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Retrofit versus repair; column jacketing

Short answer

Repair restores a damaged building to its original condition, while retrofitting upgrades its seismic capacity beyond the original. Column jacketing for retrofitting involves adding a reinforced concrete, steel, or FRP layer around the column to increase strength and ductility, with new vertical bars and closely spaced ties anchored to the footing and slabs.

How does retrofitting differ from repair? Write a note on jacketing of column for retrofitting.

Retrofit versus repair

BasisRepairRetrofit
AimRestore damaged building to its original stateUpgrade capacity to resist future earthquakes
Strength after workSame as before damageGreater than original
Applied toDamaged buildingsDamaged or undamaged, deficient buildings
Seismic resistanceNot improvedImproved
ExamplesFilling cracks, plastering, replacing broken bricksJacketing, shear walls, bracing, FRP

Jacketing of columns

Column jacketing increases the strength, ductility and confinement of weak columns by adding a layer of material around them.

  • RCC jacket: after roughening the column surface, new vertical bars and closely spaced ties (6-8 mm at 75-100 mm c/c) are placed, dowelled to the footing and slabs, and concrete (min. 75-100 mm thick) is cast with a bonding agent.
  • Steel jacket: steel plates or angles with battens are placed around the column and the gap is grouted.
  • FRP wrap: carbon/glass fibre wrapped around the column.
 +-----------+
 | +-------+ |
 | |column | |  <- new bars + ties
 | +-------+ |
 +-----------+

It increases axial and shear capacity, but increases the column size.

✓ Answer checked by Claude Opus 5.5 (high effort)

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