For the brick walls in a rectangular tank, the centre-line length of a wall is

2[(L + t) + (B + t)] using the clear size L x B and wall thickness t

Why is the top cover slab 2.46 x 1.46 m?

It rests on the 23 cm walls, so size = clear size + 2 x 0.23

It is the clear size plus 2 x 0.35

It equals the clear internal size

It is the clear size plus the slab thickness

What is the extra length of a cranked (bent-up) bar over a straight bar?

0.42 x (depth - covers - bar dia) per crank, about 0.059 m here

2082 Bhadra

Underground RCC tank: brickwork, steel (fig a)

Short answer

Brickwork in 1:4 mortar = 2.780 m³. Steel in top RCC cover slab: 10 mm bars at 15 cm c/c both ways, with hooks and alternatte cranked bars, total weight = 33.3 kg.

Calculate quantities for the following items of works for an underground RCC water tank given below: a) First class brickwork in 1:4 c/s mortar b) Steel reinforcement in top RCC cover slab [Figure a: Underground RCC water tank. Plan: outer 300 cm wide, brick wall 23 cm thick with 12 cm and 35 cm offsets/projections, inner opening 200 cm × 100 cm, 200 cm. Section A-A: overall 276 cm wide, top RCC cover slab 20 cm thick with 10 mm dia all-bent-up bars and 10 mm dia main bars @ 15 cm c/c, 10 mm dia distribution bars @ 15 cm c/c, internal height 60 cm + 137 cm + 60 cm as marked, brickwork (1:4) 23 cm at top and 35 cm at base, M20 RCC floor, PCC (1:3:6) and flat brick soling below. Figure dimensions are hard to read in the scan.]

Assumptions (figure dimensions are hard to read)

Clear internal size of tank $2.00 \times 1.00$ m; internal clear height $1.37$ m.
Brick wall (1:4): bottom part $0.35$ m thick and $0.60$ m high (12 cm offset on the outer face), top part $0.23$ m thick and $0.77$ m high; total $1.37$ m.
Top cover slab: $20$ cm thick RCC, resting on the 23 cm wall at both ends, so its size is $(2.00 + 2 \times 0.23) \times (1.00 + 2 \times 0.23) = 2.46 \times 1.46$ m. Clear cover $25$ mm.
10 mm bars at 15 cm c/c in both directions; main bars in the short direction, alternate bars cranked up; distribution bars in the long direction; hooks $9d = 0.09$ m at each end of main and distribution bars; crank extra $= 0.42 \times (0.20 - 2 \times 0.025 - 0.010) = 0.059$ m at each of the two cranks.

(a) Brickwork in 1:4 mortar (centre-line method)

Part	Centre-line length (m)	Thickness (m)	Height (m)	Volume (m³)
Lower wall	$2\,[(2.00+0.35)+(1.00+0.35)] = 7.40$	0.35	0.60	1.554
Upper wall	$2\,[(2.00+0.23)+(1.00+0.23)] = 6.92$	0.23	0.77	1.226
Total				2.780

(b) Steel in the top cover slab

Number of main bars $= 1 + (2.46 - 0.05)/0.15 = 17$ ; of these 8 are cranked and 9 are straight.
Straight main bar length $= 1.46 - 0.05 + 2 \times 0.09 = 1.590$ m; cranked bar $= 1.590 + 2 \times 0.059 = 1.708$ m.
Number of distribution bars $= 1 + (1.46 - 0.05)/0.15 = 10$ , each $= 2.46 - 0.05 + 2 \times 0.09 = 2.590$ m.
Weight per metre of 10 mm bar $= d^2/162 = 100/162 = 0.617$ kg/m.

Bars	Number	Length each (m)	Total length (m)	Weight (kg)
Main, straight	9	1.590	14.31	8.83
Main, cranked	8	1.708	13.66	8.43
Distribution	10	2.590	25.90	15.99
Total				33.25

Answer: brickwork = 2.780 m³; steel in top slab = 33.3 kg.

✓ Answer checked by Claude Opus 5.5 (high effort)

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Underground RCC tank: brickwork, steel (fig a)

Assumptions (figure dimensions are hard to read)

(a) Brickwork in 1:4 mortar (centre-line method)

(b) Steel in the top cover slab

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