Problem:
Design a rectangular water tank with fixed base for a given capacity in litres.
- Draw cross section of tank showing reinforcement details of vertical wall and base slabs.
- Draw plan of tank showing reinforcement details.
Design steps:
- Capacity of circular water tank ( V ) in liters.
- Length and breadth of tank ( L x B ) in m.
- Free board ( f ) in mm.
- Strength of concrete (ex : M20, M35)
- Strength of steel in (ex : Fe415, Fe-500)
IS: 3370 (Part II) Table 1, Clause 3.3.1 and IS: 456-2000, Clause B-2.1.1 and Table 21.
- Unit weight of water , γ = 9.8 kN/m3.
- Permissible stress in concrete , σcbc.
- Permissible tensile stress in steel , σst.
h = Depth of water tank. This can be found out using following equation.
\[h = \frac{{{W_{capacity}}}}{{L \times B}}\]
Choose required depth of water tank.
Total height tank = depth of the tank + Free board
H = h + f
Check for L/B ratio : If L / B ratio is greater than two. The cantilever action is predominate in wall. Hence, cantilever action is considered for analysis.
Calculate modular ratio.
\[m = \frac{{280}}{{3 \times {\sigma _{cbc}}}}\]
Neutral axis depth factor.
\[n = \frac{{m \times {\sigma _{cbc}}}}{{m \times {\sigma _{cbc}} + \times {\sigma _{st}}}}\]
Lever arm.
\[j = 1 - \frac{n}{3}\]
Moment of resistance.
\[k = \frac{1}{2} \times {\sigma _{cbc}} \times j \times n\]
Design moment at corner.
Provide vertical reinforcement.
\[{M_{long}} = \frac{{\gamma \times {H^3}}}{6}\]
Area of steel due to design bending moment.
\[{A_{st}} = \frac{{{M_{long}}}}{{{\sigma _{st}} \times j \times d}}\]
Consider the desired bar diameter.
\[{S_v} = \frac{{As{t_{provided}}}}{{Ast}} \times 1000\]
Provide diameter of bar at distance C/C.
Provide horizontal reinforcement.
Direct tensile transferred by short wall on long wall.
\[{T_{long}} = \gamma \times \left( {H - h_{c}} \right) \times \frac{B}{2}\]
Area of steel due to direct tension.
\[{A_{st}} = \frac{{{T_{Long}}}}{{{\sigma _{st}}}} \times 1000\]
Consider the desired bar diameter.
\[{S_v} = \frac{{As{t_{provided}}}}{{Ast}} \times 1000\]
Provide diameter of bar at distance C/C.
Provide reinforcement in vertiacal, horizontal direction and in middle span.
Provide reinforcement in horizontal direction.
\[{M_{short}} = \frac{{\gamma \times H \times {h^2}}}{6}\]
Area of steel due to design bending moment.
\[{A_{st}} = \frac{{{M_{short}}}}{{{\sigma _{st}} \times j \times d}}\]
Consider the desired bar diameter.
\[{S_v} = \frac{{As{t_{provided}}}}{{Ast}} \times 1000\]
Provide diameter of bar at distance C/C.
Provide reinforcement in horizontal direction.
Design moment at corner.
Water pressure.
\[{P_h} = \gamma \times \left( {H - {h_c}} \right)\]
Fixed-end moment.
\[{M_{short-end}} = \frac{{{P_h} \times {B^2}}}{{12}}\]
Direct tensile transferred by long wall on short wall.
Area of steel due to design bending moment.
\[{A_{st1}} = \frac{{{M_{short-end}}}}{{{\sigma _{st}} \times j \times d}}\]
Area of steel due to direct tension.
\[{A_{st2}} = \frac{{{T_B}}}{{{\sigma _{st}}}} \times 1000\]
Total area of steel.
\[{A_{st}} = {A_{st1}} + {A_{st2}}\]
Consider the desired bar diameter.
\[{S_v} = \frac{{As{t_{provided}}}}{{Ast}} \times 1000\]
Provide diameter of bar at distance C/C.
Design moment at centre.
\[{M_{middle}} = \gamma \times \left( {H - {h_c}} \right) \times \frac{{{B^2}}}{{24}}\]
\[{A_{st}} = \frac{{{M_{middle}}}}{{{\sigma _{st}} \times j \times d}}\]
Consider the desired bar diameter.
\[{S_v} = \frac{{As{t_{provided}}}}{{Ast}} \times 1000\]
Provide diameter of bar at distance C/C.
The base slab is laid on 75mm thick lean conrete mix. Provide thickness of 150 mm or more to avoid leakage of water.
Provide minimum nominal reinforcement in both direction.
Reinforcement bar should be continuous and bent in junction of rectangular water tank.
Sectional elevation and plan of rectangular water tank.
Indian standard code IS 3370-Part ( 2 ).
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