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T-beam decking: RCC and wearing coat

Short answer

RCC work (excluding steel) volume: sum of slab, rib, fillet, kerb and post volumes = 17.402 m³. Wearing coat C.C. (1:2:4) quantity: 7.00×6.90×0.10 = 4.830 m³.

Find out the quantities of the following items of work of a T-beam decking of a bridge with 6 m span and 45 cm bearing at ends. i) RCC work (1:2:4) excluding steel ii) Cement concrete (1:2:4) in wearing coat [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 figure

  • Length of decking =6.00+2×0.45=6.90= 6.00 + 2 \times 0.45 = 6.90 m (clear span plus bearing at both ends).
  • Overhang of slab beyond outer ribs =(7.70−3×0.35−2×2.25)/2=1.075= (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.

(i) RCC work (1:2:4), excluding steel

MemberWorkingVolume (m³)
Slab7.70×6.90×0.207.70 \times 6.90 \times 0.2010.626
Ribs (3)3×0.35×0.75×6.903 \times 0.35 \times 0.75 \times 6.905.434
Fillets (6, 15 × 15 cm triangular)6×12×0.15×0.15×6.906 \times \tfrac12 \times 0.15 \times 0.15 \times 6.900.466
Kerbs (2)2×0.20×0.20×6.902 \times 0.20 \times 0.20 \times 6.900.552
Railing posts (12 nos, 15 × 15 × 120 cm)12×0.15×0.15×1.2012 \times 0.15 \times 0.15 \times 1.200.324
Total RCC (1:2:4)17.402

(ii) Cement concrete (1:2:4) in wearing coat

V=7.00×6.90×0.10=4.830V = 7.00 \times 6.90 \times 0.10 = 4.830 m³

Answer: RCC = 17.402 m³; wearing coat = 4.830 m³.

Materials for information (1:2:4, dry factor 1.54): RCC needs 110.3 bags cement, 7.66 m³ sand, 15.31 m³ aggregate; wearing coat needs 30.6 bags, 2.13 m³, 4.25 m³.

✓ Answer checked by Claude Opus 5.5 (high effort)

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