IDENTIFICATION OF CRACKS

Q.1 Mode of failure or damage of the beams in the given figure, are the damages repairable.

Ans:                                                                                                                                                                                                                                               fig a)  Observation of the beam.                                                                                                                                                                                                             * 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.
                                                                                                                                                                                                                                                                    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 can not be repaired.  

       b)  Observation of the beam.                                                                                                                                                                                                             * 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 joint.                                                                                                                                                                     * Concrete is not severely crushed.

            Solution:                                                                                                                                                                                                                                       * It's a Plastic hinge failure.
             * The darnage 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.

      c)  Observation of the beam.                                                                                                                                                                                                             * 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.

          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.

Q.2 Mode of failure or damage of the beams in the figure above, are the damages repairable.

Ans:                                                                                                                                                                                                                                              fig a)  Observation of the beam.                                                                                                                                                                                                           * 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.                                           

         Solution:                                                                                                                                                                                                                                          * 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.

   fig  b)  Observation of the beam.                                                                                                                                                                                                           * Concrete developed complete breakage diagonally.
               * Longitudinal reinforcements are intact.
               * Shear reinforcement spacing looks wider (which means probably lesser shear rebar provided)

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

   fig c)  Observation of the beam.                                                                                                                                                                                                           * Column failed completely
             * Failure at top of column.
             * There are two slabs connected to the column,
             * The wooden piles might be a Post failure support after column failed, providing temporary prop to avoid collapse of the entire structure.

           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.