Identification of Cracks

1)

a)

Aim - Identification of Modes of Failures

Introduction -

i) Generally RC beams fails in Shear failure or in Flexure .

ii) The Shear failure occurs when the imposed load exceeds the flexural capacity of the beam's materials,

iii) The Flexure failure occurs due to insufficient bond between concrete and reinforcement .

i) This crack will be formed due to the flexural failure of a beam.

ii) The flexural failure beam occurs when beam is over reinforced beam ( Mulimit is geater the Design Moment )

iii) The insufficient the cover is provided in the beam .

Explanation

i) The damages are repairable, To repair damaged beams, locate a local welder or metal shop and request angle iron, cut and drilled to the

length of the beam being repaired.

ii) Be sure to turn off the water, power, etc. before doing so. Pry the joist hanger away from the beam.Mount the angle iron on the jack and the

temporary post.

iii) Get the angle iron in place and slowly raise the jack until the angle iron is wedged up against the damaged beam . Screw the angle iron into the

beam and remove the temporary post .

b)

i) This cracks are formed due to lack of mistakes done at the construction and honeycombing in concrete.

ii) This type of cracks are developed due to used of High Slump concrete

iii) If there is an improper vibration during the concreting of column .

iv) Consolidation of concrete is also as reason of Honeycombing .

Explanation

i) To avoid cracks in concrete, avoid using high slump concrete and use adequate vibration technique .

ii) Concrete of moderate slump results in less cracking.

iii) High slump concrete can only be used if it is controlled by concrete admixtures or designed such that segregation and bleeding of concrete

is controlled.

iv) The honeycombing occurs when the fine mortar fails to thoroughly fall and fill the gaps created by the coarse aggregate.

v) This cracks can be repaired by grounting method

c)

i) This cracks are formed due to the beam-column joint failure.

ii) In the strong column-weak beam design, beams are expected to form plastic hinges at undesirable locations and develop flexural strength

beyond the design strength.

Explanation -

i) It has high chances of failure in strength and structure may collapse .

ii) The high internal forces developed at plastic hinges cause critical bond conditions in the longitudinal reinforcing bars passing through the joint

and also impose high shear demand in the joint core.

iii) The bond performance of the bars anchored in a joint affects the shear resisting mechanism to a significant extent.

Q.2)

a)

i) This crack will be formed due to the flexural failure of a column .

ii) This is due to the Buckling of columns .

Explanation

i) Due to high compressive load acting on the column, the column will fail without undergoing any lateral deformation.

ii) Column failure generally occurs when axially loaded stresses exceeds the allowable stress .

ii The concrete gets crushed and the steel will yield and then column failure occurs .

b)

i) This crack will be formed due to the shear failure of a column.

ii) Shear failure occurs when the shear resistance is less than the flexural strength

iii) Spacing between the Links should be minimum .

Explanation -

i) When there are no shear walls, columns carry these lateral loads.

ii) Lateral loads are generated by winds, earthquake loads, from retaining structures, etc.

iii) Shear links are provided to columns based on the shear forces excreted on them.

iv) The size of the columns is increased in the direction of shear to increase the shear capacity.

v) Jacketing technique can be used to repaired this

c)

i) This cracks are formed due to the Short column failure.

ii) In Short Columns, failure takes place due to yielding and causes crushinng .

Explanation -

i) Short Columns are classified based upon Slenderness Ratio ( Leff / B) < 12

ii) Short column will fail only because of direct compressive stress developed in the column or we can also say that short column will usually fail

due to direct compression or crushing.

iii) It can be rectified by using Retrofitting technique