Identification of Cracks

Challenge 1 - Identification of Cracks

Q1, Q2 - What is the mode of failure or damage of the beams in the figure above? Are the damages repairable? Elaborate

Identification of Cracks:

Crack identification in structures by detecting changes in their dynamic behavior has been studied in the past, and various methods have been developed, enabling the calculation of crack location and depth along a beam. Most of these methods utilize the frequency changes caused by the crack.

Q1, Q2 - What is the mode of failure or damage of the beams in the figure above? Are the damages repairable? Elaborate

Qusetion 1:

a)

Observations:

• A concrete is crushed and the reinforcement is fully exposed
• Concrete spalled behind the reinforcement, which may be a sign of cracking
• The upper part of the beam is safe due to the advantage of plate flange
• The crack develops from the bottom up, which means that the yielding of the reinforcement occurs only at the bottom of the support

Answer:

• Its a form of flexural failure due to earthquake stress reversal
• During stress reversal, the upper part of the support is in compression and the lower part is in tension
• The top compression is controlled by the slab plate advantage. The bottom tension stress was not satisfied by the reinforcement provided
• Since the reinforcement got yielded, it cannot be repaired

b)

Observations:

• Cracks occur along the edge of the beam-column
• Cracks appear to have developed in the structure as it appears much wider
• The beam looks separate from the column at the joints
• The concrete is not heavily crushed.

Answer:

• It is a failure by pulling out the beam due to insufficient development of the length of the reinforcement in the joints
• During an earthquake, the horizontal movement of the structure makes this condition wors and separates the beam from the column
• Ensuring the anchorage length between two existing concretes is very difficult
• So it is not repairable

c)

Observations:

• Cracks are exactly at the joint of Column-Beam
• Cracks in Beam developed through its entire width. The cracks actually at the face of the beam. It has been developed on both sides
• Slab also developed more cracks along the beam width direction

Mode of failure:

• It's a Plastic hinge failure.
• The damage occured only in the joint zone first of all.
• Cyclic lateral loading & stress reversal at the joints led to the damage.
• Even the slab participated to its best to handle the tension (Slab is severely cracked means it has undergone tension with its flange condition), But unable to control the damage.
• The joint can be strengthened.

Question 2:

a)

Observations:-

• Concrete damaged at top of a column
• Concrete damaged all around the column face
• Beam are safe as shown
• The location of column looks at edge of the building
• No walls are built along the column means it is probably at ground floor, for parking car movement access

Mode of failure:

• It is 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 development of crush of concrete, it can either be repairable or non-repairable
• Based on the severity of column that is concrete spalling

b)

Observations:

• Concrete developed complete breakage diagonally
• Longitudinal reinforcement are intact
• Shear reinforcement spacing looks wider (which means probably lesser shear rebar provided)

Mode of failure:

• It's a pure shear failure
• Inadequate shear reinforcement compels concrete takes all the shear stresses

c)

Observations:

• Column failed completely
• Failure at top of column
• There are two slabs connected to the column, Probably one at mid height of the column
• The wooden piles might be a post failure support after column failed, providing temporary prop to avoid collapse of the entire structure

Mode of failure:

• It's a short column failure
• An additional slab or beam conneted to a column in mid-height leads to this effects
• This leads to failure especially if the connection is unintentional and not accounted in design
• The failure given in the picture is not at all repairable