Collapse Mechanism in RCC members can be in the following category:
Bond Failure: Brittle
Shear Failure: Brittle
Flexural Failure
Brittle: if over-reinforced section (compression failure)
Ductile: if under-reinforced section (tension failure)
Hence, We need to ensure that bond failure does not take place. Shearfailure does not precede flexural yielding. Beam is under-reinforced. IS:13920 code has stipulated this condition. In Clause-6.2.2, it says- the maximum steel ratio on any face of a flexural member should not exceed row, max=0.025
Failure of RC Section : This may be in the following form:
Yielding of tension bars- this type of failure is having the following category-
Crushing of compression concrete this-type of failure is having the following category-
Tension failure more likely if:
Section ductility increases as-
Generally, columns are less ductile than beams.
Capacity Design Concept:
For instance, in a RC member:
Shear failure is brittle Flexural failure can be made ductile Element must yield in flexure and not fail in shear
Capacity Design of Frames:
We need to consider the following:
Materials in RC Members:
Concrete and steel have very different characteristics
Steel ductile: strain capacity: ~12% to 25%
Concrete brittle: strain capacity: ~0.35%
Confinement of concrete:
It considerably improves its strain capacity:
Main Steps:
To ensure ductility:
Storey collapse Mechanism:
Beam –Hinge Mechanism (Sway Mechanism):
Preferred mechanism
Ensure that beams yield before columns do
Strong Column –Weak Beam Design