Identification of Cracks

1.

a) Observations:

• The concrete is crushed and the reinforcement of the beam is exposed.
• There are signs of rupture with the concrete in the beam spalled beyond the reinforcement.
• There are no severe or visible damages to the top of the beam due to flange advantage from the slab.
• The rebar yielding occurs in the support bottom only as the crack is developing from bottom to top.

Answer:

• The mode of failure in the picture is a form of flexural failure.
• It is caused by the Stress reversal that occurs during earthquakes.
• Stress reversal is when the top of the beam experiences compression and bottom experiences tension
• The compression that occured in the top is managed by slab advantage, while the bottom reinforcement could not withstand the stress and yielded.
• Therefore it cannot be repaired.

b) Observations:

• Cracks have occered along the lines of the column and beam edges.
• Concrete is not crushed severely.
• At the joints the beam is seperated from the columns.
• The cracks may have developed throughout the whole length of beams and columns as they look wide.

Answer:

• The mode of failure in the picture is Beam pull out failure.
• It is caused due to insufficient development length of the reinforcement in the Beam-column joints.
• The horizontal movement of the structure that occurs during earthquake leads to the detachment of the beam from the column.
• It is not repairable because providing anchorage length between two existing concrete members is difficult.

c) Observations:

• There are cracks along the entire width of the beam.
• There are cracks on the joints of the column- beam.
• There are cracks on the slab in the direction of the beam.

Answer:

• The mode of failure in the picture is Plastic hinge failure.
• Cyclic lateral loading and stress reversal at the joints led to the damage.
• The damage has occured in the joint zone and then spread to the slab which also cracked when it couldnt withstand the tension.
• The damage is not critical and can be repaired by strengthening the joint.

2.

a) Observations:

• Concrete is damaged at the top of the column and around the face.
• There is no damage to the beams.
• There is no wall joining the sturctural members therefore the members maybe in the groundfloor .
• The column appears to be located in the edge of the structure.

Answer:

• The mode of failure in the picture is Soft storey failure.
• Plastic hinges are formed in the top of the columns during Lateral movement in the ground storey.
• It can be repaired or not based on the development of the damage of the concrete.

b) Observations:

• Longitudnal reinforcements of the beams are intact and visible while the concrete is completely damaged on the face of the column.
• Insufficient shear reinforcement is provided.

Answer:

• The mode of failure in the picture is Pure shear failure.
• The insufficient shear reinforcement compelled in the concrete taking all the shear stress and resulted in the damage.

c) Observations:

• Column has failed completely and is seperated from the column above.
• The failure is at the top of the column.
• There are two slabs connected to it, one at midheight .
• Wooden piles are provided for support of the beam after the failure to avoid failure.

Answer:

• The mode of failure in the picture is Short column failure.
• This maybe caused by the adiitional slab connected to the column at its middle.
• This leads to failure if the connection is not accounted in the design.
• It is not repairable.