Seismic force evaluationProcedure in codesLimitations of IS
1893:1984
Seismic force evaluation
During base excitationStructure is subjected to accelerationFrom
Newtons second lawForce = mass x accelerationHence, seismic force
acting on structure
= Mass x acceleration
Seismic force evaluation
For design, we need maximum seismic force Hence, maximum
acceleration is requiredThis refers to maximum acceleration of
structureThis is different from maximum acceleration of
groundMaximum ground acceleration is termed as peak ground
acceleration, PGAMaximum acceleration of rigid structure is same as
PGA.
Seismic force evaluation
Seismic force = mass x maximum accelerationCan be written as:Force
= (maximum acceleration/g) x (mass x g)
= (maximum acceleration/g) x W
W is weight of the structureg is acceleration due to
gravityTypically, codes express design seismic force as:
V = (Ah) x (W)
V is design seismic force, also called design base shearAh is base
shear coefficient
Seismic force evaluation
Maximum acceleration of structure depends on Severity of ground
motionSoil conditionsStructural characteristicsThese include time
period and dampingMore about time period, laterObviously, base
shear coefficient, Ah, will also depend on these parameters
Seismic force evaluation
Seismic design philosophy is such that, design seismic forces are
much lower than actual seismic forces acting on the structure
during severe ground shakingBase shear coefficient has to ensure
this reduction in forcesHence, base shear coefficient would also
have a parameter associated with design philosophy
Seismic force evaluation
Thus, base shear coefficient depends on:Severity of ground
motionSoil conditionStructural characteristicsDesign
philosophy
Seismic force evaluation
Let us examine how following codes have included these parameters
in base shear coefficientIS 1893 (Part 1): 2002IS
1893:1984International Building code (IBC) 2003 from USAStudy of
IBC provisions will help us understand the present international
practice
IS 1893 (Part 1):2002
Ah = (Z/2). (I/R). (Sa/g)Z is zone factorI is importance factorR is
response reduction factorSa/g is spectral acceleration
coefficient
IS 1893 (Part 1):2002
Zone factor, ZDepends on severity of ground motionIndia is divided
into four seismic zones (II to V)Refer Table 2 of IS
1893(part1):2002Z = 0.1 for zone II and Z = 0.36 for zone V
IS 1893 (Part 1):2002
Importance factor, IEnsures higher design seismic force for more
important structuresValues for buildings are given in Table 6 of
IS :1893
Values for other structures will be given in respective partsFor
tanks, values will be given in Part 2
IS 1893 (Part 1):2002
Response reduction factor, REarthquake resistant structures are
designed for much smaller seismic forces than actual seismic forces
that may act on them. This depends on
DuctilityRedundancyOverstrengthSee next slide
Design force
Maximum
Load Capacity
Total Horizontal Load
Roof Displacement ()
Non linear
Response
First
Significant
Yield
Linear Elastic
Response
max
Fy
Fs
Fdes
y
w
Fel
Load at First Yield
Due to
Overstrength
Due to
Redundancy
Due to
Ductility
Maximum force
if structure remains elastic
0
Total
Horizontal
Load
Figure: Courtesy Dr. C V R Murty
IS 1893 (Part 1):2002
IS 1893 (Part 1):2002
Response reduction factor (contd..)A structure with good ductility,
redundancy and overstrength is designed for smaller seismic force
and has higher value of RFor example, building with SMRF has good
ductility and has R = 5.0 as against R = 1.5 for unreinforced
masonry building which does not have good ductilityTable 7 gives R
values for buildingsFor tanks, R values will be given in IS:1893
(Part 2)
IS 1893 (Part 1):2002
Spectral acceleration coefficient, Sa/g Depends on structural
characteristics and soil conditionStructural characteristics
include time period and dampingRefer Fig. 2 and Table 3 of
IS:1893See next slide
IS 1893 (Part 1):2002
For 5% damping
IS 1893 (Part 1):2002
For other damping, Sa/g values are to be multiplied by a factor
given in Table 3 of IS:1893Table 3 is reproduced belowFor higher
damping, multiplying factor is lessHence, for higher damping, Sa/g
is less%
damping02571015202530Factor3.201.401.000.900.800.700.600.550.50
IS 1893:1984
Let us now look at the provision of IS 1893:1984IS 1893:1984
suggests two methods for calculating seismic forcesSeismic
coefficient method (SCM)Response spectrum method (RSM)These have
different expressions for base shear coefficient
IS 1893:1984
Ah= KCIo Seismic Coefficient Method (SCM)
= KIFoSa/g Response Spectrum Method (RSM)
K is performance factorC is a coefficient which depends on time
period is soil-foundation system coefficientI is importance factoro
is seismic coefficientFo is zone factorSa/g is average acceleration
coefficient
IS 1893:1984
Seismic coefficient, o Depends on severity of ground motionUsed in
seismic coefficient methodZone factor, FoDepends on severity of
ground motionUsed in response spectrum method
IS 1893:1984
IS 1893:1984
is soil foundation coefficientDepends on type of soil and
foundationIn IS 1893:2002, type of foundation does not have any
influence on base shear coefficient
IS 1893:1984
Importance factor, IEnsures higher design seismic force for more
important structures IS 1893 (Part 1):2002, gives values only for
buildings
IS 1893:1984
Performance factor, KDepends on ductility of structureSimilar to
response reduction factor of IS1893(Part 1):2002K is in numerator
whereas, R is in denominatorFor buildings with good ductility, K =
1.0For ordinary buildings, K = 1.6Thus, a building with good
ductility will have lower value of base shear coefficient than
ordinary building
IS 1893:1984
IS 1893:1984
Coefficient, CDepends on time period see next slideSpectral
acceleration, Sa/gDepends on time period and dampingSee next
slide
IS 1893:1984
Graphs for C and Sa/g from IS 1893:1984
Natural Period (Sec)
Natural Period (Sec)
IS 1893:1984
IS 1893:1984 has provisions for elevated tanks onlyGround supported
tanks are not consideredFor elevated tanks, it suggests
Ah = IFoSa/g
Performance factor, K is not presentImplies, K = 1.0 for all types
of elevated tanksUnlike buildings, different types of tanks do not
have different values of K This is one of the major limitation of
IS1893:1984More about it, later
IBC 2003
International Building Code (IBC) 2003In IITK-GSDMA guidelines IBC
2000 is referred This is now upgraded to IBC 2003In USA codes are
regularly upgraded every three yearThere is no change in the base
shear coefficient expression from IBC 2000 to IBC 2003
IBC 2003
Base shear coefficient
Ah = SD1 I/(R T)
SDS I/R
Ah shall not be less than 0.044 SDSI for buildings and not less
than 0.14 SDSI for tanksThis is a lower limit on AhIt ensures
minimum design seismic forceThis lower limit is higher for tanks
than for buildingsVariation with time period is directly given in
base shear coefficientHence, no need to have response spectrum
separately
IBC 2003
T is time period in secondsSDS and SD1 are design spectral
accelerations in short period and at 1 sec. respectivelySDS and SD1
depend on seismic zone and soilI is importance factor and R is
response modification factorIBC suggests I = 1.0, 1.25 and 1.5 for
different types of structuresValues of R will be discussed
later
IBC 2003
More about SDS and SD1SDS = 2/3 Fa SS and SD1 = 2/3 Fv S1SS is
mapped spectral acceleration for short periodS1 is mapped spectral
acceleration for 1-second periodSS and S1 are obtained from seismic
map This is similar to zone map of our code It is given in contour
formFa and Fv are site coefficientsTheir values for are given for
different soil types
IBC 2003
Response modification factor, RIS 1893(Part 1):2002 calls it
response reduction factorValues of R for some selected structures
are given in next slide
IBC 2003
Type of structureBuilding with special reinforced concrete moment
resisting concrete frames R8.0Building with intermediate reinforced
concrete moment resisting concrete frames5.0Building with ordinary
reinforced concrete moment resisting concrete frames3.0Building
with special steel concentrically braced frames8.0Elevated tanks
supported on braced/unbraced legs3.0Elevated tanks supported on
single pedestal2.0Tanks supported on structural towers similar to
buildings3.0Flat bottom ground supported anchored steel
tanks3.0Flat bottom ground supported unanchored steel
tanks2.5Ground supported reinforced or prestressed concrete tanks
with reinforced nonsliding base2.0
Base shear coefficient
In summary,Base shear coefficient from these three codes are:IS
1893 (Part 1): 2002IS 1893: 1984IBC2003Ah = (Z/2).(I/R).(Sa/g)SCM:
Ah = KCIo RSM: Ah = KIFoSa/g For tanks: Ah = IFoSa/g Ah = SD1 I/(R
T) SDS I/R> 0.044 SDS I for buildings> 0.14 SDS I for
tanks
Base shear coefficient
Important to note that:IS codes specify base shear coefficient at
working stress levelFor limit state design, these are to be
multiplied by load factors to get factored loadsIBC specifies base
shear coefficient at ultimate load levelFor working stress design,
seismic forces are divided by a factor of 1.4
Base shear coefficient
Once, base shear coefficient is known, seismic force on the
structure can be obtainedRecall, seismic force, V = Ah. WThis is
same as force = mass x acceleration
Base shear coefficient
Let us compare base shear coefficient values from these codes
Comparison will be done at working stress levelIBC values are
divided by 1.4 to bring them to working stress levelThis shall be
done for similar seismic zone or seismic hazard level of each
codeThis comparison is first done for buildings
Base shear coefficient
Comparison for buildingsFollowing parameters are chosenThey
represent similar seismic hazard levelIS 1893 (Part 1): 2002IS
1893: 1984IBC2003Z = 0.36; Zone VI = 1.0; R = 5.0Soft soil5%
dampingo = 0.08; Fo = 0.4; Zone V = 1.0K = 1.0; I = 1.0Soft soil,
raft foundation5% dampingSDs = 1.0; SD1 = 0.6 I = 1.0; R = 8.0Soil
type D, equivalent to soft soil of IS codes5% damping
Base shear coefficient
Building with good ductility is chosenSay, buildings with SMRFIn
IBC, for buildings with SMRF, R = 8.0Refer Table shown earlier
Base shear coefficient
For building with T = 0.3 secIS 1893(Part 1):2002Sa/g =2.5Ah =
Z/2.I/R.Sa/g = (0.36/2 )x (1.0/5.0) x 2.5 = 0.09IS 1893:1984C = 1.0
and Sa/g = 0.2SCM: Ah = KCIo = 1.0 x 1.0 x1.0 x1.0x0.08 = 0.08 RSM:
Ah = KIFoSa/g = 1.0 x 1.0 x1.0x 0.4x0.2 = 0.08 IBC 2003Ah =
SDSI/(1.4xR) = 1.0 x1.0/(1.4 x 8.0) = 0.089
Base shear coefficient
For building with T = 1 secIS 1893(Part 1):2002Sa/g = 1.67Ah =
Z/2.I/R.Sa/g = (0.36/2 )x(1.0/5.0)x1.67 = 0.06IS 1893:1984C = 0.53
and Sa/g = 0.11SCM: Ah = KCIo = 1.0 x0.53x1.0 x1.0x0.08 = 0.042
RSM: Ah = KIFoSa/g = 1.0x1.0x1.0x0.4x0.11 = 0.044 IBC 2003Ah =
SD1I/(1.4xRxT) = 0.6x1.0/(1.4 x 8.0x1.0) = 0.054
Base shear coefficient
For building with T = 1.5 secIS 1893(Part 1):2002Sa/g = 1.11Ah =
Z/2.I/R.Sa/g = (0.36/2 )x(1.0/5.0)x1.11 = 0.040IS 1893:1984C = 0.4
and Sa/g = 0.078SCM: Ah = KCIo = 1.0 x0.4x1.0 x1.0x0.08 = 0.032
RSM: Ah = KIFoSa/g =1.0x1.0x1.0x0.4x0.078 = 0.031 IBC 2003Ah =
SD1I/(1.4RT) = 0.6x1.0/(1.4 x 8.0x1.5) = 0.036
Base shear coefficient
Base shear coefficients for four time periods
* Due to lower bound, this value is higher
Graphical comparison on next slideT (Sec)IS 1893 (Part 1): 2002IS
1893:
1984IBC2003SCMRSM0.30.090.080.080.0891.00.060.0420.0440.0541.50.0400.0320.0310.0362.00.030.0240.0240.0314*
Base shear coefficient
Comparison of base shear coefficient (Buildings)
Note the lower
bound of IBC
IS 1893(Part 1):2002
IS 1893:1984; SCM
IS 1893:1984; RSM
IBC 2003
Chart400000.050.10.030.050.10.20.060.10.150.30.080.150.20.40.090.20.250.50.10.250.30.60.120.30.350.70.30.350.40.80.350.40.450.90.40.450.510.50.50.551.10.60.550.61.20.70.60.671.40.80.650.71.60.90.70.751.810.750.821.10.80.852.21.20.850.92.41.30.90.952.61.40.9512.81.511.0531.61.051.11.71.11.151.81.151.221.21.252.21.251.32.41.31.352.61.351.42.81.41.4531.451.51.51.551.551.61.61.651.651.71.71.751.751.81.81.851.851.91.91.951.95222.052.052.12.12.152.152.22.22.252.252.32.32.352.352.42.42.452.452.52.52.552.552.62.62.652.652.72.72.752.752.82.82.852.852.92.92.952.9533IS
1893(Part 1):2002IS 1893:1984; SCMIS 1893:1984; RSMIBC 2003Time
Period (S)Base shear
coefficient0.0360.080.040.08928571430.0630.080.0640.08928571430.090.080.0720.08928571430.090.080.0760.08928571430.090.0720.0780.08928571430.090.0640.07920.08928571430.090.05840.080.08928571430.090.05360.080.08928571430.090.04960.080.08928571430.090.04640.0740.08928571430.090.04320.06720.08928571430.090.040.060.08928571430.090.03840.05520.08928571430.090.03360.05080.08241758240.08588571430.030.04720.07653061220.080160.02640.04320.07142857140.075150.0240.040.06696428570.07072941180.02160.03760.06302521010.06680.020.03520.05952380950.06328421050.01840.0320.05639097740.060120.01720.030.05357142860.05725714290.0160.0280.05102040820.05465454550.0260.04870129870.05227826090.0240.04658385090.05010.02240.04464285710.0480960.02080.04285714290.04624615380.01920.04120879120.04453333330.0180.03968253970.04294285710.01680.03826530610.0414620690.0160.03694581280.040080.03571428570.03878709680.0345622120.0375750.03348214290.03643636360.03246753250.03536470590.0315126050.03435428570.03142857140.03340.03142857140.03249729730.03142857140.03164210530.03142857140.03083076920.03142857140.030060.03142857140.02932682930.03142857140.02862857140.03142857140.02796279070.03142857140.02732727270.03142857140.026720.03142857140.02613913040.03142857140.02558297870.03142857140.025050.03142857140.02453877550.03142857140.0240480.03142857140.02357647060.03142857140.02312307690.03142857140.02268679250.03142857140.02226666670.03142857140.02186181820.03142857140.02147142860.03142857140.02109473680.03142857140.02073103450.03142857140.0203796610.03142857140.020040.0314285714bldgIS
1893:1984; bldgIBC2000IS1893:2002; bldg1.4IA1893:1984
(new)timeCV/wtimebldgbldg/1.4timeSa/gV/W010.0800.1250.0892857143010.036timesa/gV/W0.110.080.050.1250.08928571430.051.750.06300.10.040.210.080.10.1250.08928571430.12.50.090.030.160.0640.310.080.150.1250.08928571430.152.50.090.060.180.0720.40.90.0720.20.1250.08928571430.22.50.090.080.190.0760.50.80.0640.250.1250.08928571430.252.50.090.090.1950.0780.60.730.05840.30.1250.08928571430.32.50.090.10.1980.07920.70.670.05360.350.1250.08928571430.352.50.090.120.20.080.80.620.04960.40.1250.08928571430.42.50.090.30.20.080.90.580.04640.450.1250.08928571430.452.50.090.350.20.0810.540.04320.50.1250.08928571430.52.50.090.40.1850.0741.10.50.040.550.1250.08928571430.552.50.090.50.1680.06721.20.480.03840.60.1250.08928571430.62.50.090.60.150.061.40.420.03360.650.11538461540.08241758240.672.50.090.70.1380.05521.60.3750.030.70.10714285710.07653061220.72.38571428570.08588571430.80.1270.05081.80.330.02640.750.10.07142857140.752.22666666670.080160.90.1180.047220.30.0240.80.093750.06696428570.82.08750.0751510.1080.04322.20.270.02160.850.08823529410.06302521010.851.96470588240.07072941181.10.10.042.40.250.020.90.08333333330.05952380950.91.85555555560.06681.20.0940.03762.60.230.01840.950.07894736840.05639097740.951.75789473680.06328421051.30.0880.03522.80.2150.017210.0750.053571428611.670.060121.40.080.03230.20.0161.050.07142857140.05102040821.051.59047619050.05725714291.50.0750.031.10.06818181820.04870129871.11.51818181820.05465454551.60.070.0281.150.06521739130.04658385091.151.4521739130.05227826091.70.0650.0261.20.06250.04464285711.21.39166666670.05011.80.060.0241.250.060.04285714291.251.3360.04809620.0560.02241.30.05769230770.04120879121.31.28461538460.04624615382.20.0520.02081.350.05555555560.03968253971.351.2370370370.04453333332.40.0480.01921.40.05357142860.03826530611.41.19285714290.04294285712.60.0450.0181.450.05172413790.03694581281.451.15172413790.0414620692.80.0420.01681.50.050.03571428571.51.11333333330.0400830.040.0161.550.04838709680.0345622121.551.07741935480.03878709681.60.0468750.03348214291.61.043750.0375751.650.04545454550.03246753251.651.01212121210.03643636361.70.04411764710.0315126051.70.98235294120.03536470591.750.0440.03142857141.750.95428571430.03435428571.80.0440.03142857141.80.92777777780.03341.850.0440.03142857141.850.90270270270.03249729731.90.0440.03142857141.90.87894736840.03164210531.950.0440.03142857141.950.85641025640.030830769220.0440.031428571420.8350.030062.050.0440.03142857142.050.81463414630.02932682932.10.0440.03142857142.10.79523809520.02862857142.150.0440.03142857142.150.7767441860.02796279072.20.0440.03142857142.20.75909090910.02732727272.250.0440.03142857142.250.74222222220.026722.30.0440.03142857142.30.72608695650.02613913042.350.0440.03142857142.350.71063829790.02558297872.40.0440.03142857142.40.69583333330.025052.450.0440.03142857142.450.68163265310.02453877552.50.0440.03142857142.50.6680.0240482.550.0440.03142857142.550.65490196080.02357647062.60.0440.03142857142.60.64230769230.02312307692.650.0440.03142857142.650.63018867920.02268679252.70.0440.03142857142.70.61851851850.02226666672.750.0440.03142857142.750.60727272730.02186181822.80.0440.03142857142.80.59642857140.02147142862.850.0440.03142857142.850.58596491230.02109473682.90.0440.03142857142.90.5758620690.02073103452.950.0440.03142857142.950.56610169490.02037966130.0440.031428571430.55666666670.020043.050.0440.03142857143.10.0440.03142857143.150.0440.03142857143.20.0440.03142857143.250.0440.03142857143.30.0440.03142857143.350.0440.03142857143.40.0440.03142857143.450.0440.03142857143.50.0440.03142857143.550.0440.03142857143.60.0440.03142857143.650.0440.03142857143.70.0440.03142857143.750.0440.03142857143.80.0440.03142857143.850.0440.03142857143.90.0440.03142857143.950.0440.031428571440.0440.0314285714chartNew
comparisonchart00000.050.10.030.050.10.20.060.10.150.30.080.150.20.40.090.20.250.50.10.250.30.60.120.30.350.70.30.350.40.80.350.40.450.90.40.450.510.50.50.551.10.60.550.61.20.70.60.671.40.80.650.71.60.90.70.751.810.750.821.10.80.852.21.20.850.92.41.30.90.952.61.40.9512.81.511.0531.61.051.11.71.11.151.81.151.221.21.252.21.251.32.41.31.352.61.351.42.81.41.4531.451.51.51.551.551.61.61.651.651.71.71.751.751.81.81.851.851.91.91.951.95222.052.052.12.12.152.152.22.22.252.252.32.32.352.352.42.42.452.452.52.52.552.552.62.62.652.652.72.72.752.752.82.82.852.852.92.92.952.9533IS
1893(Part 1):2002IS 1893:1984; SCMIS 1893:1984; RSMIBC 2003Time
Period (S)Base shear
coefficient0.0360.080.040.08928571430.0630.080.0640.08928571430.090.080.0720.08928571430.090.080.0760.08928571430.090.0720.0780.08928571430.090.0640.07920.08928571430.090.05840.080.08928571430.090.05360.080.08928571430.090.04960.080.08928571430.090.04640.0740.08928571430.090.04320.06720.08928571430.090.040.060.08928571430.090.03840.05520.08928571430.090.03360.05080.08241758240.08588571430.030.04720.07653061220.080160.02640.04320.07142857140.075150.0240.040.06696428570.07072941180.02160.03760.06302521010.06680.020.03520.05952380950.06328421050.01840.0320.05639097740.060120.01720.030.05357142860.05725714290.0160.0280.05102040820.05465454550.0260.04870129870.05227826090.0240.04658385090.05010.02240.04464285710.0480960.02080.04285714290.04624615380.01920.04120879120.04453333330.0180.03968253970.04294285710.01680.03826530610.0414620690.0160.03694581280.040080.03571428570.03878709680.0345622120.0375750.03348214290.03643636360.03246753250.03536470590.0315126050.03435428570.03142857140.03340.03142857140.03249729730.03142857140.03164210530.03142857140.03083076920.03142857140.030060.03142857140.02932682930.03142857140.02862857140.03142857140.02796279070.03142857140.02732727270.03142857140.026720.03142857140.02613913040.03142857140.02558297870.03142857140.025050.03142857140.02453877550.03142857140.0240480.03142857140.02357647060.03142857140.02312307690.03142857140.02268679250.03142857140.02226666670.03142857140.02186181820.03142857140.02147142860.03142857140.02109473680.03142857140.02073103450.03142857140.0203796610.03142857140.020040.0314285714tank0000.050.050.030.10.10.060.150.150.080.20.20.090.250.250.10.30.30.120.350.350.30.40.40.350.450.450.40.50.50.50.550.550.60.60.60.70.650.670.80.70.70.90.750.7510.80.81.10.850.851.20.90.91.30.950.951.4111.51.051.051.61.11.11.71.151.151.81.21.221.251.252.21.31.32.41.351.352.61.41.42.81.451.4531.51.51.551.551.61.61.651.651.71.71.751.751.81.81.851.851.91.91.951.95222.052.052.12.12.152.152.22.22.252.252.32.32.352.352.42.42.452.452.52.52.552.552.62.62.652.652.72.72.752.752.82.82.852.852.92.92.952.9533Time
Period (S)Base shear
coefficient0.08928571430.0360.040.08928571430.0630.0640.08928571430.090.0720.08928571430.090.0760.08928571430.090.0780.08928571430.090.07920.08928571430.090.080.08928571430.090.080.08928571430.090.080.08928571430.090.0740.08928571430.090.06720.08928571430.090.060.08928571430.090.05520.08241758240.090.05080.07653061220.08588571430.04720.07142857140.080160.04320.06696428570.075150.040.06302521010.07072941180.03760.05952380950.06680.03520.05639097740.06328421050.0320.05357142860.060120.030.05102040820.05725714290.0280.04870129870.05465454550.0260.04658385090.05227826090.0240.04464285710.05010.02240.04285714290.0480960.02080.04120879120.04624615380.01920.03968253970.04453333330.0180.03826530610.04294285710.01680.03694581280.0414620690.0160.03571428570.040080.0345622120.03878709680.03348214290.0375750.03246753250.03643636360.0315126050.03536470590.03142857140.03435428570.03142857140.03340.03142857140.03249729730.03142857140.03164210530.03142857140.03083076920.03142857140.030060.03142857140.02932682930.03142857140.02862857140.03142857140.02796279070.03142857140.02732727270.03142857140.026720.03142857140.02613913040.03142857140.02558297870.03142857140.025050.03142857140.02453877550.03142857140.0240480.03142857140.02357647060.03142857140.02312307690.03142857140.02268679250.03142857140.02226666670.03142857140.02186181820.03142857140.02147142860.03142857140.02109473680.03142857140.02073103450.03142857140.0203796610.03142857140.02004chart1IS1893:1984IBC2000
R =3IS1893:2002; bldgtimesa/gV/Wtimetank r=3tank/1.4R=1.5tank/1.4R
= 2.0/1.4timeSa/gtank
r=1.1tank4=2.2500.10.0600.41666666670.29761904760.83333333330.59523809520.4464285714010.24545454550.120.030.160.0960.050.41666666670.29761904760.83333333330.59523809520.44642857140.051.750.42954545450.210.060.180.1080.10.41666666670.29761904760.83333333330.59523809520.44642857140.12.50.61363636360.30.080.190.1140.150.41666666670.29761904760.83333333330.59523809520.44642857140.152.50.61363636360.30.090.1950.1170.20.41666666670.29761904760.83333333330.59523809520.44642857140.22.50.61363636360.30.10.1980.11880.250.41666666670.29761904760.83333333330.59523809520.44642857140.252.50.61363636360.30.120.20.120.30.41666666670.29761904760.83333333330.59523809520.44642857140.32.50.61363636360.30.30.20.120.350.41666666670.29761904760.83333333330.59523809520.44642857140.352.50.61363636360.30.350.20.120.40.41666666670.29761904760.83333333330.59523809520.44642857140.42.50.61363636360.30.40.1850.1110.450.41666666670.29761904760.83333333330.59523809520.44642857140.452.50.61363636360.30.50.1680.10080.50.41666666670.29761904760.83333333330.59523809520.44642857140.52.50.61363636360.30.60.150.090.550.41666666670.29761904760.83333333330.59523809520.44642857140.552.50.61363636360.30.70.1380.08280.60.41666666670.29761904760.83333333330.59523809520.44642857140.62.50.61363636360.30.80.1270.07620.650.38461538460.27472527470.76923076920.54945054950.41208791210.672.50.61363636360.30.90.1180.07080.70.35714285710.25510204080.71428571430.51020408160.38265306120.72.38571428570.58558441560.286285714310.1080.06480.750.33333333330.23809523810.66666666670.47619047620.35714285710.752.22666666670.54654545450.26721.10.10.060.80.31250.22321428570.6250.44642857140.33482142860.82.08750.51238636360.25051.20.0940.05640.850.29411764710.21008403360.58823529410.42016806720.31512605040.851.96470588240.48224598930.23576470591.30.0880.05280.90.27777777780.19841269840.55555555560.39682539680.29761904760.91.85555555560.45545454550.22266666671.40.080.0480.950.26315789470.18796992480.52631578950.37593984960.28195488720.951.75789473680.43148325360.21094736841.50.0750.04510.250.17857142860.50.35714285710.267857142911.670.40990909090.20041.60.070.0421.050.23809523810.17006802720.47619047620.34013605440.25510204081.051.59047619050.39038961040.19085714291.70.0650.0391.10.22727272730.16233766230.45454545450.32467532470.24350649351.11.51818181820.37264462810.18218181821.80.060.0361.150.21739130430.15527950310.43478260870.31055900620.23291925471.151.4521739130.35644268770.174260869620.0560.03361.20.20833333330.14880952380.41666666670.29761904760.22321428571.21.39166666670.34159090910.1672.20.0520.03121.250.20.14285714290.40.28571428570.21428571431.251.3360.32792727270.160322.40.0480.02881.30.19230769230.13736263740.38461538460.27472527470.2060439561.31.28461538460.31531468530.15415384622.60.0450.0271.350.18518518520.13227513230.37037037040.26455026460.19841269841.351.2370370370.30363636360.14844444442.80.0420.02521.40.17857142860.12755102040.35714285710.25510204080.19132653061.41.19285714290.29279220780.143142857130.040.0241.450.1750.1250.34482758620.24630541870.1847290641.451.15172413790.28269592480.13820689661.50.1750.1250.33333333330.23809523810.17857142861.51.11333333330.27327272730.13361.550.1750.1250.32258064520.23041474650.17281105991.551.07741935480.2644574780.12929032261.60.1750.1250.31250.22321428570.16741071431.61.043750.25619318180.125251.650.1750.1250.3030303030.21645021650.16233766231.651.01212121210.24842975210.12145454551.70.1750.1250.29411764710.21008403360.15756302521.70.98235294120.24112299470.11788235291.750.1750.1250.28571428570.20408163270.15306122451.750.95428571430.23423376620.11451428571.80.1750.1250.27777777780.19841269840.14880952381.80.92777777780.22772727270.11133333331.850.1750.1250.27027027030.19305019310.14478764481.850.90270270270.22157248160.10832432431.90.1750.1250.26315789470.18796992480.14097744361.90.87894736840.21574162680.10547368421.950.1750.1250.25641025640.18315018320.13736263741.950.85641025640.21020979020.102769230820.1750.1250.250.17857142860.133928571420.8350.20495454550.10022.050.1750.1250.2439024390.17421602790.13066202092.050.81463414630.19995565410.09775609762.10.1750.1250.23809523810.17006802720.12755102042.10.79523809520.19519480520.09542857142.150.1750.1250.23255813950.16611295680.12458471762.150.7767441860.19065539110.09320930232.20.1750.1250.22727272730.16233766230.12175324682.20.75909090910.1863223140.09109090912.250.1750.1250.22222222220.15873015870.1190476192.250.74222222220.18218181820.08906666672.30.1750.1250.21739130430.15527950310.11645962732.30.72608695650.17822134390.08713043482.350.1750.1250.21276595740.15197568390.11398176292.350.71063829790.17442940040.08527659572.40.1750.1250.20833333330.14880952380.11160714292.40.69583333330.17079545450.08352.450.1750.1250.20408163270.14577259480.10932944612.450.68163265310.1673098330.08179591842.50.1750.1250.20.14285714290.10714285712.50.6680.16396363640.080162.550.1750.1250.19607843140.14005602240.10504201682.550.65490196080.16074866310.07858823532.60.1750.1250.19230769230.13736263740.1030219782.60.64230769230.15765734270.07707692312.650.1750.1250.18867924530.13477088950.10107816712.650.63018867920.15468267580.07562264152.70.1750.1250.18518518520.13227513230.09920634922.70.61851851850.15181818180.07422222222.750.1750.1250.18181818180.12987012990.09740259742.750.60727272730.14905785120.07287272732.80.1750.1250.17857142860.12755102040.09566326532.80.59642857140.14639610390.07157142862.850.1750.1250.17543859650.12531328320.09398496242.850.58596491230.14382775120.07031578952.90.1750.1250.1750.1250.093752.90.5758620690.14134796240.06910344832.950.1750.1250.1750.1250.093752.950.56610169490.13895223420.067932203430.1750.1250.1750.1250.0937530.55666666670.13663636360.06683.050.1753.10.1753.150.1753.20.1753.250.1753.30.1753.350.1753.40.1753.450.1753.50.1753.550.1753.60.1753.650.1753.70.1753.750.1753.80.1753.850.1753.90.1753.950.17540.175000000.030.050.050.050.050.060.10.10.10.10.080.150.150.150.150.090.20.20.20.20.10.250.250.250.250.120.30.30.30.30.30.350.350.350.350.350.40.40.40.40.40.450.450.450.450.50.50.50.50.50.60.550.550.550.550.70.60.60.60.60.80.650.650.670.670.90.70.70.70.710.750.750.750.751.10.80.80.80.81.20.850.850.850.851.30.90.90.90.91.40.950.950.950.951.511111.61.051.051.051.051.71.11.11.11.11.81.151.151.151.1521.21.21.21.22.21.251.251.251.252.41.31.31.31.32.61.351.351.351.352.81.41.41.41.431.451.451.451.451.51.51.51.51.551.551.551.551.61.61.61.61.651.651.651.651.71.71.71.71.751.751.751.751.81.81.81.81.851.851.851.851.91.91.91.91.951.951.951.9522222.052.052.052.052.12.12.12.12.152.152.152.152.22.22.22.22.252.252.252.252.32.32.32.32.352.352.352.352.42.42.42.42.452.452.452.452.52.52.52.52.552.552.552.552.62.62.62.62.652.652.652.652.72.72.72.72.752.752.752.752.82.82.82.82.852.852.852.852.92.92.92.92.952.952.952.95333320022002Time
period (S)Base shear
coefficient0.060.29761904760.59523809520.24545454550.120.0960.29761904760.59523809520.42954545450.210.1080.29761904760.59523809520.61363636360.30.1140.29761904760.59523809520.61363636360.30.1170.29761904760.59523809520.61363636360.30.11880.29761904760.59523809520.61363636360.30.120.29761904760.59523809520.61363636360.30.120.29761904760.59523809520.61363636360.30.120.29761904760.59523809520.61363636360.30.1110.29761904760.59523809520.61363636360.30.10080.29761904760.59523809520.61363636360.30.090.29761904760.59523809520.61363636360.30.08280.29761904760.59523809520.61363636360.30.07620.27472527470.54945054950.61363636360.30.07080.25510204080.51020408160.58558441560.28628571430.06480.23809523810.47619047620.54654545450.26720.060.22321428570.44642857140.51238636360.25050.05640.21008403360.42016806720.48224598930.23576470590.05280.19841269840.39682539680.45545454550.22266666670.0480.18796992480.37593984960.43148325360.21094736840.0450.17857142860.35714285710.40990909090.20040.0420.17006802720.34013605440.39038961040.19085714290.0390.16233766230.32467532470.37264462810.18218181820.0360.15527950310.31055900620.35644268770.17426086960.03360.14880952380.29761904760.34159090910.1670.03120.14285714290.28571428570.32792727270.160320.02880.13736263740.27472527470.31531468530.15415384620.0270.13227513230.26455026460.30363636360.14844444440.02520.12755102040.25510204080.29279220780.14314285710.0240.1250.24630541870.28269592480.13820689660.1250.23809523810.27327272730.13360.1250.23041474650.2644574780.12929032260.1250.22321428570.25619318180.125250.1250.21645021650.24842975210.12145454550.1250.21008403360.24112299470.11788235290.1250.20408163270.23423376620.11451428570.1250.19841269840.22772727270.11133333330.1250.19305019310.22157248160.10832432430.1250.18796992480.21574162680.10547368420.1250.18315018320.21020979020.10276923080.1250.17857142860.20495454550.10020.1250.17421602790.19995565410.09775609760.1250.17006802720.19519480520.09542857140.1250.16611295680.19065539110.09320930230.1250.16233766230.1863223140.09109090910.1250.15873015870.18218181820.08906666670.1250.15527950310.17822134390.08713043480.1250.15197568390.17442940040.08527659570.1250.14880952380.17079545450.08350.1250.14577259480.1673098330.08179591840.1250.14285714290.16396363640.080160.1250.14005602240.16074866310.07858823530.1250.13736263740.15765734270.07707692310.1250.13477088950.15468267580.07562264150.1250.13227513230.15181818180.07422222220.1250.12987012990.14905785120.07287272730.1250.12755102040.14639610390.07157142860.1250.12531328320.14382775120.07031578950.1250.1250.14134796240.06910344830.1250.1250.13895223420.06793220340.1250.1250.13663636360.06680000.030.050.050.060.10.10.080.150.150.090.20.20.10.250.250.120.30.30.30.350.350.350.40.40.40.450.450.50.50.50.60.550.550.70.60.60.80.650.650.90.70.710.750.751.10.80.81.20.850.851.30.90.91.40.950.951.5111.61.051.051.71.11.11.81.151.1521.21.22.21.251.252.41.31.32.61.351.352.81.41.431.451.451.51.51.551.551.61.61.651.651.71.71.751.751.81.81.851.851.91.91.951.95222.052.052.12.12.152.152.22.22.252.252.32.32.352.352.42.42.452.452.52.52.552.552.62.62.652.652.72.72.752.752.82.82.852.852.92.92.952.9533IS
1893:1984; All types of elevated tanksIBC 2003; Tanks on frame
stagingIBC 2003; Tanks on shaft stagingTime period (S)Base shear
coefficient0.060.29761904760.44642857140.0960.29761904760.44642857140.1080.29761904760.44642857140.1140.29761904760.44642857140.1170.29761904760.44642857140.11880.29761904760.44642857140.120.29761904760.44642857140.120.29761904760.44642857140.120.29761904760.44642857140.1110.29761904760.44642857140.10080.29761904760.44642857140.090.29761904760.44642857140.08280.29761904760.44642857140.07620.27472527470.41208791210.07080.25510204080.38265306120.06480.23809523810.35714285710.060.22321428570.33482142860.05640.21008403360.31512605040.05280.19841269840.29761904760.0480.18796992480.28195488720.0450.17857142860.26785714290.0420.17006802720.25510204080.0390.16233766230.24350649350.0360.15527950310.23291925470.03360.14880952380.22321428570.03120.14285714290.21428571430.02880.13736263740.2060439560.0270.13227513230.19841269840.02520.12755102040.19132653060.0240.1250.1847290640.1250.17857142860.1250.17281105990.1250.16741071430.1250.16233766230.1250.15756302520.1250.15306122450.1250.14880952380.1250.14478764480.1250.14097744360.1250.13736263740.1250.13392857140.1250.13066202090.1250.12755102040.1250.12458471760.1250.12175324680.1250.1190476190.1250.11645962730.1250.11398176290.1250.11160714290.1250.10932944610.1250.10714285710.1250.10504201680.1250.1030219780.1250.10107816710.1250.09920634920.1250.09740259740.1250.09566326530.1250.09398496240.1250.093750.1250.093750.1250.09375
Base shear coefficient
We have seen that:Codes follow similar strategy to obtain design
base shear coefficient In similar seismic zones, base shear
coefficient for buildings matches reasonably well from these three
codes
Base shear coefficient
Similarly, let us compare design base shear coefficients for tanks
From IS1893:1984 and IBC 2003IS 1893(Part 1):2002 is only for
buildingsHence, cant be used for tanksOnly elevated tanks will be
consideredIS 1893:1984 has provisions for elevated tanks onlyZone
and soil parameters will remain same as those considered for
buildingsImportance factor for tanks are different than those for
buildings
Base shear coefficient
In IBCI = 1.25 for tanksR = 3.0 for tanks on frame staging (braced
legs)R = 2.0 for tanks on shaft or pedestalIn 1893:1984I = 1.5 for
tanksK is not present in the expression for base shear coefficient
(implies k=1.0). Hence, base shear coefficient will be same for all
types of elevated tanks
Base shear coefficient
For tank with T = 0.3 secIS 1893:1984I = 1.5, Sa/g = 0.2Ah =
IFoSa/g = 1.0 x 1.5 x 0.4x0.2 = 0.12This value is common for frame
and shaft stagingIBC 2003For frame staging, I = 1.25, R = 3.0
Ah = SDSI/(1.4xR) = 1.0 x1.25/(1.4 x 3.0) = 0.298
For shaft staging, I = 1.25, R = 2.0
Ah = SDSI/(1.4xR) = 1.0 x1.25/(1.4 x 2.0) = 0.446
Base shear coefficient
For tank with T = 1 secIS 1893:1984I = 1.5, Sa/g = 0.11Ah = IFoSa/g
=1.0x1.5x0.4x0.11 = 0.066IBC 2003For frame staging, I = 1.25, R =
3.0
Ah = SD1I/(1.4xRxT) = 0.6x1.25/(1.4 x 3.0x1.0) = 0.178
For shaft staging, I = 1.25, R = 2.0
Ah = SD1I/(1.4xRxT) = 0.6x1.25/(1.4 x 2.0x1.0) = 0.268
Base shear coefficient
Base shear coefficients for tanks
* Base shear coefficient values are common for frame and shaft
staging
Graphical comparison on next slideT (Sec)IS 1893:1984*IBC 2003Frame
stagingShaft staging0.30.120.2980.4461.00.0660.1780.268
Base shear coefficient
Comparison of base shear coefficient (Tanks)
IS 1893:1984; All types of
elevated tanks
IBC 2003; Tanks on shaft staging
IBC 2003; Tanks on frame staging
Chart50000.030.050.050.060.10.10.080.150.150.090.20.20.10.250.250.120.30.30.30.350.350.350.40.40.40.450.450.50.50.50.60.550.550.70.60.60.80.650.650.90.70.710.750.751.10.80.81.20.850.851.30.90.91.40.950.951.5111.61.051.051.71.11.11.81.151.1521.21.22.21.251.252.41.31.32.61.351.352.81.41.431.451.451.51.51.551.551.61.61.651.651.71.71.751.751.81.81.851.851.91.91.951.95222.052.052.12.12.152.152.22.22.252.252.32.32.352.352.42.42.452.452.52.52.552.552.62.62.652.652.72.72.752.752.82.82.852.852.92.92.952.9533IS
1893:1984; All types of elevated tanksIBC 2003; Tanks on shaft
stagingIBC 2003; Tanks on frame stagingTime period (S)Base shear
coefficient0.060.44642857140.29761904760.0960.44642857140.29761904760.1080.44642857140.29761904760.1140.44642857140.29761904760.1170.44642857140.29761904760.11880.44642857140.29761904760.120.44642857140.29761904760.120.44642857140.29761904760.120.44642857140.29761904760.1110.44642857140.29761904760.10080.44642857140.29761904760.090.44642857140.29761904760.08280.44642857140.29761904760.07620.41208791210.27472527470.07080.38265306120.25510204080.06480.35714285710.23809523810.060.33482142860.22321428570.05640.31512605040.21008403360.05280.29761904760.19841269840.0480.28195488720.18796992480.0450.26785714290.17857142860.0420.25510204080.17006802720.0390.24350649350.16233766230.0360.23291925470.15527950310.03360.22321428570.14880952380.03120.21428571430.14285714290.02880.2060439560.13736263740.0270.19841269840.13227513230.02520.19132653060.12755102040.0240.1847290640.1250.17857142860.1250.17281105990.1250.16741071430.1250.16233766230.1250.15756302520.1250.15306122450.1250.14880952380.1250.14478764480.1250.14097744360.1250.13736263740.1250.13392857140.1250.13066202090.1250.12755102040.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.125bldgIS
1893:1984; bldgIBC2000IS1893:2002; bldg1.4IA1893:1984
(new)timeCV/wtimebldgbldg/1.4timeSa/gV/W010.0800.1250.0892857143010.036timesa/gV/W0.110.080.050.1250.08928571430.051.750.06300.10.040.210.080.10.1250.08928571430.12.50.090.030.160.0640.310.080.150.1250.08928571430.152.50.090.060.180.0720.40.90.0720.20.1250.08928571430.22.50.090.080.190.0760.50.80.0640.250.1250.08928571430.252.50.090.090.1950.0780.60.730.05840.30.1250.08928571430.32.50.090.10.1980.07920.70.670.05360.350.1250.08928571430.352.50.090.120.20.080.80.620.04960.40.1250.08928571430.42.50.090.30.20.080.90.580.04640.450.1250.08928571430.452.50.090.350.20.0810.540.04320.50.1250.08928571430.52.50.090.40.1850.0741.10.50.040.550.1250.08928571430.552.50.090.50.1680.06721.20.480.03840.60.1250.08928571430.62.50.090.60.150.061.40.420.03360.650.11538461540.08241758240.672.50.090.70.1380.05521.60.3750.030.70.10714285710.07653061220.72.38571428570.08588571430.80.1270.05081.80.330.02640.750.10.07142857140.752.22666666670.080160.90.1180.047220.30.0240.80.093750.06696428570.82.08750.0751510.1080.04322.20.270.02160.850.08823529410.06302521010.851.96470588240.07072941181.10.10.042.40.250.020.90.08333333330.05952380950.91.85555555560.06681.20.0940.03762.60.230.01840.950.07894736840.05639097740.951.75789473680.06328421051.30.0880.03522.80.2150.017210.0750.053571428611.670.060121.40.080.03230.20.0161.050.07142857140.05102040821.051.59047619050.05725714291.50.0750.031.10.06818181820.04870129871.11.51818181820.05465454551.60.070.0281.150.06521739130.04658385091.151.4521739130.05227826091.70.0650.0261.20.06250.04464285711.21.39166666670.05011.80.060.0241.250.060.04285714291.251.3360.04809620.0560.02241.30.05769230770.04120879121.31.28461538460.04624615382.20.0520.02081.350.05555555560.03968253971.351.2370370370.04453333332.40.0480.01921.40.05357142860.03826530611.41.19285714290.04294285712.60.0450.0181.450.05172413790.03694581281.451.15172413790.0414620692.80.0420.01681.50.050.03571428571.51.11333333330.0400830.040.0161.550.04838709680.0345622121.551.07741935480.03878709681.60.0468750.03348214291.61.043750.0375751.650.04545454550.03246753251.651.01212121210.03643636361.70.04411764710.0315126051.70.98235294120.03536470591.750.0440.03142857141.750.95428571430.03435428571.80.0440.03142857141.80.92777777780.03341.850.0440.03142857141.850.90270270270.03249729731.90.0440.03142857141.90.87894736840.03164210531.950.0440.03142857141.950.85641025640.030830769220.0440.031428571420.8350.030062.050.0440.03142857142.050.81463414630.02932682932.10.0440.03142857142.10.79523809520.02862857142.150.0440.03142857142.150.7767441860.02796279072.20.0440.03142857142.20.75909090910.02732727272.250.0440.03142857142.250.74222222220.026722.30.0440.03142857142.30.72608695650.02613913042.350.0440.03142857142.350.71063829790.02558297872.40.0440.03142857142.40.69583333330.025052.450.0440.03142857142.450.68163265310.02453877552.50.0440.03142857142.50.6680.0240482.550.0440.03142857142.550.65490196080.02357647062.60.0440.03142857142.60.64230769230.02312307692.650.0440.03142857142.650.63018867920.02268679252.70.0440.03142857142.70.61851851850.02226666672.750.0440.03142857142.750.60727272730.02186181822.80.0440.03142857142.80.59642857140.02147142862.850.0440.03142857142.850.58596491230.02109473682.90.0440.03142857142.90.5758620690.02073103452.950.0440.03142857142.950.56610169490.02037966130.0440.031428571430.55666666670.020043.050.0440.03142857143.10.0440.03142857143.150.0440.03142857143.20.0440.03142857143.250.0440.03142857143.30.0440.03142857143.350.0440.03142857143.40.0440.03142857143.450.0440.03142857143.50.0440.03142857143.550.0440.03142857143.60.0440.03142857143.650.0440.03142857143.70.0440.03142857143.750.0440.03142857143.80.0440.03142857143.850.0440.03142857143.90.0440.03142857143.950.0440.031428571440.0440.0314285714chartNew
comparisonchart00000.050.10.030.050.10.20.060.10.150.30.080.150.20.40.090.20.250.50.10.250.30.60.120.30.350.70.30.350.40.80.350.40.450.90.40.450.510.50.50.551.10.60.550.61.20.70.60.671.40.80.650.71.60.90.70.751.810.750.821.10.80.852.21.20.850.92.41.30.90.952.61.40.9512.81.511.0531.61.051.11.71.11.151.81.151.221.21.252.21.251.32.41.31.352.61.351.42.81.41.4531.451.51.51.551.551.61.61.651.651.71.71.751.751.81.81.851.851.91.91.951.95222.052.052.12.12.152.152.22.22.252.252.32.32.352.352.42.42.452.452.52.52.552.552.62.62.652.652.72.72.752.752.82.82.852.852.92.92.952.9533IS
1893(Part 1):2002IS 1893:1984; SCMIS 1893:1984; RSMIBC 2003Time
Period (S)Base shear
coefficient0.0360.080.040.08928571430.0630.080.0640.08928571430.090.080.0720.08928571430.090.080.0760.08928571430.090.0720.0780.08928571430.090.0640.07920.08928571430.090.05840.080.08928571430.090.05360.080.08928571430.090.04960.080.08928571430.090.04640.0740.08928571430.090.04320.06720.08928571430.090.040.060.08928571430.090.03840.05520.08928571430.090.03360.05080.08241758240.08588571430.030.04720.07653061220.080160.02640.04320.07142857140.075150.0240.040.06696428570.07072941180.02160.03760.06302521010.06680.020.03520.05952380950.06328421050.01840.0320.05639097740.060120.01720.030.05357142860.05725714290.0160.0280.05102040820.05465454550.0260.04870129870.05227826090.0240.04658385090.05010.02240.04464285710.0480960.02080.04285714290.04624615380.01920.04120879120.04453333330.0180.03968253970.04294285710.01680.03826530610.0414620690.0160.03694581280.040080.03571428570.03878709680.0345622120.0375750.03348214290.03643636360.03246753250.03536470590.0315126050.03435428570.03142857140.03340.03142857140.03249729730.03142857140.03164210530.03142857140.03083076920.03142857140.030060.03142857140.02932682930.03142857140.02862857140.03142857140.02796279070.03142857140.02732727270.03142857140.026720.03142857140.02613913040.03142857140.02558297870.03142857140.025050.03142857140.02453877550.03142857140.0240480.03142857140.02357647060.03142857140.02312307690.03142857140.02268679250.03142857140.02226666670.03142857140.02186181820.03142857140.02147142860.03142857140.02109473680.03142857140.02073103450.03142857140.0203796610.03142857140.020040.0314285714tank0000.050.050.030.10.10.060.150.150.080.20.20.090.250.250.10.30.30.120.350.350.30.40.40.350.450.450.40.50.50.50.550.550.60.60.60.70.650.670.80.70.70.90.750.7510.80.81.10.850.851.20.90.91.30.950.951.4111.51.051.051.61.11.11.71.151.151.81.21.221.251.252.21.31.32.41.351.352.61.41.42.81.451.4531.51.51.551.551.61.61.651.651.71.71.751.751.81.81.851.851.91.91.951.95222.052.052.12.12.152.152.22.22.252.252.32.32.352.352.42.42.452.452.52.52.552.552.62.62.652.652.72.72.752.752.82.82.852.852.92.92.952.9533Time
Period (S)Base shear
coefficient0.08928571430.0360.040.08928571430.0630.0640.08928571430.090.0720.08928571430.090.0760.08928571430.090.0780.08928571430.090.07920.08928571430.090.080.08928571430.090.080.08928571430.090.080.08928571430.090.0740.08928571430.090.06720.08928571430.090.060.08928571430.090.05520.08241758240.090.05080.07653061220.08588571430.04720.07142857140.080160.04320.06696428570.075150.040.06302521010.07072941180.03760.05952380950.06680.03520.05639097740.06328421050.0320.05357142860.060120.030.05102040820.05725714290.0280.04870129870.05465454550.0260.04658385090.05227826090.0240.04464285710.05010.02240.04285714290.0480960.02080.04120879120.04624615380.01920.03968253970.04453333330.0180.03826530610.04294285710.01680.03694581280.0414620690.0160.03571428570.040080.0345622120.03878709680.03348214290.0375750.03246753250.03643636360.0315126050.03536470590.03142857140.03435428570.03142857140.03340.03142857140.03249729730.03142857140.03164210530.03142857140.03083076920.03142857140.030060.03142857140.02932682930.03142857140.02862857140.03142857140.02796279070.03142857140.02732727270.03142857140.026720.03142857140.02613913040.03142857140.02558297870.03142857140.025050.03142857140.02453877550.03142857140.0240480.03142857140.02357647060.03142857140.02312307690.03142857140.02268679250.03142857140.02226666670.03142857140.02186181820.03142857140.02147142860.03142857140.02109473680.03142857140.02073103450.03142857140.0203796610.03142857140.02004chart1IS1893:1984IBC2000
R =3IS1893:2002; bldgtimesa/gV/Wtimetank r=3tank/1.4R=1.5tank/1.4R
= 2.0/1.4timeSa/gtank
r=1.1tank4=2.2500.10.0600.41666666670.29761904760.83333333330.59523809520.4464285714010.24545454550.120.030.160.0960.050.41666666670.29761904760.83333333330.59523809520.44642857140.051.750.42954545450.210.060.180.1080.10.41666666670.29761904760.83333333330.59523809520.44642857140.12.50.61363636360.30.080.190.1140.150.41666666670.29761904760.83333333330.59523809520.44642857140.152.50.61363636360.30.090.1950.1170.20.41666666670.29761904760.83333333330.59523809520.44642857140.22.50.61363636360.30.10.1980.11880.250.41666666670.29761904760.83333333330.59523809520.44642857140.252.50.61363636360.30.120.20.120.30.41666666670.29761904760.83333333330.59523809520.44642857140.32.50.61363636360.30.30.20.120.350.41666666670.29761904760.83333333330.59523809520.44642857140.352.50.61363636360.30.350.20.120.40.41666666670.29761904760.83333333330.59523809520.44642857140.42.50.61363636360.30.40.1850.1110.450.41666666670.29761904760.83333333330.59523809520.44642857140.452.50.61363636360.30.50.1680.10080.50.41666666670.29761904760.83333333330.59523809520.44642857140.52.50.61363636360.30.60.150.090.550.41666666670.29761904760.83333333330.59523809520.44642857140.552.50.61363636360.30.70.1380.08280.60.41666666670.29761904760.83333333330.59523809520.44642857140.62.50.61363636360.30.80.1270.07620.650.38461538460.27472527470.76923076920.54945054950.41208791210.672.50.61363636360.30.90.1180.07080.70.35714285710.25510204080.71428571430.51020408160.38265306120.72.38571428570.58558441560.286285714310.1080.06480.750.33333333330.23809523810.66666666670.47619047620.35714285710.752.22666666670.54654545450.26721.10.10.060.80.31250.22321428570.6250.44642857140.33482142860.82.08750.51238636360.25051.20.0940.05640.850.29411764710.21008403360.58823529410.42016806720.31512605040.851.96470588240.48224598930.23576470591.30.0880.05280.90.27777777780.19841269840.55555555560.39682539680.29761904760.91.85555555560.45545454550.22266666671.40.080.0480.950.26315789470.18796992480.52631578950.37593984960.28195488720.951.75789473680.43148325360.21094736841.50.0750.04510.250.17857142860.50.35714285710.267857142911.670.40990909090.20041.60.070.0421.050.23809523810.17006802720.47619047620.34013605440.25510204081.051.59047619050.39038961040.19085714291.70.0650.0391.10.22727272730.16233766230.45454545450.32467532470.24350649351.11.51818181820.37264462810.18218181821.80.060.0361.150.21739130430.15527950310.43478260870.31055900620.23291925471.151.4521739130.35644268770.174260869620.0560.03361.20.20833333330.14880952380.41666666670.29761904760.22321428571.21.39166666670.34159090910.1672.20.0520.03121.250.20.14285714290.40.28571428570.21428571431.251.3360.32792727270.160322.40.0480.02881.30.19230769230.13736263740.38461538460.27472527470.2060439561.31.28461538460.31531468530.15415384622.60.0450.0271.350.18518518520.13227513230.37037037040.26455026460.19841269841.351.2370370370.30363636360.14844444442.80.0420.02521.40.17857142860.12755102040.35714285710.25510204080.19132653061.41.19285714290.29279220780.143142857130.040.0241.450.1750.1250.34482758620.24630541870.1847290641.451.15172413790.28269592480.13820689661.50.1750.1250.33333333330.23809523810.17857142861.51.11333333330.27327272730.13361.550.1750.1250.32258064520.23041474650.17281105991.551.07741935480.2644574780.12929032261.60.1750.1250.31250.22321428570.16741071431.61.043750.25619318180.125251.650.1750.1250.3030303030.21645021650.16233766231.651.01212121210.24842975210.12145454551.70.1750.1250.29411764710.21008403360.15756302521.70.98235294120.24112299470.11788235291.750.1750.1250.28571428570.20408163270.15306122451.750.95428571430.23423376620.11451428571.80.1750.1250.27777777780.19841269840.14880952381.80.92777777780.22772727270.11133333331.850.1750.1250.27027027030.19305019310.14478764481.850.90270270270.22157248160.10832432431.90.1750.1250.26315789470.18796992480.14097744361.90.87894736840.21574162680.10547368421.950.1750.1250.25641025640.18315018320.13736263741.950.85641025640.21020979020.102769230820.1750.1250.250.17857142860.133928571420.8350.20495454550.10022.050.1750.1250.2439024390.17421602790.13066202092.050.81463414630.19995565410.09775609762.10.1750.1250.23809523810.17006802720.12755102042.10.79523809520.19519480520.09542857142.150.1750.1250.23255813950.16611295680.1252.150.7767441860.19065539110.09320930232.20.1750.1250.22727272730.16233766230.1252.20.75909090910.1863223140.09109090912.250.1750.1250.22222222220.15873015870.1252.250.74222222220.18218181820.08906666672.30.1750.1250.21739130430.15527950310.1252.30.72608695650.17822134390.08713043482.350.1750.1250.21276595740.15197568390.1252.350.71063829790.17442940040.08527659572.40.1750.1250.20833333330.14880952380.1252.40.69583333330.17079545450.08352.450.1750.1250.20408163270.14577259480.1252.450.68163265310.1673098330.08179591842.50.1750.1250.20.14285714290.1252.50.6680.16396363640.080162.550.1750.1250.19607843140.14005602240.1252.550.65490196080.16074866310.07858823532.60.1750.1250.19230769230.13736263740.1252.60.64230769230.15765734270.07707692312.650.1750.1250.18867924530.13477088950.1252.650.63018867920.15468267580.07562264152.70.1750.1250.18518518520.13227513230.1252.70.61851851850.15181818180.07422222222.750.1750.1250.18181818180.12987012990.1252.750.60727272730.14905785120.07287272732.80.1750.1250.17857142860.12755102040.1252.80.59642857140.14639610390.07157142862.850.1750.1250.17543859650.12531328320.1252.850.58596491230.14382775120.07031578952.90.1750.1250.1750.1250.1252.90.5758620690.14134796240.06910344832.950.1750.1250.1750.1250.1252.950.56610169490.13895223420.067932203430.1750.1250.1750.1250.12530.55666666670.13663636360.06683.050.1753.10.1753.150.1753.20.1753.250.1753.30.1753.350.1753.40.1753.450.1753.50.1753.550.1753.60.1753.650.1753.70.1753.750.1753.80.1753.850.1753.90.1753.950.17540.175000000.030.050.050.050.050.060.10.10.10.10.080.150.150.150.150.090.20.20.20.20.10.250.250.250.250.120.30.30.30.30.30.350.350.350.350.350.40.40.40.40.40.450.450.450.450.50.50.50.50.50.60.550.550.550.550.70.60.60.60.60.80.650.650.670.670.90.70.70.70.710.750.750.750.751.10.80.80.80.81.20.850.850.850.851.30.90.90.90.91.40.950.950.950.951.511111.61.051.051.051.051.71.11.11.11.11.81.151.151.151.1521.21.21.21.22.21.251.251.251.252.41.31.31.31.32.61.351.351.351.352.81.41.41.41.431.451.451.451.451.51.51.51.51.551.551.551.551.61.61.61.61.651.651.651.651.71.71.71.71.751.751.751.751.81.81.81.81.851.851.851.851.91.91.91.91.951.951.951.9522222.052.052.052.052.12.12.12.12.152.152.152.152.22.22.22.22.252.252.252.252.32.32.32.32.352.352.352.352.42.42.42.42.452.452.452.452.52.52.52.52.552.552.552.552.62.62.62.62.652.652.652.652.72.72.72.72.752.752.752.752.82.82.82.82.852.852.852.852.92.92.92.92.952.952.952.95333320022002Time
period (S)Base shear
coefficient0.060.29761904760.59523809520.24545454550.120.0960.29761904760.59523809520.42954545450.210.1080.29761904760.59523809520.61363636360.30.1140.29761904760.59523809520.61363636360.30.1170.29761904760.59523809520.61363636360.30.11880.29761904760.59523809520.61363636360.30.120.29761904760.59523809520.61363636360.30.120.29761904760.59523809520.61363636360.30.120.29761904760.59523809520.61363636360.30.1110.29761904760.59523809520.61363636360.30.10080.29761904760.59523809520.61363636360.30.090.29761904760.59523809520.61363636360.30.08280.29761904760.59523809520.61363636360.30.07620.27472527470.54945054950.61363636360.30.07080.25510204080.51020408160.58558441560.28628571430.06480.23809523810.47619047620.54654545450.26720.060.22321428570.44642857140.51238636360.25050.05640.21008403360.42016806720.48224598930.23576470590.05280.19841269840.39682539680.45545454550.22266666670.0480.18796992480.37593984960.43148325360.21094736840.0450.17857142860.35714285710.40990909090.20040.0420.17006802720.34013605440.39038961040.19085714290.0390.16233766230.32467532470.37264462810.18218181820.0360.15527950310.31055900620.35644268770.17426086960.03360.14880952380.29761904760.34159090910.1670.03120.14285714290.28571428570.32792727270.160320.02880.13736263740.27472527470.31531468530.15415384620.0270.13227513230.26455026460.30363636360.14844444440.02520.12755102040.25510204080.29279220780.14314285710.0240.1250.24630541870.28269592480.13820689660.1250.23809523810.27327272730.13360.1250.23041474650.2644574780.12929032260.1250.22321428570.25619318180.125250.1250.21645021650.24842975210.12145454550.1250.21008403360.24112299470.11788235290.1250.20408163270.23423376620.11451428570.1250.19841269840.22772727270.11133333330.1250.19305019310.22157248160.10832432430.1250.18796992480.21574162680.10547368420.1250.18315018320.21020979020.10276923080.1250.17857142860.20495454550.10020.1250.17421602790.19995565410.09775609760.1250.17006802720.19519480520.09542857140.1250.16611295680.19065539110.09320930230.1250.16233766230.1863223140.09109090910.1250.15873015870.18218181820.08906666670.1250.15527950310.17822134390.08713043480.1250.15197568390.17442940040.08527659570.1250.14880952380.17079545450.08350.1250.14577259480.1673098330.08179591840.1250.14285714290.16396363640.080160.1250.14005602240.16074866310.07858823530.1250.13736263740.15765734270.07707692310.1250.13477088950.15468267580.07562264150.1250.13227513230.15181818180.07422222220.1250.12987012990.14905785120.07287272730.1250.12755102040.14639610390.07157142860.1250.12531328320.14382775120.07031578950.1250.1250.14134796240.06910344830.1250.1250.13895223420.06793220340.1250.1250.13663636360.06680000.030.050.050.060.10.10.080.150.150.090.20.20.10.250.250.120.30.30.30.350.350.350.40.40.40.450.450.50.50.50.60.550.550.70.60.60.80.650.650.90.70.710.750.751.10.80.81.20.850.851.30.90.91.40.950.951.5111.61.051.051.71.11.11.81.151.1521.21.22.21.251.252.41.31.32.61.351.352.81.41.431.451.451.51.51.551.551.61.61.651.651.71.71.751.751.81.81.851.851.91.91.951.95222.052.052.12.12.152.152.22.22.252.252.32.32.352.352.42.42.452.452.52.52.552.552.62.62.652.652.72.72.752.752.82.82.852.852.92.92.952.9533IS
1893:1984; All types of elevated tanksIBC 2003; Tanks on frame
stagingIBC 2003; Tanks on shaft stagingTime period (S)Base shear
coefficient0.060.29761904760.44642857140.0960.29761904760.44642857140.1080.29761904760.44642857140.1140.29761904760.44642857140.1170.29761904760.44642857140.11880.29761904760.44642857140.120.29761904760.44642857140.120.29761904760.44642857140.120.29761904760.44642857140.1110.29761904760.44642857140.10080.29761904760.44642857140.090.29761904760.44642857140.08280.29761904760.44642857140.07620.27472527470.41208791210.07080.25510204080.38265306120.06480.23809523810.35714285710.060.22321428570.33482142860.05640.21008403360.31512605040.05280.19841269840.29761904760.0480.18796992480.28195488720.0450.17857142860.26785714290.0420.17006802720.25510204080.0390.16233766230.24350649350.0360.15527950310.23291925470.03360.14880952380.22321428570.03120.14285714290.21428571430.02880.13736263740.2060439560.0270.13227513230.19841269840.02520.12755102040.19132653060.0240.1250.1847290640.1250.17857142860.1250.17281105990.1250.16741071430.1250.16233766230.1250.15756302520.1250.15306122450.1250.14880952380.1250.14478764480.1250.14097744360.1250.13736263740.1250.13392857140.1250.13066202090.1250.12755102040.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.125
Base shear coefficient
Base shear coefficient for elevated tanks from IS1893:1984 is on
much lower side than IBC 2003IBC value is about 2.5 times for frame
staging and 3.5 times for shaft staging than that from
IS1893:1984Recall, for buildings, IS 1893:1984 and IBC have much
better comparison
Base shear coefficient
Reason for lower values in IS 1893:1984IBC uses R = 2.0 and R = 3.0
for tanks as against R = 8.0 for buildings with good ductilityIS
1893:1984 uses K = 1.0 for tanks. Same as for buildings with good
ductility.Clearly ,elevated tanks do not have same ductility,
redundancy and overstrength as buildings.This is a major limitation
of IS 1893:1984
Base shear coefficient
Another limitation of IS 1893:1984In Lecture 1, we have seen,
liquid mass gets divided into impulsive and convective massesIS
1893:1984, does not consider convective massIt assumes entire
liquid mass will act as impulsive mass, rigidly attached to wallIn
IITK-GSDMA guidelines, these limitations have been removed
Base shear coefficient
Let us now, get back to seismic force evaluation for tanksDesign
base shear coefficient is to be expressed in terms of parameters of
IS 1893(Part 1):2002Ah = (Z/2). (I/R). Sa/gZ will be governed by
seismic zone map of Part 1I and R for tanks will be different from
those for buildingsR depends on ductility, redundancy and
overstrength Sa/g will depend on time period
Base shear coefficient
Impulsive and convective masses will have different time
periodsHence, will have different Sa/g valuesProcedure for finding
time period in next lecture
At the end of Lecture 2
Seismic force = (Ah) X (W)Base shear coefficient, Ah, depends
onSeismic ZoneSoil typeStructural characteristicsDuctility,
Redundancy and overstrengthIS 1893:1984 has some serious
limitations in design seismic force for tanks
