---
title: "Bent-up bars in shear strength"
subject: "Design of RCC Structure"
chapter: 5
key: "semester_7/design_of_rcc_structure:bent-up-bars-in-shear-strength"
source: https://www.bctengineer.com/q/semester_7/design_of_rcc_structure/bent-up-bars-in-shear-strength
site: BCT Engineering
---

# Bent-up bars in shear strength

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

- Asked in: 2065 Shrawan (old course), 4 marks
- Video: [Why the crank Bars are provided in Beam & Slab | Bent up Bars](https://www.youtube.com/watch?v=v5sBgQUotKQ) — Visual Civil
- 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/bent-up-bars-in-shear-strength
- Whole chapter: https://www.bctengineer.com/md/semester_7/design_of_rcc_structure/chapter-5

## Question

How do the bent-up bars contribute in shear strength of beam? Explain it.

## Short answer

Bent-up bars resist diagonal tension with a vertical component Vus = 0.87fy Asb sinα. They contribute to shear resistance but code limits them to at most 50% of total shear reinforcement; the rest is carried by stirrups.

## Answer

**Bent-up bars** are part of the main tension bars that are bent upwards at 45$^\circ$ (or 30$^\circ$ to 60$^\circ$) near the supports, where the bending moment is small but shear is large. They carry the diagonal tension across the inclined cracks, as well as serving as flexural steel at mid-span.

```text
   crack
     \       bent-up bar (alpha = 45 deg)
 ====o\=====o=====
        \        \
         \_______/ stirrup
```

**Contribution to shear**

The tension $T = 0.87f_yA_{sb}$ in a bar inclined at angle $\alpha$ to the beam axis has a vertical component:

$$
V_{us}=0.87f_yA_{sb}\sin\alpha
$$

Here $A_{sb}$ is the total area of the bent-up bars in one plane. For $\alpha=45^\circ$, $V_{us}=0.615f_yA_{sb}$.

**Code provisions (IS 456 cl. 40.4)**

- Bent-up bars should not carry more than **50%** of the total shear to be resisted by shear reinforcement; the rest is carried by vertical stirrups.
- For a single bar or a single group of parallel bars all bent at the same cross-section, $V_{us}$ is as above; for a series of bars bent at different sections, spacing is also considered.
- Bent-up bars must be properly anchored and bent at gradual radius; bends are placed where they are no longer needed for flexure.

**Total shear resistance:** $V_u=V_c+V_{us}(\text{stirrups})+V_{us}(\text{bent-up})$, with $V_c=\tau_cbd$.

## Check yourself

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

1. Where are bent-up bars usually bent up in a beam?
   A. Near the supports, where bending moment is small but shear is large
   B. At mid-span, where bending moment is maximum
   C. At the top of the beam only at mid-span
   D. Anywhere, since position does not matter
   Answer: A. Bars are bent up near supports where they are no longer needed for flexure but can cross diagonal shear cracks. (Key point: Where bars are bent up)

2. What is the shear resistance of bent-up bars inclined at angle alpha?
   A. Vus = 0.87 fy Asb cos(alpha)
   B. Vus = 0.87 fy Asb sin(alpha)
   C. Vus = 0.87 fy Asb
   D. Vus = tau_c b d sin(alpha)
   Answer: B. Only the vertical component of the bar tension, 0.87fy Asb, resists shear, which gives the sin(alpha) factor. (Key point: Shear contribution formula)

3. What is the IS 456 limit on shear carried by bent-up bars?
   A. Not more than 25% of the total design shear
   B. They may carry 100% of the shear if well anchored
   C. Not more than 50% of the total shear to be resisted by shear reinforcement
   D. At least 50% of the shear reinforcement shear
   Answer: C. Cl. 40.4 caps bent-up bars at half of the shear reinforcement; vertical stirrups carry the rest. (Key point: 50% rule)

## Related in Design of RCC Structure

- [Bent-up bars shear, 550 mm effective depth](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Abent-up-bars-shear-550-mm) — Design of RCC Structure, chapter 5, asked 3×
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- [Shear design for 230x450 beam, 5 m span](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Ashear-design-for-230x450-beam-5) — Design of RCC Structure, chapter 5

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