Section 51(9)(b) in Tamil Nadu Combined Development and Building Rules, 2019
(b)Seismic Strengthening or Retrofitting. - Prior to seismic strengthening or retrofitting of any existing structure, evaluation of the existing structure as regards structural vulnerability in the specified windor seismic hazard zone shall be carried out by a Registered Structural Engineer. If as per the evaluation of the Registered Structural Engineer the seismic resistance is assessed to be less than the specified minimum seismic resistance as given in the "note" below, action should be initiated to carry out the upgrading of the seismic resistance of the building as per applicable standard guidelines.