Identification of Cracks
1) IDENTIFICATION OF FAILURES IN BEAM
(a) Observations
- It seems like concrete is spalled beyond the reinforcement which can indicate signs of rupture.
- Beam top portion looks safe, which may be due to the flange action from slab.
- The crack developed from bottom to top implies rebar yielding occurs in support bottom only.
Conclusions
- From the observations, it can be concluded that, it is a form of flexural failure, due to reversal of stress during earthquake.
- During stress reversal, the top of beam will undergo compression and bottom of beam will undergo tension.
- The top compressive stresses can be managed by the beam by taking advantage of the flange action of slab above the beam.
- But the bottom tension is not well managed and the provided reinforcement yields out of its tensile strength. It can be due to lack of adequate reinforcement supports at the bottom of the beam.
- Since the reinforcement is yielded, a repair work isn't possible and practical.
(b) Observations
- From the figure, cracks can be noted along the beam-column edge.
- These cracks seems to have developed throughout the structure as it looks much wider.
- The beams looks to get separated from the column at joints.
- The concrete is not seem to be crushed severely.
Conclusions
- The failure occurred here is beam pull out failure.
- It occurs due to inadequate development length of reinforcement in joints.
- During the action of seismic loads, the lateral movement of structure can worsen the adverse effect of insufficient reinforcement and will result in detachment of beam member from column.
- The beam and column in the figure seems to be two existing structures with same age. It is difficult to provide anchorage length between two existing concrete members.
- So its not repairable.
(c) Observations
- It is observed that the cracks are formed exactly at the beam-column joint.
- The cracks are developed through the entire width of the beam.
- The slabs are also seemed to develop random cracks along the beam width direction.
- Slab is severely cracked which implies it has undergone tension with its flange condition.
Conclusions
- The failure happened here is a plastic hinge failure.
- The damage had occurred only in the joint zone.
- Cyclic lateral loading and stress reversal at the joints had led to the damage.
- The slab had also helped to manage with the tension due to its flange action, but not able to control the damage.
- The joint can be strengthened.
2) IDENTIFICATION OF FAILURE IN COLUMNS
(a) Observations
- It is noted that, the concrete at the top of the column is damaged.
- The concrete all around the column face got damaged.
- The beams seem to be safe.
- It seems that, the columns which get damaged are at the edge columns of a floor.
- No walls are seem to be built along the column.
- This indicates that, the column is located at the ground floor.
Conclusions
- The failure raised here is a soft storey failure.
- Due to the absence of infill walls in the ground floor and the columns left without such walls, it can lead to the development of plastic hinge at the top of the ground storey columns during earthquake.
- Based on the development of crush of concrete, the damage can either be repairable or non-repairable.
(b) Observations
- From the figure, it is understandable that, the concrete developed complete breakage diagonally.
- It seems that the longitudinal reinforcement are intact.
- But the shear reinforcement bars are spaced very widely. This detailing is inadequate to withstand the lateral movement.
Conclusions
- It is a pure shear failure or diagonal tension failure.
- Due to insufficient reinforcement, the member is unable to withstand the shear forces, which leads to diagonal cracking and eventual collapse.
- Inadequate shear reinforcement compels concrete to take all the shear stresses.
- The damage is not repairable.
(c) Observations
- The column seems to be failed completely in the figure.
- The failure occurred at the top of the column.
- It seems that, two slabs are connected to the column; one is a structural slab and the other slab constructed for any miscellaneous activities.
- The wooden piles in the figure might be a temporary support given after the failure to support the column, to avoid collapse of the entire structure.
Conclusions
- It is a failure due to short column effect.
- This happens due to the reduction in the effective length of the column, because of the addition of additional slabs at the mid-heights of the columns.
- This leads to failure especially when the connection is unintentional and not accounted in the actual design.
- The failure is nit at all repairable.