Identification of Cracks

NOTE : WORD FILE CONTAINING ANSWERS AND ASSOCIATED PICTURES IS ALSO ATTACHED FOR PERSUAL AND REFERENCE

Q-1 What is the mode of failure or damage of the beams in the given figure. Are damages repairable ? Elaborate

1(a)

Answer :

Aim & Introduction : Mode of failure or damages shown in the given figures are required to be identified and need to explain whether damages are repairable.

Observations from the given picture :

• Concrete crushed and Reinforcement is exposed
• Concrete spalled beyond the reinforcement which may be the sign of rupture
• Beam top portion looks safe because of flange advantage from the slab.
• Crack developed from the bottom to the top implies that rebar yielding occurred in support bottom only.

Ans :

• Its from flexural failure due to reversal of stress during earthquake.
• During stress reversal, Support top experiences compression Bottom experiences tension.
• Top compression is managed by slab advantage. Bottom tension was not satisfied by the provided reinforcement.
• Since the reinforcement got yielded, it can not be repaired.

1 (b) Observation:

• Cracks are observed along the edge beam and columns
• Cracks seems to have developed through the structure as it looks much wider.
• Beam has been separated from the column at joints
• Concrete is not severely crushed

Ans :

• Beam pull out failure took place due to insufficient development length of reinforcement in joints
  
• During the earthquake due to the horizontal forces the beam got separated from the column
• In such failure it is very difficult to provide sufficient anchorage length in existing concrete, so it is not repairable

1(c) Observation :

• Cracks are exactly at the joints of the column-Beam
• Cracks are observed along the entire width of the Beam.
• Cracks are also developed along the width direction

Ans :

• Its a plastic hinge failure
• Cyclic lateral loading & stress reversal at the joints led to the damage
• Even slab participated to its best to handle the Tension still slab is severely cracked which means it has undergone tension with its flange condition, so unable to control the damage.
• Joint can be strengthened.

Q-2

Ans :

1(c) Observation :

• Concrete damaged at the top of the column.
• Concrete damaged all around the column face
• Beam is safe, no damage observed.
• Column appears to be located at the corner of the building.
• From the picture it is clear the column is of ground floor as no wall connecting to the column have been observed, area may be for access of car parking.
• 
  

Ans :

• Its a soft storey failure, technically plastic hinge formation
• Due to absence of infill walls at the ground floor, the plastic hinge forms at the top of ground storey columns during lateral movement
• .Based on the extent of damage that took place , it can either be repairable or non repairable.

2 (b)

Observation :

• Concrete developed complete breakage. diagonally.
• Longitudinal reinforcement are intact i.e. no damage to the reinforcement.
• From the picture , it seems that shear reinforcement are provided at larger spacing which means less shear reinforcement was provided.
• In existing concrete it is not possible to provide further shear reinforcement.

Ans :

• Its pure shear failure
• Due to inadequate shear reinforcement , the concrete has been compelled to take up entire shear stress resulting in to the damage to the concrete
• Even slab participated to its best to handle the Tension still slab is severely cracked which means it has undergone tension with its flange condition, so unable to control the damage.
• Joint can be strengthened.

2(c)

Observation :

• Column failed completely.
• There are two slabs connected to the column, probably one at mid height of the column.
• The wooden piles have been temporarily provided to prop the beam to avoid the collapse the entire structure as column has got separated from the beam and as such there is no connection between beam and column.

Ans :

• Its a short column failure
• Due to intermediate beam or slab , column is subjected to heavy shear force. This leads to a failure especially if the connection is unintentional and not accounted in design.
• Failure is not repairable.