Definition of shear reinforcement and it’s type
Shear Reinforcement means reinforcement that is designed to withstand shear or diagonal tension stresses. Shear reinforcement is generally arranged in the form of stirrups to retain the longitudinal reinforcement as well as capture the shear to which the structure is exposed to.
TYPES OF SHEAR REINFORCEMENT - Described below, common types of shear reinforcement:
1. Vertical stirrups.
2. Bent up bars along with stirrups.
3. Inclined stirrups.
Vertical Stirrups: These belong to the steel bars arranged vertically around the tensile reinforcement at proper distance along the length of the beam. Their diameter differs from 6 mm to 16 mm.
The free ends of the stirrups are fastened in the compression zone of the beam to the anchor bars (hanger bar) or the compressive reinforcement. Based on the magnitude of the shear force to be defended the vertical stirrups may come as one legged, two legged, four legged and so on.
It is recommended to utilize narrowly spanned stirrups to get rid of the diagonal cracks in a better manner. The distance of stirrups adjacent to the supports is less relating to the distance close to the mid-span as shear force remains extreme at the supports.
Bent up Bars along with Vertical Stirrups: Some of the longitudinal bars in a beam are bent up adjacent to the supports where it is unnecessary to use them for withstanding bending moment as bending moment remains very less adjacent to the supports. These bent up bars defend against diagonal tension. Equal numbers of bars should be bent on both sides to maintain consistency. The bars are bent up at more than one point evenly along the length of the beam.
These bars are normally bent at 45º.
This system is very effective for higher shear forces. The total shear resistance of the beam is measured with the inclusion of the bent up bars and vertical stirrups.
The provision of bent up bars should not be in excess of half of the total shear reinforcement.
Inclined Stirrups: Normally, inclined stirrups are arranged at 45º for countering diagonal tension. They are arranged all through the length of the beam.