Repair: To bring back the position of the structure to its previous condition so its gives performance same as previously. It doesn’t cover the strength aspect of the structure.
Rehabilitation: Rehabilitation of a building means returning of a building or a structure to a usual state by means of repair, modification or alteration. It is related to the strength aspect of structure.
Retrofitting: Earthquake create great devastation in terms of life, money and failure of structure. Earthquake mitigation is an important field of study from a long time now.
It is the modification of existing structure to make them more resistance to seismic activity, ground motion or soil failure due to earthquakes.