Maximum permissible shear stress in BIS 456-1978

Diagonal Compression Failure

- The maximum permissible shear stress given in BIS 456-1978 is based on diagonal compression failure.
- Diagonal compression failure occurs when the concrete in the compression zone of a beam fails in diagonal compression due to the inclined nature of the compressive stresses.
- This type of failure is more likely to occur in short and stocky beams where the depth is less than the span.
- The maximum permissible shear stress for diagonal compression failure is given by the expression τ_c = 0.16f_ck^0.5, where τ_c is the maximum permissible shear stress and f_ck is the characteristic compressive strength of concrete.

Factors affecting maximum permissible shear stress

- The maximum permissible shear stress depends on several factors such as the type of loading, the type of material, the geometry of the member, and the boundary conditions.
- In addition to diagonal compression failure, the maximum permissible shear stress can also be based on flexural tension failure, flexural compression failure, and diagonal tension failure depending on the type of loading and the geometry of the member.

Importance of maximum permissible shear stress

- The maximum permissible shear stress is an important parameter in the design of concrete structures as it ensures the safety and stability of the structure.
- If the shear stress exceeds the maximum permissible shear stress, it can lead to shear failure, which can result in the collapse of the structure.
- Therefore, it is important to ensure that the shear stress in concrete members is within the permissible limits specified by the design codes such as BIS 456-1978.