---
title: "T-beam decking: PCC for RCC and steel"
subject: "Estimating and Costing"
chapter: 6
key: "semester_7/estimating_and_costing:t-beam-pcc-rcc-reinforcement"
source: https://www.bctengineer.com/q/semester_7/estimating_and_costing/t-beam-pcc-rcc-reinforcement
site: BCT Engineering
---

# T-beam decking: PCC for RCC and steel

Estimating and Costing · Chapter 6: Detailed Estimate

- Asked in: 2080 Baisakh, 4+3 marks
- Video: [ESTIMATION OF RCC T BEAM DECKING](https://www.youtube.com/watch?v=HmdpoBWqEWo) — ADV. LEARNING
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/estimating_and_costing/t-beam-pcc-rcc-reinforcement
- Whole chapter: https://www.bctengineer.com/md/semester_7/estimating_and_costing/chapter-6

## Question

From the given figure of RCC T-beam decking of one span of 6 m, of which the section is given, calculate the following items of works: a) PCC for RCC work b) Reinforcement quantities for all RCC members.
[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.]

## Short answer

Concrete for RCC members (PCC) = 17.402 m³. Reinforcement: ribs+fillets 1157.8 kg, slab+kerbs 877.5 kg, posts 25.4 kg; total 2060.7 kg.

## Answer

#### Assumptions from the figure

- 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.
- Percentage of steel is not stated; the usual values for T-beam decking are taken: beams 2.5%, slab and kerbs 1%, posts 1%. Density of steel 7850 kg/m³.

#### (a) Concrete for the RCC work (1:2:4)

| 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** |

#### (b) Reinforcement

| Member | Concrete (m³) | % steel | Steel (kg) |
|---|---:|---:|---:|
| Ribs and fillets | 5.899 | 2.5 | 1,157.8 |
| Slab and kerbs | 11.178 | 1.0 | 877.5 |
| Posts | 0.324 | 1.0 | 25.4 |
| **Total** | | | **2,060.7** |

**Answer: concrete in RCC members = 17.402 m³; reinforcement = 2,060.7 kg (2.061 tonne).**

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What length of decking is used in the quantities?
   A. 6.00 m (clear span only)
   B. 6.45 m (one bearing)
   C. 6.00 + 2 x 0.45 = 6.90 m (clear span plus bearing at both ends)
   D. 7.70 m (overall width)
   Answer: C. Decking rests on bearings at both ends so length is 6.90 m. (Key point: Decking length)

2. How is the slab volume found?
   A. 7.00 x 6.90 x 0.20 = 9.66 m3
   B. 7.70 x 6.00 x 0.20 = 9.24 m3
   C. 7.70 x 6.90 x 0.10 = 5.31 m3
   D. 7.70 x 6.90 x 0.20 = 10.626 m3
   Answer: D. Slab spans full overall width 7.70 m and decking length 6.90 m. (Key point: Slab volume)

3. How is the volume of the three ribs found?
   A. 3 x 0.35 x 0.75 x 6.90 = 5.434 m3
   B. 3 x 0.35 x 1.075 x 6.90
   C. 3 x 2.25 x 0.75 x 6.90
   D. 3 x 0.35 x 0.75 x 6.00
   Answer: A. Each rib is 0.35 m wide and projects 0.75 m below the slab. (Key point: Rib volume)

4. How is total reinforcement obtained?
   A. 17.402 x 2.5% x 7850 for all members
   B. Percentage of steel x concrete volume x 7850 for each member group: ribs/fillets 2.5%, slab/kerbs 1%, posts 1%, totalling 2,060.7 kg
   C. 17.402 x 1% x 7850 for all members
   D. Sum of concrete volumes in tonnes
   Answer: B. Different members have different steel percentages. (Key point: Total steel)

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