Identification of Cracks
1) Objective: The main objective of this question is to identify the mode of failure or damage of the beams in the above figures and explain the reason of failure and whether the damages are repairable or not.
Ans: Fig 1a: Observation:
a) Concrete has been crushed and reinforcement has been exposed.
b) The damage can be seen that it has occured just before the beam column junction.
c) The damage is bottom portion of beam means rebar yielding in bottom portion only.
d) It is a sign of rupture.
Suggested Ans:
a) Since reinforcement got yielding so it cannot be repaired.
b) During the reversal stress forces that acted on the beam the top portion experienced compression and bottom portion experienced tension.
c) It is form of flexural failure due to reversal of stresses in earthquake.
Ans: Fig 1b: Obs:ervation:
a) Cracks are seen along the beam column edge.
b) Beams looks seperated from the column at joints.
c) Here the concrete is not crushed only cracks have occured.
Suggested Ans:
a) Its is beam pull out failure due to insufficient anchorage and development length.
b) Providing anchorage length between two column face is very duffucult and hence not repairable.
c) Horizontal movement due to earthquake is responsible for this cracks and detachment.
Ans: Fig 1C: Observation:
a) Cracks are at the joint of the columns.
b) Cracks in the beam are developed along the entire width of the beam.
c) Slab bottom has also developed cracks along with the beams.
d) There is visible bukling of reinforcement.
Suggested ans:
a) It is a plastic hinge failure since the damage occured only at the joint zone first.
b)Cyclic lateral loading along with stress reversal has occured.
c) Slab has also developed cracks under tension but couldnot control the damage.
d) Here the joint can be strengthened as only surface cravcks have devoloped and it is repairable.
2) The main obejective of this question is to identify the mode of failure or damage in the given figures and explain the reason of failure and state whether it is repairable or not.
Ans. Fig 2a: Observations:
a) Concrete damage is at the top of column and all around the face of the column.
b) Beams seems to have no damage and looks safe.
c) Location of the column looks at the edge of the building.
d) There also no walls under the beam seems to be a ground floor, parking space or movement access.
Suggested Ans:
a) It is a failure due plastic hinge formation.
b) Due to the absence of the infill walls the plastic hinge occured at the top of ground due to the lateral force distribution.
c) Based on the observation it can either be repairable or non-repairable.
Ans: Fig 2b) Observation:
a) It has a complete breakage of concrete, reinforcemrent is entirely visible.
b) Longitudinal reinforcement is visible and seems intact.
c) Shear reinforcement / stirrups looks wider in spacing.
Suggested ans:
a) It is shear failure.
b) Inadequate shear reinforcement could not take all the shear stresses thus leads to shear failure.
Ans: Fig 2c) Observation:
a) Column is completely failed and it is mostly at the top of the column.
b) There is two slabs connected with column one at the top and other at the mid.
c) Wooden columns are provided post column failure to temporary avoid the collapse of the entire structure.
Suggested ans:
a) It is a short column failure.
b) Additional slab connected to column at mid position lead to this failure.
c) May be the connection is not accounted in the design and the failure is not at all repairable.