Sump Design

RCC SUMP DESIGN REFERENCE : 1. IS 456-2000. 2. IS 3370-2009 Part 1&2. 3. SP-16 -1978. DATA : Sump Size : 5.0m (L) X 2.0m(B) X 1.25m(H) Concrete Grade : For cover slab M20. For Tank M25. Steel Grade : Fe 415 Unit weight of water : 10 KN/m3 Live Load for Cover slab 2 KN/m2 DESIGN: DESIGN OF COVER SLAB: Slab size : 2.0m x5.0m L/B =5.0/2.0=2.50> 2.0 Hence the slab has to be designed as oneway slab. d required =2000/25 =80mm. However from deflection point of view provide D=120mm d=120-20-10/2=95mm. Loads: Live Load =2.0KN/m2 Self weight 0.12x25 =3.0KN/m2 Finishing =1.0KN/m2 Total Load =6.0KN/m2 Effective span =2.0+0.095=2.095m Bending Moment =Wl2/8 = 6.0x2.0952/8 = 3.29 KN.m. Factored B.M. =4.94 KN.m. Mu.lim. =0.138 fck b d2 =0.138 x 20x 1000 x 952 =24.91 KN.m Hence under reinforced section. K= Mu/b d2 =4.94 x106/1000 x 952 =0.55 From Table 2 of SP 16 pt =0.158 Ast= 0.158 x 1000 x 95 =150 mm2 100 Using 10mm bars spacing = ast x 1000 Ast =78.5 x 1000 =523 mm 150 Max spacing limit to 3d (3x95=285) or 300mm whichever is less. Provide 10mm dia bars at 200mm C/c. (Ast provided=392.5mm2)

Distribution Steel : Mini. Ast = 0.12 x 1000x 120 =144mm2 100 Using 8mm bars spacing = ast x 1000 Ast =50 x 1000 =347 mm 144 Max spacing limit to 5d (3x85=430) or 450mm whichever is less. Provide 8mm dia bars at 200mm C/c. Check for Deflection : Actual span ratio = 2095/95 =22.05 d For pt= 392.5 x 100 = 0.4132 1000 x 95 Max. Permissible Span ratio from Chart 23 of SP16 =25.20 > 22.05 d Hence O.k.

DESIGN OF WATER TANK DESIGN OF SIDE WALL:

This has to be designed by Working Stress Method with the following permissible stresses to avoid leakage problem..Using M25 concrete and Fe415 (HYSD) steel

σcbc = 8.50N/mm

2

σst=150 N/mm

2

Design Constants: m=Modular ratio =280/3

σcbc = 280

=10.98 =11.00

3x8.5

σcbc m σcbc+ σst

n=m

= 11

x 8.5

= 0.384

11x8.5+150

j= 1 – n = 1- 0.384/3 = 0.872 3 K=½

σcbc

n j =1/2 x 8.50 x 0.384 x 0.872 =1.423 The water tank has to be designed for the following two cases. 1) Tank is full and no earthfill outside. 2) Tank is empty and active earth pressure acting from outside. Case 1: When Tank is full and no earth pressure outside

Long Wall: Ph = w xH=10 x 1.25 =12.5 KN/m2 Cantilever moment M= (1/2x12.5 x 1.25) x1.25/2=4.88 KN.m Ast =

M/

σst

x j = 4.88 x 106

=327 mm2

150x0.872x120 Using 10mm dia bars spacing required = = 78.5 x 1000 = 240 mm 327 Provide 10 mm bars at 150 mm C/c near inner face in vertical direction. Horizontal bars in Long wall Since long wall is predominantly acting as a cantilever, distribution steel is provided & checked for axial Tension when tank is full without earth pressure from outside. Mini. % of steel = 0.30 x 1000 x 150 = 450mm2 100 Using 10 mm bars spacing required = 78.5 x 1000 = 174 mm 450 Provide 10mm bars at 150mm C/c inside the face. Check for Direct Tension : TL= w (H-h) B/2 = 10 x (1.25-1.0) 2.0/2=2.50KN, Ast required = 2.50 x 103 = 17 mm2 150 Distribution steel takes care of this Tensile forces . Case 2: When Tank is empty Ph =k

1

+ wH where K= 1- sin Φ = 1-sin 30 =1/3

1+ sin Φ 1

s=

s-

1+ sin 30 w =16-10=6 KN/m2

Ph= (1/3 x 6x 1.25) +(10x1.25) =15.0KN/m2 M=(1/2 x 15.0x HxH/3) =(1/2x 15.0 x 1.25x 1.25/3) =3.91 KN.m. Depth of balanced section = sqrt M/k b = Sqrt 3.91 x 106 1.423x1000 =52.42mm However provide D=150mm, d=150-20-10/2=128mm

Ast required = M/ σst j = 3.91 x 106 150 x0.872x 128 =234mm2 Using 10mm bars spacing required = 78.5 x 1000 =335mm 234 Provide 10mm bats at 150mm C/c near inner face of the wall. DESIGN OF SHORT WALL : Vertical reinforcement : Cantilever action height for lower portion h= H/4 or 1m whichever is more =1m. When water tank is empty and outside soil is saturated ph=(1/3x6x1.25)+(10x1.25)=15KN.m2 M= 1/2x15.0x1.0x1.0/3 =2.50KN.m Ast = M σst x j

= 2.50 x 106 150x0.872x128

= 129mm2 Direct compression due to load on 1m wide long wall P= 15.0 x (1.25-1.0) x1.0 =3.75 KN. Concrete alone can resist if water tank is full and no earth fill. Ph= 10 x 1.25 =12.50KN/m2 M= ½ x 12.50 x 1.0x 1.0/3 =2.08 KN.m quite small. Provide mini reinforcement in vertical direction which is 10mm at 150mm C/c At Mid span : B.M. is half of 2.08/2 =1.04 KN.m Provide same reinforcement 10mm bars at 150mm C/c near outer face.

DESIGN OF BASE SLAB: Assume thickness of base slab =200mm d = 200-50-12/2=144mm Height from base slab =1.25+0.20=1.45m Upward pressure when soil is saturated =10x1.45 =14.50 KN/m2 In bottom slab there is no projection. Downward Loads: Weight of top slab =0.12x5.30x2.3x25 =36.57KN. Weight of long wall =2x0.15x5.30x1.25x25 =49.69KN Weight of short wall =2x0.15x2.3x1.25x25 =21.56KN Weight of bottom slab =5.30x2.30x0.20x25 =60.95KN Total Load =168.77KN Uplift force on bottom slab= 14.50(5.30+2.30)=110.20KN Since downward force is more than uplift force on bottom slab, projection is not required. Provide 150mmx 150mm haunches at junction. Provide junction reinforcement 10mm bars at 150mm C/c. Self weight of slab directly get transmitted to soil. Net upward soil pressure=(10x1.45)- (0.2x1x1x25) =14.50-5.0=9.50KN/m2 Bending moment: Considering net upward pressure B.M.=9.50x2.152/8=5.49 KN.m Considering weight of water alone B.M. =(10x1.25)x 2.152/8=7.22KN.m Considering higher moment, Ast required = M = 7.22 x 106 σst x j 150x0.872x144 = 383mm2

Minimum Ast = 0.3 x 1000x 200 = 600mm2 100 Using 12mm bars spacing = 113 x 1000= 188mm 600 Provide 12mm bars at 150mm C/c Distribution Steel: Mini. Ast = 600mm2 Ast on each face =600/2 = 300mm2 Using 10mm dia bars spacing = 78.5 x 1000 300 Provide 10mm dia bars at 150mm C/c in longitudinal direction near both faces.