REINFORCEMENT DETAILING IN BEAMS
Reinforcement are provided to resist tensile stresses due to bending and shear in beams for singly reinforced sections. But when depth of section is restricted due to reasons such as architectural reasons, or basement floors, the beam section is designed as doubly reinforced to resist tensile as well as compressive stresses and are provided with reinforcement in compression face.
Beams when subjected to torsion are provided additional longitudinal and shear reinforcement to resist bending and shear stresses developed due to torsion.
In practice, for singly reinforced beams, two additional bars are provided in compression face of the beam so that stirrups can be tied with bars. These additional reinforcement are of nominal diameter of 8mm or 10mm.
When the width of beam is insufficient for number of bars to be provided, keeping minimum clear distance bars based on maximum size of aggregate as per standard code guidelines, the reinforcement can be provided in layers in both tension and compression face of the beam. These reinforcement are provided as straight bars in both zones.
When a beam is designed with slab, called slab beam or Tee-beam, reinforcements are provided as shown in figure below. The beam is generally designed as simple beam but additional reinforcement are provided on top with slab to make it behave like a Tee-beam.
Fig: Mid-span Details of Tee-Beam.
Fig: Slab-Beam Details
Following are the types of stirrups provided in beams:
Fig: Types of stirrups in beams
Standard bends and hooks required for reinforcing bars are shown in figure below. The specification for detailing of reinforcement in beams are given in cl.26.5.1 of IS 456 – 2000.
Fig: Standard bends and hooks in beams
Curtailment of Reinforcement in Beams:
Reinforcements are curtailed along its length in beams depending on the bending moment at the section. Anchorage or development length required at support is provided during curtailment of reinforcement. The anchorage length required for main reinforcement in tension and compression is given in cl.26.2 of IS 456 – 2000.
Typical details of curtailment of reinforcement in cantilever and continuous beams are shown in figure below:
Fig: Typical Details of Reinforcement curtailment in beams
Details of anchorage length required for main reinforcement in tension and compression is shown below:
Fig: Typical Details of anchorage length of reinforcement in beams