Identification of Cracks

Q1.a)

Observation:

• Concrete crush and exposed reinforcement at the lower part of the beam-column joint.
• No defect was noticed at the upper part of the beam-column joint.
• Cracks developed from bottom to top.

Comments:

• Flexural failure due to reversal stresses of an earthquake.
• During stress reversal, the top compression is managed by the slab flange, however, the bottom tension was not accommodated by the bottom reinforcement of the beam.
• Yielding occurs in the bottom rebar of the beam.

Repairing Availability:

• This defect is not repairable due to the yielding that occurred in the bottom reinforcement of the beam.

Q1.b)

Observation:

• Horizontal & vertical cracks were noticed along with beam-column edges.
• The beam is almost separated from the column at the joint.
• No severe crushes.

Comments:

• Pull-out failure due to insufficient development lengths of steel rebar at the beam-column Joint.
• The horizontal movement during an earthquake detached the beam from the column in the lack of development lengths.

Repairing Availability:

• This defect is not repairable due to the difficulty of inserting the development lengths.

Q1.c)

Observation:

• Cracks are noticed at the beam-column Joint.
• Beam Cracks developed through the full width.
• Longitudinal cracks are also noticed at the slab's soffit along with the beam direction.

Comments:

• Plastic hinge failure due to reversal stresses of an earthquake.
• The stress reversal cycles of tension & compression produced damage to the joint.
• The slab also couldn't accommodate the severe tension & compression that occurred by the reversal stresses.

Repairing Availability:

• This defect is repairable by strengthening the joint (e.g. by carbon fibers).

Q2.a)

Observation:

• Concrete damages were noticed at the upper part of a column.
• The column is an exterior column with no walls attached to its side face.
• No damages were noticed at the beam.

Comments:

• Plastic hinge failure at the upper part of the column due to an earthquake.
• Due to the absence of infill walls, the mass of the story became relatively lesser than other stories.
• A formation of a soft story has occurred & has led to a plastic henge at the top of the column.

Repairing Availability:

• This defect is repairable as there are no severe damages or spalls in the concrete.

Q2.b)

Observation:

• The concrete is completely broken diagonally.
• A lack of shear reinforcement is seen in terms of large spacing between column ties.

Comments:

• Concrete shear failure.
• Lack of shear reinforcement resulted in an overdue of shear stresses on concrete.

Repairing Availability:

• This defect is not repairable due to the severity of the damages.

Q2.c)

Observation:

• The column is completely damaged in its upper part.
• A mezzanine slab was noticed at the mid-height of the column that splits the height of the column into two parts.
• All wooden props made by locals are to be neglected.

Comments:

• Short Column failure at the top of the column.
• The mezzanine slab at the mid-height of the columns led to a short column formation.
• The short column attracted more shear force during the earthquake causing a shear overstrength at the upper part of the column.

Repairing Availability:

• This defect is not repairable due to the severity of the damages.

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