What length of decking is used in the quantities?

6.00 + 2 x 0.45 = 6.90 m (clear span plus bearing at both ends)

How is the volume of the three ribs found?

3 x 0.35 x 0.75 x 6.90 = 5.434 m3

How is steel in the beams found?

(ribs + fillets) 5.900 m3 x 2.5% x 7850 = 1,157.8 kg

2076 Chaitra · 8 marks

T-beam decking quantities (6 m clear span)

Short answer

RCC (1:2:4) = 17.402 m³, wearing coat = 4.830 m³, total reinforcement = 2060.7 kg (2.5% steel in beams/fillets, 1% in slab/kerbs/posts), 40 mm G.I. pipe = 55.2 m.

Estimate the quantities of a T-beam decking of a single span bridge which has 6 m clear span and bearing on either side is 45 cm, from the accompanying bridge drawing. (Reinforcement: beam 2½%, slab and posts 1%.) [Figure: RCC T-beam decking cross-section. Overall width 7.7 m, 7 m roadway, 20×20 cm kerb on each side, 10 cm wearing coat of C.C., 20 cm slab, three ribs each 35 cm wide with 225 cm clear between ribs, rib depth below slab 75 cm (107.5 cm projections at the edges), 15×15 cm fillets, 15×15 cm RCC railing posts 120 cm high at 136 cm c/c, 40 mm dia G.I. pipe 4 nos., railing height 120 cm.]

Assumptions from the drawing

Length of decking $= 6.00 + 2 \times 0.45 = 6.90$ m (clear span plus bearing at both ends).
Overhang of slab beyond outer ribs $= (7.70 - 3 \times 0.35 - 2 \times 2.25)/2 = 1.075$ m (matches the 107.5 cm in the figure).
Fillets are taken as triangles of 15 × 15 cm at both sides of each rib (6 in total). The railing posts are at 1.36 m c/c: with 6.90 m length this gives 6 posts per side, 12 in all.
The 20 cm slab is taken from the figure; the kerb is 20 × 20 cm above the slab, and the wearing coat (10 cm) is laid between the kerbs over the 7.0 m roadway.
Reinforcement as given: beams (ribs and fillets) 2.5%, slab and kerbs 1%, posts 1% of the volume of concrete; density of steel 7850 kg/m³.
The railing has 4 lines of 40 mm G.I. pipe on each side, running the full length of the decking (assumption; the figure shows "4 nos").

Quantities

Member	Working	Volume (m³)
Slab	$7.70 \times 6.90 \times 0.20$	10.626
Ribs (3)	$3 \times 0.35 \times 0.75 \times 6.90$	5.434
Fillets (6, 15 × 15 cm triangular)	$6 \times \tfrac12 \times 0.15 \times 0.15 \times 6.90$	0.466
Kerbs (2)	$2 \times 0.20 \times 0.20 \times 6.90$	0.552
Railing posts (12 nos, 15 × 15 × 120 cm)	$12 \times 0.15 \times 0.15 \times 1.20$	0.324
Total RCC (1:2:4)		17.402

Item	Working	Quantity
Wearing coat C.C. (1:2:4)	$7.00 \times 6.90 \times 0.10$	4.830 m³
Steel in beams	$(5.434 + 0.466) \times 0.025 \times 7850$	1,157.8 kg
Steel in slab and kerbs	$(10.626 + 0.552) \times 0.01 \times 7850$	877.5 kg
Steel in posts	$0.324 \times 0.01 \times 7850$	25.4 kg
Total steel		2,060.7 kg
G.I. pipe 40 mm dia.	$4 \times 2 \times 6.90$	55.2 m

Answer: RCC (1:2:4) = 17.402 m³; wearing coat = 4.830 m³; reinforcement = 2,060.7 kg; 40 mm G.I. pipe = 55.2 m.

✓ Answer checked by Claude Opus 5.5 (high effort)

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T-beam decking quantities (6 m clear span)

Assumptions from the drawing

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