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Lecture 2
January 19, 2006
In this lecture
Seismic force evaluationProcedure in codesLimitations of IS 1893:1984Seismic 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 coefficientSeismic 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 parametersSeismic 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 philosophySeismic force evaluation
Thus, base shear coefficient depends on:Severity of ground motionSoil conditionStructural characteristicsDesign philosophySeismic 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 practiceIS 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 coefficientIS 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 VIS 1893 (Part 1):2002
Importance factor, IEnsures higher design seismic force for more important structuresValues for buildings are given in Table 6 ofIS :1893
Values for other structures will be given in respective partsFor tanks, values will be given in Part 2IS 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 slideDesign 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 slideIS 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% damping02571015202530Factor3.201.401.000.900.800.700.600.550.50IS 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 coefficientIS 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 coefficientIS 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 methodIS 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 coefficientIS 1893:1984
Importance factor, IEnsures higher design seismic force for more important structures IS 1893 (Part 1):2002, gives values only for buildingsIS 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 buildingIS 1893:1984
IS 1893:1984
Coefficient, CDepends on time period see next slideSpectral acceleration, Sa/gDepends on time period and dampingSee next slideIS 1893:1984
Graphs for C and Sa/g from IS 1893:1984Natural 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 suggestsAh = 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, laterIBC 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 2003IBC 2003
Base shear coefficientAh = 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 separatelyIBC 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 laterIBC 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 typesIBC 2003
Response modification factor, RIS 1893(Part 1):2002 calls it response reduction factorValues of R for some selected structures are given in next slideIBC 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 base2.0Base 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 tanksBase 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 1.4Base 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 accelerationBase 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 buildingsBase 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% dampingBase shear coefficient
Building with good ductility is chosenSay, buildings with SMRFIn IBC, for buildings with SMRF, R = 8.0Refer Table shown earlierBase 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) = 0.089Base 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) = 0.054Base 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) = 0.036Base 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 coefficient0.060.29761904760.44642857140.0960.29761904760.44642857140.1080.29761904760.44642857140.1140.29761904760.44642857140.1170.29761904760.44642857140.11880.29761904760.44642857140.120.29761904760.44642857140.120.29761904760.44642857140.120.29761904760.44642857140.1110.29761904760.44642857140.10080.29761904760.44642857140.090.29761904760.44642857140.08280.29761904760.44642857140.07620.27472527470.41208791210.07080.25510204080.38265306120.06480.23809523810.35714285710.060.22321428570.33482142860.05640.21008403360.31512605040.05280.19841269840.29761904760.0480.18796992480.28195488720.0450.17857142860.26785714290.0420.17006802720.25510204080.0390.16233766230.24350649350.0360.15527950310.23291925470.03360.14880952380.22321428570.03120.14285714290.21428571430.02880.13736263740.2060439560.0270.13227513230.19841269840.02520.12755102040.19132653060.0240.1250.1847290640.1250.17857142860.1250.17281105990.1250.16741071430.1250.16233766230.1250.15756302520.1250.15306122450.1250.14880952380.1250.14478764480.1250.14097744360.1250.13736263740.1250.13392857140.1250.13066202090.1250.12755102040.1250.12458471760.1250.12175324680.1250.1190476190.1250.11645962730.1250.11398176290.1250.11160714290.1250.10932944610.1250.10714285710.1250.10504201680.1250.1030219780.1250.10107816710.1250.09920634920.1250.09740259740.1250.09566326530.1250.09398496240.1250.093750.1250.093750.1250.09375Base 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 codesBase 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 buildingsBase 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 tanksBase 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 = 3.0Ah = SDSI/(1.4xR) = 1.0 x1.25/(1.4 x 3.0) = 0.298
For shaft staging, I = 1.25, R = 2.0Ah = 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 = 3.0Ah = SD1I/(1.4xRxT) = 0.6x1.25/(1.4 x 3.0x1.0) = 0.178
For shaft staging, I = 1.25, R = 2.0Ah = 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 staging0.30.120.2980.4461.00.0660.1780.268Base 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 coefficient0.060.29761904760.44642857140.0960.29761904760.44642857140.1080.29761904760.44642857140.1140.29761904760.44642857140.1170.29761904760.44642857140.11880.29761904760.44642857140.120.29761904760.44642857140.120.29761904760.44642857140.120.29761904760.44642857140.1110.29761904760.44642857140.10080.29761904760.44642857140.090.29761904760.44642857140.08280.29761904760.44642857140.07620.27472527470.41208791210.07080.25510204080.38265306120.06480.23809523810.35714285710.060.22321428570.33482142860.05640.21008403360.31512605040.05280.19841269840.29761904760.0480.18796992480.28195488720.0450.17857142860.26785714290.0420.17006802720.25510204080.0390.16233766230.24350649350.0360.15527950310.23291925470.03360.14880952380.22321428570.03120.14285714290.21428571430.02880.13736263740.2060439560.0270.13227513230.19841269840.02520.12755102040.19132653060.0240.1250.1847290640.1250.17857142860.1250.17281105990.1250.16741071430.1250.16233766230.1250.15756302520.1250.15306122450.1250.14880952380.1250.14478764480.1250.14097744360.1250.13736263740.1250.13392857140.1250.13066202090.1250.12755102040.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.1250.125Base 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 comparisonBase 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 1893:1984Base 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 removedBase 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 periodBase shear coefficient
Impulsive and convective masses will have different time periodsHence, will have different Sa/g valuesProcedure for finding time period in next lectureAt 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)
(F
Force
Design
)
(F
Force
Elastic
Maximum
Factor
Reduction
Response
des
el
=
0
0.1
0.2
0.3
0.4
0.5
00.511.522.53
Time period (S)
Base shear coefficient
0
0.025
0.05
0.075
0.1
00.511.522.53
Time Period (S)
Base shear coefficient