Identification of Cracks
Q1.What is the mode of failure or damage of the beams in the figure above? Are the damages repairable? Elaborate
a.
Observations
- Concrete is crushed and the reinforcement is exposed
- Concrete spalled beyond the reinforcement which may be the sign of rupture
- Beam top portion looks safe because of the flange advantage of the slab
- The crack is developed from bottom to top means rebar yielding occurs in support bottom only
Answer
- The failure occurred may be in the form of flexural failure due to reversal of stress during earthquake.
- During stress reversal, support top experiences compression and the bottom support experiences tension.
- The main point is, top compression is managed by the advantage of the slab support and the bottom support is not satisfied by the provided reinforcement.
- Since the reinforcement got yielded, it cannot be repaired.
b.
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
Answer
- It’s a 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.
c.
Observations
- Cracks are exactly at the joints of column-beam
- Cracks in beam developed through its entire width
- Slab also developed more cracks along the beam width direction
Answer
- 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 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 joints can be strengthened.
Q2.What is the mode of failure or damage of the beams in the figure above? Are the damages repairable? Elaborate
a.
Observations
- Concrete damaged at top of 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 the ground floor, for parking car movement access
Answer
- It’s a soft storey failure, technically plastic hinge formation.
- Due to absence of infill walls at the ground floor, the plastic hinge forms at the top of ground storey columns during lateral movement.
- Based on the development of crush of concrete, it can either be repairable or non-repairable.
b.
Observations
- Concrete developed complete breakage diagonally
- Longitudinal reinforcement are intact.
- Shear reinforcement spacing looks wider (which means probably lesser shear rebar provided)
Answer
- It’s a pure shear failure.
- Inadequate shear reinforcement compels concrete takes all the shear stresses.
c.
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.
Answer
- 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