Bonding Mechanism in RCC Structure

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Bonding Mechanism in RCC Structure

 In an RCC structure is considered safe when the relevant loads on the structure is under the permissible limits for that structure, the impact of load is sustained by the RCC main components like concrete & steel. The composite action of reinforced concrete is mainly due to the bonding or the adhesion between the reinforcement steel’s ribs provide better bonding with the surrounding concrete. This bonding between the reinforcement steel & concrete enables the transfer of axial force from the reinforcement steel to the surrounding concrete & the bond also ensures strain compatibility and composite action of the composite material (Reinforced Concrete). The assumption of plain section remains plain even after bending in the simple bending theory, is valid only when there is effective bond between the steel & surrounding concrete.

In steel reinforcement of an RCC member, the stress varies from point to point along its length mainly due to the bond resistance. If there is no bond, the stress in the steel member will be constant throughout its length as it is found in the case of straight cable used in prestressed concrete section.

Bond Mechanisms:

The Bond between the concrete & steel develops due to the following important factors:

  • Chemical Adhesion- It is the grip force generated due to the gum like properties of the hydration products of cement in a concrete. It provides initial adhesion properties within RCC structure.
  • Frictional Resistance- The resistance generated between the steel & surrounding concrete due to their relative movement is termed as frictional resistance. It depends upon the ribs present in the steel & the grip developed after shrinkage of concrete.
  • Shearing Resistance- It is the mechanical interlock developed due to surface protrusions or ribs provided in deformed bars.
Ribs in steel is an important factor in determining the bond resistance between steel & surrounding concrete, without which the interlocking effect cannot be achieved in an RCC structure. That is why plain bars cannot develop the bond resistance.

Bond Stresses:

A shear stress or tangential stress is developed along the contact surface of the steel & concrete in a RCC structure, which is generally termed as bond stress. Bond stress is expressed by tangential force per unit nominal surface area of the reinforcing bar. If the bond stresses are very high or beyond permissible limits then horizontal cracks develops at the reinforcement level of such locations.

Different types of bond stresses are mentioned below:

  • Flexure Bond Stress- Stresses that develop in an RCC member under flexure due to variation of bending moment or shear force at a section is termed as Flexure Bond Stress.
  • Anchorage (Development) bond stress- The stress developed at the end portion of a steel bar in an RCC structure under compression or tension is termed as Anchorage (Development) bond stress. Therefore, Development length is provided in reinforcements at the termination components.
Design Bond Stress in Limit state method for plain bars in Tension, Design Bond stress, Concrete, steel
Design Bond Stress in Limit state method for plain bars in Tension


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