Identification of Cracks

1.Ans

1a. AIM

To identify the mode of failure or damage of the beams in the given figure

OBSERVATIONS

• Concrete 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 slab.
• The crack develops from bottom to top means rebar yielding occurs in support bottom only.

Type, Reason, And Solution

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

Type:

• From the above image we can say that, this Crack is formed due to flexural failure in beams.

Reason:

• The cracks which are formed as a result of flexural stress is called as flexural crack.
• Damage is caused due to insufficient of reinforcement or concrete, The flexural strength, known as modulus of rupture, bend strength, or fracture strength is a material property, defined as the stress in a material just before it yields in a flexure test.
• The flexural strength represents the highest stress experienced within the material at its moment of rupture, it is measured in terms of stress.

Solution:

• These cracks can be controlled by providing proper tension reinforcement.
• This failures steel must be provided at top/bottom of beam.
• These damages are repairable, while repairing this we need to remove pipes, wires and turn off the water and power connection.
• It can be repaired by adding cement to the damaged part

1b. AIM

To identify the mode of failure or damage of the beam-column edge in the given figure

OBSERVATIONS

• 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.

Type, Reason, And Solution

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

Type:

• From the above image we can say that, this type of Cracks is formed due to high slump concrete, and also due to the mistakes done in the construction and honeycombing in concrete,

Reason:

• Beams and columns carry heavy load.

Solution:

• To avoid cracks in concrete, avoid using high slump concrete.
• Concrete of moderate slump (less than 5 inches) results in less cracking.
• High slump concrete con only be used it is controlled by concrete admixtures or designed such that segregation and bleeding of concrete is controlled.
• Concrete admixtures such as water reducers or super plasticizers can be used to increase slump while reducing addition of water content.
• Air entertained concrete can also be produced to increase stump especially when concrete is to be subjected to freeze and thaw cycles.
• The honeycombing occurs when the fine mortar fails to thoroughly fall and fill the gaps created by the coarse aggregate.
• As mentioned previously, poor concrete consolidation is usually the top cause of honeycombing, along with poor vibration, improper ratio of fine to coarse aggregate, dry concrete and construction conditions that are not up to standard

1c. AIM

To identify the mode of failure or damage of the column beam joint in the given figure

OBSERVATIONS

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

Type, Reason, And Solution

• It's a Plastic hinge failure
• The damage occurred 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.

Type:

• From the above image we can say that, this type of Crack is formed due to the beam-column joint failure.

Reason:

• In the strong column-weak beam design, beams are expected to form plastic hinges at their ends and develop flexural overstrength beyond the design strength.
• The high internal forces developed at plastic hinges Couse critical bond conditions in the longitudinal reinforcing bars passing through the joint and also impose high shear demand in the joint core, it occurred due to high shear forces during seismic activity.
• If it is not properly repaired excessive loss in strength, then structure will collapse.

2.Ans

2a. AIM

To identify the mode of failure or damage at top of a Column in the given figure

OBSERVATIONS

• Concrete damaged at top of a Column.
• Concrete damaged all around the Column face.
• Beams are safe.
• 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.

Type, Reason, And Solution

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

Type:

• From the above image we can say that this Crack is formed due to the flexural failure of a column or failure in column due to buckling

Reason:

• Columns have the most important role in all structural members of a building, Buckling is the sudden change in shape of a structural component under load.
• If a structure is subjected to gradually increase in load member may suddenly changes the shape

Solution:

• According to the base civil engineering concept, columns failure wants to be occurring after bears and the other components damages Performance of existing buildings in earthquakes indicates that the bears are less vulnerable to damage during earthquakes and their damage appears to be less critical to performance as compared with that of columns and column-beam joints.

2b. AIM

To identify the mode of failure or damage of the beams which is complete breakage in the given figure

OBSERVATIONS

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

Type, Reason, And Solution

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

Type:

• From the above image we can say that, this Crack is formed due to Shear failure in column

Reason:

• Lateral loads in a structure are carrying by vertical elements such as columns and shear walls.
• Size of columns is increased in direction of shear to increase shear capacity.
• High shear forces are attracted by shorter columns. These failures occur during earthquake at open ground floor level.

Solution:

• Lateral loads are generated by winds, earthquake loads, from retaining structures, etc.
• Shear links are provided to columns based on the shear forces excreted on them.
• Further, the size of the columns is increased in the direction of shear to increase the shear capacity.

2c. AIM

To identify the mode of failure or damage of the column in the given figure

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.

Type, Reason, And Solution

• It's a Short Column failure.
• An additional slab or a Beam connected to a Column in mid-height leads to this effect.
• 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.

Type:

• From the above image we can say that this Crack is formed due to the short column failure.

Reason:

• Failure of column usually occurs due to anyone of the following stresses developed in the column.
• Short column will fall only because of direct compressive stress developed in the column or we can also say that short column will usually fall due to direct compression or crushing.

Solution:

• In Short Columns, failure takes place due to yielding and we define this phenomenon as CRUSHING, Short Columns are classified based upon Slenderness Ratio which is the ratio of the effective length (Length between point of zero moments) and least lateral dimension of the column.