Question

What are the types of reinforcements used to resist shear? Explain the action of different types of shear steel in resisting shear.

Answer 1

Types of shear reinforcement : Vertical stirrups, Bent up bars along with stirrups, Inclined stirrups, contribution of bent up bars

TYPES OF SHEAR REINFORCEMENT

The following three types of shear reinforcement are used :

   Vertical stirrups.

   Bent up bars along with stirrups.

   Inclined stirrups.

Vertical Stirrups

These are the steel bars vertically placed around the tensile reinforcement at suitable spacing along the length of the beam. Their diameter varies from 6 mm to 16 mm. The free ends of the stirrups are anchored in the compression zone of the beam to the anchor bars (hanger bar) or the compressive reinforcement. Depending upon the magnitude of the shear force to be resisted the vertical stirrups may be one legged, two legged, four legged and so on as shown in

Vertical Stirrups

Vertical Stirrups

It is desirable to use closely spaced stirrups for better prevention of the diagonal cracks. The spacing of stirrups near the supports is less as compared to spacing near the mid-span since shear force is maximum at the supports.

Bent up Bars along with Vertical Stirrups

Some of the longitudinal bars in a beam can be bent up near the supports where they are not required to resist bending moment (Bending Moment is very less near the supports). These bent up bars resist diagonal tension. Equal number of bars are to be bent on both sides to maintain symmetry. The bars can be bent up at more than one point uniformly along the length of the beam. These bars are usually bent at 45º as shown in Fig. 5.6.

Bent up Bars along with Vertical Stirrups

Bent up Bars along with Vertical Stirrups

This system is used for heavier shear forces. The total shear resistance of the beam is calculated by adding the contribution of bent up bars and vertical stirrups. The contribution of bent up bars is not greater than half of the total shear reinforcement.

Inclined Stirrups

Inclined stirrups are also provided generally at 45º for resisting diagonal tension. They are provided throughout the length of the beam.

Inclined Stirrups

Answer 2

The types of reinforcements used to resist shear are vertical stirrups, inclined stirrups and bent up bars along with stirrups.

Explanation:

Shear reinforcements:

• The reinforcements used to resist shear are called shear reinforcements.
• They are capable to withstand diagonal stress or shear.
• The different types of shear reinforcements are:

   Vertical stirrups:

• Vertical stirrups are steel bars placed horizontally at sufficient spacing around the tensile reinforcement along the beam’s length.
• The diameter of these bars lies between 6 mm and 16 mm.
• There are various types of vertical stirrups such as single-legged stirrups, two-legged stirrups, four-legged stirrups and six-legged stirrups.

   Inclined stirrups:

• Inclined stirrups are placed at right angles to the diagonal tension cracks.
• They are used for resisting diagonal stress applied at $\[45^\circ \]$.
• The availability of these stirrups is made throughout the beam’s duration.

   Bent up bars along with stirrups:

• These bars are bent evenly around the length or at more than one level.
• They are resistant to diagonal stress.
• They are bent at $\[45^\circ \]$.

Action of shear steel in resisting shear:

• It is observed that bend-up steel bars are good in restricting crack width.
• The dowel action is maintained by the longitudinal tension-steel with the help of stirrups.
• Vertical stirrups are considered to be superior to inclined bars. However, the use of unwanted tension bars for resisting shear can be more economical.
• The combination of bend-up bars and stirrups is a more economical and technically effective solution.
• In such a combination, both the restriction of crack and dowel action to resist shear are present.

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