ECET 2026 Civil Engineering – Bond, Shear & Torsion in RCC

Concept Notes (Deep Explanation + Examples)

🔹 Introduction

In Reinforced Cement Concrete (RCC), the steel and concrete must work together as one unit.
For this composite action to occur effectively, bond, shear, and torsion play key roles.
These three factors ensure that loads transfer safely between steel and concrete — keeping beams, slabs, and columns strong and durable.

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🔹 1️⃣ Bond in RCC

Bond is the adhesion between concrete and steel reinforcement.
It ensures that no slip occurs when the member is under load.

There are three types of bond:

1. Adhesion bond → Due to chemical adhesion between cement paste and steel.
2. Friction bond → Caused by surface roughness of the bar.
3. Mechanical bond → Provided by ribs or deformations in HYSD (TMT) bars.

Example:
In a beam, when load acts downward, tension develops at the bottom.
Bond ensures the tensile force in steel is safely transferred to the surrounding concrete.

If bond fails → steel slips → cracks appear → structure becomes unsafe.

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🔹 2️⃣ Development Length ()

To fully develop the strength of the reinforcement, it must be anchored for a certain minimum length — called the development length.

Formula:

Where:

• = diameter of the bar (mm)
• = stress in bar at section considered (N/mm²)
• = design bond stress (N/mm²) from IS 456:2000 (Table 26)

Example:
For a 16 mm HYSD bar in tension,


Hence,

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🔹 3️⃣ Shear in RCC

Shear is the internal force that tries to slide one layer of concrete over another.

In beams, maximum shear acts near supports.
Concrete is weak in shear, so stirrups are provided to resist it.

Shear force diagram (SFD) shape → triangular, max at support.
Cracks due to shear are inclined (diagonal tension cracks).

Design Shear Strength:

If → Safe
If → Provide shear reinforcement

Shear reinforcement (vertical or inclined stirrups):

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🔹 4️⃣ Torsion in RCC

Torsion = twisting moment acting on a beam or member.

Occurs when a beam is eccentrically loaded, such as in L-shaped staircases, beams at corners, or spandrel beams supporting projections.

Concrete alone cannot resist torsion → so both longitudinal and transverse reinforcement are provided.

Equivalent Bending Moment & Shear (as per IS 456:2000):

• Equivalent bending moment:
  
  where
• Equivalent shear:

,
breadth , depth
then

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🔹 5️⃣ Field Example

At a construction site:

• When checking beam-column junctions, ensure that bars are properly bent and anchored → this provides sufficient bond.
• Shear stirrups must be closely spaced near supports.
• In L-shaped staircases or edge beams, torsion reinforcement (extra closed stirrups + top and bottom bars) must be tied properly.

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🔹 6️⃣ ECET-Important Points

• IS 456:2000 gives design bond stresses for plain and deformed bars.
• HYSD bars give higher bond stress → smaller .
• Shear cracks → 45° inclination.
• Torsion causes diagonal + longitudinal cracks.
• For beams with torsion → both top and bottom bars are designed.

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🔹 7️⃣ Summary

• Bond ensures load transfer between steel and concrete.
• Shear prevents sliding between concrete layers.
• Torsion prevents twisting failure in special members.
  Together, they form the strength triangle of RCC design!

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⚙️ Formulas (Plain LaTeX Only)

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🔟 10 MCQs (GATE + ECET Mix)

1. Development length in tension depends on
   A) Bar diameter only
   B) Bar diameter and bond stress
   C) Concrete strength only
   D) None
2. The value of for HYSD bars in tension as per IS 456:2000 is approximately
   A) 1.2 N/mm²
   B) 1.6 N/mm²
   C) 1.92 N/mm²
   D) 2.5 N/mm²
3. Diagonal tension cracks in RCC beams occur due to
   A) Bending
   B) Shear
   C) Bond
   D) Torsion
4. Shear strength of concrete depends mainly on
   A) Tensile strength of concrete
   B) Compressive strength of concrete
   C) Flexural strength
   D) Modulus of elasticity
5. Torsion reinforcement is generally provided in
   A) Cantilever slabs
   B) Columns
   C) Edge beams and spandrel beams
   D) Simply supported beams
6. If bond stress is increased, development length
   A) Increases
   B) Decreases
   C) Remains constant
   D) Doubles
7. The function of stirrups in RCC beam is to resist
   A) Bending moment
   B) Torsion
   C) Shear and diagonal tension
   D) Longitudinal stress
8. In RCC, the bond between concrete and steel is due to
   A) Friction only
   B) Adhesion and friction
   C) Mechanical anchorage
   D) All of the above
9. Equivalent bending moment in torsion is given by
   A)
   B)
   C)
   D)
10. The shear stress in RCC beam is given by
    A)
    B)
    C)
    D)

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✅ Answer Key

Q.No Answer
1 B
2 C
3 B
4 B
5 C
6 B
7 C
8 D
9 B
10 C

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🧠 Explanations (Step-by-Step)

1️⃣ Bond stress relates both to bar diameter and bond strength → B
2️⃣ For HYSD bars, IS 456 gives → C
3️⃣ Shear causes diagonal tension cracks → B
4️⃣ Shear strength = 0.17√fck → depends on compressive strength → B
5️⃣ Torsion acts on edge beams, spandrels → C
6️⃣ ; higher τbd → lower Ld → B
7️⃣ Stirrups resist shear + diagonal tension → C
8️⃣ Bond is a combination of adhesion, friction, mechanical interlock → D
9️⃣ IS 456 gives → B
10️⃣ → C

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🎯 Motivation / Why Practice Matters (ECET 2026 Civil)

“Bond, shear, and torsion” are repeated every year in ECET and GATE Civil because they represent the true strength of RCC design.
Understanding these concepts means you can design beams, slabs, and columns confidently.
Keep practicing numerical problems — they improve your speed and accuracy.
Remember: Civil engineering becomes easy when your basics are rock-solid!
Stay consistent — your hard work will definitely reflect in ECET 2026 results.

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📲 CTA

Join our ECET 2026 Civil WhatsApp Group for daily quizzes & study notes:
👉 https://chat.whatsapp.com/GniYuv3CYVDKjPWEN086X9

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