 (Part 4) : 2005
liquify or slide due to loss of strength during vibrations.
analysis unless a more definite value is available for usc in sllch condition (see IS 456. IS 800 and IS 1343).
.'lettie,
The design approach adopted in th is standard is to ensure thal structures possess 111 in il1lull1 strength to withstilnd minor eart.hquakes « DBE) which OCCLlr frequently, without damage; resist moderate earthquakes (DBE) without significant structural damage though some nOll-structural damage may oce LI r: all d vv i t hst a n cl a III aj or earthq 1I ake (M C E) withollt collapse. Actual forces that appear on structures during earthquakes arc much greater than tile design forces speci1Jed in this standard. However, ductility. arising fwm inclastic material behaviour and detailing, and overstrength, arising from the additional reserve strength in structures over and above the design strength, are relied upon to account for this difference in actual and design lateral loads.
6.1.3
Reinforced and prestressed concrete members shall be due the provisions of IS 456 (lnel IS 1343. Provisions ror ~lppropriale ductile detailing of reinforced concrete members ~lIT given in IS 13920.
su it(lbly designed to ensure that j)\"emature fai lure to shear or bond docs not occur, subject to
In steel structures, members and their connections should be so proportioned that high ductility is obt(lincd, as specified in SP 6 (6), avoiding premature failure due to clastic or inelastic bLickling orany type.
SECTION 1 INDUSTRIAL STRUCTURES 7 DESIGN CRITERIA 7.1 Categorizatioll of Structures
To perform well in an earthquake, the industrial structure should possess adequate strength. sl.iflllCSS, and ductility. Generally structures have large capacities of energy absorption in its inelastic regioll. Structures wll ieh are delai led as per IS 13920 or SP 6 (6) and equipment which are ma(16 of ductile materials can withstJnd earthquakes many folel higher than the design spectra without collapse; and damage in slIch cases is restricted to cracking only.
Structures are classified into the following four categories: a)
Category
Structures whose Llilure call cause conditions that can lead directly or indirectly to extensive loss ofli fe/property to population
b)
Category 2
S t r u c t LI res w 11 0 s e fa i ILI r e can calise cond it ions that can lead directly or indirectly to serious fire hazard/extensive damage \V it hi 11 the p Ia 11 teo III pie x. Structures. which are required to halldle emergencies imlllcdiately aftcr ~lll earthquake. are also inc ludcd.
c)
Category 3
Structures whose failure, although expensive, does not lead to serious hazard within the plallt complex.
d)
Category 4:
A II other structures.
6.1.4 The design force specified in this standard shall be cOllsiuercd ill each of the two prillcip'-1l horizontal
direct ions of the structure and in vertical directioll. 6.1.5 Equipment and other systems, which arc supported at vclriolls noor levels ortllc structure, shall be subjected to motions corresponding to vibration at their support points. III important cases. it may be necessary to obtain floor response spectra for analysis and design or equipment. 6.2 AsslImptions
Tile following assLimptions shall be made in the earthquake rcsistJllt design of structures: a)
Earthquake ({llISeS impUlsive ground motions. which are complex and irregular ill charncter, challging in period and amplitude each lasting for ,I small eluration. cfhcreforc, resonance of the type as visualized under steady-st(1[C sinusoicbl cxci(;lIiol1s. will 110t occLir. as it would Ileed time to build up such amplitudes. NOTL--l::\ceptioll
:il'Clllll llCCllf helWCcllllll1g
b) Earthquake is not likely to occur simultaneously
\\' i thIn (l x i III LI III W i 11 cl maximum sea \vaves. c)
0
r
111 a x i 1l1Ll m
fI () 0 d
0
r
The value of clastic modulus or materials, wilercvcr required. may be taken as for static
Typical categorization in Table 5 .
or industrial structures is given
NOTI': ----- Ti1~ 't~rlll (ail lire used in the tieiillitioll
ur categories irnplies loss offlinetiull ,1IHIIl(lt completC" WIl;1jlSC. Pressurizcd equipmcilt "hcre cracking call lead III rupture milV be catl'gorized by tl1~' cOI1:--equcnccs nl'rllplurc. 7.2 Design
LO~ltrs
7.2.1 Dead Load (Df-)
These shall be taken as per IS 875 (Part 1). 7.2.2 Super Ill/jJosed Dead [,()ods (S[DL)
Industrial structures contain scveriti equiplllcnt associated· auxiliaries and
~lnd
~lre
IS 1893 (Part 4) : 2005 response due to earthquake force (EL) is the maximum of the following cases:
permanently mounted all the structures. These loads shall be taken as per equipment spccincatiolls. 7.2.3 Il1Iposed Loads (IL)
EL
EL
These shall be taken as per IS 875 (Part 2). I~(/r'hqllake
7.2.4
00
Loads (EL)
EL =
In the limit state design of reinforced and prestressed concrete structures, the following load combinations shall be accounted for:
1.2 (DL -+ SIDL + IL :1:: EL),
c)
1.5 (DL + SID!. :1: EL), and
d)
0.9 (DL + SIDL) ± 1.5 EL.
1
is
!c1~L , )2 +
(EL y )2 -+- (EL /. )2 0(' 7..1.2.1
and 7.3.2.2
When earthquake forces are considered along with other normal design forces, the permissible stresses in material, in the clastic method of design, may be increased by one-third. However, for steels having a definite yield stress, the stress be limited to the yield stress, for steels without a definite yield point, the stress \,vill be limited to 80 percent of the ultimate strength or 0.2 percent proof stress, whichever is smaller; and that in pre-stressed concrete members, the tens iIe stress in the extreme fibers of the concrete may be penn ilted so as not to exceed two-thirds oftlle modulus orrupture of concrete.
,,,"rue/ures
b)
'.
7.4.] Increase in Permissiblc .')'Iresses il1 Ala1erials
7.3.2 Purtitt! S({/ely Foclotsfor Limit Slate Design q/ Rt'injiHced COl7crete and Prestressed C Ol1crele
1.5 (OL -+ 5'IDL + IL),
EL
7.4 Increase in Permissible Stresses
Nt)'lT -- Ilnposed load (II,) in load combination shall not include crcclion 1():lds and crane payload.
a)
0.3
fl.).. -1:
7.3.3 For structures under Category I, wh icll are designed under MCE (see 7.5.1) and checked under DBE, all load factors in combination with MeE shall be taken as unity.
In the plastic design of steel structures, the following load combinations shall be accollntedn)r:
1.3 (DL -[- S'ID!. +- IL:l: EL).
LI. 1. ± 0.3
apply to the samc response quanlily (say. 1l1OI11elll in a colulllll about its major axis. or storey shear in a i'ralllL~) due lo dillnelll componenls ui'lhe ground motion. Tlte~e cOlllbinalinns arc In be made at the; member i'orce/stress levels.
Load Faclol's for Plastic Design of Sleel
c)
0.3 EL!
c1.:
NOTE - The combination procedures
S'tructures
I. 7 CD!. -I- SI DO ± F.L, and
± 0.3 EL>:,
7.3.2.2 As an alternative to the procedure in 7.3.2.1, the response (EL) due to the combined effect of the three components can be obtained on the square root of the Sllm of the squares (SRSS) basis, that is
DBE (sce 7.5).
b)
0.3 EL.1.
the vertical direction.
When earthquake forces arc considered on a structure, the response quantities due to dead load (OL), imposed 10;ld (ll.), super imposed dead loads (SIDL) and design earthquake load (EL) shall be combined as per 7.3.1 and 7.3.2. The factors defined in 7.3.1 and 7.3.2 are applicable for Category 1 to 4 structures only under
1.7 (DL -+- SIOL + IL),
i- 0.3 EL J:: y
where x and y arc (wo orthogonal directions (lnd
7.3 Load Combinations
a)
L f
The earthquake load 011 the different members of a structure shall be determined by carrying aLit analysis following the procedure described in to Llsing the design spectra specified in 8. Earthquake loads in x and y (horizontal) d ircctiol1s are denoted by ELx and EI ... and earthquake loads in vertical direction are del~oted by EL z •
7.3.1
[L n,'
7.4.2 Il1crease il1 Allowable Pressures in ,\'oils
When earthquake forces are illcluded, the allowable bearing pressure in soils shall be increased as per 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 and soils falling under classification SP with standard penetration N values less than 15 in scism ic zones Ill, IV, V and less than 10 in seismic zone II. lhe vibration caused by earthquake may cause liquefaction or excessive total and differential settlcmcnts. Such sites sh ou Id pre fera bly be avo ided w hi Ie loca tin g 11 ew set{ [C 111 en ts or i III porta n t proj eclS. Ot h erw i S('. t his asp.egt of the problem needs to be investigaled and npprc;priatc methods 0 r com paction nr st,lb iIi z~ll ion
7.3.2.1 When responses from the three earthquake components are to be considered, the response due to each component may be combined using the assllmption that when the maximum response from one component occurs, the responses from the other two components are 30 percent of the corresponding maximum. All possible combinations of the three c()mponents (El." EL\, and EL) including variation~ in sign (plus or minus) shall be considered. Thus, the
5
IS 1893 (Part 4) : 2005
adopted to achieve suitable N values as indicated in Note 3 under Table I. Alternatively, deep pile foundation may be provided and taken to depths well into the layer. which is 110t likely to liquify. Marine clays and other sensitive clays are also known to liquefy clue to collapse of soil structure and wi!! need special treatment according to site condition.
NOTE - Structures in Category I shall be designed for seismic force twice that fOllnd lIsing the provisions of this clause.
where zone factor, given in Annex A [Th is is in accordance with Table 2 of IS 1893 (Part I)]. S/g = spectral acceleration co.efficient for rock and soil sites given in Annex B [This is in accordance with Fig. 1 of IS 1893 (PaI1 1)]. I = importance factor given in Table 2 is relative importance assigned to the structure to take into account consequences of its damage.
7.5 Design Basis Earthquakc (DBE)
Design basis earthquake (DBE) for a specific site is to be determined based on either: (a) site specific stud ies, or (b) in accordance with provisions of IS 1893 (Part I). 7.5. I Structures in Category I shall be designed for maximum considered earthquake (MCE) (which is twice of DBE).
Z
=
R
=
response reduction factor to take into account the margins of safety, redundancy and ductility of the structure given in Table 3.
Categorization of some individual structure and components of typical industries are given in Table 5.
7.5.2 Structures in Category 2, 3 and 4 shall be designed for DBE for the project site.
8.4 Vertical acceleration values are to be taken as 2/3 of the corresponding horizontal acceleration
8 DESIGN SPECTRUM
values.
For all important projects, and all industries dealing with highly hazardous chemicals, evaluation of site-specific spectra for earthquake with probability of exccedence of 2 percent in 50 years (MCE) and 10 percent in 50 years (DBE) is recommended. All Category 1 industrial structures shall be analyzed using site-speciflc spectra. However, if site-specific studies arc not carried out, the code specified spectra may be L1sed with modifications as per 8.3.2. If time-history analysis is to be carried out, spectra-compliant timehistory shall be determined based on the site-specific spectra. 8.1
9 MATHEMATICAL MODELLING 9. t Modelling Requirements
The mathematical model of the physical structure shall include all elements of the lateral force-resisting system. The model shall also include the stiffness and strength of clements. which are significant to the distribution of forces. The model shall properly represent the spatial distribution of the mass and stiffness oCthe structures, as well as mass of equipment, cable trays and piping system along with associated accessories, 25 percent of the live load shall also be included 8S suitably distributed mass on the structure.
8.2 For all other structures not covered in 8. t, the spectra and seismic zone as given in Annex A and Annex B is recommended [these are in accordance 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 supporting foundation medium on the motion of structure. The soil-structure intpraction may not be considered in the seIsmIc ana1]ysis for structures supported on rock or rock-like material.
The horizontal seismic coefficient Ah , shall be obtained using the period 7: described as under. When lIsing site specific spectra, the seism ic coeflicient shall be calculated from the expression:
8.3.1
9.2 Interaction Effects lJetween Structure and Equipmcnt
Ah=
Interaction effects between structure and equipment shall be considered as under:
(R./!)
where
Sn/ / g = spectral acceleration coefficient . corresponding to site specific spectra.
a) For Category 2, 3 and 4, simplified considerations as pCI' 9.2.1 may be used.
8.3.2 When llsing code specific spectra, the seismic
b) For Category I, dctailed considerations as per 9.2.2 shall be adopted.
co-effiCient shall be calculated from the expression: r~.. "I
I' l
r cr
9.2.1 For the purpose of 9.2, the following notations shall be used:
"I
: 1')3/. I
2 J L/ g
J
/1,( = total mass of the structural system on which the . secondary system is supported,
-----------
(R/J)
6
IS 1893 (Part 4) : 2005 Table 1 Percentage of Permissible Increase in Allowable Bearing Pressure, Resistance of Soils
( Clause 7.4.2 ) SI No.
Type of Soil Mainly Constituting the Foundatioll
Foundation
~--------------------------~----------------------------~ Type I Rock or Hard Soils: Well graded gravel and sand gravel mixtures with or without clay binder, and clayey sands poorly graded or sand clay mixtures (Gil, CW, SB, SW and SC) having N above 30, where N is the standard penetration value (2)
(I)
i)
Piles passing through any soil hut resting on soil Type I
ii)
Piles not covered under Sl No. (i)
Type II Mediul11 Soils: All soils with N between 10 and 30, and poorly graded sands or gravelly sands \-vith little or no tines (SP) with N> 15
Type III Soft Soils: All soils other that~.SP with N< 10
(3)
(4)
(5)
50
50
50
25
25
iii)
Raft foundations
50
50
50
iv)
Combined / Isolated RCC j()()tings with tie beams
50
25
25
v)
Well foundations
50
25
25
NOTES 1 The allowable bearing pressure shall be determined in accordance with IS 6403 or IS 1888.
2 If any increase in bearing pressure has already been permitted lor forces other than seismic forces, the total increasc in allowable
bearing pressure when seismic i<:'H"ce is also included shall not cxceed the limits specified above. 3 Desirable minimul1l field values ofN arc as 1Dllows:
--r----------. SI /1/0.
Seismic Zone
Depth Beloll'
N Vallie
Remarks
Ground Level (m)
111. IV and V
i)
::;5
15
~10
25
-
i)
- . -r - - ' - -
II
l
j ---~
---15
::;5
20
~10
For values of depths betweell 5 III and 10 Ill, linear interpolation is recommcnded.
Ifsoils orsmallcr N values arc l11et, compaction may be adopted 10 achieve these values or deep pile foundations going to stronger strata should be used. 4 Thc piles should be designed for lateral loads neglecting lateral resistance of soil layers liable to liquify.
=' Following Indian Standards may also be referred: a) IS 1498 Classification and identification of soils lDr general engineering purposcs. b) IS 2131 Method of standard penetration test f(x soils. c) IS 6403 Code of practice for determination of bearing capacity of shallow tDundations. d) IS 1888 Method of load tests on soils. 6 Isolated RCC IDoting without tic beams or unreinlDfced strip tDulldation shall not he permitted in son soils with N <1 0.
7
IS 1893 (Part 4) : 2005 Table 2 Importance Factor for Various Industrial Structures
(Clause 8.3.2) hli porta IH~l~
Categories ofStTllctlll'CS
SI No.
Factor
(see 7.1) (2)
(3)
i)
Structures in Category I
2.00
(I)
ii)
Structures in Category 2
1.75
iii)
Structures in Category 3
1.50
iv)
Structures in Category 4
1.00
NOTE--- Higher importance ractor may be assigned to difrcrcnl structurcs at the discretion of the project authorities.
MI{
total 1113SS of all the equipment that are rigidly mOllnted at different locations in the structure, and
/'v/l
total mass or all the equipment that are flexible mounted at different locations in the structure.
be considered and the most restrictive combination shall be used. 9.2.2.3 Coupled analysis of a primary structure and secondary system shall be performed when the effects of interaction are significant based on 9.2.2.9 and 9.2 2.11.
9.2.1.1 Wherever equipment are rigidly fastened to the !loor, the equipment mass (!vIR) shall be taken as IUlTlped mass at appropriate locations. No interaction between the structures and equipment shall be considered.
9.2.2.4 Coupling is not required, if the total mass of the equipment or secondary system is I percent or less of the mass of the supporting primary structure. If a coupled analysis will not increase the response of the primary system over that of a decoupled analysis by more than 10 percent then a coupled analysis is not requireci. However, the requirements of section 9.2.2.11 regarding the Inultiple supports should be considered.
9.2.].2 < 0.25
If A/s/-' Mt{
No interaction between the structures and equipment shall be considered. In such case A1F should be considered as lumped l11ass at appropriate locations.
9.2.2.5 In applying sections 9.2.2.9 and 9.2.2.11, one sub-system at a time may be considered, unless the sub-systems are identical and located together, in which case the sub-system masses shall be lumped together.
9.2.1.3 I I' A1" /(k/R -+ k/s) ~ 0.25, interaction between the flexibly mounted equipment and the structure shall be considered by suitably modelling the flexible equipment support system while considering the equipment (IS lumped mJSs.
9.2.2.6 When coupling is required, a detailed model of the equipment or secondary system is not required, provided that the simple 1lI0del adequately represents the major effects of interaction between the two parts. When a simple model is used, the secondary system sl1all be re-analyzed in appropriate detai I using the output motions frolll the first analysis as input at the points of connectivity .
9.2.2 Dccoupling criteria as given below shall be used for all Category 1 systems. 9.2.2.1 For the purpose of this clause, the following notations shall be used. . air
M . Ub .. ---AI 0..I
,.~,------
o, T
Participation
9.2.2.7 For applying the criteria of this section to have a modal mass greater than 20 percent of the total system mass, the total system mass is c1enned by
where A1 = mass matrix of tile structural system,
o
I
cc"
.
ith normalized Illode shalJC ' .0IT M0 j
=
AI
1, and
CO"
f ([')2 I
in f1ucncc vector, displacement vector of the slrllctunll system when the base is displaced by unity in the direction of earthquake motion.
9.2.2.8 When carrying out simplified analysis (as per 9.3), equipment or secolldary system shall be considered as per 9.2.2.4, 9.2.2.5 and 9.2.2.6.
9.2.2.2 All combinations of the dominant secondary system modes and the dom inant primary modes must
9.2.2.9 When detailed analysis is to be carried Ollt for structures with equipment attached at a single point,
U,)
cco
8
IS 1893 (Part 4) : 2005 Table 3 Response Reduction Factor
I),
R for I ndustrial Structures
(Clallse 8.3.2) SINo.
Lateral Load Resisjing Syst('m
Il
(I)
(2)
(3)
Bllildil1g Frome S:rsrems i)
Ordinary RC Moment-Resisting frame (OMRF) 1)
3.0
ii)
Special RC Moment--Rcsisting Frame (s rvlR F) »
5.0
iii)
Steel Frame with: a)
iv) .
COllcentric brace
4.0
h) Eccentric hraces
5.0
Stecll11()ll1ent resisting frame designed as
pCI'
SI> 6(())
s.u
Building 1I'ilh Shear Walls 4)
Load bearing masonry wall buildings.')
v)
a)
Unreinforced
b)
Reinforced with horizontal RC bands
2.5
c)
Reinforced with horizontal RC bands and vertical bars at corners of roo illS andjambs of openings
3.0
1.5
vi)
Ordinary reinforced concrete shear walls")
3.0
vii)
Ductile shear walls 7)
4.0
!Jllildings lI'i/1i f)uaI5)'sfcms S)
viii)
Ordinary shear wall with OMRF
3,0
ix)
Ordinary shear wall with SMRF
4.0
Ductile shear wall with OMRF
4,5
Ductile shear wall with SMRF
5.0
xi)
I) The values or response reduction j~lclors arc to be used for hllildings with lateral load resisting elements. and not just lor the lateral load resisting clements built in isolation.
OivlRF are those designed and detailed as per [S 456 or [S XO(), llowe"cr. OivlRF shall not he used in situations explained in IS IJ92(),
2)
1)
SMRF has been defined in 4_15.2 of IS 1893 (Part I).
I)
Buildings with shear walls also include buildings having walls an(! 1I·,1Il11:S. but where: a) frames arc not designed to carry lateral loads. or b)
1I-<1Il1CS
are designcd to carry lateral loads but do not rulfil the rcquiremcnts or dual systell1s.
'1
Reinforcement should be as per IS 4326.
I,)
Prohibitcd in zones IV and V,
7)
Ductile shear walls arc those designed and detailed as per IS 13920.
X)
Buildi!lgS wilh duill systcms consist of shear walls (or braced Ii'amcs) and moment resisting frall1es such that: a) the two systems arc designed to resist the total design fim.:e in proportion to their lateral stiniless considering the illtcraction of the dual system at al1l1oor levels. and· b)
NOTI:
til(':
moment resisting li'ames arc cksigncd to indepcmkntly resist at least 25 percent ortl1L: Jcsign seismic base shear.
I'm sled buildings not covL:rcd in Table 3, value or!? shall be 2.
IS 1893 (Part 4): 2005
the coupling criteria SllOWli in Fig. I shall be used. The Illass ratio ill Fig. I is the modal mass ratio computed as per 9.2.2.10 and the frequency ratio is the ratio or ullcoupled modal frequencies of the s(,COI1(I~lry and primary systems.
. shall be made to specialized literature. 9.3 Time Period Estimation The time period ofdiJTercnl industrial structures would vary considerably depending on the type or soiL span and height of the structure, distribution of load in the structure and the type of structure (concrete, steel and aluminium). It would be difficult to give one or two generalized formulae to cover all such structures. Accordingly, no simple guidelines can be given for estimation of time periods of industrial structures.
9.2.2.10 For a secondary system dom inant mode and the primary system mode i, the modal mass ratio can be estimated by: M A,
9.3.1 The time perioel shall be estimated ba~del on Eigen value analysis of the structural mathematical model developed in accordance with 9.1 and 9.2.
\vhcre fl,1pI .:: (lei :-".
(lio",.... Y: the Illode vector value from the primary system's modal displacement at the location where the secondary system is connected, from the ith normalised modal vector, (0), 0' ci
111,> 0
9.3.2 For prelim inary desigll, the time period can be established based on its static deflection under mass proportional loading in each of the three principal directions. This load is applied by applying a force equal to the weight of the structure or equipment at each mode in X, Y or Z direction. Where the founding soil is soft soil, the effect of the same shall be considered in the estimates for static deflection.
I;
"i
/I.'~,:"
mas.s matrix of tire primary system; and
M,
total mass of the secondary syskm.
9.2.2. J I Multisupport secondary system shall be reviewed for the possibility of interaction of structure and equipment stiffness between the support points, and for tile eCfect of equipment mass distribution bet ween support points. When these eHects can significantly inlluence the structure response, reference
The time period T, would then be :
DO (UX) \
Flc;.
I
O.llX) .
0.010
Dr:COUPI.ING CRITERIA H)R EQUIPMENT OR SLCONDAI
10
S YSTEt,,!
i.lXX)
IS 1893 (Part 4) : 2005 Where 8 is the maximum value of deflection at any mode out of b" by bz and 'g' is acceleration due to' gravity in the cOl-responding unit.
10.2.2.1 The design eccentricity, eoi to be used at floor j shall be taken as: (
e
9.4 Damping The damping factor to be used in determining spectral acceleration coefficient (S/g) depends upon the material and type of construction of the structure and the strain level. The recol11mended damping factors are given in Table 4.
to
l.5 e. + 0.05 bi
i
or e
SI
._ ~I
0.05 b.
I
whichever of these gives more severe effect. e si = static eccentricity at floor i, defined as the distance between centre of mass .and centre of rigidity; and
ANALYSIS PROCEDURE
b;
=
10.1 Classification of Analysis Techniques
floor plan dimension of floor i. perpendicular to direction of force.
The factor 1.5 represents dynamic amplification factor, while the factor 0.05 represents the extent of accidental eccentricity.
10.1.1 Detailed analysis shall be carried alit for
structures of Category 1, in all seismic zones. 10.1.2 Detailed analysis shall be carried out for all structures of Category 2 and 3 in seismic zones Ill, IV and V.
NOTE - For the purposes of this clause, ull steel or aluminiull1 1looring system may be considered as llexible unless properly designed tloor brneings havc becn rrovided.
Reinforced
concrete l100ring system at;) level shall be considered rigid only if the total arc;) oralltl1e cul-outs altha! \c\'el is less than 25 percent of its plan floor area.
1n.l.3 Simplified analysis may be lIsed for structures of Category 2 and 3 in seismic zone [I. 10.1.4 Simplified analysis may be used for structures of Category 4 in all seismic zones. However, those structures of Category 4, which could be identified as bu i Idings, ll1ay be analysed as per provisions of IS 1893 (Part 1).
10.2.3 Seism ie analysis shall be performed for the three orthogonal (two horizontal ane! aile vertical) components of earthquake motion. The earthquake motion in each direction shall be combined as specified in 7.3.
10.2 Detailed Analysis 10.2.4 Til77e-l-lisiol)' Analysis I'defiJoc/ 10.2.1 Second({!y Effcc:t Time-history analysis of structures subjected to s e i s 111 i c loa d s s h a \I b c per fo r me d II sin g I i 11 ear analysis technique. The analysis shall be based on well-established procedures. Both direct solution of the equations or motion or model superposition method can be Llsed for this purpose.
The analysis shall also include the influence of P -- 6. effect. 10.2.2 Torsion The effect of accidental eccentricity shall be considered for rigid floors/diaphragms. This shall be applied as an additional torsion force equal to product of the mass at floor level and 5 percent of the structure dimcnsion perpendicular to the earthquake direction at the centre of mass of the floor.
10.2.4.1 In model superposition method, su fficiently large number of modes shall be used for analysis to include the influence of at least 90 percent of the total scism ic mass.
Table 4 Damping Ratio Coefficient for Different Construction Materials for DBE and MCE Conditions ( Clause 9.4 ) SI No.
Material
DBE
l\lCE
(I)
(2)
(3)
(4)
i)
Aluminium
0.02
0.04
ii)
Stet:1
OJ)2
0.04
jii)
Reinforced Concrete
0.05
O.()7
NOTE -- For combined structures, damping ratio coefficient shall be determined based on well establ ished procedures. ira composite d~llllpillg ratio cocf'Jicient is not evaluated. it shall be taken as lhal corresponding to material having lower damping.
11
IS 1893 (Part 4) : 2005
modes, then the peak response quantity ( A ) due to all modes considered shall be obtained as:
10.2.4.2 Aloe/al mass The modal
1l1,\SS
(M1) of mode k is given by : ( ,v--' 2
li .
1'-1
Af~
iV I
(h f"k
.'II
.J' 1
g I, IF;
where
(
i I
absolute value of quantity, in mode k; and
\vhere
g :::. acceleration due (!J
ik
IV;
:::;
=:=
10.2.5
to
gravity,
r ,-= number of modes being considered.
mode shape coefficient at floor i, in mode k, and
b) If the structure has a few closely-spaced modes [see 3.2 of IS 1893 (Part I )], then the peak response quantity X due to these modes shall be obtained as :
scism ic weight of noor i.
Response Spec/rul1I Analysis
Response spectrum method of analysis shall be performed using the design spectrum. 10.2.5.1 Suf1iciently large number of modes shall be used for analysis to include the influence of at least 90 percent of the total seism ic mass. The model seismic mass shall be calculated as per the provisions of 10.2.4.1.
\vhere the summation is for the closely spaced modes only. This peak response quantity due to the closely spaced modes (,.t*) is then combined with those of the remaining well-separated modes by the method described in 10.2.5.2(a)_
10.2.5.2 Aloe/cd combination
10.3 Simplified Analysis
The peak response quantities (for example, member forces, displacements, storey forces, and shears and base rcuctions) should be combined as per complete quadratic combination (CQC) method as follows:
Structures of category 2, 3 and 4 located ill seismic zones II and III may be analyzed using the provisions of this clause. For all other industrial structures, the analysis procedure specified in 10.1 shall be used. 10.3.1 Simplified analysis shall be carried Ollt by applying equivalent static lateral loads along each of the three principal directions. The equivalent static lateral loads shall be determined from design acceleration spectrum value (AI) calculated from 8 ..3.2 and 9.3.2. Th~ static load at each node shall equal the product of its !11(lSS and the design spectral acceleration value.
where A':C: peak response quantity;
A, A,
response quantity, in mode i (including sign); .c-c
response quantity. in mode j (including sign);
II
(1" ~-:: cross-modal correlation co-'efficient;
DEFORMATIONS
11.1 Drift Limitations
1':::'::
The drift limitati.ons of horizontal and vertical members shall be taken as those specified in IS 1893 (Part I).
number of modes being considered;
11.2 Separation Between Adjacent Units
C; ';.-. modal damping ratio as specified in 9.4; w. Il frequency ratio =
oi-
Two adjacent buildings, or adjacent units of the same structure '.vith separation joint in between shall be separated by a distance equal to the alllount R times the sum of the calculated storey displacements as per 11.1 of each of them, to avoid damaging contact when the two un its deflect towards each other. When floor levels of t\'\'o adjacent Ull its or structures are at the same elevation levels, factor R in this requirement lllay be rcpbced by Ni2 +25 111m.
I
circular frequency, in jth mode; and
Wi
w; ~c- circular frequency, in ith mode. !\ Iternativcly. the peak response quantities Illay be
combined as follows: (I)
[I' the structure does not have Closely-spaced 12
IS 1893 (Part 4) : 2005 12 MISCELLANEOUS
Table 5 Categorization of Indllstrial (Typic~ll)
Structures
12.1 Foundations
( Clause 7.1
Tilt: use of fOLln dat ion s vulnerab Ie to sign ific an t differential settlcment duc to ground shaking shall be ;lvoided for structures in seismic zones III, IV and V. [n seismic zones IV and V, individual spread footings ()r pile caps shall be interconnected with tics (.)'(!e 5.3.4.1 of IS 4326) except when individual spread footings arc directly supported on rock. All tics shall be capable of carrying, in tension and in compression. an axial force equal to A/4 titTles the larger of the column or pile cap load. in addition to the 0 the r w i sec 0 111 put c d 1'0 I' C C s. Her e. A his as per 8.3.1 or 8.3.2. 12.2 Call tilever Projections
12.2.1 //eJ'lico/
Towers. tanks. parapets, smoke stakes (chimneys) and
SI No.
SlrucllllTS
(t)
(2)
(3)
I.
Adminislration building
2.
Air waslh:r pump
3.
Air pre-hcallTs
2
4.
Ash colleclion silos
1
:".
Ash dyke
2
(l.
Ash watel punlp hOlls\:
2
7.
Ash watel
8.
Ash/slurry pUIllP hOllse
0.
Auto base
2
11OUSl:
rl~-c;in.;ulali()n
2
building
10.
Bagging and pallctizing building
II.
11all111ill and silos
2
11.
Boikr and bnikr house
2.
13.
Ihidgcs l)Vl:r rivC)'s
2.
14.
C&'I nwinlenance stores
I:".
Canteen building
16.
Callstic tanks
17.
Chiller pl;lIll
18.
Chlorine storage handling/ dozing buildillgs
19.
Clarilloculalor
20.
Coal handling plmlt
21
Coal slurry settling pond
2
22.
Comprcssor foundatiun
2
23.
Compressor house
2
13 DESIGN CRITERIA
24.
Condenst:r polishing unit
SLack-like structures nre those in which the mass and stillness is more or less uniformly distributed along the height. Cantilever structures like reinforced or prl'stressed cement concrete electric poles; reinforced concrete brick and steel chimneys (including ll1u!titllle eh illlncys), venti latioll stacks and refinery vessels are e:\alllples of slich structures. The guyed structures arc not covered here.
25.
Construction \\orkshop
26.
Control and inSlrLllllcllLllion building
27.
Control building
lR.
Clll1trol building (blast resistant)
29.
Converters
2
30.
Conveyor galleries
2
31.
Cooling towcrs (wei alld dry) and control
32.
Corex gas sl;ttioll (for cn-genl:ration plant)
33.
Crus iter house
34.
Crushers
3:"
Cryugcnic storage lank (double walled)
other vertical cantilever projections attached to structures and projecting above the roof. shall be designed for rive times the design horizontal a c c e I era t ion s p c c t r U 111 valli e s pc c ifi cd i\1 8.3. I and 8.3.2.
12.2.2 llo/'izonto/ horizont,ll projections like cornices and balconies sh::111 Le dcsiglled for five times the design vertical accelcration spectrum valuc specified in 8.4. All
12.2.3 The increased design forces specified ill J 2.2.1 and 12.2.2 are only for designing the
projecting pal1s and their connections with the main structures. For the design of the main structure, such increase need not be considered. SECTION 2 STACK-LIKE STRUCTURES
14 TIME PERIOD OF VIBRATION
Tillle period of vibration, T of such structures when lixcd (It basco sh(lll be calculated using either of the following two formulae given (see J 4.1 and t 4.2). 'rlle formulac given (It 14.1. is more accurate. Only one of these two formulnc should be lIsed for design. Tillle period of strucrure, ifavailablc. through vibration mcasurement on similar structure and foundation soil condition can also be adopted.
2
:2
1'\J(1I11
2
2
2
(etitv!cnc)
36.
Cryogenic storage tanks with refrigerated
liquefied
13
g
2
IS 1893 (Part 4) : 2005
Table 5 --.-- Concluded
Table 5---- COl1tinued SI No,
Sfrurtun's
Cah'gory
SINo.
Strudul'cs
Catq~ory
(I)
(2)
(3 )
( I)
(2)
(3)
.17.
ew pllmp house
2
74 .
PolYlllcrisation building
2
38.
DG hall
2
75.
Process huilding (closed)
2
J9.
Dirty and ckan oil building
2
76.
Process column on elevated structures
·10.
DM plant
2
41
Erllucnttreallm:nl plant
3
·12.
Electro static precipitator- ESP
2
n.
Process water storage lank
,13.
ESP cuntl'lll
2
79.
Product storage sheds/building
2
·14.
Extrusion building
2
gO.
RailloaJing gantry
3
45.
F.O. pump house
2
81.
ReC chimney
2
46.
F.O. storage tank and day tank
2
82.
Regeneration huilding
2
·17.
Fans - Pi\., FD, CR and ID fans
2
83.
Scrubber
2
-lX.
Filler
2 84.
Settling tanks (ReC)
2
'I().
Filtralion and chlorination plant
3
Sheds (tall and large span, high capacity cranes) 2
Fin; statiun
2
85.
'iO. 'il.
Firl'lender
2
86.
Silos
2
5~.
I:ire water pUIl1P hOllse
2
87.
Smelters on RC'C/stccl structllres
2
.'13.
I·ir.: water res.:rv(lir
2
88.
Sphcre/bulkts
2
'i4
rlar.: stack suppurting structure
2
89.
Start-LIp Iransll)I'Jner
3
)).
Gat.: and galc housc
4
90.
Storage silos (RCC/steel/aluminum) on
2
roOIll
77.
Process column/vessel/reactors on low Ree pedestal
elevated structure
'i6.
Ge ncralor transformer
.':;7.
He plant building
2
:'iX.
I kater /furnace
:'it) .
91.
Storage tank (dome/cone roof)
2
2
92.
Stores
J
I katcrs with sled raek
2
9J.
Substation
2
h()
Iloriwntal VL:ssl'l/h.:at exchanger
2
94.
Substation buildings
(>I.
Intake stI'llCluJ'l:
9:'i.
Switch-gear building
h2.
Laboratory btl i Id i ng
4
96.
Switchyard
(13
LP(i storage
2
97.
Switchyard strLlctun.:s
M.
[\'Iain conciensate storage lank
2
98.
Tanks for refrigerated liquefied gases
2
(I).
Main plant building (TCi, 13FI' including hUllker h,lY)
2
99.
Technological structures in RCC/stcd nr both
2
l'''lake-up \\'aU:r pump hOllse alld fore-bay
100.
Track hopper
2
2
(lh.
ivl iermv;J\\: I(l\N(TS
2
101.
(l7.
Trnnsforll1crs alld radiator bank
2
hX.
()J)
102.
Truck loading gantry
3
(,()
(J11l,'r nOll-plant hllildillgS and utility structures
103.
'I'unne I/trenclll:S
7()
()verhe;lll water lallk
101.
W;lgun lippkr
71.
Pipt.: Pl:(k:slal ;111(1 clhlc trl:st\cs
2
I US.
Warel1ollsl:
2
72.
Pipe rack
2
]06.
Water treatment plant
2
73.
Pipe supports including anchor.~
2
107.
Workshop
Ii
duch
2
14
2
IS IS93 (Part 4) : 2005
15 DAMPING
The fundamental time period for stack-like 14.1 structures. 'r is given by:
The damping factor to be lIsed in determining .\/g depends upon thc material and type of construCI iOIl of the structure and the strain level. The following clamping factors arc recolllmcnded as gu iclance for different materials for fixed base condition and are given in the Table 7.
where
Cl
coefficient depending upon the slenderness ratio of the strllcture given in Table 6,
IV,
total weight of the structure including weight oj' lining and contents above the base,
"0= Es':
A
::=
16 HORIZONTAL SEISMIC FORCE
Using the period 7: as indicated in 14. the horizontal seismic coefficient A" sllall be obtained from the spectrum given in IS 1893(P~Ht I). The design horizontal seismic coefficient for 1\ desigll basis earthquake (DBE) shall be determined by the following expression adopted in IS 1893 (Part I) :
height of structure above the base, III od u Ius
of elasticity of material of the structural shell,
area of cross-section at the base of the structural shell.
J
Ail
I = importance
The fundamental tirne period, T of a stacklike structure can be determilled by Rayleigh's approximatiuJ1 for fundamental Illode of vibration as follows: T 14.2
I~lctor
as given ill Table g,
R = response recluction factor as given in Table 9. The ratio (lUI) shall not be less than 1.0, and
S,,/ /g
N
=
spectral acceleration coefficient for rock and soil sites as given in Annex B. This is in accordance with Fig. I of IS 1893 (Part I).
WiD;
The horizontal earthquake force shall be assumed to act alone in ol1e lateral direction at a time.
i_ol
N
L 11'0. 2 I
I
The effects clue to vertical component of c~lrthql1akcs are generally small and can be ignored. The vertical seismic coefficient where applicable may be taken as 2/3 of horizontal seismic coefficient, unless evidence of factor larger than above is available.
i-I
where
N
(lVI)
Z = zone factor given in Annex A. This is in accordance with Table 2 of" IS I Xl)3 (Part I),
NOTE - This rormula is only applicable to stack-like structure in which the Illass and stiflill':ss are more or less 1I11irormly distrihilled along the height.
H'
==
where
g:.:: acceleration due to gravity.
L
lr z/I 2 [Sa//g/] .11
For circular sections, A = 2 J[ rt, where r is the mean radius of structural shell and I its til ickness, and
weight lumped at jth location with the weights applied simultaneously with the force applied horizontally, lateral static deflection under its own lumped weight at Ith location (eh imney weight lumped at 10 or more locations),
The effect of earthquake and maximum wind on the structure shall not be considered simultaneously.
number of locations of lumped weight, and
17 DES1GN SHEAR FORCE AND MOMENT
Either simplified method (that is. equivalent static lateral force method) or the dynam ic respollse spectrulll modal analysis method is n:commcnded for calculating the seismic forces developed in such structures. Site
acceleration due to gravity. Norvs
g
I /\11) clastic analysis procedure like illOlllent area theorclll or colunlll
spectra compatible lime history analysis may also be
carried out instead of response spectrum analysis.
2 For determining the lime period of vibration of structures resling on frames (lr skirts like bins. silos. hyperbolic cooling [(l\\\:rs. relillcry columns. nnly the Ihrmlila given at 14.2 shnuld he used. Approximate methods may bc adopted to estimate tlt-: lalL'ral stilllless of the frame or skirt in order to dctnilline the laleral stalic delkctioll. Dynamic response spcclrull1l1lodal '1l1alysis will be Ill:cessary ill such caSl~S.
17.1 Simplified Method (Equivalent Static Lateral Force -Method)
The simplified method can be lIsed for ordinary stacklike structures. The design shellr force, V, and design 15
IS 1893 (Part 4) : 2005 Table 6 Valul's of C r and C" (Clauses 14.1 and 17.1) SI No.
k = Itlre
(I)
(2)
Cocrlicil~lIt,
i)
Coefficient, Cv
CT
(3)
(4)
14.4
1.02
ii)
10
21.2
1.12
ii)
15
29.6
I. F)
iv)
20
38.4
1.25
v)
25
47.2
1.30
vi)
30
56.0
1.35
vii)
35
65.0
1.39
viii)
40
73.8
1.43
ix)
45
82.8
1.47
x)
50 or more
1.8 k
1.50
NOTE - k
=.
slenderness ratio, and
ro = radius orgyration ofthe structural shcll at the base section.
Table 7 Material Damping Factor
(Clause \5) SI No.
l\ latcrial
DUE
MCE
(I)
(2)
(3)
(4)
i)
Stecl
0.02
0.04
ii)
ReinlclI-ced Concrete
0.05
0.07
iii)
Brick Masonry and Pla:n Concrete
0.07
0.10
NU'ITS I For clastic basc represcntcd by raft on soft soil or pilc foundation, the damping may be worked out as wcighted damping based on IllOdal strain energics in superstructurc and substructures. As an approximation the values may bc assul1leu as 7 perccnt of critical damping for rcinforced concrete structures.
2 Fur riveted steel stacks/chimneys, etc, a 5 perccnt of critical damping may be adopted to account for the frictional losses. 3 The damping values obtained from experimental tests on similar structures can also bc used. ... 111 case oj'l11ulti-llue RC chimncys, 3 percent of critical value for DBE anu 5 pcrcent for MCE is recommendcu.
WI = total weight of structure including weight
bending moment, lvi, for such structures at a distance )( from the top, shall be calculated by the following formulae: a)
of lining and contents above the base, h = height of centre of gravity of structure
above base, and
/l= Cv . A h W. DI' I
D", Dill =-~ distribution factors for shear and moment
Cv = coefficient of shear force depending on slenderness ratio k given in Table 6,
respectively at a distance X from the top as given in Table 10. The expressions for these distribution for moment and shear along the height is given in Table 11 for LIse in computer programll)e.
des ign horizontal seism ic coefficient determ ined in accordance with 16,
The appropriate foundation soil and pile group stiffness are given in Table 12.
where
/Ih =--=
16
IS 1893 (P~lrt 4) : 2005
Table 8 Importance Factor Applicable to Stack-Lil\c Structures (Clallse 16) SI No.
Type ofStructllrc
tm porIa nce Fado ..
(I)
(2)
(3)
Reillfc)J"(.:cd concretc vcntilation stacks
1.:1
Reilltl)rced concrete chimllcys
1.5
iii)
Reillforccd brick l11asonry chimncy for imlustry
1.5
iv)
Un-rcinl(lrI.;cd brick masonry chimney
v)
Reinforced concrctc T.V. towers
i)
ii)
rur industry 1.5
vi)
Eketric/trartic light polr..:s
vii)
Stcel stack
1.5
Sillls
1"
viii) NOTI:S
1 In casc ofilllport:tllt 1;lctur givcn in Table 2 alld Table 8 fOlllld ditTcn:lll. higher values shall be considcn:d.
2 The vall1l:s oi"illlportance 1~lct()r.1 given in this table are j()r gllidance. A designer lIlil)' ch()ose suitabk V,t!IH:S depending ol11hc irnportallce hased 011 economy, strategy and other consideration,.
Table 9 Reduction Factor Applicable to Stack-Like Structures (Clallse 16) SI No.
Type ofSlructul"c
Rcdudioll Factor. R
(I)
(2)
(3)
i)
COil crete,
T. V. towcr
3.0
ii)
Reinforced concrete ventilation stack
3.0
iii)
Rcinfl)rced cOllcrete chimney
3.0
iVj
Rcinl()rccd brick masonry
2.0
Steel chill1lley
2.0
Sted relincry vessels
2.0
vii)
Un-reinforced brick masonry chimlll'Y
1.0
viii)
Rc i n forced ekclric/trartic pole
2.0
v)
vi)
17.2
Reinforced
Dynamic Response (Spectrum
component 1110tion, sec 7.3.2.2 ofScctioll I 'Industrial Structures' .
Modal
Analysis)
17.2.1 ;Halliclllolic'o! Model
Till' dynam ie analysis using respollse spectrulll method s h 0 II I d bee a r r ie d 0 U t 1'0 r i III port a 11 t s t a c k -I ike structures. The number of mode to be considered in the analysis should be such that about 90 percent of tlh)dal lllass is excited. The modes could then be combined by Inodal combination of corresponding re~;ponse I ike shear, moment, etc, as suggested in IS 1893 (Part I). The detailed dynamic analysis lIsing lime history shall be required where analysis is based un s~te-speci lic response spectrum and compatible time history of ground motioll. For cornbination of three-
The matllem3ticallllodel of stack-I ike structures should be able to represent sufficiently the variation in its stiffness (variation in cross-section and Ih ickness of shell), lining mass and foundation modelling (that is foundation stiffness, soil clefolTnations). 'fhe nUl1lber of clements should be such as to capture the variation of stiffness and n18SS of the system. A rninimul11 of ten beam clements should in general be suff~cicllt. For axi-s),llllTlctric structures axi-symmetric linitc elements shall be used. 17
IS 1893 (Part 4) : 2005 Table 10 Digitized MonH'nt and Shear Distribution Factors Dm and Dv along the Hdght (Clause 17.1) SI1\o.
X/IJII
1\'I01I\('lIt
Distribution (D,)
Shea,' Distrihutioll (D)
~-~ (I)
Fi\ccl
Soil
0)
(.1)
(2)
---_._---------
~
,
Pile Foundation
Fixl'd
Soil
Pile I'(lundal inn
(:'I)
(6)
(7)
(X)
-.-----.----.--------------------.--~-
i)
O.no
(lOll
O.()(J
O()O
0.00
(j()O
(jO()
ii)
0.05
0.09
0.13
0.11
O.2X
0.21
014
iii)
n.lo
0.13
0.19
0.16
0.'12
027
O.Il)
iv)
0.20
0.1 X
0.27
0.22
O.6·1
0.34
O.2()
v)
0.30
0.22
0.33
o.n
0.83
0.38
0.31
\i)
OAO
0.27
0.39
0.33
1.00
0.41
0.35
vii)
OJ()
0.32
(J.45
OJx
1.00
0.44
(lAO
viii)
()()()
0.39
()j2
0.45
I.O()
U.49
() ,Ill
i,..; )
0.70
OAX
0.60
0.54
I.OU
055
0.54
,..;)
(l.80
0.60
0.70
OJ))
1.00
0.65
0.65
,\i)
O,9()
o,n
O,X3
(J.XO
1,00
0,80
(J.80
,iii
0.95
0.88
0.91
0.89
1.00
0.89
,..;iii)
I.no
LOO
1.00
1.00
1.00
i.O()
:) 'X' is the distance hom top and 'fI'
1.00 i~
the height
()rehillln('~'
above the base.
Table 11 Values of
J) jH
and D
\'
(Clause] 7.1) SI i\'o.
Soil FOlllldatioll COlldition
( I)
(2)
i)
Fix.:d
ha~i':
(h
Ull
or nil'!
(Ill
D, (3)
(4)
hard soil
II
N V:tllIl~S)
rL-~]JI2
·1·
0.75
X
I-lh
j
- - - I Ill)
'X J.I rl.hj ---I
hut :':'; 1
'
:r ' II'
ii)
I{all
(Ill
(bas~d
suil ()Il
N valll~s)
0.6
I--=---1 ,--II j
r .\' J'
iii)
Pill.: rOlintlaliull
0.5\---
'-- II
18
(;r
~11
tlHI'-:.-1 II ' )
\...
+())
' '\," 1112 --:-1 r~.hj
r--j''1,1 o.66l--r III: I X
li2
1.1
'- h .
("
_
X
.h )
-o.20
( X
""'I
.. O. 7) l-~;-II' j
+ O.())
i'
1-----1
LhJ
r
r
l h)
l
X '') X j.1 1--1 +0.)41--.-
h
IS 1893 (Part 4) : 2()OS
Table 12 Foundation Soil and Foundation Pile G roup Stiffness (Clause 17.1) SI No.
Type of FOllndation
Stiffness
(I)
(2)
(3)
CirClilar rajijimlldul/nl/ 01/ soil:
i)
I)
Ilorizontai soil slilfness
;:.:" "" 32 ( 1-- v) Gr,.l (7
2)
Rocking soil stiffness (full circular ran)
;:':,'"" S G/'oJ /3 ( I --
S IJ)
IJ)
.1 1111 l/Iar roll:
ii)
I)
Friction pile fi.)ulldation (under reamed piles not covered)
;:':10 .;.:,
11El,IO! 1.27:'
2)
Translational stilllless of piles at the base ofpik cap
7~~"
(U",! 17 Y'"
-J
Ill/F! 2
1
where
G
shear modulus
or soil == l' \1/,
r "" shear wave velocity (lfthe medium, radius of circular ran foundation,
v
PIlisson's ratio ofsnil,
II '"
number or pi lcs,
,~. ,,=
modulus llfclasticity of pile material,
I,,,
==
mOlTlent ofincrtia ofpilc section,
{=
characteristic length ofpiic,
II"~
thickness ofpilc cap or rali. and
'II,
_co
modulus ol'sub grade reaction ofsnil ill horizontal directiun.
NO"ll':S I For rectangular foundation cllcctivc radius /'" = lilUllllatiull.
f::h may be taken. wllcre
(I
and b are the dimension of the rectang.ular
2 For N valucs > 50. li"ed base condition may be assumed. 3 Classilication of soil shall be as pcr IS 1893 (Part I). 4 Whcn soil structure interaction effects are to be considered; shear wave wlocitics are to be determined by suitable mcthods.
In case of chimneys, no stiffness is considered to be provided by the lining, however, the mass of lining above any corbel is assumed to be IUlllped at the corbel level. .
two layers of reinforcement arc required, thc circumferential reinforccment in each l~lCC shall nut be less than 0.1 percent of the concrete area at the section.
NOTF --_. MillilllUlll number ofcicmcnts should be adequate \.() ensure tll,lt thc m(ldel represent lhe lI'cqucllcics up to 33 Hz.
18.3 The circumferential rcinfiJI"Celllent for a disrance of 0.2 times diameter of the chimney (from top of the chimney) shall be twice the normal reinforcement.
18 SPECIAL DESIGN CONSIDERATIONS FOR
RElNFORCED CONCRETE STACKS 18.4 Extra rein ro)'cement shall have to be provided in addition to the reinforcement determined by design at the sides, top, bottom and corners of these orenings. The extra reinl~)\"Cell1el1t shall be placed on both faces of1he chimney shell as close to thc opening as rroj)cr spacing of bars wil! permit. Ulliess othenvise specified, all extra reinforccment shall extend past the opening a suff~cient distance [0 devclop the full bond strength.
18.1 The total vertical reinforcement shall not be less
than 25 percent of the concrete area. When two layers are required, the outside vertical reinforcement sh311not be less than 50 percent of the n:in forcel11ent.
or reinforcement
18.2 The (otal circLlmferential reinforcement shall not be less than 0.20 percent of the concrete area. When
19
IS 1893 (Part 4) : 2005 18.5 At cach side of the opening, the additional vertical reinforcement shall have an area at least equal to the L'Slabl ished design reinforcement for one-half of thc width of the opening.
steel shall be placed as close to the open ing as practicable, but vvithin a height not to exceed twice the thickness.
18.6 A I both the top and bottom or each opcn ing, additional reinforcement shall be placed having an area ~It /t.:ast equal to olle-half of the establishcd design circumfercntial reinforcement interrupted by the open ing.
The rnaxinllllll 1~ltcral deflection of the top or a st(lcklike structure undcr ,til service conditions, prior to the applicatioll of load factors, shall not exceed the limits set forth by the following equation:
18.7 Dcllcction Criterion
Di\Ia,
Ol1e half or this extra rcinforcement shall extend completely arollnd the circumfercntial ofihe chimney, ,1IId the other half shall extend beyond the opening to a su fficicnt distance to dcvelop the bars in bond. The
"CC
0.003 II
where D~h\.
"'-
Ii
maximum lateral deflection, and height of structure above the b(lse.
ANNEX A
(Clauses 8.2 and 16) ZONE FACTOn Zone Factor Z for MCE
i\
SeislIl ie ll Zone
II
In
IV
v
I
0.10
0.16
0.24
0.36
Till"
I()Jlill~
is as pcr IS I W)3 (part I).
20
IS 1893 (Part 4) : 2005
ANNEX B (Clauses 8.2) DESIGN SPECTRUM
3.0 / Type I (Rock! or Hard Soil)
Type II (Medium Soil)
2.5
~co ~ C
o 'fij
Type III (Soft Soil)
2.0
L-
CD
Q)
o
1.5
o
« (ij
.b
o
1.0
~
en
0.5
---------=-==--------~~"::~~
0.0 1L---_-L-_--'--_---'_ _- L - _ - - L 1.0 1.5 2.0 2.5 0.5 0.0 1
_---11
_ - - L 1 _ _..L 1
3.0
3.5
Period (s) FIG.
2
RrSI'ONSF S['I:CTR;\ FOR ROCK ;\ND SUIL SilLS rem
GMGIPN-47 BIS/ND/2008-··500
5
Pr:RCl-NT D;\i\1PIN(i
4.0
