Identification of Cracks

IDENTIFICATION OF CRACK

AIM -

TO STUDY THE IDENTIFICATION OF CRACK

INTRODUCTION -

Crack is damage that often occurs in members of structures. It is the separation of an object or material into two, or more, pieces under the action of stress. Cracks in any structural systems are very common due to various effects concerning time, due to natural calamities (such as earthquakes, cyclones; etc.), construction defects, Shrinkage of concrete, chemical reactions in concrete, etc.

Generally, structures are not collapsed on the initial growth of cracks. A crack must be detected in the early stage, as it may cause the serious failure of the structures in due course of time. However, it is difficult to recognize a crack by visual inspection techniques, when it is too fine. Hence nondestructive testing such as vibration technique is used for crack detection. It is essential to study the behavior of structures having cracks. If a structure is defective, there is a change in the stiffness and damping of the structure in the region of the defect. A crack on a structural member introduces local flexibility which is a function of the crack depth. This flexibility changes the dynamic behavior of the structure, and from this change, the crack position and magnitude can be identified.

OBJECTIVE -

• Awareness of Structural failures.
• Distinguishing Structural and Non-structural failures
• To know how to observe a structural issue
• Understanding Seismic failures

TASK 1: what is the mode of failure or damage of the beam? Would you categorize the case as damage or as a failure? Is the damage repairable? Elaborate

a)

OBSERVATION -

• Concrete is crushed and the reinforcement is exposed.
• Concrete spalled beyond the reinforcement which may be a sign of rupture.
• Beam top portion looks safe because of the flange advantage from a slab.
• the crack develops from bottom to top means rebar yielding occurs in the support bottom only.

EXPLANATION -

• Its form of Flexural failure due to the reversal of stress during an earthquake.
• During stress reversal, the Support top experience Compression, and the Bottom experience tension.
• Top compression is managed by slab advantage. Bottom tension was not satisfied by the provided reinforcement.
• Since the reinforcement got yielding, it can not be repaired.

b)

OBSERVATION -

• Cracks along Beam-Column edge.
• Cracks seem to have developed through the structure as it looks much wider.
• Beam looks separated from the column at joints.
• Concrete is not severely crushed.

EXPLANATION -

• Its Beam pull-out failure due to insufficient development length of reinforcement in Joints.
• During an earthquake, The horizontal movement of the structure makes this condition worse and detached the beam member from the column.
• Providing anchorage length between two existing concrete is very difficult. So not repairable.

c)

OBSERVATION -

• Cracks are exactly at the joint of the Column-Beam.
• Cracks in Beam developed through its entire width.
• Slabs also developed more cracks along the beam width direction.

EXPLANATION -

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

TASK 2: What is the mode of failure or damage of the beams in the figure above? Are the damages repairable? Elaborate

a)

OBSERVATION -

• Concrete damaged at top of a column
• Concrete damaged all around the column face.
• Beams are safe.
• The location of the column looks at the edge of the building.
• No walls are built along the column means it is probably on the Ground floor, for Parking Car movement access.

EXPLANATION -

• It's a Soft story failure, Technically Plastic hinge formation.
• Due to the absence of Infill walls on the Ground floor, The plastic hinge forms at the top of ground-storey columns during Lateral movement.
• Based on the development of crushed concrete, it can either be repairable or Non-repairable.

b)

OBSERVATION

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

EXPLANATION -

• It's a Pure Shear failure.
• Inadequate shear reinforcement compels concrete and takes all the shear stresses.

c)

OBSERVATION -

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

EXPLANATION -

• It's a Short column failure.
• An additional slab or a Beam connected to a column in mid-height lead to this effect.
• This leads to failure, especially if the connection is unintentional and not accounted for in the design.
• The failure given in the picture is not at all repairable.