Ultimate Guide to Shear Cracks in R.C.C Beams

Shear cracks in R.C.C beams are observed during its hardened stage. It is caused either high shear stress due to self-weight or structural loading or movement. 

Ultimate Guide to Shear Cracks in R.C.C Beams - Explained With Video
Ultimate Guide to Shear Cracks in R.C.C Beams - Explained With Video

Shear cracks are a also called as diagonal tension failure, which if crosses marginal values, will be dangerous than bending failure of beams.

Types of Shear Cracks in R.C.C Beams

There are two types of shear cracking or inclined cracking in concrete beams. They are:
  1. Web-Shear Cracking
  2. Flexure-Shear Cracking
Types of Shear Cracks in R.C.C Beams
Fig.2. Types of Shear Cracks in R.C.C Beams

Web-Shear Cracking: As shown in the figure-2, web shear cracking starts from the interior point of the member when the principal tensile stress on the beam exceeds the tensile strength of the concrete. 
These are observed near to the supports of the flexural member like beams, within the thin webs mainly near to the bar cutoff points or near inflection point. Especially when the beam is subjected to axial tension.

Flexure-Shear Cracking: The flexure-shear cracking is initiated due to flexural cracking. When flexural cracks or the cracks due to bending of the beams occur, the shear stresses in the area of concrete above the flexural crack is increased. This would show the combined effect of shear and tensile stress exceeded in the form of flexure-shear crack.

The flexural cracks precedes flexural-shear cracks. The formation of flexural shear cracks are not predictable.

Features of Shear Cracks in R.C.C Beams

1. It is observed as diagonal tension cracks that are a combined effect of flexure or bending of beams and the shear action in beams.

2. It is observed near to the supports and seen in single or in groups.

3. The width of the shear cracks is maximum near to the neutral axis or at the bottom of the beam, near to the supports (shear is maximum at support).
As shown in figure-3 below, the shear stress is maximum at the neutral axis, hence cracks are more seen there.
Fig.3. Shear Stress Diagram of R.C.C Beam

4. Shear cracks are generally inclined at 45 degrees with the horizontal

Causes of Shear Cracks in R.C.C Beams

1. The shear capacity of the beam element is inadequate.

2. Load coming over the structure is more than design load.

3. Inadequate amount of shear reinforcement.

How to Repair Shear or Diagonal Cracks in Beams?

An RC beam in shear can be repaired by several methods. This includes:
  1. Bolted Steel Plate System
  2. FRP Jacketing
  3. External Post Tensioning

How to Prevent Shear Cracks in R.C.C Beams?

  1. Shear cracks in concrete beams can be avoided by providing additional shear reinforcement near to the supports, where the shear is maximum.
  2. Shear stress is maximum at a distance of d/2 from the support ( d = effective depth of beam).

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