Design of foundation for tank 1301B08, 1301B11, 1303B02, 1803B12
Design Data
1 Dia of tank d = 3.6m
2 Height of tank H = 3.2m
3 Cone height H1 = 0.5m
Calculation of wind velocity as per IS 875 (P3-1987)
4 Basic wind speed Vb = 44m/s
5 Risk Coefficient k1 = 1
6 Terrain, ht, stru. Size Coefficient
as per Class B, terrain category 2 k2 = 0.98
7 Topography Factor k3 = 1
Design Wind Speed Vz = 43.12 m/s
= 156 km/hr
8 Designwind pr 1115.601
9 Inward drag associated with open tank
as per cl. 3.9.7.1(a)- API 650 = 240
10 Total external Pressure P = 1355.601
As per cl. 3.9.7.1(a)- API 650 formula for for max. ht. of unstiffened shell is based on total Equivalent wind velocity corresponding to wind pr. Of 1355.601 N/m2 is calculated by
11 V = 142.0436 km/hr
As a conservative consideration design wind vel. = 156 km/hr 12 wind load on cylindrical shell/m2
of projected area = 83.33716
13 Projected area of shell = D*H = 11.52
14 Wind load on shell = 960.044 Kg
15 Wind moment due to shell MWs = 1536.07 Kgm 16
of projected area = 69.77064
17 Projected area of cone roof = 0.9
18 wind load on cone roof = 62.79358 Kg
19 C.G. of cone roof from bottom = 3.366667 m 20 Wind moment due to cone roof MWr = 211.405 Kgm
21 Total overturning moment due to wind M = 1.748 Tm N/m2 N/m2 N/m2 external pressure of 1720 N/m2 which is result of wind velocity of 160km/hr.
Kg/m2 m2
wind load on cone roof/m2
Kg/m2 m2
Calculation of seismic force as per IS 1893 (1984)
22 b = 1
23 I = 1.5
24 = 0.04for Zone III
25 Horizontal Coefficient = 0.06
26 Empty wt. of tank = 4.5T
27 Total operating wt. = 37.5T
28 Seismic Lateral force
a) when tank is empty = 0.27 T
b) when tank is full = 2.25 T
29 Overturning moment due to earthquake
a) when tank is empty = 0.432 Tm
b) when tank is full = 3.60 Tm
Design Data for Ring Beam
1 Grade of concrete = M25
2 Grade of steel = Fe500
3 Dia of tank d = 3.6m
4
Coefficient of soil pressure at rest
u = 0.45 Density of liquid store = 10
6 Density of earth considered = 18
7 Angle of repose = 30degree
8 Coefficient of active earth pressure Ka = 0.33 9 Net safe bearing capacity of soil = 50
10 Self weight of tank = 45 kN
11 Self weight of liquid store = 330 kN
12 Inner dia of ring wall = 3.3m
13 Outer dia of ring wall = 3.9m
15 Dia of foundation = 5.7m
16 Horizontal Shear at top of ring beam
a) Due to wind force = 10.228 kN
b) Due to earthquake force = 22.5 kN
17 Overturning Moment at top of ring beam
a) Due to wind = 17.48 kNm b) Due to earthquake = 36.00 kNm ao ah kN/m3 kN/m3 kN/m2
300mm 3300mm 300mm 96 5m m DP= 15 50 m m DF= 900mm 45 0 5700mm
Design of ring wall
loading Data
Seismic moment when tank empty = 4.32 kNm
No. of basic loading cases = 4
Loads At tank bottom
Load case Description of load vertical Load KN Horizontal load KN Moment KN.m
1 Empty Wt. of tank 45 0 0
2 Operating Wt. of tank 375 0 0
3 Seismic Load when 0 22.5 36
tank full
4 Seismic Load when 0 2.7 4.32
tank empty
Load combination for stability check 101 = Load case 2 102 = Load case 1+4 103 = Load case 2+3 Load combination for design 201 = (Load case 2)*1.5
202 = (Load case 1)*0.9+(4)*1.5 203 = (Load case 2)*0.9+(3)*1.6
Combation of loads for stability check: Loads At top of Ring Beam
Load case vertical Load KN Horizontal load KN Moment KN.m
101 375 0 0
102 45 2.7 4.32
103 375 22.5 36
Weight of ring wall Wrb = 213.33 kN
Weight of sand mat Ws = 387.1937 kN
Loads At botton of Ring Beam
Load case vertical Load KN Horizontal load KN Overturning Moment KN.m
101 975.52 0 0
102 645.52 2.7 11.1105
103 975.52 22.5 92.5875
Calculation of Resisting Moment at bottom of Ring Beam Loads At botton of Ring Beam
Load case vertical Load KN Resisting Moment KN.m
101 975.52 977.32353
102 645.52 647.32353
103 975.52 977.32353
Check for Stability Check for Overturning
Overturning Safety Factor = Resisting Moment overturning Moment Load case Overturning safety factor Check
101 #DIV/0! >1.5 hence safe
102 58.26 >1.5 hence safe
103 10.56 >1.5 hence safe
Check for sliding
Sliding Safety Factor = u*Vertical Load
Load case sliding safety factor Check
101 #DIV/0! >1.5 hence safe
102 95.63 >1.5 hence safe
103 17.34 >1.5 hence safe
Check for crushing strength of concrete
Pmax/Pmin = P + M
A Z
where A= Area of Ring beam = 3.39292
where Z= section modulus of Ring beam = 2.295522 Pmax shouldnot be greater than crushing strengh of Concrete = 25 N/mm2 Pmin shouldnot be less than 0
Load case Pmax (N/mm2) Check Pmin (N/mm2) Check 101 0.29 <25N/mm2 hence safe 0.29 >0 hence safe 102 0.20 <25N/mm2 hence safe 0.19 >0 hence safe 103 0.33 <25N/mm2 hence safe 0.25 >0 hence safe Calculation of Reinforcement of Ring beam
Ring beam should be design for case for which factored load at top of ring beam is maximum. Loads At top of Ring Beam
Load case vertical Load KN 201 562.5 202 40.5 203 337.5 Pu Pu Tu qu1 qu2 m2 m3
Hoop tension on ring beam due to vertical load qu1 = 21.92217 Hoop tension at ring beam botton due to sand qu2 = 22.635 Avg Hoop tension on ring beam /m
Pu=(qu1+(qu1+qu2))*Dp+Df/2 Pu = 83.59777 kN/m Direct tension on ring beam /m Tu = 137.9363 kN Ast req. for ring beam = Tu/0.87*fy Ast = 317.095
ptmin = 0.2%
Astmin = 1509
use 12dia. Bar
cover = 40mm
d1 = 2423 mm
spacing of bar = 181.6003 mm
Provide 12 mm dia. @ 150 mm C/C as a main reinforcement
Calculation of shear reinforcement
use 8dia. Bar
spacing = 364.4247 mm
Provide 2 legged 8 mm dia. @ 200 mm C/C as a shear reinforcement
Load calculations for Base Slab
Total load coming on the top of foundation = 375 kN
Weight of ring wall = 213.33 kN
Weight of soil = 387.19 kN
Self weight of foundation = 287.07 kN
Total weight of foundation = 1262.60 kN
A Total weight coming on the foundation P = 1262.60 kN B Moment at base of ring beam M = 102.7125 kNm
c Gross pressure at base G = 50
Checking of base pressure A Check for max. Gross Pressure
Maximum pressure coming = P
A = 1262.60
25.51759
= 49.48 <Gross pr. of soil so safe
Calculation of Ast at top
Base slab is designed for max. pressure of 50KN/m2 for simlicity
Maximum Factored B.M. at face of ring beam = 30.375 kNm kN/m2 kN/m2 mm2 mm2 kN/m2 kN/m2
Depth required d = 93.83 mm
Depth provided = 394 mm O.K.
Area of steel required Ast = 788.00
Provide 16 mm dia bar @ spacing = 255.1547 mm C/C Provide 16 mm dia @200 mmC/C
Calculation of Ast at bottom
Pr. From bottom = 49.48
Pr. From top due to tank wt. & internal soil wt. = 100.36
Balance pr. = 50.88
Maximum Factored B.M. at centre of raft = 103.9006 kNm
Area of steel required Ast = 788.00
Provide 16 mm dia bar @ spacing = 255.1547 mm C/C Provide 16 mm dia @200 mmC/C
Check for punching shear
Perimeter = 13.49 m
Area of resisting shear = 25.13931
Shear force = 3784.635 KN Tv = 0.712059 Bc = 1 Ks = 1 Tc = 1.25 O.K. mm2 kN/m2 kN/m2 kN/m2 mm2 m2 N/mm2 N/mm2
