Identification of Cracks

challenge 1:

Identification of Cracks

Question 1:

What is the mode of failure or damage of the beams in the figure above? Are the damages repairable? Elaborate

a)

answer:

Observation:

• In this picture we observe that, concrete get damaged/broken and reinforcement are visible at bottom of the beam.
• The concrete spoiled beyond the reinforcement that is indicates the segregation
• The top portion of the beam is not exposed due to covered from the slab projection so, it's look safe and no major issue/severe issue on top of the beam.
• Cracks developed in bottom and gradually increasing towards the top. The pressure on beam is more than its yielding point on the bottom supports but the reinforcement is still active at the supports top so there is no crack on top of the beam.

Conclusion:

• At the time of the earthquake, the stress on the beam is reversal, so this is a kind of the flexural failure.
• During the earthquake, beams get in tension zone and the structure feels in compression due to the stress reversal support at top.
• Bottom reinforcement is not sufficient to resist the tension in beam and the top reinforcement resist by the slab due to the concrete.
• The bottom reinforcement of the beam lost there elastic limit, so that its impossible to repair the bottom crack.

b)

answer:

Observation:

• In above picture, we observed the cracks developed in column-beam corners
• It look like much wider crack that have developed through the column-beam joint
• In this picture, the beam has separeated from the column.
• the picture shows, the concrete has not crushed , thre is only crack developes.

Conclusion:

• The reinforcement of the beam is not sufficient to anchor the vertical rebars of the column, that is insufficient development length of the rebar.
• Due to inadequate reinforcement, beam not bonded to the column that's why the horizontal members gets attatched from the vertical member during the earthquake.
• The lateral movement cannot be satisfied due to the insufficient anchorage length of beam rebar so it kepps on separeated frrom the column.
• It is very tough to provide the development length in the casted concrete between two members, so it is not repairable.

c)

answer:

Observation:

• In this picture, we obsereve that cracks generated in column-beam junction
• The cracks occured in the entire width of the beam.
• Some cracks have developed in the slab along the direction of beam

Conclusion:

• This is an plastic hinge failure, the deformation in beam means no capability to resist the moment and its permitt to free rotation.
• The plastic hinge failure is happened at the joint only, so the damage occur in the junction.
• The main reason of damage are cyclic lateral bloading and stress reversal at the junction.
• Asper the image, the slab has tried for handle the tension, but still it get craced, so it clear that the tension is more on the slab and slab is unable to control the damage.
• To recover from the damage, we can strengthen the column-beam junction.

Question 2:

a)

answer:

Observation:

• In this picture, we observed that, the column has damaged from the top, bottom of the column is safe.
• The damage is all around the face of column
• No damage found in the neam.
• No connected walls along with column, so this could be ground floor, probably parking area.
• It is the most outer ar the external column of the building.

Conclusion:

• From these observations its clear, this is a soft storey failure, technically plastic hinge formation at column.
• Due to the lateral movement in the building and obsence of walls, columns got affected because of the plastic hinge formed at the upper side of the ground floor.
• Based on spall out the concrete from column and the severity of column is to be decide either repairabe or non-repairable.

b)

answer:

Observation:

• The breakage of concrete has diagonally developed in column. so this is not a crack it's a completely crushed and concrete detached from the column.
• Lateral and longitudinal reinforcements are visible. Rebar has not damaged and not separated.
• The clear vision of lateral reinforcement, i.e., shear links spacing is more than as per codel requirements which means that they have provided lesser shear reinforcemnt.

Conclusion:

• By observing the picture we can conclude this is a pure shear failure because the crack is in diagonal direction and the complete concrete had spoiled and get crushed.
• The shear reinforcements were not sufficent so it had detached and spolilled throughout the column, it had compelled concrete to breakdown into the pieces.

c)

answer:

Observation:

• From the given picture, we can observed that, the column is completely fail.
• Damage happens at top of the column and bottom of the column is safe.
• As per picture. there are two slabs connected with the column and the space between both slab is not the floor height so this is probably for the mechanical equipment.
• The beam has temporary supported with the wooden piles after the column failure to avoid the collapse of the structure.

Conclusion:

• From the observation we can conclude that the failure is short column failure.
• The column is attached with intermediate slab and the height of column is not similar than the other columns, so there is the heavy shear load on the column.
• The intermediate slab load is unintentional and not accounted in the design so this leads to the failure.
• This failure is not repairable.