Identification of Cracks

1a

ANS:

observations:

• concrete crushed and the reinforcement is exposed
• concrete spalled beyoond the reinforcement which may be a sign of rupture
• beam top portion looks safe because of the flange advantages from slab
• the crack develops from bottom to top means rebar yielding occurs in support bottom only

causes of failures

• its form of flexure due to reversal of stress during earthquake
• during stress reversal, support top experience tension
• top compression is managed by slab advantage. bottom tension was not satisfied by the provided reinforcement
• since the reinforcement got yielded it cannot be repaired

1b

Ans:

observation:

• cracks along beam -column edges
• cracks seem to have developed through the structures as it looks much wider
• beam looks separated from the column at joints
• concrete is not severely crushed

causes of failure:

• its beam pulls out failure due to insufficient development length of reinforcement in joints
• during earthquake the horizontal movement of structural makes this condition worse and detached the beam member from column
• providing anchorage length between two existing concrete is very difficult so not repairable

1C

ANS

observations:

• 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

causes:

• it's a plastic hinge failure
• the damage occurred only in the joint zone first of all
• cyclic lateral loading &stress reversable at the joints led to damage
• even the slab participated to its best to handle the tension (slab is severely cracked means its has undergone tension with it flange condition but unable to control the damage
• the joint can be strengthened

2a)

ANS:

OBSERVATION:

• concrete damaged at top of a column
• concrete damged all around the column face
• beams are safe
• the location of column looks at edges of the building
• no walls are built along the column means it is probably at ground floor, for parking car movement acesses

causes of failure:

• its'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 be repairable or non -repairable
• 2b)

Ans:

observations:

• concrete developed complete breakage diagonally
• longitudinal reinforcement is intact
• shear reinforcement spacing looks wider (which means probably lesser shear rebar provided)

causes of failure:

• it's a pure shear failure
• inadequate of shear reinforcement compels concrete takes all the shear stresses

2c)

Ans:

observation:

• column failed completely
• failure at top 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

casues of failure:

• 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