Analysis And Design Of Circular Water Tank Rested On Soil

Soil Bearing Capacity = 1.2 Kg/c m2 fcu = 30 MPa

For Dome :

Geometry :r = 6.2 m y = 2.5 m ts = 0.12 ma = a = = 8.94 msin = = sin-1 ( = ( = 43.91A = 2 a y

= 2 * 8.94 * 2.5 = 140.4 m Loads :

Assume covering = 50 kg/ m2 & Live Load = 100 kg/ m2g = c * ts + cover = 2.5 * 0.12 + 0.05 = 0.35 t/ m2P = 0.1 t/ m2W = g Asur + P A = 0.35 *140.4 + 0.1 * ( 6.22) = 61.2 tonsV = W / 2 r = 61.2 / 2 6.2 = 1.57 t/ mH = V/ tan = 1.57/ tan (43.91) = 1.63 t/ mN = 2.26 t/ m

Edge moments: x = 0.6 = 0.6 = 0.52 mM = = (g+p) * = (0.35+0.1) * = 0.0608 mt (very small value)The stress is very small; however, the thickness (t) may be increased from 12 to 15 cm within a distance 5 x, where; x = 0.65 x = 5 * 0.52 = 2.6 mReinforcement:As = 5 8 for both directions.

Ring Beam

Ring beam is under tension

H = N cos = 2.26 * 0.72 = 1.36 t/m'T= H r = 1.63 * 6.2 = 10.12 t

As = As = = 452.6 mm2Use minimum reinforcing ( 16 16 )

Stresses On soil

W water = w = 13 * W wall = c = 13 * W floor = c = 1*

W cantilever = c = 0.975 * * 2.5 = 452 ton

W dome = 61.2 ton

q total = = 10.59 t/m2

stress under Floor = c * tf + w * H = 2.5 *1 + 1 *15 = 17.5 t/m2

stress under cantilever = c * c = 2.5 * ((1.3+0.65)/2) = 2.44 t/m2

Stresses, in case of, there are a fill over the cantilever:

W fill = Afill * Hfill * fill = * = 165.8 tonqtotal = 10.59 + = 11.09 t/m2 Ok, tank is safe over the soil.

Earthquake forces; g = 9.81 m/s2 H = 15 m Ct = 0.05T1 = 0.05 * 153/4 = 0.4278 secSubsoil class; C S= 1.5, TB = 0.1 , TC = 0.25 , TD = 1.2Tc T TDSd (T1) = ag 1 s = 0.125 * 9.81 * 1 * 1.5 * * ( ) = 0.579 = 0.2 *0.125 * 9.81 * 1 = 0.245Sd (T1) OkWtotal = = 3723.56 tonFbase = Sd (T1) . . = 0.579 * 1 * = 219.7 tonDistribution of base shear ; fi = () . Fb Mbase = 2438.55 mtwind forcesF= Cf . K. q. A = 1.13 * 1 * * ( ) = 16.5 tonMbase = F.H = 16.5 * 10 = 165 mtEarthquake force is more critical than wind forces.Check of stresses on soil; f1,2 = - yN= 3723.56 tonA = = 326.85 m2M = 2438.5 mtI = = 8501.4 m4 y = 10.2 m fallowable = 1.25 * BC = 1.25 * 12 = 15 t/m2 f1 = - + *10.2 = 8.46 t/m2 f1 = - *10.2 = 14.3 t/m2 Ok, safecheck of overturning; F.O.S = = = 15.5 Ok, safe.

Total stresses on tank ;

Net stresses ;

Bending Moment diagram

H2 /Dt = 152 / 12.4 * 0.5 = 36.2 32

Tmax = coefficient * H * R = 0.782 * 15 * 6.2 = 72.73 ton

Mwf +ve = coefficient * H3 = 0.0009 * 153 = 3.04 mt

Mwf -ve = coefficient * H3 = -o.004 * 153 = -13.5 mt

MR = coefficient * p *r = 0.125 * 6.91 * 6.22 = 33.2 mt MT = coefficient * p *r = 0.075 * 8.15 * 6.22 = 19.93 mt

= 1/a = 1/7.2 = 0.139P = 8.15 t/m2 b = 10.2 mMcantilever = p { 3 b2 + 1.2 a2 } = 8.15 * 0.139 { 10.23 / 3 _ 3* 10.22 + 1.2 *7.22 } = 46.8 mt

For joint equilibrium ;

46.8 _ 13.5 _ 33.2 = 0.1 0.0

Design Of Tank

Design wall for Ring tension (water-side section)

fct = fct =

= = = 1.933 N/mm2 fct Ok, section is adequate.

As = fy ' = fy *cr = 360 * 0.75 = 270 N/mm2for18 mm

As = (use 9 18/ m'/ side )

Design of section 1 (water-side section)

Mw ve = 13.5 mt

N = Asection * c * Fy (dome)

= (1*0.5* 13 + 1*0.75*2) * 2.5 + 1.57 = 21.57 tons

fct =

fct = = 0.5943 N/mm2 = = = 1.933 N/mm2 Ok, section is adequate.

e = = 0.626 mes = e + t/2 cover

= 0.626 + 1/2 0.04 = 1.086 mMus = Nu * es = 1.4 * 21.57 * 1.086 = 32.79 mt

d= c1

960= c1 C1 = 9.18(c/d)mintake J = 0.826As =

As = = 327.65 mm2 (use 5 16/ m')

Design of section 2 (air-side section)

M = 46.8 mt

d= c1

1260= c1

C1 = 8.52(c/d)mintake J = 0.826

As = = = 1748 mm2

( use 5 18/ m' + 5 16/m' from section "1" )

Design of section 3 (air-side section)

Shear at base = coefficient *

V = 0.089*152 + (-10.36)* = 29.35 tM = 33.2 mt

e = = 1.13 m

es = 1.131/2 + 0.04 = 0.671

Mus = Nu * es = 1.4 * 29 * 0.671= 27.57 mt

d= c1

960= c1

C1 = 8.46(c/d)mintake J = 0.826

As =

As = = 2278.38 mm2

(use the same 5 18/ m' from section "2" )

Design Of section 4 (air-side section)

M = MT + MR = 33.2 + 19.93 = 53.13 mtN = 29.35 t "tension"

e = = 1.81 m

es = 1.811/2 + 0.04 = 1.35 mMus = Nu * es = 1.4 * 29.35 * 1.35 = 55.47 mt

d= c1

960= c1

C1 = 7.06(c/d)mintake J = 0.826

As = As = = 3255.74 mm2

( use 9 22 / m' )