Identification of Cracks

AIM: To identify the mode of failure or damage of the beams in the figure above.

1a)

1. The mode of failure is due to flexural failurein beams. As we can seen that damaged is caused more to the beam than the column damage.
2. Damaage is caused due to the insufficient of reinforcement and also due to insufficient of vibration of concrete.
3.  The vertical crack at the face of the support across the full depth of the beam tends to remain open and increase in width for each cycle of deformation.
4. To over come this failure teel must provide at bot the face of the beam.

• The damage can be repairable and can be done b providing proper cover and reinforcenent at the joint.

1b)

1. The failure in the 1b fig is due to the insufficent bond strength and improper curing.
2. The beam cannot develop its full moment of resistance at the end sectionand the force resistance and stiffness of the frame it belongs to drop accordingly.
3. The loss of beam anchorage prevents a proper plastic hinge from froming at the end of beams.
4. This can be avoided by cavities inside the column that were not filled properly with construction ground reduce the compresssive area of the column as a result its axial capacity will be reduced.

• It can be repairable by providing proprer anchorage of beam bars.

1C)

1. The failure in the fig 1c i,e at beam column joint connection failure in the reinforced concrete frame.
2. In capacity design beams experience to plastic hinges at their ends and develop flexural overstrength beyond design strength.
3. The high internal forces developed at plastic hinges cause critical bond conditions in the longituidinal reinforcing bars passing through the joint and also imposes high shear resisting mechanism to a significant extent.
4. Such elements are usually subjected to very high shear force durig seismic activity and inadequately reinforced results in an excessive loss in strength and stiffness of the frame and even collapse.

Q2)

2a)

1. The failure is due to the flexural damage , columns may be damaged or fail in flexural as shoen in the fig.
2. Flexural damage are concentrated in horizontal bonds at the very top or bottom of a column in a storey.
3. Such region are the physical manifestation of flexural plastic hinge where plastic rotation takes place.
4. Flexural damage always includes a visible horizontal cracks and loss of concrete cover often accompained by bar buckling, opening of stirrups of partially disintegration of the concrete core inside the cage of the reinforcenent.

• The issue is resolved by providing adequate length for the longitudinal bars is to be ensured within the joint taking yield penetration into the consideration.

2b)

1. This kind of defect occurs due to shear failure of the columns.
2. Lateral loads are generated by wind and seismic in a structure and are carried by vertical elements such as columns and shear wall.
3. The shear links are provided to columns bases on the shear forces excreted on them. Futher the sizes of the columns is increased in the direction of shear to increase the shear capacity.
4. In general failure of columns due to shear can be identified as the failure of design. 

• So while designing we must provide adequate shear links or sections to carry shear force which induced in to the structure.

2c)

1. This kind of defect may occur due to short column failure, it take place due to yielding and we define this phenomenon as crushing.
2. Columns are classified based on the slenderness ratio which the ratio of effective length and the least lateral dimension of the column.
3. By using EULERS FORMULA we can find wheater a column is short or long. Short column subjects to more shear.
4. Inthe fig it it made short unintentionally as the secondary elements supported by the columns between its two ends split its free height in to tho short ones.

• In existing building with short column different retrofit solutions can be employed to avoid damage in the future earthquakes. Where walls of partial height are present the simplest solution is to close the openings by building a wall of full height which will eliminate the short column effect.