Retrofitting is the process of modifying or improving existing structures to enhance their performance, safety, and functionality. It can involve adding new technologies, features, or components to a structure. 

Retrofitting can be necessary for a number of reasons, including:

• The need to accommodate new uses or demands 

• Making a building more energy efficient 

• Improving a building's climate resilience 

• Changing codes, standards, or regulations 
• Aging or deteriorating materials 
• Damage from natural or human-induced hazards 

Some common retrofitting methods include:

• Concrete jacketing

  A method that involves adding concrete to a structure to increase its performance 

• Shear wall

  A method that involves adding a shear wall to a structure to increase its performance 

• External plate bonding

  A method that involves wrapping steel plates around the joint of a column and beam to increase shear strength 

• Base isolation

  A method that involves creating an additional floor or column to isolate the foundation's superstructure from the ground