Construction of overhead water tank should be according to specific procedures to control its load and possible leakage problems in building. Details of construction procedure is as follows having two phases
A-Design phase procedure
B-Construction phase procedure
Firstly we will discuss design phase procedure.
1- Adjust size according to capacity of water tank, suppose required capacity is 2000 Gallons and size according to this capacity can be calculated as
Volume of tank in Cft = (Capacity in Gallons x 3. 78) /28.32
=(2000x3.78)/28.32 = 266.95 Cft
Now we know that
Volume of tank in Cft = Length x width x Depth
Here taking consideration for square tank we should also match the size (Length x Width) of water tank according to span of load bearing walls or avail columns spans. This span should be near external walls.
266.95 Cft = 8ft x 8ft x Depth of water
Depth of water = 4.17 ft say 4ft-2 Inches.
Adding free board of 6 inches
Total depth of water tank will be 4ft-8 inches
Suppose we have a available load bearing wall span of 8ft x 8ft.
2- Here we will raise all walls of lower span of 8ft x 8ft up to the height of 3 ft to 4ft or planted columns may also be raised by providing 4 equal length beam in slab.
3- Base slab size can be obtained by adding 6 inch thick RCC load bearing walls and 2 inch wide cavities along with 4.5 thick walls on external side of tank.
Cavities will provide insulation to keep water cool in summer and warm in winter.
So the base slab size= clear span +2 load bearing walls+2 cavities?+2 walls 4.5 inch wide.
Putting values= (8)+(2x.5ft)+(2x.16ft)+(2x.375ft)+ finishing margins of. 75 inches on 4-faces of walls (4x.06)= 10.32 ft say 10ft-4inches
4- Considering 4 planted columns sized 12inch x 12inch and height of 3 ft with 4 beams having width of 14 inches (To accommodate load bearing wall of 6 inch+2 inch cavity +4.5 inch wide brick wall and 1.5 inch finishing margin. Slab thickness should be 8 inches having concrete cover of 1.5 Inches on top and bottom of slab, using ½” Dia bars @6 inch c/c both ways at top and bottom of slab. And same bars with same spacing will be provided in walls. Top slab will be 5 inch thick having 3/8 “ Dia bars @ 6” c/c both ways single mesh. 4 columns will be provided with 8 nos of ½ “Dia bars and stirrups of 3/8 “ Dia bars will be provided at 9”c/c.
Secondly we will discuss construction phase procedure in following steps.
1- Construction of 4 planted columns sized 12inch x 12inch using Rcc (1:2:4) and 8 vertical main bars of ½ “Dia plus 3/8 “ Dia bars stirrups @9” c/c, Use water tight shuttering along with proper bracing complete in all aspects.
2- Construction of Rcc (1:2:4) for 8 inch thick slab (using 1/2”Dia main bars@ 6” c/c both ways on top and bottom) and side Beams sized 14 inch width x 9 inch depth having 3 nos bottom bars of ¾ “ Dia and stirrups of 3/8” Dia bars @ 6”c/c on entire span of all beams.
3- Construction of Rcc (1:2:4) load bearing walls 6 inch wide and 4ft-8inch high using ½”Dia bars @6”c/c both ways and on both faces of wall, use 1” concrete cover, use good class of shuttering along with complete bracing, Use water stopper on construction joint at base slab and load bearing walls.
4- Construction of Brick walls 4.5 inch thick using cement sand mortar (1:4) spacing 2 inch away from load bearing walls to create cavity for insulation, applying of cement plaster (1:4) ¾” thick complete in all aspects.
5- Construction of Rcc (1:2:4) slab 5 inch thick including shuttering and scaffolding maintaining slopes for rain water, use 3/8” Dia bars @6”c/c both ways.
6- Supply and fixing of water supply pipes near bottom of slab including all type of valves, overflow pipe, complete in all aspects.
7- Supply and applying of chips plaster ¾ “ thick on bed and walls of water at internal side maintaining required slopes.
8- Supply and fixing of manhole in top slab of water tank including fixing of L-shaped angle iron complete in all aspects.
9- Supply and fixing of motor pumps for pumping of water in case of low pressure in main supply line.
10- Supply and fixing of drain pipe at bed of water tank to empty, cleaning and repair activities.
11- Provision of electric connections for installation of motor pumps complete in all aspects.
