---
title: "Design shear reinforcement of flanged beam"
subject: "Design of RCC Structure"
chapter: 5
key: "semester_7/design_of_rcc_structure:design-shear-reinforcement-of-flanged-beam"
source: https://www.bctengineer.com/q/semester_7/design_of_rcc_structure/design-shear-reinforcement-of-flanged-beam
site: BCT Engineering
---

# Design shear reinforcement of flanged beam

Design of RCC Structure · Chapter 5: Design for Shear and Torsion

- Asked in: 2074 Chaitra, 5 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/design_of_rcc_structure/design-shear-reinforcement-of-flanged-beam
- Whole chapter: https://www.bctengineer.com/md/semester_7/design_of_rcc_structure/chapter-5

## Question

Explain how you would design shear reinforcements for flanged beam sections.

## Short answer

For flanged beams, shear design uses the web width bw. Check τv = Vu/(bw d) ≤ τc,max. If τv ≤ τc, provide minimum stirrups; if greater, design steel for Vus = Vu − τc bw d with spacing sv = 0.87fy Asv d/Vus, limited to 0.75d and 300 mm. Closed stirrups extend into flange.

## Answer

In flanged beams (T- and L-beams), the web carries almost all the shear; the flange contributes little. IS 456 therefore uses the **web width $b_w$** in all shear calculations.

#### Procedure

1. **Factored shear force:** find $V_u$ at the support; the critical section is taken at $d$ from the face of the support (when the support reaction compresses the end region).
2. **Nominal shear stress:**
   $$
   \tau_v=\frac{V_u}{b_wd}
   $$
   Check $\tau_v\le\tau_{c,max}$ (Table 20); else enlarge the web.
3. **Percentage of steel:** $p_t=\dfrac{100A_{st}}{b_wd}$ (tension steel continuing to the support). Find design shear strength $\tau_c$ of concrete from Table 19.
4. **Decide reinforcement:**
   - If $\tau_v\le\tau_c$: provide minimum shear reinforcement, $\dfrac{A_{sv}}{b_ws_v}\ge\dfrac{0.4}{0.87f_y}$.
   - If $\tau_v>\tau_c$: design for $V_{us}=V_u-\tau_cb_wd$ and
   $$
   s_v=\frac{0.87f_yA_{sv}d}{V_{us}}
   $$
5. **Spacing limits:** $s_v\le0.75d$ and $\le300$ mm, and not more than $\dfrac{0.87f_yA_{sv}}{0.4b_w}$.
6. **Bent-up bars (optional):** $V_{us}=0.87f_yA_{sb}\sin\alpha$, at most half of the total shear reinforcement.
7. **Detailing:** stirrups are closed (two-legged vertical), carried into the flange top and anchored around the top bars. Vary spacing along the span: closer near supports, up to the maximum where $V_u\le\tau_cb_wd$.

```text
  bf
 +------------------+
 |       flange     |  Df
 +-----+      +-----+
       |  bw  |   <- shear area = bw x d
       |      |
       | o  o |   stirrups around bars
```

## Check yourself

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

1. Which width is used for shear stress?
   A. Web width bw
   B. Flange width bf
   C. Average
   D. Overall D
   Answer: A. The web carries nearly all shear. (Key point: Width used)

2. When only minimum stirrups?
   A. tau_v > tau_c
   B. tau_v <= tau_c
   C. tau_v > tau_c,max
   D. Never
   Answer: B. Provide Asv/(bw sv) >= 0.4/(0.87fy). (Key point: Reinforcement need)

3. Stirrup spacing from Vus is?
   A. sv = Vus/fy
   B. sv = 0.4bw
   C. sv = 0.87 fy Asv d / Vus
   D. sv = d
   Answer: C. Limited to 0.75d and 300 mm. (Key point: Spacing)

4. Bent-up bars may carry?
   A. All of it
   B. None
   C. Twice stirrups
   D. Not more than half of the total shear reinforcement
   Answer: D. Vus = 0.87fyAsb sin(alpha), limited to half. (Key point: Bent-up bars)

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