Permissible Shear stress as per is: 456
As per the Indian Standard IS 456:2000, which deals with the "Code of Practice for Plain and Reinforced Concrete," the permissible shear stress for reinforced concrete structures is specified based on the type of structural member and its intended use. Here are the general guidelines for permissible shear stress according to IS 456:
Shear Stress in Beams:
- For simply supported beams without shear reinforcement (stirrups), the permissible shear stress is typically limited to 0.25 times the characteristic compressive strength of concrete . This value may vary depending on factors such as the concrete grade and exposure conditions.
- For beams with shear reinforcement (stirrups), the shear strength of the member is enhanced due to the presence of stirrups. The design shear stress is calculated based on the principles of shear friction and diagonal tension, considering the contribution of both concrete and stirrups to resisting shear forces.
Shear Stress in Columns:
- The permissible shear stress in columns is generally not explicitly specified in IS 456. Instead, the design of columns for shear is typically based on the principles of axial compression and bending, with due consideration given to the capacity of the concrete and longitudinal reinforcement to resist shear forces.
Shear Stress in Slabs and Footings:
- Similar to columns, IS 456 does not provide specific limits for permissible shear stress in slabs and footings. Instead, the design of these structural elements for shear is based on empirical equations, analytical methods, and shear strength principles, considering factors such as load distribution, support conditions, and reinforcement detailing.
It's important to note that the permissible shear stress specified in IS 456 is based on empirical data, experimental studies, and engineering judgment and may be subject to revision in subsequent revisions of the code or based on specific project requirements and considerations. Engineers and designers should always refer to the latest version of the code and consult with structural experts to ensure compliance with relevant standards and guidelines.